Objective: 

The aim of this study was to acquire non-invasively and to analyze plethysmografic waves by measuring the electrical impedance of a peripheral segment.

Methods: 

We built a device that is designed as an injection module with a microcontroller which generates a sinusoidal pulse with adjustable frequency (10 – 200 kHz) and adjustable intensity. In output, the device delivers an analogical signal representing the variation of the impedance of the explored section. Disposable electrodes were used for the injection of the sinusoidal pulse and the collection of the bioimpedance signal. The acquisition of the bioimpedance signal on PC was made easier by the use of a National Instrument data acquisition device, the NI USB 6009. The bioimpedance signal processing, the user interface and the display were managed by MATLAB.

Results: 

We synchronized the plethysmographic wave with the electrocardiographic wave and we calculated some important parameters, such as: blood flow, amplitude, height of the dicrote incision, maximum dicrotic height, rise time, index Kunert, sfigmic velocity. We have also calculated the Fourier and the phase coefficients which describe the shape of the pulse curve and are useful for the automatic pulse wave analysis. The relationship between Fourier coefficients allows the evaluation of the elasticity of the arterial vessels in the measured segment.

Conclusions: 

The novelty of our method is that it analyses non-invasively the plethysmographic wave in the peripheral segments. Our device assists the physician in the diagnosis and continual monitoring of the peripheral vascular status of the patient. Knowledge of the vascular changes affected by different physiological or pathological conditions (obliterative processes, stenoses, angiopathies) will provide valuable information.