Nonlinear associations between chronic stress and cardiovascular reactivity and recovery.

A mixed literature on the influence of chronic and acute stress on cardiovascular reactivity (CVR) and recovery suggests a need for improved modeling of these associations. We examined these associations using both linear and nonlinear (quadratic) models. Data were collected on 129 healthy adults [59% female, ages 18-29 years]. Participants completed the Perceived Stress Scale (PSS) after engaging in a mental arithmetic and a stress recall task. Heart rate (HR), systolic and diastolic blood pressure (SBP, DBP) were measured during rest, task, and recovery periods. Hierarchical ordinary least squares regression was used to examine the association of chronic stress to CVR and recovery with initial cardiovascular values and body mass index entered first as covariates. Hierarchical linear modeling (HLM) was also used for recovery. For reactivity, a quadratic relationship between PSS scores and DBP was observed in females such that those scoring at moderate levels of stress displayed lesser reactivity than those scoring either low or high. For recovery, a quadratic model was supported for SBP among females, with moderate levels of stress associated with greater recovery relative to either low or high levels. For females the quadratic model was also supported for SBP and DBP when examined using HLM. Quadratic modeling may better represent current theories of how chronic stress influences CVR and recovery. Our findings further suggest that these associations may be differentially evident by gender, perhaps due to gender differences in reported stress levels or gender-related task relevance.