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The BodPod® (COSMED, Concord, CA) uses predicted (pTGV) or measured thoracic gas volume (mTGV) during estimations of percentage body fat (%BF). In young adults, there is inconsistent evidence on the variation between pTGV and mTGV, and the effect of sex as a potential covariate on this relationship is unknown. This study examined the difference between TGV assessments and its effect on %BF and potential sex differences that may impact this relationship. A retrospective analysis of BodPod® pTGV and mTGV for 95 men and 86 women ages 18–30 years was performed. Predicted TGV was lower than mTGV for men (−0.49 ± 0.7 L; p p p > .05) or %BF (−0.03 ± 0.2%; p > .05). The two-predictor model of sex and height was able to account for 57.9% of the variance in mTGV, F(2, 178) = 122.5, p p

Objectives Body composition measurements with air displacement plethysmography (ADP) define body volume, which must be corrected for thoracic gas volume (TGV). We hypothesized that physiologic changes owing to pregnancy could affect the accuracy of predicted TGV and introduce errors into body composition measurements. Methods We investigated the effect of measuring versus predicting TGV on the accuracy of body composition calculations measured with ADP in overweight and obese pregnant women. The fat and fat-free masses of 110 women were determined with ADP with predicted and measured TGV. Results Measured TGV decreased from early to late pregnancy (P = 0.0002). Compared with measured TGV, predicted TGV was 6.3% higher during early gestation and 12.6% higher during late gestation (both P ≤ 0.001). The use of predicted instead of measured TGV in body composition calculations resulted in an overestimation of fat mass by 0.8% during the early stage, and 2.6% during the late stage of pregnancy (both P ≤ 0.001). Conclusions Measuring TGV increases the accuracy of body composition measurement by ADP in overweight and obese women, particularly during the late stage of pregnancy.

We investigated the effect of rapid weight loss (RWL) and weight regain (WR) on thoracic gas volume (VTG) and body composition assessment using air displacement plethysmography (ADP) in male wrestlers. Eight male elite collegiate wrestlers completed a RWL regimen (6% of body mass) over a 53-h period, which was followed by a 13-h WR period. ADP was used at three time points (baseline (T1), post-RWL (T2) and post-WR (T3)) according to the manufacturer&rsquo, s testing recommendations. The total body water and bone mineral content were estimated using the stable isotope dilution method and dual energy X-ray absorptiometry, respectively, at the same time points. Body composition was assessed with two-component (2C) or four-component (4C) models using either the measured VTG (mVTG) or predicted VTG (pVTG). Measured VTG increased from T1 to T2 (0.36 &plusmn, 0.31 L, p &lt, 0.05) and decreased from T2 to T3 (&minus, 0.29 &plusmn, 0.15 L, p &lt, 0.01). However, the changes in fat mass and fat free mass, which were calculated by both 2C and 4C models, were not significantly different when compared between calculations using mVTG and those using pVTG. Our results indicate that VTG significantly changes during RWL and WR, but both measured and predicted VTG can be used to assess changes in body composition during RWL and WR.

Air displacement plethysmography (ADP) is a popular method for estimating body density (Db). Most ADP tests are performed once, with test-retest investigations scarce. Therefore, we investigated test-retest reliability of ADP. Active men (n = 25) and women (n = 25) volunteered and followed standard pretest guidelines. Participants wore dry, form-fitting swimwear and manufacturer-supplied swim caps. In a single session, two ADP trials with measured thoracic gas volume (TGV) were performed without repositioning participants. Separate 2 (sex) × 2 (ADP trial) repeated-measures ANOVAs were performed to investigate within-between comparisons of Db, TGV, body volume (Vb), and relative fatness (%BF). Paired t tests were used to investigate significant differences as appropriate. The Bland and Altman technique was used to depict individual intertrial variations. For all analyses, α =.05. A significant main effect for sex was found; men were lower in %BF and higher in all other variables compared with women. Individual variability was notable (ADP1–ADP2). The range of individual intertrial differences were larger for women than men, respectively, for Db (-0.0096–0.0045 g/cc; -0.0019–0.0054 g/cc), TGV (-0.623–1.325 L; -0.584–0.378 L), Vb (-0.249–2.10 L; -0.234–0.397 L), and %BF (-2.1–4.4%; -0.2–0.9%). When assessing body composition of women via ADP or using Db from ADP in a multicomponent model, at least two trials with measured TGV should be performed and the average of the values recorded and reported.

Background: Body composition assessment has become increasingly popular in clinical and research areas. But any body composition measurement technique that is used in both clinical and research settings should be reliable and valid. Objectives: Our first aim was to compare predicted thoracic gas volume (Vtgpred) with measured thoracic gas volume (Vtgmeas) using the BOD POD in people living with HIV/AIDS (PLWHA) in Southwest Ethiopia. The second aim was to determine the effect of thoracic gas volume (Vtg) measurement ways on estimation of body fat (BF) using the BOD POD in PLWHA in Southwest Ethiopia. Method: Cross-sectional study was conducted on 68 PLWHA who had follow up at Jimma University Specialized Hospital (JUSH). Subjects were collected using convenience sampling technique. Agreement between the methods was tested using paired t-test, Pearson’s correlation, linear regression, and Bland-Altman plot. Result: Much percent of study subjects were malnourished (60.3%). Vtg and percent body fat (%BF) did not differ significantly (p>0.05) between the two modes of assessment (predicted and measured). Strong correlation was observed between Vtgpred and Vtgmeas (r=0.82, p

1. The pattern of breathing in 12 patients with severe irreversible airflow obstruction has been studied during ventilatory stimulation by rebreathing CO2. Mean maximum tidal volume response was only 1·23 ± 0·30 litres (mean ± sd); this represented 65% of mean measured vital capacity and 82% of mean measured inspiratory capacity. During the course of rebreathing mean total breath duration was reduced from 3·48 ± 0·93 to 2·44 ± 0·48 s. 2. End-expiratory thoracic gas volume (FRC) was elevated at rest in all subjects and increased significantly by a further 0·50–1·90 litres during ventilatory stimulation in 10 of the 12 subjects. The maximum increase in FRC was proportional to the degree of airflow obstruction afforded by the airways in each subject. 3. It is suggested that the increase in FRC during ventilatory stimulation is responsible for the diminished tidal volume response and is an important determinant of breathing pattern and symptomatology in patients with airflow obstruction.

The aim of the study was to evaluate air-displacement plethysmography (ADP) thoracic gas volume (TGV) prediction equations in children representing a wide range of body mass index (BMI).254 children (5 to 17 years) were recruited from two centres (England and the United States). Subjects were stratified into three BMI categories according to the International Obesity TaskForce (IOTF) criteria: lean (48 male, 42 female), overweight (15 male, 29 female), and obese (52 male, 68 female). As part of the normal ADP procedure, TGV was measured (TGV(Meas)), predicted using child specific equations developed by Fields (TGV(Fields)) and adult derived equations by Crapo (TGV(Crapo)) with percentage body fat (PF) estimates subsequently calculated (PF(Meas), PF(Fields), PF(Crapo)).Compared with the mean TGV(Meas), the TGV(Fields) estimates were within+/-0.2 L in all groups, except obese males (+0.5 L), while the mean TGV(Crapo) estimates were greater than+/-0.3 L in all groups except lean males (+0.1 L). When converted to PF, the mean PF(Fields) estimates were within+/-1% of the measured value in all groups, except obese males (+1.1%), while the mean PF(Crapo) estimates were greater than+/-1% in all groups, except lean males (+0.5%). Using either prediction equation, Bland-Altman analysis revealed that the greatest PF+/-95% limits of agreement were in the lean and overweight groups and lowest in the obese groups.The Fields child-specific TGV prediction equations provide accurate mean PF estimates and appear better than using the Crapo equations if a measured TGV cannot be achieved in children of a wide range of BMI. However, individual predictions may result in large PF errors especially in lean children.

Despite the increasing prevalence of asthma in Viet Nam, the country has limited means for respiratory function testing. A previous study using the forced oscillation technique suggested lower respiratory resistance between French and Vietnamese children at 10 years but not 6 years of age. If the hypothesis of a significant ethnic difference in airway caliber is correct, then similar differences should exist at adult age. To test the hypothesis, a plethysmographic study was set up to measure airway resistance and specific airway resistance in healthy young adults in France and Viet Nam. We took advantage of the study to provide reference values for lung volume in these populations. Airway resistance is significantly larger in Vietnamese than in Caucasians but there is no difference in specific airway resistance. Altogether the study does not support the consequence of a putative ethnic difference in childhood airway caliber on airway resistance normalized for lung volume at adult age. The standing height is the best predictor of the total lung capacity, while ethnicity is an important predictor of vital capacity and of the residual volume to total lung capacity ratio. This is the first study which provides reference values for airway resistance, specific airway resistance and lung volumes by plethysmography in healthy young Vietnamese adults. Plethysmography was validated in the north of Viet Nam, and the study allowed initiating a young working group on asthma diagnosis in Vietnam; La fréquence de l’asthme augmente au Vietnam, mais les moyens de diagnostic et d’évaluation fonctionnelle sont limités. Une étude précédente utilisant la technique des oscillations forcées a montré une différence de résistance des voies aériennes entre enfants français et vietnamiens à l’âge de 10 ans mais pas à 6 ans. Si l’hypothèse d’une différence ethnique significative est correcte, alors des différences semblables devraient aussi exister à l’âge adulte. Pour tester l’hypothèse, une étude par pléthysmographie a été mise en place pour mesurer la résistance des voies aériennes et la résistance spécifique des voies aériennes chez de jeunes adultes sains en France et au Vietnam. Nous avons profité de l’étude pour établir des valeurs de référence pour les volumes pulmonaires dans ces populations. La résistance des voies aériennes est significativement plus grande chez les sujets vietnamiens que chez les caucasiens, mais il n’y a aucune différence de résistance spécifique des voies aériennes. Au final, l’étude ne montre pas de différence de calibre des voies aériennes normalisé pour le volume pulmonaire liée l’ethnie, à l’âge adulte. La taille debout est le facteur prédictif le plus important pour la capacité pulmonaire totale, tandis que l’ethnicité est un facteur important pour la capacité vitale et le rapport du volume résiduel à la capacité pulmonaire totale. Cette étude est la première qui fournit des valeurs de référence pour la résistance des voies aériennes, la résistance spécifique des voies aériennes et les volumes pulmonaires par pléthysmographie chez l’adulte vietnamien. La pléthysmographie a été validée à Hanoi et l’étude a permis la formation d’un nouveau groupe de travail sur le diagnostic et la prise en charge de l’asthme au Vietnam

Despite the increasing prevalence of asthma in Viet Nam, the country has limited means for respiratory function testing. A previous study using the forced oscillation technique suggested lower respiratory resistance between French and Vietnamese children at 10 years but not 6 years of age. If the hypothesis of a significant ethnic difference in airway caliber is correct, then similar differences should exist at adult age. To test the hypothesis, a plethysmographic study was set up to measure airway resistance and specific airway resistance in healthy young adults in France and Viet Nam. We took advantage of the study to provide reference values for lung volume in these populations. Airway resistance is significantly larger in Vietnamese than in Caucasians but there is no difference in specific airway resistance. Altogether the study does not support the consequence of a putative ethnic difference in childhood airway caliber on airway resistance normalized for lung volume at adult age. The standing height is the best predictor of the total lung capacity, while ethnicity is an important predictor of vital capacity and of the residual volume to total lung capacity ratio. This is the first study which provides reference values for airway resistance, specific airway resistance and lung volumes by plethysmography in healthy young Vietnamese adults. Plethysmography was validated in the north of Viet Nam, and the study allowed initiating a young working group on asthma diagnosis in Vietnam; La fréquence de l’asthme augmente au Vietnam, mais les moyens de diagnostic et d’évaluation fonctionnelle sont limités. Une étude précédente utilisant la technique des oscillations forcées a montré une différence de résistance des voies aériennes entre enfants français et vietnamiens à l’âge de 10 ans mais pas à 6 ans. Si l’hypothèse d’une différence ethnique significative est correcte, alors des différences semblables devraient aussi exister à l’âge adulte. Pour tester l’hypothèse, une étude par pléthysmographie a été mise en place pour mesurer la résistance des voies aériennes et la résistance spécifique des voies aériennes chez de jeunes adultes sains en France et au Vietnam. Nous avons profité de l’étude pour établir des valeurs de référence pour les volumes pulmonaires dans ces populations. La résistance des voies aériennes est significativement plus grande chez les sujets vietnamiens que chez les caucasiens, mais il n’y a aucune différence de résistance spécifique des voies aériennes. Au final, l’étude ne montre pas de différence de calibre des voies aériennes normalisé pour le volume pulmonaire liée l’ethnie, à l’âge adulte. La taille debout est le facteur prédictif le plus important pour la capacité pulmonaire totale, tandis que l’ethnicité est un facteur important pour la capacité vitale et le rapport du volume résiduel à la capacité pulmonaire totale. Cette étude est la première qui fournit des valeurs de référence pour la résistance des voies aériennes, la résistance spécifique des voies aériennes et les volumes pulmonaires par pléthysmographie chez l’adulte vietnamien. La pléthysmographie a été validée à Hanoi et l’étude a permis la formation d’un nouveau groupe de travail sur le diagnostic et la prise en charge de l’asthme au Vietnam

Electrical stimulation of intercostal muscles was employed to measure thoracic gas volume (TGV) during airway occlusion in the absence of respiratory effort at different levels of lung inflation. In 15 tracheostomized and mechanically ventilated CBA/Ca mice, the value of TGV obtained from the spontaneous breathing effort available in the early phase of the experiments (TGVsp) was compared with those resulting from muscle stimulation (TGVst) at transrespiratory pressures of 0, 10, and 20 cmH2O. A very strong correlation ( r2 = 0.97) was found, although with a systematically (∼16%) higher estimation of TGVst relative to TGVsp, attributable to the different durations of the stimulated (∼50 ms) and spontaneous (∼200 ms) contractions. Measurements of TGVst before and after injections of 0.2, 0.4, and 0.6 ml of nitrogen into the lungs in six mice resulted in good agreement between the change in TGVst and the injected volume ( r2 = 0.98). In four mice, TGVsp and TGVst were compared at end expiration with air or a helium-oxygen mixture to confirm the validity of isothermal compression in the alveolar gas. The TGVst values measured at zero transrespiratory pressure in all CBA/Ca mice [0.29 ± 0.05 (SD) ml] and in C57BL/6 ( N = 6; 0.34 ± 0.08 ml) and BALB/c ( N = 6; 0.28 ± 0.06 ml) mice were in agreement with functional residual capacity values from previous studies in which different techniques were used. This method is particularly useful when TGV is to be determined in the absence of breathing activity, when it must be known at any level of lung inflation or under non-steady-state conditions, such as during pharmaceutical interventions.

There are no data published about the agreement between the measurement of thoracic gas volume (TGV) during the airway resistance (TGV-Raw) and the conventional technique described by Dubois. The aim of this study was to establish the agreement between both methods to measure TGV. We studied eighty consecutive subjects. Only sixty-six performed acceptable plethysmography maneuvers. The patients were measured with a constant volume plethysmograph (Medical Graphics 1085 DL). TGV was performed in the same patient with two techniques: 1) during the airway resistance (Raw) measurement (TGV-Raw) and 2) during quiet breathing at the end of expiration (TGV). The panting frequency was 1 to 2 Hz with both maneuvers. The differences between both techniques were expressed in percentage (D TGV %) and absolute values (D TGV). The TGV-Raw of the whole group was higher than TGV (3.69 ± 1.08l vs 3.28 ± 1.05l, p < 0.001). Similarly, the subgroups of patients had a greater TGV-Raw than TGV (Normal: 3.44 ± 0.77l vs 2.98 ± 0.72l, p < 0.001; Obstructive: 4.08 ± 1.19l vs 3.71 ± 1.15l, p < 0.001; Restrictive: 2.62 ± 0.49l vs 2.25 ± 0.51l, p < 0.01). There was a considerable lack of agreement between the TGV-Raw and TGV, with discrepancies of up to +0.95l or +34%. The D TGV % was similar between the patients' subgroups and between the subjects with different degree of airflow obstruction (Normal: 16.5 ± 10%, Obstructive: 10.8 ± 9.4%, Restrictive: 18 ± 14.3%, p NS; mild obstruction: 10.7 ± 11%, moderate obstruction: 12.3 ± 5.7, severe obstruction: 10.1± 6.6, p NS). In conclusion, TGV-Raw was larger than TGV. This was because the patients generally panted at a volume above FRC when performing the TGV-Raw maneuver. TGV-Raw should not be used to estimate FRC because FRC would be overestimated and the diagnosis of air trapping may be erroneous.No hay datos publicados sobre el acuerdo entre la medición del volumen de gas torácico (VGT) durante la maniobra de resistencia de la vía aérea (Raw) y la técnica de medición convencional del VGT descripta por Dubois . El objetivo del estudio fue establecer el grado de acuerdo entre ambos métodos para medir VGT. Se estudiaron 80 sujetos consecutivos que concurrieron al laboratorio pulmonar para hacerse un examen funcional respiratorio. Solo 66 individuos realizaron maniobras pletismográficas adecuadas. Los pacientes fueron medidos con un pletismógrafo de volumen constante (MG 1085 DL). El VGT fue realizado en el mismo paciente con dos técnicas: 1) Durante la maniobra de la Raw (VGT- Raw) ; 2) Durante la respiración tranquila al final de la espiración (VGT). Las diferencias entre ambas técnicas se expresaron en porcentaje (D TGV %) y en valores absolutos (D TGV). El VGT- Raw del grupo total fue mayor que el VGT (3.69 ± 1.08l vs 3.28 ± 1.05l, p < 0.001). Del mismo modo el VGT- Raw de los diferentes subgrupos fue mayor que el VGT (Normal: 3.44 ± 0.77l vs 2.98 ± 0.72l, p < 0.001; Obstructivo: 4.08 ± 1.19l vs 3.71 ± 1.15l, p < 0.001; Restrictivo: 2.62 ± 0.49L vs 2.25 ± 0.51l, p < 0.01). Se observó falta de acuerdo entre el VGT- Raw y el VGT con diferencias de hasta +0.95L o +34% entre ambos métodos. El D TGV % fue similar entre los subgrupos y con los diferentes grados de obstrucción al flujo aéreo (Normal: 16.5 ± 10%, Obstructivo: 10.8 ± 9.4%, Restrictivo: 18 ± 14.3%, p NS; obstrucción leve: 10.7 ± 11%, obstrucción moderada: 12.3 ± 5.7, obstrucción grave: 10.1± 6.6, p NS). El VGT- Raw fue sistemáticamente mayor que el VGT. Esto se debió a que los pacientes generalmente jadearon a un volumen pulmonar por arriba de FRC cuando realizaron la maniobra de Raw . No debería usarse el VGT- Raw para estimar FRC ya que la misma puede sobreestimarse y el diagnóstico de atrapamiento aéreo puede ser erróneo.

Thoracic gas volume (Vtg) can be measured with body plethysmography by either repetitive panting or one single inspiratory effort against a shutter occluding the airways. The panting technique is preferred, but may be demanding. We aimed to assess the precision of these two methods and the degree of agreement between them. Vtg and functional residual capacity (FRC) were measured in 155 subjects with a standard, commercially available plethysmograph, acting as a variable-pressure, constant-volume device when Vtg is determined. Total lung capacity (TLC) and residual lung volume (RV) were calculated subsequent to a full vital capacity manoeuvre. For non-asthmatic healthy subjects, the standard deviations (SD) of the differences between two replicate measurements of FRC, TLC and RV were respectively 0.16, 0.13 and 0.14 litres with the panting technique, and 0.18, 0.18 and 0.23 litres with the single inspiratory effort technique. In percentage of the respective lung volumes, the corresponding 1.96 SDs were 20%, 8% and 40% with the panting technique and 23%, 12% and 67% with the single inspiratory effort technique. Between the two techniques, 95% limits of agreement were 21% for FRC, 11% for TLC and 58% for RV. The variability of Vtg and FRC accounted for most of the variability of TLC and RV. In conclusion, the panting and the single inspiratory effort technique produced results that were comparable in magnitude, however with a better precision with the panting technique. The single inspiratory effort technique can be used as an alternative if the panting technique fails.

We have previously measured thoracic gas volume (V-TG) in spontaneously breathing mice using a whole body plethysmograph and have now extended our technique to allow for V-TG measurements during paralysis. BALB/c mice were anesthetized and placed in a body-box and ventilated via a tracheostomy cannula through the box wall. Box pressure (P-b) and tracheal pressure (P-ao) were measured during spontaneous breathing, and again after paralysis while mechanically compressing the chest. V-TG was much larger after paralysis (0.49+/-0.06 ml, positive end-expiratory pressure=2 cmH(2)O) when compared with spontaneous breathing (0.31+/-0.01 ml). External chest compression produced looping in the plots of P-b versus P-ao that was attributable to gradual changes in P-b upon release of the mechanical chest compression and had the character of thermal transients. Under the assumption that the rate of heating of the air in the chamber was proportional to the pressure applied to the animal's chest, and that any increase in air temperature was dissipated by heat absorption by the chamber walls, we developed an algorithm that corrected for the thermal events. This yielded similar results for V-TG (0.30+/-0.02 ml) as obtained during spontaneous efforts. Our method may prove particularly useful when paralysis is required for the precise measurement of lung mechanics. (Less)

Abstract: The role of strong emotions in eliciting asthmatic exacerbations has been discussed in psychosomatic theory for decades. This relationship has mostly been studied in asthmatic individuals, while healthy control groups have received limited attention. Measuring procedures have partially been held responsible for conflicting results. We tested a new laboratory method on 20 healthy volunteers to examine the influence of emotions on airway obstructions. Short affective states were induced by presenting a negative (sadness), a positive (amusement), and a neutral movie clip lasting about 2 min with participants being seated in the glass box of a whole body plethysmograph - the gold standard for measuring airway resistance (Raw). Raw, specific airway resistance (sRaw), and thoracic gas volume (TGV) were measured in a baseline condition and immediately after each video presentation; in addition, sRaw was measured before and during each clip presentation. Based on subjects' ratings, the relevant affective states were successfully induced, while no specific state was provoked by the neutral movie. Airway obstructions, expressed as increases of sRaw, were observed during both the negative and positive clip but also in the neutral condition. No substantial effect of mood induction on Raw and TGV was obtained. The findings show a nonspecific effect of watching affective film clips on airway obstruction as measured by whole body plethysmography. Recommendations for a modified experimental protocol are given for future studies using this technique as a promising method.

The aim of our study was to examine the effect of labor and birth canal compression on the rate of clearance of lung fluid. We recruited 10 babies born by vaginal delivery and 10 born by elective cesarean section (ECS). Thoracic gas volume (TGV) was measured using total body plethysmography, and functional residual capacity (FRC) by argon dilution, at ages 4-6 h and 24 h. Additional measurements were obtained at age 48 h in the infants born by ECS. Our results showed significant increases in mean TGV (from 23.1 mL/kg to 27.4 mL/kg, P = 0.002) and FRC (from 21.2 mL/kg to 24.1 mL/kg, P = 0.04) between 4-6 h and 24 h of age after ECS delivery. Lung volumes did not change significantly over the next 24 h (TGV, 27.4 mL/kg, P = 0.97; FRC, 25.5 mL/kg, P = 0.42). In those infants born by vaginal delivery, the mean TGV at 4-6 h and 24 h were 26.7 and 28.7 mL/kg, respectively (P = 0.09), and the mean FRC results were 23.1 and 24.9 mL/kg, respectively, P = 0.08). The TGV tended to be lower at 4-6 h in those born by ECS than in infants born vaginally (23.1 vs. 26.7 mL/kg, P = 0.05). We conclude that there is a delay of up to 24 h in the establishment of final lung volumes in babies born without exposure to labor or passage through the birth canal, and that this may explain the increased respiratory morbidity associated with delivery by ECS.

The purpose of this study was to test a plethysmographic method of measuring thoracic gas volume (TGV) that, contrary to the usual panting method, would not require any active cooperation from the subject. It is based on the assumption that the out-of-phase component of airway impedance varies linearly with frequency. By using that assumption, TGV may be computed by combining measurements of total respiratory impedance (Zrs) and of the relationship between the plethysmographic signal (Vpl) and airway flow (V˙) during forced oscillations at several frequencies. Zrs and Vpl/V˙were measured at 10 noninteger multiple frequencies ranging from 4 to 29 Hz in 15 subjects breathing gas in nearlybtps conditions. Forced oscillation measurements were immediately followed by determination of TGV by the standard method. The data were analyzed on different frequency ranges, and the best agreement was seen in the 6- to 29-Hz range. Within that range, forced oscillation TGV and standard TGV differed little (3.92 ± 0.66 vs. 3.83 ± 0.73 liters, n = 77, P < 0.05) and were strongly correlated ( r = 0.875); the differences were not correlated to the mean of the two estimates, and their SD was 0.35 liter. In seven subjects the differences were significantly different from zero, which may, in part, be due to imperfect gas conditioning. We conclude that the method is not highly accurate but could prove useful when, for lack of sufficient cooperation, the panting method cannot be used. The results of computer simulation, however, suggest that the method would be unreliable in the presence of severe airway inhomogeneity or peripheral airway obstruction.

The Bod Pod has been found to be both reliable and valid against several criterion methods such as hydrostatic weighing, and dual energy x-ray absorptiometry, and under different conditions, such as clothing level, dehydrated states, and body temperature changes. However, questions still remain regarding the effects of an acute bout of exercise on the Bod Pod. Therefore, the purpose of this study was to determine the effects of an acute bout of exercise on the estimations made by the Bod Pod. Participants (15 males and 22 females) ranged in age from 18-27 years and were currently exercising. Height and weight were measured prior to entering the Bod Pod. Baseline Bod Pod measures were completed followed by a 30 minute cycling trial at 75% of heart rate max. Bod Pod measures were taken immediately following exercise and 2-hr post-exercise. Statistical differences between males and females were found at baseline between height (p

When using Boyle's Law for thoracic gas volume (Vtg) measurement, it is generally assumed that the alveolar pressure (Palv) does not differ from barometric pressure (Pbar) at the start of rarefaction and compression and that the product of the change in volume and pressure (delta P x delta V) is negligibly small. In a gentle panting maneuver in which the difference between Palv and Pbar is small, errors introduced by these assumptions are likely to be small; however, this is not the case when Vtg is measured using a single vigorous inspiratory effort. Discrepancies in the Vtg between the "complex" version of Boyle's Law, which does not ignore delta P x delta V and accounts for large swings in Palv, and the "simplified" version, during both a panting maneuver and a single inspiratory effort were calculated for normal control subjects and patients with cystic fibrosis or asthma. Defining the Vtg from the complete version as "correct," the errors introduced by the simplified version ranged from -3 to +3% for the panting maneuver whereas they ranged from 2 to 9% for the inspiratory maneuver. Using the simplified equation, the Vtg for the inspiratory maneuver was 0.135 +/- 0.237 L greater (p < 0.02) than for the panting maneuver. This discrepancy disappeared when the complete equation was used. While the errors introduced by the use of the simplified version of Boyle's Law are small, they are systematic and unnecessary.

In order to determine if inspiratory time in preterm infants was influenced by lung volume, two studies were carried out. In the first investigation, carbon dioxide was used to stimulate tidal volume to a level three to six times normal. The anticipated decrease in inspiratory time at increased tidal volumes was not found. These preterm infants behaved in a similar fashion to vagotomized animals studied in the same way by Clark and von Euler. In the second investigation, Hering-Breuer activity was measured in relation to lung volume changes occurring with growth, measured in a body plethysmograph. Although thoracic gas volume correlated well with age and weight, inspiratory slowing with airway occlusion was found to be independent of both age and lung volume. These investigations suggest that neurologic factors have a significant influence on the inspiratory time in newborn human infants.

Background To determine the validity of the recently developed child-specific thoracic gas volume (TGV) prediction equations for use in air-displacement plethysmography (ADP) in diverse pediatric populations. Methods Three distinct populations were studied: European American and African American children living in Birmingham, Alabama and European children living in Lisbon, Portugal. Each child completed a standard ADP testing protocol, including a measured TGV according to the manufactures software criteria. Measured TGV was compared to the predicted TGV from current adult-based ADP proprietary equations and to the recently developed child-specific TGV equations of Fields et al. Similarly, percent body fat, derived using the TGV prediction equations, was compared to percent body fat derived using measured TGV. Results Predicted TGV from adult-based equations was significantly different from measured TGV in girls from each of the three ethnic groups (P < 0.05), however child-specific TGV estimates did not significantly differ from measured TGV in any of the ethnic or gender groups. Percent body fat estimates using adult-derived and child-specific TGV estimates did not differ significantly from percent body fat measures using measured TGV in any of the groups. Conclusion The child-specific TGV equations developed by Fields et al. provided a modest improvement over the adult-based TGV equations in an ethnically diverse group of children.

Air-displacement plethysmography (ADP) is now widely used for body composition measurement in pediatric populations. However, the manufacturer's software developed for adults leaves a potential bias for application in children and adolescents, and recent publications do not consistently use child-specific corrections. Therefore we analyzed child-specific ADP corrections with respect to quantity and etiology of bias compared with adult formulas. An optimal correction protocol is provided giving step-by-step instructions for calculations. In this study, 258 children and adolescents (143 girls and 115 boys ranging from 5 to 18 y) with a high prevalence of overweight or obesity (28.0% in girls and 22.6% in boys) were examined by ADP applying the manufacturer's software as well as published equations for child-specific corrections for surface area artifact (SAA), thoracic gas volume (TGV), and density of fat-free mass (FFM). Compared with child-specific equations for SAA, TGV, and density of FFM, the mean overestimation of the percentage of fat mass using the manufacturer's software was 10% in children and adolescents. Half of the bias derived from the use of Siri's equation not corrected for age-dependent differences in FFM density. An additional 3 and 2% of bias resulted from the application of adult equations for prediction of SAA and TGV, respectively. Different child-specific equations used to predict TGV did not differ in the percentage of fat mass. We conclude that there is a need for child-specific equations in ADP raw data analysis considering SAA, TGV, and density of FFM.

Objective: To develop child-specific thoracic gas volume (TGV) prediction equations for use in air-displacement plethysmography in 6- to 17-year-old children. Research Methods and Procedures: Study 1 developed TGV prediction equations using anthropometric variables after completing a measured TGV and air-displacement plethysmography test in 224 healthy boys and girls (11.2 ± 3.2 years, 45.3 ± 18.7 kg, 149.9 ± 18.5 cm). Study 2 cross-validated the prediction equations in a separate cohort of 62 healthy boys and girls (11.2 ± 3.4 years, 44.2 ± 15.3 kg, 149.4 ± 19.3 cm). Results: In Study 1 (development of TGV prediction equations), the quadratic relationship using height as the independent variable and the measured TGV as the dependent variable yielded the highest adjusted R2 and the lowest SE of estimate in both genders, thus producing the following prediction equations: TGV = 0.00056 × H2 − 0.12422 × H + 8.15194 (boys) and TGV = 0.00044 × H2 − 0.09220 × H + 6.00305 (girls). In Study 2 (cross-validation), no significant difference between the predicted and measured TGVs (−0.018 ± 0.377 liters) was observed. The regression between the measured TGV and the predicted TGV yielded a slope and intercept that did not significantly differ from the line of identity. Prediction accuracy was good as indicated by a high R2 (0.862) and low SE of estimate (0.369 liters). Discussion: The new child-specific TGV prediction equations accurately, precisely, and without bias estimated the actual TGV of 6- to 17-year-old children.

Pressure, flow and volume characteristics of the lung were measured using a body plethysmograph. The body plethymograph is a large airtight box used to measure thoracic gas volume and airway resistance. Using a volume displacement body plethysmograph, with rebreathing bag to minimize thermal exchange between lung and plethysmograph air, alveolar pressures were measured over a wide range of airflow rates and lung volumes. To collect isovolume pressure versus flow curves, software was custom designed. The results provide information concerning the mechanics of the respiratory system for use with the airflow perturbation device.

Previous studies have shown that the added resistance of a mini-Wright peak expiratory flow (PEF) meter reduced PEF by approximately 8% in normal subjects because of gas compression reducing thoracic gas volume at PEF and thus driving elastic recoil pressure. We undertook a body plethysmographic study in 15 patients with chronic obstructive pulmonary disease (COPD), age 65.9 +/- 6.3 yr (mean +/- SD, range 53-75 yr), to examine whether their recorded PEF was also limited by the added resistance of a PEF meter. The PEF meter increased alveolar pressure at PEF (Ppeak) from 3.7 +/- 1.4 to 4.7 +/- 1.5 kPa (P = 0.01), and PEF was reduced from 3.6 +/- 1.3 l/s to 3.2 +/- 0.9 l/s (P = 0.01). The influence of flow limitation on PEF and Ppeak was evaluated by a simple four-parameter model based on the wave-speed concept. We conclude that added external resistance in patients with COPD reduced PEF by the same mechanisms as in healthy subjects. Furthermore, the much lower Ppeak in COPD patients is a consequence of more severe flow limitation than in healthy subjects and not of deficient muscle strength.

The aim of this study was to determine which lung function test employed in the perinatal period gave the results most significantly associated with respiratory problems in infancy. The ratio of the proportion of time to reach peak tidal expiratory flow to total expiratory time (tPTEF:tE), thoracic gas volume (TGV) and airway resistance (R(aw)) (from which specific conductance (SG(aw)) was calculated) measurements were examined from 85 infants born at or near term. The infants were followed until at least one year of age and described as symptomatic if they wheezed for at least 24 hours. Twenty-three infants were symptomatic in the first year. The symptomatic group, compared to the asymptomatic, had a higher median FRC (p0.01) and R(aw) (p0.001); their median SG(aw) was lower (p0.001). It was possible to obtain tPTEF:tE results from only 61 infants; the median tPTEF:tE did not differ significantly between symptomatic and asymptomatic infants. Logistic regression analysis demonstrated a high R(aw) and FRC, but not a low tPTEF:tE, independently related to positive symptom status. A high R(aw) (26 cm H2O (1 s(-1))(-1)) was the most sensitive (83%) predictor of subsequent respiratory problems, but all the tests examined had low positive predictive values.

The purpose of this study was to evaluate a procedure for measurement of specific airway resistance (sRaw) by whole body plethysmography in young awake children accompanied by an adult. sRaw was measured by a single-step procedure, omitting the measurement of the thoracic gas volume. The frequency dependency of sRaw was investigated and the accuracy of simulating body temperature, atmospheric pressure and saturation with water vapour (BTPS) conditions by electronic compensation was assessed. One hundred and thirty one children with asthma were studied. In 57 children (mean (SD) age 5.6 (1.8) yrs) who performed measurements with and without an accompanying adult, the mean value of sRaw was 1.45 (0.36) and 1.44 (0.38) kPa x s, respectively, with a mean difference of 0.008 (0.152) kPa x s, and mean within-subject coefficients of variations (CV) of 8% and 10%, respectively. In 52 children (mean age 3.3 (0.8) yrs), for whom measurements made only in the presence of an accompanying adult, the CV was 8.5%. No measurements could be obtained in 22 children (17%) (mean age 2.8 (0.5) yrs). Measurements exhibited a significant frequency dependency, and electronic BTPS compensation substantially overestimated SRaw. In conclusion, the use of electronic compensation for simulating body temperature, atmospheric pressure and saturation with water vapour introduces a bias that affects the accuracy of the estimate of specific airway resistance. Nevertheless, plethysmographic measurements with and without an accompanying adult yielded comparable and equally repeatable estimates of specific airway resistance. The single-step plethysmographic procedure with an accompanying adult is a clinically useful method for evaluating airway function in children too young to perform plethysmographic measurements alone.

This study determined whether proportional assist ventilation (PAV) applied during constant power submaximal exercise could enable individuals with severe but stable COPD to increase their exercise tolerance.Prospective controlled study having a randomized order of intervention.Pulmonary function exercise laboratory.Ten subjects with severe stable COPD (mean [SD]: age=59 [6] years; FEV1=29 [7]% predicted; FEV1/FVC=33 [7]%; thoracic gas volume=201 [47]% predicted; diffusion of carbon monoxide=36 [10]% predicted; PaO2=76 [8] mm Hg; and PaCO2=41 [4] mm Hg).Each subject completed five sessions of cycling at 60 to 70% of their maximum power. The sessions differed only in the type of inspiratory assist: (1) baseline (airway pressure [Paw]=0 cm H2O); (2) proportional assist ventilation (PAV) (volume assist=6 [3] cm H2O/L, flow assist=3 [1] cm H2O/L/s); (3) continuous positive airway pressure (CPAP) (5 [2] cm H2O); (4) PAV+CPAP; and (5) sham (Paw=0 cm H2O).Dyspnea was measured using a modified Borg scale. Subjects reached the same level of dyspnea during all sessions but only PAV+CPAP significantly (p0.05) increased exercise tolerance (12.88 [8.74] min) vs the sham session (6.60 [3.12] min). Exercise time during the PAV and CPAP sessions was 7.10 [2.83] and 8.26 [5.54] min, respectively. Minute ventilation increased during exercise but only during PAV+CPAP was the end exercise minute ventilation greater than the unassisted baseline end exercise minute ventilation (36.2 [6.7] vs 26.6 [6.4] L/min, respectively; p0.05).In this study, PAV+CPAP provided ventilatory assistance during cycle exercise sufficient to increase the endurance time. It is now appropriate to evaluate whether PAV+CPAP will facilitate exercise training.

Introduction The aim of the study was to evaluate whether subject positioning would affect the measurement of raw body volume, thoracic gas volume, corrected body volume and the resulting percent body fat as assessed by air displacement plethysmography (ADP). Methods Twenty-five young adult men (20.7±1.1y, BMI = 22.5±1.4 kg/m2) were measured using the BOD POD® system using a measured thoracic gas volume sitting in a ‘forward bent’ position and sitting up in a straight position in random order. Results Raw body volume was 58±124 ml (p