Autonomic Response Latency Revisited: Assessment of Repeatability in Healthy Subjects.

Background: Autonomic function assessment provides valuable information regarding the status of the autonomic nervous system. The time lag between the onset of orthostasis and the peak/nadir of heart rate response is a surrogate of the integrity of underlying autonomic neural pathways. Autonomic response latency (ARL) is a relatively novel yet underreported parameter in this context. Test-retest repeatability of this parameter has not been evaluated previously. Materials and Methods: We recruited 31 healthy adults (17 males and 14 females; 29.00 ± 5.44 years) and subjected them to postural challenge tests on five instances - forenoon and afternoon of day 1, the next day, 1 week later, and 1 month later. Tachycardia and bradycardia latencies (TL and BL) were computed using heart rate derived from digital ECG data. Repeatability was assessed using the intraclass correlation coefficient (ICC) and coefficient of variation (CoV). Results: ICCs for TL and BL were 0.69 (0.56, 0.82) and 0.77 (0.66, 0.87), respectively. The CoVs for TL and BL were 14.8% and 12.4%, respectively. Sex-based subgroup analysis revealed ICCs for TL and BL in males to be 0.71 (0.53, 0.86) and 0.74 (0.57, 0.88) and in females to be 0.68 (0.64, 0.86) and 0.82 (0.66, 0.93), respectively. CoVs for TL and BL were 14.4% and 13.8% in male subjects and 15.4% and 10.7% in female subjects, respectively. Conclusion: ARL to orthostatic challenge demonstrated moderate to good test-retest repeatability. Based on our observations, we propose that ARL has potential as a consistent and repeatable index for the assessment of the integrity of autonomic neural pathways and therefore can help in the diagnosis of autonomic neuropathy.