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Free AccessPolysomnography

Normative Heart Rate Parameters During Sleep for Children Aged 6 to 11 Years

Published Online:https://doi.org/10.5664/jcsm.27709Cited by:11

ABSTRACT

Objective:

Normative values for pediatric heart rates during sleep are not known. The purpose of this study was to describe the average sleeping heart rate of children and to determine if age, sex, body mass index (BMI) or ethnicity is related to sleeping heart rate.

Methods:

Electrocardiogram (ECG) data were obtained from healthy children during in-home polysomnography in the Tucson Children's Assessment of Sleep Apnea study (TuCASA) or home cardiorespiratory sleep studies in the Cleveland Children's Sleep and Health Study (CCSHS). Data were described then compared in separate cohort analyses using least square means from analysis of variance models that controlled for age, sex, ethnicity, and BMI. Student t tests were used to compare groups within cohorts for significant differences.

Results:

In the cohort of 470 TuCASA children, 50.3% were female, 41% were Hispanic; mean age (SD) was 8.7 (1.7) years. Hispanics and Caucasians did not differ significantly on mean sleeping heart rate. The CCSHS cohort consisted of 561 children; 50.2% female and 33% African American, aged 8.9 (0.6) years. African Americans had significantly faster sleeping heart rates than Caucasians in the CCSHS cohort. In both cohorts, younger children demonstrated significantly faster sleeping heart rates than older children; girls had significantly faster sleeping heart rates than boys (TuCASA: girls 77.6 [9.9] vs boys 73.6 [8.2]; CCHS: girls 81.5 [8.4] vs boys 78.4 [8.1]) and obese children (BMI ≥ 95th percentile for age) had significantly faster sleeping heart rates than nonobese children (TuCASA: obese children: 79.3 [12.3] vs nonobese children 75.0 [8.7]; CCHS: obese children: 83.3 [8.4] vs nonobese children 79.4 [8.3]).

Conclusions:

Children aged 6 to 11 years have sleeping heart rates that decrease significantly with age. African American ethnicity, female sex, and obesity were associated with faster sleeping heart rates.

Citation:

Archbold KH; Johnson NL; Goodwin JL; Rosen CL; Quan SF. Normative heart rate parameters during sleep for children aged 6 to 11 years. J Clin Sleep Med 2010;6(1):47-50.

INTRODUCTION

Sleep disorders are being evaluated with overnight polysomnographic studies at an increasingly frequent rate in children. Normative values for polysomnographic variables such as sleep architecture patterns and sleep disordered breathing are currently being developed and proposed for use in the pediatric population. 1 Data currently exist for normative pediatric heart rates during wakefulness, 2 but normative data for heart rate during sleep in children are limited. 3 The purpose of this report is to provide a description of heart rates during sleep for 2 geographically separate cohorts of children between the ages of 6 and 11 years that include 3 diverse ethnic groups and to determine whether age, sex, ethnicity, or obesity are factors with a significant influence on childhood heart rates during sleep.

METHODS

Tucson Cohort

Electrocardiogram (ECG) heart rate data were obtained from the Tucson Children's Assessment of Sleep Apnea study (TuCASA), comprised of 503 children who underwent in-home full polysomnography that included a bipolar ECG recording. 4 , 5 The 2 ethnic groups represented in TuCASA are children of Hispanic (41%) and Caucasian (59%) descent. Polysomnography data were available from 470 children aged 6 to 11.9 years who were without major medical comorbidities and who had respiratory disturbance indices (RDI) of fewer than 5 events per hour of sleep. Sleep was staged for each polysomnography record according to standard criteria, and total sleep time was defined as the total amount of time scored as sleep. 6 The heart rate was computed using a sample rate of 64 cycles per second, with the average calculated for each second. An average sleeping heart rate was derived over all time scored as sleep. Bedtime and wake-time data were collected from parent report of the time the child actually went to bed the night of the in-home polysomnogram (Bedtime), and the time the following morning the child woke up (Wake time).

Brief Summary

Current Knowledge/Study Rationale: Little information is available for the sleep researcher and practioner regarding normative values for heart rate during sleep in school-aged children. We conducted this study to determine what the normative sleeping heart rate values are, and if they differed among girls, boys and children of different ethnicities.

Study Impact: The data from this study will provide a high-impact set of normative sleeping heart-rate values for clinicians and researchers alike. The sex and ethnic differences found here in sleeping heart rate contribute to the growing body of evidence that these variables should be accounted for in pediatric sleep medicine and research.

Cleveland Cohort

Participants were enrolled in the Cleveland Children's Sleep and Health Study (CCSHS), a cohort that has been previously described. 7 Represented in the CCSHS are children of African American (n = 187) and Caucasian (n = 374) descent. The CCSHS cohort is unique in that it is a stratified random sample of full-term and preterm children who were born between 1988 and 1993, where preterm was defined as less than 36 weeks' gestational age at birth. Heart rate data were collected during unattended in-home limited-channel cardiorespiratory recordings that included ECG monitoring of heart rate using a bipolar ECG lead. Sleep was scored when physiologic parameters such as very little movement and decrease in heart rate corresponded to sleep-wake times recorded in a sleep diary. Scoring software generated the average heart rate during sleep. 8 Bedtime and wake-time data were collected from parent report of the time the child actually went to bed the night of the in-home cardiorespiratory study (Bedtime) and the time the following morning the child woke up (Wake time).

Data Analysis

Data for both cohorts were summarized and compared with least square means from analysis of variance models using SPSS v. 16.0 (SPSS, Inc., Chicago, IL). Independent variables were age, sex, ethnicity and body mass index (BMI) percentile. BMI percentile was calculated based on formulas from the Center for Chronic Disease Prevention and Health Promotion website, 9 and children with BMI percentiles at or greater than 95% were considered obese. Within each cohort, independent sample t tests were used to determine significant differences in age, BMI percentiles, and sleeping heart rates between the ethnic groups.

RESULTS

Tucson Cohort

The Tucson cohort consisted of 470 children (female = 237), of whom 195 (40.4%) classified themselves as Hispanic/Non-Caucasian. The average age of the group was 8.9 (0.9) years. Average sleeping heart rate was 75.6 (9.3) beats per minute (95% confidence interval 74.8, 76.5) and average BMI percentile was 58.6 (31.5) for the sample as a whole. Average Bedtime was reported as 21:33 and ranged from 19:00 to 24:00. Wake time for the sample was 06:50 on average, with a range of 02:10-11:00.

Results of least square means analysis of variance indicated that there were no significant differences in sleeping heart rate between Caucasian or Hispanic children ( Table 1a ), so data were subsequently combined and analyzed together. Girls had significantly faster sleeping heart rates than boys ( F = 23.3, p = < 0.001) at all ages ( Table 2a ), and younger children had significantly faster sleeping heart rates than older children ( F = 5.99, p < 0.001) ( Table 3a ). BMI percentile was also a significant factor in the analysis. On average, obese children had faster sleeping heart rates than nonobese children (79.3 [12.3] vs 75.0 [8.7], F = 11.8, p = 0.001), after controlling for sex and ethnicity.

Table 1 Cohorts' characteristics and sleeping heart rate by ethnicity

a. Tucson Cohort: N = 470Entire Samplea (n = 470)Caucasian (n=275)Hispanic (n=195)p Valueb
Age8.9 (0.9)8.6 (1.6)8.7 (1.5)NS
BMI percentile58.6 (31.5)54.6 (31.5)64.4 (30.8)0.001
Sleeping HR75.6 (9.3) [74.8, 76.5] 90.175.4 (8.4) [74.4, 76.4] 89.875.9 (10.5) [74.4, 77.4] 91.9NS
b. Cleveland Cohort: N = 561Entire Samplea (n = 561)Caucasian (n = 374)African American(n = 187)p Valueb
Age8.9 (0.6)8.9 (0.8)9.0 (0.9)NS
BMI percentile57.7 (30.6)55.7 (31.1)60.9 (29.6)NS
Sleeping HR79.9 (8.4) [79.3, 80.7] 95.078.3 (7.9) [77.6, 79.2] 89.383.2 (8.5) [81.9, 84.4] 98.0< 0.001

aResults are shown as mean (standard deviation). Sleeping heart rate (HR) is displayed as mean (standard deviation), [95% confidence interval of mean], and 95th percentile. BMI refers to body mass index.

bp values from t test Caucasian vs Hispanic.

Table 2 Cohorts' characteristics and sleeping heart rates by sex

a. Tucson CohortEntire Samplea (n = 470)Male (n = 233)Female (n = 237)p Valueb
Age8.9 (0.9)8.6 (1.6)8.7 (1.5)NS
BMI percentile58.6 (31.5)54.6 (31.5)64.4 (30.8)NS
Sleeping HR75.6 (9.3) [74.8, 76.5] 90.173.6 (8.2) [72.5, 74.6] 88.477.6 (9.9) [76.4, 78.9] 91.6< 0.001
b. Cleveland CohortEntire Samplea (n = 561)Male (n = 279)Female (n = 282)p Valueb
Age8.9 (0.6)9.0 (0.9)8.9 (0.8)NS
BMI percentile57.7 (30.6)59.1 (29.6)55.8 (31.6)NS
Sleeping HR79.9 (8.4) [79.3, 80.7] 95.078.4 (8.1) [77.5, 79.4] 94.081.5 (8.4) [80.6, 82.5] 98.0< 0.001

aResults are shown as mean (standard deviation). Sleeping heart rate (HR) is displayed as mean (standard deviation), [95% confidence interval of mean], and 95th percentile. BMI refers to body mass index.

bp values from t test male vs female.

Table 3 Cohorts' sleeping heart rate by age group and sex

a. Tucson CohortSleeping HR
Age GroupaTotalb (n = 470)Male (n = 233)Female (n = 237)
679.5 (7.6) [77.4, 81.5] 90.278.8 (6.8) [75.5, 82.0] 90.680.3 (8.4) [76.9, 83.7] 103.6
778.0 (8.5) [75.9, 80.1] 93.576.5 (8.8) [73.6, 79.5] 93.879.5 (8.0) [76.5, 82.5] 95.9
875.3 (8.3) [73.5, 76.9] 88.373.4 (7.6) [70.8, 76.0] 83.677.1 (8.6) [74.5, 79.7] 92.6
976.6 (10.8) [74.3, 78.9] 91.974.2 (8.2) [71.5, 76.9] 93.178.6 (12.4) [76.1, 81.1] 90.1
1072.8 (9.1) [70.9, 74.6] 89.970.4 (6.9) [68.1, 72.8] 85.176.0 (10.6) [73.3, 78.7] 94.1
1173.3 (9.3) [71.1, 75.5] 88.670.0 (8.5) [66.7, 73.4] 89.375.5 (9.2) [72.7, 78.2] 88.5
b. Cleveland CohortSleeping HR
Age GroupaAllc (n = 561)Male (n = 279)Female (n = 282)
881.4 (7.8) [80.2, 82.5] 98.080.1 (7.1) [78.5, 81.6] 94.082.5 (8.2) [80.9, 84.1] 98.0
979.6 (8.7) [78.5, 80.7] 98.078.2 (8.3) [76.7, 79.7] 94.081.3 (8.9) [79.6, 82.9] 98.0
1078.5 (8.4) [76.9, 80.0] 94.076.4 (8.8) [74.1, 78.8] 89.580.5 (7.8) [78.4, 82.5] 94.0
1179.9 (7.9) [76.7, 82.9] 101.078.8 (6.7) [75.1, 82.5] 89.081.7 (9.6) [75.3, 88.2] 102.0

aResults are shown as mean (standard deviation). Sleeping heart rate (HR) is displayed as mean (standard deviation), [95% confidence interval of mean], and 95th percentile.

bp values from least squares analysis ( F = 5.99, p = < 0.001)

cp values from least squares analysis ( F = 3.05. p = 0.028)

Cleveland Cohort

The Cleveland cohort consisted of 561 children between the ages of 8 and 11, with a mean age of 8.9 (0.6) years, 33% (n = 187) of whom were African American. The average sleeping heart rate for the entire cohort was 79.9 (8.4) beats per minute (95% confidence interval 79.3, 80.7), and the average BMI percentile was 57.7 (30.6). Average Bedtime was reported as 22:03 and ranged from 18:50 to 02:22. Wake time for the sample was 07:23 on average, with a range of 03:30 to 10:45.

Significant differences were found between African American children and Caucasian children, with African American children having significantly faster sleeping h than the Caucasian children ( Table 1b ). In addition, girls were found to have significantly faster sleeping heart rates than boys ( Table 2b ), and heart rate decreased significantly with increasing age ( F = 3.05, p = 0.028) ( Table 3b ). Former preterm status or gestational age was not associated with sleeping heart rate (data not shown). Obese children had faster sleeping heart rates than nonobese children after controlling for age, sex, and ethnicity (83.3 [8.4] vs 79.4 [8.3], F = 14.8, p < 0.001).

DISCUSSION

Pediatric data to describe heart rate during sleep were reported in this study. Younger age, female sex, African American ethnicity, and obesity were each found to be associated with faster sleeping heart rates among children aged 6 to 11 years.

The youngest children in both cohorts had the fastest sleeping heart rates. This finding is consistent with previously published pediatric resting heart rate values during wakefulness. 1013 However, similar to adults, heart rates in children in our study were substantially slower during sleep than as reported during wakefulness.

In both cohorts, girls had significantly faster sleeping heart rates than boys that, on average, were approximately 3.5 beats per minute faster than the boys' heart rates. Previous studies of waking heart rate in children and as well as during 24-hour Holter monitoring have also found that girls have slightly faster heart rates than do boys. 10 , 11 This difference appears to persist into adulthood and may reflect hormonally related differences in autonomic function. 11

In the current analysis, African American children had faster sleeping heart rates than Caucasian children. In contrast, waking heart rates in African American children have been reported as significantly slower than Caucasian children. 12 The reason for this difference between waking and sleeping heart rates is unclear, but perhaps there is greater parasympathetic activity in Caucasians during sleep. In support of this finding, African American children have been reported to have higher daytime blood pressure levels than Caucasian children, and African American girls were the children with the highest childhood blood-pressure levels. 14 In contrast, we found no differences in sleeping heart rates between Hispanic and Caucasian children. Limited data are available to suggest that, during wakefulness, Hispanic boys have slower heart rates than their Caucasian peers. 13 Again, the explanation for this finding is unclear. Genetics and environmental factors are likely to contribute to the patterns of sleeping heart rate we report here. Further understanding of the genetic and environmental components of sleeping heart rate is warranted to determine the effects, if any, sleeping heart rate may have on health status during childhood development.

Children with a BMI percentile-for-age of greater than or equal to the 95th percentile had significantly faster heart rates during sleep than nonobese children. Published reports indicate that the daytime resting heart rate of overweight children is also significantly faster than nonoverweight children. 15 , 16 A recent paper by Lurbe and colleagues reported the findings of a 24-hour monitor study of heart rate in obese and nonobese children. Ambulatory sleeping heart rates were significantly and positively associated with BMI, whereby BMI was found to predict 23% of the variance in sleeping heart rate. 17 A potential explanation for the increase in sleeping heart rate seen in our obese sample (who did not have sleep disordered breathing) may be related to decreased rates of cardiac parasympathetic activity that have generally been reported in sedentary obese children. In a study by Gutin and colleagues, 18 obese children showed a significant inverse correlation between indices of adiposity and cardiac parasympathetic activity. 18

The primary limitation of this study is that the data were collected from 2 different sites that used 2 different collection methods. The TuCASA cohort had data collected with an in-home polysomnographic sleep study, 5 and sleep was staged according to established parameters. The Cleveland cohort's data were collected with a limited-channel unit that indirectly measured onset of sleep. In the Cleveland cohort, sleep was scored according to the start and stop time of the recording unit, in conjunction with patient-reported sleep diary data. 8 It is possible that the Cleveland cohort's data included some measurement of quiet wakefulness in addition to sleep, thereby inflating the value of the mean sleeping heart rate of the sample. It is for this reason that we elected not to combine the data from both cohorts for analyses. Nevertheless, our findings with respect to differences in heart rate from wake to sleep parallel those observed in adults. Moreover, our findings that sleeping heart rate decreases with an increase in age are consistent with the change in waking heart rates with age. Both these observations support the validity of our findings.

In conclusion, we have found that sleeping heart rates in preadolescent children are generally slower than during wakefulness and decrease with advancing age. Furthermore, faster sleeping heart rates are observed in girls, obese children, and those of African-American ancestry. These data should prove useful in interpreting polysomnography data in children.

DISCLOSURE STATEMENT

This was not an industry supported study. The authors have indicated no financial conflicts of interest.

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