Non-invasive electromagnetic measurement of the peripheral pulsatile blood flow: experimental study and clinical applications.

The non-invasive electromagnetic blood flowmeter described in this paper allows us to measure pulsatile flow through a limb. The limb is placed in a magnetic field and the blood flow rate induces electromagnetic forces which are detected at the skin surface with ECG electrodes (Faraday's law). A special computer technique is necessary to isolate the signal from artefacts (local ECG, BCG, EMG). In vitro calibration is performed using a circulatory model and in vivo using mongrel dogs. Its validity is assessed by comparing the results with the responses obtained from the invasive electromagnetic flowmeter. Sources of error in the measurement such as blood composition (Na+, K+), haematocrit (45% to 29%), and venous flow are reported here. The results indicate that the method is reliable, easy to utilise and offers a unique non-invasive way of measuring true pulsatile blood flow rate in humans. Various clinical applications are discussed for possible use of the device.

Myocardial contractility: non-invasive assessment after cardiac surgery.

The shape of the carotid blood-flow signal in the assessment of myocardial contractility is important. The non-invasive electromagnetic method permits the measurement of the pulsatile carotid flow rate and thus to estimate the maximum blood flow acceleration (max. dF/dt), which is directly related to myocardial contractility. The electromagnetic flowmeter method, routinely used in the superficial arteries of arteriosclerotic patients, has been modified to record the blood flow rate in the carotid artery. Two ECG electrodes on both sides of the common carotid artery record the signal given by a small magnet located above the electrodes. Using this method, we have studied the effects of isoprenaline infusion in a normal subject. In patients after cardiac surgery we measured max. dF/dt in the region of the carotid artery and compared changes in it with parameters obtained by invasive methods such as the cardiac index, and the pulmonary and systemic pressures. The first results of blood flow recordings in the ascending aorta are presented here.