Autonomic dysfunction in patients with nocturnal hypoventilation in extrapulmonary restrictive disease

In chronic obstructive pulmonary disease, persistent hypoxia may be associa ted with autonomic dysfunction. The effect of nocturnal oxygen desaturation on autonomic function in patients,vith chest wall deformities and neuromus cular disease is unknown. This study examined the effect of nocturnal oxyge n desaturation upon heart rate variability, a sensitive measure of autonomi c function. Twenty-seven patients with chest wall deformity or neuromuscular disease un derwent analysis of overnight oximetry, blood gases, and 24 h heart rate va riability (HRV), specifically the standard deviation of normal-to-normal (S DNN) RR intervals, and the number of increases in successive NN intervals > 50 ms (sNN(50)). Subjects were grouped according to nocturnal arterial oxyg en saturation (Sa,O-2): group 1 had episodes of Sa,O-2 <90%, group 2 had Sa ,O-2 >90% throughout the night, and group 3 were 27 healthy age-matched con trols who also underwent HRV analysis. The mean +/- SD SDNN for group 1 was 79.3 +/- 23.7 ms, less than group 2 (1 49.8 +/- 58.9 ms, p < 0.02) and group 3 (155.1 +/- 37.1 ms, p < 0.001). The geometric mean sNN50 was less in group 1 than group 2 (1,530 versus 5,843, p < 0.01), but not significantly different from group 3 (2,712, p = 0.053) . There was no significant difference between groups 2 and 3. Within group 1, both SDNN and sNN(50) were significantly lower in those patients with mo re severe nocturnal hypoxia. The minimum overnight Sa,O-2 was the best pred ictor of abnormal HRV. In conclusion, patients with nocturnal hypoxia have evidence of autonomic d ysfunction, even in cases with only transient episodes of nocturnal oxygen desaturation. The severity of autonomic dysfunction is related to the degre e of nocturnal oxygen desaturation.