Age‐related changes in autonomic response: A pupillary light reflex and heart rate variability study

Background Autonomic nervous system (ANS) dysfunction has been implicated with cardiovascular diseases, sudden‐cardiac‐death, and aging. The pupillary light reflex (PLR) and heart rate variability (HRV) are noninvasive tools of autonomic evaluation. However, the former remains underutilized in clinical practice. Purpose We investigated the relationship between PLR, HRV, and aging to determine the normal distribution of age‐adjusted PLR and HRV measurements and to determine which method is best correlated with age. Methods Healthy participants aged 18–65 years were recruited. Following a dark adaptation period, pupillary reactivity parameters were collected using an automated, commercial pupillometer. HRV measurements were derived using a high‐resolution electrocardiogram. Correlations of PLR and HRV parameters to age were computed using linear‐regression analysis. Results A total of 111 healthy participants were included. Older age was correlated with lower maximum and minimum pupillary diameters following dark adaptation and illumination ( R = −0.51, p < 0.001 and R = −0.47, p < 0.001, respectively). Average constriction and dilatation velocity were correlated with age ( R = 0.33, p < 0.001 and R = −0.21, p = 0.025, respectively). HRV parameters were also associated inversely with age (SDNN; R = −0.31, p < 0.001 and RMSSD; R = −0.33, p < 0.001). Other parameters showed lower significance levels. Conclusion Pupillary light reflex measurements demonstrated stronger age correlation than short‐term HRV time‐domain indices. Due to its merit in depicting normal age‐related ANS changes, PLR can be utilized to differentiate between pathological and physiological deviations from age‐adjusted norms, seemingly better than HRV. Further research is warranted on incorporating PLR‐based ANS dysfunction evaluation and monitoring the increasingly aging population.