Effect of age and coronary heart disease on the circulatory responses to graded lower body negative pressure.

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Previous reports have demonstrated that haemodynamic responses to various autonomic stresses such as head-up tilt, Valsalva's manoeuvre, face immersion, cold pressor, and static exercise are altered with increasing age and cardiac disease. In the present investigation, we compared the responses of 20 to 27 year old and 50 to 59 year old healthy men and 50 to 59 year old ambulatory coronary heart disease patients to graded lower body negative pressure (LBNP). Noninvasive methods including transthoracic impedance cardiography and venous occlusion plethysmography were used to monitor changes in stroke index, thoracic blood volume and vascular resistance. The tachycardia and stroke index decline of the older men and cardiac patients at higher levels of LBNP were similar but less than those of the younger men; we also noted greater increases in forearm and total peripheral resistance during LBNP in the two older groups than in the younger group. However, the decreases in thoracic blood volume were less in the two older groups at the higher levels of LBNP indicating that older subjects had been subjected to a lesser stress. These differences in thoracic blood volume displacement may be due to a decreased peripheral venous compliance in older subjects. When we compared responses to similar decreases in thoracic blood volume, the heart rate and stroke index changes were similar in the three groups but the exaggerated forearm vascular resistance and total peripheral resistance index increases in the older groups persisted. Our data suggest: (1) the decreased haemodynamic response to postural stress previously reported in older subjects and cardiac patients is due at least in part to a lesser peripheral sequestration of blood in the older individuals; (2) the lesser heart rate and stroke index responses in coronary heart disease patients to diminished preload stress may be due primarily to normal aging; and (3) the greater increases in peripheral vascular resistance in the two older groups during LBNP may be a function of the higher baseline resistance levels in these older subjects.