A novel and simple technique to allow detection of the position of the R-waves from intraventricular pressure waveforms: application to the conductance catheter method.
A simple and novel technique that utilizes the zero-crossing points of the first time derivative of intra-ventricular pressure (dP/dt) to mark systole, is proposed. Discrete differentiation of the sampled pressure waveform is calculated using a difference equation. Filtration of high-frequency noise in dP/dt is achieved using a low-pass Butterworth filter of order 4 and a cutoff frequency of 10 Hz. The filter is realized digitally using infinite impulse response filter stages. Double filtering of discrete dP/dt is used to eliminate time shifts. The methods are evaluated on data obtained from six large, white, anaesthetised and open chest pigs, instrumented with a conductance catheter. The zero-crossing points of the filtered dP/dt compare very well with the R-waves of the electrocardiogram (ECG) as markers of systole. The mean error is 1.3% of the duration of the heartcycle. Significantly, our results provide a solution to a problem often encountered with multiuse pressure-volume catheters when an ECG signal cannot be obtained. In this situation, the zero-crossing points of dP/dt, rather than the R-waves of the ECG, can be used as a marker of systole, thus enabling the construction of end-systolic pressure-volume relations to assess cardiac contractility.
Al-Khalidi
A H
AH
Department of Physiology, The Medical School, The University of Birmingham, Edgbaston, UK. a.h.al-khalidi@bham.ac.uk
Lewis
M E
ME
Townened
J N
JN
Bonser
R S
RS
Coote
J H
JH
D000818:Animals; D002138:Calibration; D004562:Electrocardiography; D005260:Female; D008297:Male; D012815:Signal Processing, Computer-Assisted; D013552:Swine; D013599:Systole / Q000502:physiology*; D016277:Ventricular Function, Left / Q000502:physiology*