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Circadian variation of haemodynamics in patients with essential hypertension: comparison between early morning and
Y Kawano1, O Tochikubo, K Minamisawa
1Second Department of Internal Medicine, Yokohama City University School of Medicine, Urafune Hospital, Japan.
Insights
Morning cardiovascular events may be linked to increased sympathetic nervous activity and vascular resistance. These hemodynamic changes, including higher peripheral resistance and lower cardiac output, may stress the cardiovascular system.
Area of Science:
- Cardiovascular Physiology
- Chronobiology
- Hypertension Research
Background:
- Increased incidence of cardiovascular accidents reported in the morning.
- The underlying physiological mechanisms remain unclear.
Purpose of the Study:
- To investigate the 24-hour hemodynamic variations.
- To focus on specific hemodynamic changes occurring in the morning.
Main Methods:
- 24-hour direct blood pressure and ECG monitoring via telemetry in 21 untreated essential hypertension patients.
- Cardiac output measured using dye-dilution (morning, evening, sleep).
- Beat-to-beat cardiac output, total peripheral resistance, and low- to high-frequency ratio analyzed via power spectral analysis of R-R intervals.
Main Results:
- Significant increase in systolic and diastolic blood pressure in the early morning.
- Higher total peripheral resistance and low- to high-frequency ratio in the morning compared to the evening.
- Lower cardiac output observed in the morning.
Conclusions:
- Sympathetic nervous activity and vascular resistance appear elevated in the morning.
- These morning hemodynamic shifts may pose a risk to the cardiovascular system.
Objective:
An increased incidence of cardiovascular accidents in the morning has been reported, but the reason why is not clear. We measured 24-h haemodynamics and focused on its change in the morning.
Design:
To study the circadian variation of haemodynamics, we recorded 24-h direct blood pressure and electrocardiogram using a telemetry method, in 21 untreated inpatients with essential hypertension, and measured cardiac output using the dye-dilution method in the morning, in the evening and during sleep. We also determined the beat-to-beat cardiac output (using the pulse-contour method), the total peripheral resistance and the ratio of low- to high-frequency components (using power spectral analysis of the R-R interval during 24 h), and made comparisons between morning and evening values.
Results:
Both systolic and diastolic blood pressure increased rapidly in the early morning. Although the comparison of blood pressure between morning and evening showed no difference, total peripheral resistance and low- to high-frequency ratio were significantly higher in the morning than in the evening, but cardiac output was lower in the morning.
Conclusions:
Sympathetic nervous activity and vascular resistance seem to be higher in the morning than in the evening, and these haemodynamic changes may stress the cardiovascular system.