CONTINUOUS, NONINVASIVE VOLUME-CLAMP BLOOD-PRESSURE - DETERMINANTS OFPERFORMANCE

Objective: To test a prototype hydraulic, non-invasive, continuous fin ger blood pressure monitor based on the volume-clamp principle for pro cedure-related factors likely to influence precision. Design: The infl uence of these factors was determined by repeatability of finger blood pressure measurement and the relationship to contralateral arm-cuff b lood pressure. Methods: Repeated blood pressure measurements from thre e different fingers were made in 60 subjects following re-initializati on of the device and re-insertion of the finger into the cuff. Repeata bility was assessed in relation to simultaneous arm-cuff readings. Dri ft in arm-finger discrepancy was measured over a 1-h period. Finger di ameter, drug therapy and presence of peripheral vascular disease were correlated with arm-finger blood pressure difference. Results: Repeata bility coefficients (twice the SD of the arm-finger difference) across device re-initialization were large, but similar to parallel repeated arm blood pressure determinations: 17.6 and 17.1 mmHg for systolic bl ood 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 coef ficient. A trend towards a progressive 9-mmHg increase was observed in overestimation of SBP over the 1-h period. Mean +/- SD pooled arm-fin ger blood pressure differences were -10.8 +/- 14.6 mmHg for SBP and 4. 5 +/- 9.4 mmHg for DBP. Blood pressure measured in different fingers w as similar on average, with repeatability no poorer than for re-insert ion 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 i nfluences blood pressure measurement during volume-clamp plethysmograp hy, reducing its precision. Finger SBP exceeds brachial auscultatory r eadings and has similar precision.