EFFECT OF CARDIAC DENERVATION ON CARDIORESPIRATORY RESPONSES TO EXERCISE IN GOATS

The purpose of this study was to determine whether intact cardiac innervation and a normal cardiovascular (CV) response are required for a normal ventilatory (VE) response to mild and moderate treadmill exercise in awake goats. Accordingly, we measured CV and respiratory responses to two levels of exercise in seven normal (N) and six cardiac-denervated (CD) goats. Evidence of surgical CD included 1) absence of a cardiac response during surgery when the left thoracic cardiac nerves, thoracic vagi, and right and left stellate ganglia were electrically stimulated, 2) total and 80% attenuation of baroreflex changes in heart rate (HR) when arterial blood pressure was raised or lowered, respectively, by infusion of vasoactive agents in awake goats, and 3) attenuation of the CV responses to exercise. At each level of exercise in the CD goats, the HR response was significantly reduced relative to the response observed before CD (P < 0.05) and the recovery HR response was delayed. Cardiac index increased in a work rate-dependent manner in N and CD goats but was significantly lower in the CD animals (P < 0.05). Hypotension was consistently observed during exercise following CD. There was no effect of CD on steady-state VE at any metabolic rate or on the VE-O2 uptake relationship (P < 0.05). The rest-to-work and work-to-work transition responses of arterial PCO2 were similar between N and CD goats, but there was a tendency toward greater hypocapnia at the exercise onset in CD goats at the highest work rate. We conclude that 1) intact afferent and efferent innervation of the heart is not requisite for a normal VE response to exercise and 2) the normal VE response is not dependent on a normal cardiovascular response.