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Difficulties have risen while managing Acute Respiratory Distress Syndrome (ARDS) caused by COVID-19, although it meets the Berlin definition. Severe hypoxemia with near-normal compliance was noted along with coagulopathy. Understanding the precise pathophysiology of this atypical ARDS will assist researchers and physicians in improving their therapeutic approach. Previous work is limited to postmortem studies, while our report addresses patients under protective lung mechanical ventilation. An open-lung minithoracotomy was performed in 3 patients who developed ARDS related to COVID-19 and were admitted to the intensive care unit to carry out a pathological and microbiological analysis on lung tissue biopsy. Diffused alveolar damage with hyaline membranes was found, as well as plurifocal fibrin microthrombi and vascular congestion in all patients' specimens. Microbiological cultures were negative, whereas qualitative Reversed Transcriptase Polymerase Chain Reaction (RT-PCR) detected SARS-CoV-2 in the pulmonary parenchyma and pleural fluid in two patients. COVID-19 causes progressive ARDS with onset of severe hypoxemia, underlying a dual mechanism: shunt effect through diffused alveolar damage and dead space effect through thrombotic injuries in microvascular beds. It seems reasonable to manage this ventilation-perfusion ratio mismatch using a high dose of anticoagulant combined with glucocorticoids. [ABSTRACT FROM AUTHOR]

Proton magnetic resonance (MR) imaging to quantify regional ventilation–perfusion (V˙A/Q˙) ratios combines specific ventilation imaging (SVI) and separate proton density and perfusion measures into a composite map. Specific ventilation imaging exploits the paramagnetic properties of O2, which alters the local MR signal intensity, in an FIO2‐dependent manner. Specific ventilation imaging data are acquired during five wash‐in/wash‐out cycles of breathing 21% O2 alternating with 100% O2 over ~20 min. This technique assumes that alternating FIO2 does not affect V˙A/Q˙ heterogeneity, but this is unproven. We tested the hypothesis that alternating FIO2 exposure increases V˙A/Q˙ mismatch in nine patients with abnormal pulmonary gas exchange and increased V˙A/Q˙ mismatch using the multiple inert gas elimination technique (MIGET).The following data were acquired (a) breathing air (baseline), (b) breathing alternating air/100% O2 during an emulated‐SVI protocol (eSVI), and (c) 20 min after ambient air breathing (recovery). MIGET heterogeneity indices of shunt, deadspace, ventilation versus V˙A/Q˙ ratio, LogSD V˙, and perfusion versus V˙A/Q˙ ratio, LogSD Q˙ were calculated. LogSD V˙ was not different between eSVI and baseline (1.04 ± 0.39 baseline, 1.05 ± 0.38 eSVI, p =.84); but was reduced compared to baseline during recovery (0.97 ± 0.39, p =.04). There was no significant difference in LogSD Q˙ across conditions (0.81 ± 0.30 baseline, 0.79 ± 0.15 eSVI, 0.79 ± 0.20 recovery; p =.54); Deadspace was not significantly different (p =.54) but shunt showed a borderline increase during eSVI (1.0% ± 1.0 baseline, 2.6% ± 2.9 eSVI; p =.052) likely from altered hypoxic pulmonary vasoconstriction and/or absorption atelectasis. Intermittent breathing of 100% O2 does not substantially alter V˙A/Q˙ matching and if SVI measurements are made after perfusion measurements, any potential effects will be minimized. [ABSTRACT FROM AUTHOR]

Proton magnetic resonance (MR) imaging to quantify regional ventilation–perfusion (V˙A/Q˙) ratios combines specific ventilation imaging (SVI) and separate proton density and perfusion measures into a composite map. Specific ventilation imaging exploits the paramagnetic properties of O2, which alters the local MR signal intensity, in an FIO2‐dependent manner. Specific ventilation imaging data are acquired during five wash‐in/wash‐out cycles of breathing 21% O2 alternating with 100% O2 over ~20 min. This technique assumes that alternating FIO2 does not affect V˙A/Q˙ heterogeneity, but this is unproven. We tested the hypothesis that alternating FIO2 exposure increases V˙A/Q˙ mismatch in nine patients with abnormal pulmonary gas exchange and increased V˙A/Q˙ mismatch using the multiple inert gas elimination technique (MIGET).The following data were acquired (a) breathing air (baseline), (b) breathing alternating air/100% O2 during an emulated‐SVI protocol (eSVI), and (c) 20 min after ambient air breathing (recovery). MIGET heterogeneity indices of shunt, deadspace, ventilation versus V˙A/Q˙ ratio, LogSD V˙, and perfusion versus V˙A/Q˙ ratio, LogSD Q˙ were calculated. LogSD V˙ was not different between eSVI and baseline (1.04 ± 0.39 baseline, 1.05 ± 0.38 eSVI, p =.84); but was reduced compared to baseline during recovery (0.97 ± 0.39, p =.04). There was no significant difference in LogSD Q˙ across conditions (0.81 ± 0.30 baseline, 0.79 ± 0.15 eSVI, 0.79 ± 0.20 recovery; p =.54); Deadspace was not significantly different (p =.54) but shunt showed a borderline increase during eSVI (1.0% ± 1.0 baseline, 2.6% ± 2.9 eSVI; p =.052) likely from altered hypoxic pulmonary vasoconstriction and/or absorption atelectasis. Intermittent breathing of 100% O2 does not substantially alter V˙A/Q˙ matching and if SVI measurements are made after perfusion measurements, any potential effects will be minimized. [ABSTRACT FROM AUTHOR]

Objective: To assess the association between the use of a flowchart incorporating Wells score, PERC rule and age‐adjusted D‐dimer and subsequent imaging and yield rates of computed tomography pulmonary angiogram and nuclear medicine ventilation perfusion scans being ordered in the ED for the assessment of pulmonary embolism. Methods: A flowchart governing ED pulmonary embolism investigation was introduced across three EDs in Melbourne, Australia for a 12 month period. Comparison of pulmonary embolism imaging rates and yield with the preceding 12 months was performed. Results: A total of 1815 pre‐implementation scans were performed compared with 1116 scans post‐implementation. Because of growth in patient attendances over this time, this equated to an imaging rate of 14.5 per 1000 presentations pre‐implementation and 8.6 per 1000 presentations post‐implementation (P < 0.001). Overall pulmonary embolism imaging yield rates rose from 9.9% to 16.5% (P < 0.001). A total of 179 pre‐implementation pulmonary embolisms were identified, with an incidence of 1.4 per 1000 presentations. This compared to 184 pulmonary embolisms post‐implementation, with an incidence of 1.4 per 1000 presentations (P = 0.994). Conclusion: The introduction of a clinical flowchart incorporating Wells score, PERC rule and age‐adjusted D‐dimer was associated with an increase in ED computed tomography pulmonary angiogram and nuclear medicine ventilation perfusion yield rate from 9.9% to 16.5% across the three enrolment hospitals when investigating possible pulmonary embolism. This corresponded to a 40% relative reduction in pulmonary embolism imaging. Diagnosis rates remained unchanged and no cases of missed pulmonary embolism attributable to the flowchart were identified. [ABSTRACT FROM AUTHOR]

Key Clinical Message: Any gas will flow down the path of least resistance and highest compliance. This is a problem in the treatment of severe unilateral lung disease in the intensive care unit (ICU). Deep sedation interferes with the diaphragm's ability to distribute air into the lower lung. Spontaneous breathing in a conscious patient, in combination with mechanical ventilation via an endotracheal tube inserted into the left main stem bronchus, can recruit collapsed alveoli. Any gas will flow down the path of least resistance and highest compliance. This is a problem in the treatment of severe unilateral lung disease in the intensive care unit (ICU). Deep sedation interferes with the diaphragm's ability to distribute air into the lower lung. Spontaneous breathing in a conscious patient, in combination with mechanical ventilation via an endotracheal tube inserted into the left main stem bronchus, can recruit collapsed alveoli. [ABSTRACT FROM AUTHOR]

Objective: The objective was to quantify the potential economic value of single-photon emission computed tomography (SPECT) with computed tomography (CT; SPECT/CT) versus CT pulmonary angiography (CTPA), ventilation-perfusion (V/Q) planar scintigraphy, and V/Q SPECT imaging modalities for diagnosing suspected pulmonary embolism (PE) patients in an emergency setting. Methods: An Excel-based simulation model was developed to compare SPECT/CT versus the alternate scanning technologies from a payer's perspective. Clinical endpoints (diagnosis, treatment, complications, and mortality) and their corresponding cost data (2016 USD) were obtained by performing a best evidence review of the published literature. Studies were pooled and parameters were weighted by sample size. Outcomes measured included differences in 1) excess costs, 2) total costs, and 3) lives lost per annum between SPECT/CT and the other imaging modalities. One-way (±25%) sensitivity and three scenario analyses were performed to gauge the robustness of the results. Results: For every 1,000 suspected PE patients undergoing imaging, expected annual economic burden by modality was found to be 3.2 million (SPECT/CT), 3.8 million (CTPA), 5.8 million (planar), and 3.6 million (SPECT) USD, with a switch to SPECT/CT technology yielding per-patient-per-month cost savings of $51.80 (vs. CTPA), $213.80 (vs. planar), and $36.30 (vs. SPECT), respectively. The model calculated that the incremental number of lives saved with SPECT/CT was six (vs. CTPA) and three (vs. planar). Utilizing SPECT/CT as the initial imaging modality for workup of acute PE was also expected to save $994,777 (vs. CTPA), $2,852,014 (vs. planar), and $435,038 (vs. SPECT) in "potentially avoidable"' excess costs per annum for a payer or health plan. Conclusion: Compared to the currently available scanning technologies for diagnosing suspected PE, SPECT/CT appears to confer superior economic value, primarily via improved sensitivity and specificity and low nondiagnostic rates. In turn, the improved diagnostic accuracy accords this modality the lowest ratio of expenses attributable to potentially avoidable complications, misdiagnosis, and underdiagnosis. [ABSTRACT FROM AUTHOR]

An editorial is presented on the changes made in the nuclear medicine including integration of imaging technology in personalized medicine. Also discusses the use of single photon emission computed tomography (SPECT) and positron emission tomography (PET) for scans to diagnose various diseases, and its application in treatment of patients with metastatic castrate-resistant prostate carcinoma using imaging biomarkers.

Background Deep vein thrombosis ( DVT) and pulmonary embolism ( PE) are connected with a poor outcome in cancer patients. We aimed to investigate the impact of cancer on the effectiveness of cardiac Troponin I ( cTnI) to predict right ventricular dysfunction ( RVD) in acute PE. Methods We retrospectively analyzed the data of 182 patients with confirmed PE. PE patients were subdivided into two groups: (i) with concomitant active cancer disease or history of cancer, and (ii) without known cancer. Receiver operating characteristic (ROC) curves with area under the curve ( AUC) was calculated for cTnI predicting RVD and related cut-off levels for both groups. Results Thirty-seven PE patients (20.3%) had an active cancer disease or a history of cancer. In contrast, 145 (79.7%) of the included PE patients did not have a known cancer disease or a history of cancer. In the PE group with cancer, analysis of the ROC curve showed an AUC of 0.76 for cTnI predicting RVD with an optimal cut-off value of 0.04 ng/mL; the risk of misclassification was 25.0%. In the PE group without cancer, AUC was 0.81 for cTnI predicting RVD with an optimal cut-off value of 0.015 ng/mL; the risk of misclassification was 24.9%. Conclusions cTnI is effective for predicting RVD in PE patients with and without cancer. However, the effectiveness of cTnI to predict RVD was higher in PE patients without cancer than in those with cancer or a history of cancer. [ABSTRACT FROM AUTHOR]

The field of proton lung MRI is advancing on a variety of fronts. In the realm of functional imaging, it is now possible to use arterial spin labeling (ASL) and oxygen-enhanced imaging techniques to quantify regional perfusion and ventilation, respectively, in standard units of measurement. By combining these techniques into a single scan, it is also possible to quantify the local ventilation-perfusion ratio, which is the most important determinant of gas-exchange efficiency in the lung. To demonstrate potential for accurate and meaningful measurements of lung function, this technique was used to study gravitational gradients of ventilation, perfusion, and ventilation-perfusion ratio in healthy subjects, yielding quantitative results consistent with expected regional variations. Such techniques can also be applied in the time domain, providing new tools for studying temporal dynamics of lung function. Temporal ASL measurements showed increased spatial-temporal heterogeneity of pulmonary blood flow in healthy subjects exposed to hypoxia, suggesting sensitivity to active control mechanisms such as hypoxic pulmonary vasoconstriction, and illustrating that to fully examine the factors that govern lung function it is necessary to consider temporal as well as spatial variability. Further development to increase spatial coverage and improve robustness would enhance the clinical applicability of these new functional imaging tools. In the realm of structural imaging, pulse sequence techniques such as ultrashort echo-time radial k-space acquisition, ultrafast steady-state free precession, and imaging-based diaphragm triggering can be combined to overcome the significant challenges associated with proton MRI in the lung, enabling high-quality three-dimensional imaging of the whole lung in a clinically reasonable scan time. Images of healthy and cystic fibrosis subjects using these techniques demonstrate substantial promise for non-contrast pulmonary angiography and detailed depiction of airway disease. Although there is opportunity for further optimization, such approaches to structural lung imaging are ready for clinical testing. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Objectives To determine whether the Wells clinical prediction rule for pulmonary embolism ( PE), which produces a point score based on clinical features and the likelihood of diagnoses other than PE, combined with normal D-dimer testing can be used to exclude PE in older unhospitalized adults. Design Prospective cohort study. Setting Primary care and nursing homes. Participants Older adults (≥60) clinically suspected of having a PE (N = 294, mean age 76, 44% residing in a nursing home). Measurements The presence of PE was confirmed using a composite reference standard including computed tomography and 3-month follow-up. The proportion of individuals with an unlikely risk of PE was calculated according to the Wells rule (≤4 points) plus a normal qualitative point-of-care D-dimer test (efficiency) and the presence of symptomatic PE during 3 months of follow-up within these patients (failure rate). Results Pulmonary embolism occurred in 83 participants (28%). Eighty-five participants had an unlikely risk according to the Wells rule and a normal D-dimer test (efficiency 29%), five of whom experienced a nonfatal PE during 3 months of follow-up (failure rate = 5.9%, 95% confidence interval ( CI) = 2.5-13%). According to a refitted diagnostic strategy for older adults, 69 had a low risk of PE (24%), two of whom had PE (failure rate = 2.9%, 95% CI = 0.8-10%). Conclusion The use of the well-known and widely used Wells rule (original or refitted) does not guarantee safe exclusion of PE in older unhospitalized adults with suspected PE. This may lead to discussion among professionals as to whether the original or revised Wells rule is useful for elderly outpatients. [ABSTRACT FROM AUTHOR]

Background The way in which hyperoxia affects pulmonary ventilation and perfusion is not fully understood. We investigated how an increase in oxygen partial pressure in healthy young volunteers affects pulmonary ventilation and perfusion measured by thoracic electrical impedance tomography ( EIT). Methods Twelve semi-supine healthy male volunteers aged 21-36 years were studied while breathing room air and air-oxygen mixtures ( FiO2) that resulted in predetermined transcutaneous oxygen partial pressures ( tcPO2) of 20, 40 and 60 kPa. The magnitude of ventilation (Δ Zv) and perfusion (Δ ZQ)-related changes in cyclic impedance variations, were determined using an EIT prototype equipped with 32 electrodes around the thorax. Regional changes in ventral and dorsal right lung ventilation ( V) and perfusion ( Q) were estimated, and V/ Q ratios calculated. Results There were no significant changes in Δ Zv with increasing tcPO2 levels. Δ ZQ in the dorsal lung increased with increasing tcPO2 ( P = 0.01), whereas no such change was seen in the ventral lung. There was a simultaneous decrease in V/ Q ratio in the dorsal region during hyperoxia ( P = 0.04). Two subjects did not reach a tcPO2 of 60 kPa despite breathing 100% oxygen. Conclusion These results indicate that breathing increased concentrations of oxygen induces pulmonary vasodilatation in the dorsal lung even at small increases in FiO2. Ventilation remains unchanged. Local mismatch of ventilation and perfusion occurs in young healthy men, and the change in ventilation/perfusion ratio can be determined non-invasively by EIT. [ABSTRACT FROM AUTHOR]

It has been shown that the critical power (CP) in cycling estimated using a novel 3‐min all‐out protocol is reliable and closely matches the CP derived from conventional procedures. The purpose of this study was to assess the predictive validity of the all‐out test CP estimate. We hypothesised that the all‐out test CP would be significantly correlated with 16.1‐km road time‐trial (TT) performance and more strongly correlated with performance than the gas exchange threshold (GET), respiratory compensation point (RCP) and V̇O2 max. Ten club‐level male cyclists (mean±SD: age 33.8±8.2 y, body mass 73.8±4.3 kg, V̇O2 max 60±4 ml·kg−1·min−1) performed a 10‐mile road TT, a ramp incremental test to exhaustion, and two 3‐min all‐out tests, the first of which served as familiarisation. The 16.1‐km TT performance (27.1±1.2 min) was significantly correlated with the CP (309±34 W; r=−0.83, P<0.01) and total work done during the all‐out test (70.9±6.5 kJ; r=−0.86, P<0.01), the ramp incremental test peak power (433±30 W; r=−0.75, P<0.05) and the RCP (315±29 W; r=−0.68, P<0.05), but not with GET (151±32 W; r=−0.21) or the V̇O2 max (4.41±0.25 L·min−1; r=−0.60). These data provide evidence for the predictive validity and practical performance relevance of the 3‐min all‐out test. The 3‐min all‐out test CP may represent a useful addition to the battery of tests employed by applied sport physiologists or coaches to track fitness and predict performance in atheletes. [ABSTRACT FROM AUTHOR]

This paper presents a personal view of research into the exercise drive to breathe that can be observed to act immediately to increase breathing at the start of rhythmic exercise. It is based on a talk given at the Experimental Biology 2013 meeting in a session entitled 'Recent advances in understanding mechanisms regulating breathing during exercise'. This drive to breathe has its origin in a combination of central command, whereby voluntary motor commands to the exercising muscles produce a concurrent respiratory drive, and afferent feedback, whereby afferent information from the exercising muscles affects breathing. The drive at the start and end of rhythmic exercise is proportional to limb movement frequency, and its magnitude decays as exercise continues so that the immediate decrease of ventilation at the end of exercise is about 60% of the immediate increase at the start. With such evidence for the effect of this fast drive to breathe at the start and end of rhythmic exercise, its existence during exercise is hypothesised. Experiments to test this hypothesis have, however, provided debatable evidence. A fast drive to breathe during both ramp and sine wave changes in treadmill exercise speed and grade appears to be present in some individuals, but is not as evident in the general population. Recent sine-wave cycling experiments show that when cadence is varied sinusoidally the ventilation response lags by about 10 s, whereas when pedal loading is varied ventilation lags by about 30 s. It therefore appears that limb movement frequency is effective in influencing ventilation during exercise as well as at the start and end of exercise. [ABSTRACT FROM AUTHOR]

Precursor T lymphoblastic lymphoma (T-LBL) often manifests as a mediastinal mass sometimes compressing vital structures like vessels or large airways. This case was a 40-year-old male who developed T-LBL presenting as respiratory failure caused by mediastinal T-LBL. He presented with persistent life threatening hypoxia despite tracheal intubation. We successfully managed this respiratory failure using venovenous (VV) ECMO. Induction chemotherapy was started after stabilizing oxygenation and the mediastinal lesion shrank rapidly. Respiratory failure caused by compression of the central airway by tumor is an oncologic emergency. VV ECMO may be an effective way to manage this type of respiratory failure as a bridge to chemotherapy. [ABSTRACT FROM AUTHOR]

In hominoids, the broad thorax has been assumed to contribute to their dorsal scapular position. However, the dorsoventral diameter of their cranial thorax was found in one study to be longer in hominoids. There are insufficient data on thoracic shape to explain the relationship between broad thorax and dorsal scapular position. The current study presents data on multilevel cross-sectional shape and volume distribution in a range of primates. Biplanar radiographs of intact fluid-preserved cadavers were taken to measure the cross-sectional shape of ten equally spaced levels through the sternum (called decisternal levels) and the relative volume of the nine intervening thoracic segments. It was found that the cranial thorax of hominoids is larger and broader (except in the first two decisternal levels) than that of other primates. The cranial thorax of hominoids has a longer dorsoventral diameter because the increase in dorsoventral diameter caused by the increase in the volume of the cranial thorax overcompensates for the decrease caused by the broadening of the cranial thorax. The larger and broader cranial thorax in hominoids can be explained as a locomotor adaptation for scapular gliding and as a respiratory adaptation for reducing the effects of orthograde posture on ventilation-perfusion inequality. [ABSTRACT FROM AUTHOR]

Purpose: Four-dimensional computed tomography (4DCT) can be used to make measurements of pulmonary function longitudinally. The sensitivity of such measurements to identify change depends on measurement uncertainty. Previously, intrasubject reproducibility of Jacobian-based measures of lung tissue expansion was studied in two repeat prior-RT 4DCT human acquisitions. Difference in respiratory effort such as breathing amplitude and frequency may affect longitudinal function assessment. In this study, the authors present normalization schemes that correct ventilation images for variations in respiratory effort and assess the reproducibility improvement after effort correction. Methods: Repeat 4DCT image data acquired within a short time interval from 24 patients prior to radiation therapy (RT) were used for this analysis. Using a tissue volume preserving deformable image registration algorithm, Jacobian ventilation maps in two scanning sessions were computed and compared on the same coordinate for reproducibility analysis. In addition to computing the ventilation maps from end expiration to end inspiration, the authors investigated the effort normalization strategies using other intermediated inspiration phases upon the principles of equivalent tidal volume (ETV) and equivalent lung volume (ELV). Scatter plots and mean square error of the repeat ventilation maps and the Jacobian ratio map were generated for four conditions: no effort correction, global normalization, ETV, and ELV. In addition, gamma pass rate was calculated from a modified gamma index evaluation between two ventilation maps, using acceptance criterions of 2 mm distance-to-agreement and 5% ventilation difference. Results: The pattern of regional pulmonary ventilation changes as lung volume changes. All effort correction strategies improved reproducibility when changes in respiratory effort were greater than 150 cc (p < 0.005 with regard to the gamma pass rate). Improvement of reproducibility was correlated with respiratory effort difference (R = 0.744 for ELV in the cohort with tidal volume difference greater than 100 cc). In general for all subjects, global normalization, ETV and ELV significantly improved reproducibility compared to no effort correction (p = 0.009, 0.002, 0.005 respectively). When tidal volume difference was small (less than 100 cc), none of the three effort correction strategies improved reproducibility significantly (p = 0.52, 0.46, 0.46 respectively). For the cohort (N = 13) with tidal volume difference greater than 100 cc, the average gamma pass rate improves from 57.3% before correction to 66.3% after global normalization, and 76.3% after ELV. ELV was found to be significantly better than global normalization (p = 0.04 for all subjects, and p = 0.003 for the cohort with tidal volume difference greater than 100 cc). Conclusions: All effort correction strategies improve the reproducibility of the authors' pulmonary ventilation measures, and the improvement of reproducibility is highly correlated with the changes in respiratory effort. ELV gives better results as effort difference increase, followed by ETV, then global. However, based on the spatial and temporal heterogeneity in the lung expansion rate, a single scaling factor (e.g., global normalization) appears to be less accurate to correct the ventilation map when changes in respiratory effort are large. [ABSTRACT FROM AUTHOR]

This paper summarizes current knowledge about electrical impedance tomography (EIT) and its present and possible applications in clinical practice in pediatric respiratory medicine. EIT is a relatively new technique based on real-time monitoring of bioimpedance. Its possible application in clinical practice related to ventilation and perfusion monitoring in children has gained increasing attention in recent years. Most of the currently published data is based on studies performed on small and heterogenous groups of patients. Thus the results need to be corroborated in future well-designed clinical trials. Firstly a short theoretical overview summarizing physical principles and main advantages and disadvantages is provided. It is followed by a review of the current data regarding EIT application in ventilation distribution monitoring in healthy individuals. Finally the most important studies utilizing EIT in ventilation and perfusion monitoring in critically ill newborns and children are outlined. [ABSTRACT FROM AUTHOR]

Single-photon emission computed tomography ( SPECT) ventilation perfusion ( V/Q) scanning with low-dose computed tomography ( LDCT) is an emerging imaging technique for investigation of suspected pulmonary embolism ( PE). We aimed to estimate diagnostic utility of the combined technique using results from all patients referred in 2009 compared with final diagnosis and 6-month follow-up status. PE was diagnosed in 28 of 106 patients (26%), including in 2 of 80 (2%) with negative SPECT V/Q and LDCT. The estimated negative predictive value of SPECT V/Q for PE was 97%. LDCT was abnormal in 43 (41%) patients, including 41 patients who had negative SPECT V/Q. In 29 (27%) patients, LDCT provided information on alternative pathologies that accounted for presenting symptoms, and the combined technique had a diagnostic yield of 52%. [ABSTRACT FROM AUTHOR]

During one-lung ventilation, ventilation-perfusion mismatch decreases the arterial concentration of inhaled anaesthetics due to the arterial-to-venous concentration difference. This study tested the hypothesis that in humans, the 'presumed effect-site concentration' (taken as the mid-point between the arterial and superior jugular venous concentrations) of inhaled anaesthetic falls during one-lung (vs two-lung) ventilation. Four patients scheduled for elective prostatectomy (two-lung ventilation) and four patients for elective thoracotomy (one-lung ventilation) were randomly selected and assigned to receive sevoflurane (vaporiser -dial setting, 1.5%). Sevoflurane concentrations were measured periodically from radial artery and superior jugular vein (via a catheter advanced cephalad from the jugular vein ). During one-lung ventilation, the end-expiratory sevoflurane concentration was stable at ∼1.3% but the mean (SD) presumed effect-site concentration declined initially from 58 (6.7) to 43 (4.7) μg.ml−1 (p = 0.011) before slowly recovering. A period of insufficient depth of anaesthesia is thus a risk during one-lung ventilation. [ABSTRACT FROM AUTHOR]

ABSTRACT Physiologically based pharmacokinetic modeling and occupational exposure assessment studies often use minute ventilation rates ( VE), alveolar ventilation rates ( VA) and cardiac outputs ( Q) that are not reflective of the physiological variations encountered during the aggregate daytime activities of individuals from childhood to adulthood. These variations of VE, VA and Q values were determined for healthy normal-weight individuals aged 5-96 years by using two types of published individual data that were measured in the same subjects ( n = 902), namely indirect calorimetry measurements and the disappearance rates of oral doses of deuterium (2H) and heavy-oxygen (18O) in urine monitored by gas-isotope-ratio mass spectrometry. Arteriovenous oxygen content differences (0.051-0.082 ml of O2 consumed ml−1 of blood) and ratios of the physiological dead space to the tidal volume (0.232-0.419) were determined for oxygen consumption rates (0.157-0.806 l min−1) required by minute energy expenditures ranging from 0.76 to 3.91 kcal min−1. Generally higher values for the 2.5th up to the 99th percentile for VE (0.132-0.774 l kg−1 min−1, 4.42-21.69 l m−2 min−1), VA (0.093-0.553 l kg−1 min−1, 3.09-15.53 l m−2 min−1), Q (0.065-0.330 l kg−1 min−1, 2.17 to 9.46 l m−2 min−1) and ventilation-perfusion ratios (1.12-2.16) were found in children and teenagers aged 5-<16.5 years compared with older individuals. The distributions of cardiopulmonary parameters developed in this study should be useful in facilitating a scientifically sound characterization of the inter-individual differences in the uptake and health risks of lipophilic air pollutants, particularly as they relate to younger children. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Purpose: Diagnosis of acute pulmonary embolism (PE) is commonly done by acquiring SPECT scans of lung ventilation and of lung perfusion. The two image sets are compared, to identify regions which are ventilated but not perfused ('mismatched defects'). This paper describes the application of histogram matching to the calculation of a ventilation/perfusion difference image, and an investigation of the feasibility of the technique using phantom data. Methods: An empty balloon was inserted into the lung compartment of an anthropomorphic torso phantom. The lungs were filled with polystyrene beads and with water containing 0.20 kBq/ml of 99mTc. Two scans were acquired to mimic a matched ventilation/perfusion pair. Then, 30 ml of water containing 0.01 kBq/ml of 99mTc was injected into the balloon and the phantom was rescanned. This was repeated four more times, adding 30 ml each time. Each perfusion scan thus had a mismatched defect of a different size. A CT scan was also performed after each perfusion scan, to verify the size and location of the balloon. Histogram matching was applied to each perfusion scan, which was then subtracted from the ventilation scan, yielding a difference image in which voxels with positive values identified mismatched defects. For each scan, a volume of interest (VOI) was automatically generated on the defect and was also copied across to the contralateral side to determine target to background ratios. Results: All mismatched defects were clearly visible in the difference images, including the smallest, which corresponded in size to a small subsegmental defect. Voxel values for the mismatched defects ranged from 17 to 26, compared with contralateral regions, which had voxel values of 0 or 1. Conclusions: Histogram matching provides a simple, automatic data-driven method for scaling ventilation and perfusion studies without user intervention. [ABSTRACT FROM AUTHOR]

In this study, it is described how to use ultrasonography ( US) for real-time imaging of the airway from the mouth, over pharynx, larynx, and trachea to the peripheral alveoli, and how to use this in airway management. US has several advantages for imaging of the airway - it is safe, quick, repeatable, portable, widely available, and it must be used dynamically for maximum benefit in airway management, in direct conjunction with the airway management, i.e. immediately before, during, and after airway interventions. US can be used for direct observation of whether the tube enters the trachea or the esophagus by placing the ultrasound probe transversely on the neck at the level of the suprasternal notch during intubation, thus confirming intubation without the need for ventilation or circulation. US can be applied before anesthesia induction and diagnose several conditions that affect airway management, but it remains to be determined in which kind of patients the predictive value of such an examination is high enough to recommend this as a routine approach to airway management planning. US can identify the croicothyroid membrane prior to management of a difficult airway, can confirm ventilation by observing lung sliding bilaterally and should be the first diagnostic approach when a pneumothorax is suspected intraoperatively or during initial trauma-evaluation. US can improve percutaneous dilatational tracheostomy by identifying the correct tracheal-ring interspace, avoiding blood vessels and determining the depth from the skin to the tracheal wall. [ABSTRACT FROM AUTHOR]

Objective To review the topic of ventilator waveforms analysis with emphasis on interpretation of ventilator waveforms and their use in the management and monitoring of mechanically ventilated small animal patients. Data sources Human clinical studies, scientific reviews, and textbooks, as well as veterinary textbooks and clinical examples of ventilator waveforms in mechanically ventilated dogs. Summary Ventilator waveforms are graphic representations of data collected from the ventilator and reflect patient-ventilator interactions. The 4 parameters pressure, volume, flow, and time are most descriptive of mechanical ventilation. Typically, 3 different graphs, also referred to as scalars, consisting of pressure versus time, volume versus time, and flow versus time, with time always plotted on the x-axis, are used. Changes in the ventilator settings as well as in the characteristics of the lungs such as airway resistance ( R aw) and respiratory system compliance ( C rs) can be recognized from specific variations in the waveforms. Flow-volume and pressure-volume loops provide additional information about changes in lung function. Patient-ventilator dyssynchrony is a common problem during mechanical ventilation and can lead to patient discomfort and an increased work of breathing. Ventilator waveforms are helpful to identify dyssynchrony, which can be divided into trigger, flow, cycle, and expiratory dyssynchrony. Ventilator waveforms allow the clinician to assess changes in respiratory mechanics, and can be useful in monitoring the progression of disease pathology and response to therapy. Adjustments in ventilator settings based on proper analysis and interpretation of these waveforms can help the clinician to optimize ventilation therapy. Conclusions Ventilator waveforms are graphic representations of patient-ventilator interactions. Proper interpretation of ventilator waveforms affords the critical care clinician a better understanding of the patient's respiratory function, response to therapy, and causes for patient-ventilator dyssynchrony. Ventilator waveform interpretation is an important tool in the assessment and management of mechanically ventilated small animal patients. [ABSTRACT FROM AUTHOR]

Background and objective: Little is known about the value of procalcitonin in predicting mortality in patients with an exacerbation of COPD. This study evaluated the clinical and biological predictors of intensive care unit (ICU) mortality in patients with a severe acute exacerbation of COPD. Methods: A prospective observational cohort study was conducted of consecutive patients with severe acute exacerbation of COPD requiring intubation and mechanical ventilation. At ICU admission, data were collected on the patients' clinical condition, blood leukocyte count, C-reactive protein and procalcitonin. Cox proportional hazards model was used to determine the risk factors for ICU mortality. Results: One hundred and sixteen patients were included in this study. Mean age was 67 years. The mean simplified acute physiology score was 43. Sixty-five per cent of study patients had chronic respiratory insufficiency. Bacteria were cultured at levels considered significant in 36% of study patients. Logistic organ dysfunction score (hazard ratio (95% CI) = 1.19 (1.03–1.37), P = 0.013), rapidly fatal underlying disease (3.33 (1.40–7.87), P = 0.003) and procalcitonin level (1.01 (1–1.03), P = 0.018) were independently associated with increased risk for ICU mortality. Non-invasive mechanical ventilation use before intubation was independently associated with reduced risk for ICU mortality (0.34 (0.14–0.84), P = 0.020). Conclusions: In patients with severe acute exacerbation of COPD requiring intubation and mechanical ventilation, logistic organ dysfunction score, rapidly fatal underlying disease and procalcitonin are independently associated with increased risk for ICU mortality. Non-invasive mechanical ventilation use before intubation was independently associated with reduced risk for ICU mortality. [ABSTRACT FROM AUTHOR]

Background: One-lung ventilation (OLV) affects respiratory mechanics and ventilation/perfusion matching, reducing functional residual capacity of the ventilated lung. While the application of a lung-recruiting manoeuvre (RM) on the ventilated lung has been shown to improve oxygenation, data regarding the impact of RM on respiratory mechanics are not available. Methods: Thirteen patients undergoing lung resection in lateral decubitus were studied. During OLV, a lung-recruiting strategy consisting in a RM lasting 1 min followed by the application of positive end-expiratory pressure 5 cmH2O was applied to the ventilated lung. Haemodynamics, gas exchange and respiratory mechanics parameters were recorded on two-lung ventilation (TLVbaseline), OLV before and 20 min after the RM (OLVpre-RM, OLVpost-RM, respectively) and TLVend. Haemodynamics parameters were also recorded during the RM. Results: The PaO2/FiO2 ratio was 358±126 on TLVbaseline; it decreased to 235±113 on OLVpre-RM ( P<0.01) increased to 351±120 on OLVpost-RM ( P<0.01 vs. OLVpre-RM), and remain stable thereafter. During the RM, CI decreased from 3.04±0.7 l/m2 OLVpre-RM to 2.4±0.6 l/m2 ( P<0.05), and returned to baseline on OLVpost-RM (3.1±0.7 l/m2, NS vs. OLVpre-RM). The RM resulted in alveolar recruitment and caused a significant decrease in static elastance of the dependent lung (16.6±8.9 cmH2O/ml OLVpost-RM vs. 22.3±8.1 cmH2O/ml OLVpre-RM) ( P<0.01). Conclusions: During OLV in lateral decubitus for thoracic surgery, application to the dependent lung a recruiting strategy significantly recruits the dependent lung, improving arterial oxygenation and respiratory mechanics until the end of surgery. However, the transient haemodynamic derangement occurring during the RM should be taken into account. [ABSTRACT FROM AUTHOR]

The article presents two case studies of two males aged 55 and 57 with acute pulmonary embolism. The two patients have been examined with the use of combined lung ventilation perfusion (V/Q) SPECT/MSCT angiography. Results from the examination found no hints of pulmonary embolism and illustrate the potential for the fused 3-D imaging's additional value.

Background Conductance catheter in vivo ventricular volume measurements during lung ventilation may provide important information on left ventricular (LV) function. Breathing potentially may alter parallel conductance ( Vc), complicating interpretation of the conductance-derived volume signals. The effects of controlled positive pressure lung inflation (PPLI) on measured parallel conductance with dual-field conductance volumetry were investigated. Methods Eight anaesthetized pigs were instrumented with an LV dual-field conductance volumetry catheter. Vc was measured repeatedly, using the hypertonic saline injection method, at three different levels of lung insufflation: continuous positive airway pressure (PPLI) 0, 5, and 10 cmH2O. Results Vcs measured at PPLI 0, 5 and 10 cmH2O were 70·9 ± 4·8, 70·7 ± 5·5 and 70·5 ± 5·9 ml, respectively. The corresponding uncalibrated end-diastolic volumes (EDVu) were 115·5 ± 7·1, 117·0 ± 7·5 and 117·5 ± 7·7 ml, respectively. Mean coefficients of variance for Vc and EDVu at all three PPLI levels were 3·8% and 1·25%, respectively. Discussion Several levels of PPLI demonstrated no systematic change in parallel conductance for LV dual-field conductance volume signal. We concluded that lung inflation at these levels does not generate changes in Vc. [ABSTRACT FROM AUTHOR]

Theoretical modelling predicts that the concentrating effect of nitrous oxide (N2O) uptake on alveolar oxygenation is a persisting phenomenon at typical levels of ventilation – perfusion (V/Q) inhomogeneity under anaesthesia. We sought clinical confirmation of this in 20 anaesthetised patients. Arterial oxygen pressure ( Pao2) was measured after a minimum of 30 min of relaxant general anaesthesia with an inspired oxygen ( FIo2) of 30%. Patients were randomly allocated to two groups. The intervention group had N2O introduced following baseline blood gas measurements, and the control group continued breathing an identical FIo2 in nitrogen (N2). The primary outcome variable was change in Pao2. Mean (SD) in Pao2 was increased by 1.80 (1.80) kPa after receiving a mean of 47.5 min of N2O compared with baseline conditions breathing O2/N2 (p = 0.01). This change was significantly greater (p = 0.03) than that in the control group: + 0.09 (1.37) kPa, p = 0.83 and confirms the presence of significant persisting concentrating and second gas effects. [ABSTRACT FROM AUTHOR]

Photoplethysmography (PPG) is a non-invasive optical technique used, for instance, in pulse oximetry. Beside the pulse synchronous component, PPG has a respiratory synchronous variation (PPGr). Efforts have been made to utilize this component for indirect monitoring of respiratory rate and volume. Assessment of the clinical usefulness as well as of the physiological background of PPGr is required. We evaluated if anaesthesia and positive-pressure ventilation would affect PPGr. We recorded reflection mode PPGr, at the forearm, and the respiratory synchronous changes in central venous pressure (CVP), peripheral venous pressure (PVP) and arterial blood pressure (ABP) in 12 patients. Recordings for each patient were made on three occasions: awake with spontaneous breathing; anaesthetized with spontaneous breathing; and anaesthetized with positive-pressure ventilation. We analyzed the sensitivity, specificity, coherence and time relationship between the signals. PPGr sensitivity for breath detection was [mean (SD)] >86(21)% and specificity >96(12)%. Respiratory detection in the macrocirculation (CVP, PVP and ABP) showed a sensitivity >83(29)% and specificity >93(12)%. The coherence between signals was high (0.75–0.99). The three measurement situations did not significantly influence sensitivity, specificity or time shifts between the PPGr, PVP, ABP, and the reference CVP signal despite changes in physiological data between measurements. A respiratory synchronous variation in PPG and all invasive pressure signals was detected. The reflection mode PPGr signal seemed to be a constant phenomenon related to respiration regardless of whether or not the subject was awake, anaesthetized or ventilated, which increases its clinical usefulness in respiratory monitoring. [ABSTRACT FROM AUTHOR]

In man assuming the upright position, end-tidal PCO2 (PETCO2) decreases. With the rising interest in cerebral autoregulation during posture change, which is known to be affected by PETCO2, we sought to determine the factors leading to hypocapnia during standing up from the supine position. To study the contribution of an increase in tidal volume (VT) and breathing frequency, a decrease in stroke volume (SV), a ventilation-perfusion (V/Q) gradient and an increase in functional residual capacity (FRC) to hypocapnia in the standing position, we developed a mathematical model of the lung to follow breath-to-breath variations in PETCO2. A gravity-induced apical-to-basal V/Q gradient in the lung was modelled using nine lung segments. We tested the model using an eight-subject data set with measurements of VT, pulmonary O2 uptake and breath-to-breath lumped SV. On average, the PETCO2 decreased from 40 mmHg to 36 mmHg after 150 s standing. Results show that the model is able to track breath-to-breath PETCO2 variations (r⊃2 = 0.74, P < 0.05). Model parameter sensitivity analysis demonstrates that the decrease in PETCO2 during standing is due primarily to increased VT, and transiently to decreased SV and increased FRC; a slight gravity-induced V/Q mismatch also contributes to the hypocapnia. The influence of cardiac output on hypocapnia in the standing position was verified in experiments on human subjects, where first breathing alone, and then breathing, FRC and V/Q were controlled. [ABSTRACT FROM AUTHOR]

Objective:The purpose of this study was to report a novel electrocardiographic (ECG) phenomenon in acute pulmonary embolism characterized by QT interval prolongation with global T-wave inversion.Methods:Among a total of 140 study patients with a confirmed diagnosis of acute pulmonary embolism, patients who fulfilled the inclusion criteria for QT interval prolongation with global T-wave inversion were examined. Each of these patients had undergone a detailed clinical evaluation including testing for myocardial injury and echocardiography.Results:QT interval prolongation with global T-wave inversion was found in five patients (age 51–68 years) with acute pulmonary embolism. Four were women. Acute pulmonary embolism was diagnosed by ventilation-perfusion scan in three patients and by spiral computed tomography in other two patients. None of the patients had any right or left ventricular regional wall motion abnormalities on echocardiography. All patients had changes characteristic of hemodynamically significant pulmonary embolism, including right ventricular stunning or hypokinesis and dilatation in five patients with paradoxical septal motion in four. Acute coronary syndrome was ruled out in each patient by clinical evaluation, serial ECGs and cardiac markers, and lack of regional wall motion abnormalities on echocardiography. Prolongation of QT intervals (QTc 456–521 ms) with global T-wave inversion was noted on presentation. The ECG changes gradually resolved in 1 week in all patients with appropriate treatment of acute pulmonary embolism. One patient died. None of the patients developed torsade de pointes.Conclusions:Acute pulmonary embolism may occasionally result in reversible QT interval prolongation with deep T-wave inversion, and, thus should be considered among the acquired causes of the long QT syndrome. [ABSTRACT FROM AUTHOR]

The effects of macroscopic background field gradients upon 2D gradient echo images of inhaled 3He in the human lung were investigated at 1.5 T. Effective compensation of in-slice signal loss in 3He gradient echo images was then demonstrated using a multiple acquisition interleaved single gradient echo sequence. This method restores signal dephasing through a combination of separate images acquired with different slice refocusing gradients. In vivo imaging of volunteers with the sequence shows substantial restoration of signal at the lung periphery and close to blood vessels. The technique presented may be useful when using 3He MRI for volumetric measurements of lung ventilation and in studies using 3He combined with intravenous contrast as a means of assessing lung ventilation/perfusion (V/Q). Magn Reson Med 50:417–422, 2003. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Abstract Background: Computed tomography pulmonary ­angiography (CTPA) plays an increasingly important role in the diagnosis of pulmonary embolism (PE). Although accurate in the detection of large PE, its accuracy in other patient groups is yet to be defined. Aim: To compare CTPA with pulmonary angiog­raphy as a second-line investigation in patients with a ventilation/perfusion (VQ) scan indicating an intermediate probability of PE. Methods: We recruited 25 patients over a 17-month period. Subjects were eligible if they: (i) had clinically suspected PE, (ii) had a VQ scan indicating an intermediate probability of PE and (iii) were referred for pulmonary angiography. Subjects underwent CTPA within 36 h of the VQ scan. CTPA was interpreted without knowledge of the results of the pulmonary angiogram by two of the authors. Results: PE was prevalent (i.e. embolus detected at pulmonary angiography) in seven of 25 subjects (28%). The sensitivity of CTPA was 57% and the specificity was 94%. Conclusions: In the setting of intermediate-probability VQ scanning, CTPA may be used to clarify the diagnosis of PE. However, a negative CTPA cannot ­definitely exclude PE. Conventional pulmonary angiography may be necessary to determine the presence of PE if CTPA is negative. (Intern Med J 2003; 33: 74-78). [ABSTRACT FROM AUTHOR]

Objective: Patients with heart failure have slow metabolic gas exchange kinetics, which may contribute to the elevated slope of the relationship between ventilation and carbon dioxide production (Ve/Vco2 slope). Setting: A tertiary referral centre for cardiology. Subjects: Eleven patients with stable chronic heart failure and 11 age-matched controls. Design: Each subject underwent maximal bicycle-based peak exercise testing with metabolic gas exchange analysis and three further repeated tests at 15%, 25% and 50% of the load achieved at peak exercise. The ventilation and carbon dioxide production from each of these steady-state tests was used to re-calculate the Ve/Vco2 slope and compared with the Ve/Vco2 slope derived from the maximal test. Results: Peak oxygen consumption [mean (S.D.)] was lower in heart failure patients [18.2 (4.0) vs. 31.2 (6.3) ml/kg per min; P<0.001] than in controls. The Ve/Vco2 slope was steeper in patients than controls [32.7 (8.3) vs. 27.1 (1.6); P<0.05]. There was no difference between the Ve/Vco2 slope reconstructed from the three steady state tests and resting data and that gained from the maximal test [35.3 (7.8) vs. 25.9 (3.2); P=0.43]. Conclusions: The elevated slope of the relationship between ventilation and carbon dioxide production is not a consequence of the short stages of a standard incremental exercise test combined with delayed metabolic gas kinetics in heart failure patients. [Copyright &y& Elsevier]

Purpose: To study the use of a combination of a clinical and scintigraphic protocol in relation to the final outcome diagnosis in patients with clinical suspicion of acute pulmonary embolism (PE).Material and Methods: A total of 170 patients with clinical suspicion of acute PE were all examined with ECG, blood chemistry, chest X-ray, pulmonary scintigraphy and selective pulmonary arteriography. The scintigraphic and clinical probabilities of PE were estimated on visual analogue scales (VASs) by different readers unaware of each others' results. The follow-up time was 6 months. In order to establish the final diagnosis a final outcome committee was created. They analysed in retrospect all the clinical and laboratory data and established whether the patient had had PE or not.Results: The final outcome committee concluded that 53 patients had PE. When the scintigraphic and clinical probability judgements were congruent, a combined probability of 1-25% (i.e low probability) had a negative predictive value of 98%. When the combined probability was 26-75% (i.e. intermediate) half of the cases had PE. With a combined probability of 76-100% (i.e. high) the positive predictive value was 100%.Conclusion: By applying a model of combined clinical and scintigraphic probabilities for PE, the diagnosis is ruled in when the combined probability is high, and ruled out when the combined probability is low. However, nearly half of the patients will still have an uncertain diagnosis for which further diagnostic procedures may be allocated. [ABSTRACT FROM AUTHOR]

Background: Acute lung injury is characterized by hypoxemia which may be caused by hypoventilation, ventilation-perfusion (V(A)/Q) mismatch, intrapulmonary shunting and oxygen diffusion impairment. The multiple inert gas elimination technique (MIGET) allows analysis of these four causes of hypoxemia and is therefore the most comprehensive approach to investigate blood gas abnormalities. Using MIGET, we studied whether specific patterns of gas exchange abnormalities occur in different lung injury models and whether gas exchange abnormalities can be related to pathogenic aspects of lung injury.Methods: Lung injury was induced with oleic acid injection, endotoxin infusion or repeated lung lavage in groups of 6 mechanically ventilated pigs.Results: PaO2 decreased and PaCO2 increased significantly in all three lung injury models, but gas exchange was more impaired in the oleic acid and lavage, as compared to the endotoxin group. Shunt was the major cause of hypoxemia in our lung injury models, whereas V(A)/Q mismatch contributed to venous admixture only after oleic acid injection and lung lavage. Oxygen diffusion limitation was not observed. Although alveolar ventilation was maintained after induction of lung injury, hypercapnia developed due to an increase of the ventilatory mean towards higher V(A)/Q ratios, increased shunt and increased carbon dioxide production.Conclusions: Shunt and ventilation-perfusion mismatch fully explain the gas exchange disturbances observed in our lung injury models. Although V(A)/Q distributions can be related to pathogenic aspects of the three study groups, we did not observe specific V(A)/Q patterns which allow diagnosis of the type of lung injury from a recovered V(A)/Q distribution. [ABSTRACT FROM AUTHOR]

The respiratory tissue in the lung receives nitric oxide (NO) from two sources; NO produced in upper airways, and NO produced in lung parenchyma. It has been hypothesized that optimal local matching of ventilation and perfusion (which is necessary for effective gas exchange) is ensured because well-ventilated lung tissue has a higher concentration of NO and thereby higher blood flow owing to the vasodilatory effect of NO. To test this hypothesis, we simultaneously measured the distributions of local (regions of ≈1.5 cm3) blood flow (radioactive microspheres) and local ventilation (fluorescent aerosol) in five tracheostomized, awake and standing sheep. Tracers for perfusion and ventilation were administered (1) at baseline, (2) during endogenous NO production blockage (L-NAME 25 mg kg–1) and administration of NO free air, and (3) when the sheep received exogenous NO (≈30 p.p.m.), but having its endogenous NO production blocked. The intrapulmonary distribution of ventilation was similar in all three situations. Within horizontal levels of the lung, distribution of perfusion was not affected by variable access to NO, but along the gravitational axis perfusion was more evenly distributed when the sheep had no access to NO. Exogenous NO tended to restore the baseline vertical profile. These changes in vertical distribution of perfusion can be explained by the effect of variable NO concentrations on pulmonary arterial pressure and cardiac output. Variable access to NO had no effect on arterial blood gases. We conclude that NO is important for the vertical distribution of pulmonary perfusion, but has no apparent effect on the local matching of ventilation and perfusion within horizontal layers of the lung. [ABSTRACT FROM AUTHOR]

The aim of the present study was to develop and evaluate a method for semi-quantification of ventilation-to-perfusion ratios in small regions in planar pulmonary scintigrams using 99mTc-Technegas (Tetley Manufacturing Ltd, Sydney, Australia) and 99mTc-macro-aggregated human albumin. Eight emphysematous patients and eight healthy volunteers were investigated in the supine position. Anterio-posterior and posterio-anterior images of ventilation and ventilation-and-perfusion were acquired consecutively. Perfusion images were obtained by subtracting the corrected ventilation images from ventilation-and-perfusion images. Lung regions of interest were divided into 2·03 × 2·03 cm regions. The ratio of normalized counts of ventilation-to-perfusion (V/Q) was calculated in each square region. The log (V/Q)s of healthy volunteers were distributed symmetrically and similarly around 0, whereas the corresponding ratios in patients distributed unevenly. The standard deviations of log (V/Q)s were significantly higher in patients than in healthy volunteers. Parametric images of V/Q distribution were constructed to visualize the magnitude and location of ‘waste ventilation’ and ‘shunt’ effects. In conclusion, the present semi-quantitative method is validated by confirming the expected dispersed V/Q distribution in emphysematous patients compared to healthy volunteers. [ABSTRACT FROM AUTHOR]

Considerable heterogeneity unrelated to the effect of gravity has been demonstrated for both local ventilation (V) and perfusion (Q) in the lung. Local ventilation and perfusion are well matched, so that the heterogeneity of the V/Q ratio is less than for ventilation or perfusion alone (Melsom et al. 1997). We are searching for the mechanisms responsible for the coordinate heterogeneity of ventilation and perfusion. Here, we ask how and to what extent physical exercise induces changes in the distribution of ventilation and perfusion. We measured local (≈1.5 cm3 tissue volume) pulmonary ventilation and perfusion simultaneously in six sheep before, during and after running on a treadmill. Local ventilation was determined from the deposition of labelled aerosol particles and local perfusion from trapping of radioactive microspheres. Cardiac output increased ≈2.5-fold during exercise. V/Q-ratios were not normally distributed and we therefore present the heterogeneity as the interquartile range. At rest, the average interquartile ranges for local ventilation, perfusion and V/Q-ratio were 0.48, 0.51 and 0.39, respectively. During exercise, the corresponding values were 0.44, 0.40 and 0.32. Thus, the distribution of local V/Q-ratio was narrower than for ventilation and perfusion also during exercise. We found a moderate redistribution of relative flow towards the dorsal parts of the lungs when perfusion increased, but the increase in total perfusion and ventilation was for the most part throughout the lung. The results indicate that the coupling between local ventilation and perfusion is at least as potent during exercise as at rest. The correlation (r) between paired values in the two resting periods was 0.93 for ventilation and 0.91 for perfusion and thus indicates time stability for the two variables. [ABSTRACT FROM AUTHOR]

Studies the efficacy of diagnosis of pulmonary emboli by computed tomographic pulmonary angiography (CTPA) in patients who underwent both CTPA and ventilation-perfusion scanning. Comparison with conventional pulmonary angiography; Ventilation-perfusion probability categories.

We describe a technique to obtain non-invasively regional pulmonary ventilation–perfusion ratios (VA/Q) using single photon emission computed tomography (SPECT) and continuous infusion of 133Xe. Single photon transmission tomography was used for attenuation correction, for delineation of the lungs and for VA/Q calculations. Data are presented for six normal subjects and compared to those for two patients with moderate chronic obstructive pulmonary disease (COPD). The mean VA/Q for the whole lung of the normal subjects ranged from 0·49 to 0·65, group mean 0·56 ± 0·07 (1 SD), and there was no significant difference between the right and left lung. The consistently too low VA/Q values are related to the inability to measure regional blood volume and the low resolution of the scintillation camera, giving an under-estimation of tracer input. For the normal subjects, the dispersion of VA/Q, as defined by the standard deviation of the individual distribution functions, ranged from 0·12 to 0·19. One of the patients was characterized by a low mean VA/Q of 0·35, and the other patient had a wide dispersion (SD) of VA/Q of 0·37. In the normal subjects, a consistent VA/Q gradient was found only in the ventrodorsal direction. 133Xe and SPECT can be used to obtain meaningful biological information regarding ventilation/perfusion relationships of potential clinical value. [ABSTRACT FROM AUTHOR]

Background: End-stage liver disease is accompanied by a hyperkinetic circulation sometimes combined with hypoxaemia. Nitric oxide overproduction has been described as a possible cause by dilating the vasculature and decreasing cardiac afterload. The aim of this study was to evaluate haemodynamics, ventilation/perfusion matching, alveolar and alveolar dead space ventilation and resistance of systemic and pulmonary vasculature during liver transplantation. Methods: Ten liver transplantation patients were studied. Cardiac output, CO, was measured with thermodilution technique. Pulmonary shuntflow was calculated from standard formulas. Effective cardiac output, COeff, was defined as the CO in contact with alveolar ventilation, VA. Effective alveolar ventilation, VAeff, was defined as VA in contact with pulmonary circulation. Measurements were performed during dissection, anhepatic and reperfusion phases. Results: During the dissection phase the shunt was 23±3%, COeff was 7.9±0.6 l/min, SVR was 620±67 dyn · s/cm5, VAeff was 3.4±0.5 l/min, SaO2 was 98±1% and SvO2 was 86±2%. Corresponding values during the anhepatic phase were 16±2%, 5.6±0.4 l/min, 931±78 dyn · s/cm5, 3.1±0.2 l/min, 99±1% and 88±1%. During the reperfusion phase the values returned to levels close to that of the dissection phase. The reduction of COeff between the dissection and the anhepatic phase was significant (P<0.01). Conclusions: The low vascular resistance is accompanied by a high cardiac output. In spite of the high shunt fraction, these patients were not hypoxaemic. This is explained by the fact that the increased cardiac output leads to a decrease in arterio-mixed venous oxygen content difference and an increase in mixed venous oxygenation level, SvO2 86–88%, normal value ≈70%. The VAeff/COeff in this study was ≈0.5, i.e. the effective cardiac output, COeff is 235, 180 and 197% of the effective alveolar ventilation, VAeff during the three phases. Thus, about twice the amount blood is oxygenated as compared to a normodynamic situation, which compensates for the effect of the shunt flow on oxygenation. [ABSTRACT FROM AUTHOR]

Each of 40 college students received 6 presentations of white noise at an intensity of either 80 or 110 dB during either inspiration or expiration. Changes in tidal volume, inspiratory period, and expiratory period elicited by that stimulation were studied. Auditory stimulation produced respiratory changes which could be regarded conveniently as two phasic responses. We labeled these responses the initial phasic response and the delayed phasic response. The initial response was limited to the respiratory period during which stimulation was delivered. It consisted of a brief inspiratory movement which increased the speed of inspiratory periods during which it occurred but decreased the speed of expiratory periods daring which it occurred. In either case, the initial phasic response increased ventilation. The delayed phasic response was an increase both in speed and tidal volume of respiratory cycles subsequent to the period during which stimulation was delivered. Like the initial response, the delayed response increased ventilation. The effects of the delayed response were more widespread when stimulation was delivered during expiration rather than during inspiration. Stimulus intensity and stimulus repetition respectively potentiated and attenuated both the initial and the delayed phasic response. The findings are compared with those of earlier research on respiratory changes elicited by auditory stimulation. [ABSTRACT FROM AUTHOR]

Background: We aimed to investigate the physiological mechanism and spatial distribution of increased physiological dead-space, an early marker of ARDS mortality, in the initial stages of ARDS. We hypothesized that: increased dead-space results from the spatial redistribution of pulmonary perfusion, not ventilation; such redistribution is not related to thromboembolism (ie, areas with perfusion = 0 and infinite ventilation-perfusion ratio, V ˙ / Q ˙ ), but rather to moderate shifts of perfusion increasing V ˙ / Q ˙ in non-dependent regions., Methods: Five healthy anesthetized sheep received protective ventilation for 20 hours, while endotoxin was continuously infused. Maps of voxel-level lung ventilation, perfusion, V ˙ / Q ˙ , CO 2 partial pressures, and alveolar dead-space fraction were estimated from positron emission tomography at baseline and 20 hours., Results: Alveolar dead-space fraction increased during the 20 hours (+0.05, P = .031), mainly in non-dependent regions (+0.03, P = .031). This was mediated by perfusion redistribution away from non-dependent regions (-5.9%, P = .031), while the spatial distribution of ventilation did not change, resulting in increased V ˙ / Q ˙ in non-dependent regions. The increased alveolar dead-space derived mostly from areas with intermediate V ˙ / Q ˙ (0.5≤ V ˙ / Q ˙ ≤10), not areas of nearly "complete" dead-space ( V ˙ / Q ˙ >10)., Conclusions: In this early ARDS model, increases in alveolar dead-space occur within 20 hours due to the regional redistribution of perfusion and not ventilation. This moderate redistribution suggests changes in the interplay between active and passive perfusion redistribution mechanisms (including hypoxic vasoconstriction and gravitational effects), not the appearance of thromboembolism. Hence, the association between mortality and increased dead-space possibly arises from the former, reflecting gas-exchange inefficiency due to perfusion heterogeneity. Such heterogeneity results from the injury and exhaustion of compensatory mechanisms for perfusion redistribution., (© 2020 The Acta Anaesthesiologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.)

Objective: To compare the effects of two different intraoperative CO 2 pressures (8 and 15 mmHg) during laparoscopic hysterectomy for benign uterine pathologies in terms of postoperative abdominal and shoulder pain, laparoscopy-mediated vegetative alterations, pain medication requirement, arterial CO 2 pressure (pCO 2 ), surgical parameters, and safety., Design: Prospective randomised controlled study., Setting: German university hospital., Population: Female patients undergoing laparoscopic hysterectomy for benign uterine pathologies., Methods: Patients were randomised to a standard pressure (SP; 15 mmHg, control) or low-pressure (LP; 8 mmHg, experimental) group., Main Outcome Measures: Primary outcomes were postoperative abdominal and shoulder pain intensities, measured via numeric rating scale (NRS) and vegetative parameters (fatigue, nausea, vomiting, bloating) at 3, 24, and 48 hours postoperatively. Secondary outcomes were pain medication requirement (mg) and arterial pCO 2 (mmHg). Surgical parameters and intra- and postoperative complications were also recorded., Results: In total, 178 patients were included. Patients in the LP group (n = 91) showed significantly lower postoperative abdominal and shoulder pain scores, fewer vegetative alterations, lower pain medication requirements, a shorter postoperative hospitalization, and lower intra- and postoperative arterial pCO 2 values compared with the SP group (n = 87; P ≤ 0.01). No differences in intra- and postoperative complications were observed between groups., Conclusions: Low-pressure laparoscopy seems to be an effective and safe technique for the reduction of postoperative pain and laparoscopy-induced metabolic and vegetative alterations following laparoscopic hysterectomy for benign indications., Tweetable Abstract: Low-pressure laparoscopy seems to be an effective and safe technique for reduction of pain following laparoscopic hysterectomy., (© 2019 Royal College of Obstetricians and Gynaecologists.)

Pulmonary gas exchange is the primary function of the lung, and during my lifetime, its measurement has passed through many stages. When I was born, many physiologists still believed that the lung secreted oxygen. When I was a medical student, the only way we had to recognize defective gas exchange was whether the patient was cyanosed. The advent of the oximeter soon showed that this sign could be very misleading. A breakthrough was the introduction of blood gas electrodes that could measure the PO2, PCO2, and pH of a small sample of arterial blood. It was soon recognized that the commonest cause of hypoxemia was ventilation‐perfusion inequality, and that this could also be responsible for CO2 retention. In the early days, the understanding of the mechanisms of pulmonary gas exchange relied on graphical analysis because the oxygen and carbon dioxide dissociation curves are nonlinear and interdependent which precluded algebraic methods. However, with the introduction of digital computing, problems that had hitherto been impossible to tackle became amenable to study. A key advance was the development of the Multiple Inert Gas Elimination Technique. Now, noninvasive methods for measuring gas exchange show promise, and the whole subject continues to develop. I have devoted much of my life thinking about pulmonary gas exchange. The topic has changed enormously from the erroneous view that the lung actively secretes oxygen, to very sophisticated computer analyses of the distribution of ventilation and blood flow in the lung. Exciting advances continue to occur. [ABSTRACT FROM AUTHOR]

The author argues against a proposal to stop the use of the anticoagulant warfarin. He describes his battle with a ventilation-perfusion lung scan, with pulmonary embolus (PE). He comments on the mantra that the chances of a warfarin-induced haemorrhage and a recurrence of venous thromboembolism (VTE) in the absence of the anticoagulant were similar.

Endothelial (EC) surface expressions of P-selectin and von WIllebrand factor (vWf) underlie lung recruitment of leukocytes and platelets, respectively. We determined surface versus intracellular expressions, respectively in control and Triton-permeabilized EC. From isolated blood-perfused rat lungs (IBPLs) given 2 h of high (HV) or low (LV) tidal volume ventilation at 6 or 12 ml/kg, respectively, we recovered fresh EC (FLEC). We exposed FLEC to specific, fluorescence-tagged mAbs, then viewed them by confocal microscopy. As compared with LV, HV increased surface P-selectin and vWf by 98±8 and 69±8 %, respectively (mean±SE; n=3, P<.05). By contrast intracellular P-selectin increased 89±8%, while vWf decreased 10±13% (n=3, P<.05). In HV, leukocyte- and platelet-depleted blood perfusion decreased surface P-selectin and vWf by 40±9 and 35±6% (n=3, P<.05), respectively and the corresponding stores by 22±2 and 25±6% (P<0.05). Thus in HV, stress-induced increases of surface EC expression depleted intracellular stores of vWf, but not of P-selectin. Leukocyte- and platelet-depletion reduced store contents of both receptors equally. We conclude that ventilation stress differentially regulates EC stores by increasing P-selectin and decreasing vWf. These differential effects are determined by EC interactions with leukocytes and platelets. [ABSTRACT FROM AUTHOR]

Background: During cardiopulmonary resuscitation (CPR) the ventilation/perfusion distribution (VA /Q) within the lung is difficult to assess. This experimental study examines the capability of multiple inert gas elimination (MIGET) to determine VA /Q under CPR conditions in a pig model., Methods: Twenty-one anaesthetised pigs were randomised to three fractions of inspired oxygen (1.0, 0.7 or 0.21). VA/ Q by micropore membrane inlet mass spectrometry-derived MIGET was determined at baseline and during CPR following induction of ventricular fibrillation. Haemodynamics, blood gases, ventilation distribution by electrical impedance tomography and return of spontaneous circulation were assessed. Intergroup differences were analysed by non-parametric testing., Results: MIGET measurements were feasible in all animals with an excellent correlation of measured and predicted arterial oxygen partial pressure (R(2)  = 0.96, n = 21 for baseline; R(2)  = 0.82, n = 21 for CPR). CPR induces a significant shift from normal VA /Q ratios to the high VA /Q range. Electrical impedance tomography indicates a dorsal to ventral shift of the ventilation distribution. Diverging pulmonary shunt fractions induced by the three inspired oxygen levels considerably increased during CPR and were traceable by MIGET, while 100% oxygen most negatively influenced the VA /Q. Return of spontaneous circulation were achieved in 52% of the animals., Conclusions: VA /Q assessment by MIGET is feasible during CPR and provides a novel tool for experimental purposes. Changes in VA /Q caused by different oxygen fractions are traceable during CPR. Beyond pulmonary perfusion deficits, these data imply an influence of the inspired oxygen level on VA /Q. Higher oxygen levels significantly increase shunt fractions and impair the normal VA /Q ratio., (© 2014 The Acta Anaesthesiologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.)