CARDIAC AUTONOMIC MECHANISM UNDERLYING THE ATTENUATION OF HEART RATE RESPONSE TO HEAD-UP TILT WITH LOWER-BODY COMPRESSION IN HEALTHY ADULTS

K. Oyake¹, M. Katai², A. Yoneyama³, H. Ikegawa¹, S. Kani¹, K. Momose¹

¹Shinshu University, Department of Physical Therapy, Matsumoto, Japan, ²Toyama Prefectural Central Hospital, Department of Rehabilitation, Toyama, Japan, ³Fujimi Kogen Medical Center, Department of Rehabilitation, Fujimi, Japan

Background: Postural tachycardia syndrome is the most common form of orthostatic intolerance in young people. Lower-body compression has been shown to prevent an excessive increase in heart rate during head-up tilt (HUT) in individuals with postural tachycardia syndrome. Cardiac autonomic function is a major determinant of heart rate, which can be assessed by heart rate variability. However, to our knowledge, the cardiac autonomic mechanism underlying the attenuation of heart rate response to HUT with lower-body compression has not been reported.

Purpose: This study aimed to investigate autonomic activity associated with the attenuation of heart rate response to HUT with lower-body compression using heart rate variability analysis in healthy adults.

Methods: A total of 28 healthy volunteers (20 females, aged 20.6 ± 1.0 years) underwent 2 HUT tests, with and without an inflatable abdominal band (40 ± 5 mmHg pressure on the abdominal wall) and a medical compression stocking (40 ± 5 mmHg pressure at the ankle) in a randomized-crossover design with a 10-min washout period between the tests. The HUT test protocol consisted of 5-min supine rest and 10-min 70 degrees HUT. During each test, R-R intervals were continuously recorded using a portable electrocardiograph. Supine heart rate was calculated by taking the overall mean of the 5-min supine rest. Heart rate during each minute of HUT was calculated by averaging 60 s intervals of heart rate. Maximum heart rate during HUT was taken from the minute with the highest average heart rate during the last 5 min of 10 min of tilting. Heart rate variability parameters were analyzed from 5 min intervals selected during supine rest and the last 5 min of 10 min of tilting. The stress index (SI) and the root mean square of successive R-R interval differences (RMSSD) were calculated to assess sympathetic and parasympathetic activities of the heart, respectively.

Results: Heart rate (65.0 ± 9.8 vs. 64.6 ± 10.0 bpm), SI (10.1 ± 4.0 vs. 9.5 ± 3.5), and RMSSD (58.9 ± 36.0 vs. 59.7 ± 32.7 ms) in the supine position were not significantly different between with and without compression. During HUT, maximum heart rate (78.1 ± 12.5 vs. 88.0 ± 13.5 bpm) and SI (15.9 ± 5.8 vs. 19.4 ± 6.2 %/s²) were significantly lower with than without compression, while RMSSD (26.0 ± 11.5 vs. 15.7 ± 6.7 ms) was significantly higher with than without compression. A significant correlation was observed between the decreases in maximum heart rate (-9.9 ± 4.4 bpm) and SI (-3.5 ± 6.3 %/s) with compression during HUT (r = 0.52, 95% confidence interval: 0.19–0.75). However, there was no significant correlation between the changes in maximum heart rate and RMSSD (10.3 ± 10.3 ms) with compression during HUT (r = -0.37, 95% confidence interval: -0.65–0.01).

Conclusions: The decreased cardiac sympathetic activity may be associated with the attenuation of heart rate response to HUT with lower-body compression in healthy adults.

Implications: The findings provide insights into the autonomic mechanism underlying the attenuation of orthostatic tachycardia with lower-body compression.

Funding acknowledgements: This study was supported by JSPS KAKENHI (JP21K17489) and by the fund of Nagano Prefecture to promote scientific activity (NPS2022308).

Keywords:
Autonomic nervous system
Compression therapy
Postural tachycardia syndrome

Topics:
Neurology
Cardiorespiratory

Did this work require ethics approval? Yes

Institution: Shinshu University

Committee: The Ethics Committee of Shinshu University

Ethics number: 5254