Assessment of Parasympathetic Activity in Athletes: Comparing Two Different Methods.

Introduction: A variety of methods are used to assess parasympathetic activity in athletes targeting different organs; however, the reliability of or interchangeability between measurement procedures is not clear.

Objective: The purpose of this study is to identify the repeatability of two parasympathetic activity measurement procedures, the HR variability during a 4-s exercise test (4sET), and the contractile properties of the pupil (pupillometry), and to assess their agreement. The secondary objective of this study is to assess their relationship with the bronchodilating effect of inhaled ipratropium bromide (iIB), blocking parasympathetic signals to the lungs.

Methods: Forty athletic subjects were enrolled in a cross-sectional study. After 15-min resting in semidarkness, subjects underwent pupillometry (PLR-200™, NeurOptics Inc., CA), followed by 4sET on a cycle ergometer. HR variability was assessed by Polar Electro® HR monitor (RS-800CX/G3; Oy, Kempele, Finland). Both protocols were repeated after 5 min. Statistical analysis was performed according to Bland and Altman and by using Pearson's correlation coefficient and intraclass correlation. Lung function measurements by flow volume curves were performed before and 45 min after iIB.

Results: The means of differences were 1.21% (limits of agreement, -3.59 to 6.02) for pupil constriction and 0.05 mm (-0.28 to 0.39) for pupil amplitude. The mean of differences for 4sET was 0.005 (-0.31 to 0.32). A very weak intraclass correlation (r = -0.01, P = 0.58) showed no agreement between the methods. No correlation was observed between pupillometry variables or 4sET with the change in lung function after iIB.

Conclusion: Pupillometry showed better repeatability compared with the 4sET. There is poor agreement between parasympathetic activity levels measured in three different target organs of athletic subjects; the heart, the pupil, and the lung. Thus, methods assessing parasympathetic activity in different target organs cannot be used interchangeably.