Which came first, obstructive sleep apnea or hypertension? A retrospective study of electronic records over 10 years, with separation by sex
Authors: An Eunjoo , Irwin Michael R. , Doering Lynn V. , Brecht Mary-Lynn , Watson Karol E. , Aysola Ravi S. , Aguila Andrea P. , Harper Ronald M. , Macey Paul M. 
Published: January 2020

AbstractObjectivesObstructive sleep apnea (OSA) is a risk factor for hypertension (HTN), but the clinical progression of the sleep disorder to the high blood pressure condition is unclear. There are also sex differences in prevalence, screening and symptoms of OSA. The objective was to estimate the time from OSA to HTN diagnoses, with sex-specific quantification.DesignRetrospective analysis of electronic health records (EHR) over a 10-year period (2006 to 2015 inclusive).SettingUCLA Health System in Los Angeles, California, USA.Participants4848 patients: female N=2086, mean [age±std] = 52.8±13.2 years; male N=2762, age=53.8±13.5 years. These patients were selected from 1.6 million patients with diagnoses in the EHR who met the criteria of: diagnoses of OSA and HTN; in long-term care defined by ambulatory visits at least one year prior and one year subsequent to the first OSA diagnosis; no diagnosis of OSA or HTN at intake; and a sleep study performed at UCLA.Primary and secondary outcome measuresThe primary outcome measure in each patient was time from the first diagnosis of OSA to the first diagnosis of HTN (in days). Since HTN and OSA are progressive disorders, a secondary measure was relationship between OSA-to-HTN time and age.ResultsThe mean, std and 95% confidence intervals of the time from OSA to HTN diagnoses were: all - 732 ± 1094.9 [-764.6, -701.8] days; female -815.9 ± 1127.3 [-867.3, -764.2] days; and male -668.6 ± 1065.6 [-708.1, -626.8] days. Age was negatively related to time from OSA to HTN diagnosis in both sexes.ConclusionsHTN was on average diagnosed years prior to OSA, with a longer separation in females. Our findings suggest under-screening of OSA, more so in females than males. Undiagnosed OSA may delay treatment for the sleep disorder and perhaps affect the development and progression of HTN.Brief SummaryOSA is a risk factor for HTN so, in people with both conditions, the sleep disorder should typically precede the high blood pressure. However, the clinical sequence of these two conditions is unclear.For patients in long-term care in the UCLA health system, the diagnosis of OSA usually precedes by years the diagnosis of HTN in patients with both conditions. The later diagnosis of OSA versus HTN may reflect a lack of OSA screening for years after sleep disorder onset.Strengths and limitations of this studyApproximately 5000 is a large enough sample to provide reliable effect size and confidence interval calculations.Inclusion criteria ensure observations are from patients likely to be in regular contact with the UCLA health system, and hence to be in a position to be regularly screened for HTN and OSA.Separation by sex highlights the presence of clinical differences in patients with HTN and OSA, although the nature of the differences (for example under-screening, or different progression in females and males) cannot be inferred.Limited generalizability due to data in a single health system and to the specific 10-year time period, the latter encompassing a change in diagnostic criteria for OSA.No data on diagnoses in other clinical settings or prior to 2006, meaning 1) many patients with HTN and OSA were likely excluded because the diagnoses were not recorded at UCLA and 2) of the included patients some may have had prior diagnoses thus affecting interpretation of the time from OSA to HTN measure.