Abstract 4146866: Associations Between Short-term Outdoor Heat Measures and Arterial Stiffness are Modifed by Neighborhood Greenness: The Green Heart Project

Introduction: Accumulating evidence suggests that cardiovascular disease (CVD) risk is associated with climatic variables and the impact of these factors is likely to be increasing with changes in the global climate. Nevertheless, the underlying physiological mechanisms remain unclear, and it remains unknown whether urban greenspaces could contribute to climatic resilience by mitigating these mechanisms. Moreover, to-date most studies assessing CVD risk consider only ambient temperature, which may not fully capture physiologically relevant thermal conditions. Accordingly, using varied measures of heat, our objective was to assess how short-term heat exposure is related to arterial stiffness, and whether these associations are modified by area greenness. Methods: Adult participants, aged 25-70 years, were recruited from a neighborhood in Louisville, KY during the summer months of 2018 and 2019. Arterial Stiffness was measured by augmentation index (AIX) via pulse wave analysis in 714 participants. We assessed 7 heat metrics, including ambient temperature, dew point temperature, net effective temperature, Heat Index, and Universal Thermal Climate Index (UTCI), calculated as the 24h mean on the day of participants’ visit. Greenness surrounding participants’ homes was assessed by tree canopy within a 500m buffer. Linear regression was used to estimate associations between heat metrics and arterial stiffness, adjusting for socio-demographic and behavioral factors. Subgroup analysis was performed by tertiles of greenness. Results: Participants were predominantly female (61%) and White (77%), with an average age of 49.5 years. The median daily temperature during study visits was 24.4°C (range=12.2 to 28.9°C) and the median daily UTCI was 26.1°C (IQR=5.4°C). The strongest association between heat metrics and AIX was observed for UTCI (2.0% per IQR; 95% CI:0.4, 3.6), followed by net effective temperature (1.8% per IQR; 95% CI: 0.1, 3.6), while dew point temperature had the weakest association (0.6% per IQR; 95% CI: -0.8, 2.0). Stratifying our analysis by tertiles of tree canopy, we observed significant associations between heat metrics and AIX in low canopy areas, with a dose response decrease in associations among medium and high canopy areas. Conclusion: Increased arterial stiffness could be an important contributor to excessive CVD risk associated with physiologically relevant measures of heat exposure, which could be mitigated by surrounding greenspaces.