Integral Pulse Frequency Modulated Ultrasound for the Detection and Quantification of Gas Microbubbles in Flowing Blood

Abstract

An integral pulse frequency modulated gas microbubble detector is described. When used in conjunction with an electromagnetic blood flowmeter, the ultrasound pulse repetition frequency can be regulated to reduce multiple counting errors due to variations in blood flow rate. A special detector mounting head eliminates problems due to wall curvature and pulsation, permits reliable and reproducible transducer coupling and makes it possible to gate the ultrasound field electronically in order to avoid spurious counts due to crystal and wall artefacts and low intensity regions.Results obtained from the detector during an in vifro evaluation of bubble oxygenators suggest that the number of arterial line gas microbubbles is less than has been claimed previously and that the total volume of gas liberated in the form of microbubbles may be too small to have any demonstrable priman/ clinical effects.

Can an oxygenator design potentially contribute to air embolism in cardiopulmonary bypass? A novel method for the determination of the air removal capabilities of neonatal membrane oxygenators

“…6,13 This inconsistency probably has its origin in the nonquantitative nature of the data generated by bubble counters and in the severe limitations of accurately counting GME by ultrasonic techniques. 10,14 Indeed, problems can occur from the angle and coupling of the ultrasonic transducer, the frequency and pulse length of the device, the electrical circuitry employed, bubble diameter and shape, tubing diameter and curvature, amount of air and speed at which air is introduced, red cell interference, and the rate of blood flow. 5,11 Finally, the bubbles themselves may produce the most serious problems.…”

“…8 However, this method is not sufficiently quantitative and has low reproducibility due to the limitations of the working principle. [9][10][11] Therefore, an objective assessment could contribute to the airhandling improvement of a given device.…”