Effects of paraplegia on cardiac autonomic regulation during static exercise

OBJECTIVES: The aim of this study was to examine whether autonomic modulation of heart rate as measured by heart rate variability and heart rate complexity at rest and during static handgrip exercise differs between individuals with and without paraplegia. This study also examined the relationships between heart rate complexity and heart rate variability parameters. Design: Heart rate variability and complexity were evaluated in 20 individuals with paraplegia and in 20 individuals without paraplegia during 3 mins of rest and 2 mins of static handgrip exercise at 30% of maximum isometric strength. Spectral decomposition of heart rate variability was used to obtain total power, power in low-frequency and high-frequency ranges, and the ratio of low- to high-frequency power. Heart rate complexity was quantified with sample entropy, a measure of irregularity of the beat-to-beat time series. Results: Sample entropy was lower (P < 0.05) at rest and during exercise in participants with paraplegia. Total, high-, and low-frequency powers as well as the ratio of low- to high-frequency power did not differ between groups. Sample entropy did not significantly correlate with low- and high-frequency powers or their ratio. Conclusions: Individuals with paraplegia show lower heart rate complexity at rest and during static exercise. This finding may have implications for cardiovascular morbidity in persons with paraplegia. Heart rate complexity may provide unique information regarding cardiac autonomic modulation, different from that provided by traditional heart rate variability measures.