Influence Of Sitting And Supine Blood Pressure On The Pattern Of 24-h Ambulatory Blood Pressure

Objective: Hypertension is closely associated with the organ target damage such as heart, brain, and kidney. The familiar damage is the stroke and cardiovascular event by hypertension. Many studies have shown that the characteristic of circadian blood pressure rhythm is associated with the complication and prognosis of hypertension. It is known that the dipper rhythm is a healthy pattern, while the risk of stroke, renal function impairment, and left ventricular hypertrophy is higher in non-dippers and extreme-dippers than dippers. It is important in the reversion and prognosis of target organ to understand the machnism and influence factors of circadian blood pressure rhythm. The studies have shown that various factors contribute to the pattern of circadian blood pressure rhythm, while the machnism remains unclear. At present, there are different conclusions about the influence of postural change on blood pressure. Recently, a few studies show that the blood pressure is different between supine and sitting position in healthy adults, some of which show that the blood pressure in supine position is higher than sitting position. However, some conclusions are reversed. The nocturnal blood pressure was measured in supine position; therefore the postural change may influence the pattern of 24-h ambulatory blood pressure. However, previous studies didn't draw attention to the influence of circadian rhythm and postural change on ambulatory blood pressure monitoring. This study aims to investigate the influence of sitting and supine position on the pattern of 24-h ambulatory blood pressure, understand the influence of postural change on blood pressure, and explore the risk factors of non-dippers.Methods: One hundred and three individuals who underwent ambulatory 24-h mean BP in our ward during June 2008 and December 2008 were enrolled in this study (57 men, 46 women, and average age 59.58±13.48). 24-h ambulatory blood pressure monitoring instrument was used for ambulatory blood pressure monitoring. Using brachial artery with cuff deflation interval, the pressure wave signal in cuff was recorded in these enrolled patients. The diurnal blood pressure was recorded every 30 minutes, and nocturnal blood pressure was recorded every 60 minutes. Diurnal time is set from 6 AM to 10 PM, and nocturnal time from 10 PM to 6 AM. The patients whose nighttime blood pressures descend between 10%-20% are dippers, less than 10% are dippers. At the same time, we measured the blood pressure of every patient in sitting position, after the patient rest in supine position 30 minutes; the brachial blood pressure was measured again. The collected information for every patient includes sex, age, body mass index, coronary heart disease history, hypertension history, plasma cholesterol, plasma sugar, stroke or TIA history, smoke history, drink history, dipper or non-dipper, sitting and supine position blood pressure.Result: (1)There is no significant statistical difference between the sitting and supine position in blood pressure(P>0.05). (2) There is no significant statistical difference between the rate that supine blood pressure is higher than sitting blood pressure (10mmHg) in non-dippers and dippers (P>0.05). (3) Logistic regression shows that postural change is not associated with the pattern of 24-h ambulatory blood pressure. Compared with the dippers, the age of the non-dippers is older in non-dippers. Compared with the dippers, the rate of patients whose plasma cholesterol and plasma sugar are abnormal is higher in non-dippers. (4) In non-dippers, the nocturnal mean SBP and DBP of men (SBP 131.97±19.37mmHg, DBP 75.94±11.5mmHg) are higher than women (SBP 121.17±18.21 mmHg, DBP 69.12±10.76mmHg). However, in dippers, there is no significant difference between them (P>0.05).Conclusion: (1) There is no significant difference between sitting and supine blood pressure. (2) There is no significant correlation between circadian blood pressure rhythm and postural change. (3) Age, history of dyslipidemia, and diabetes history are the risk factors of non-dippers.