Development of a tonometric sensor for measurement and recording of arterial pressure waveform

Abstract

There are many techniques and devices for measurement and recording of arterial blood pressure. Some of them allow (enable) additionally to observe the shape of a wave of arterial pressure, which can be regarded as one of the most important diagnostic parameters of human cardiovascular system. This paper presents a novel design and prototype of a new, non-invasive blood waveform measuring device. It expounds theoretical and experimental (including latest preliminary clinical) results obtained during several years of extensive investigations into blood pressure waveform measuring and monitoring problem. According to investigations performed in the laboratory and preliminary clinical evaluation, the sensor has linear steady-state characteristics and satisfactory dynamic properties. It is an efficient and accurate tool for blood pressure waveform monitoring and assessing the cardiovascular condition of the patients. The novelty of this solution is that the device is equipped with a pneumatic pressure sensor based on the pneumatic nozzle flapper amplifier principle with negative feedback. Due to such a technical solution, the device does not require any cuff, which remains an essential component of the majority of contemporary non-invasive blood pressure measurement devices; therefore, it can be used on the artery where the application of a cuff would be impossible (e.g., carotid artery). This advantage makes possible to obtain an accurate shape of blood pressure waveform with high fidelity, comparable to a direct measurement method. Moreover, during the measurement the device converts directly "pressure into pressure." Such a principle of operation makes possible to eliminate additional calibration (at the current stage of research we have eliminated the necessity of calibration in laboratory conditions).

Calibration methods of new device for human blood pressure measurement

“…The pneumatic generator supplied the pressure to the groove simulating desired blood pressure waveform (during the dynamic flow changes). The input and output pressures were measured with manometers and recorded with transducers on a digital oscilloscope [5]. Results of this experiment proved that the device static characteristic is linear [5] and has excellent dynamic parameters just as presented on Figure 2.…”

“…Comparison of pressure inside the artery imitation (p1) and device's readings (p2), xpressure calculated based on static characteristic. [5] The experiment was the starting point to optimisation and improvement of newly developed device, since the measurements performed on volunteers were less accurate than those performed in laboratory conditions on the artificial artery. It was assumed that the difference had its source in the geometric dimensions of human and artificial artery and current built of the device had to be calibrated, since the bare transducer equation provided by the manufacturer was insufficiently accurate.…”

“…Transducer's k-factor is calculated using Equation 3, where A1 is the area of membrane on the external side of measurement chamber's membrane and A2 is the area of membrane on the internal side of the measurement chamber's membrane. Sensor's k-factor is calculated using Equation 4, where Δu is the increment of transducer's voltage and Δp2 is the increment of pressure inside the measuring chamber [5]. px= -61 + ux · 118 (5) px= -61 + ux · 105.5 (6)…”

“…Sensor's k-factor is calculated using Equation 4, where Δu is the increment of transducer's voltage and Δp2 is the increment of pressure inside the measuring chamber [5]. px= -61 + ux · 118 (5) px= -61 + ux · 105.5 (6)…”

“…Due to this fact, one of the error sources is eliminated. A new measurement method with use of the newly developed device also allows to examine the blood pressure waveform [5], which can be a source of important data for general practice and clinical diagnosis. Even though current build does not allow the continous monitoring of the blood pressure waveform, the ability to aquire the blood pressure waveform scaled in pressure units with noninvasive method is a novelity.…”