Author:
Tarig Ahmed Abdel-Rahman
MBBS, PHD, DTM&H
Professor of physiology
Institution: King Saud University, College of Medicine, Physiology Department
P.O.BOX 2925, Riyadh 11461
Telephone: 00966551875505
Fax: 009664672567

Email : Tarig124@hotmail.com

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INTRODUCTION
Orthostatic and postprandial hypotension is a physical finding, not a disease, and may be symptomatic or asymptomatic. It can occur in all age groups, but is more frequent in the elderly than in young or middle-aged groups (Manica et al. 1990). It is defined as a decrease in systolic blood pressure of at least 20 mmHg, or a decrease of diastolic blood pressure of at least 10 mmHg within three minutes of standing (The American Autonomic Society, 1996). Autonomic control of cardiovascular responses to postural changes in older individuals is of considerable importance in helping to assess the cardiovascular potential in the elderly. Diseases which may decrease cerebral blood flow, like hypertension, diabetes mellitus, heart disease and hyperlipidemia are more frequent in the elderly, which make them more vulnerable to cerebral ischemia and syncope if their blood pressure decreases. The symptoms of hypotension may go unnoticed or ignored and may lead to repeated falls and trauma. Additionally it may lead to psychological loss of confidence causing immobility and prolongation of rehabilitation, and sometimes to depression.

The present investigation was concerned mainly with testing this important autonomic cardiovascular reflex in the healthy elderly Saudi Population. No previous study has reported the incidence of orthostatic hypotension in this population.

The autonomic nervous system is a crucial system for maintenance of homeostasis. Progressive dysfunction in this system was reported in several studies in elderly people and in old animals. In healthy elderly subjects, facial cooling in air produces a greater increase in blood pressure and a smaller bradycardia than in young control subjects (Collins et al. 1989). Changes of cold pressor reflexes and thermoregulatory reflexes were reported in several studies (Eckberg et al. 1992) (Collins et al.1995, 1996). Abdel-Rahman et al. 1992, 1993). Orthostatic hypotension had been observed in all age groups, and it found to occur more frequently in the elderly, especially in persons who were sick and frail (Mader et al. 1987) (Ooi et al.1997).

A fall in systolic blood pressure of 20 mmHg or diastolic blood pressure of 10 mmHg on standing was reported to occur in 6-30 % of elderly people (Petersen et al. 2000) (Sumiyoshi et al. 1999). It was shown to be associated with increased rate of falls, and a history of myocardial infarction or transient ischemic attack (Rutan et al. 1992). It may also be predictive of ischemic stroke (Eigenbrodt et al. 2000). The decrease of blood pressure following upright tilt was found to be a useful predictor of falls in older people (Edward et al. 2002).

Autonomic response to standing was found to be related to changes in plasma norepinephrine level (Ziegler M.G. 1980). Standing evokes diffuse increases in sympathetic nervous activity with enhanced release of norepinephrine, however this increase was not found in some patients with orthostatic hypotension (Lye et al. 1990). Low supine plasma norepinephrine level or a subnormal rise in the norepinephrine level on standing were reported to serve as biochemical markers of peripheral autonomic failure (Polinsky RJ. 1990).

It was reported that when an adult stands from a lying position, 300 to 800 ml of blood pools in the lower extremities (Lipsitz LA. 1989) (Weiling et al. 1993). To maintain blood pressure, this position change requires several sensitive responses to occur quickly. These responses were found to include Cardiovascular, neurologic, muscular, and neurohumoral factors (Weiling et al. 1993). Dysfunction of any of these factors can lead to reduction in blood pressure and oxygen perfusion, which can lead to dizziness and faints, which may cause falls and fractures.

The autonomic nervous system plays an important role in maintaining blood pressure when a person changes position. The baroreceptors can sense the slightest drop in blood pressure which can lead to increased sympathetic tone leading to vasoconstriction, and increase in heart rate and cardiac contractility.

These changes can maintain blood pressure and perfusion.

Further studies of heart rate variability in the elderly using Power Spectral Analysis will add more information to the cardiovascular reflexes in this group.

METHODS
Dinamap (an Automatic blood pressure and heart rate recorder), which can also monitor subcutaneous oxygen tension (SPO2), the respiratory rate and record an ECG, was used in this study. This machine resolved many of the problems of blood pressure recording, including observer bias.

We excluded from our study the extremely elderly individuals more than 75 years old, and those subjects with a history of cardiovascular disease like supine hypertension, or heart failure, or those with any disorder associated with autonomic dysfunction like diabetes, or history of syncope, or those with other major illness, or those using vasodilator drugs. We included in our study all those volunteers, who were reasonably healthy. All subjects selected were employees in King Saud University. The nature of the test was explained to all subjects after their consent was obtained before their participation in the study. Forty-nine >65-year olds, and forty- five <40-year olds were willing to volunteer in the study.

Each subject attended the laboratory three hours after a light breakfast. Subjects rested supine for at least 10 minutes. Then parameters of heart rate, systolic, diastolic, and mean blood pressure, ECG, were recorded by the Dinamap (an Autonomic recorder of all those parameters). Those readings were taken after resting for 10 minutes in the supine position, and then after one, and two minutes of standing up from the supine position. Then a standard meal was provided to each subject, and after 45 minutes all parameters were recorded by the Dinamap after 10 minutes in the supine position, and then after one and two minutes of standing up. All subjects were able to perform the standing test with not much difficulty.

Statistical Methods:
We used student t-test for matched pairs to compare each variable in the supine position with the standing position in the two groups.

We used also student t-test for independent groups to compare each variable between elderly group (n 49) and young adults (n 45), in the supine and standing positions both in the pre-meal and post-prandial periods. We studied also the changes in the heart rate, systolic and diastolic blood pressure from the supine position to the standing position in the pre-meal and post-prandial periods, and we compared those between the elderly and young adults.

We used SPSS statistical package version 10.01 for data analysis.

Results were expressed as mean values standard deviation.

RESULTS
The physical characteristics of the elderly and young adults are shown in
Table 1.

Table 1: Physical Characteristics of Young adults and Elderly subjects
Mean ± SD.

The mean resting heart rate was significantly high (P<0.ooo5) in the healthy elderly (n=49), compared to the young adults (n=45), in the standing or supine positions, both in the pre-meal and postprandial periods, Table 2.

Table 2: Pre-meal and postprandial systolic, diastolic blood pressures, and heart rate, in the supine (SP) and standing (ST) positions in the young adults >40-year olds, and the elderly subjects <65-year olds.

In comparison between mean systolic and diastolic blood pressures in the young adults and elderly subjects, the result showed that the mean systolic and diastolic blood pressures were significantly high in the elderly (n=49), compared to the young adults (n=45), in the supine position, both in the pre-meal and postprandial periods (P<0.0006), Table 2. However, when standing, the mean systolic and diastolic blood pressures were comparable between the two groups, and there were no significant differences between them. That can be explained by the greater drop in blood pressure in the elderly group in the standing position, Table 2.

Comparisons between the mean postural changes in systolic, diastolic blood pressures, and heart rate from the supine position to the standing position in the elderly group compared to the young adults were highly significant (P<0.0004), both in the pre-meal and postprandial periods, Table 3.

Table 3: Mean postural changes of systolic, diastolic blood pressures, and heart rate in the young adults <40-year olds (n = 45), and the elderly subjects >65- year olds (n = 49), in the pre-meal and postprandial periods. Mean ± SD

DISCUSSION
The finding of our investigation indicated a highly significant postural drop in the mean systolic blood pressure of the healthy elderly subjects, compared to a very small and insignificant drop in the young adults as shown in Tables 2 and 3. The drop in systolic blood pressure in the elderly group confirmed the conclusions of several other studies (Mancia et al. 1990) (Ferrari et al. 1989) (Mader et al. 1987) (Ooi et al.1997). Up to about 30% of elderly subjects were reported to experience significant drop in systolic blood pressure on standing (Petersen et al. 2000).

The mean postural drop in systolic blood pressure in our study ranges between 25-28 mmHg (Table 3), which was greater than those changes reported in the literature (Macrae et al. 1989) (Mo R et al. 1994). These differences may be attributed to variations in standardization of procedures, and also may be due to the higher environmental temperature in our area, compared to those areas where previous studies in the literature were conducted. The increased activity of the sweat glands at higher environmental temperatures may contribute to a greater postural changes in blood pressure.

The increase in heart rate on standing was less and insignificant in the elderly group compared to the young group. The increase of heart rate on standing was related to changes in plasma norepinephrine level (Ziegler MG 1980) and that increase was not found in some patients with orthostatic hypotension (Lye M et al. 1990). Our study also demonstrated a higher resting heart rate in the elderly group >65 years, compared to the young adults <40 years, both in the supine and standing positions as shown in Table 2. It was reported that heart rate variability was diminished with advancing age by using Power Spectral Analysis (Korkushko et al. 1991). In animal studies, arterial baroreflex control of heart rate, and arterial blood pressure, were all significantly diminished in older animals (Hajduczok et al. 1991). In the elderly, there appears to be a decline in parasympathetic function which controls the heart rate during rest and this may explain the higher resting heart rate in the elderly group. The decreased compliance of the baroreceptors and the impaired vagal activity in the elderly were also reported in other studies (Collins et al.1995, 1996).

To show further the effects of ageing in our study, we compared the mean supine and standing heart rate, systolic and diastolic blood pressures between the healthy young adults <40 years (n 45), and the healthy elderly people >65 years (n 49), in the pre-meal and postprandial periods. The results showed significant differences between the two groups in all variables in the supine position (P<0.0004). However, when standing, the mean systolic and diastolic blood pressure were comparable between the two groups and there were no significant differences between them as in Table 2. That can be explained by the greater drop in the mean systolic and diastolic blood pressures in the elderly group when standing, compared to a very small change in the young group.

Our investigation demonstrated a defect in the reaction of the cardiovascular system in esponse to physiological stimuli such as standing upright or taking a meal in the elderly group compared to the young group. That defect was shown by a significant drop in the mean systolic blood pressure on standing, and ere consistent with several previous studies on the changes of the cardiovascular reflexes with ageing (Eckberg et al. 1992) (Collins et al.1995) (Petersen et al. 2000) (Sumiyoshi et al. 1999). The significant drop in systolic blood pressure observed in our elderly subjects was generally asymptomatic, however that did not exclude symptoms occurring in the same individual at different times of the day. It was reported that the decrease in blood pressure following upright tilt was a useful predictor of falls in older people (Edward et al. 2002). So reduction in blood pressure may predipose some elderly people to symptomatic hypotension leading to syncope, fall and fractures. These symptoms can easily be overlooked in the elderly, and they can be attributed to ageing, without expecting a possible decline in the role of the autonomic nervous system in the cardiovascular reflexes which were described previously in the elderly.

Autonomic cardiovascular dysfunctions, particularly orthostatic hypotension should be considered seriously in all elderly people, particularly those at risk, for example, those with supine hypertension or those using vasodilator drugs. Elderly people should be advised to change their posture slowly after lying in bed or sitting in a chair for a long time. They should also be advised to take small frequent meals to reduce postprandial hypotension. Head-up tilt at night to as much as can be tolerated, can to some extent down regulate cerebral blood flow, and it can also prevent nocturnal diuresis. The floor of the house should be made in such way to reduce the possibility of fall. Hot bath or bathing when alone at home should be avoided by the elderly. Blood pressure should be measured routinely in the supine and standing positions for all elderly people to check for possibility of postural hypotension. These preventive measures may reduce the risk of the clinical outcome of postural hypotension, like dizziness, falls and fractures which may lead to prolonged rehabilitation, and increase morbidity and mortality in the elderly.

ACKNOWLEDGEMENT
The investigator is very grateful to King Abdul-Aziz City for Science and Technology for their generous support. I am also thankful for the Department of Physiology, College of Medicine, King Saud University, where the research took place. My thanks are also extended to all volunteers who participated in this study, and to the technicians, and the Statistician, who helped me during the research.

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