AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 2 252-R258, Copyright © 1988 by American Physiological Society
Carotid bifurcation sympathectomy and deafferentation: respiration during hypercapnia
D. B. Jennings and P. C. Szlyk
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
The respiratory effects of hypercapnia were studied in six awake cats 1)
after bilateral sympathectomy of the carotid bifurcations and 2) after
bilateral section of the carotid sinus nerves. When cats breathed either 2
or 4% CO2 in air, neither denervation affected the absolute level of
ventilation, the percent change in ventilation, or the range of
breath-to-breath variability in ventilation (V). However, in all six cats
tidal volume (VT) increased for some levels of breath V after sympathectomy
of the carotid bifurcations during inhalation of 4% CO2 in air. Moreover,
after the subsequent carotid deafferentation, increased VT during
fractional concentration of inspired CO2 (FICO2) of 4% persisted in four of
six cats. Thus increased VT after sympathectomy could not be attributed to
increased carotid chemoreceptor afferent activity but may have been due to
reduced baroreceptor activity. On the other hand, sympathectomy-induced
differences in breath timing, present during inhalation of 2% CO2, were
reversed to intact values after sinus nerve section. In contrast to 2% CO2,
changes in respiratory timing in intact cats associated with 4% CO2 were
not altered significantly by sympathectomy or deafferentation of the
carotid bifurcations. The latter indicates that above a critical FICO2
central mechanisms, unrelated to the carotid bifurcation, dominated
respiratory timing in the hypercapnic awake cats.
