Analysis of cardiovascular responses to passive head‐up tilt using continuous pulse wave analysis and impedance cardiography

OBJECTIVE: To non-invasively measure central haemodynamics, arterial stiffness, cardiac function and vascular resistance, with the subject in the supine position and during head-up tilt, in order to examine the haemodynamic changes associated with alterations in the augmentation index, and to investigate repeatability and reproducibility of the measurement protocol. MATERIAL AND METHODS: Thirty-three healthy volunteers (21-51 years) were investigated using continuous pulse wave analysis from the radial artery with a tonometric sensor, whole-body impedance cardiography and plethysmographic blood pressure (BP) recordings from the fingers. The measurements were performed with the subject supine and during passive head-up tilt, and repeated during the same session and on four separate days. RESULTS: During the head-up tilt, diastolic BP (5.2+/-0.6%), heart rate (27.6+/-1.9%) and vascular resistance (12.5+/-1.7%) increased (all p<0.05), while systolic BP (-3.2+/-0.6%), aortic pulse pressure (-23.3+/-1.4%), augmentation index (-11.6+/-0.7%), aortic reflection time (-7.0+/-1.0%), ejection duration (-21.4+/-0.7%), stroke volume (-26.1+/-1.2%) and cardiac output (-5.0+/-1.5%) decreased (all p<0.05). Augmentation index at rest correlated with aortic systolic BP (r = 0.423), aortic reflection time (r = -0.647), pulse wave velocity (r = 0.287) and age (r = 0.480). The change in augmentation index during head-up tilt correlated with the change in aortic systolic BP (r = 0.469), aortic pulse pressure (r = 0.606), ejection duration (r = 0.374) and heart rate (r = -0.445). According to Bland-Altman and repeatability index analyses, repeatability and reproducibility of the measurements were good during the same session and on separate days. CONCLUSIONS: Combined pulse wave analysis and impedance cardiography with the subject in the supine position and during head-up tilt is a repeatable and reproducible method for comprehensive investigation of the cardiovascular function.