Effect of age on cardiovascular responses to static muscular contraction in beagles.

Induced muscular contraction in anesthetized animals results in significant hemodynamic and regional blood flow (RBF) changes. Although reflex cardiovascular responses initiated in contracting muscle have been firmly established, little is known about the effects of age on these responses. Because other reflex responses that involve sympathetic activation appear to be attenuated with age, it was hypothesized that reflex efferent cardiovascular responses that normally occur during muscular contraction would be impaired in senescent dogs. Therefore, hemodynamic and RBF responses to induced static hindlimb contraction (HLC) were evaluated in 8- to 14- and 2- to 3-yr-old beagles during alpha-chloralose anesthesia. Most baseline hemodynamic parameters were similar in both groups, but heart rate was significantly (P < 0.05) higher in old dogs. During HLC, heart rate and blood pressure increased in the young and old dogs. However, increases in stroke volume and cardiac output were greater in old dogs, combined with a reduction in systemic vascular resistance not observed in young dogs. No age-related difference in baseline RBF (microspheres) was observed in six of eight abdominal regional circulations and in each of four skeletal muscle groups. During HLC, RBF reductions occurred in six of eight abdominal organs in young and old dogs. However, the reduction in RBF and concomitant increase in vascular resistance in all eight abdominal regions combined was almost twice as great in young vs. old dogs. In noncontracting skeletal muscle, RBF decreased and vascular resistance increased four times more in young vs. old dogs.(ABSTRACT TRUNCATED AT 250 WORDS)