Baroreflex mechanisms and response to exercise in patients with heart disease

Background Past reports showed that the baroreflex continuously regulates hemodynamics during exercise. However, it is still clinically unclear. If baroreflex mechanism is able to influence actually exercise cardiovascular control, baroreflex sympathetic and/or parasympathetic function relates to response to exercise. Therefore, we examined the relationship of heat rate changes to both blood pressure increment and decrement with tolerance and chronotropic response to peak exercise in patients with heart disease. Methods In 25 male heart disease patients (60 +/- 9 years) without decompensated heart failure, baroreceptor reflex sensitivity (BRS ms mmHg-1) was measured by reflex heart rate responses to changes in blood pressure after phenylephrine (P-BRS) and nitroglycerin (N-BRS) injection, respectively. Symptom-limited treadmill exercise test was performed according to Bruce's protocol. Results (i) The absolute values of blood pressure change after the administrations were similar between the agents because the dosages of nitroglycerin and phenylephrine were set to equalize absolute changes in blood pressure. (ii) In this study population, the ratio of N-BRS to P-BRS was not significantly correlated with hypertension and diabetes mellitus. (iii) Exercise capacity (METs) (r = -0.626) and heart rate response to exercise per METs (r = 0.670) was significantly related to N-BRS but not to P-BRS. Conclusion We found that the abnormality of baroreflex function in the presence of blood pressure decrements can lead to insufficient capacity and easy sympathetic activation during exercise.