The place of respiratory function tests in clinical medicine.

Introduction It is difficult to settle on a precise date for the introduction of objective methods of measurement into clinical medicine. Perhaps a good case can be made out for the year I867 when Clifford Allbutt arranged for the first clinical thermometer to be manufactured. This technique survived the ridicule with which it was greeted, but perhaps even then it was realized that the substitution of a thermometer for the sensitive hand of the physician was a dangerous precedent, likely eventually to lead to the substitution of one technique of diagnosis by another. It is important that certain erroneous preconceptions are cleared away therefore, before the particular question of the place of respiratory function tests is considered. The days when a vain search was made for tests which were infallible in the diagnosis of this or that condition, have passed. It is quite clear that the best contemporary practice assembles its information, the history, the physical examination, the X-ray, the blood count, etc., with care and with knowledge of what may be misleading in each of them; and then reaches a diagnosis by putting this information together as neatly and as coherently as it will allow, guided by its experience. No-one expects the blood urea to diagnose chronic nephritis, so there need be no surprise if the vital capacity does not diagnose emphysema. Further one can recall that all investigations, from the measurement of the body temperature onwards, have started essentially as research investigations used only by one or two laboratories by one or two physicians. A general application of the method has followed a general understanding of its usefulness. Some contemporary investigations are in the border country between being' research ' and ' clinical' investigations; the electroencephalogram, the serum lipo-proteins perhaps being examples of these. To the question, there fore, should every hospital have facilities for studying the serum lipo-proteins, the answer might be that it should be available in any department where vascular disease is particularly studied, but not necessarily elsewhere. There seems little doubt that the full range of contemporary respiratory function tests should be available to every chest hospital, but this is not the same as suggesting that every hospital should have a pulmonary function laboratory. Lastly, there are some difficulties that particularly apply to respiratory function tests. The co-operation of the patient is required, though this very rarely presents a problem. Indeed I have come to the conclusion that if the patient complains of dyspnoea, the idea of measuring his lung performance seems at the moment more logical and reasonable to the patient than it does to the physician. Some of the recent techniques of measurement of respiratory function are complicated and all of them require trained staff. We need not be deterred by the fact that these tests cannot be applied in every doctor's consulting room. The value of simple tests, like the maximal breathing capacity, tends to be overstressed because they can be easily measured, and it is most important that the practical value of the test in clinical practice receives very critical attention, since if nothing is going to be learned of real value to the physician, any test, however simple, is a waste of time. The last ten years have seen the completion of a great deal of the essential foundation work in the study of pulmonary physiology. These advances have been most excellently brought together and simply described in a recent book by J. H. Comroe and his colleagues. The purpose of this article is, firstly, to describe contemporary tests of function and to discuss the information they are capable of yielding; and secondly to discuss the clinical situations in which this information is