Faculty Bibliography

Sixteen patients with the obstructive sleep apnea syndrome (OSAS) were studied for 1-2 h while receiving continuous positive airway pressure (CPAP) delivered via a nasal mask. Obstructive apneas were obliterated in all. Eight patients had studies of genioglossal muscle activity (GG EMG) and one patient had computed tomograms (CT) of the upper airway while on nasal CPAP. The GG EMG studies showed two patterns: suppression and augmentation of GG EMG while on CPAP. The CT scan showed the airway to be narrowed while the patient was awake off CPAP. It returned to a normal caliber when CPAP was applied, despite sleep. These results are interpreted to suggest three potential mechanisms of action for nasal CPAP in OSAS: 1) reduced upper airway resistance due to prevention of sleep-induced collapse of the airway; 2) reduced upper airway resistance due to dilatation of the airway by nasal CPAP beyond its dimension in the awake state; and 3) possible stimulation of mechanoreceptors leading to an increase in airway tone while CPAP is applied

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

Described in this study are eight patients with alveolar hypoventilation syndromes who presented with carbon dioxide narcosis and coma. After reversal of severe hypercapnia, all patients were discharged and maintained at home for an average period of 10 years utilizing 'noninvasive' nocturnal mechanical ventilation. The use of 'noninvasive' mechanical ventilation at home attempted to void the hazards of tracheostomy and the difficulties inherent in continuous daytime use of oxygen. This form of treatment has allowed these patients to continue their previously productive lives. This study represents the first published long-term follow-up regarding this mode of treatment in patients with alveolar hypoventilation