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.


METHODS
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 determinations: 17.6 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 +/- 9.4 mmHg 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.
Lal
S K
SK
Department of Cardiology, Royal North Shore Hospital, Sydney, New South Wales, Australia.
Mihailidou
A S
AS
Cejnar
M
M
Henderson
R J
RJ
Jones
M
M
Hunyor
S N
SN
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001132:Arm; D001795:Blood Pressure Determination / Q000295:instrumentation* / Q000379:methods / Q000706:statistics & numerical data; D003971:Diastole; D005069:Evaluation Studies as Topic; D005260:Female; D005385:Fingers; D006331:Heart Diseases / Q000503:physiopathology; D006801:Humans; D006973:Hypertension / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D011247:Pregnancy; D015203:Reproducibility of Results; D013599:Systole; D014652:Vascular Diseases / Q000503:physiopathology