ASSESSMENT OF AUTONOMIC FUNCTION IN TRAUMATIC QUADRIPLEGIC AND PARAPLEGIC PATIENTS BY SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY

We analyzed by means of autoregressive spectral analysis the spontaneo us beat-to-beat heart rate variability (HRV) of quadriplegic and parap legic male subjects at rest in the supine position. In agreement with our previous study, in nine of 15 quadriplegic patients only the high- frequency (HF: center frequency = respiratory frequency) component (a marker of vagal modulation of heart rate) was observed. In contrast, i n six of the quadriplegic patients both the KF component and the low-f requency (LF: center frequency at approx. 0.1 Hz, 0.03-0.15 Hz in this study) component (a marker of sympathetic and vagal modulation of hea rt rate) were observed. However, in six quadriplegic patients who pres ented the LF component, (i) the center frequency of the LF component w as lower than that in 10 healthy, sedentary, age-matched males (contro l I) (P < 0.01), (ii) the power of the HF component was smaller than t hat in the control-I group (P < 0.01) and (iii) the LF/HF power ratio (an index of sympathovagal balance) was larger than that in the contro l-I group (P < 0.05). On the other hand, in nine paraplegic patients w ith an intact 1st-4th thoracic spinal cord, from which the cardiac sym pathetic nerves originate, the total power, the power of the LF compon ent and that of the HF component were smaller than those in nine healt hy, sedentary, age-matched males (control II) (P < 0.05, P < 0.01 and P < 0.01, respectively). These results suggest that (i) in quadriplegi c patients who presented the LF component, the physiological mechanism of the LF component may be different from that in the control-I subje cts (e.g., contribution of spinal sympathetic nervous system), (ii) in paraplegic patients having both the intact cardiac sympathetic nerves and the intact vagal cardiac nerves, the dysfunction of the sympathet ic nerves to the vessels below the level of the lesion and/or the comp ensatory vagal suppression may contribute in part to the low HRV and ( iii) it is possible that in some clinical pathophysiological condition s the dysfunction of the sympathetic nerves to the vessels and/or the compensatory vagal suppression may affect the HRV. Therefore, one must give careful consideration to the definition (e.g., center frequency) and interpretation of the LF component and to the interpretation of r esults when analyzing the HRV in humans by means of power spectral ana lysis.