COMPARATIVE STUDY OF HAEMODYNAMIC RESPONSES TO ACTIVE AND PASSIVE POSTURE INDUCING HEAD-WARD POOLING OF' BLOOD IN MAN

Abstract

Objective: To study the relative effects of passive head-down tilt and squatting on the
cardiovascular dynamics in man.
Design: A pre-testlpost -test study.
Serfting: Physiology Research Laboratories in the Schools of Medicine at Addis Ababa
University and the University of Dundee, UK.
Subjects: Ten normal healthy subjects aged nineteen to twenty two years.
Intervention: Cardiovascular variables measured in Passive body tilt and squatting.
Mlzin outcome measures. Similar responses in forearm blood flow, arterial blood pressure,
peripheral vascular resistance, and pulse rate observed in both active and passive postural
changes.
Results: A change from the sitting to the squatting position resulted in marked changes of
forearm blood flow (FBF=1.63niV100 mumin, p<0.05), mean arterial blood pressure
(BP=9mmHg, p<0.05), mean forearm vascular resistance I PVR=-10 PRU, p<0.05) and mean
pulse rate (PR =-5 beats/min, p>0.05). The corresponding changes in the head-down position
were: FRF=2.37mV100 mumin, p<0.05; BP=11.0 mmHg. p<0.05; VR=-12.85 PRU, p<0.05;
PR=-10 beatslmin, p>0.05)
Conclusion: These results wggest that the movement of blood towards the head is only
slightly more marked in the head-down tilt than in the squatting position. The changes in
flow and arterial blood pressure are similarly correlated 1 r=0.6291 in squatting and r=0.553
in 30' head-down tilt). In both positions, blood moves to the thorax, neck and the head thus
traversing the same baroreflex regions. This means that changes in cardiovascular variables
in the two positions are detected by the same receptors signalling information to integrating
centres via the same afferent pathways. Squatting and head-down tilt can, therefore, be used
alternately to counteract orthostatic dizziness and to assess the significance of cardiovascular
autonomic neuropathy in patients with disease conditior~s like diabetes mellitus.