Experimental air embolism: measurement of microbubbles using the Coulter counter.

Microbubbles in the range 20-250 μm were produced with fine hypodermic needles (0·001, 0·002 and 0·003 inch internal diameter) and were measured using a conventional Coulter Counter. Various bubble sizes could be obtained by varying combinations of needle size, gas pressure, liquid surfactant content and liquid flow rate. Bubbles produced and measured in this way were found to have a very narrow size distribution (80% of the bubbles falling within ± 2 μm of the mean radius) and could be generated at relatively constant frequencies. Over the entire bubble size range, the Coulter Counter method correlated well with two other bubble measuring methods: terminal rise velocity and volume flow rate of gas divided by bubble frequency. It is suggested that this method will enable the introduction of a known number of accurately sized microbubbles into the circulation for the purpose of studying experimental gas embolism.