It has recently been proposed that afferent fibers from skeletal muscl
e could sense the state of the microvascular circulation, linking vent
ilation to the degree of peripheral perfusion or vascular distension (
Huszczuk et al., Respir. Physiol., 91: 207-226, 1993). Ventilatory and
circulatory responses to manipulation of peripheral vascular pressure
s in the hind limbs of anaestetized (sodium thiopental) sheep were exa
mined. Inflatable balloons were placed at the caudal ends of the abdom
inal aorta and the vena cava (Vc). Aortic (Ao) occlusion induced a con
sistent normocapnic decrease in minute ventilation (VE). In contrast,
VE increased significantly during vena cava obstruction, leading to hy
pocapnia. Small changes in systemic blood pressure were observed (+7 m
mHg for Ao occlusion and -12 mmHg during Vc obstruction). Moreover, in
flation of the caval balloon superimposed on a previously established
Ao occlusion, preventing venous drainage of anastomotic inflow, result
ed in a significant rise in distal vascular pressures with trivial cha
nges in systolic blood pressure. This led to a gradual rise of VE, des
pite further reduction of the CO2 flux to the lungs. The subsequent de
flation of the aortic balloon, exposing the hindlimb vasculature to ao
rtic pressure, resulted in an even more profound hypocapnic hyperpnea.
The concurrent arterial blood pressure changes were too small to poss
ibly involve the ventilatory component of the arterial baroreflex. We
therefore hypothesize, that perfusion-related afferent signals within
the muscles could contribute to respiratory homeostasis by maintaining
ventilation of the lungs commensurate with the circulatory state of t
he muscular apparatus.