Autonomic nervous function and blood volume monitoring during hemodialysis.

We studied the autonomic reflex response to hypovolemia during HD by means of spectral analysis of heart rate variability (SAHRV) in 10 hypotension prone (group A) and 10 hemodynamically stable patients (group B). UF rate normalized per total body water and blood volume fall were similar in the two groups. The sympatho-vagal balance index, calculated as the ratio between the integrals of the spectrum in the low (0.02-0.15 Hz) and in the high frequency range (0.2-0.35 Hz) rose in group B progressively from the beginning of the treatments, reaching a top at the 90th minute and remained subsequently high until the end. On the contrary this index did not show remarkable increases in group A. The differences between the two groups were statistically significant at 0 (4.6 +/- 2.9 vs 1.5 +/- 1.3), 60th (8.3 +/- 7.8 vs 2.2 +/- 2.6), 90th (17.9 +/- 13.4 vs 3.7 +/- 2.8), 150th (8.8 +/- 3.7 vs 2.7 +/- 2.8) and 210th minute (8.6 +/- 5.0 vs 2.9 +/- 2.5). In conclusion SAHRV shows an impairment of autonomic reflex response to hypovolemia in hypotension-prone patients.