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Patient-specific differences between blood pressure estimated from 24 h ambulatory measurements and serial office
1Stress Clinic, Heimdalsvägen 14, SE-756 52 Uppsala, Sweden. karel.pavek@telia.com
Insights
Serial self-measurements (SELF) of blood pressure are less reliable than 24-hour ambulatory monitoring (24 hAmb) due to significant patient-specific variations. While SELF can detect major changes, it is too uncertain for estimating true long-term blood pressure levels.
Area of Science:
- Cardiovascular Medicine
- Biomedical Engineering
- Clinical Diagnostics
Background:
- Accurate long-term blood pressure monitoring is crucial for cardiovascular health and clinical decisions.
- 24-hour ambulatory monitoring (24 hAmb) provides a reliable estimate of true blood pressure.
- Serial self-measurements (SELF) offer convenience but introduce uncertainty.
Purpose of the Study:
- To quantify the uncertainty in serial self-measurements (SELF) of blood pressure compared to 24-hour ambulatory monitoring (24 hAmb).
- To identify and separate the sources of variability in SELF blood pressure readings.
- To assess the reliability of SELF for estimating true long-term blood pressure.
Main Methods:
- Analysis of differences between SELF readings and reference 24 hAmb values from 72 recordings in 59 subjects.
- Replicated, at-random measurement sessions to isolate systematic and random variability.
- Comparison of repeatability and uncertainty intervals between SELF and 24 hAmb methods.
Main Results:
- Uncertainty in SELF arises from patient-specific systematic differences, method-specific systematic differences, and random variability.
- An initial alerting reaction impacts the first six SELF readings, increasing random variability.
- Patient-specific differences in SELF readings are persistent and cannot be reduced by averaging, contributing over +/-10 mmHg to uncertainty.
Conclusions:
- Averaged SELF readings show higher standard deviations for repeatability (50-100%) compared to 24 hAmb.
- SELF is suitable for detecting significant blood pressure trends but is unreliable for estimating precise long-term true blood pressure.
- 24 hAmb monitoring, with an uncertainty interval of +/-5 mmHg for two recordings, remains the gold standard for accurate long-term blood pressure assessment.
Abstract:
The long-term true blood pressure, estimated in terms of the repeatable 24 h ambulatory mean (24 hAmb) pressure, is probably best related to progressive cardiovascular deterioration and is vital for clinical decision-making. Serial self-measurements (SELF) under quiet conditions may reflect this level, but with an annoying uncertainty in individual patients. This uncertainty is characterized by analyzing differences between the SELF readings of seated/supine patients on their own and the reference 24 hAmb values based on 72 recordings. From at-random replicated sessions of 59 subjects, the sources of uncertainty can be separated into three components: a systematic (non-random) variable difference in level from person to person, a mean systematic difference in level between methods, and random variability determining repeatability between sessions. An unstable alerting reaction distorts about six initial self-recordings and increases the random variability. The following 7-12 or 13-24 'steady-state' values show a comparable random variability but reflect the 24 hAmb level only when compared as the average of all patients. The standard deviation for repeatability is about 50-100% higher for SELF than for 24 hAmb. The patient-specific difference between methods contributes more than +/-10 mmHg to the uncertainty interval of the SELF results. These patient-specific differences recur at repeat sessions and thus cannot be reduced by averaging the results of sequential SELF sessions. In contrast, two 24 hAmb results provide a 95% uncertainty interval of +/-5 mm Hg. Thus, the averaged results of multiple SELF sessions can be used to detect major changes in blood pressure but are, as a result of patient-specific differences, too unreliable when the value to be estimated (the true value) is the expected long-term value of 24 hAmb results.