Arterial wave reflection decreases gradually from supine to upright

Background. An increase in total peripheral resistance (TPR) usually increases arterial wave reflection. During passive head-up tilt (HUT), however, arterial wave reflection decreases with increasing TPR. This study addressed whether arterial wave reflection gradually decreases during HUT. Methods. In 10 healthy volunteers (22-39 years, nine males), we recorded finger arterial pressures in supine position (0 degrees), and 30 degrees and 70 degrees degrees HUT and active standing (90 degrees). Aortic pressure was constructed from the finger pressure signal and hemodynamics were calculated. Arterial wave reflection was quantified as the augmentation index (AIx) and the reflection magnitude (RM). Results. During HUT, heart rate increased (p < 0.001), stroke volume and cardiac output decreased (p < 0.001 and p < 0.01), diastolic blood pressure increased (p < 0.001), whereas systolic blood pressure did not change. TPR increased from 0.9 dyn s/cm(5) at 0 degrees to 1.2, 1.4 and 1.4 dyn s/cm(5) at 30 degrees, 70 degrees and 90 degrees (p < 0.001). AIx fell gradually from 25% at 0 degrees to 16%, -1% and -10% at 30 degrees, 70 degrees and 90 degrees (p < 0.001). The RM decreased from 0.572 at 0 degrees to 0.456 at 90 degrees (p < 0.001). Conclusion. From supine to upright, arterial wave reflection represented as AIx and RM gradually decreases in the presence of increasing TPR.