Journal of Applied Physiology, Vol 57, Issue 3 874-880, Copyright © 1984 by American Physiological Society
Temporal delay of venous blood correlates with onset of exercise hyperpnea
K. M. VanBenthuysen, G. D. Swanson and J. V. Weil
We tested the hypothesis that humoral factors contribute to the onset of
exercise hyperpnea in an electrically induced model of isocapnic exercise
in alpha-chloralose-anesthetized dogs. A cannula placed in the inferior
vena cava (IVC) permitted hindlimb venous blood to flow either directly to
the lungs or through a variable-length extracorporeal circuit. Mean transit
times (MTT) of blood from exercising hindlimbs were measured from the
arrival at the pulmonary artery of green dye injected into the saphenous
vein. Onset of hyperpnea was determined by the half time of the ventilatory
response (T 1/2), the time required to reach 50% of the steady-state
ventilation. In seven dogs, T 1/2 was directly related to MTT (P less than
0.001), suggesting that blood-borne substances released at the onset of
exercise contribute to the hyperpneic response. The T 1/2-MTT relation
persisted following L2 cord transection (n = 4), suggesting that
intraspinal afferents are not required for this response. Chemoreceptor
denervation (n = 4) slowed the onset of exercise hyperpnea but did not
alter the T 1/2-MTT relation. In this model of electrically induced
"exercise" in which neurogenic influences have been minimized, humoral
factors alone may stimulate ventilation sufficiently to produce arterial
isocapnia.
