Haemodynamic response to head-up tilt in elderly hypertensives and diabetics

Age and Ageing, July, 1995 by Sinikka Luutonen, Kari Antila, Matti Erkko, Ismo Raiha, Tapio Rajala, Leif Sourander

To examine the haemodynamic mechanism associated with postural hypotension (PH) in elderly people, haemodynamic response to head-up tilt was studied in 14 elderly hypertensived and 13 elderly diabetics. Hypertensives and diabetics were divided into those with or without PH, defined as |10 mmHg decline in mean blood pressure in response to head-up tilt. There was no significant change in cardiac output in hypertensives or diabetics with PH, whereas there was a significant increase during tilt in hypertensiles without PH (p < 0.0001) and diabetics without PH (p = 0.0054). Hypertensives without PH showed a significant decrease in total peripheral resistance in response to head-up tilt (p = 0.0043). In hypertensives with PH and in both diabetic groups, there was no change in total peripheral resistance in response to head-up tilt. There was no difference in ejection fractions or heart rate responses between subjects with and without PH in either disease group.

The difference in cardiac output change was not explained by myocardial changes observed at echocardiography nor by heart rate response nor by differences in total peripheral resistance. The results suggest that an increase in cardiac output in response to changing posture may be more important than vasoconstriction in protecting elderly subjects from PH.

Introduction

Mean blood pressure (BP) is influenced by heart rate (HR), stroke volume (SV) and total peripheral resistance (TPR): Mean BP = HR x SV x TPR. The assumption of upright position prompts a shift of blood to the lower extremities, which causes a decrease in stroke volume and blood pressure. To restore blood pressure level, heart rate and vascular peripheral resistance increase.

Elderly people are less efficient than younger adults in maintaining their upright blood pressure. This may be due to blunted heart rate response to upright posture [1, 2]. It has also been found that the rise in total peripheral resistance in elderly subjects is less than would be expected in younger subjects [1].

Postural hypotension is a common finding in elderly people [3]. In previous studies on heterogeneous groups of elderly subjects with postural hypotension [1, 4], postural hypotension was associated with failure to increase total peripheral resistance on tilting. There was a large inter-individual variation in haemodynamic responses in subjects with postural hypotension [1,4]. Subjects with postural hypotension had lower stroke volume levels at rest and, during head-up tilt than controls, and this was thought to be due to age-associated changes in myocardial function [4]. Echocardiography was not performed.

To examine the blood pressure control in homogeneous groups of elderly subjects, echocardiography and haemodynamic response to head-up tilt were studied in elderly subjects with hypertension or diabetes, both known risk factors for postural hypotension [5-7].

Subjects and Methods

The study was approved by the Ethical Committee of Turku City Hospital.

Subjects: Fourteen hypertensive subjects taking thiazide diuretics and 13 type 2 diabetics taking oral hypoglycaemic agents (fasting blood glucose 5.4 mmol/1 to 13.7 mmol/1) were studied. All the subjects lived at home. The subjects were recruited from senior citizens clubs or were referred for the test by colleagues working at the health centre of Turku. The characteristics of the subjects are seen in Tables I and II. Subjects with dementia or other diseases of the central nervous system, and any taking neuroleptic or antidepressive medication, were excluded. Some of the subjects were taking long-acting nitrates or 3-blockers for coronary disease or verapamil for extrasystoles. These drugs were withdrawn a week before the test. Other medications, including diuretics in the hypertensive group and hypoglycaemic agents in the diabetic group, were continued until the day of the test.

Design: The examination included a physical examination, chest radiograph and a standard 12-lead electrocardiogram. Evaluation of electrocardiograms was made according to the Minnesota criteria [8). Twelve hypertensives and all the diabetics underwent colour-doppler echocardiography (Aloka SSD-860 model CP 100E, Mitsubishi Electric Corporation, Tokyo, Japan). Observed valvular insufficiencies were graded from 1 to 4. The head-up tilt tests were performed on a hospital ward between 09 h 00 and 11 h 00. The subjects did not eat any breakfast before the test. The tilt test made use of a tilt table with foot support. The subjects lay supine for 40 minutes, then they were passively tilted to a 70[degrees] head-up position for 10 minutes, and then returned to the supine position. Heart rate, blood pressure and transthoracic impedance were recorded during the tilt and the preceding 10 minutes of supine rest. Six time-points were chosen for comparison: 2.5 min before tilt and 1, 3, 5, 7 and 9 min during tilt. At each point, five successive cardiac cycles were included in the analysis. The subjects were cannulated in order to examine the neurohumoral response to head-up tilt. The results are discussed elsewhere [9]. The cannulation took place 15 minutes before changing posture. Thus, the influence of cannulation on autonomic responses is minimal. In our study, autonomic function was not evaluated by Valsalva manoeuvre, deep breathing test or isometric handgrip test. However, the accuracy of these traditional cardiovascular tests is not as good as for elderly subjects as for younger [10].