Original article

Differences Between the Fourth and Fifth Korotkoff Phases Among Children and Adolescents

David S. Freedman,1 Jennifer L. Foltz,1 and Gerald S. Berenson2

background

The relative importance of the fourth (K4) and fifth (K5) Korotkoff phases as the indicator of diastolic blood pressure (DBP) levels among children remains uncertain.

methods

In a sample of 11,525 youth aged 517, we examined interexaminer dif-ferences in these 2 phases and the relation of theses 2 phases to adult blood pressure levels and hypertension. The longitudinal analyses were conducted among 2,156 children who were re-examined after age 25 years.

results

Mean (SD) levels of DBP were 62 (9) mm Hg (K4) and 49 (13) mm Hg (K5). K4 showed less interobserver variability than did K5, and 7% of the children had at least 1 (of 6) K5 value of 0 mm Hg. Longitudinal analyses indicated that K4 was more strongly associated with adult blood pressure levels and hypertension. In correlational analyses of

subjects who were not using antihypertensive medications in adult-hood (n = 1,848), K4 was more strongly associated with the adult DBP level than was K5 (r = 0.22 vs. 0.17; P < 0.01). Analyses of adult hypertension (based on high blood pressure levels or use of antihy-pertensive medications) indicated that the screening performance of childhood levels of K4 was similar to that of systolic blood pressure and was higher than that of K5, with areas under the receiver operator characteristic curves of 0.63 (systolic blood pressure), 0.63 (K4), and 0.57 (K5).

conclusions

As compared with K5 levels among children, K4 shows less interobserver variability and is more strongly associated with adult hypertension.

Keywords: blood pressure; children; diastolic blood pressure; hyperten-sion; Korotkoff phases; longitudinal; systolic blood pressure.

doi:10.1093/ajh/hpu064

Although the onset of the fifth Korotkoff phase (K5, beginning of silence) is widely used among adults as the indicator of diastolic blood pressure (DBP), it is unclear whether K5 or the fourth Korotkoff phase (K4, muffling of sounds) should be used for children and adolescents. The most recent (2004) recommendation1 is to use K5 for all children and adolescents, but a 2008 meta-analysis found that adult DBP levels show a slightly stronger cor-relation with childhood levels of K4 than K5.2 Neither K4 nor K5 correlates strongly with the intra-arterial DBP of children.35

The recommendations for the assessment of DBP among children in the United States have changed considerably over time. In 1977, the National Heart, Lung, and Blood Institute Task Force Report on Blood Pressure Control in Children recommended that K4 be used for all children and adolescents,6 whereas the 1987 recommendation was to use K4 only for children aged 1 examination.To follow these children as they aged, adults were exam-ined in studies conducted from 1977 through 2010,11 and our longitudinal analyses are restricted to subjects who were re -examined after age 25 years. Of the 5,504 exami-nations conducted among these adults, we excluded 78 examinations with missing blood pressure data or among women who were pregnant. These exclusions resulted in a group of 2,156 adults aged 2551 years, and we used data from only their final examination. Of these adults, 401 were considered to have hypertension based on either reported use of antihypertensive medication, SBP 140 mm Hg, or DBP 90 mm Hg.

Examination methods

The standardized examination procedures used in the Bogalusa Heart Study have been described.10 Body mass index (BMI) was calculated as kilograms per meter squared, and obesity among those aged 517 years was defined as a BMI-for-age 95th percentile of the Centers for Disease Control and Prevention growth charts12 or a BMI 30 kg/m2. Adult obesity is based on a BMI 30 kg/m2.

Blood pressure observers, who were monitored through-out the examinations, recorded the onset of the first, fourth (muffling of sounds), and fifth (beginning of silence) Korotkoff phases. Observer training, including audiomet-ric tests and the use of double stethoscopes with 2 mercury columns, was emphasized throughout the study period.13,14 Attempts were made to minimize the influence of the emo-tional state of the child.15 Cuff sizes were selected according to a protocol based on the circumference and length of the upper arm, using a bladder width as large as possible while leaving room for the stethoscope at the elbow skin crease.15,16

Right arm sitting levels of SBP, K4, and K5 were each measured 3 times by 2 observers using a mercury sphyg-momanometer.10,13 As has been done in previous analyses of data from the Bogalusa Heart Study,10,13,15,17,18 we used the mean of the 6 recorded measurements for SBP, K4, and K5. There were 1,962 (7.4%) children who had at least 1 (of 6) K5 values recorded as 0 mm Hg, and most analyses treat these 0 values no differently than any other when calculating the

mean K5 value. Only 34 (0.1%) children had all 6 K5 meas-urements recorded as 0 mm Hg.

The longitudinal analyses, which contrasted the rela-tion of childhood levels of K4 and K5 to adult blood pres-sure levels and hypertension, also compare our method for calculating mean K5, which treated the 0 mm Hg values no differently than any other recorded value, with 3 other methods. In addition to using all recorded values of K5, we also calculated the mean K5 after (i) excluding the 0 mm Hg values, (ii) replacing the K5 value of 0 mm Hg with the corresponding K4 value, and (iii) replacing the K5 read-ings