Journal of Applied Physiology, Vol 57, Issue 4 1211-1221, Copyright © 1984 by American Physiological Society
Effects of hypercapnia on Breuer-Hering threshold for inspiratory termination
T. L. Clanton and W. T. Lipscomb
The effects of CO2 concentration on the timing of inspiratory duration (TI)
and expiratory duration (TE) and the responses to lung inflation were
studied in decerebrate paralyzed cats. With lung volume held at functional
residual capacity during the breath cycle, hypercapnia (fractional
concentration of inspired CO2 = 0.04) caused variable changes in TI and
significant increases in TE. To obtain the Breuer-Hering threshold
relationship [tidal volume (VT) vs. TI] and the timing relationship between
TE and the preceding TI (TE vs. TI), ramp inflations of various sizes were
used to terminate inspiration at different times in the breath cycle.
Hypercapnia caused the VT vs. TI curves to shift in an upward direction so
that at higher lung volumes TI was lengthened. Also, the slope of the TE
vs. TI relationship was increased. The results suggest that hypercapnia
diminished the sensitivity of the Breuer-Hering reflex to the lung volume,
thus allowing volume to increase with little effect on TI. In addition, TE
appears to become more sensitive to changes in the preceding TI. A model is
presented which provides a possible neural mechanism for these responses.
