Changes of cardiac function and autonomic nervous regulation after lower body negative pressure or physical exercise or joint training of both

AIM: To observe the changes of cardiac function and autonomic regulation after lower body negative pressure or physical exercise, or joint training of both, and to develop special anti-G endurance training programs. METHODS: Twenty-four healthy male subjects were randomly divided into three groups: physical exercise group (EX), lower body negative pressure group (LBNP) and lower body negative pressure plus physical exercise group (LBNP+EX). EX group conducted muscle exercise for two consecutive weeks for muscle-based explosive and static strength. LBNP group conducted -50 mmHg lower body negative pressure training for 10 min each day. LBNP+EX group conducted joint exercise of both EX and LBNP groups. Before and after training, cardiac pumping function, systolic function and heart rate variability testing were performed. RESULTS: After 10 days’ training, stroke volume (SV), cardiac output (CO) and cardiac index (CI) in LBNP+EX group were significantly higher than those before training (P<0.05), and total peripheral resistance (TPR) significantly decreased (P<0.05). No significant changes were observed in these parameters in EX or LBNP group. PEP/LVET (pre-ejection period /left ventricular ejection time) in LBNP+EX group was significantly lower than that before training. Heart rate variability analysis showed that LFn (low frequency of normalized) and LF/HF(low frequency/high frequency) of EX group significantly decreased (P<0.01), and HFn (high frequency of normalized) significantly increased as compared with that of pre-exercise (P<0.01). Compared with that of pre-exercise, LFn and LF/HF of LBNP group increased significantly (P<0.01). No significant difference was observed in these parameters in LBNP+EX group between pre- and post-training. CONCLUSION: Ten days’ joint training of LBNP and EX is more effective than LBNP training or physical exercise alone in improving cardiac pump and systolic function, and LBNP training alone could improve the sympathetic tone. The three different training programs may improve the anti-G endurance of convalescent pilots from different aspects.