Continuous, non-invasive volume-clamp blood pressure: determinants of performance

OBJECTIVE:To test a prototype hydraulic, non-invasive, continuous finger blood pressure monitor based on the volume-clamp principle for procedure-related factors likely to influence precision DESIGN:The influence of these factors was determined by repeatability of finger blood pressure measurement and the relationship to contralateral arm-cuff blood pressure METHODS:Repeated blood pressure measurements from three different fingers were made in 60 subjects following re-initialization of the device and re-insertion of the finger into the cuff. Repeatability was assessed in relation to simultaneous arm-cuff readings. Drift in arm-finger discrepancy was measured over a 1-h period. Finger diameter, drug therapy and presence of peripheral vascular disease were correlated with arm-finger blood pressure difference RESULTS:Repeatability coefficients (twice the SD of the arm-finger difference) across device re-initialization were large, but similar to parallel repeated arm blood pressure determinations17.6 and 17.1 mmHg for systolic blood pressure (SBP) and 13.9 and 13.6 mmHg for diastolic blood pressure (DBP), respectively. Withdrawing and re-inserting the finger reduced repeatability substantially, with a 50% increase in repeatability coefficient. A trend towards a progressive 9-mmHg increase was observed in overestimation of SBP over the 1-h period. Mean±SD pooled arm-finger blood pressure differences were -10.8 ±14.6 mmHg for SBP and 4.5±9.4mmHg for DBP. Blood pressure measured in different fingers was similar on average, with repeatability no poorer than for re-insertion of the same finger. The presence of peripheral vascular disease in 15 subjects correlated with a smaller arm-finger difference for DBP CONCLUSIONS:Variations in positioning of the finger within the cuff influences blood pressure measurement during volume-clamp plethysmography, reducing its precision. Finger SBP exceeds brachial auscultatory readings and has similar precision