The study was motivated by the increasing recognition of the frequent occurrences of sleep-disordered breathing in the general population and mounting evidence that sleep-disordered breathing may increase risk for cardiovascular diseases, including coronary artery disease and stroke, and for hypertension, and may reduce quality of life generally. Many clinical questions remain unanswered concerning sleep-disordered breathing as well: for example, when, in the natural history of the disorder, intervention is warranted; and how to determine who is at risk so that recently developed treatments can be applied in a cost-effective manner.
The initiative was developed by the Pulmonary Diseases Advisory Committee, approved by the full Committee in February, 1993, and given concept clearance by the October, 1993 National Heart, Lung, and Blood Advisory Council. The Request for Applications was released in January, 1994.
The SHHS adds in-home polysomnography to the data collected in each of the cohorts under study. Using the Compumedics SleepWatch polysomnograph, a single over-night polysomnogram is obtained at home for the subjects; the montage includes oximetry, heart rate, chest wall and abdominal movement, nasal/oral airflow, body position, EEG, ECG, and chin EMG. In-home monitoring provides data on the occurrence of sleep-disordered breathing and on arousals.
Although the SHHS is a prospective cohort study, the cross-sectional findings will provide new information on patterns of sleep and sleep-disordered breathing in the general population. Consequently, initial analyses will be descriptive and will also address cross-sectional associations of sleep-disordered breathing with prevalent cardiovascular disease and quality of life and with risk factors for cardiovascular disease. Longitudinal analyses will address sleep-disordered breathing as a predictor of cardiovascular outcomes and change in blood pressure.
The extent of information available on key cardiovascular risk factors varies among the parent cohorts. Some additional data are collected on covariates at enrollment into the SHHS. However, the parent studies are the principal source of information on risk factors for cardiovascular disease in the participants. The cardiovascular outcomes for all sites include hospitalized acute myocardial infarction, nonfatal coronary heart disease, stroke, and death due to cardiovascular or cerebrovascular disease. Change in blood pressure and diagnosis of hypertension is considered, and all participants complete a standardized instrument on quality of life. The cardiovascular outcomes are adjudicated by methods already in place for the ARIC, CHS, SHS, and Framingham Field Centers and by the CHS process for the New York and Tucson Field Centers. Ancillary studies address other outcomes, such as cognitive functioning, that cannot be considered in the full SHHS cohort.
Over 80 manuscripts were published based on substudies and ancillary investigations. Three primary outcomes papers were published in 2009 and 2010, based on follow-up as of 2006-2007.
The study was renewed several times to provide for continued data collection and follow-up, including new polysomnograms. The formal funding for SHHS sites, which ended as of August 31, 2008, was followed by a one-year no- cost extension. Funding ceased for the participating sites as of August 31, 2009, but the Data Coordinating Center and the PSG Reading Center were granted additional no-cost extensions to support additional data collection from the parent cohorts to obtain follow up through 2009, 2010 or 2011 (depending on the cohort), on all-cause mortality, incident CVD, and stroke. The updated results were presented in a session at the ATS 2012 meetings in San Francisco.