BLOOD-PRESSURE INTRODUCTION The study of blood-pressure is unique in that it is the only subject employing a method of precision which enjoys an almost universal field of application, and that, unlike other clinical investigations which require special apparatus, its employment is not confined to the internist and the laboratory worker. The blood-pressure test being easily applied and the results more than satisfactory, it has rightly found general favor at the hands of widely varying branches of the healing art. This great and sudden popularity has had certain drawbacks, as a tendency has been created in some directions to jump at extreme conclusions regarding the value or non-value of the test, so that either unlimited reliance has been placed in the findings to the elimination of other perhaps equally important data, or the value of the study of blood-pressure has not been adequately considered by other clinicians who as a result have failed to give their patients the benefit of its undoubted advantages. In spite of the comparatively recent development of this test in its present form, there has already accumulated a most extensive literature making it almost impossible to keep abreast with it. The author has in this work endeavored to collate and sift out the many points of value on blood-pressure found in recent and current literature, In and to place them in such shape that the busy practitioner may speedily acquire a general view of the subject. so doing, the author has been forced, for reasons of economy of space, to limit the discussion to certain fixed lines. Thus, no attempt has been made to devote great space to a consideration of the theoretical and experimental sides of the subject, either from the physiologic or the pathologic standpoint, except in so far as they have an immediate and practical application. It was thought advisable, however, to insert a number of extra references for the benefit of those who wish to consider the subject more comprehensively. Neither has unnecessary space been occupied in describing the large number of blood-pressure testing instruments, many of which have become either obsolete or nearly so, while others vary so little in character, design, or in operating principle that detailed description was deemed unnecessary. Others again are so complicated in mechanism or mode of operation as to render them practically without value in clinical medicine. The preparation of this revised work has entailed the reading and sifting of an immense amount of "literature" for which due credit has been given to the authors, whenever practical; while the great volume of material to review has increased the probability of inadvertent omissions, which are, it is believed, neither many or serious. At the same time rules for the admission of material have had at times to be closely drawn in the interests of brevity, that perhaps some omissions have been made which may perhaps be deplored by the reader. CHAPTER I PHYSIOLOGY THE CIRCULATION As practice makes perfect, so has the extended and universal application of the sphygmomanometer perfected and reduced to a practical basis a large amount of theoretical and conjectural material bearing on blood-pressure which, until recently, was without scientific foundation. For this reason, in order to gain a proper appreciation of the function of the sphygmomanometer and the relation of blood-pressure readings of systolic, diastolic and pulse pressure, to the changing conditions in the cardiovascular system which this study reveals, it is primarily essential to possess a working knowledge of the theory of hydrostatics, and its relation to the human physiology, together with its modification by physical and vital conditions surrounding the human circulation both in health and disease. It is only by the knowledge of at least the essentials of this subject, that a proper appreciation of the factors controlling the cardiovascular system in both health and disease and the relation of this system to the kidneys and other organs closely associated with it can be had. It is proper, therefore, to preface a clinical study of blood-pressure with a brief general discussion of the circulation, even though to so do may seem to some to be a needless waste of time and space. |