Purpose. The aim of this study was to investigate the effect of circadian change of autonomic tone on heart rate turbulence (HRT) and variability (HRV) in patients with essential hypertension and matched controls.
Methods. In 25 essential hypertension patients (dippers) and matched 25 controls (mean age 54,83 +/- 1 years; 47,9% female) with at least 100 ventricular premature beats in 24-hour Holter monitoring, turbulence onset, turbulence slope, and heart rate variability parameters were calculated in 2 equal 12-hour periods during day and night.
Results. There were 15% and 13% with abnormal turbulence onset (TO) and turbulence slope (TS) values in patients. No circadian changes in TO values were found, while TS displayed significantly lower values during day than during night hours ((mean±std. err.) controls: 8.07±0.68, vs. 12.29±0.9 ms/RR, respectively; patients: 5.11±0.89, vs. 9.04±0.97 ms/beat, respectively; p <0.05). Absolute value of daytime TO was significantly lower in the patients with hypertension compared to controls. (-0.95±0.2l% vs. -1.92±0.37% p <0.05) and daytime levels of TS were higher in controls (p<0.01). Nighttime TO and TS values were not significantly different between the patients and controls. Spectral analysis showed that power in the high-frequency range (0.15 to 0.40 Hz) was lower among the hypertensive patients during night (269.1±50.5 ms2 vs. 689.9±33.04 ms2, p<0.01). Power in the low-frequency range (0.04 to 015 Hz) was higher among the hypertensive patients at day (1697.5±89.2 vs. 769.9±57.9, p<0.01) and at night (2499.3±94.4 vs. 1703.4±60.5, p<0.01). The group mean cosinor analysis and the acrophase-amplitude analysis demonstrated significant differences in circadian rhythm in pLF, pHF and LF between the group with essential hypertension and controls. In analysis the relationship between HRT and HRV parameters, TS has higher correlation with HRV than TO values.
Conclusions. Circadian change of TS values is more prominent than TO. Our findings indicate that hypertensive subjects were characterized with a decreased physiological circadian fluctuation on autonomic functions compared with controls.