[The effect of chronic intermittent hypoxia caused by obstructive sleep apnea hypopnea syndrome on blood pressure].

OBJECTIVE: To explore the effect of chronic intermittent hypoxia caused by obstructive sleep apnea hypopnea syndrome (OSAHS) and chronic continuous hypoxia caused by chronic obstructive pulmonary disease (COPD) on blood pressure and levels of nitric oxide (NO)/endothelin (ET).

METHODS: A total of 85 cases were selected, including OSAHS patients over 18 years old visited this hospital from June to August 2006, stable COPD patients and healthy volunteers. According to the results of clinical questionnaire, pulmonary function test and polysomography (PSG), they were divided into 4 groups: non-smoking OSAHS patients (n = 26), smoking OSAHS patients (n = 22), patients with stable COPD (n = 17) and healthy control subjects (n = 20). Blood pressure measurement was performed before and after the PSG examination while the subjects were resting. The levels of ET and NO in blood samples and exhaled breath condensates (EBC) were measured by radioimmunoassay and nitrate reductase, respectively. Measurement data were analyzed by ANOVA, numeration data were analyzed by chi-square test, data of normal distribution were analyzed by Pearson correlation analysis, and non-normal data were analyzed by Spearman correlation analysis. Multiple linear regression analysis was also performed.

RESULTS: Regardless of the smoking status, the difference of morning-evening diastolic blood pressure (DBP) in the morning of patients with OSAHS [non-smoking OSAHS: (88 +/- 10) mm Hg, 1 mm Hg = 0.133 kPa; smoking OSAHS: (95 +/- 17) mm Hg] was higher than that of patients with COPD [(76 +/- 7) mm Hg] and healthy subjects [(70 +/- 6) mm Hg]. The difference of morning-evening NO level in EBC of patients with OSAHS [non-smoking OSAHS: (-4.5 +/- 7.9) micromol/L; smoking OSAHS: (-3.4 +/- 5.5) micromol/L] was lower than that of patients with COPD [(1.4 +/- 6.1) micromol/L] and healthy subjects [(3.1 +/- 4.0) micromol/L]. The ratio of NO to ET in serum of the smoking OSAHS group (1.0 +/- 0.5) was lower than that of the COPD group (1.4 +/- 0.7). After adjustment for sex, age, BMI, waist circumference, history of smoking and alcohol, level of hypertension, and category of antihypertensive drugs, the morning-evening difference of NO level in EBC was negatively associated with the morning-evening difference of DBP (r = -0.301, P = 0.021), and was positively associated with apnea hypopnea index (AHI) (r = 0.116, P < 0.05). The morning-evening difference of DBP was associated with AHI (r = -0.303, P = 0.011), amplitude of oxygen desaturation with pulse oxygen saturation (SpO(2)) less than 90% (OLA90%, r = -0.281, P = 0.018), and gradient of oxygen desaturation with SpO(2) less than 90% (OLG90%, r = 0.286, P = 0.035). Multiple linear regression analysis showed that, if AHI increased by 1/h, the morning-evening difference of DBP would increase 0.41 mm Hg; if the morning-evening difference of NO level in EBC increased by 1 micromol/L, the morning-evening difference of DBP would decrease 0.27 mm Hg; and if AHI increased by 1/h, the morning-evening difference of NO level in EBC would increase 0.40 micromol/L.

CONCLUSION: The DBP of OSAHS patients in the morning is significantly higher than that in the evening. The morning-evening difference of NO level in EBC reflects indirectly the consumption of NO in the body, and is associated with the degree of OSAHS and the morning-evening difference of DBP.