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Blood pressure in infancy
American
Heart Journal
October, 1977, Vol. 94, No. 4
Editorial Blood pressure in infancy Michael de Swiet, M.D.* Elliott A. Shinebourne, M.D. London, England
Hypertension is a major risk factor in death from all vascular diseases. ~ There have been several epidemiological studies on the prevalence of hypertension in the adult population. ~'~ However, there are few studies on the prevalence and evolution of hypertension from the neonatal period. There are also few accurate crosssectional studies of blood pressure in an adequate population of infants or young children. 3-~ One of the main reasons for this lack of data has been the practical difficulty of measuring blood pressure accurately by a non-invasive technique in neonates and small children. This difficulty has now largely been overcome by the Doppler ultrasound technique which detects blood flow by the Doppler shift produced by moving blood particles. A sphygmomanometer cuff is placed around a limb, inflated above systolic blood pressure, and then deflated in the normal way. The pressure at which blood flow is first detected by an ultrasound probe placed over an artery distal to the cuff, is taken as the systolic blood pressure. We have found ~t h a t intra-arterial blood pressure is closely correlated with blood pressure measured by doctors or nurses using the Parkes Doppler ultrasound system. We have also evaluated the Roche Doppler Arteriosonde From The Cardiothoracic Institute, Brompton Hospital, Fulham Road, London, England. Received for publication Jan. 26, 1977. Reprint requests: Michael de Swiet, M.D., Dept. of Paediatrics. The Cardiothoracic Institute, Brompton Hospital, Fulham Road, London S W 3 6 H P England. *Michael de Swiet was supported by a Grant from The Medical Research Council.
October, 1977, Vol. 94, No. 4, pp. 399.401
system ~ which is said to measure diastolic as well as systolic blood pressure in infants. Indirect measurements were again compared with intraarterial measurements. The correlation of Arteriosonde b l o o d pressure and intra-arterial systolic blood pressure was not so close as the correlation of Parkes and intra-arterial blood pressure measurements. The correlation of the Roche diastolic blood pressure measurements with intra-arterial blood pressure measurements was poor (r -- 0.51). We therefore do not believe that the Arteriosonde can measure diastolic blood pressure accurately in infants though the Infrasonde 8 machine may well do so. We have continued to use the Parkes instrument since we find it convenient. Since systolic blood pressure is a better predictor of cardiovascular mortality in adults than is diastolic blood pressure, 9 we are not concerned t h a t we have been measuring systolic blood pressure only in our epidemiological studies. Since we wished to obtain a representative measurement of blood pressure in the neonatal period, we first studied blood pressure variability in the first six days of life. 1~We found t h a t blood pressure increased most rapidly during the first four days of life and thereafter it became more stable. We therefore chose to measure blood pressure in the infants of the population study at age 4 to 6 days when they were not crying or feeding, activities which both raise blood pressure. We and others 11have found t h a t blood pressure is higher in babies awake than in babies who are asleep. The difference was 11 mm. Hg in our neonatal series. 1~ Therefore, in our epidemiolog-
American Heart Journal
399
de S w i e t a n d S h i n e b o u r n e
ical s t u d y ~ we corrected blood pressure for level of consciousness. We h a v e s u b s e q u e n t l y e m b a r k e d on a p o p u l a tion s t u d y of 2,000 i n f a n t s in a n a t t e m p t to identify a s u b - g r o u p who m a y develop h y p e r t e n sion. We elected to s t u d y a relatively stable, well defined p o p u l a t i o n - a l l i n f a n t s b o r n a t F a r n b o r ough Hospital, K e n t , whose m o t h e r s live in the L o n d o n B o r o u g h of B r o m l e y . Blood pressure is m e a s u r e d by a t e a m of four nurses a t h o m e or in hospital at 4 days, a n d in t h e i n f a n t s ' h o m e s a t age 6 weeks, 6 m o n t h s , 1, 2, a n d 3 years. Analysis of the d a t a f r o m t h e first 500 i n f a n t s t o e n t e r the s t u d y 1~ has enabled us to p r e s e n t cross-sectional d a t a on the n o r m a l blood pressure distribution a t age 4 to 6 d a y s a n d a t 5 to 7 weeks of age. T h e distributions are t h e s a m e for b o y s and girls. We h a v e confirmed o u r previous finding TM t h a t wakefulness is associated w i t h increased blood pressure a t b o t h 4 to 6 days, a n d at 5 to 7 weeks. We h a v e also f o u n d a highly significant (r < 0.001) relationship b e t w e e n blood pressure at age 4 to 6 d a y s a n d blood pressure a t age 5 to 7 weeks. 12 I f the correlation holds in l a t e r m e a s u r e ments, it would suggest t h a t it m a y indeed be possible to identify a t b i r t h a s u b - g r o u p of children a t risk f r o m h y p e r t e n s i o n , p a r t i c u l a r l y as it h a s a l r e a d y been s h o w n t h a t blood pressure in infants aged 2 t o 1 4 y e a r s is c o r r e l a t e d with blood pressure m e a s u r e d in the s a m e i n f a n t s four y e a r s later. ~3 T h e correlation t h a t we observed was n o t strong (r -- 0.20), b u t this is of t h e s a m e order as h a d been n o t e d in o t h e r studies s u c h as Zinner, L e v y a n d K a s s ' s familial s t u d i e s . " H e n n e k e n s a n d associates 1~ f o u n d evidence of familial aggregation of blood pressure a t age one m o n t h b u t n o t at age 2 days. T h i s was based on m e a s u r e m e n t s of blood pressure m a d e in the siblings of the index infant. We h a v e not m a d e a n y m e a s u r e m e n t s in siblings b u t we h a v e f o u n d n o correlation b e t w e e n m o t h e r ' s or f a t h e r ' s blood pressure a n d i n f a n t ' s blood pressure a t age 4 to 6 d a y s or a t age 5 to 7 weeks, r-' Lee a n d c o - w o r k e r s " also did not find a correlation b e t w e e n m a t e r n a l a n d child systolic blood pressure in the n e o n a t a l period, a l t h o u g h t h e y did find a w e a k c o r r e l a t i o n in diastolic blood pressures. W e would expect to find a significant relationship as the children grow older a n d their blood pressure v a r i a b i l i t y b e c o m e s less. T h e m o t h e r ' s blood pressure could also h a v e been affected by p r e g n a n c y even six weeks a f t e r
400
delivery TM a n d t h e m o t h e r ' s blood pressure variability will also be less o n c e s h e is p a s t t h e i m m e d i a t e p o s t p a r t u m period. Despite the evidence t h a t s o d i u m i n t a k e m a y be related to the d e v e l o p m e n t of h y p e r t e n sion, 17~9 we h a v e been u n a b l e to find a n y relationship b e t w e e n blood pressure m e a s u r e d in i n f a n c y and sodium intake. Miall 2~ was u n a b l e to find a correlation b e t w e e n blood pressure m e a s u r e d in a d u l t life a n d sodium intake. We h a v e e x a m i n e d this relationship in two ways: First, t h e m a j o r i t y of i n f a n t feeding p r e p a rations used in t h e U n i t e d K i n g d o m h a v e a b o u t twice t h e sodium c o n c e n t r a t i o n of h u m a n m i l k ~ a n d this c o n c e n t r a t i o n m a y be increased still f u r t h e r if the feed is mixed incorrectly. ~" B u t a t ages 4 d a y s and 6 weeks t h e r e was no difference between the blood pressures of bottle-fed a n d breast-fed babiesP 3 Secondly, blood pressure was n o t r e l a t e d to t h e sodium c o n t e n t of feeds in m e a s u r e m e n t s t a k e n at age 6 weeks in a group of babies who were being b o t t l e fed aloneP 3 T h i s relationship will be reexamined as the children b e c o m e older. At present, we believe t h a t we can identify a p o p u l a t i o n of i n f a n t s w i t h a risk of developing h y p e r t e n s i o n b u t because correlations are weak, t h o u g h highly significant, we c a n n o t identify individual babies a t risk. R e p e a t e d m e a s u r e m e n t s m a y reduce the v a r i a b i l i t y as m a y m e a s u r e m e n t s u n d e r m o r e s t a n d a r d conditions such as exercise. I f this occurs we will t h e n be obliged to consider w h e t h e r we should i n t e r v e n e in the progress of these i n f a n t s t o w a r d s h y p e r t e n s i o n and, if so, how. REFERENCES
1. Kannel, W. B., and Dawber, T. R.: Hypertension as an ingredient of a cardiovascular risk profile, Br. J. Hosp. Med. 11:508, 1974. 2. Miall, W. E., and Oldham, P. 0.: A study of arterial blood pressure and its inheritance in a sample of the general population, Clin. Sci. 14:459, 1955. 3. Graham, A. W., Hines, E. A., and Gage, R. P.: Blood pressures in children between the ages of five and sixteen years, Am. J. Dis. Child. 69:203, 1945. 4. Johnson, T: O.: Arterial blood pressures and hypertension in an urban African population sample, Br. J. Prev. Soc. Med. 25:26, 1971. 5. Voors,A. W., Theda, A. F., Frerichs, R. R., Webber, L. S., and Berenson, G. S.: Studies of blood pressure in children ages 5-14 years in a total biracial community, Circulation 54:319, 1976. 6. Elseed, A: M., Shinebourne, E. A, and Joseph, M. C.: Assessment of techniques for measurement of blood pressure in infants and children, Arch. Dis. Child. 48:932, 1973.
October, 1977, VoL 94, No. 4
Blood pressure in infancy 7. Whyte, R. K., Elseed, A. M., Fraser, C. B., Shinebourne, E. A., and de Swiet, M.: Assessment of Doppler ultrasound to measure systolic blood pressures in infants and young children, Arch. Dis, Child. 50:542, 1975. 8. Rolfe, P.: Monitoring equipment for the neonate, Br. J. Clin. Equipment 1:189, 1976. 9. Kannel, W. B., Gordon, T., and Scwartz, M. J.: Systolic versus diastolic blood pressure and risk of coronary heart disease. The Framingham Study, Am. J. Cardiol. 27:335, 1971. 10. de Swiet, M., Fancourt, R., and Peto, J.~ Systolic blood pressure variation during the first 6 days of life, Clin. Sci. Molec. Med. g9:557, 1975. 11. Lee, Y., Rosner, B., Gould, J, B., and Kass, E. H.: Familial aggregation of blood pressures of newborn infants and their mothers, Pediatrics 58:722, 1976. 12. de Swiet, M., Fayers, P., and Shinebourne, E. A.: Blood pressure survey in a population of newborn infants, Br. Med. J. 2:9, 1976. 13. Zinner, S. H., Martin, L. F., Sacks, F., Rosner, B., and Kass, E. H.: A longitudinal study of blood pressure in childhood, Am. J. Epidemiol. 100:437, 1974. 14. Zinner, S. H., Levy, P. S., and Kass, E. H.: Familial aggregation of blood pressure in childhood, N. Engl. J. Med. 284:401, 1971. 15. Hennekens, C. H., Jesse, M. J., Klein, B. E., Gourley, J. E., and Blumenthal, S.: Aggregation of blood pressure in infants and their siblings, Am. J. Epidemiol. 103:457, 1976.
American Heart Journal
16. MacGillivray, I., Rose, C. A., and Rowe, B.: Blood pressure survey in pregnancy, Clin. Sci. 37:395, 1969. 17. Dahl, L. K., Heine, M., and Tassinari, L.: Role of genetic factors in susceptibility to experimental hypertension due to chronic excess salt ingestion, Nature 194:480, 1962: 18. Dahl, L. K., Heine, M., and Tassinari, L.: Effects of chronic salt ingestion: Further demonstration that genetic factors influence the development of hypertension: Evidence from experimental hypertension due to cortisone and to adrenal regeneration, J. Exp. Med. 122:533, 1965. 19. Prior, I. A. M., Grimley Evans, J., Harvey, H. P. B , Davidson, F., and Lindsey, M.: Sodium intake and blood pressure in two Polynesian populations, N. Engl. J. Med. 279:515, 1968, 20. Miall, W. E.: Follow-up study of arterial pressure in the population of a Welsh mining valley', Br. Med. J. 2:1204, 1959. 21. Department of Health and Social Security: Present-day practice in infant feeding, London, 1974, Her Majesty's Stationery Office. 22. Oates, R. K.: Infant feeding practices, Br. Med. J. 2:762, 1973. 23. de Swiet, M., Cooper, L. V., and Fayers, P.i Unpublished observations.
401
Heart Journal
October, 1977, Vol. 94, No. 4
Editorial Blood pressure in infancy Michael de Swiet, M.D.* Elliott A. Shinebourne, M.D. London, England
Hypertension is a major risk factor in death from all vascular diseases. ~ There have been several epidemiological studies on the prevalence of hypertension in the adult population. ~'~ However, there are few studies on the prevalence and evolution of hypertension from the neonatal period. There are also few accurate crosssectional studies of blood pressure in an adequate population of infants or young children. 3-~ One of the main reasons for this lack of data has been the practical difficulty of measuring blood pressure accurately by a non-invasive technique in neonates and small children. This difficulty has now largely been overcome by the Doppler ultrasound technique which detects blood flow by the Doppler shift produced by moving blood particles. A sphygmomanometer cuff is placed around a limb, inflated above systolic blood pressure, and then deflated in the normal way. The pressure at which blood flow is first detected by an ultrasound probe placed over an artery distal to the cuff, is taken as the systolic blood pressure. We have found ~t h a t intra-arterial blood pressure is closely correlated with blood pressure measured by doctors or nurses using the Parkes Doppler ultrasound system. We have also evaluated the Roche Doppler Arteriosonde From The Cardiothoracic Institute, Brompton Hospital, Fulham Road, London, England. Received for publication Jan. 26, 1977. Reprint requests: Michael de Swiet, M.D., Dept. of Paediatrics. The Cardiothoracic Institute, Brompton Hospital, Fulham Road, London S W 3 6 H P England. *Michael de Swiet was supported by a Grant from The Medical Research Council.
October, 1977, Vol. 94, No. 4, pp. 399.401
system ~ which is said to measure diastolic as well as systolic blood pressure in infants. Indirect measurements were again compared with intraarterial measurements. The correlation of Arteriosonde b l o o d pressure and intra-arterial systolic blood pressure was not so close as the correlation of Parkes and intra-arterial blood pressure measurements. The correlation of the Roche diastolic blood pressure measurements with intra-arterial blood pressure measurements was poor (r -- 0.51). We therefore do not believe that the Arteriosonde can measure diastolic blood pressure accurately in infants though the Infrasonde 8 machine may well do so. We have continued to use the Parkes instrument since we find it convenient. Since systolic blood pressure is a better predictor of cardiovascular mortality in adults than is diastolic blood pressure, 9 we are not concerned t h a t we have been measuring systolic blood pressure only in our epidemiological studies. Since we wished to obtain a representative measurement of blood pressure in the neonatal period, we first studied blood pressure variability in the first six days of life. 1~We found t h a t blood pressure increased most rapidly during the first four days of life and thereafter it became more stable. We therefore chose to measure blood pressure in the infants of the population study at age 4 to 6 days when they were not crying or feeding, activities which both raise blood pressure. We and others 11have found t h a t blood pressure is higher in babies awake than in babies who are asleep. The difference was 11 mm. Hg in our neonatal series. 1~ Therefore, in our epidemiolog-
American Heart Journal
399
de S w i e t a n d S h i n e b o u r n e
ical s t u d y ~ we corrected blood pressure for level of consciousness. We h a v e s u b s e q u e n t l y e m b a r k e d on a p o p u l a tion s t u d y of 2,000 i n f a n t s in a n a t t e m p t to identify a s u b - g r o u p who m a y develop h y p e r t e n sion. We elected to s t u d y a relatively stable, well defined p o p u l a t i o n - a l l i n f a n t s b o r n a t F a r n b o r ough Hospital, K e n t , whose m o t h e r s live in the L o n d o n B o r o u g h of B r o m l e y . Blood pressure is m e a s u r e d by a t e a m of four nurses a t h o m e or in hospital at 4 days, a n d in t h e i n f a n t s ' h o m e s a t age 6 weeks, 6 m o n t h s , 1, 2, a n d 3 years. Analysis of the d a t a f r o m t h e first 500 i n f a n t s t o e n t e r the s t u d y 1~ has enabled us to p r e s e n t cross-sectional d a t a on the n o r m a l blood pressure distribution a t age 4 to 6 d a y s a n d a t 5 to 7 weeks of age. T h e distributions are t h e s a m e for b o y s and girls. We h a v e confirmed o u r previous finding TM t h a t wakefulness is associated w i t h increased blood pressure a t b o t h 4 to 6 days, a n d at 5 to 7 weeks. We h a v e also f o u n d a highly significant (r < 0.001) relationship b e t w e e n blood pressure at age 4 to 6 d a y s a n d blood pressure a t age 5 to 7 weeks. 12 I f the correlation holds in l a t e r m e a s u r e ments, it would suggest t h a t it m a y indeed be possible to identify a t b i r t h a s u b - g r o u p of children a t risk f r o m h y p e r t e n s i o n , p a r t i c u l a r l y as it h a s a l r e a d y been s h o w n t h a t blood pressure in infants aged 2 t o 1 4 y e a r s is c o r r e l a t e d with blood pressure m e a s u r e d in the s a m e i n f a n t s four y e a r s later. ~3 T h e correlation t h a t we observed was n o t strong (r -- 0.20), b u t this is of t h e s a m e order as h a d been n o t e d in o t h e r studies s u c h as Zinner, L e v y a n d K a s s ' s familial s t u d i e s . " H e n n e k e n s a n d associates 1~ f o u n d evidence of familial aggregation of blood pressure a t age one m o n t h b u t n o t at age 2 days. T h i s was based on m e a s u r e m e n t s of blood pressure m a d e in the siblings of the index infant. We h a v e not m a d e a n y m e a s u r e m e n t s in siblings b u t we h a v e f o u n d n o correlation b e t w e e n m o t h e r ' s or f a t h e r ' s blood pressure a n d i n f a n t ' s blood pressure a t age 4 to 6 d a y s or a t age 5 to 7 weeks, r-' Lee a n d c o - w o r k e r s " also did not find a correlation b e t w e e n m a t e r n a l a n d child systolic blood pressure in the n e o n a t a l period, a l t h o u g h t h e y did find a w e a k c o r r e l a t i o n in diastolic blood pressures. W e would expect to find a significant relationship as the children grow older a n d their blood pressure v a r i a b i l i t y b e c o m e s less. T h e m o t h e r ' s blood pressure could also h a v e been affected by p r e g n a n c y even six weeks a f t e r
400
delivery TM a n d t h e m o t h e r ' s blood pressure variability will also be less o n c e s h e is p a s t t h e i m m e d i a t e p o s t p a r t u m period. Despite the evidence t h a t s o d i u m i n t a k e m a y be related to the d e v e l o p m e n t of h y p e r t e n sion, 17~9 we h a v e been u n a b l e to find a n y relationship b e t w e e n blood pressure m e a s u r e d in i n f a n c y and sodium intake. Miall 2~ was u n a b l e to find a correlation b e t w e e n blood pressure m e a s u r e d in a d u l t life a n d sodium intake. We h a v e e x a m i n e d this relationship in two ways: First, t h e m a j o r i t y of i n f a n t feeding p r e p a rations used in t h e U n i t e d K i n g d o m h a v e a b o u t twice t h e sodium c o n c e n t r a t i o n of h u m a n m i l k ~ a n d this c o n c e n t r a t i o n m a y be increased still f u r t h e r if the feed is mixed incorrectly. ~" B u t a t ages 4 d a y s and 6 weeks t h e r e was no difference between the blood pressures of bottle-fed a n d breast-fed babiesP 3 Secondly, blood pressure was n o t r e l a t e d to t h e sodium c o n t e n t of feeds in m e a s u r e m e n t s t a k e n at age 6 weeks in a group of babies who were being b o t t l e fed aloneP 3 T h i s relationship will be reexamined as the children b e c o m e older. At present, we believe t h a t we can identify a p o p u l a t i o n of i n f a n t s w i t h a risk of developing h y p e r t e n s i o n b u t because correlations are weak, t h o u g h highly significant, we c a n n o t identify individual babies a t risk. R e p e a t e d m e a s u r e m e n t s m a y reduce the v a r i a b i l i t y as m a y m e a s u r e m e n t s u n d e r m o r e s t a n d a r d conditions such as exercise. I f this occurs we will t h e n be obliged to consider w h e t h e r we should i n t e r v e n e in the progress of these i n f a n t s t o w a r d s h y p e r t e n s i o n and, if so, how. REFERENCES
1. Kannel, W. B., and Dawber, T. R.: Hypertension as an ingredient of a cardiovascular risk profile, Br. J. Hosp. Med. 11:508, 1974. 2. Miall, W. E., and Oldham, P. 0.: A study of arterial blood pressure and its inheritance in a sample of the general population, Clin. Sci. 14:459, 1955. 3. Graham, A. W., Hines, E. A., and Gage, R. P.: Blood pressures in children between the ages of five and sixteen years, Am. J. Dis. Child. 69:203, 1945. 4. Johnson, T: O.: Arterial blood pressures and hypertension in an urban African population sample, Br. J. Prev. Soc. Med. 25:26, 1971. 5. Voors,A. W., Theda, A. F., Frerichs, R. R., Webber, L. S., and Berenson, G. S.: Studies of blood pressure in children ages 5-14 years in a total biracial community, Circulation 54:319, 1976. 6. Elseed, A: M., Shinebourne, E. A, and Joseph, M. C.: Assessment of techniques for measurement of blood pressure in infants and children, Arch. Dis. Child. 48:932, 1973.
October, 1977, VoL 94, No. 4
Blood pressure in infancy 7. Whyte, R. K., Elseed, A. M., Fraser, C. B., Shinebourne, E. A., and de Swiet, M.: Assessment of Doppler ultrasound to measure systolic blood pressures in infants and young children, Arch. Dis, Child. 50:542, 1975. 8. Rolfe, P.: Monitoring equipment for the neonate, Br. J. Clin. Equipment 1:189, 1976. 9. Kannel, W. B., Gordon, T., and Scwartz, M. J.: Systolic versus diastolic blood pressure and risk of coronary heart disease. The Framingham Study, Am. J. Cardiol. 27:335, 1971. 10. de Swiet, M., Fancourt, R., and Peto, J.~ Systolic blood pressure variation during the first 6 days of life, Clin. Sci. Molec. Med. g9:557, 1975. 11. Lee, Y., Rosner, B., Gould, J, B., and Kass, E. H.: Familial aggregation of blood pressures of newborn infants and their mothers, Pediatrics 58:722, 1976. 12. de Swiet, M., Fayers, P., and Shinebourne, E. A.: Blood pressure survey in a population of newborn infants, Br. Med. J. 2:9, 1976. 13. Zinner, S. H., Martin, L. F., Sacks, F., Rosner, B., and Kass, E. H.: A longitudinal study of blood pressure in childhood, Am. J. Epidemiol. 100:437, 1974. 14. Zinner, S. H., Levy, P. S., and Kass, E. H.: Familial aggregation of blood pressure in childhood, N. Engl. J. Med. 284:401, 1971. 15. Hennekens, C. H., Jesse, M. J., Klein, B. E., Gourley, J. E., and Blumenthal, S.: Aggregation of blood pressure in infants and their siblings, Am. J. Epidemiol. 103:457, 1976.
American Heart Journal
16. MacGillivray, I., Rose, C. A., and Rowe, B.: Blood pressure survey in pregnancy, Clin. Sci. 37:395, 1969. 17. Dahl, L. K., Heine, M., and Tassinari, L.: Role of genetic factors in susceptibility to experimental hypertension due to chronic excess salt ingestion, Nature 194:480, 1962: 18. Dahl, L. K., Heine, M., and Tassinari, L.: Effects of chronic salt ingestion: Further demonstration that genetic factors influence the development of hypertension: Evidence from experimental hypertension due to cortisone and to adrenal regeneration, J. Exp. Med. 122:533, 1965. 19. Prior, I. A. M., Grimley Evans, J., Harvey, H. P. B , Davidson, F., and Lindsey, M.: Sodium intake and blood pressure in two Polynesian populations, N. Engl. J. Med. 279:515, 1968, 20. Miall, W. E.: Follow-up study of arterial pressure in the population of a Welsh mining valley', Br. Med. J. 2:1204, 1959. 21. Department of Health and Social Security: Present-day practice in infant feeding, London, 1974, Her Majesty's Stationery Office. 22. Oates, R. K.: Infant feeding practices, Br. Med. J. 2:762, 1973. 23. de Swiet, M., Cooper, L. V., and Fayers, P.i Unpublished observations.
401