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Absence of sympathetic overactivity in Afro-Caribbean hypertensive subjects studied by heart rate variability
1Centro Ricerche Cardiovascolari, CNR, Medicina Interna II, Ospedale 'L. Sacco', Dipartimento Scienze Precliniche L.I.T.A. Vialba, Universita' Studi di Milano, Italy.
Insights
Black hypertensives show reduced cardiac sympathetic activity compared to white hypertensives. This study analyzed heart rate variability (HRV) in 52 untreated patients, finding lower sympathetic markers in Black individuals, suggesting racial differences in cardiac autonomic function.
Area of Science:
- Cardiology
- Autonomic Nervous System Research
- Hypertension Studies
Background:
- Black hypertensives exhibit higher rates of left ventricular hypertrophy and mortality than white hypertensives.
- Racial disparities in hypertension outcomes may be linked to differences in sympathetic nervous system activity.
- Previous research has not consistently shown increased cardiac sympathetic activity in Black individuals.
Purpose of the Study:
- To investigate cardiac sympatho-vagal balance in Black and white essential hypertensive patients.
- To analyze 24-hour heart rate variability (HRV) to assess racial differences in cardiac autonomic modulation.
- To determine if race is an independent predictor of cardiac sympathetic activity in hypertension.
Main Methods:
- Analysis of 24-hour Holter recordings from 52 treatment-naive essential hypertensive patients (26 Black, 26 white).
- Time and frequency domain analysis of heart rate variability (HRV) using consecutive beat series.
- Calculation of low frequency spectral component (LF power) and LF/HF ratio as markers of cardiac sympathetic modulation and sympatho-vagal balance.
Main Results:
- Black hypertensives demonstrated significantly lower mean 24-hour normalized LF power (a marker of sympathetic modulation) compared to white hypertensives (40.0 ± 2.1 vs. 53.6 ± 3.6 nu, P < 0.01).
- The LF/HF ratio, an index of sympatho-vagal balance, was also significantly lower in Black patients (4.11 ± 0.58 vs. 5.98 ± 0.79, P < 0.05).
- Multiple regression analysis identified race and age as independent predictors of normalized LF power and LF/HF ratio.
Conclusions:
- The findings suggest a blunted cardiac sympathetic neural modulation in Black hypertensives compared to white hypertensives over a 24-hour period.
- These differences in cardiac autonomic function may contribute to observed racial disparities in hypertension-related cardiovascular outcomes.
- Further research is warranted to elucidate the mechanisms underlying these racial differences in cardiac sympathetic activity.
Abstract:
Black hypertensives present a greater prevalence of left ventricular hypertrophy and an increased mortality compared to white hypertensives. Differences in sympathetic activity might contribute to explain these racial differences in hypertension. Nevertheless, previous laboratory studies did not show any increase of sympathetic activity direct to the heart in black subjects. The aim of the present study was to investigate the cardiac sympatho-vagal balance in black and white hypertensives analysing heart rate variability, during the entire 24 h. We analysed Holter recordings of 52 essential hypertensive patients, who had never received antihypertensive treatment, 26 of whom were black and 26 were white. Consecutive series of 300 beats, with 150 beats overlapped (approximately 600 series/day), were considered for the analysis in time and frequency domain. The mean 24-h value of the power of the low frequency spectral component (0.04-0.15 Hz), expressed in normalised units, ie a marker of sympathetic modulation, was significantly lower in the group of black patients compared to whites (respectively 40.0 +/- 2.1 vs 53.6 +/- 3.6 nu, P < 0.01). Similar results were observed for the LF/HF ratio, an index of the sympatho-vagal balance (respectively 4.11 +/- 0.58 vs 5.98 +/- 0.79; P < 0.05). In a multiple linear regression analysis, considering diastolic blood pressure, left ventricular mass index, race and age as independent variables, only race (P < 0.002) and age (P < 0.01) could independently predict the normalised low frequency power or the LF/HF ratio, as dependent variables. The results of this study suggest some blunting of the cardiac sympathetic neural modulation in black hypertensives compared to white hypertensives, during the entire 24 h.