Letter to the Editor
What's New in Childhood Hypertension?
DKK Ng, LCK Leung, KL Kwok
We are writing in response to the article "What's new in childhood hypertension?" by Dillon MJ.1 We read with interest that obstructive sleep apnoea syndrome (OSAS) was not mentioned as a cause of secondary hypertension. Obstructive sleep apnoea has been extensively studied in adults, and there is now strong epidemiological evidence that it is an independent risk factor for hypertension, including essential hypertension.2 Many cross-sectional and prospective population studies have demonstrated a modest but definite association between sleep disordered breathing and hypertension, independent of confounding factors.3-5 Nieto et al in a cross sectional sample of 6,132 subjects in the Sleep Heart Health Study found that the adjusted odds ratio for hypertension in patients with OSAS category was 1.37.4 The prospective longitudinal analysis from the Wisconsin Sleep Cohort followed up 709 participants over 4 years and found an adjusted odds ratio of 2.9 (CI 1.5-5.6) in new development of hypertension for an AHI of 15 versus an AHI of 0.5. In fact, Silverberg found so many similarities between OSAS and essential hypertension2 and the evidence that OSAS contributes to essential hypertension (at least in adults) so compelling, that he urges physicians not to neglect this important reversible factor in assessing any hypertensive patient.6
In children, the causal link admittedly is not so strong. Marcus found that those with OSAS had significantly higher diastolic BP during both wakefulness and sleep, compared with primary snoring subjects.7 Apnoea index, as well as BMI and age, were independent determinants of BP. Kohyama et al reported similar findings and the absence of nocturnal dip of blood pressure.8 We have also found in a study of 96 children investigated for sleep disordered breathing, that those with OSAS were associated with significantly higher nocturnal BP (unpublished data).9
It is also important to bear in mind that OSAS affected 0.7% of 4- to 5-year-old children.10 Based on a population survey of primary school children for observed apnoea during sleep, we estimated the prevalence of OSAS in this age group to be 1 to 2%.11
As the author noted, obesity is an important part of primary hypertension, and that obese children have approximately a 3-fold higher risk for hypertension. We are also surprised to notice that OSAS was not mentioned by Dillon to play a role in the so-called primary hypertension in obese children. A review by the authors showed that obese children were far more likely develop OSAS which is a risk factor for hypertension as mentioned before.12 The triad of obesity, OSAS and resulting hypertension pose a far greater cardiovascular risk than the sum of the individual effect of each disease.
In conclusion, we would urge paediatricians to ask for symptoms of OSAS in any children with hypertension. Three questions should be asked when one assess a child suspected of being hypertensive:
1. Do you snore often?
1. Dillon MJ. What's new in Childhood Hypertension? HKJ Paediatr (new series) 2004;9:3-8.
2. Silverberg DS, Oksenberg A, Iaina A. Sleep-related breathing disorders as a major cause of essential hypertension: fact or fiction? Curr Opin Nephrol Hypertens 1998;7:353-7.
3. Silverberg DS, Oksenberg A. Essential hypertension and abnormal upper airway resistance during sleep. Sleep 1997;20:794-806.
4. Nieto FJ, Young TB, Lind BK, et al. Association of sleep-disordered breathing, sleep apnea, and hypertension in a large community-based study. Sleep Heart Health Study. JAMA 2000;283:1829-36.
5. Peppard PE, Young T, Palta M, Skatrud J. Prospective study of the association between sleep-disordered breathing and hypertension. N Engl J Med 2000;342:1378-84.
6. Silverberg DS, Oksenberg A, Iaina A. Sleep related breathing disorders are common contributing factors to the production of essential hypertension but are neglected, underdiagnosed, and undertreated. Am J Hypertens 1997;10(12 Pt 1):1319-25.
7. Marcus CL, Greene MG, Carroll JL. Blood pressure in children with obstructive sleep apnea. Am J Respir Crit Care Med 1998;157(4 Pt 1):1098-103.
8. Kohyama J, Ohinata JS, Hasegawa T. Blood pressure in sleep disordered breathing. Arch Dis Child 2003;88:139-42.
9. Leung LC, Lau WF, Ng DK, et al. Ambulatory blood pressure measurement in children with obstructive sleep apnoea. Proceedings of the Joint Scientific Meeting, Hong Kong College of Physicians and Hong Kong College of Paediatricians 2002 Oct 26-27.
10. Ali NJ, Pitson DJ, Stradling JR. Snoring, sleep disturbance, and behaviour in 4-5 year olds. Arch Dis Child 1993;68:360-6.
11. Ng DK, Kwok KL, Chow PY, et al. Prevalence of sleep-related problems in primary school children. 40th Annual Scientific Meeting 2002.
12. Ng DK, Lam YY, Kwok KL, Chow PY. Obstructive sleep apnoea syndrome and obesity in children. Hong Kong Med J 2004;10:44-8.
Department of Paediatrics
Kwong Wah Hospital
I am grateful to Drs Ng, Leung and Kwok for pointing out the omission of obstructive sleep apnoea syndrome (OSAS) as a possible factor in the causality of childhood hypertension in my recent review article in the Journal.1 Its lack of inclusion was more to do with the need for a degree of selectivity, as reflected by exclusion of other aspects of childhood hypertension, than to do with a lack of awareness of its potential relevance.
I entirely concur with the views that they have expressed both in terms of the role of OSAS in causing increased blood pressure in isolation and in the context of obesity. The latter association, as they pointed out, may carry a significant cardiovascular risk and be a greater problem in time due to the increasing incidence of childhood obesity worldwide.
The mechanisms involved in OSAS causing an increase in blood pressure remain unclear but sympathetic nervous system activation secondary to arousal is thought to play a part with perhaps hypoxaemia also having a contribution.2,3
I am sure that it is, as Drs Ng, Leung and Kwok suggested, important for paediatricians to enquire about symptoms suggestive of OSAS when evaluating children with hypertension and also in those with obesity.
1. Dillon MJ. What's new in childhood hypertension? HK J Paediatr (new series) 2004;9:3-8.
2. Ringler J, Basner RC, Shannon R, et al. Hypoxemia alone does not explain blood pressure elevations after obstructive apneas. J Appl Physiol 1990;69:2143-8.
3. Marcus CL, Greene MG, Carroll JL. Blood pressure in children with obstructive sleep apnea. Am J Respir Crit Care Med 1998;157(4 Pt 1):1098-103.
Emeritus Professor of Paediatric Nephrology
Institute of Child Health
30 Guilford Street
London WC1N 3J
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