Letters to the Editor

LETTERS TO THE EDITOR Dear Editors : We read with great interest Prof. Hirsch's essay on the transfer and conversion of muscle energy to the mass of lifted objects as older individuals engage in the lifting process ("Gerontological Observations Supporting Einstein and Mao", this Journal, Summer, 1997). We not only find ourselves in substantial agreement with this conclusion, we think that some important correlates may follow from it. For example, if with increasing age there is a transfer of muscle energy to the mass of a lifted object, the reciprocal might also be true for young individuals. For such younger persons, the mass present in an object may be transferred, as energy, to the individual doing the lifting; not only making the object lighter but also providing increased strength to the lifter. Indeed, there is some subjective evidence supporting both propositions as well as the possibility that a dynamic state or flux may exist between an object being lifted and older and younger lifters. Consider the following , not unfamiliar situation. At a social event (for example, a picnic) an older and a younger individual are asked to move a heavy table. Visualize that when first lifted, both the younger and older individuals raise the object to approximately the same height but that, with time, an imbalance occurs such that the end of the table held by the older individual falls below that held by the younger person. The time interval required for this shift to occur becomes, therefore, the basis for measuring the kinetics ofthe exchange; first muscle energy from the older individual to table mass, then table mass to muscle energy in the younger lifter. Although we suspect that the overall kinetics of this exchange will be second order, this remains to be determined . We also expect that the difference in elevation of the ends of the table held by the two lifters (along with the table's mass) will give some quantitative measure of the energy-mass transformation and of the efficiency of the exchange. We thank Prof. Hirsch for his considerable contribution to our understanding of one important aspect of the aging process. We hope that our few comments will add further support to his insight. Arnold Kahn for the Members of the High Table Moffit Hospital University of California, San Francisco 612 Letters to the Editor Dear Editors : We concur with Michell that sodium "enables," "aggravates," and is the "sine qua non" of progressive edema. Our main point, however, is to emphasize the primacy of the lymph circulation and specifically the balance between lymph formation and absorption as the key but neglected unknown in the edema formula. By shifting the conceptual framework one step backward from renal salt and water metabolism to lymph circulatory dynamics, we endeavor, like Michell, to focus attention on events on the "dark side" of the blood microcirculation (i.e. the interstitium ) rather than fixating on the plasma-renal interface (the kidney) . As Michell emphasizes, the "central conundrum of sodium regulation is our inability to explain how extracellular fluid (ECF) volume (plasma and interstitial fluid) is regulated ". Although the expressions "optimal intravascular volume" and "optimal urine output'' are admittedly vague, they do convey the inadequacy and even futility of trying to indirecüy assess interstitial events by reasoning from plasma measurements of electrolyte, renal, and endocrine status and doing so in sick patients with complex disorders involving nonlinear (chaotic) interrelationships among multiple organ systems. Could it be that sensors of interstitial volume expansion lie within the lymphangions (vestiges of the amphibian cor lymphaticum)? These pulsating contractile functional units of lymphatic collectors between intraluminal valves, which are normally incompletely filled, gradually become fluid-filled columns in conditions of heightened lymph formation such as hepatic cirrhosis and congestive heart failure. What more strategic site than the thoracic duct-subclavian veinjunction for sensing and signaling, through stretch receptors and release of chemical mediators, simultaneous shifts in both intravascular and extravascular volumes?Just imagine, a whole axis of neurohumoral agents originating in tissue fluid, lymph, and plasma emitting a cascade ofantagonistic and synergistic messages to the brain, heart, adrenal glands, and kidney, and who knows where else, regarding ECF volume and particularly its intra/extravascular distribution...