Orthostatic influence on heart rate and blood pressure variability in trained persons with tetraplegia.

To examine the orthostatic influence on heart rate and blood pressure variability in persons with tetraplegia playing wheelchair basketball, ten trained persons with tetraplegia, ten untrained persons with tetraplegia, and ten able-bodied participated in this study. Spectrum analysis of the ECG R-R interval and blood-pressure on a beat-by-beat basis during head-up tilt 60 degrees sitting were performed. The ratio of the high frequency to total frequency (HF/TF) in the R-R interval decreased from supine (0.5 +/- 0.2) to sitting (0.3 +/- 0.2), and the low frequency (LF) power in systolic blood pressure increased from 4.7 +/- 9.1 to 15.0 +/- 13.1 mmHg(2) only in the untrained persons with tetraplegia (P < 0.01). The decrease in the HF/TF ratio in the untrained persons with tetraplegia indicates attenuated parasympathetic activity to the orthostatic challenge and the similar increase in LF power indicate that parasympathetic activity was reduced and sympathetic activity increased only in these persons. These results suggest that training enhances cardiovascular stability in tetraplegic subjects.