Ventilatory and mouth occlusion pressure responses to hypercapnia in chronic tetraplegia.

Abstract

To compare the ventilatory response to hypercapnia and the mouth occlusion pressure measured at 0.1 second following inspiration (P0.1) in hypercapnia between chronic tetraplegic and normal subjects. A case-control study with an uneven sample size for the study of clinical disorders. Patients were recruited from the outpatient clinic of a rehabilitation department. Seven normal men and 9 men with tetraplegia who had cervical cord injuries (C5-C8), with a mean injury duration of 9.7 yrs. Pulmonary function tests were performed during resting, whereas minute ventilation (VE) and P0.1 were measured during CO2 rebreathing. The maximal voluntary ventilation (MVV), vital capacity (VC), and maximal respiratory muscle strength in the tetraplegic subjects were significantly less than in the normal subjects. Both the ventilatory and P0.1 responses to hypercapnia were significantly reduced in tetraplegic as compared with normal subjects, but the reductions were eliminated by normalizing with maximal ventilatory performance (MVV or VC) and maximal inspiratory muscle strength (PImax), respectively. Chronic tetraplegic persons have diminished ventilatory and P0.1 responses to hypercapnia. Respiratory muscle weakness may be a primary factor contributing to the diminished ventilatory response observed in these patients.