Treatment of obstructive sleep apnea with a simple CPAP device.

PURPOSE: CPAP is the "gold standard" treatment for obstructive sleep apnea (OSA). Current CPAP models have developed additional functions including automatic CPAP and pressure relief. However, CPAP adherence has not improved over the last three decades. Many patients in low-income countries cannot afford these CPAP devices. A novel simple CPAP device with a fixed pressure without pressure controller was developed. METHODS: Manual CPAP pressure titration was performed in 127 patients with OSA. Six patients with a titration pressure higher than 11 cmH2O and 14 patients who could not tolerate CPAP were excluded, leaving 107 participating in the following 2 studies. In study one, 54 of 107 patients were treated by both conventional fixed CPAP and simple CPAP in random order. In the second study, another 53 patients were treated by both autoCPAP in automatic function and simple CPAP in random order. Simple CPAP was fixed at 10 cmH2O, 8 cmH2O, and 6 cmH2O for patients whose titration pressure was between 9-10, 7-8, and ≤ 6 cmH2O, respectively. Conventional fixed CPAP device was set exactly the same as manual titration pressure. RESULTS: All patients whose manual titration pressure ≤ 10 cmH2O were effectively treated by simple CPAP (AHI 40.7 ± 2.3 events/h before vs 2.5 ± 0.3 events/h after, p < 0.001). Patients expressed similar preferences for simple CPAP, autoCPAP, and conventional fixed CPAP (p > 0.05). CONCLUSIONS: We conclude that a novel simple CPAP is an alternative treatment for most patients with OSA, which may widen access to CPAP therapy in the developing countries because of its low cost.

ERS statement on respiratory muscle testing at rest and during exercise.

Assessing respiratory mechanics and muscle function is critical for both clinical practice and research purposes. Several methodological developments over the past two decades have enhanced our understanding of respiratory muscle function and responses to interventions across the spectrum of health and disease. They are especially useful in diagnosing, phenotyping and assessing treatment efficacy in patients with respiratory symptoms and neuromuscular diseases. Considerable research has been undertaken over the past 17 years, since the publication of the previous American Thoracic Society (ATS)/European Respiratory Society (ERS) statement on respiratory muscle testing in 2002. Key advances have been made in the field of mechanics of breathing, respiratory muscle neurophysiology (electromyography, electroencephalography and transcranial magnetic stimulation) and on respiratory muscle imaging (ultrasound, optoelectronic plethysmography and structured light plethysmography). Accordingly, this ERS task force reviewed the field of respiratory muscle testing in health and disease, with particular reference to data obtained since the previous ATS/ERS statement. It summarises the most recent scientific and methodological developments regarding respiratory mechanics and respiratory muscle assessment by addressing the validity, precision, reproducibility, prognostic value and responsiveness to interventions of various methods. A particular emphasis is placed on assessment during exercise, which is a useful condition to stress the respiratory system.

Coexistence of OSA may compensate for sleep related reduction in neural respiratory drive in patients with COPD.

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<0.001) and those with overlap syndrome (8.3±2.0 to 6.1±1.8 L/min). Neural respiratory drive from wakefulness to sleep decreased significantly for patients with COPD alone (29.5±13.3% to 23.0±8.9% of maximal, p<0.01) but it changed little in those with overlap syndrome. The ratio of tidal volume to EMGdi was unchanged from wakefulness to sleep in patients with COPD alone and healthy subjects but was significantly reduced in patients with OSA or overlap syndrome (p<0.05). CONCLUSIONS: Stage 2 sleep-related hypoventilation in COPD alone is due to reduction of neural respiratory drive, but in overlap syndrome it is due to increased upper airway resistance.

Thiosulfate transfer mediated by DsrE/TusA homologs from acidothermophilic sulfur-oxidizing archaeon Metallosphaera cuprina.

Conserved clusters of genes encoding DsrE and TusA homologs occur in many archaeal and bacterial sulfur oxidizers. TusA has a well documented function as a sulfurtransferase in tRNA modification and molybdenum cofactor biosynthesis in Escherichia coli, and DsrE is an active site subunit of the DsrEFH complex that is essential for sulfur trafficking in the phototrophic sulfur-oxidizing Allochromatium vinosum. In the acidothermophilic sulfur (S(0))- and tetrathionate (S4O6(2-))-oxidizing Metallosphaera cuprina Ar-4, a dsrE3A-dsrE2B-tusA arrangement is situated immediately between genes encoding dihydrolipoamide dehydrogenase and a heterodisulfide reductase-like complex. In this study, the biochemical features and sulfur transferring abilities of the DsrE2B, DsrE3A, and TusA proteins were investigated. DsrE3A and TusA proved to react with tetrathionate but not with NaSH, glutathione persulfide, polysulfide, thiosulfate, or sulfite. The products were identified as protein-Cys-S-thiosulfonates. DsrE3A was also able to cleave the thiosulfate group from TusA-Cys(18)-S-thiosulfonate. DsrE2B did not react with any of the sulfur compounds tested. DsrE3A and TusA interacted physically with each other and formed a heterocomplex. The cysteine residue (Cys(18)) of TusA is crucial for this interaction. The single cysteine mutants DsrE3A-C(93)S and DsrE3A-C(101)S retained the ability to transfer the thiosulfonate group to TusA. TusA-C(18)S neither reacted with tetrathionate nor was it loaded with thiosulfate with DsrE3A-Cys-S-thiosulfonate as the donor. The transfer of thiosulfate, mediated by a DsrE-like protein and TusA, is unprecedented not only in M. cuprina but also in other sulfur-oxidizing prokaryotes. The results of this study provide new knowledge on oxidative microbial sulfur metabolism.

Effect of tiotropium on neural respiratory drive during exercise in severe COPD.

BACKGROUND: Studies have shown that tiotropium once daily reduces lung hyperinflation and dyspnea during exercise and improves exercise tolerance in patients with COPD. Mechanisms underlying the effects of the muscarinic receptor antagonist tiotropium on COPD have not been fully understood. OBJECTIVE: In this study, we investigated whether improvement in neural respiratory drive is responsible for reducing dyspnea during exercise and improving exercise tolerance in COPD. METHODS: Twenty subjects with severe COPD were randomized into two groups: no treatment (Control, n = 10, 63.6 ± 4.6 years, FEV1 29.6 ± 13.3%pred) or inhaled tiotropium 18 µg once daily for 1 month (n = 10, 66.5 ± 5.4 years, FEV1 33.0 ± 11.1%pred). All subjects were allowed to continue their daily medications other than anti-cholinergics during the study. Constant cycle exercise with 75% of maximal workload and spirometry were performed before and 1 month after treatment. Diaphragmatic EMG (EMGdi) and respiratory pressures were recorded with multifunctional esophageal catheter. Efficiency of neural respiratory drive, defined as the ratio of minute ventilation (VE) and diaphragmatic EMG (VE/EMGdi%max), was calculated. Modified British Medical Research Council Dyspnea Scale (mMRC) was used for the evaluation of dyspnea before and after treatment. RESULTS: There was no significant difference in spirometry before and after treatment in both groups. Diaphragmatic EMG decreased significantly at rest (28.1 ± 10.9% vs. 22.6 ± 10.7%, P < 0.05) and mean efficiency of neural respiratory drive at the later stage of exercise increased (39.8 ± 2.9 vs. 45.2 ± 3.9, P < 0.01) after 1-month treatment with tiotropium. There were no remarkable changes in resting EMGdi and mean efficiency of neural respiratory drive post-treatment in control group. The score of mMRC decreased significantly (2.5 ± 0.5 vs. 1.9 ± 0.7, P < 0.05) after 1-month treatment with tiotropium, but without significantly difference in control group. CONCLUSION: Tiotropium significantly reduces neural respiratory drive at rest and improves the efficiency of neural respiratory drive during exercise, which might account for the improvement in exercise tolerance in COPD.

[Comparative proteomics study of different processing technology for pilose antler using iTRAQ technology coupled with 2D LC-MS].

This study was designed to use iTRAQ technology coupled with 2D LC-MS/MS to study the comparative proteomics of different processing technology for pilose antler. 1015 proteins were identified with 2D LC combined with MOLDI TOF/TOF mass spectrometry. Comparative analysis with Protein Pilot (Version 4.5) revealed that 87 proteins were changed (P ≤ 0.05, the ratio of > 1.50 or < 0.60 as the threshold selection of difference proteins), of which 24 were up regulated and 33 were down regulated in the traditional frying process (TFP) compared with the fresh pilose antler (P ≤ 0.05). 7 significant different proteins (P ≤ 0.001), most of these significantly changed proteins were found to be involved in calcium ion binding and ATP binding associated with human healthy. Freeze drying with protective agent (FDP) (Trehalose) can improve the content of significantly different proteins (P ≤ 0.001) including Collagen alpha-1 (XII) chain (COL12A1) and Collagen alpha-1 (II) chain (COL2A1). The significant function involves in platelets activating, maintenance of spermatogonium, and disorder expression in tumor cells. The functional annotation by Hierarchical clustering and GO (gene ontology) showed that the main molecule functions of the proteins significantly changed in these processes were involved in binding (52.7%), catalytic (25.3%), structural molecule and transporter (6.6%).

[Neural respiratory drive and nocturnal hypoventilation in patients with chronic obstructive pulmonary disease].

OBJECTIVE: To explore the effects of neural respiratory drive on ventilation in patients with chronic obstructive pulmonary disease (COPD) during sleep. METHODS: Diaphragm electromyogram (EMG) from a multipair esophageal electrodes and airflow derived from pneumotachography were recorded during overnight polysomnography in 13 patients with stable COPD recruited from outpatient clinic of First Affiliated Hospital of Guangzhou Medical College from May 2010 to May 2011. Changes in diaphragm EMG and ventilation during wakefulness and different sleep stages were observed. RESULTS: Diaphragm EMG decreased by 26% in non-rapid eye movement sleep (NREM) stage and 39% in rapid eye movement (REM) as compared with wakefulness. Coinciding with change in diaphragm EMG, ventilation (VE) (ml×min(-1)×kg(-1)) significantly decreased from wakefulness (156 ± 53) ml×min(-1)×kg(-1) to steady NREM stage (112 ± 35) ml×min(-1)×kg(-1) (P < 0.05) and further decreased from NREM stage to REM stage (95 ± 27) ml×min(-1)×kg(-1) (P < 0.05). Oxygen saturation also decreased significantly from 97.1% ± 1.8% in wakefulness to REM stage (94.0% ± 3.9%) (P < 0.01). CONCLUSION: Reduced neural respiratory drive contributes to nocturnal hypoventilation in COPD patients.

[Prevalence of central sleep apnea in different age groups of children with sleep apnea-hypopnea].

OBJECTIVE: To explore the prevalence of central sleep apnea in different age groups of children with sleep apnea-hypopnea (SAH). METHODS: A total of 431 children with SAH diagnosed by overnight polysomnography at our Sleep Center were retrospectively studied. They were divided into 3 groups based on their ages: toddler group (1 - < 3 years old), preschool group (3 - < 6 years old) and school group (6 - < 13 years old). The relationship between age and different types of apnea-hyponea index (AHI) was analyzed. And the prevalence of central sleep apnea and sleep structure were compared between the groups. RESULTS: A negative correlation existed between age and central sleep apnea index (r = -0.322, P < 0.01). However, there was no correlation between age and obstructive apnea index (P > 0.05). AHI was similar in different age groups, but the medians of central sleep apnea index for toddler, preschool and school groups were 2.35, 1.50 and 0.90 events/h respectively (all P < 0.01). Sleep structure was similar between the groups (P > 0.05). CONCLUSIONS: Central sleep apnea is common in children with sleep disordered breathing. The younger their ages, a higher prevalence of central sleep apnea.

[Comparison of manual versus automatic titration in pressure determination for long-term therapy of continuous positive airway pressure in patients with obstructive sleep apnea hypopnea syndrome].

OBJECTIVE: To compare the continuous positive airway pressure (CPAP) of automatic titration with that of manual titration. METHODS: A total of 58 patients with obstructive sleep apnea and hypopnea syndrome (OSAHS) diagnosed by overnight polysomnography at sleep center of First Affiliated Hospital, Guangzhou Medical University were studied between December 2010 and December 2012. Manual titration was performed under full polysmnography and auto-titration at home for 3-7 nights. RESULTS: There were 52 males and 6 females with an age range of (48 ± 11) years. CPAP pressure titrated by automatic device (10.0 ± 2.2) cm H2O (1 cm H2O = 0.098 kPa) was significantly higher than that titrated manually (7.5 ± 1.5) cm H2O (P = 0.000). Apnea-hyponea index decreased significantly from (54.0 ± 21.0) events/h pre-treatment to (3.8 ± 2.5) events/h post-treatment under manual titration (P < 0.01). CONCLUSIONS: CPAP pressure titrated by automatic device is usually higher than that titrated manually. Manual titration should be performed if a patient can not tolerate the CPAP pressure titrated by an automatic device.

[Assessment of neural respiratory drive in humans].

OBJECTIVE: Assessment of neural respiratory drive is useful for diagnosis of dyspnea and respiratory failure with unknown causes. The purpose of the study was to compare the sensitivity of trandiaphragmatic pressure (Pdi) and diaphragm electromyogram (EMGdi) in assessment of neural respiratory drive. METHODS: A combined catheter with 10 electrodes and 2 balloons was used to record EMGdi and Pdi during CO2 rebreathing. Three different inspiratory maneuvers-inspiration from functional residual capacity to total lung capacity (TLC), deep inspiration from functional residual capacity against closed airway (MIP), and short sharp inspiration through the nose (Sniff) were performed. Ten healthy subjects [male 4 and female 6; age (26 ± 4) years] were studied. RESULTS: Linear relationship between EMGdi and end-tidal CO2 (r = 0.83-0.98, all P < 0.01) was better than that between Pdi and end-tidal CO2 (r = 0.48-0.96, all P < 0.01) during CO2 rebreathing, Z = -2.731, P < 0.05. The slope of linear relation between EMGdi and end-tidal CO2 (16.3-32.5) was significantly higher than that between Pdi and end-tidal CO2 (0.4-11.1), Z = -3.780, P < 0.01. The maximal EMGdi derived from TLC maneuver (211 ± 48) µV was larger than those from the MIP maneuver (161 ± 48) µV and the Sniff maneuver (145 ± 37) µV, F = 5.931, P < 0.05, whereas the maximal Pdi derived from TLC maneuver (58 ± 27) cm H2O (1 cm H2O = 0.098 kPa) was significantly lower than those from the MIP maneuver (92 ± 32) cm H2O and the Sniff maneuver (95 ± 27) cm H2O, F = 5.155, P < 0.05. CONCLUSION: EMGdi is more sensitive than Pdi in the assessment of neural respiratory drive.

Central sleep apnea treated by a constant low-dose CO2 supplied by a novel device.

CO2 inhalation has been previously reported as a treatment for central sleep apnea both when associated with heart failure or where the cause is unknown. Here, we evaluated a novel CO2 supply system using a novel open mask capable of comfortably delivering a constantly inspired fraction of CO2 ([Formula: see text]) during sleep. We recruited 18 patients with central sleep apnea (13 patients with cardiac disease, and 5 patients idiopathic) diagnosed by diaphragm electromyogram (EMG) recordings made during overnight full polysomnography (PSG) (night 1). In each case, the optimal [Formula: see text] was determined by an overnight manual titration with PSG (night 2). Titration commenced at 1% CO2 and increased by 0.2% increments until central sleep apnea (CSA) disappeared. Patients were then treated on the third night (night 3) with the lowest therapeutically effective concentration of CO2 derived from night 2. Comparing night 1 and night 3, both apnea-hypopnea index (AHI; 31 ± 14 vs. 6 ± 3 events/h, P < 0.01) and arousal index (22 ± 8 vs. 15 ± 8 events/h, P < 0.01) were significantly improved during CO2 treatment. Sleep efficiency improved from 71 ± 18 to 80 ± 11%, P < 0.05, and sleep latency was shorter (23 ± 18 vs. 10 ± 10 min, P < 0.01). Heart rate was not different between night 1 and night 3. Our data confirm the feasibility of our CO2 delivery system and indicate that individually titrated CO2 supplementation with a novel device including a special open mask can reduce sleep disordered breathing severity and improve sleep quality. Randomized controlled studies should now be undertaken to assess therapeutic benefit for patients with CSA.NEW & NOTEWORTHY A novel device using a special mask was developed and proved that CO2 therapy using the device could eliminate central sleep apnea (CSA) events and improve sleep quality including reducing arousal index in patients with heart failure. The device would become a useful clinical treatment for heart failure patients with CSA.

[Distinguishing central from obstructive sleep apnea with chest wall surface electrodes].

OBJECTIVE: To determine whether or not diaphragm electromyography recorded from chest wall surface electrodes (EMGsur) can be used to distinguish central from obstructive sleep apnea. METHODS: Ten patients (age (44 ± 10) years, body mass index (25.9 ± 1.8) kg/m²) with suspected obstructive sleep apnea referred from Guangzhou Institute of Respiratory Disease were studied between January and September 2009. EMGsur and diaphragm electromyography from esophageal electrode (EMGeso) were recorded during conventional overnight full polysomnography. And chest-abdominal movement was measured with chest and abdominal bands. RESULTS: High-quality EMGsur and EMGeso were recorded in all subjects except for one who could not tolerate a multipair esophageal electrode. Excellent correlation was found between EMGsur and EMGeso during sleep including apnea events (r = 0.81 ± 0.06, P < 0.05). The central sleep apnea events diagnosed by EMGeso were exactly the same as those diagnosed by EMGsur. However, the central sleep apnea events diagnosed by EMGsur were less than those diagnosed by conventional thoracic-abdominal bands (7 ± 11 vs 28 ± 31, P < 0.05). CONCLUSION: EMGsur may be used to distinguish central from obstructive sleep apnea events.

Proteomic analysis of the sea-island cotton roots infected by wilt pathogen Verticillium dahliae.

Verticillium wilt of cotton is a vascular disease mainly caused by the soil-born filamentous fungus Verticillium dahliae. To study the mechanisms associated with defense responses in wilt-resistant sea-island cotton (Gossypium barbadense) upon V. dahliae infection, a comparative proteomic analysis between infected and mock-inoculated roots of G. barbadense var. Hai 7124 (a cultivar showing resistance against V. dahliae) was performed by 2-DE combined with local EST database-assisted PMF and MS/MS analysis. A total of 51 upregulated and 17 downregulated proteins were identified, and these proteins are mainly involved in defense and stress responses, primary and secondary metabolisms, lipid transport, and cytoskeleton organization. Three novel clues regarding wilt resistance of G. barbadense are gained from this study. First, ethylene signaling was significantly activated in the cotton roots attacked by V. dahliae as shown by the elevated expression of ethylene biosynthesis and signaling components. Second, the Bet v 1 family proteins may play an important role in the defense reaction against Verticillium wilt. Third, wilt resistance may implicate the redirection of carbohydrate flux from glycolysis to pentose phosphate pathway (PPP). To our knowledge, this study is the first root proteomic analysis on cotton wilt resistance and provides important insights for establishing strategies to control this disease.

Proteomic identification of differentially expressed proteins in the Ligon lintless mutant of upland cotton (Gossypium hirsutum L.).

Cotton fiber is an ideal model for studying plant cell elongation. To date, the underlying mechanisms controlling fiber elongation remain unclear due to their high complexity. In this study, a comparative proteomic analysis between a short-lint fiber mutant (Ligon lintless, Li(1)) and its wild-type was performed to identify fiber elongation-related proteins. By 2-DE combined with local EST database-assisted MS/MS analysis, 81 differentially expressed proteins assigned to different functional categories were identified from Li(1) fibers, of which 54 were down-regulated and 27 were up-regulated. Several novel aspects regarding cotton fiber elongation can be illustrated from our data. First, over half of the down-regulated proteins were newly identified at the protein level, which is mainly involved in protein folding and stabilization, nucleocytoplasmic transport, signal transduction, and vesicular-mediated transport. Second, a number of cytoskeleton-related proteins showed a remarkable decrease in protein abundance in the Li(1) fibers. Accordingly, the architecture of actin cytoskeleton was severely deformed and the microtubule organization was moderately altered, accompanied with dramatic disruption of vesicle trafficking. Third, the expression of several proteins involved in unfolded protein response (UPR) was activated in Li(1) fibers, indicating that the deficiency of fiber cell elongation was related to ER stress. Collectively, these findings significantly advanced our understanding of the mechanisms associated with cotton fiber elongation.

Distinct symmetry and limited peptide refolding activity of the thermosomes from the acidothermophilic archaea Acidianus tengchongensis S5(T).

Recombinant thermosomes from the Acidianus tengchongensis strain S5(T) were purified to homogeneity and assembled in vitro into homo-oligomers (rATcpnalpha or rATcpnbeta) and hetero-oligomers (rATcpnalphabeta). The symmetries of these complexes were determined by electron microscopy and image analysis. The rATcpnalpha homo-oligomer was shown to possess 8-fold symmetry while both rATcpnbeta and rATcpnalphabeta oligomers adopted 9-fold symmetry. rATcpnalphabeta oligomers were shown to contain the alpha and beta subunits in a 1:2 ratio. All of the complexes prevented the irreversible inactivation of yeast alcohol dehydrogenase at 55 degrees C and completely prevented the formation of aggregates during thermal inactivation of citrate synthase at 45 degrees C. All rATcpn complexes showed trace ATP hydrolysis activity. Furthermore, rATcpnbeta sequestered fully chemically denatured substrates (GFP and thermophilic malic dehydrogenase) in vitro without refolding them in an ATP-dependent manner. This property is similar to previously reported properties of chaperonins from Sulfolobus tokodaii and Sulfolobus acidocaldarius. These features are consistent with the slow growth rates of these species of archaea in their native environment.

Identification and quantification of mycothiol in Actinobacteria by a novel enzymatic method.

Mycothiol (MSH) was reported to be the dominant low molecular weight thiol in members of the Actinobacteria. In this study, a simple, fast, and sensitive method for qualitative and quantitative determination of MSH molecules was developed based on maleylpyruvate isomerase (MPI) from Corynebacterium glutamicum. The principle of this method is that the activity of MPI from C. glutamicum was dependent on MSH molecules. It was found that this MPI activity displayed a linear response (R (2) = 0.9928) at MSH amounts ranging from 0.12 to 3.98 pmol in the defined assay system. This observation was applied to calculate the MSH levels, and the newly developed method was compared with thiol-specific fluorescent-labeling high-performance liquid chromatography method. Forty-eight genera of Actinobacteria were screened for MSH and 43 genera were reported for MSH occurrence, and the MSH levels in Actinobacteria were determined to be 0.01 to 9.69 µmol/g of residual dry cell weight.

Absence of dynamic hyperinflation during exhaustive exercise in severe COPD reflects submaximal IC maneuvers rather than a nonhyperinflator phenotype.

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.

[Neural respiratory drive in patients with obstructive sleep apnea].

OBJECTIVE: To evaluate the variability of neural respiratory drive in patients with obstructive sleep apnea (OSA) and the effect of continuous positive airway pressure (CPAP) upon neural respiratory drive. METHODS: We recorded diaphragm electromyogram (EMGdi) with multi-pair esophageal electrodes and its variability during wakefulness, sleep and treatment with CPAP in 13 patients with moderate to severe OSA diagnosed by an overnight full polysomnography (OSA group). Six normal subjects (control group) were also studied. RESULTS: Coefficient of variation of EMGdi (CV-EMGdi) during wakefulness (15.4% +/- 3.8%) was similar to that during sleep (17.3% +/- 5.2, P > 0.05) in the control group. The CV-EMGdi during wakefulness, sleep, sleep apnea events and treatment with CPAP in OSA group was 14.7% +/- 1.9%, 40.7% +/- 12.0%, 29.1% +/- 7.5% and 15.4% +/- 4.6% respectively, CV-EMGdi during sleep or sleep apnea events was larger than that during wakefulness (P < 0.01). However, there was no difference in the CV-EMGdi during wakefulness and during treatment with CPAP (P > 0.05). CONCLUSION: The variability of neural respiratory drive in patients with OSA is higher than that in normal subjects, and CPAP can reduce the variability of neural respiratory drive in patients with OSA.