AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 3 538-R547, Copyright © 1987 by American Physiological Society
Effects of hypercapnia on variability of normal respiratory behavior in awake cats
P. C. Szlyk and D. B. Jennings
Resting quiet awake cats breathing air in a steady state have a range of
respiratory behavior, and this encompasses nonpurring and purring (D. B.
Jennings and P. C. Szlyk, Can. J. Physiol. Pharmacol. 63: 148-154, 1985).
On a given study day, individual cats usually breathed in a limited part of
their potential respiratory range. Respiratory pattern, such as average
breath frequency (f) and average tidal volume (VT) utilized for a given
level of ventilation (V), could be predicted when cats breathed air; as
well, inspiratory (TI) and expiratory (TE) times were specific for a given
breath f. Inhalation of 2% and 4% CO2 in air caused an average increase in
ventilation of 16 and 100%, respectively but breath-to-breath variability
of V, f, and VT persisted at each fractional concentration of inspired CO2
(FICO2). The range of different V utilized breath to breath when breathing
2% CO2 overlapped with V during air control studies. Substantial overlap
with control V also occurred in three of six cats when breathing 4% CO2.
The most consistent effect of progressive hypercapnia was to increase VT
and decrease f at a given level of V; increase in V during hypercapnia was
accounted for by an increase in mean inspiratory flow (VT/TI). Hypercapnia
also caused the fraction of breathing cycle devoted to inspiration (TI/TT)
to increase at low f but not at high f.
