The essential function of the heart is to act as a pump,and the efficiency of a pump is gauged by its output per unit of time. Thus the importance of the quantitative study of the output of the heart has long been recognised. Yet, though physiologists have for many years studied this function both in animals and in man, the difficulties have been such that accurate knowledge has accumulated but slowly. Text books do not yet contain figures relative to the circulation rate, as the output of the heart per minute has been termed, in man at rest or during the various phases of bodily activity. Little wonder, therefore, that the conception of quantitative study of the blood flow has not yet entered, to any large extent, into the clinical field. Yet, were a suitable method of estimation available, the study of circulation rate in disease would yield much valuable information.
This is especially obvious in cardiac disease. The effect of the various types of cardiac lesions on the output of the heart could be definitely determined and their relative severity thus evaluated. Further information regarding the mechanism of cardiac failure could be obtained and the value of various therapeutic agents used in circulatory disease could be more accurately determined. At present there is no generally accepted and accurate test of the functional efficiency of the heart. If the cardiac output could be measured, such a test could probably be evolved. In myxoedema and hyperthyroidism circulatory changes are to be expected, and by following such cases during treatment interesting facts regarding the relationship of the circulation and the metabolism might be obtained. In anaemias, fevers, and various other pathological states information of value would probably also result from a study of the circulation rate.
Recently a method was introduced by two American workers, Henderson and Haggard of Yale; which they Claim is suitable for estimating the circulation rate in patients untrained to respiratory experiments. This method has since been employed by others, in the study of circulation rate in normal individuals. The method has now been applied by the writer to pathological conditions and the results thus obtained are the basis of this thesis.
Since there is as yet no generally accepted opinion 'regarding the average circulation rate in normal individuals, and the extent of its variation under varying physiological conditions, a resume of the work done on the subject will first be given. What little work has already been done on circulation rate in pathological states will then be reviewed, before the results of the present investigation are set forth and discussed.