Characteristics of Obstructive Sleep Apnea Syndrome Related Hypertension and the Effect of Continuous Positive Airway Pressure Treatment on Blood Pressure
Condition: Hypertension Secondary
MeSH terms: Hypertension
Study type: Observational [Patient Registry]

Summary: 
      Obstructive sleep apnea syndrome (OSAS) causes nocturnal chronic intermittent hypoxia (CIH)
      that contributes to the development of hypertension. CIH profiles, including the its length,
      speed and intensity were widely different in individuals. Until recently, the influence of
      OSAS-related IH profiles on hypertension development has not been fully explored. The present
      study aimed to investigate the effects of different CIH properties on blood pressure (BP) and
      short-term blood pressure variability (BPV) in severe OSAS patients.

      Continuous positive airway pressure (CPAP) prevents the airway collapse, avoids the
      occurrence of intermittent hypoxemia and arousal, is the preferred treatment for OSAS and has
      been widely used in clinical. In theory, CPAP maintains upper airway patency and preserves
      ventilation, thereby inhibits the chain reaction over activation of the sympathetic nervous
      system and blood pressure regulating mechanism, thus CPAP treatment have adequate scientific
      basis to cause a substantial reduction arterial blood pressure, but controlled studies showed
      either no effect or only a minor decrease in arterial blood pressure by 1.4 and 2.5 mmHg
      respectively.The current, which type of combination of hypertension OSA patients can obtain
      the best antihypertensive benefit from CPAP therapy is still under debate.
    

Detailed description: 
      Nocturnal BP was continuously monitored via measurement of pulse transmit time (PTT). The
      value of apnea-related systolic BP elevation (△BP) was used to reflect short-term BPV.
      Beat-to-beat RR interval data were incorporated in polysomnography for heart rate variability
      analysis. LF/HF band ratio was compared between two groups which used to reflect
      sympatho-vagal balance. The length of the desaturation event was measured to the nearest 0.5
      second (△t). The fall in SpO2 during apnea was calculated as the gap from start of the
      desaturation to the nadir of the desaturation. The rate of fall in SpO2 was counted as the
      change in the percentage of SpO2 per second (△SpO2 /△t) and expressed as oxygen desaturation
      rate (ODR), which reflected the speed and efficacy of oxygen desaturation during an apnea
      event. One hundred and two severe OSAS subjects were divided into two groups according to the
      their median ODR: faster ODR and slower ODR.

      In addtion,patient were categorized into three groups: Group l: systolic blood pressure index
      was less than 30% of AHI; Group 2: systolic blood pressure index was less than 60% but more
      than 30%; Group 3: systolic blood pressure index is more than 60% of AHI. The investigator
      would compare the effect of CPAP treatment on awake and sleep BP level at the first night and
      2 weeks therapy among three groups. Moreover, whether or not the sympathetic-parasympathetic
      nerve balance and the renin-angiotensin-aldosterone system are different in three groups
      would also be evaluated. The main purpose of study is to confirm the OSA with hypertension
      and OSA secondary hypertension are two different concepts. Basis for the clinical treatment,
      the former, CPAP might have no effect or only a minor decrease in arterial blood pressure,
      while the latter CPAP treatment might achieve significant antihypertensive effect.
    

Intervention name(s): continuous positive airway pressure
Intervention type(s): Other
Intervention description(s): Continuous positive airway pressure (CPAP) prevents the airway collapse, avoids the occurrence of intermittent hypoxemia and arousal, is the preferred treatment for OSAS and has been widely used in clinical. The investigator would compare the effect of CPAP treatment on awake and sleep BP level at the first night and 2 weeks therapy among three groups. Moreover, whether or not the sympathetic-parasympathetic nerve balance and the renin-angiotensin-aldosterone system are different in three groups would also be evaluated.
Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        1. age between 18 to 70 yrs;

          2. newly diagnosed OSAS without treatment;
      
Keywords: blood pressure fluctuation; hypertension; continuous positive airway pressure; intermittent hypixa; oxygen desaturation