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Published on: May 3, 2018
Implications of alternative methods of computing blood pressure means
1Department of Psychology, University of California, San Diego, California, USA.
Insights
Calculating mean blood pressure differs based on weighting time intervals versus heartbeats. Pulse-based averaging yields higher blood pressure means during high variability, emphasizing the need for researchers to specify their method.
Area of Science:
- Cardiovascular Physiology
- Biostatistics
Background:
- Traditional blood pressure measurement involves averaging over a period.
- Two methods exist: time-interval weighting and heartbeat weighting.
- These methods yield different results when cardiovascular levels vary significantly.
Purpose of the Study:
- To illustrate the difference between time-based and pulse-based mean blood pressure calculations.
- To highlight the impact of cardiovascular variability on mean blood pressure results.
Main Methods:
- Continuous monitoring of heart rate and blood pressure using the Finapres 2300.
- Calculation of mean blood pressure using both time-interval and heartbeat-weighting methods.
- Analysis during two distinct episodes with varying cardiovascular stability.
Main Results:
- During high heart rate and blood pressure variability, pulse-based means were substantially higher than time-based means.
- During stable cardiovascular episodes, both methods produced identical mean blood pressure results.
- Significant differences in calculated mean systolic and diastolic blood pressure were observed with pulse-based methods during variability.
Conclusions:
- The choice of averaging method (time-based vs. pulse-based) significantly impacts mean blood pressure values, especially during periods of high cardiovascular variability.
- Theoretical justifications exist for both calculation methods.
- Researchers must clearly state their chosen method when reporting blood pressure findings to ensure clarity and reproducibility.
Abstract:
BACKGROUND: Blood pressure measures are traditionally averaged to compute a level across a period. There are, however, two ways of calculating such means: by assigning equal weights to each time interval or to each heartbeat. The former method is used commonly with intermittent measures, the latter with continuous measurements, though either can be calculated with either monitoring technique. For periods during which there is substantial variability in the cardiovascular levels, and in which the pulse is correlated with the blood pressure, the two techniques will produce different results. METHODS: We illustrated the difference between the two techniques by calculating mean blood pressure levels during two episodes, with the heart rate and blood pressure monitored continuously using the Finapres 2300 blood pressure monitor. RESULTS: During the first episode, there was dramatic variability in heart rate and blood pressure. The pulse-based calculations, which give greater weight to the periods during which the pulse is elevated, gave means for the systolic and diastolic blood pressures substantially higher than those obtained using time-based methods. During the second episode, both the heart rate and the blood pressure were stable, and we observed no difference between the results from the two methods of calculating the means. CONCLUSIONS: Because there are theoretical justifications for both methods of computation, and they can produce different results, it is important that researchers attend to the difference, and describe the technique used when presenting results.
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