A Cross-sectional Study of the Occurrence and Effect of Obstructive Sleep Apnea in Subjects With Resistant Hypertension
Condition: Obstructive Sleep Apnea; Resistant Hypertension
MeSH terms: Apnea; Sleep Apnea Syndromes; Sleep Apnea, Obstructive; Hypertension
Study type: Observational

Summary: 
      This study aims to investigate the prevalence of obstructive sleep apnea (OSA) in subjects
      with resistant hypertension and to evaluate the relationship between parameters of OSA
      severity and blood pressure control
    

Detailed description: 
      Obstructive sleep apnea (OSA) is characterized by intermittent upper airway collapse during
      sleep, which results in hypoxia, arousals and surge in sympathetic activity. There is robust
      evidence to support a contributing role of OSA in hypertension (HT). The Sleep Heart Health
      Study (1), which recruited more than 6000 subjects having polysomnogram at home, found an
      independent association between OSA and HT. The adjusted odds ratio was 1.37 for subjects
      with and apnea-hypopnea index >= 30/hour compared to those without apnea. The Wisconsin Sleep
      Cohort Study , which provided prospective longitudinal follow-up for OSA subjects over 4
      years, have shown dose dependency of the severity of OSA and the risk of development of HT.
      Current available data suggests that in hypertensive patients with severe OSA, there is a BP
      drop of about 10mmHg with CPAP treatment (2-5). The blood pressure (BP) lowering effect of
      CPAP treatment in the group with mild asymptomatic OSA is less consolidated.

      The relationship between BP and risk of cardiovascular events is continuous, consistent, and
      independent of other risk factors. A strict blood pressure control is imperative in subjects
      with diabetes mellitus or renal impairment. Resistant hypertension is defined as blood
      pressure that remains above goal in spite of concurrent use of 3 antihypertensive agents of
      different classes. (6) Resistant hypertension is defined in order to identify patients who
      are at risk of having secondary causes of hypertension, and who may benefit from specific
      diagnostic and therapeutic applications. Despite the fact that OSA is listed as one of the
      causes of resistant HT (6), paucity of works has demonstrated the scale of problems of
      untreated OSA in subjects with resistant HT. (7-9) There is so far one study demonstrating
      the beneficial effect of CPAP treatment in subjects with resistant HT, though no
      randomization was implemented and the sample size was limited (n=11). (10) We aim at
      conducting a cross-sectional study to explore the situation which would guide further
      clinical trial.
    

Observational model: Case-Only
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Consecutive sampling of subjects who attend Hypertension clinic , Department of Medicine,
        Queen Mary Hospital, and who fulfill the inclusion criteria.
      
Biospecimen description: 
      Blood test for glucose, lipid, vascular and metabolic markers
    
Keywords: prevalence; obstructive sleep apnea; resistant hypertension