Impaired sympathetic response before intradialytic hypotension: a study based on spectral analysis of heart rate and pressure variability

The purpose of this study was to evaluate the autonomic response to standard haemodialysis and the changes associated with the onset of intradialytic hypotension in 12 normotensive patients with uraemia. Power spectra of R–R interval and of blood pressure fluctuations were obtained during a standard dialysis session and estimated in the low-frequency (LF, 30–150 ;mHz) and high-frequency (HF, 150–400 ;mHz) range. The absolute power of the LF component of blood pressure variations and the LF/HF ratio of R–R interval were assumed as indexes of sympathetic activity. Standard haemodialysis induced hypotension in six patients (unstable) while a minor pressure decline was present in the other six (stable). Normalized blood volume before dialysis and percentage volume reduction were similar in the two groups. Tachycardia in response to pressure and volume decrease was more pronounced in stable than in unstable patients, as evidenced by a higher slope of the relation between R–R interval and systolic blood pressure (7.9 versus 0.9 ;ms/mmHg, P 2 and +7.2±2 ;mmHg 2 for absolute LF power of diastolic and of systolic blood pressure respectively, P 2 and -8.6±4.0 ;mmHg 2 for absolute LF power of diastolic and of systolic blood pressure respectively, P 2 and +13.3±6.2 ;mmHg 2 for LF of diastolic and of systolic blood pressure, P