Beyond heart health: Consequences of obstructive sleep apnea

September 3, 2019|Cleveland Clinic Journal of Medicine
Harneet K. Walia, MD, FAASM
Author and Disclosure Information

Harneet K. Walia, MD, FAASM
Associate Professor of Medicine, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH; Staff, Sleep Disorders Center, Neurological Institute, Cleveland Clinic

Correspondence: Harneet K. Walia, MD, FAASM, Sleep Disorders Center, Neurological Institute, S73, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195; waliah@ccf.org

Dr. Walia is principal investigator of a ResMed funded grant.

This article is based on Dr. Walia’s “Beyond Heart Health: Consequences of Obstructive Sleep Apnea” webcast released March 29, 2019, part of the “Obstructive Sleep Apnea: A Cleveland Clinic State-of-the-Art Review” online series (available at www.clevelandclinicmeded.com/online/sleep-apnea). The article was drafted by Cleveland Clinic Journal of Medicine staff and was then reviewed, revised, and approved by Dr. Walia.

Release date: September 1, 2019
Expiration date: August 31, 2022
Estimated time of completion: 0.75 hour

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ABSTRACT

Obstructive sleep apnea (OSA) is a serious condition associated with impaired quality of life, depression, drowsy driving and motor vehicle accidents, metabolic disease, and cognitive decline. The mechanisms accounting for OSA and metabolic disease include hypoxia, sleep fragmentation, and systemic inflammation. OSA appears to advance cognitive decline, and the relationship between the 2 conditions may be bidirectional. Treatment of patients with continuous positive air pressure therapy improves many of the impaired outcomes associated with OSA. Greater awareness, screening, and treatment of patients with OSA can reduce the negative consequences associated with OSA.

KEY POINTS

  • OSA is associated with negative health consequences such as depression, drowsy driving, metabolic disease, and cognitive decline.
  • Several possible mechanisms to explain the health consequences of OSA have been explored.
  • Treatment of patients with OSA may improve outcomes for many of the health consequences associated with OSA.
  • Screening for OSA is important to identify and treat patients to reduce the associated health risks.

Mechanisms of altered metabolic regulation in OSA

Mechanisms implicated in altering metabolic regulation in OSA include intermittent hypoxia, sleep fragmentation and glucose homeostasis, and obesity. Intermittent hypoxia from OSA results in sympathetic nervous system activation that affects the pancreas, skeletal muscle, liver, and fat cells resulting in altered insulin secretion, lipid-bile synthesis, glucose metabolism, and lipoprotein metabolism.35

Sleep fragmentation is a cardinal feature of OSA and the resulting suppression of sleep may alter insulin sensitivity. Studies have implicated disruptions to slow-wave sleep specifically, as well as disruption of any stage of sleep in reduced insulin sensitivity.35,36 In addition to decreased insulin sensitivity, sleep fragmentation also increases morning cortisol levels and increases sympathetic nervous system activation.37

Obesity and OSA share a pathway imparting increased cardiometabolic risk.38 Fat tissue causes higher systemic inflammation and inflammatory markers. A recent report describes a bidirectional relationship between metabolic syndrome and OSA.39 While OSA increases the risk for metabolic syndrome, metabolic syndrome by virtue of body mass index with changes in mechanical load and narrow airway and physiology can predispose for OSA.

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Effect of treatment for OSA on metabolic syndrome

Several studies have evaluated the effect of CPAP treatment for OSA on metabolic syndrome overall, as well as the specific conditions that comprise metabolic syndrome. In evaluating CPAP use and metabolic syndrome overall, studies have found a reduced prevalence of metabolic syndrome,40,41 CPAP benefit only in complying patients,42 and a reduction in oxidative stress with a single-night use of CPAP.43

With respect to insulin sensitivity, a study of 40 men with moderate OSA using CPAP therapy (mean use 5 hours) reported an increase in the insulin sensitivity index after 2 days, and a further increase after 3 months.44 Another study found no improvement in insulin resistance in severe OSA.45 A meta-analysis reported improved insulin resistance with CPAP,46 although a recent meta-analysis assessing hemoglobin A1c level, fasting insulin level, and fasting glucose did not show improvement in these parameters. Large-scale clinical trials with longer treatment duration and better CPAP compliance are warranted.47

CPAP use in patients with OSA has been found to affect hypertension in a number of studies (Table 2).48–55 In a comparison of therapeutic CPAP with suboptimal CPAP for 9 weeks, ambulatory blood pressure was reduced in the therapeutic group, and no change was seen in the subtherapeutic group, illustrating the importance of optimal pressure settings in treating OSA.48

Figure 1. Blood pressure trends in patients before and after continuous positive airway pressure (CPAP) use.
A randomized controlled trial of nearly 300 individuals found improvement in 6 blood pressure parameters in a group using CPAP compared with a group using sham CPAP after 12 weeks.50 A large clinic-based cohort of 894 individuals with hypertension and resistant hypertension (15%) found that after 1 year, CPAP use was associated with 2 to 3 mm Hg of reduction in blood pressure (Figure 1).56 Meta-analysis of randomized controlled trials on the effectiveness of CPAP on hypertension found reductions of 2 mm Hg to 3 mm Hg in blood pressure.57 Another meta-analyses showed a reduction of 2.6 mm Hg in 24-hour mean blood pressure with CPAP therapy (Table 2).48–55 This reduction may appear modest in nature; however, any reduction in blood pressure can result in decreased cardiovascular morbidity and mortality. A meta-analysis of randomized controlled trials indicated reductions in mean systolic blood pressure of 5.4 mm Hg and diastolic blood pressure of 3.86 mm Hg after CPAP in those with resistant hypertension and OSA.58

Weight loss has been shown to reduce the AHI and other parameters related to sleep apnea such as oxygen desaturation index in patients with obesity and diabetes.59 Weight loss combined with CPAP compared with CPAP or weight loss alone showed an incremental benefit in improving glucose parameters, triglycerides, and possibly systolic blood pressure and triglycerides.60