Changes in vascular parameters caused by local orthostatic stress

Abstract

A well established peripheral vascular response to orthostasis is the venoarteriolar reflex. It is considered to be due mostly to axon reflex and therefore can be elicited by local positional changes in the extremities. In the present study we examined whether such positional changes can produce a more generalized response and corresponding changes in some common vascular parameters. The local orthostatic stress was induced by lowering of the right arm 40 cm below heart level while the subject was in supine position after initial rest. Precordial single channel ECG and index finger photoplethysmography were recorded simultaneously before, during, and after the lowering of the arm using MP 100 Biopac modular system. The orthostatic response was evaluated by the changes in the amplitude of the photoplethysmography (aPPG), pulse wave analysis (stiffness index, SI, and reflection index, RI), and changes in the pulse transit time (PTT). The results showed that all of the above parameters change in a consistent way with the local positional change. It is concluded that the local orthostatic stress causes both local response as reflected by the changes in the aPPG and a more generalized vascular change evident from the changes in SI, RI, and PTT.