Use of External Counting Technics In Studies of the Circulation

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Abstract
A variety of external counting technics has been used to study the circulation. Brief consideration has been given to some of those concerned with measurement of cardiac output, myocardial and other regional blood flows, and cardiopulmonary volumes, and to those related to the evaluation of vascular shunts. These technics have much in common. They are simple to carry out, require little time to accomplish, and entail little risk for the subject. At the same time, they are to varying extents imprecise, and are not as accurate as methods currently available or methods of undetermined validity or both. They do not offer the means to measurement of intravascular pressures and so cannot replace cardiac catheterization. As yet, little new information about the circulation has been gained by application of these methods. The ultimate place of external counting technics in the study of the circulation is still undetermined. The best prediction is that these methods will probably supplement but not replace diagnostic methods now in use. They should serve a valuable function as tests for screening of subjects being considered for more definitive and laborious procedures and as supplementary tools in the performance of these more definitive astudies.