Breathing pattern in tetraplegics during exposure to hypoxia and hypercapnia

The question was investigated of whether thoracic feedback could play a role in shaping the tidal and frequency components of the breathing pattern. The changes in the breathing pattern of tetraplegic subjects were examined and compared with those of normal subjects during hypoxic and hypercapnic rebreathing tests, using data from our previous study. The breathing pattern was evaluated from diagramatic spirograms, constructed at an SaO2 80% and P(ET)CO2 of 55 mmHg. Chemical drive increased VT and shortened T1 and TE in both groups, but tetraplegics responded with a 60% smaller increase in VT. Since the mean inspiratory flow, VT/T1, was the same in either gas condition in both groups, the smaller VT in tetraplegics was due entirely to a shorter T1. These results show that ventilation in tetraplegics is more shallow and rapid, and it implicates thoracic feedback in modulation of the respiratory pattern.