Journal of Applied Physiology, Vol 45, Issue 5 756-761, Copyright © 1978 by American Physiological Society
Dissociated ventilatory and central respiratory responses to CO2 at raised N2 pressure
D. Linnarsson and C. M. Hesser
The effects of hyberbaric nitrogen on the responses of ventilation and
central inspiratory activity (CIA) to progressive hypercapnia were studied
in eight subjects rebreathing a) O2 at an ambient pressure of 1.3 bar
(control), and b) air at 6.1 bar (PO2 = 1.3 bar, PN2 = 4.8 bar).
Inspiratory occlusion pressure (P0.1), pulmonary ventilation, and end-tidal
PCO2 were used for the computation of individual CIA and ventilatory CO2
response curves. Increasing the inspired PN2 to 4.8 bar caused, on the
average, a 40% increase of P0.1 at PCO2 = 50 Torr, whereas the slope of the
ventilatory CO2 response curve was reduced by 39%. It was concluded that,
at raised air and nitrogen pressures, CIA is increased, although not
sufficiently to prevent a reduction of ventilation brought about by the
increased gas density and consequent increase in airway resistance. The
increased airway resistance is thought to be responsible for the increase
in CIA by causing a reflex stimulation of the respiratory centers.
