Sex differences in estimates of cardiac autonomic function using heart rate variability: effects of dietary capsaicin

Purpose Heart rate variability (HRV) estimates the autonomic nervous system (ANS) influence on the heart and appears sex-specific. Sensory afferents exhibit sex-specificity; although, it is unknown if Capsaicin, an agonist for transient receptor potential vanilloid channel-1 (TRPV 1 ), alters cardiac ANS activity in a sex-dependent manner, which could be important given the predictive nature of HRV on risk of developing hypertension. Thus, we explored if there was sex-specificity in the effect of capsaicin on estimated cardiac ANS activity. Methods HRV was measured in 38 young males (M: n = 25) and females (F: n = 13), in a blinded-crossover design, after acute ingestion of placebo or capsaicin. Resting HR, RR-interval, root-mean-square of successive differences (RMSSD), natural log-transformed RMSSD (LnRMSSD), standard deviation of n–n intervals (SDNN), number of pairs of successive n–n intervals differing by > 50 ms (NN50), and percent NN50 (PNN50) were obtained using standard techniques. Results Significant sex differences were observed in mean HR (M: 59 ± 9.3 vs. F: 65 ± 12 beats/min, p = 0.036, η 2 = 0.098), minimum HR (M: 47 ± 8.3 vs. F: 56 ± 12 beats/min, p = 0.014, η 2 = 0.124), and NN50 (M: 177 ± 143 vs. F: 29 ± 17, p