Autonomic dysfunction in patients with nocturnal hypoventilation in extrapulmonary restrictive disease

In chronic obstructive pulmonary disease, persistent hypoxia may be associated with autonomic dysfunction. The effect of nocturnal oxygen desaturation on autonomic function in patients with chest wall deformities and neuromuscular disease is unknown. This study examined the effect of nocturnal oxygen desaturation upon heart rate variability, a sensitive measure of autonomic function. Twenty-seven patients with chest wall deformity or neuromuscular disease underwent analysis of overnight oximetry, blood gases, and 24 h heart rate variability (HRV), specifically the standard deviation of normal-to-normal (SDNN) RR intervals, and the number of increases in successive NN intervals >50 ms (SNN50). Subjects were grouped according to nocturnal arterial oxygen saturation (Sa,O2): group 1 had episodes of Sa,O2 <90%, group 2 had Sa,O2 >90% throughout the night, and group 3 were 27 healthy age-matched controls who also underwent HRV analysis. The mean+/-SD SDNN for group 1 was 79.3+/-23.7 ms, less than group 2 (149.8+/-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 sNN50 were significantly lower in those patients with more severe nocturnal hypoxia. The minimum overnight Sa,O2 was the best predictor of abnormal HRV. In conclusion, patients with nocturnal hypoxia have evidence of autonomic dysfunction, even in cases with only transient episodes of nocturnal oxygen desaturation. The severity of autonomic dysfunction is related to the degree of nocturnal oxygen desaturation.