Effect of posture on baroreflex sensitivity in healthy subjects

In this study we investigated whether body position has significant effects on baroreflex sensitivity in healthy subjects. Baroreflex sensitivity was calculated from pressure overshoot after the release of a Valsalva strain in the supine and sitting positions in 10 subjects. At rest, no difference was found in supine and sitting mean R-R intervals (837 +/- 82 and 858 +/- 86 ms, respectively), whereas systolic and diastolic blood pressures were lower in the supine position (111.3 +/- 24.6 vs. 141.2 +/- 12.6 mmHg, P < 0.01 and 54.8 +/- 14.7 vs. 75.6 +/- 13.4 mmHg, P < 0.001, respectively). Baroreflex sensitivity in the supine (9.0 +/- 4.1 ms x mmHg-1) and sitting positions (8.8 +/- 4.9 ms x mmHg-1) did not differ significantly from each other. The correlation between supine and sitting baroreflex sensitivity was 0.96 (P < 0.001) and in 9 out of 10 subjects the discrepancy between supine and sitting baroreflex sensitivity was < 2.0 ms x mmHg-1. We conclude that baroreflex sensitivity measured in the supine and sitting positions do not differ significantly from each other.