PERSONAL BLOOD PRESSURE VARIABILITY IS NOT ASSOCIATED WITH SEASONAL BLOOD PRESSURE EFFECTS: A 4-YEAR PROSPECTIVE COHORT OF 1,151 PARTICIPANTS FROM ELDERLY CENTRES IN HONG KONG

Objective: Personal blood pressure variability (BPV) is demonstrated to be an important risk factor for cardiovascular diseases, but blood pressure fluctuates over the years with seasonal effects. This study aimed to investigate the association between personal BPV and year-round seasonal blood pressure fluctuations among the elderly in Hong Kong. Design and method: Elderly participants aged above 55 years were recruited from 76 elderly centres and were prospectively followed up between September 2016 and January 2020. Personal interviews were conducted to assess personal health conditions. Nursing calls and social worker engagement were offered for those with suboptimal BP readings. The inclusion criteria were the participants who reported more than 80% of weekly BP records in at least 2 years of follow-up. Standard deviation (SD) was applied to quantify the personal variability levels of systolic and diastolic BPV. A machine learning classification method, K-means, was used to further classify participants into low, medium, and high levels of overall BPV. The seasonal fluctuations of blood pressure readings were extracted by a time series model. Temperature data were extracted from the Hong Kong Observatory and were correlated with the seasonal blood pressure variability across the participants with different levels of BPV. Results: A total of 500,914 blood pressure records were collected from 1,151 elderly participants with a mean age of 79 years. Machine learning classified 588 (51%), 462 (40%), and 101 (9%) participants with low, medium and high levels of BPV, respectively. Seasonal fluctuations were shown to be reversely correlated with the temperature data (r > 85% with all p-values < 0.001) (Figure 1) regardless of the personal BPV levels. Conclusions: Blood pressure variability is a personal risk factor that is irrelevant to seasonal blood pressure fluctuations. Early intervention to control for suboptimal blood pressure variability would provide additional benefits to patients with a higher risk of cardiovascular diseases.