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Circadian variation of hemodynamics and baroreflex functions in patients with essential hypertension
O Tochikubo1, Y Kawano, E Miyajima
1Second Department of Internal Medicine, Urafune Hospital of Yokohama City University, Japan.
Insights
Cardiovascular events often happen in the morning. This study reveals that morning hemodynamic imbalances, including increased vascular resistance and reduced baroreflex sensitivity, may contribute to these risks in hypertensive patients.
Area of Science:
- Cardiology
- Chronobiology
- Hypertension Research
Background:
- Cardiovascular events like myocardial infarction show a diurnal pattern, frequently occurring in the morning.
- The precise mechanisms triggering these morning cardiovascular events remain unclear.
- Understanding circadian variations in hemodynamic and baroreflex functions is crucial for explaining morning event incidence.
Purpose of the Study:
- To investigate the circadian variations of hemodynamic parameters and baroreflex sensitivity in patients with essential hypertension.
- To identify potential triggering mechanisms for morning cardiovascular events by analyzing 24-hour physiological data.
Main Methods:
- Twenty-three patients with essential hypertension underwent 24-hour ambulatory monitoring of direct blood pressure (BP) and ECG.
- Cardiac output (CO) and total peripheral vascular resistance (TPR) were measured using the pulse-contour method.
- Power spectral analysis of RR-interval (LF/HF ratio) and baroreflex sensitivity index (BRI) were calculated. Circadian variations of hematocrit (Ht) were also assessed.
Main Results:
- Maximum values for BP and CO were observed in the evening, while maximum TPR and LF/HF occurred in the early morning (06:30-08:00).
- The minimum baroreflex sensitivity index (BRI) was recorded at 08:00.
- Positive load component (PC), related to cardiovascular function, peaked in the late morning, while negative load component (NC), related to baroreflex function, reached its minimum at the same time. Hematocrit (Ht) was highest upon waking.
Conclusions:
- Significant circadian variations exist in hemodynamic and baroreflex functions in hypertensive patients.
- The observed morning pattern of increased TPR, elevated LF/HF ratio, and reduced BRI, alongside peak Ht after waking, suggests a prothrombotic and hypertensive state.
- These hemodynamic imbalances occurring in the morning may contribute to the increased risk of cardiovascular events, such as myocardial infarction, during this period.
Abstract:
It is well known that cardiovascular accidents such as myocardial infarction frequently occur in the morning, but their triggering mechanisms are not clear. The present study investigated circadian variations of hemodynamics and baroreflex functions. Twenty-three patients with essential hypertension were studied. Direct blood pressure (BP) and ECG were recorded by telemeter over 24 h, and then computer-analyzed. The pulse-contour method was used to measure cardiac output (CO) and total peripheral vascular resistance (TPR). The ratio of low to high frequency components (LF/HF) of the RR-interval on ECG was calculated by power spectral analysis. The baroreflex sensitivity index (BRI) was measured on the basis of the ratio delta RR/delta Ps (delta Ps = spontaneous decrease in systolic BP, delta RR = change in RR). Furthermore, 24-h BP changes were transformed algebraically into positive load component (PC) and negative load component (NC) by using a Windkessel model. The circadian variation of hematocrit (Ht) was also measured. The least squares method was used to determine the time at which the maximum and minimum value of each measurement occurred. Whereas the maximum values for BP and CO occurred in the evening (18:30, 17:00), the maximum values for TPR and LF/HF occurred between 06:30 and 08:00, and the minimum value for BRI occurred at 08:00. PC significantly correlated with Ps, heart rate, and CO (r = 0.81, 0.92, 0.67), and NC significantly correlated with BRI and LF/HF (r = 0.71, 0.64). PC (related to cardiovascular function) reached a maximum and NC (related to baroreflex function) reached a minimum in the late morning (11:00). Ht was highest immediately after the subjects got out of bed. These hemodynamic imbalances may negatively influence coronary blood flow in the morning.