Abstract 2605: Effect of Body Position on Heart Rate Recovery
Background: Heart rate recovery (HRR) after dynamic exercise reflects the restoration of normal autonomic tone. Delayed HRR after clinical exercise testing has been associated with increased mortality. However the role of body position on HRR has not been well established. The purpose of this study was to determine whether HRR is different after maximal exercise between the supine and standing positions. We hypothesized that HRR would be blunted when standing versus supine due to persistent baroreceptor unloading.
Methods: 11 healthy volunteers (27 ± 4 yrs) (3 m;8 f) were randomly assigned to undergo two maximal treadmill tests with recovery in either the supine or standing position. Non-invasive measurements of heart rate (ECG), blood pressure (BP;Portapres), and stroke volume (SV)/cardiac output (Modelflow) were made immediately following maximal exercise at 15 s intervals for a total of 2 min.
Results: The mean standing HR was significantly higher at 60 s than supine HR (146 ± 13 v 127 ± 15 bpm, P<0.001). This difference in HRR was evident at every recovery time interval (fig⇓, P<0.001), but was not due to differences in either BP or SV (SBP 168 v 164 mmHg, p=0.74; SV 91 v 94 ml, p=0.76).
Conclusions: HRR after maximal exercise is substantially greater between standing and supine positions and could lead to misclassification of some patients. The lack of major hemodynamic differences suggest that central command is restored more quickly when supine. We suggest that for accurate measurement of HRR, values for distinguishing high from low risk patients be standardized for body position during recovery.