Oxygen therapy is known to reduce loop gain (LG) in patients with obstructive sleep apnoea (OSA), yet its effects on the other traits responsible for OSA remain unknown. Therefore, we assessed how hyperoxia and hypoxia alter four physiological traits in OSA patients. Eleven OSA subjects underwent a night of polysomnography during which the physiological traits were measured using multiple 3-min 'drops' from therapeutic continuous positive airway pressure (CPAP) levels. LG was defined as the ratio of the ventilatory overshoot to the preceding reduction in ventilation. Pharyngeal collapsibility was quantified as the ventilation at CPAP of 0 cmH 2 O. Upper airway responsiveness was defined as the ratio of the increase in ventilation to the increase in ventilatory drive across the drop. Arousal threshold was estimated as the level of ventilatory drive associated with arousal. On separate nights, subjects were submitted to hyperoxia (n = 9; F iO2 ∼0.5) or hypoxia (n = 10; F iO2 ∼0.15) and the four traits were reassessed. Hyperoxia lowered LG from a median of 3.4 [interquartile range (IQR): 2.6-4.1] to 2.1 (IQR: 1.3-2.5) (P < 0.01), but did not alter the remaining traits. By contrast, hypoxia increased LG [median: 3.3 (IQR: 2.3-4.0) vs. 6.4 (IQR: 4.5-9.7); P < 0.005]. Hypoxia additionally increased the arousal threshold (mean ± s.d. 10.9 ± 2.1 l min -1 vs. 13.3 ± 4.3 l min -1 ; P < 0.05) and improved pharyngeal collapsibility (mean ± s.d. 3.4 ± 1.4 l min -1 vs. 4.9 ± 1.3 l min -1 ; P < 0.05), but did not alter upper airway responsiveness (P = 0.7). This study demonstrates that the beneficial effect of hyperoxia on the severity of OSA is primarily based on its ability to reduce LG. The effects of hypoxia described above may explain the disappearance of OSA and the emergence of central sleep apnoea in conditions such as high altitude. © 2014 The Physiological Society.

The co-existence of chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA), termed the overlap syndrome (OVS), is associated with adverse outcomes that may be reversed with treatment. However, diagnosis is limited by the apparent need for in-laboratory polysomnography (PSG). WatchPAT is a portable diagnostic device that is validated for the diagnosis of OSA that might represent an attractive tool for the diagnosis of OVS.Subjects with established COPD were recruited from a general population. Subjects underwent PSG and simultaneous recording with WatchPAT. Pulmonary function testing and questionnaires were also performed.A total of 36 subjects were recruited and valid data was obtained on 33 (age 63 ± 7, BMI 28 ± 7, 61% male, FEV₁ 56 ± 20% predicted). There was no significant difference in the apnea-hypopnea index (AHI) between PSG and WatchPAT (19 ± 20 versus 20 ± 15 events/h; mean difference 2(-2, 5) events/h; p = 0.381). The AHI was not significantly different in rapid eye movement (REM) and non-rapid eye movement (NREM) determined by PSG versus REM and NREM determined by WatchPAT. WatchPAT slightly overestimated total and REM sleep time, and sleep efficiency. The sensitivity of WatchPAT at an AHI cut-off of ≥5, ≥15, and ≥30 events/h for corresponding PSG AHI cut-offs was 95.8, 92.3, and 88.9, respectively; specificity was 55, 65.0, and 95.8, respectively.WatchPAT is able to determine OSA reliably in patients with COPD. The availability of this additional diagnostic modality may lead to improved detection of OVS, which may in turn lead to improved outcomes for a group of COPD patients at high risk of poor outcomes.

The co-existence of chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA), termed the overlap syndrome (OVS), is associated with adverse outcomes that may be reversed with treatment. However, diagnosis is limited by the apparent need for in-laboratory polysomnography (PSG). WatchPAT is a portable diagnostic device that is validated for the diagnosis of OSA that might represent an attractive tool for the diagnosis of OVS.Subjects with established COPD were recruited from a general population. Subjects underwent PSG and simultaneous recording with WatchPAT. Pulmonary function testing and questionnaires were also performed.A total of 36 subjects were recruited and valid data was obtained on 33 (age 63 ± 7, BMI 28 ± 7, 61% male, FEV₁ 56 ± 20% predicted). There was no significant difference in the apnea-hypopnea index (AHI) between PSG and WatchPAT (19 ± 20 versus 20 ± 15 events/h; mean difference 2(-2, 5) events/h; p = 0.381). The AHI was not significantly different in rapid eye movement (REM) and non-rapid eye movement (NREM) determined by PSG versus REM and NREM determined by WatchPAT. WatchPAT slightly overestimated total and REM sleep time, and sleep efficiency. The sensitivity of WatchPAT at an AHI cut-off of ≥5, ≥15, and ≥30 events/h for corresponding PSG AHI cut-offs was 95.8, 92.3, and 88.9, respectively; specificity was 55, 65.0, and 95.8, respectively.WatchPAT is able to determine OSA reliably in patients with COPD. The availability of this additional diagnostic modality may lead to improved detection of OVS, which may in turn lead to improved outcomes for a group of COPD patients at high risk of poor outcomes.

Copyright © 2015 by the Society of Criti. Objective: Global lung stress varies considerably with low tidal volume ventilation for acute respiratory distress syndrome. High stress despite low tidal volumes may worsen lung injury and increase risk of death. No widely available parameter exists to assess global lung stress. We aimed to determine whether the volume delivered during a recruitment maneuver (VRM) is inversely associated with lung stress and mortality in acute respiratory distress syndrome. Design: Substudy of an acute respiratory distress syndrome clinical trial on esophageal pressure-guided positive end-expiratory pressure titration. Setting: U.S. academic medical center. Patients: Forty-two patients with acute respiratory distress syndrome in whom airflow, airway pressure, and esophageal pressure were recorded during the recruitment maneuver. Interventions: A single recruitment maneuver was performed before initiating protocol-directed ventilator management. Recruitment maneuvers consisted of a 30-second breath hold at 40 cm H2O airway pressure under heavy sedation or paralysis. VRM was calculated by integrating the flow-time waveform during the maneuver. End-inspiratory stress was defined as the transpulmonary (airway minus esophageal) pressure during end-inspiratory pause of a tidal breath and tidal stress as the transpulmonary pressure difference between end-inspiratory and end-expiratory pauses. Measurements and Main Results: VRM ranged between 7.4 and 34.7 mL/kg predicted body weight. Lower VRM predicted high end-inspiratory and tidal lung stress (end-inspiratory: β = -0.449; 95% CI, -0.664 to -0.234; p < 0.001; tidal: β = -0.267; 95% CI, -0.423 to -0.111; p = 0.001). After adjusting for Pao2/Fio2 and either driving pressure, tidal volume, or plateau pressure and positive end-expiratory pressure, VRM remained independently associated with both end-inspiratory and tidal stress. In unadjusted analysis, low VRM predicted increased risk of death (odds ratio, 0.85; 95% CI, 0.72-1.00; p = 0.026). VRM remained significantly associated with mortality after adjusting for study arm (odds ratio, 0.84; 95% CI, 0.71-1.00; p = 0.022). Conclusions: Low VRM independently predicts high lung stress and may predict risk of death in patients with acute respiratory distress syndrome.