EFFECT OF TRANSRESPIRATORY PRESSURE ON PETCO2-PACO2 AND VENTILATORY REFLEXES IN HUMANS

Inspiratory muscle activity increases when lung volume is increased by continuous positive-pressure breathing in conscious human subjects (Green et al., 1978). Because end-tidal CO2 pressure (PETCO2) does not change, these increases have not been attributed to chemoreflexes. Continuous positive-pressure breathing at 20 cmH2O influences the end-tidal to arterial CO2 pressure differences (Folkow and Pappenheimer, 1955). PETCO2 was compared with arterial CO2 pressure (PaCO2) in healthy human subjects exposed to continuous negative pressure around the torso (-15 cmH2O) sufficient to increase mean lung volume by about 650 ml. The difference between PETCO2 and PaCO2 was not decreased, PETCO2 is probably a valid measure of chemical drive to ventilation in such circumstances. Substantial increases in respiratory muscle electromyograms were observed during pressure breathing as seen previously. This response must originate by proprioception. On average, the compensation of tidal volume afforded was complete, but the wide variability of individual responses suggests that there was a large cerebral cortical component in these responses.