Journal of Applied Physiology, Vol 68, Issue 2 503-507, Copyright © 1990 by American Physiological Society
Hypocapnia does not alter collateral ventilation in sheep
B. B. Hudak, P. B. Terry, H. A. Menkes, M. D. Jones Jr and R. J. Traystman
Department of Pediatrics, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
Hypocapnic constriction has been proposed as a mechanism by which
collateral pathways might rapidly alter ventilation to match perfusion. We
studied the changes in response to hypocapnia with age in sheep, a species
with collateral resistance (Rcoll) similar to those measured in humans.
Measurements of Rcoll were made with either 5 or 10% CO2 and with air
(hypocapnia) in 29 anesthetized sheep, ages 6 mo to 10 yr, with the wedged
bronchoscope technique. Rcoll was 0.42 +/- 0.12, 0.58 +/- 0.18, 0.32 +/-
0.18, and 0.17 +/- 0.04 (SE) cmH2O.ml-1.min in 6-mo- and 1-, 2-, and
10-yr-old animals, respectively. These values were unchanged with
hypocapnia. Despite the lack of a change in Rcoll with hypocapnia,
administration of histamine aerosol (8 animals) through the bronchoscope
increased Rcoll by 151 +/- 35% (P less than 0.05). These data suggest that
although collateral pathways exist in sheep and are capable of
constriction, they do not respond to hypocapnia. Furthermore, the response
to hypocapnia is not influenced by age.
