Casual blood pressure and ambulatory blood pressure measurement in children

ABSTRACT Some epidemiological studies on blood pressure among children and adolescents have revealed that blood pressure levels in childhood are the strongest predictors of adult blood pressure levels. In the adult population, hypertension causes a two to threefold increase in an individual's risk of cardiovascular morbidity. Cardiovascular risk depends on blood pressure itself, coexistent risk factors and whether there is hypertensive end-organ damage. Therefore, accuracy in determining blood pressure is essential and a standardized protocol should be considered for blood pressure measurement, which would make the comparison of results obtained by different studies in different countries possible. This article reviews the main determinants of accuracy for casual and ambulatory blood pressure measurements in children.

peated within a visit and between visits in order to determine a child's blood pressure.The work by Gillman and Cook (1993)  6 demonstrated that it depends on the instrument and technique.For auscultatory equipment, using a mercury manometer or random zero manometer, among 162 children aged 8 to 12 years, the systolic blood pressure values obtained after four weekly visits with three measurements per visit leveled off after about 2-3 measurements per visit, but the difference between visits was large until about the third or fourth visit.For oscillometric equipment, using the Dinamap model 845XT, among 106 children aged 9 to 13 years, the systolic blood pressure values obtained after three weekly visits with four measurements per visit demonstrated that for the Dinamap device the first of several measurements during one particular visit was generally higher than the following ones.The values obtained started to level off after 4-5 measurements within a visit, with the "first measurement effect" reproducible even after 3 consecutive visits.

The diastolic dilemma
There has been an ongoing controversy over whether the muffling (Korotkoff 4-K4) or disappearance of sounds (Korotkoff 5-K5) should be preferentially considered for the measurement of diastolic blood pressure in children. 11Neither value correctly defines intra-arterial diastolic blood pressure, since K5 is approximately 9 mmHg higher than direct diastolic blood pressure and K5 is easier for the human ear to discern than K4 12 .Current recommendations therefore favor the use of K5.

The stethoscope diaphragm versus the bell
The bell is preferred for blood pressure auscultation in adults.This issue is still controversial in children, since placing the bell adequately in small children may compress the artery and produce falsely low diastolic values.Thus, some authors advocate the use of the diaphragm for small children, 13 while others suggest that the bell, when properly used, should accomplish better auscultatory results. 11

Time of the day and ambient temperature
It is clear from ambulatory blood pressure studies that blood pressure varies over the 24 hours of the day, presenting lower values during sleep and higher values during wakefulness, with a peak in the morning and another in late afternoon. 14There is a negative relationship between blood pressure and temperature.An increase of 10°C leads to a fall of approximately 5-7 mmHg in systolic and in diastolic blood pressure. 15,16

Do we have normative blood pressure data for children?
Unfortunately we don't have normative blood pressure data for the pediatric population.Table 1 shows the lack of homogeneous methodology in nine studies that made up the Second Task Force of Blood Pressure Measurement in Children, reviewed by Rosner et al. in 1993. 17,18The Update of the Second Task Force of Blood Pressure Measurement in Children added a tenth study to this list (National Health and Nutrition Examination Survey  NHANES III). 19Table 2 shows the same lack of methodological homogeneity in the six studies from which the European pediatric blood pressure normative data is at present derived. 20t is important to emphasize that this lack of homogeneity is not a consequence of carelessness but rather of the multiple difficulties involved in performing epidemiological studies in the pediatric age group.Unfortunately, according to Nielsen et al. (1989)  21 , "confusion concerning the most suitable cuff… is responsible for at least some of the scatter between blood pressure studies".Arafat and Mattoo (1999), 10 referring to the Update of the Second Task Force of Blood Pressure Measurement in Children, suggested that "a new multicenter study, using uniform criteria for cuff selection, may be necessary to establish the accuracy of the published nomogram on normal blood pressure in children".

What blood pressure measuring device should be used in the future?
The mercury manometer is our old friend.It is simple, accurate and easy to service.Standard Hg readings are the main basis for blood pressure-disease associations and, although  blood pressure readings with this instrument are subject to terminal digit preference and observer bias, observer training could possibly eliminate this problem.Unfortunately, mercury has toxic effects on the environment and the mercury manometer will have to be gradually replaced.
The aneroid sphygmomanometer registers blood pressure through a mechanically intricate system.Its accuracy is affected by everyday use.When calibrated against a mercury manometer a mean difference of 3 mmHg is acceptable, although up to 30% have errors of more than 7 mmHg.Readings are also subject to terminal digit preference and observer bias 22 .
What about automated sphygmomanometry?The most widely used oscillometric devices are manufactured under the name "Dinamap".Several models have been developed, each with an updated algorithm.Validation data has to be obtained separately each model.Systolic and diastolic blood pressures are calculated as a function of the mean arterial pressure, which is the point of maximal oscillation and are calibrated to be equivalent to intra-aortic pressures.The devices are easy to use and strongly correlated to intraarterial readings.Accuracy is affected by arm movement and measurements are affected by the "first-reading effect". 23utomated oscillometric devices have to be validated before they can be recommended for clinical use.Validation protocols based on comparative measurements between oscillometric equipment and the mercury manometer were devised by the British Hypertension Society and the American Association of Medical Instruments. 24The two protocols have now been reconciled and are used in association to validate oscillometric devices.Table 3 presents the instruments currently validated and recommended for hospital use and self-measurement (home blood pressure). 25,26s it possible to use auscultatory and oscillometric devices interchangeably?Unfortunately not, as Korotkoff is approximately 3 mmHg lower than direct systolic blood pressure and, as we mentioned earlier, K5 is approximately 9 mmHg higher than direct diastolic blood pressure 12 .Park et al. ( 2001) 27 tested the Dinamap 8100 against the standard mercury manometer and found that the equipment detected mean systolic and diastolic blood pressure values significantly above auscultatory readings.On the other hand, Barker et al. (2000) 28 tested the Omron M1 against the standard mercury manometer and concluded that the Omron M1 overestimates higher pressures and underestimates lower pressures.There is a lack of validated and approved automated devices for use in clinical and epidemiological setting for the pediatric age group. 29

Ambulatory blood pressure monitoring in children
The current general indications for ambulatory blood pressure monitoring are: identification of white coat hypertension, borderline hypertension, identification of nocturnal hypertension, drug resistant hypertension, indication of antihypertensive medication, hypertension of pregnancy and identification of hypotension. 30Among the current issues for ambulatory blood pressure monitoring use in pediatrics, the main problem is the lack of definite normative data.The methodology is promising, since recordings show good accuracy and reproducibility in children. 31Up-to-date definitions of sleep/wake periods, using actigraphy or a detailed diary of daily activities, are necessary for accurately determining the sleep blood pressure decline. 32The white coat effect (white coat hypertension or white coat normotension) known within the literature relating to adults has also been confirmed in the pediatric population.In the same way as for adults, the left ventricular mass index and left ventricular hypertrophy are more closely related in children to 24-hour systolic blood pressure than with casual systolic blood pressure. 33According to Kapuku et al. (1999), 34   hypertrophy can be predicted by initial ambulatory systolic parameters.
In a recent study, 35 our group compared casual blood pressure and ambulatory blood pressure monitoring parameters among normotensive and hypertensive adolescents.Casual blood pressure was measured by two trained observers in two different and separate environments (clinic and ambulatory blood pressure monitoring unit).For systolic and diastolic blood pressure, in both normotensive and hypertensive populations, an alarm reaction was demonstrated during exposure to an unknown environment and observer (the ambulatory blood pressure monitoring unit).It should also be noted that, contrary to findings in adult populations, the mean casual systolic/ diastolic blood pressure measured in the clinic was lower than the mean ambulatory blood pressure monitoring parameters while awake, for normotensive and hypertensive adolescents.The same study compared findings from casual auscultatory measurements (in the clinic and ambulatory blood pressure monitoring unit) and ambulatory blood pres-sure monitoring parameters among hypertensive adolescents.The parameters included systolic and diastolic ambulatory blood pressure monitoring methods, systolic and diastolic blood pressure descent during sleep (systolic/diastolic sleep blood pressure descent), systolic and diastolic blood pressure load.This led us to conclude that, although normality parameters are still under development for ambulatory blood pressure monitoring in the pediatric age range, ambulatory blood pressure monitoring is a promising tool for the follow-up of pediatric hypertensive patients.In this respect it seems superior to casual blood pressure evaluation, since it uncovers the white coat effect.
Ambulatory blood pressure monitoring device validation data for children is scarce.The Spacelabs 90207, widely used in pediatric studies, and the TM 2421, used in a recent large pediatric study 36 are equipment that has not scored well enough to be recommended according to the protocols of the British Hypertension Society and the American Association of Medical Instruments.At present, the only device recommended for children, ac-cording to these protocols, is the QuietTrak 37 Amazingly, this is a piece of auscultatory equipment, a type of device generally not adopted in pediatric studies because the noise of children in movement interferes with the accuracy of the microphone determination of the measured blood pressure value.Table 4 shows a list of some large pediatric ambulatory blood pressure monitoring studies 36,[38][39][40][41][42] and demonstrates that, as for casual blood pressure, studies are being performed without methodological homogeneity.Different devices, with different measurement protocols, cannot be considered together to generate norms.
In conclusion, as of today, the main problem for the diagnosis and management of hypertension in children is the lack of good normative data for casual and ambulatory blood pressure values.The only solution for this issue is to propose a multicenter study with a homogenous protocol, in order to obtain normal multiethnic casual and ambulatory pediatric blood pressure values.Only then will studies to correlate blood pressure level and hypertensive end-organ damage be possible.Estudos epidemiológicos envolvendo medida de pressão arterial em crianças e adolestêm demonstrado que o valor da medida de pressão arterial na infância constituise no maior preditor dos níveis pressóricos do adulto.A hipertensão arterial no adulto eleva em duas a três vezes o risco individual de desenvolvimento de morbidade cardiovascular.O risco cardiovascular depende da pressão arterial propriamente dita, de fatores coexistentes e da presença de lesão instalada de órgãos-alvo.A acurácia na de-

left ventricular Table 3 .
Automated oscillometric blood pressure measuring devices recommended for hospital use and self measurement (upper arm)23 for the Advancement of Medical Instruments; BHS: British Hypertension Society: A and B represent grading criteria for evaluating the devices proposed by the BHS for systolic/diastolic pressure.Criteria for fulfilling protocol are that the mean difference between the standard sphygmomanometer and the device being validated should be within < 5 mmHg (SD < 8 mmHg).Grades represent the cumulative percentage of readings in agreement with 5 mm Hg, 10 mm Hg, and 15 mm Hg of the mercury standard.Grade A denotes greatest agreement with mercury standard and D denotes least agreement.A=best agreement (recommended for clinical use); B=good agreement (recommended); C=poor agreement (not recommended); D=worst agreement (not recommended).25

Table 1 . Methodology parameters of the nine studies that made up the Second Task Force of Blood Pressure Measurement in Children 17,18 Source Age (years) Instrument Cuff width Cuff length Number of observers Place of measurement
NIH: National Institutes of Health; AC: arm circumference.