Circadian variability and nocturnal dipping pattern in blood pressure in young normotensive subjects

Blood pressure variability (BPV) is one of the recognized risk factors for different types of cardiovascular diseases (CVDs). Several physiological, behavioral and ethnic factors are known to modulate blood pressure (BP). Such studies on the population of southeast India are altogether absent. It is worthwhile, therefore, to examine the circadian variability in systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) and nocturnal dipping pattern in BP in apparently healthy human subjects as a function of gender. Sixty females and 40 males voluntarily participated in the study. All subjects wore an Ambulatory Blood Pressure Monitor (ABPM, TM 2430) for two to four consecutive days. SBP, DBP and HR was measured every 15 and 30 minutes between 07: 00-22: 00 and 22: 00-07: 00 hrs, respectively. In addition, double product (DP) and mean arterial pressure (MAP) were also computed. Data were analyzed using A&D, Cosinor and Spectre software. Prevalence of extreme dipper, dipper and non-dipper was 13%, 63% and 24%, respectively. A statistically significant circadian rhythm was validated in all studied variables, irrespective of gender and dipping pattern in BP. However, the rhythm detection ratio was low among non-dippers. Chi-square test revealed a statistically significant association of the frequency of prominent periods of SBP and MAP with nocturnal dipping categories. Further, significant differences for the circadian Mesors of SBP, DBP, HR, DP and MAP and acrophase of DBP and MAP were noticed between males and females. Dipping pattern produced a significant effect on the rhythm characteristics of all the studied variables. On the basis of our findings we can conclude that variability in BP may be associated with factor gender to some extent, whereas nocturnal dipping in BP is independent of gender. Interestingly in the present study about 24% subjects are non-dippers, which may be an indication of higher risk of CVDs among individuals belonging to younger generation of this region. However, further extensive study is desirable to strengthen the above conjecture.