Low reserve kidney

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We have presented a description of the present theories relating to the functions of the kidneys, and have attempted to indicate how these functions are affected in pathologic conditions. We have discussed the various types of nephritides, as well as general vascular conditions associated with hypertension and leading later to renal involvement.A follow-up study of 313 patients with low reserve kidney is presented. The evidence, as revealed in subsequent pregnancies, strongly supports the concept of low reserve kidney and speaks against a general vascular disease or condition, whether of sclerotic, nervous, chemical, or familial origin, as the basis for this entity. Furthermore, it appears to be an entity distinct from any of the known nephritides, whether of the hemorrhagic, degenerative, or sclerotic type. It also does not seem to fall into the category of a mild preeclampsia. That this entity cannot very well be explained on the basis of a general vascular condition is the opinion, expressed in personal communications, of both Van Slyke and Marshall. The former has had an opportunity, in his nephritic service in the Rockefeller Institute Hospital to study various phases of hypertension and of the different forms of nephritis, while the latter has been responsible for an important part of our newer knowledge relating to the functions of the kidney. These investigators concur with us in the view that the concept of low reserve kidney appears to be sound. It must be pointed out, however, that it is not our opinion that the existence of such an entity has been proved and much further investigative work, especially upon maximum excretion capacity, is needed before we can prove or disprove this theory. Richards and Landis have given us some very valuable suggestions along these lines and we hope, in the near future, to be able to follow these.We believe that in this group of low reserve kidney patients, one or other of the factors influencing glomerular and perhaps also tubular function, may be involved. Such factors are rate of blood flow through the kidney, permeability of glomerular membrane as well as tubular walls, extent of filtration surface (glomerular), and perhaps also the effective filtration pressure. Unfortunately, very little is known as to the factors influencing tubular reabsorption, except the factor of time of contact of the glomerular filtrate with the tubular epithelium. That the involvement of one or other or combination of these factors, bringing about the signs of this entity (low reserve kidney), is dependent on inherent or inherited differences from the normal, or on a specific pregnancy condition such as hormonal or chemical or vegetative nervous, cannot at present be decided. Pressure on the renal veins or kidney pedicle, as suggested by Marshall, in a personal communication, should also be borne in mind as a cause of the albuminuria, although this may not explain the hypertension. We have discussed at some length the nervous reflex mechanism, as well as the other factors influencing blood flow through the kidney.