ARTERIAL COMPLIANCE MAY INFLUENCE BAROREFLEX FUNCTION IN ATHLETES AND HYPERTENSIVES

The present study investigated arterial compliance as a possible influence on mean arterial pressure-heart rate (MAP-HR) reflex function in athletes and hypertensives. Aortic stiffness and systemic arterial compliance (SAC) were estimated in 25 elite male athletes and 25 age-matched sedentary controls. Blood pressure did not vary between groups, but SAC was higher in the athletic compared with the sedentary group (0.46 +/- 0.04 vs. 0.37 +/- 0.02 arbitrary compliance units; P = 0.03). In five hypertensives and six age-matched normals and in a subgroup of seven athletes and seven age-matched controls the sigmoidal MAP-HR reflex was assessed using phenylephrine and nitroprusside. In athletes compared with sedentary subjects MAP-HR reflex sensitivity was the same; however, the maximum tachycardia in response to blood pressure reduction was lower in the athletic group (87.1.1 +/- 3.7 vs. 97.1 +/- 2.9 beats/min; P = 0.05). Athletes had a higher blood pressure corresponding to 95% of the HR range (64.2 +/- 3.2 vs. 54.0 +/- 2.1 mmHg; P = 0.02), but there was no difference in the blood pressure corresponding to 5% of the HR range. The blood pressure excursion necessary to traverse the baroreceptor transducer range (MAP(d)) was therefore less in athletes compared with normals. The beta-index of aortic stiffness correlated closely with MAP(d) (R = 0.70; P < 0.01). In hypertensives reflex sensitivity was reduced, the minimum HR was elevated, and the MAP(d) was 56% greater compared with normals. To conclude, because baroreceptor firing rate is proportional to the change in arterial circumference, the differences in the blood pressure range to traverse the entire baroreceptor transducer range for athletes and hypertensives may be accountable by differences in arterial compliance.