Correlation between heart rate variability and pulmonary function adjusted by confounding factors in healthy adults

The autonomic nervous system maintains homeostasis, which is the state of balance inthe body. That balance can be determined simply and noninvasively by evaluating heartrate variability (HRV). However, independently of autonomic control of the heart, HRVcan be influenced by other factors, such as respiratory parameters. Little is knownabout the relationship between HRV and spirometric indices. In this study, ourobjective was to determine whether HRV correlates with spirometric indices in adultswithout cardiopulmonary disease, considering the main confounders (e.g., smoking andphysical inactivity). In a sample of 119 asymptomatic adults (age 20-80 years), weevaluated forced vital capacity (FVC) and forced expiratory volume in 1 s(FEV₁). We evaluated resting HRV indices within a 5-min window in themiddle of a 10-min recording period, thereafter analyzing time and frequency domains.To evaluate daily physical activity, we instructed participants to use a triaxialaccelerometer for 7 days. Physical inactivity was defined as <150 min/week ofmoderate to intense physical activity. We found that FVC and FEV₁,respectively, correlated significantly with the following aspects of the RR interval:standard deviation of the RR intervals (r =0.31 and 0.35),low-frequency component (r =0.38 and 0.40), and Poincaré plot SD2(r =0.34 and 0.36). Multivariate regression analysis, adjustedfor age, sex, smoking, physical inactivity, and cardiovascular risk, identified theSD2 and dyslipidemia as independent predictors of FVC and FEV₁(R²=0.125 and 0.180, respectively, for both). We conclude that pulmonaryfunction is influenced by autonomic control of cardiovascular function, independentlyof the main confounders.