Faculty Bibliography

The recent recognition of the sleep apnea syndrome has forced a re-evaluation of the mechanism of hypercapnia and disordered respiratory control in obese patients. Thirteen obese patients with sleep apnea were studied in an attempt to relate the pattern of sleep abnormality and awake ventilatory control to the presence of chronic hypercapnia. Patients with hypercapnia and/or hypoxemia had reduced ventilatory responses to hypercapnic and hypoxic stimulation, respectively. The presence of hypercapnia, however, did not separate the patients with respect to type, duration, or frequency of apneas. The degree of awake chemical drives could not be related to the severity of the sleep apnea phenomenon. However, patients with intact ventilatory control demonstrated augmented ventilation after apneas, which may explain their eucapnic state

A portable, easily assembled system that allows quantitative monitoring of ventilation in the sleeping human subject is described. It is a modification of the system used by Kinney et al. (Metab. Clin. Exp. 13: 205-211, 1964) and Spencer et al. (J. Appl. Physiol. 33: 523-528, 1972). The system directly measures gas flow without reliance on indirect CO2 or temperature sensors or on chest wall motion. It is comfortable and reflects the tidal volume with an accuracy of 92%. It also allows measurement of oxygen consumption and CO2 production. The gas breathed by the subject can be varied in composition. Two illustrative examples of the use of the system are given: 1) a case of obstructive apnea; and 2) a case in which a drop in arterial oxygen saturation is explained by quantified hypoventilation undetected by a nasal CO2 probe