Higher heart rate increments on head-up tilt in control subjects are not associated with autonomic dysfunction

To determine whether there is altered autonomic function associated with elevated heart rate increments on head-up tilt (HUT) in younger individuals.

A total of 149 subjects were enrolled in this study. Subjects underwent the autonomic reflex screen including HUT and completed the Autonomic Symptom Profile.

Heart rate increment on HUT did not show a correlation with Composite Autonomic Severity Score (CASS) and the individual CASS scores were low (score 0/10, n=103; score 1/10, n=27; score 2/10, n=1; score 3/10, n=2). There was no correlation with multiple autonomic domains assessed by the Autonomic Symptom Profile. However, there were significant inverse correlations between heart rate increment and total COMPASS score including male sexual dysfunction (r=-0.318; p=0.011; n=64), bladder (r=-0.209; p=0.014; n=138), pupillomotor (r=-0.235; p=0.006; n=138) and male sexual dysfunction (r=-0.554; p<0.0001; n=64). These domains showed a positive correlation with age and a significant effect of age but not heart rate increment with regression analysis (except pupillomotor domain).

These results argue against a reduction in autonomic function underlying the higher heart rate increments seen on HUT in younger individuals.

These findings argue that the development of Postural Tachycardia Syndrome involves mechanisms that potentially occur independently of heart rate increment.