The Relation Between Blood Flow in an Isolated Muscle Measured with the Xe133 Clearance and a Direct Recording Technique

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Abstract
To allow a critical evaluation of the Xe133 clearance technique this method was compared with directly metered blood flow in the isolated gastrocnemius muscle of cats at different flow levels between rest and maximum exercise dilatation. Whether the Xe133 was applied by close intraarterial injection or intramuscularly the clearance curve had a multiexponential course. This was ascribed partly to local variations of the affinity of the tissues to the gas but mainly to an uneven perfusion of the muscle. When the first phase of the clearance curve was approximated by a monoexponential curve and was taken to represent blood flow a significant correlation to metered flow was found. With i.a. injections the calculated flow amounted to an average of 93 per cent of the drop counter flow while after i.m. injections it only averaged 62 per cent. The difference in results is ascribed to the different microcirculatory conditions created by the two modes of injections. The relative volume of the well‐perfused part of the tissue was estimated by noting at which level of activity the curve deviated from the first phase of rapid clearance. The well‐perfused fraction increased at higher blood flows. It is concluded that the Xe133 clearance technique may give valuable information about the local circulation provided the limitations of the method are considered.

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