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Calculation of mean arterial pressure during exercise as a function of heart rate
1Heller Institute of Medical Research, Sheba Medical Center, Tel Hashomer.
Insights
This study reveals that the systolic period fraction changes with heart rate during exercise. A new formula accurately calculates mean arterial blood pressure (MAP) by adjusting for this systolic fraction, improving accuracy during physical exertion.
Area of Science:
- Cardiovascular Physiology
- Exercise Physiology
- Biomedical Engineering
Background:
- Mean arterial blood pressure (MAP) assessment commonly assumes a fixed systolic proportion of the cardiac cycle.
- This assumption is inaccurate during exercise due to heart rate (HR) changes affecting ejection and filling times.
- Variable systolic/diastolic proportions at different heart rates can lead to misleading MAP evaluations.
Purpose of the Study:
- To determine the accurate systolic period fraction of the cardiac cycle across varying metabolic rates.
- To develop a method for calculating MAP that accounts for HR-dependent systolic fraction changes.
- To improve the precision of cardiovascular parameter assessment during exercise.
Main Methods:
- Twenty healthy subjects performed graded exercise on a cycle ergometer, achieving heart rates from 55-180 bpm.
- Doppler echocardiography recorded mitral and aortic flow velocity waveforms.
- Blood pressure was measured using a sphygmomanometer.
Main Results:
- A mathematical model was derived: Systolic fraction (St) = 0.01exp(4.14-40.74/HR).
- Mean arterial blood pressure (MAP) was calculated as: MAP = diastolic blood pressure + St * pulse pressure.
- The proposed model demonstrated reduced errors in evaluating arterial pressure-related parameters.
Conclusions:
- The systolic period fraction is not constant and varies significantly with heart rate.
- The developed formula provides a more accurate MAP calculation during exercise by incorporating HR-dependent systolic fraction.
- This approach enhances the evaluation of cardiovascular parameters like peripheral resistance, particularly under exercise-heat stress conditions.
Abstract:
Mean arterial blood pressure (MAP) is a common characteristic of the cardiac cycle. Usually it is evaluated by assuming that the left ventricular ejection time (systole) constitutes a constant proportion of the cardiac cycle (i.e. 1/3), regardless of the heart rate (HR). However, elevation of HR during exercise results in a reduction of the duration of the ejection period and even a greater reduction of the ventricular filling period. Therefore, a constant diastole/systole proportion at various heart rates may be misleading. The purpose of this study was therefore to evaluate the accurate proportion of the systolic period from the cardiac cycle at different metabolic rates and calculate MAP accordingly. Twenty healthy subjects (age: 20-50 yr.) exercised at different work intensities on a cycle ergometer to elicit HR in the range of 55-180 bpm. During the ride the mitral and aortic flow velocity wave form were recorded by Doppler echocardiography; the mitral flow from the apical view and the aortic flow from the apical long axis view. Blood pressure was measured using a sphygmomanometer. The fraction of systole (St) from the heart cycle was related to HR and was described in mathematical terms as: St = 0.01exp(4.14-40.74/HR) MAP was then calculated from the diastolic blood pressure (dBP) and the pulse pressure (PP) adjusted for St as follows: MAP = dBP+St.PP; (mmHg) The use of the suggested model reduces errors in the evaluation of various cardiac parameters which are related to arterial pressure, such as peripheral resistance, especially under exercise-heat stress.