Accuracy of ambulatory blood pressure monitoring in four exercise situations

Although ambulatory blood pressure monitoring (ABPM) is still considered in its investigational stage, the technique has become increasingly popular in recent years. The rationale for its utilization is its ability to continuously monitor blood pressure (BP) response to situational stressors occurring over the course of a 24-hour period which cannot be detected by casual measurements. In addition, ABPM eliminates the so-called white-coat auscultatory BP response. However, the accuracy of ABPM under situations which are at the measurement limits of the technical characteristics and/or capabilities of the ABPM equipment, such as in exercise situations commensurate with daily life activities, has not been fully documented. The purpose of this study was to evaluate the accuracy of the Spacelabs ABPM monitor against auscultatory (AUS) determinations in four exercise situations: walking, stair climbing, cycling and a progressive step test (modified Canadian Aerobic Fitness Test). Analyses of variance (ANOVA) were computed to determine if significant differences occurred between ABPM and AUS measurements for systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) over the resting and four exercise conditions. Results indicate that, particularly at low to moderate levels of exercise intensity, there is no statistically significant difference between ABPM and AUS measurements for SBP and HR. In 20 of the 26 resting and exercise determinations, the difference in SBP was less than 6 mmHg. For HR the variation was no greater than 4 bpm. However, there was no such agreement between ABPM and AUS measurements for DBP. As the intensity of the exercise situations increased, there was a tendency for SBP ABPM measurements to register higher readings than those obtained by AUS. The major drawback in ABPM is its sensitivity to artifacts due to arm movement. It was concluded that ABPM, such as provided by the Spacelabs instrument, can provide reasonably accurate readings of SBP and HR, particularly at low to moderate intensities of exercise while at higher exercise intensities ABPM has a tendency to provide consistently lower SBP values than the AUS measurements. DBP ABPM was totally ineffective under any of the exercise conditions chosen for this study.