Snoring, Snorting, and Blood Pressure — What’s the Story?
Snoring, Snorting, and Blood Pressure—What’s the Story?
abstract & commentary
Synopsis: This study found a "dose-response" curve between measures of sleep disordered breathing and degree of hypertension.
Source: Nieto FJ, et al. JAMA 2000;283:1829-1836.
The sleep heart health study (shhs) is a multicenter study of the consequences of obstructive sleep apnea. It is an ongoing prospective cohort study of subjects who are already participating in ongoing studies of cardiovascular or respiratory disease. The objectives of this report were to investigate the relationship of sleep-disordered breathing (SDB) and hypertension in a large population, controlling for confounding variables—particularly obesity. The study population included more than 6000 individuals aged 40 years or older. Nieto and colleagues used well-defined and reproducible criteria for SDB and sleep data, and collected data on relevant behavior and physical findings by questionnaire and physical examination. This study found that mean systolic and diastolic blood pressure and the prevalence of hypertension increased significantly with increasing SDB indices. After controlling for body mass index (BMI), neck circumference, alcohol use, and cigarette smoking, the odds ratio (OR) for hypertension was significantly increased for those with an Apnea/Hypopnea Index (AHI) of 30 or more events per hour of sleep and for those with oxygen desaturation of 12% or greater.
Comment by Barbara a. phillips, md, msph
This study is important because it controlled for the significant confounders that have undermined confidence in previous studies showing an association between SDB and hypertension. Previous work showing an association between SDB and hypertension has been criticized because obesity is a common predisposing factor for both conditions and has been difficult to control for. This study found a "dose-response" curve between measures of SDB and degree of hypertension. Another strength of this study is that the measures and definitions of apnea and hypopnea used in the SHHS are clearly spelled out and are rapidly becoming the consensus.
The report of Nieto et al confirmed and strengthened findings from two other large cohort studies. Grote and colleagues showed an independent linear association between Respiratory Disturbance Index ([RDI], a term essentially synonymous with AHI), blood pressure, and heart rate.1 The OR in this study was 4.15 for those with an RDI of more than 40 compared with those with an RDI of more than 5. Grote et al also controlled form BMI, age, alcohol and nicotine use, cholesterol level, and daytime arterial blood gases.
Lavie and associates also found a dose-response relationship between levels of SDB and hypertension, again controlling for important confounders.2
These reports really don’t surprise those of us who take care of sleep apnea patients, but they are vindicating. We have come a long way from the scathing analysis of the data on the "Health effects of obstructive sleep apnoea (sic) and the effectiveness of continuous positive airways pressure: A systematic review of the research evidence," in which Wright and colleagues concluded that, "The relevance of sleep apnoea to public health has been exaggerated."3
What remains to be done now is to show that treatment of sleep apnea improves blood pressure, and to try to elucidate the mechanisms by which SDB affects blood pressure. Work is already underway in these areas. Dimsdale et al compared titrated Continuous Positive Airway Pressure (CPAP) with placebo (about 2 cm H20) CPAP in 39 sleep apnea patients.4 Daytime blood pressure decreased significantly in both CPAP and placebo groups, but the mean nighttime blood pressure drop increased significantly more in the therapeutic CPAP group. Another study showed that three days of CPAP therapy converted 15 of 22 sleep apneic patients who had lost their early morning blood pressure dip (10 mm Hg systolic and 5 mm Hg diastolic) to dippers.5
Should these findings change your practice? Both sleep apnea and hypertension are common conditions, and not every hypertensive patient needs a sleep study. I think it is reasonable to screen for sleep apnea in patients who have hypertension, particularly difficult to control hypertension. A history of witnessed apneas or sleepiness that interferes with daily function ought to raise a red flag, as should the physical findings of a BMI greater than 30 or neck circumference greater than 17 inches in a man or 16 inches in a woman.6
References
1. Grote L, et al. Am J Respir Crit Care Med 1999;160: 1875-1882.
2. Lavie P, et al. BMJ 2000;320:479-482.
3. Wright J, et al. BMJ 1997;314:851-859.
4. Dimsdale JE, et al. Hypertension 2000;35:144-147.
5. Akashiba T, et al. Sleep 1999;22:849-853.
6. Kripke DF, et al. Sleep 1997;20:65-76.
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