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Approximately 20% of chronic obstructive pulmonary disease (COPD) patients have been considered to have a “nonhyperinflator phenotype.” However, this judgment depends on patients making a fully maximal inspiratory capacity (IC) maneuver at rest, since the IC during exercise is compared with this baseline measurement. We hypothesized that IC maneuvers at rest are sometimes submaximal and tested this hypothesis by measuring IC and associated neural respiratory drive at rest and during inhalation of CO2 and exercise in patients with COPD. Twenty-six COPD patients [age 66 ± 6 yr, mean forced expiratory volume in 1 s (FEV1) 40 ± 11% predicted] and 39 healthy subjects (age 39 ± 14 yr, FEV1 98 ± 12% predicted) were studied. IC and the diaphragm electromyogram (EMGdi) associated with it (EMGdi-IC) and forced inspiratory vital capacity (FIVC) and its corresponding EMGdi (EMGdi-FIVC) were measured during inhalation of 8% CO2 (8% CO2-92% O2) and room air. Incremental exhaustive cycle ergometer exercise was also performed in both patients with COPD and healthy subjects. IC, EMGdi-IC, FIVC, and EMGdi-FIVC during breathing 8% CO2 were significantly greater than those during breathing room air in both patients with COPD and healthy subjects (all P < 0.001). EMGdi-IC in patients with COPD constantly increased during exercise from 145 ± 40 µV at rest to 185 ± 52 µV at the end of exercise but change in IC was variable. Neural respiratory drive and its relevant IC increased during hypercapnia. Exercise-related hypercapnia in patients with COPD raises neural respiratory drives, which compensate for IC reduction, leading to underestimation of dynamic hyperinflation measured by IC at rest breathing room air. NEW & NOTEWORTHY Inspiratory capacity measured during hypercapnia is higher than that during eucapnia. Thus total lung capacity is not always be achieved by a standard inspiratory capacity maneuver, leading to risk of underestimation of dynamic hyperinflation in patients with severe chronic obstructive pulmonary disease after exhaustive exercise.

Background: In 2007 and 2012, the American Academy of Sleep Medicine (AASM) updated their scoring criteria for nocturnal respiratory events. We hypothesised that this could have led to changes in the apnoea-hypopnoea index (AHI) of patients with chronic obstructive pulmonary disease (COPD)/obstructive sleep apnoea (OSA) overlap syndrome. Methods: In a retrospective study, polysomnographic (PSG) recordings of 34 patients with COPD/OSA overlap syndrome were independently analysed using the AASM criteria from 2007 (AASM2007) and 2012 (AASM2012). The primary outcome was the difference in AHI, the secondary outcomes were frequency of hypopnoeas, diagnosis of overlap syndrome and differences between the AASM 2007 recommended (AASM2007Rec) and altered (AASM2007Alt) classifications. Data are presented as mean (standard deviation) if normally distributed, and as median (interquartile range) if non-normally distributed. Results: The PSGs of 34 elderly [aged 67 (7.0) years] and predominantly male (m:f, 31:3) patients with COPD [FEV1%pred 48.4% (19.6%)] were analysed. The AHI using AASM2007Rec criteria was 5.9 (2.0, 15.1) events/hour vs. 20.4 (11.5, 28.0) events/hour using the 2012 criteria (P

A fall of ≥ 20 % in forced expiratory volume in the first second (FEV1) with a cumulative dose of histamine ≤ 7.8 μmol is considered to indicate bronchial hyperactivity, but no method exists for patients who cannot perform spirometry properly. Here we hypothesized that increases in respiratory central output measured by chest wall electromyography of the diaphragm (EMGdi-c) expressed as a function of tidal volume (EMGdi-c/VT) would have discriminative power to detect a 'positive' challenge test.In a physiological study EMGdi was recorded from esophageal electrode (EMGdi-e) in 16 asthma patients and 16 healthy subjects during a histamine challenge test. In a second study, EMGdi from chest wall surface electrodes (EMGdi-c) was measured during a histamine challenge in 44 asthma patients and 51 healthy subjects. VT was recorded from a digital flowmeter during both studies.With histamine challenge test the change in EMGdi-e/VT in patients with asthma was significantly higher than that in healthy subjects (104.2 % ± 48.6 % vs 0.03 % ± 17.1 %, p0.001). Similarly there was a significant difference in the change of EMGdi-c/VT between patients with asthma and healthy subjects (90.5 % ± 75.5 % vs 2.4 % ± 21.7 %, p0.001). At the optimal cut-off point (29 % increase in EMGdi-c/VT), the area under the ROC curve (AUC) for detection of a positive test was 0.91 (p0.001) with sensitivity 86 % and specificity 92 %.We conclude that EMGdi-c/VT may be used as an alternative for the assessment of bronchial hypersensitivity and airway reversibility to differentiate patients with asthma from healthy subjects.

Background In 2007 and 2012, the American Academy of Sleep Medicine (AASM) updated their scoring criteria for nocturnal respiratory events. We hypothesised that this could have led to changes in the apnoea-hypopnoea index (AHI) and thus diagnosis of COPD associated obstructive sleep apnoea (OSA) overlap syndrome. Patients and methods In a retrospective study, polysomnographical recordings (PSG) of 11 patients with COPD/OSA overlap syndrome were independently analysed using the AASM criteria from 2007 and 2012. The primary outcome was the difference in AHI between the AASM 2012 and the AASM 2007 recommended and alternative scoring rules, secondary outcomes were the percentage of hypopnoeas and the diagnosis of overlap syndrome. Data are presented as mean (standard deviation) if normally distributed, and as median (interquartile range) for non-normally distributed data. Results The PSG of 11 obese, elderly and predominantly male patients with mild-moderate COPD were analysed (table). The AHI using AASM 2007 (recommended) criteria was 12.9 (5.8, 16.9) h-1 vs 18.7 (11.3, 24.7) h-1 using the 2012 criteria (p Conclusion The AHI significantly increases when the AASM 2012 instead of 2007 criteria are used in patients with COPD/OSA overlap syndrome, in parts due to a higher number of arousal-associated hypopnoeas. These observations will impact on the definition of the COPD/OSA overlap syndrome.

The magnitude of tidal volume (VT) depends on neural respiratory drive overcoming respiratory resistance. We hypothesized that the ratio of EMGdi, an index of neural drive, to VT could detect histamine induced changes in lower airway resistance given the assumption that respiratory resistance (except for the lower airway resistance) is unaffected by histamine. Conventional histamine challenge tests were undertaken in 44 asthma patients (age 47±14 years; FEV1% 76±14) diagnosed by a history of repeated attack of asthma and positive bronchial challenge test and 51 healthy subjects (age 36 ± 13 years; FEV1% 96 ± 11). Diaphragm EMG was recorded from chest wall surface electrodes (EMGdi) under the fixed breathing frequency (18 times/min.) and an additional inspiratory load to improve a signal–noise ratio. Airflow was recorded with a digital output flowmeter. ΔFEV1 correlated with ΔEMGdi /VT (r=0.63). Corresponding to ≥20% fall in FEV1 during histamine challenge test, change in EMGdi/VT in patients with asthma was significantly higher than that in healthy subjects who received maximal dose (7.8 µmol) of histamine (90.5% ± 75.5% vs 2.4% ± 21.7%, p

Rationale Dynamic hyperinflation in patients with COPD is usually assessed by inspiratory capacity (IC) manoeuvres with the assumption that maximal activation of the respiratory muscles can be reliably achieved. Objectives We hypothesized that the neural output to the respiratory muscles during an IC manoeuvre will increase under the condition of exercise or hypercapnia, since these are known to increase neural output from the brainstem to the respiratory muscles. Methods Nineteen patients with COPD (mean FEV 1 =29.7±12.5%) and 31 normal subjects were studied. Diaphragm electromyogram (EMGdi) and IC were measured during exhaustive exercise and during inhalation of 8%CO 2 with or without hypoxia. Measurements and Main Results IC changed from 1.78 ± 0.50 L and 1.41 ± 0.40 L at rest to 2.18 ± 0.58 L and 1.29 ± 0.46 L at the end of exercise for normal subjects and COPD patients, respectively. The mean EMGdi during an IC manoeuver increased during exercise from 0.158 ± 0.036 mV and 0.172 ± 0.048mV at rest to 0.203 ± 0.041 mV and 0.220 ± 0.056mV at the end of exercise for normal subjects and patients with COPD, respectively. Both the IC and EMGdi observed during an IC manoeuver during inhalation of 8%CO 2 in normal subjects was significantly larger than those breathing room air (2.10±0.80L vs 1.87±0.60L for IC and 0.183±0.038 mV vs 0.154±0.040 mV for EMGdi, p Conclusions We conclude that the neural drive generated by an IC manoeuvre increases during exercise and hypercapnia, leading to potential underestimation of dynamic hyperinflation assessed by IC manoeuvres.

We compared the physiological work, judged by oxygen uptake, esophageal pressure swing and diaphragm electromyography, elicited by Tai Chi compared with that elicited by constant rate treadmill walking at 60% of maximal load in eleven patients with COPD (Mean FEV1 61% predicted, FEV1/FVC 47%). Dynamic hyperinflation was assessed by inspiratory capacity and twitch quadriceps tension (TwQ) elicited by supramaximal magnetic stimulation of the femoral nerve was also measured before and after both exercises. The EMGdi and esophageal pressure at the end of exercise were similar for both treadmill exercise and Tai Chi (0.109±0.047 mV vs 0.118±0.061 mV for EMGdi and 22.3±7.1 cmH2O vs 21.9±8.1 cmH2O for esophageal pressure). Moreover the mean values of oxygen uptake during Tai Chi and treadmill exercise did not differ significantly: 11.3 ml/kg/min (51.1% of maximal oxygen uptake derived from incremental exercise) and 13.4 ml/kg/min (52.5%) respectively, p>0.05. Respiratory rate during Tai Chi was significantly lower than that during treadmill exercise. Both Tai Chi and treadmill exercise elicited a fall in IC at end exercise, indicating dynamic hyperinflation, but this was statistically significant only after treadmill exercise. TwQ decreased significantly after Tai Chi but not after treadmill. We conclude that Tai Chi constitutes a physiologically similar stimulus to treadmill exercise and may therefore be an acceptable modality for pulmonary rehabilitation which may be culturally more acceptable in some parts of the world.