Joint Modeling of Longitudinal Systolic and Diastolic Blood Pressure Measurements of Hypertensive Patients Receiving Treatment in Jimma University Specialized Hospital

Abstract

Background: Hypertension is a chronic disease that has a major health problem over the centuries due to its significant contribution to the global health burden. In developing countries, there is a rapid increase in hypertension prevalence, and in developed countries, the previous trend of an increase in hypertension prevalence is actually reversing. According to World health organization hypertension is the seventh leading cause of death in Ethiopia. Hypertension is also called high blood pressure, described by two numbers SBP and DBP. Hence, joint longitudinal model was used to address how the evolution of SBP is associated with the evolution of DBP. Objective: The main objective of this study is to investigate the joint evolution and association of systolic and diastolic blood pressure measurements of hypertensive patients and identify the potential risk factors affecting the two end points in Jimma University Specialized hospital. Methods: In this study secondary data was used from Jimma university specialized hospital in Hypertensive Outpatient Clinic. The study population consists of 354 hypertensive patients, measured repeatedly at least three times on each patient who are 18 years old or older those treated with antihypertensive drugs from September 2011 to July 2013 were used in this study. First, each of the outcomes is analyzed separately using linear mixed model. Then, a joint model is considered to study the joint evolution and identify the potential risk factors affecting the two end points. Results: On average both SBP and DBP measures slightly decrease a linear pattern over time. In addition, the progression of both outcomes depends on patient‟s baseline socio-demographical characteristics. Fit statistics showed that the joint model resulted in better fit to the data than the separate models, implying a significant association among the two end points. Based on the joint model, sex, baseline age, and place of residence are the significant factor for the progression of blood pressure, but family history and all the interaction term except age by time, did not appear significant at 5% level of significance. Conclusion: The results of the separate and joint model analysis are consistent. When the joint model is compared with the separate model, the joint model fitted the data better than the separate model. The result from the joint model suggested a strong association between the evolutions and a slowly increasing evolution of the association between SBP and DBP.