EFFECT OF PROVOCATIVE MANEUVERS ON HEART-RATE-VARIABILITY IN SUBJECTSWITH QUADRIPLEGIA

This study investigated heart rate variability (HRV) in individuals wi th quadriplegia who have disruption of autonomic control of the heart. Seven male subjects with neurological complete quadriplegia and seven with incomplete quadriplegia were studied at rest and during provocat ion. HRV was measured by power spectral analysis using a fast Fourier transform. Two spectral components were generated: 1) the high-frequen cy (HF) peak, a reflection of parasympathetic activity, and 2) the low -frequency (LF) peak, primarily sympathetic activity with some parasym pathetic input. Results of the provocative maneuvers were grouped into one composite variable. Significant differences in the LF spectral co mponent were found between the groups with complete and incomplete les ions in the supine position and after provocation (LF supine: P = 0.01 ; LF provocation: P = 0.002). After provocation, significant differenc es were demonstrated in the HF spectral component between these groups (P = 0.005). In contrast to previous findings, a LF component in subj ects with complete quadriplegia was observed; this LF component decrea sed after provocation, suggesting the parasympathetic component withdr ew during stressful maneuvers. There also appeared to be general downr egulation of parasympathetic activity to the heart in subjects with co mplete quadriplegia. The presence of an increased LF spectral componen t during provocation in those with incomplete lesions implies sympathe tic stimulation of the heart and may be used as a marker of sympatheti c activity in individuals with quadriplegia.