Associations of cardiac autonomic function and physical functional capacity with self-rated health in aging population

Abstract

How an individual rates her or his own health is an outcome of complex psychological and physiological mechanisms not well known. Self-rated health (SRH) is a subjective clinical survey tool, which associates with health outcomes and a number of biomarkers. Physical functional capacity (PFC) measured as 6-minute walk test (6MWT) walking distance (6MWD) is associated with health outcomes in aging population. Similarly, cardiac autonomic function (CAF) measured as heart rate response to exercise (HRRTE), and heart rate recovery (HRR) associate with health. However, 6MWD, HRRTE, or HRR associations with SRH have not been studied. Thus, the aim of this study is to investigate if CAF measured as HRRTE and HRR and PFC measured as 6MWD associate similarly with SRH. It was hypothesized that SRH's positive association with 6MWD would be stronger than with HRRTE or HRR.

518 individuals, in age groups of 75-, 80- and 85-year-olds, participated in this observational cohort study. Participants rated their health based on SRH 5-point scale. SRH results were binarily encoded into excellent/good and satisfactory/poor. No one rated their health as “very poor”. 6MWD and heart rate (HR) were recorded at the 6-minute mark. Post-exercise HR was recorded after sitting for 30 and 60 seconds. HRRTE was calculated from exercise HR minus resting HR. HRR was calculated from exercise HR minus post-exercise HR after 30 and 60 seconds. Chi-square test and t-test were run to investigate significant differences between categories and means, respectively. Pearson correlations explored the direction and strength of correlations (r). Logistic regression analysis examined independent associations and the predictive accuracy of models in relation to SRH.

SRH association with 30-second HRR was positive (r=0.088; p=0.043), 60-second HRR positive (r=0.117; p=0.007), 6MWD positive (r=0.410; p=<0.001), and with age negative (r=-0.251; p=<0.001). HRR and HRRTE variables lost association with SRH when adjusted for 6MWD. Only model 1 (6MWD) and model 2 (6MWD and age) associated with SRH. Model 2 had slightly higher accuracy, but only 6MWD independently associated with SRH. Models were weaker at accurately predicting poorer SRH than better SRH (model 2: 56.3% vs. 73.9%). Thus, 6MWD independently associates with SRH, however, studies show that HRRTE and HRR are important predictors of cardiovascular health, and HR is a critical contributor to PFC. Inaccurate predictions of poorer SRH are likely due to aging-related diseases causing variance in 6MWD, thus control of diseases, age, and physical fitness is critical. For future research, a study of CAF variables may require a graded exercise stress test to minimize confounding factors.