Cardiac contractility assessment from arm impedance plethysmography (IPG)

Impedance plethysmography (IPG) is a non-invasive technique for measuring total electrical conductivity of a specific body section and its changes along time. It permits several haemodynamic parameters to be derived including stroke volume, heart rate and cardiac output. The upper arm IPG and control thorax IPG data from 8 cases within the research team was recorded using a commercial IPG & ECG integrated recording system for comparative analysis between the two methods of electrodes placement (arm versus thorax). Three IPG waveform parameters were assessed in the signal averaged IPG (SAIPG), for establishing the signal parametric relation between the conventional thorax-IPG and upper arm-IPG. ECG R-wave event to IPG peak time difference (ms): the average [Arm-IPG timing] - [Thorax IPG timing], was of 37.3ms (±9.5ms SD). Thus, a delay was identified in the 8 cases. The IPG pulse peak amplitude (Ω) in the arm-IPG is about 18.3% (±10.4% SD) of the amplitude of thorax-IPG. Metrics of the mid-amplitude IPG pulse-waveform time width (ms), revealed that the arm-IPG pulse-waveform width is an average of 26.3ms (±10.6ms SD) narrower than thorax-IPG. This initial study shows the feasibility of obtaining a long-term clinical profile of the cardiac contractibility or heart pumping activity from an accessible part of the body, as is the upper arm, by means of a rolling SAIPG signal denoising method.