Relationship between arterial baroreflex sensitivity and exercise capacity in patients with acute myocardial...

To investigate the relationship between arterial baroreflex sensitivity (BRS) and exercise capacity, we examined arterial BRS and its relation to exercise capacity during upright bicycle exercise in 40 uncomplicated patients with acute myocardial infarction. Arterial BRS was measured 3 weeks (20 +/- 5 days) after acute myocardial infarction and assessed by calculating the regression line relating phenylephrine-induced increases in systolic blood pressure to the attendant changes in the R-R interval. All patients underwent graded symptom-limited bicycle exercise with direct measurements of hemodynamic and metabolic measurements. In all patients, the average arterial BRS was 5.6 +/- 2.6 ms mmHg(-1). There were no significant correlations between arterial BRS and hemodynamic measurements at rest. However, arterial BRS was negatively related to systemic vascular resistance at peak exercise (r = -0.60, P = 0.0001) and percent change increase in systemic vascular resistance from rest to peak exercise (r = -0.45, P = 0.003), whereas arterial BRS was positively related to cardiac output (r = -0.48, P = 0.002) and stroke volume at peak exercise (r = 0.42, P = 0.007), and percent change increase in cardiac output (r = -0.55, P = 0.0002) and stroke volume from rest to peak exercise (r = 0.41, P = 0.008). Furthermore, arterial BRS had modest but significant correlations with peak oxygen consumption (r = -0.48, P = 0.002) and exercise duration (r = 0.35, P = 0.029), indicating that patients with better arterial BRS have better exercise capacity in patients with acute myocardial infarction. These results suggest that arterial BRS was linked to central and peripheral hemodynamic responses to exercise and hence, contributed to exercise capacity after acute myocardial infraction.