VARIATIONS IN BLOOD FLOW WITH CHANGES IN POSITION IN NORMAL AND PATHOLOGIC SUBJECTS

Tilt test in essential hypertension. Differential responses in heart rate and vascular resistance

Changes in hemodynamic parameters following 50-degree head-up tilt were studied in a population of 56 men, including 35 subjects with sustained essential hypertension and 21 age-matched normotensive controls. The increase in heart rate following tilt was similar in groups and exhibited the same reduction in response with age. The increase in vascular resistance following tilt was strongly and positively correlated with both age and baseline vascular resistance. The latter finding was observed mainly in hypertensive subjects. The study provided evidence that differentiated responses of heart rate and vascular resistance may be observed following orthostasis. In both normal and hypertensive subjects, the age dependence of heart rate response possibly reflected differences in baroreceptor reflex control of parasympathetic and sympathetic activity. In hypertensive subjects, the vascular response was amplified with age and baseline vascular resistance, suggesting a role for structural changes of the vessels in the increased vascular response.

The nursing position after operation and the work of breathing

Patients after operation are often nursed with the foot of the bed raised in order to facilitate drainage of blood from the legs and of secretions from the trachea. Measurements of the changes in lung volume, of the oxygen cost of breathing, and of the movements of the rib cage and abdomen in the sitting, supine, and 15 degree head-down positions have been made in three subjects. The subjects selected were one overweight, one of medium, and one of lean body build. The oxygen cost of breathing was considerably increased in the head-down position in the overweight subject, less so in the one of medium build, and not at all in the lean subject. The cause of the increased oxygen cost of breathing and of its influence on the position in which patients are nursed after operation is discussed.

Influence of Posture on Cardiac Output and Minute Ventilation During Exercise

In four normal subjects, cardiac output, oxygen uptake, and ventilatory volume were compared on 8 occasions at rest and on 20 occasions during exercise in the recumbent and sitting postures. The oxygen uptake was not significantly different in the two postures either at rest or at equal external work loads. In the sitting posture during exercise, the cardiac index was approximately 12 per cent and stroke index 19 per cent lower than in the supine posture. Ventilation was signifi cantly higher because of an increase in respir atory frequency.