Chest
Volume 101, Issue 2, February 1992, Pages 379-384
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Clinical Investigations
Evening-to-Morning Blood Pressure Variations in Snoring Patients with and without Obstructive Sleep Apnea

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This study was designed to test a hypothesis that patients with sleep apnea have higher blood pressure in the morning, following a night spent in apnea and hypoxemia, than in the evening. To accomplish this, we prospectively studied a set of 611 patients referred to our clinic because of suspicion of sleep apnea. All patients had full nocturnal polysomnography, including measurement of snoring. Blood pressure was measured in the evening, prior to onset of sleep, and in the morning, immediately on awakening. We found that patients without apnea and hypoxemia had lower blood pressure in the morning compared with the evening value, while patients with severe sleep apnea and hypoxemia had higher blood pressure in the morning; these evening-to-morning blood pressure differences, although statistically significant, were small, typically 1 to 4 mm Hg. Morning blood pressures were higher in patients with sleep apnea and hypoxemia than in nonapneic normoxic patients. However, this difference disappeared after the groups were matched for age and body mass index. We conclude that (1) patients with sleep apnea and nocturnal hypoxemia lose the expected morning dip in arterial blood pressure, and (2) age and body mass index are more important correlates of blood pressure than apnea and nocturnal oxygen desaturation. We speculate that the loss of evening-to-morning drop in blood pressure, if present over a long period of time, may lead to sustained elevations in arterial blood pressure frequently observed in patients with sleep apnea.

Section snippets

Patients

This report is a part of an ongoing prospective study dealing with various clinical aspects of sleep apnea syndrome. Up to October 1990, there were 1,201 patients entered into the computer data base at the sleep clinic at St. Michaels Hospital, Toronto. Six hundred eleven of them satisfied the following criteria: (1) all were referred because of suspected sleep apnea; (2) all presented with snoring as their main complaint; (3) none had a history of hypertension; (4) none was receiving

RESULTS

Table 1 shows the anthropometric characteristics and sleep, snoring, and blood pressure data for the entire set of 611 patients, which consisted of 444 male and 167 female subjects.

Univariate regression analysis revealed that morning and evening mean arterial blood pressures correlated significantly (p<0.05) with age, BMI, AHI, SI, dBmax, and awake, lowest, and mean nocturnal oxygen saturations. However, not all of these variables are independent; for example, lowest nocturnal oxygen saturation

DISCUSSION

This study shows that patients with significant sleep apnea and oxygen desaturation do not show the expected morning decline in blood pressure. However, it appears that age and weight, rather than sleep apnea and the severity of oxygen desaturation, are major correlates of morning blood pressure.

Although the evening-to-morning changes in blood pressure found in this study are small, it would be incorrect to entirely dismiss the influence of sleep apnea and oxygen desaturation on blood pressure

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