Whole Body Impedance Cardiography & Continuous
Pulse Wave Analysis in the Measurement of Human
Haemodynamics during Passive Head-Up Tilt
By Anna Tahvanainen
Tampere University Press
Distributed By Coronet Books
$87.50 Paper original
Regulation of blood pressure is a complex interplay between several haemodynamic mechanisms, but only resting blood pressure and heart rate are commonly measured in clinical practice to determine a patient’s haemodynamic status. However, the value of single blood pressure measurements as diagnostic tests has recently been questioned. In addition, changes in for example arterial compliance, endothelial function, or the regulation of vascular resistance can already be measured before clinical manifestations of cardiovascular disease. The aim of the present study was to test the repeatability and reproducibility of a comprehensive haemodynamic measurement protocol in both supine position and during head-up tilt. In addition, the effects on two largely endothelium-dependent agents, inhaled salbutamol and intravenous L-arginine, and one endothelium independent agent, sublingual nitroglycerin, were investigated, and the haemodynamic mechanism of nitrate-induced presyncope were examined. Moreover, the age-related haemodynamic changes, supine and upright, in normotensive subjects were clarified. Finally, the application was tested in patients with either essential hypertension or metabolic syndrome.
Non-invasive haemodynamic measurements were performed by applying whole body impedance cardiography, continuous pulse wave analysis and plethysmographic finger blood pressure measurements in supine position and during head-up tilt. Thus, peripheral and central blood pressure, indices of pulse wave reflection, pulse wave velocity, vascular resistance, and cardiac function could be simultaneously assessed. Repeated measurements were performed to test the repeatability and reproducibility of the method, and to study the drug effects in a placebo-controlled manner. All study subjects, except for the subjects included in the testing of the method’s clinical application, were normotensive and had no medication affecting cardiovascular status.
The measurement protocol was repeatable and reproducible in both supine position and during head-up tilt. Inhaled salbutamol decreased blood pressure, vascular resistance and augmentation index, while heart rate and cardiac output were increased. Sublingual nitroglycerin clearly decreased blood pressure, vascular resistance, augmentation index and pulse wave velocity, and increased heart rate and cardiac output. Importantly, the haemodynamic effects of nitroglycerin were enhanced during the head-up tilt, while the salbutamol effects were more evident in the supine position. Intravenous L-arginine resulted in decreased blood pressure and increased aortic reflection time only during the tilt. During nitrate-induced presyncope, reduced vascular resistance was observed. Increasing age from 20 to 60 years was associated with increased arterial stiffness and wave reflection, while no changes were observed in cardiac function or vascular resistance. A more pronounced decrease in central systolic blood pressure in response to tilt was associated with increased age and arterial stiffness. Subjects with metabolic syndrome had higher heart rate and arterial stiffness than hypertensive subjects, despite similar elevation of blood pressure and vascular resistance. These results suggest more widespread changes in cardiovascular status than just elevated blood pressure in metabolic syndrome.
In conclusion, the present measurement protocol enables a detailed characterization of patients’ haemodynamic profile, including the assessment of the role of the endothelium in vascular responsiveness. The divergent effects of research drugs in different postures, and the age-related changes in haemodynamic responsiveness to head-up tilt underlie the importance to study upright haemodynamics.
Acta Universitatis Tamperensis No. 1677
Return to Coronet Books main page