Chest
Volume 120, Issue 3, September 2001, Pages 887-893
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Clinical Investigations
Sleep and Breathing
Effect of Continuous Positive Airway Pressure and Placebo Treatment on Sympathetic Nervous Activity in Patients With Obstructive Sleep Apnea

https://doi.org/10.1378/chest.120.3.887Get rights and content

Abstract

Study objectives

We studied the effect of continuous positive airway pressure (CPAP) treatment on sympathetic nervous activity in 38 patients with obstructive sleep apnea.

Design

Randomized, placebo-controlled trial.

Setting

Patients underwent polysomnography on three occasions in a clinical research center, and had BP monitored over 24 h at home. All of the patients had sleep apnea with a respiratory disturbance index (RDI) > 15.

Interventions

The patients were randomized blindly to CPAP or placebo (CPAP at ineffective pressure) treatment.

Measurements and results

Prior to therapy, the number of apneas and the severity of nocturnal hypoxia correlated significantly with daytime urinary norepinephrine (NE) levels, but not nighttime urinary NE levels. CPAP treatment lowered daytime BP from 99 ± 2 mm Hg to 95 ± 3 mm Hg (mean ± SEM) and nighttime BP from 93 ± 3 mm Hg to 88 ± 3 mm Hg. Placebo CPAP treatment decreased both day and night mean BP only 2 mm Hg. CPAP, but not placebo, treatment lowered daytime plasma NE levels by 23%, daytime urine NE levels by 36%, daytime heart rate by 2.6 beats/min, and increased lymphocyteβ 2-adrenergic receptor sensitivity (all p < 0.05). The effect of CPAP treatment on nighttime urine NE levels and heart rate did not differ from placebo treatment. There was a suggestion of an effect of placebo CPAP treatment on nighttime measures, but not on daytime measures.

Conclusion

We conclude that daytime sympathetic nervous activation is greater with more severe sleep apnea. CPAP treatment diminished the daytime sympathetic activation; the potential nighttime effect of CPAP treatment was obscured by a small placebo effect.

Section snippets

Materials and Methods

We recruited patients for this study by advertisement and referral. All patients gave oral and written consent to this University of California at San Diego Human Subjects Committee-approved protocol. Patients were eligible if they had never received CPAP, if they were between 35 years and 65 years old, and if they were from 100 to 170% of ideal body weight. Patients underwent a blood count, chemistry panel, ECG, history, and physical examination. Patients with any major medical disorder other

Results

The 38 patients entered into this study had sleep apnea with an RDI > 15. The 11 hypertensive patients were studied when they were not receiving antihypertensive drugs. The randomized groups were of similar age, race, height, and BP status. However, those randomized to CPAP treatment were heavier and had higher urinary NE levels (Table 1).

Although all subjects had sleep apnea, the severity of their sleep disturbance and hypoxia correlated with their daytime urinary NE excretion (Table 2).

Discussion

When compared with placebo, CPAP treatment lowered RDI, plasma NE levels, daytime urine NE levels, and daytime heart rate, and increasedβ 2-adrenergic receptor sensitivity. Diseases exacerbated by sympathetic nervous activity, such as hypertension and angina pectoris, respond to placebo treatment. Wearing a mask attached to an operating machine might elicit a powerful placebo response. A trial14 of CPAP for sleep apnea used a pill as placebo and found no significant effect on BP. We recently

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  • Cited by (0)

    Supported by National Institutes of Health grants HL 44915, HL 58120, and MO1-RR0827.

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