EFFECTS OF SUDDEN AND PROLONGED STANDING FROM SUPINE POSTURE ON HEART RATE, ECG-PATTERN AND BLOOD PRESSURE

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1 J. Human Ergol.,17: 3-12,1988 Center for Academic Publications Japan. Printed in Japan. EFFECTS OF SUDDEN AND PROLONGED STANDING FROM SUPINE POSTURE ON HEART RATE, ECG-PATTERN AND BLOOD PRESSURE Satipati CHATTERJEE, C. R. DAs, S. K. DEY, and S. K. NAG Exercise and Cardiorespiratory Physiology Laboratory, Department of Physiology, University College of Science and Technology, 92, Acharya Prafulla Chandra Road, Calcutta , India Arterial blood pressure, heart rate and electrocardiogram were recorded in the supine posture after sudden standing and at 2 min-intervals over a period of 20 min in the standing posture in 31 healthy male and 32 healthy female subjects within the age range of 20 to 30 years. The heart rate, P-amplitude of the electrocardiogram and the diastolic blood pressure of both sexes in sudden and also in prolonged standing were found to be significantly higher than those in supine posture, while the systolic blood pressure and Q-T interval, T-P interval and T -amplitude of the electrocardiogram were significantly lower. Moreover, the heart rate responses to orthostasis were greater in subjects with a resting heart rate of <60 beats/min than those in subjects with higher resting heart rate (>60 beats/min). No significant difference between sudden and prolonged standing postures were found in any of these parameters. As the long axis of the human body is parallel to gravitational pull felt in the standing posture, hydrostatic pressures exist in the fluid spaces, particularly in the circulatory system, which has an influence on the heart. GROEDEL (1908), suggested that blood volume and the basic tone of the blood vessels in man are adjusted in such a way as to ensure adequate cardiac filling when standing erect. TURNER (1927) showed that the heart rate is increased in sitting as compared with reclining, and further on standing. Peripheral circulatory behaviour during orthostasis was, however, first reported by FLORKIN et al. (1930). Blood tends to accumulate in the part of the body below the level of the heart (WATERFIELD, 1931), and the band of arterial pulse pressure narrows (MACWILLIAM, 1933) in the upright posture. SWEENY and MAYERSON (1937) showed a decreased cardiac output, and also decreased stroke and minute volumes of the heart during orthostasis, in spite of compensatory vasoconstriction in the extremities (MAYERSON Received for publication December 19,

2 A S. CHATTERJEE, C. R. DAS, S. K. DEY, and S. K. NAG and ToTH, 1939). Based on these previous investigations, the present study was designed to elucidate further the effects of sudden and also prolonged standing from the supine position on heart rates, ECG patterns and arterial blood pressures of both sexes. MATERIALS AND METHODS Thirty-one male and 32 female subjects within the age range of 20 to 30 years (mean : yr in male and } 3.87 yr in female), having mean heights of }5.41 cm and }4.38 cm, and mean body weights of 55.52±6.09 kg and }7.48 kg, respectively) were randomly selected from the students and research workers in the Department of Physiology, Calcutta University. A thorough physical examination was carried out in all the subjects to exclude those suffering from any cardiovascular disorder. Physical parameters like standing height and body weight were recorded in cros and kgs, respectively. Each subject was given instructions and demonstrations regarding the performances of electrocardiogram in supine and in sudden as well as prolonged standing postures. The subjects were then allowed to rest for at least 10 min. For the best performance of ECG in this respect lead II (standard limb lead) was chosen (ZIEGLER, 1951). Initial tracings were recorded in the supine position; then in sudden standing (T0 min) followed by recordings at 2 min-intervals over a period of 20 min of prolonged standing (i.e. at T2, T4, T6s T20 min). The subjects assumed a standing posture from supine within 2 s. During the period of standing the subjects were in a relaxed state but the movement of limbs and neck was restricted. The heart rates and different intervals and amplitudes of the ECG waves were noted. In another experiment both the systolic and diastolic blood pressures in the supine position, in sudden standing and also at 2 min-intervals in a period of 20 min-standing were recorded in the same subjects. Data were statistically analysed to show the effects of both sudden and prolonged standing from supine on heart rate, ECG and arterial blood pressures.. RESULTS Mean values and standard deviations of all the parameters studied in the supine position, in sudden standing (i.e. at TO min), and also at T. 2 min, T10 min and T20 min of prolonged standing are shown in Tables 1 and 2 for male and female subjects respectively. Mean values of all the parameters studied at every time interval are also shown graphically (Figs, 1-5). Computation of Model I Anova with these data showed that the heart rates, P-amplitudes of the ECG, and the diastolic blood pressures of both sexes in sudden as well as prolonged standing (i.e. TO min to T20 min) were significantly higher (p<0.01) than those for the supine position, while the systolic blood pres-

3 EFFECTS OF STANDING ON HEART 5

4 6 S. CHATTERJEE, C. R. DAS, S. K. DEY, and S. K. NAG sures, and the Q-T intervals, T-P intervals and T -amplitudes of the ECG were significantly lower (p<0.01, except for the Q-T intervals of the females where p<0.05). No significant changes were found in R- and S-amplitudes and also in P-R intervals of the ECG of either sex. Moreover, the data showed no significant effect of prolonged standing on any of these parameters. To determine the relationship of physical parameters like height, body weight and resting heart rate to the blood pressure and ECG responses to orthostasis, however, the subjects were classified into three height groups, i.e cm (n=14), cm (n=11) and cm (n=6) in males and cm (n=7), cm (n=16) and cm (n=9) in females; three weight groups, i.e. 52 kg (n=10), kg (n=9) and > 59 kg (n=12) in males and <49 kg (n=1.3), kg (n=12) and > 56 kg (n=7) in females; and three resting heart rate groups, i.e. <60 beats/min (n=3 and 2, respectively), beats/min (n=17 and 13, respectively) and >81 beats/min (n=11 and 17, respectively) in both sexes. The responses of heart rate, blood pressures and P- and T-amplitudes of the ECG off the three resting heart rate groups are presented in Figs. 5 and 6. Height and body weight were not found to be related to the responses of heart rate, blood pressure and electrocardiographic waves to orthostasis while a clear relationship was obtained between resting heart rate and those of the heart rate and P- and T-amplitudes of the ECG DISCUSSION The cardiovascular system is generally studied in supine subjects or animals. In supine subjects, however, circulatory dynamics are most stable because most arteries and veins are horizontally oriented at or near the heart level. During orthostasis, on the other hand, most arteries and veins are oriented vertically, and, as a result, large hydrostatic pressures are produced by the long uninterrupted columns of blood. The arterial, capillary, and also the venous pressures are markedly elevated in the dependent extremities, and the circulatory system promptly makes appropriate compensatory adaptations (HELLEBRANDT and FRANSEEN, 1943; MAYERSON, 1942; WEISSLER et al., 1957). If these compensatory mechanisms are insufficient or retarded, orthostatic hypotension results (HELLEBRANDT and FRANSEEN, 1943). Fainting reactions are frequently produced in erect subjects by stimuli that would have virtually no effect on the supine subject. In our experiment no subject fainted or collapsed during standing as this posture was not a difficult one. But 3 males and 4 females sweated during the last phases of standing. Recognition of the fact that much of the active period of human life is spent in the erect position makes it appropriate to consider the cardiovascular adjustments required in this posture In the present study, when the supine subjects assumed a sudden erect posture, the heart rates of both sexes increased with similar magnitude-in males by 18

5 EFFECTS OF STANDING OF HEART 7 Fig, 1. Response of heart rate after sudden and during prolonged standing. Fig. 2. Response of blood pressure (systolic and diastolic) after sudden and during prolonged standing.

6 8 S. CHATTERJEE, C. R. DAS, S. K. DEY, and S. K. NAG Fig. 3. Response of ECG intervals after sudden and during prolonged standing. beats/min while in females by 19 beats. SCHNEIDER and TRUESDELL (1939) also reported a similar observation in which the magnitude of increase was 18 beats/min. This elevation remained almost unaltered throughout the period of experiment (Fig. 1). The increase in heart rate during orthostasis is, however, a favourable compensatory reaction, as it balances the decrease in stroke volume (BEVEGARD et al., 1960, 1963; LAGERLOF et al., 1951; NYLIN, 1934).caused by gravitational interference with cardiac filling and prevents a serious decrease in cardiac output (DoNAL et al., 1934; DONALD et al.,1953; REEVES et al.,1961; STEAD et al.,1945) As in the case of heart rate, the arterial blood pressures of both sexes were also influenced by posture. When reclining subjects stood erect, there was a fall in systolic blood pressure and a rise in diastolic (Fig. 2), resulting in a narrow band of pulse pressure. In male subjects, these bands were narrowed by about 8 mm Hg at TO min and 15 mm Hg at T20 min, while in females, by 8 mm Hg and 14 mm Hg, respectively. Similar observations were also made by MACWILLIAM (1933), WALD et al. (1937) and CURRENS (1948). During orthostasis, blood pools in the lower parts of the body under the influence of gravity, resulting in a decreased venous return to the heart (HELLEBRAND and FRANSEEN, 1943). As a

7 EFFECTS OF STANDING ON HEART 9 Fig. 4. Response of ECG amplitudes after sudden and during prolonged standing. consequence, stroke volume and cardiac output are reduced (MCMICHAEL and SHARPEY-SCHAFER, 1944). It has also been reported that the carotid sinus reflex brings about a prompt vasoconstriction in the splanchnic vessels with a resulting rise in arterial pressure that ensures an adequate blood flow to the brain as a measure of compensatory adaptation during standing erect (MOOREHOUSE and MILLEN, 1976). As a consequence of these changes, the systolic pressure declined while the diastolic pressure rose in the subjects of the present investigation. Heart rate increases during orthostasis as well as during exercise. The circumstance is, however, quite different in both cases: in the former case, heart rate is increased with a reduction in cardiac output and stroke volume (or force of contraction) while in the latter event it increases with an associated increase in stroke volume and cardiac output. Therefore, the electrical activity of the heart may also not be the same. In the present investigation, the T-P and Q-T intervals of both sexes were found to be decreased after assuming an erect posture (Fig. 3). In male subjects these two intervals were decreased respectively by about s and s at TO min and by s and s at T20 min, while in females by s and s at TO min and by s and s at T20 min. This can be explained on the basis of shortening of the cardiac cycle as a result of acceleration of heart rate. During orthostasis a decrease in T -amplitude and an increase in P-amplitude were also noted in the present investigation (Fig. 4). At TO min the T-amplitudes were decreased by about 45% in males and females, while at T20 min they were

8 10 S. CHATTERJEE, C. R. DAS, S. K. DEY, and S. K. NAG Fig. 5. Percentage increase in heart rate and blood pressure (Systolic and Diastolic) response after sudden and during prolonged standing for three different heart-rate groups. decreased by about 34% in both. The P-amplitudes were found to be increased in both male and female subjects by about 45 % and 52% at TO min, and by 47 and 55% at T20 min, respectively. LEPESCHKIN and SURAWICZ (1958) also found orthostatic T -wave changes in 3 % of 179 normal subjects (LEPESCHKIN and SuRAwICz, 1958). A higher incidence (23 %) was observed by KEMP and ELLESTAND (1968). Increased sympathetic activity in response to the upright position is believed to be the mechanism responsible. To establish correlations of different resting heart rate groups with the heart rate response to orthostasis, it had been found that the percentage change in heart rate was higher in the subjects of both sexes with lower resting heart rate (<60 beats/min) while the changes in the subjects with higher resting heart rate (>60 beats/min) were lower (Fig. 5). Moreover, the males with higher resting

9 EFFECTS OF STANDING ON HEART 11 Fig. 6. Response of ECG amplitude after sudden and during prolonged standing for three different heart rate groups. heart rate (>60 beats/min) showed more pronounced changes in P-wave amplitude in comparison to those with lower resting heart rate (<60 beats/min) while the T -wave response was found to be almost identical in both sexes with higher resting heart rate (>60 beats/min) though the absolute decrease was higher in male subjects (Fig. 6). Increased sympathetic activity in the subjects with a resting heart rate of <60 beats/min might be the mechanism responsible for a more pronounced heart rate response to orthostasis. And the changes in P- and T -waves were due obviously to those in heart rate, the P-wave changing directly and the T -wave inversely to it. The kind help of Debojyoti Das of Department of Physiology, Presidency College, Calcutta, for statistical analysis is gratefully acknowledged. REFERENCES BEVEGARD, S., HOLMGREN, A., and JONSSON, B. (1960) The effect of body position on the circulation at rest and during exercise, with special reference to the influence on the stroke volume. Acta Physiol. Scand., 49: BEVEGARD, S., HOLMGREN, A., and JONSSON, B. (1963) Circulatory studies in well trained athletes at rest and during heavy exercise, with special reference to stroke volume and the influence of body position. Acta Physiol. Scand., 57:

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