Effects of physical fitness level on cardiac autonomic activity and baroreflex function after maximal lower body negative pressure
Rina Suzuki, Kazukuni Hirabuki, Noritaka Hata, Marina Fukuie, Tomoya Suda, Takahiro Uechi, Shinya Matsushima, Ai Hirasawa, Jun Sugawara, Takeaki Matsuda, Shigeki ShibataAbstract
Introduction
This study evaluated cardiac autonomic activity and arterial‐cardiac baroreflex function before and after severe orthostatic stress induced by lower body negative pressure (LBNP) in healthy sedentary men and endurance athletes.
Methods
Thirteen healthy sedentary men (Sed) and nine age‐matched highly trained male endurance athletes (Fit) were recruited. Participants underwent a single maximal LBNP protocol, with negative pressure increased to −15, −30, and −40 mmHg every 5 min, followed by additional −10 mmHg increments every 3 min until presyncope. RR interval and systolic blood pressure were recorded for 5 min during controlled breathing at 0.2 Hz before and after recovery from maximal LBNP.
Results
Heart rate was lower in Fit than in Sed, with no significant pre‐to‐post change after LBNP. Low‐frequency transfer function gain between systolic blood pressure and RR interval showed a significant group‐by‐time interaction, increasing in Sed (5.9 ± 1.8 to 8.0 ± 1.4 ms/mmHg) but decreasing in Fit (12.2 ± 7.5 to 9.7 ± 5.2 ms/mmHg). Low‐frequency RR interval variability also showed a significant interaction, increasing in Sed and decreasing in Fit, whereas high‐frequency RR interval variability showed a similar but non‐significant pattern.
Discussion
Severe orthostatic stress induced by maximal LBNP enhanced arterial‐cardiac baroreflex gain in sedentary men but decreased it in endurance athletes. This response may be associated with enhanced vagally mediated cardiac modulation in sedentary individuals.