DIAPHRAGM FUNCTION AND ALVEOLAR HYPOVENTILATION

Abstract

A syndrome of alveolar hypoventilation was identified in a group of patients with bilateral diaphragm paralysis. Eight patients were studied in whom diaphragm weakness was suggested by paradoxical (inward) movement of the abdominal wall on inspiration, of whom 7 had evidence of a generalized neuromuscular disorder. Diaphragm function was assessed quantitatively by measurement of the change in transdiaphragmatic pressure during a maximum inspiration (.DELTA.PDi). In 5 patients, .DELTA.PDi was zero and in the others ranged from 2-6 cm H2O (normal > 25 cm H2O) indicating paralysis and severe weakness in the respective groups. Fluoroscopy of the diaphragm gave misleading results. Vital capacity ranged from 65-30% of the predicted normal in the upright posture, typically falling by about a half in the supine posture. Alveolar hypoventilation was present in 5 patients when supine and in 6 when asleep, the deterioration in blood gases associated with sleep generally being much greater in these patients than in normal subjects. Respiratory rate was significantly greater than age-matched controls. The ventilatory response to CO2 was impaired. The CO2 tension could be brought to normal levels by voluntary hyperventilation, and the unreliability of voluntary respiratory maneuvers of this kind as indices of ventilatory reserve is emphasized. Alveolar hypoventilation was associated with disturbed sleep, morning headache and day-time fatigue. Symptomatic benefit was achieved by the use of a cuirass respirator at night.