Voluntary apnea evokes diving responses in obstructive sleep apnea patients.

PURPOSE: Two potentially protective responses to apnea were studied in obstructive sleep apnea (OSA) patients; the diving response and the increase in Hb concentration [Hb] via spleen contraction. METHODS: Eight OSA patients and ten healthy controls performed apneas in air (A) and apneas with facial immersion in 15 °C water (FIA) after inspiration and without prior hyperventilation. In each condition, subjects performed three apneas of maximal voluntary duration spaced by 2 min of rest. Cardiorespiratory parameters were measured non-invasively, and venous blood samples for [Hb] analysis were drawn before and after apneas. RESULT: Mean (SD) apnea durations were similar between groups (NS). In controls, the heart rate (HR) reduction was 10 ± 10 % at apnea and 19 ± 10 % in FIA (P < 0.05). In OSA patients, however, the fall in HR was the same in both conditions, 13 ± 10 and 14 ± 8 % for A and FIA, respectively (NS). In controls, the [Hb] increase was the same in A and FIA (2.2 ± 2.9 and 2.1 ± 2.2 %), while in OSA the [Hb] increase was greater during FIA compared to A (3.3 ± 2.2 and 1.4 ± 0.9 %; P < 0.05). CONCLUSION: Apnea induces a diving response and [Hb] increase in both groups. OSA patients did not show the typical training effect of the diving response seen in apnea divers despite their frequent nocturnal apneas. However, they also deviated from normal controls in response pattern; face immersion enhanced the cardiovascular diving response in controls but not in OSA, while the hematological response was enhanced by face immersion only in OSA patients.

Lung aeration during sleep in patients with obstructive sleep apnoea.

BACKGROUND: Previous studies have indicated that patients with obstructive sleep apnoea (OSA) have altered ventilation and lung volumes awake and the results suggest that this may be a determinant of severity of desaturations during sleep. However, little is known about regional lung aeration during sleep in patients with OSA. METHODS: Twelve patients with OSA were included in the study. Computed tomography was used to study regional lung aeration during wakefulness and sleep. Lung aeration was calculated in ml gas/g lung tissue in four different regions of interest (ROI(1-4)), along the border of the lung from ventral to dorsal. RESULTS: Lung aeration in the dorsal (dependent) lung region (ROI(4)) was lower during sleep compared to wakefulness 0.78 +/- 0.19 versus 0.88 +/- 0.19 (mean +/- SD) ml gas/g lung tissue (P = 0.005). Associations were found between awake expiratory reserve volume and change in lung aeration from wakefulness to sleep in ROI(4) (r = -0.69; P = 0.012). In addition, the change in lung aeration in the dorsal region correlated to sleep time (r = 0.69; P = 0.014) but not to time in supine position. The difference in lung aeration between inspiration and expiration (i.e. ventilation), was larger in the ventral lung region when expressed as ml gas per g lung tissue. In two patients it was noted that, during on-going obstructive apnoea, lung aeration tended to be increased rather than decreased. CONCLUSIONS: Aeration in the dorsal lung region is reduced during sleep in patients with OSA. The decrease is related to lung volume awake and to sleep time.

Lung aeration during sleep.

BACKGROUND: During sleep, ventilation and functional residual capacity (FRC) decrease slightly. This study addresses regional lung aeration during wakefulness and sleep. METHODS: Ten healthy subjects underwent spirometry awake and with polysomnography, including pulse oximetry, and also CT when awake and during sleep. Lung aeration in different lung regions was analyzed. Another three subjects were studied awake to develop a protocol for dynamic CT scanning during breathing. RESULTS: Aeration in the dorsal, dependent lung region decreased from a mean of 1.14 +/- 0.34 mL (+/- SD) of gas per gram of lung tissue during wakefulness to 1.04 +/- 0.29 mL/g during non-rapid eye movement (NREM) sleep (- 9%) [p = 0.034]. In contrast, aeration increased in the most ventral, nondependent lung region, from 3.52 +/- 0.77 to 3.73 +/- 0.83 mL/g (+ 6%) [p = 0.007]. In one subject studied during rapid eye movement (REM) sleep, aeration decreased from 0.84 to 0.65 mL/g (- 23%). The fall in dorsal lung aeration during sleep correlated to awake FRC (R(2) = 0.60; p = 0.008). Airway closure, measured awake, occurred near and sometimes above the FRC level. Ventilation tended to be larger in dependent, dorsal lung regions, both awake and during sleep (upper region vs lower region, 3.8% vs 4.9% awake, p = 0.16, and 4.5% vs 5.5% asleep, p = 0.09, respectively). CONCLUSIONS: Aeration is reduced in dependent lung regions and increased in ventral regions during NREM and REM sleep. Ventilation was more uniformly distributed between upper and lower lung regions than has previously been reported in awake, upright subjects. Reduced respiratory muscle tone and airway closure are likely causative factors.