POWER SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY IN OBESE SUBJECTS -EVIDENCE OF DECREASED CARDIAC SYMPATHETIC RESPONSIVENESS

OBJECTIVE: To investigate changes in sympathetic nervous system functi on in obesity. DESIGN: Cross-sectional clinical study. SUBJECTS: 18 mi ddle-aged obese patients 143-55 years, BMI>33 kg/m(2)) and 26 age- and sex-matched normal-weight controls (44-56 years, BMI<26 kg/m(2)). MEA SUREMENTS: Post-synaptic sympathetic response studied by power spectra l analysis of heart rate variability at rest and during sympathetic st imulus obtained through passive head-up tilt. Spectral analysis compri sed two frequency domain components: high-frequency power (HF), reflec ting parasympathetic activity and low-frequency power (LF), in particu lar the LF:HF ratio, reflecting sympathetic function. Pre-synaptic sym patho-adrenal function was assessed by measurement of 8.00 am plasma n oradrenaline. RESULTS: Obese patients had significantly lower spectral indexes of sympathetic response and higher spectral markers of parasy mpathetic activity than nonobese subjects both at rest (25.9+/-3.5 vs 38.6+/-1.7 LF NUs, P<0.001) and after tilt (0.98+/-0.40 vs 2.30+/-0.39 LF:HF, P<0.05; 62.7+/-6.9 vs 41.1+/-4.9 HF NUs, P<0.05). By contrast, the obese subjects had higher noradrenaline levels (289.32+/-7.40 vs 159.80+/-19.20 pg/ml, P<0.001). No relation was found between these ne uroautonomic indexes and body mass index. CONCLUSION: Obese subjects s eem to have increased pre-synaptic sympatho-adrenal function but a dep ressed endorgan cardiovascular response.