Abnormal Respiratory Pattern Generation during Sleep in Patients with Autonomic Dysfunction

Abstract

We examined the control of breathing during wakefulness and sleep in 3 patients with autonomic nervous dysfunction who were free of respiratory and sleep-related symptoms. During wakefulness, the ability of the patients to voluntarily reproduce a breath of a given tidal volume did not differ from that of healthy control subjects, indicating normal function of the behavioral respiratory control system. Defects in the metabolic control system were indicated in all 3 patients by lack of a ventilatory response to acute hypoxia. During sleep, minute volume of ventilation in the patients with autonomic dysfunction was not significantly less than that in the healthy subjects, but their pattern of breathing was highly irregular, resulting in coefficients of variation of respiratory variables that were 2 to 3 times greater than normal (p < 0.05). This irregularity of breathing persisted during slow-wave sleep, when ventilatory pattern is normally highly regular. Three patients with Parkinson's disease were also studied, but did not have respiratory irregularities during sleep; therefore the observations in patients with autonomic dysfunction could not be attributed to their associated Parkinsonism. The combination of findings during wakefulness and sleep in the patients with autonomic dysfunction suggests a defect in the autonomic respiratory rhythm generator of the brainstem. The findings indicate that examination of breathing pattern during sleep may be useful in the investigation of patients suspected of having autonomic dysfunction, even in the absence of clinical respiratory abnormalities. The findings also support the concept that breathing during sleep, in contrast to that during wakefulness, is critically dependent upon the metabolic (automatic) respiratory control system.