COMPARISON OF CALIBRATION METHODS IN THE PRECISION OF A RING-TYPE CUFFLESS BLOOD PRESSURE MEASUREMENT DEVICE

Abstract

Objective: This study aimed to compare the efficacy of two calibration methods for a ring-type cuffless blood pressure (BP) measurement device, CART-I Plus, to assess if regular calibration with a traditional brachial arm cuff device enhances its precision. Design and method: The study involved 40 patients, with 28 completing the study. Participants underwent calibration in three different positions (sitting, standing, supine). Prior to the initial calibration, they were seated quietly for 3–5 minutes. Calibration was executed using a conventional brachial arm cuff device on the same arm. In each position, calibration was performed twice, separated by a minimum interval of one minute. A rest period exceeding two minutes was allowed between position changes for stabilization. BP estimates from the CART-I Plus, derived from photoplethysmography signals, were then compared with corresponding conventional 24-hour ambulatory BP monitoring (ABPM) measurements. Results: The mean differences between the CART-I Plus and ABPM, when calibrated using the sitting position alone (twice), were -2.12±8.53/2.36±7.82 mmHg (awake/sleep SBP) and -4.11±7.73/0.27±7.99 mmHg (awake/sleep DBP), respectively. When calibration included all three positions (six total calibrations), the mean differences remained similar; -2.14±8.95/2.17±8.53 mmHg (awake/sleep SBP) and -4.10±7.91/0.25±7.73 mmHg (awake/sleep DBP) (p > 0.5). Neither the standing nor the supine position, nor a combination of sitting and supine positions, significantly improved precision. In both standing and supine positions, the devices demonstrated a strong correlation for systolic blood pressure (SBP) (r=0.86 and r=0.90, respectively) and diastolic blood pressure (DBP) (r=0.90 for both), with all correlations being statistically significant (p < 0.001). Conclusions: Provided that patient stabilization is adequately ensured, and precise brachial BP measurements are taken by medical personnel, a single sitting position calibration appears to be sufficient. The addition of dynamic three-point calibration involving standing and supine positions did not significantly enhance precision.