The effects of abnormal sympathetic nervous function upon the ventilatory response to hypoxia

Abstract

THE VENTILATORY RESPONSE TO HYPOXIA WAS STUDIED IN TWO GROUPS OF SUBJECTS WITH ABNORMAL SYMPATHETIC NERVOUS CONTROL: (a) human subjects with familial dysautonomia (Riley-Day syndrome), and (b) unanesthetized goats treated with an alpha-adrenergic blocking agent (phenoxybenzamine). The ventilatory response to hypoxia was evaluated in two ways: (a) from the slope of the relationship between ventilation and alveolar P(Co2) ([unk]V(E)-P(ACo2) slope) during the rebreathing of hypoxic and hyperoxic gases, and (b) from the change in ventilation produced when hypoxia was abruptly relieved. The ventilatory and circulatory responses of the unanesthetized, phenoxybenzamine-treated goats were qualitatively similar to those of dysautonomic patients. In contrast to the sustained stimulation of ventilation produced by hypoxia in normal subjects, hypoxia either did not change, or decreased, the [unk]V(E)-P(ACo2) slope of dysautonomic patients and phenoxybenzamine-treated goats; CO(2)-free hypoxia produced a fleeting hyperventilation, which was followed by apnea when hypoxia was abruptly relieved. Unlike normal subjects, the dysautonomic patients and phenoxybenzamine-treated goats became hypotensive while hypoxic. The results indicate that peripheral chemoreceptor reflex responses to hypoxia are preserved in subjects in whom sympathetic nervous responses are impaired. However, the central nervous depression of ventilation by hypoxia is enhanced simultaneously. The inordinate central depression is attributed to the inability of the dysautonomic subjects and goats to maintain systemic blood pressure and, consequently, cerebral blood flow during hypoxia, thereby aggrevating central nervous hypoxia.