Implications of alternative methods of computing blood pressure means.
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.
Glynn
LM
Department of Psychology, University of California, San Diego, California, USA.
Christenfeld
N
Gerin
W