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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.

Obstructive sleep apnoea (OSA) is a global health problem of increasing prevalence. Effective treatments are available with continuous positive airway pressure (CPAP) therapy and mandibular advancement devices (MAD). However, there is limited long-term adherence to therapy, as CPAP and MAD require permanent usage to avoid recurrence of the symptoms and adverse ill health. Alternative treatments would aid in the treatment cascade to manage OSA effectively whenever standard therapy has been trialled and failed. Hypoglossal nerve stimulation (HNS), an invasive approach to stimulate the pharyngeal dilator muscles of the upper airway during sleep, has been approved for the treatment of OSA by several healthcare systems in recent years. In parallel to the development of HNS, a non-invasive approach has been developed to deliver electrical stimulation. Transcutaneous electrical stimulation in obstructive sleep apnoea (TESLA) uses non-invasive electrical stimulation to increase neuromuscular tone of the upper airway dilator muscles of patients with OSA during sleep. Data from previous feasibility studies and randomised controlled trials have helped to identify a subgroup of patients who are “responders” to this treatment. However, further investigations are required to assess usability, functionality and task accomplishment of this novel treatment. Consideration of these factors in the study design of future clinical trials will strengthen research methodology and protocols, improve patient related outcome measures and assessments, to optimise this emerging therapeutical option. In this review, we will introduce a conceptual framework for the TESLA home programme highlighting qualitative aspects and outcomes.

Purpose: Electrical stimulation of the upper airway dilator muscles is an emerging treatment for obstructive sleep apnea (OSA). Invasive hypoglossal nerve stimulation (HNS) has been accepted as treatment alternative to continuous positive airway pressure (CPAP) for selected patients, while transcutaneous electrical stimulation (TES) of the upper airway is being investigated as non-invasive alternative. Methods: A meta-analysis (CRD42017074674) on the effects of both HNS and TES on the apnea-hypopnea index (AHI) and the Epworth Sleepiness Scale (ESS) in OSA was conducted including published evidence up to May 2018. Random-effects models were used. Heterogeneity and between-study variance were assessed by I2 and τ2, respectively. Results: Of 41 identified clinical trials, 20 interventional trials (n = 895) could be pooled in a meta-analysis (15 HNS [n = 808], 5 TES [n = 87]). Middle-aged (mean ± SD 56.9 ± 5.5years) and overweight (body mass index 29.1 ± 1.5kg/m2) patients with severe OSA (AHI 37.5 ± 7.0/h) were followed-up for 6.9 ± 4.0months (HNS) and 0.2 ± 0.4months (TES), respectively. The AHI improved by − 24.9h−1 [95%CI − 28.5, − 21.2] in HNS (χ2 79%, I2 82%) and by − 16.5h−1 [95%CI − 25.1, − 7.8] in TES (χ2 7%, I2 43%; both p < 0.001). The ESS was reduced by − 5.0 (95%CI − 5.9, − 4.1) (p < 0.001). Conclusion: Both invasive and transcutaneous electrical stimulation reduce OSA severity by a clinically relevant margin. HNS results in a clinically relevant improvement of symptoms. While HNS represents an invasive treatment for selected patients with moderate to severe OSA, TES should be further investigated as potential non-invasive approach for OSA.

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

Background: Electrical current can be used to stimulate upper airway dilator muscles to treat obstructive sleep apnoea (OSA). Ultrasound devices are widely available and may be used to detect contraction of the upper airway dilator muscles assessing the functionality of electrical stimulation (ES) used for this treatment. Methods: In a physiological sub-study of a randomised controlled trial, patients with OSA underwent ultrasound examination to assess contraction of the upper airway dilator muscles in response to transcutaneous ES. Ultrasound scans were scored according to the picture quality (poor = ‘0’, acceptable = ‘1’ and good = ‘2’). Tongue base thickness was assessed in mid-sagittal and coronal planes with (D2, A2) and without ES (D1, A1), while awake and seated. The primary outcome was to determine the increase in tongue thickness during ES in both views (D2 – D1 = ΔD), as well as any increase in the cross-sectional area (CSA) in the coronal view (A2 – A1 = ΔA). Data were presented as mean and standard deviation (SD). Results: Fourteen patients [eight male, age 57.5 (9.8) years, body mass index (BMI) 29.5 (2.8) kg/m2] with OSA [Apnea-Hypopnea Index (AHI) 19.5 (10.6) × hour-1] were studied. Quality of the ultrasound scans was acceptable or good with 1.5 (0.5) points. In the mid-sagittal plane, ΔD was +0.17 (0.07) cm in midline and +0.21 (0.09) cm in the widest diameter, a percentual change of 12.2% (4%) and 12.8% (5.2%) (P

Background In COPD, functional status is improved by pulmonary rehabilitation (PR) but requires specific facilities. Tai Chi, which combines psychological treatment and physical exercise and requires no special equipment, is widely practiced in China and is becoming increasingly popular in the rest of the world. We hypothesized that Tai Chi is equivalent (ie, difference less than ±4 St. George's Respiratory Questionnaire [SGRQ] points) to PR. Methods A total of 120 patients (mean FEV 1 , 1.11 ± 0.42 L; 43.6% predicted) bronchodilator-naive patients were studied. Two weeks after starting indacaterol 150 μg once daily, they randomly received either standard PR thrice weekly or group Tai Chi five times weekly, for 12 weeks. The primary end point was change in SGRQ prior to and following the exercise intervention; measurements were also made 12 weeks after the end of the intervention. Results The between-group difference for SGRQ at the end of the exercise interventions was –0.48 (95% CI PR vs Tai Chi, –3.6 to 2.6; P = .76), excluding a difference exceeding the minimal clinically important difference. Twelve weeks later, the between-group difference for SGRQ was 4.5 (95% CI, 1.9 to 7.0; P 1 was observed. Conclusions Tai Chi is equivalent to PR for improving SGRQ in COPD. Twelve weeks after exercise cessation, a clinically significant difference in SGRQ emerged favoring Tai Chi. Tai Chi is an appropriate substitute for PR. Trial Registry ClinicalTrials.gov; No.: NCT02665130; URL: www.clinicaltrials.gov.

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.

Introduction Electrical stimulation of the upper airway dilator muscles is an emerging treatment for obstructive sleep apnea (OSA). Hypoglossal nerve stimulation (HNS) has recently been approved as treatment alternative to continuous positive airway pressure (CPAP) for selected patients with moderate to severe OSA, while transcutaneous electrical stimulation (TES) of the upper airway is being investigated as non-invasive alternative. Methods A systematic review and meta-analysis (CRD42017074674) including literature published up to May 2018 has been performed to investigate the impact of HNS and TES on OSA severity assessed by the apnoea-hypopnoea index (AHI) and the Epworth Sleepiness Scale (ESS) as measure of subjective sleepiness. Random-effects models were used. Heterogeneity and between study variance were assessed by I2 and τ2, respectively. The Robins-1 tool was utilised to assess the risk of bias for each study. Results Of the 41 clinical trials identified (n=1,853), data from 20 trials (n=895) could be pooled for meta-analysis (15 HNS [n=808], 5 TES [n=87]). Patient were predominantly middle aged (mean±SD 56.9±5.5years), overweight (body mass index, BMI 29.1±1.5kg/m2) with severe OSA (AHI 37.5±7.0h-1) and were followed-up for 6.9±4.0 month (HNS) and 0.2±0.4 months (TES), respectively. The AHI improved by -24.9 [95%CI -28.5, -21.2] h-1 in HNS (χ2 79%, I2 82%) and by -16.5 [95%CI -25.1, -7.8] h-1 in TES (χ2 7%, I2 43%; both p Discussion Both invasive and transcutaneous electrical stimulation reduce OSA severity by a clinically relevant margin. HNS results in a clinically relevant improvement of symptoms. However, data are mainly based on non-randomised trials.

Background: Electrical stimulation of the upper airway dilator muscles is an emerging treatment for obstructive sleep apnoea (OSA). Whereas invasive hypoglossal nerve stimulation (HNS) is an accepted treatment alternative to continuous positive airway pressure (CPAP), transcutaneous electrical stimulation (TES) may be a potential non-invasive alternative. Patients and Methods: A systematic review and meta-analysis (CRD42017074674) on the effect of HNS or TES on the apnoea-hypopnoea index (AHI) and the Epworth Sleepiness Scale (ESS) in OSA was conducted. Random-effects models were used. Heterogeneity and between study variance were assessed by I2 and τ2, respectively. Results: Of 41 identified clinical trials (n=1853), 20 (n=895) interventional trials could be pooled in the meta-analysis (15 HNS [n=808], 5 TES [n=87]). Middle aged (mean±SD 56.9±5.5years), overweight (body mass index, BMI 29.1±1.5kg/m2) patients with severe OSA (AHI 37.5±7.0h-1) were followed-up for 6.9±4.0month (HNS) and 0.2±0.4months (TES), respectively. The AHI improved by -23.5 (95% Confidence Interval, CI -27.0, -20.0) h-1 (p Conclusion: Invasive and transcutaneous electrical stimulation reduce OSA severity by a clinically relevant margin and improve associated symptoms.

Background The mechanisms underlying sleep-related hypoventilation in patients with coexisting COPD and obstructive sleep apnoea (OSA), an overlap syndrome, are incompletely understood. We compared neural respiratory drive expressed as diaphragm electromyogram (EMGdi) and ventilation during stage 2 sleep in patients with COPD alone and patients with overlap syndrome. Methods EMGdi and airflow were recorded during full polysomnography in 14 healthy subjects, 14 patients with OSA and 39 consecutive patients with COPD. The ratio of tidal volume to EMGdi was measured to indirectly assess upper airway resistance. Results Thirty-five patients with COPD, 12 healthy subjects and 14 patients with OSA completed the study. Of 35 patients with COPD, 19 had COPD alone (FEV1 38.5%±16.3%) whereas 16 had an overlap syndrome (FEV1 47.5±16.2%, AHI 20.5±14.1 events/hour). Ventilation (VE) was lower during stage 2 sleep than wakefulness in both patients with COPD alone (8.6±2.0 to 6.5±1.5 L/min, p

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

Inspiratory capacity (IC) is widely used to assess dynamic hyperinflation in patients with chronic obstructive pulmonary disease (COPD) based on the assumption that this maneuver maximally activates inspiratory muscle and thus reliably achieves total lung capacity (TLC). However, inspiration during inflation is partially or wholly controlled by involuntary drive from brainstem and whereas the IC is derived from voluntary drive from the motor cortex. We hypothesized that voluntary IC maneuvers initiated from the motor cortex may be increased if there is additional chemical stimulation to the brainstem by hypercapnia. Nineteen healthy subjects (Age 43±15 years, 13 men/6 women) were studied. Diaphragm EMG (EMGdi) from multipair esophageal electrode and ventilation were recorded during inhalation 8%CO 2 (8%CO 2 +92%O 2 ) and room air. The order of inhalation of gases was random and was blind to subjects. Forced inspiratory vital capacity (FIVC) from residual volume and IC were performed. The EMGdi and FIVC elicited by a FIVC maneuver breathing 8%CO 2 were 169±61 µV and 4.92±1.00 l and were significantly greater than those breathing room air (143±47 µV, 4.3±0.89 l, p 2 were 172±55 µV and 3.28±0.66 L and were significantly greater than those during breathing room air (148±42 µV, 2.83±0.72 l, p This study was supported by NSFC (no.81120108001).

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.

The mechanisms underlying sleep related hypoventilation in patients with coexisting COPD and OSA, an overlap syndrome, are incompletely understood. We compared neural drive expressed as diaphragm EMG (EMGdi) and ventilation during sleep in patients with COPD alone and patients with overlap syndrome. EMGdi and airflow via pneumotachography were recorded during overnight full polysomnography in fourteen normal subjects and 39 consecutive patients with COPD. The ratio of tidal volume to EMGdi was measured to indirectly assess upper airway resistance. 35 patients and 12 normal subjects completed the study. Of 35 patients with COPD, 19 had COPD alone [FEV138.5%±16.3%, apnea-hypopnea index (AHI), 1.9±1.6 events/h] whereas 16 had an overlap syndrome (FEV1 47.5±16.2%, AHI 20.5±14.1 events/h). Ventilation(VE) was lower during NREM sleep than wakefulness in both patients with COPD alone (8.6±2.0 L/min to 6.5±1.5 L/min, p 0.05) or normal subjects (12.6±3.7%to 12.2±3.3%p>0.05). The ratio of tidal volume to EMGdi was unchanged from wakefulness to sleep in both patients with COPD alone and normal subjects but was significantly reduced in patients with overlap syndrome (p

Inspiratory capacity (IC) is widely used to assess dynamic hyperinflation in patients with chronic obstructive pulmonary disease (COPD) based on the assumption that this maneuver maximally activates inspiratory muscle and thus reliably achieves total lung capacity (TLC). However, inspiration during inflation is partially or wholly controlled by involuntary drive from brainstem and whereas the IC is derived from voluntary drive from the motor cortex. We hypothesized that voluntary IC maneuvers initiated from the motor cortex may be increased if there is additional chemical stimulation to the brainstem by hypercapnia. Nineteen healthy subjects (Age 43±15 years, 13 men/6 women) were studied. Diaphragm EMG (EMGdi) from multipair esophageal electrode and ventilation were recorded during inhalation 8%CO 2 (8%CO 2 +92%O 2 ) and room air. The order of inhalation of gases was random and was blind to subjects. Forced inspiratory vital capacity (FIVC) from residual volume and IC were performed. The EMGdi and FIVC elicited by a FIVC maneuver breathing 8%CO 2 were 169±61 µV and 4.92±1.00 l and were significantly greater than those breathing room air (143±47 µV, 4.3±0.89 l, p 2 were 172±55 µV and 3.28±0.66 L and were significantly greater than those during breathing room air (148±42 µV, 2.83±0.72 l, p We concluded that IC and diaphragm EMG generated by IC maneuver is submaximal at normacapnia. Therefore dynamic hyperinflation assessed by IC maneuver could have been underestimated in patients with COPD if they became hypercapnic. This study was supported by NSFC (No.81120108001).

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.

Study objectives It has been hypothesized that arousals after apnea and hypopnea events in patients with obstructive sleep apnea are triggered when neural respiratory drive exceeds a certain level, but this hypothesis is based on esophageal pressure data, which are dependent on flow and lung volume. We aimed to determine whether a fixed threshold of respiratory drive is responsible for arousal at the termination of apnea and hypopnea using a flow independent technique (esophageal diaphragm electromyography, EMGdi) in patients with obstructive sleep apnea. Setting Sleep center of state Key Laboratory of Respiratory Disease. Patients Seventeen subjects (two women, mean age 53 ± 11 years) with obstructive sleep apnea/hypopnea syndrome were studied. Methods We recorded esophageal pressure and EMGdi simultaneously during overnight full polysomnography in all the subjects. Measurements and results A total of 709 hypopnea events and 986 apnea events were analyzed. There was wide variation in both esophageal pressure and EMGdi at the end of both apnea and hypopnea events within a subject and stage 2 sleep. The EMGdi at the end of events that terminated with arousal was similar to those which terminated without arousal for both hypopnea events (27.6% ± 13.9%max vs 29.9% ± 15.9%max, P = ns) and apnea events (22.9% ± 11.5%max vs 22.1% ± 12.6%max, P = ns). The Pes at the end of respiratory events terminated with arousal was also similar to those terminated without arousal. There was a small but significant difference in EMGdi at the end of respiratory events between hypopnea and apnea (25.3% ± 14.2%max vs 21.7% ± 13.2%max, P Conclusions Our data do not support the concept that there is threshold of neural respiratory drive that is responsible for arousal in patients with obstructive sleep apnea.

To explore the efficacies of continuous positive airway pressure (CPAP) for mixed sleep apnea (MSA) events in patients with sleep apnea.A total of 21 patients with sleep apnea whose MSA events10 events/h on overnight polysomnography (PSG) were studied. They were selected from the Sleep Center, Guangzhou Institute of Respiratory Disease. Ten of them were diagnosed only by conventional polysomnography (PSG group) while the diagnosis of another 11 patients was further confirmed by diaphragm electromyogram (EMG) (EMG group). All of them were treated by CPAP titrated manually on PSG.Manual CPAP titrating pressure in PSG group was (8.1 ± 2.2) cmH2O (1 cmH2O = 0.098 kPa) and it was similar to that in EMG group ((8.9 ± 1.5) cmH2O). Apnea-hypopnea index (AHI) decreased significantly after CPAP in both PSG group (6.9 (3.5, 10.2) vs 62.2 (54.7, 71.4) events/h) and EMG group (1.5 (0.5, 5.5) vs 71.3 (59.5, 79.5) events/h) (both P0.01). CPAP could eliminate MSA diagnosed either by conventional PSG (0.1 (0.0, 0.4) vs 29.6 (19.6, 32.4) events/h) or by diaphragm EMG (0.0 (0.0, 0.2) vs 18.1 (9.1, 19.3) events/h) (both P0.01).CPAP can effectively treat MSA events in patients with sleep apnea.

To the Editor: Patients with chronic obstructive pulmonary disease (COPD) experience sleep-related hypoventilation (1, 2). However, there is controversy as to whether this occurs due to an increase in upper airway resistance or a reduction in neural respiratory drive. Elevated neural respiratory drive in wakefulness is well documented in COPD (3). O’Donoghue and coworkers (4) reported in patients with COPD that a sleep-related hypoventilation was due to increased upper airway resistance, and Ballard and coworkers (5) reported an increase in upper airway resistance moving from wakefulness to sleep, although upper airway resistance was not consistently greater during sleep (see Figure 3 of their article [5]). Moreover, in healthy young adults, a poor correlation was observed between changes in ventilation and upper airway resistance (6). Morrell and coworkers (7) addressed the question directly in tracheotomized subjects, confirming hypoventilation during sleep, thus excluding an obligate contribution from upper airway resistance. To further address the question, we performed diaphragm electromyography (EMGdi) using a multipair esophageal electrode as an index of neural respiratory drive (8–11). Some of the data have been previously reported in abstract form (12). A total of 17 stable patients with moderate to very severe COPD and 14 age-matched normal subjects participated. All subjects were free from obstructive sleep apnea (OSA; apnea–hypopnea index < 5.0 events/h) and snoring confirmed by prior overnight polysomnography, and were free from clinically significant coexisting diseases, including neuromuscular disorders. The study was approved by the Ethics Committee of the Chinese State Key Laboratory of Respiratory Disease, and all patients gave their informed consent to participate. A multipair esophageal electrode catheter (Yinghui Medical Technology Co., Ltd, Guangzhou, China) was used as previously described (8) to record the EMGdi during overnight polysomnography (9–11). Airflow was recorded with a pneumotachograph connected to a full facemask. Maximal EMGdi was recorded from maximal voluntary inspiratory maneuvers. Polysomnography was manually analyzed based on standard criteria (13). The root mean square (RMS) of the EMGdi (RMSEMGdi) was calculated by computer with a time constant of 100 milliseconds. Efficacy of neural respiratory drive was defined as the ratio of minute ventilation to peak RMSEMGdi of each breath. Data were selected during stable breathing without respiratory events. Data collected for 10 minutes before sleep and for at least 15 minutes during non–rapid eye movement (NREM) and REM in the supine position were selected for analysis. Two-way ANOVA was used to test differences between wakefulness, NREM, and REM sleep; data are presented as means (±SD), and statistical significance was determined as a P value of less than 0.05. Some subjects could not tolerate the full facemask, and satisfactory measurements were therefore obtained in 10 male patients with COPD (age, 59.3 ± 11.5 yr; body mass index, 20.8 ± 3.1 kg/m2; FEV1, 34.2 ± 15.8% predicted; FEV1/FVC, 37.8 ± 11.6%; oxygen saturation