Factors affecting systolic blood pressure trajectory in low and high activity conditions.

Background: Typically, blood pressure dips during sleep and increases during daytime. The blood pressure trend is affected by the autonomic nervous system. The activity of this system is observable in the low and high activity conditions. The aim of this study was to assess the effect of individual characteristics on systolic blood pressure (SBP) across day-night under low and high activity conditions. Methods: The samples were 34 outpatients who were candidates for evaluation of 24 hours of blood pressure with an ambulatory. They were admitted to the heart clinic of Farshchian hospital, located in Hamadan province in the west of Iran. The hourly SBP during 24 hours was considered as a response variable. To determine the factors effecting SBP in each condition, the hidden semi-Markov model (HSMM), with 2 hidden states of low and high activity, was fitted to the data. Results: Males had lower SBP than females in both states. The effect of age was positive in the low activity state (ß=0.30; p<0.001) and negative in high activity state (ß= -0.21; p=0.001). The positive effect of cigarette smoking on SBP was seen in low activity state (ß=5.02; p=0.029). The overweight and obese patients had higher SBP compared to others in high activity state (ß=11.60; p<0.001 and ß=5.87; p=0.032, respectively). Conclusion: The SBP variability can be displayed by hidden states of low and high activity. Moreover, the effects of studied variables on SBP were different in low and high activity states.