Effects of hypercapnia on Breuer-Hering threshold for inspiratory termination

1211-1221, 19&k-The effects of COz concentration on the timing of inspiratory duration (TI) and expiratory duration (TE) and the responses to lung inflation were studied in decer-ebrate paralyzed cats. With lung volume held at functional residual capacity during the breath cycle, hypercapnia (frac-tional 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 TX (TE vs. Tr), 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 o