Respiratory response to co2 in the hypocapnic range in awake
humans.
Patrick, W., K. Webster, A. Puddy, R. Sanii, and M. Younes.
RESPIRATORY INVESTIGATION UNIT, DEPARTMENT OF MEDICINE, UNIVERSITY
OF MANITOBA, WINNIPEG, MANITOBA, CANADA R3A 1R8
APStracts 2:0350A, 1995.
The response of respiratory motor output to CO2 in the hypocapnic
range (PCO2<36mmHg) in the absence of hypoxemia is not well
characterised in awake normal humans. We induced hypocapnia with
hyperoxia in 16 normal volunteers by placing them on a volume-cycled
ventilator in the assist mode. Subjects were not aware of the purpose
of the study. All subjects continued rhythmic breathing despite high
tidal volumes and severe hypocapnia (PACO2 nearly equal to 25 mmHg).
FICO2 was increased in steps and changes in respiratory motor output
were quantitated from changes in airway pressure (Paw) at constant
volume and flow, changes in respiratory rate, and the change in rate
of decline in Paw prior to triggering (dp/dt). There was a
significant increase in respiratory muscle pressure (Pmus), but not
in respiratory rate (F), in the PCO2 range 26-36 mmHg. The slope of
the response increased gradually over the PCO2 range 26-41 mmHg.
Respiratory rate significantly increased only above 36 mmHg. We
conclude that the response to PCO2 in the hypocapnic range is
basically non-linear with no clear CO2 threshold and the CO2
responsiveness extends well below eupneic CO2 levels.
Received 4 October 1994; accepted in final form 13 July 1995.
APS Manuscript Number A1020-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.