Objectives

To determine the cardiovascular and other consequences of sleep-disordered breathing and to test whether sleep-disordered breathing is associated with an increased risk of coronary heart disease, stroke, all-cause mortality and hypertension by examining subjects from well-characterized and established epidemiologic cohorts.

Background

Obstructive sleep apnea syndrome (OSA) is a potentially debilitating condition characterized by repetitive episodes of apnea while asleep, nocturnal oxygen desaturation, excessive daytime sleepiness, and loud disruptive snoring. Epidemiologic data from middle-aged adults indicate that OSA is common, with prevalence rates of 4% in men and 2% in women. Prior studies implicated OSA as a risk factor for the development of hypertension, ischemic heart disease, congestive heart failure, stroke and consequently premature death. Questions arose as to whether an increased propensity for cardiovascular and cerebrovascular diseases was limited to only those with frank OSA or whether more subtle forms of sleep-disordered breathing (SDB) would also confer elevated risk. Further evidence was also needed to clarify whether, SDB, including OSA, is an independent risk factor for the development of cardiovascular or cerebrovascular disease. Known cardiovascular and cerebrovascular disease risk factors such as obesity and smoking are commonly present in those with SDB; therefore, apparent associations between SDB and cardiovascular and cerebrovascular diseases may have resulted from the effects of these concomitant risk factors. Moreover, there was no understanding as to whether such factors as race, age, gender, and prevalent cardiovascular or cerebrovascular disease might interact with SDB to alter future cardiovascular and cerebrovascular disease risk. Mechanisms underlying any propensity to develop cardiovascular or cerebrovascular disease with SDB had not been firmly established (Quan SF, Howard BV, Iber C, Kiley JP, Nieto FJ, O'Connor GT, Rapoport DM, Redline S, Robbins J, Samet JM, Wahl PW. The Sleep Heart Health Study: design, rationale, and methods. Sleep 1997; 20(12): 1077- 1085).

Participants

Participants in SHHS were recruited from nine existing NHLBI epidemiological studies in which data on cardiovascular risk factors had been collected previously. The “parent” cohorts included:

• The Hagerstown and Minneapolis/St. Paul sites of the Atherosclerosis Risk in Communities Study (ARIC)
• The Hagerstown, Sacramento and Pittsburgh sites of the Cardiovascular Health Study (CHS)
• The Framingham Offspring Cohort
• The Strong Heart Study (SHS) sites in South Dakota, Oklahoma, and Arizona
• The New York Hypertension Cohorts
• The Tucson Epidemiologic Study of Airways Obstructive Diseases and the Health and Environment Study

From these parent cohorts, a sample of participants who met the inclusion criteria (age 40 years or older; no history of treatment of sleep apnea; no tracheostomy; no current home oxygen therapy) was invited to participate in the baseline examination of the SHHS, which included an initial polysomnogram (SHHS-1). Several cohorts over-sampled snorers in order to increase the study-wide prevalence of sleep-disordered breathing. In all, 6441 individuals were enrolled between November 1, 1995 and January 31, 1998.

During exam cycle 3 (January 2001- June 2003), a second polysomnogram (SHHS-2) was obtained in 3295 of the participants.

Due to sovereignty issues, Strong Heart Study participants are not included in the shared SHHS data. Data from a total of 5804 participants (1915 ARIC, 1230 CHS, 688 Framingham Offspring and 1971 from other studies), consenting to share data are available.

Design

The Sleep Heart Health Study added in-home polysomnography to the data collected in each of the parent studies at a baseline SHHS exam and a follow-up approximately 4 years later. Using the Compumedics PS polysomnograph, sleep studies were obtained in an unattended setting, usually in the homes of the participants, by trained and certified technicians. The recording montage consisted of:

• C3/A2 and C4/A1 EEGs, sampled at 125 Hz
• right and left electrooculograms (EOGs), sampled at 50 Hz
• a bipolar submental electromyogram (EMG), sampled at 125 Hz
• thoracic and abdominal excursions (THOR and ABDO), recorded by inductive plethysmography bands and sampled at 10 Hz
• “airflow” detected by a nasal-oral thermocouple (Protec, Woodinville, WA), sampled at 10 Hz
• finger-tip pulse oximetry (Nonin, Minneapolis, MN) sampled at 1 Hz
• ECG from a bipolar lead, sampled at 125 Hz for most SHHS-1 studies and 250 Hz for SHHS-2 studies
• Heart rate (PR) derived from the ECG and sampled at 1 Hz
• body position (using a mercury gauge sensor)
• ambient light (on/off, by a light sensor secured to the recording garment)

This montage provides data on the occurrence of sleep-disordered breathing, sleep stages, heart rate, oximetry and on arousals. Each participant in the parent studies was also asked to complete the Sleep Habits Questionnaire which covers usual sleep pattern, snoring, and sleepiness. Other measurements obtained at each examination are summarized in this table.

Sleep. 1997 Dec;20(12):1077-85.

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