Continuous, Real-Time, Noninvasive Monitor of Blood Pressure: Peňaz Methodology Applied to the Finger

Estimation of arterial blood pressure variability by spectral analysis: comparison between Finapres and invasive measurements

“…The first mechanism concerns the effect of possible intrinsic technical limitations of the Finapres servo-system which continuously adapts the cuff pressure around the finger, following blood pressure fluctuations, in such a way as to maintain the wall of the arteries in a steady state of unloading (Ohmeda 1993). However, although technical specifications reported on the instrument's documentation are not exhaustive about its dynamic performance, available indirect information (Boehmer 1987) does not provide evidence for this hypothesis. Moreover, a technical limitation of the Finapres device should produce consistent effects across the different signals and populations studied, giving rise to an equal frequency response for systolic and diastolic blood pressure as well as for post-MI and CHF patients.…”

“…The fourth mechanism to be considered in the interpretation of results concerns a frequently underestimated aspect of the volume-clamp method, that is the effect of the time-varying smooth muscle forces acting on the wall of the clamped arteries under the cuff upon the measurement of the finger blood pressure. It is known that, before starting pressure monitoring, the Finapres processor establishes the so-called set point (namely the artery volume at the unloaded condition) through a start-up adjustment procedure (Ohmeda 1993, Boehmer 1987. Then it periodically re-adjusts the set point with a much quicker procedure lasting two or three beats.…”

“…This is performed about every ten beats during the first minutes of operation (the stabilization phase) and then about every 70 beats (the recording phase). Hence this method implicitly assumes a purely elastic behaviour of the walls of small arteries under the cuff, as described by their pressure-volume characteristic (Boehmer 1987), during the periods of time between two successive adjustments. As a consequence, the periodic adjustment is effective in detecting and correcting for slow-moving physiological changes, whereas it misses oscillatory fluctuations of smooth muscle tone having a period comparable or inferior to the interval between two successive adjustments.…”

“…Considering for the sake of simplicity only a small artery under the cuff, after the completion of the self-adjustment procedure its radius will be clamped at a constant size R 0 , near the point of collapse, by the servo-loop system (Boehmer 1987). This size, under the hypothesis of a purely visco-elastic arterial wall, virtually corresponds to the state of an unloaded artery, that is to zero transmural pressure.…”

Respiratory Event-Induced Blood Pressure Oscillations Vary by Sleep Stage in Sleep Apnea Patients

“…We recorded nocturnal beat-by-beat arterial BP with the Finapres (BMEYE, Amsterdam, Netherlands) [ 24 ], which uses a pressurized finger cuff to sense arterial BP in finger arteries, typically the digitus secundus, digitus medius, or digitus quartus. Details and validity of this method are well established and reported [ 24 ]. Briefly, the device uses photoplethysmographic feedback to dynamically control the inflation pressure of a finger cuff.…”