Hermann Rahn

36th APS President (1963-1964)
Hermann Rahn
(1912-1990)

When APS celebrated its seventy-fifth anniversary at the fall meeting in Coral Gables in August 1963, Hermann Rahn presided over the session. He first introduced his friend and colleague, Wallace O. Fenn, nineteenth president of APS (1946-48), who reviewed the most recent twenty- five years of the Society's history. Rahn then called on former presidents to speak briefly on topics of historical, contemporary and prospective interest to members of the Society and their guests. He began as follows:

"Our Presidents do not wear uniforms and medals and ribbons, but they wear a halo which is not easily recognized by outsiders. It shines with a soft blue light which can be seen only by those "in the know."

The twelve talks that constituted this program were subsequently published in volumes 6 and 7 of The Physiologist.

Hermann Rahn was born in East Lansing, Michigan, but from his graduation from high school in Ithaca, New York, in 1929, his professional life has been in general identified with central New York State. He received his A.B. degree from Cornell University in 1933 and his Ph.D. degree from the University of Rochester in 1938; he joined the staff of the Department of Physiology at the University of Rochester School of Medicine and Dentistry in 1941 and eventually became vice-chairman of that department. In 1956 he moved west only a few miles to become professor and chairman of the Department of Physiology at the University of Buffalo (since 1962, the State University of New York at Buffalo). In 1973 he was honored by appointment as Distinguished Professor of Physiology.

Rahn has not always been found "at home," however. He has been a visiting professor at San Marcos University, Lima, Peru (1955); at Dartmouth Medical School (1962); at the Laboratoire de Physiologie Respiratoire, Centre Nationale Recherche Scientifique, Strasbourg, France (1971); and at Max-Planck Institut fur experimentalle Medizin, Gottingen, West Germany (1977). He has received the honorary degrees of Docteur (H.C.), University of Paris (1964); LL.D., Yonsei University, Seoul, Korea (1965); D.Sc. (Hon.), University of Rochester (1973); Titulo de Profesor Honorario, Universidad Peruana, Lima, Peru (1980); and Doctor Medicinae honoris causa, Universitat Bern, Switzerland (1981). He was elected to honorary membership in the Harvey Society of New York in 1960, the American Academy of Arts and Sciences [AAAS (Boston)] in 1966, the National Academy of Sciences (NAS) in 1968, and the Institute of Medicine of the NAS in 1971. In 1976 he received a Senior U.S. Scientist Award of the Alexander von Humboldt Foundation.

Beginning with his first appointment to the Editorial Board of the Society's journals in 1953, Rahn has served APS in many different capacities. Among other appointments he has been a member of the Board of Publication Trustees (1959-61) and the Editorial Board for the Handbook of Physiology (1958-66). With Wallace Fenn, he edited the respiration section of the Handbook of Physiology. He was a member and/or chairman of the Education Committee (1958-61), the Perkins Memorial Fund Committee (1968-80), the Daggs Award Committee (1980-83), and the Honorary Membership Committee (1979-84). Elected to Council in 1960, he was chosen as president elect two years later and so continued on Council until he finished his term as past president in 1965. In 1978 he was recipient of the Society's Ray G. Daggs Award.

Another of Rahn's interests has been the International Union of Physiological Sciences (IUPS). He has been a member of the Council (1965-74) and has served as vice-president (1971-74). While serving on the U.S. Naitonal Committee (1966-74), he was a member of the Organizing Committee for the XXIV IUPS Congress (1968) in Washington, D.C. (1965-68). As a member of this committee he was given the responsibility of organizing the satellite symposia. This was the first time these symposia were officially recognized as part of the IUPS Congress. He served as chairman of the Satellite Symposium Committee for six years. There is no doubt that these symposia have contributed greatly to the viability of our IUPS Congresses and to the advancement of physiology as a science.

Rahn's graduate study and first three postdoctoral years are marked by a series of sixteen papers on the endocrinology of the avian pituitary gland and the biology of rattlesnakes the latter a subject of interest during the two years he was an instructor at the University of Wyoming at Laramie. When Wallace Fenn invited him back to Rochester, endocrinology lost a promising young investigator. With Fenn and Arthur Otis he began the research on respiration and pulmonary ventilation for which these three men and their associates have become so well known. By 1955 Rahn and Fenn had arrived at their concept, A Graphical Analysis of the Respiratory Gas Exchange: the O2-CO2 Diagram, published by APS (3). Here the partial pressure of CO2 is plotted against partial pressure of O2. The graph can represent the composition of any gas mixture of physiological significance, as well as any combination of CO2 and O2 tensions in blood, plasma, lymph, or other body fluids.

Asked to describe his training in science and his experience in the laboratory, Rahn responded as follows:

"Throughout my career it has been my special privilege to be associated with mentors and peers of unusual talents and imagination in exploring uncharted areas. It started in 1941 with Wallace Fenn and Arthur Otis in Rochester where we described the first modern version of the pressure- volume diagram of the chest (1) in support of our fighter pilots equipped with positive-pressure breathing masks. These adventures in our primitive, home-made high-altitude chamber eventually led Fenn and me to publish A Graphical Analysis of the Respiratory Gas Exchange: the O2-CO2 Diagram (3). The O2- CO2 diagram was the centerpiece of this book, equivalent to a map on which few roads had been charted, and only one's imagination limited the future paths that would later be explored and charted on this diagram in the area of high-altitude physiology, deep and shallow diving (with Lanphier and Hone), gas bubble resorption (with H. Van Liew), space travel (with L. E. Farhi), and artificial and insect gills (with C. V. Paganelli)."

"The O2-CO2 diagram also provided a map charting the alveolar gas concentration as determined by different ventilation-perfusion ratios (2) and, with L. E. Farhi, predicting the alveolar-arterial O2 differences as a consequence of a logarithmic distribution of ventilation-perfusion ratios in the lung (4). During the late years in Rochester and early years in Buffalo I had the good fortune to work with P. Dejours, P. Sadoul, J. Knowles, T. Finley, J. Piiper, P. Haab, T. Velasquez, C. Lenfant, E. Agostoni, L. E. Farhi, J. West, and P. Cerretelli, while continuing to chart the various consequences of ventilation-perfusion distribution on the O2-CO2 diagram, and to work with a young medical student, F. Klocke, who demonstarted the existence of a normal arterial-alveolar N2 difference in humans (5)."

"When gas exchange limitations of water breathers were mapped for the first time on the O2-CO2 diagram (6), it showed why their CO2 partial pressure would not exceed 5 Torr. This opened up new adventures in unraveling the evolutionary sequences of gas exchange organs from gills to lungs and, with Kylstra and Lanphier, led to the demonstration that dogs could successfully breathe water (saturated with O2 at 5 atm) and fully recover. It led also, with B. Howell, to the curious observations that at various body temperatures lower vertebrates do not regulate their acid-base balance to maintain a constant pH but rather a constant relative alkalinity or OH-/H+ ratio (7, 8). The explanation was later provided by R. B. Reeves who showed that all vertebrates, including humans, do not regulate acid-base balance to preserve a constant pH, but rather to regulate a constant protein net charge through the properties of a special protein buffer, imidazole groups of histidine."

"With O. D. Wangensteen it was demonstrated that gas exchange of the hen's egg is limited to diffusive transport. In more recent years, with C. V. Paganelli and A. Ar, we have charted this gas exchange on the O2-CO2 diagram (9, 10) and gained new insights in the limitations of gas transfer operating under Fick's law and the importance and limitations set by diffusion coefficients. In the egg, O2 and CO2 concentrations are determined by diffusion-perfusion ratios instead of ventilation-perfusion ratios, and this may eventually serve as a model for the gas transfer processes at the alveolar gas-capillary interface of the lung.

"Much of this work was carried out under unusual circumstances, which in themselves provided new adventures for me. It started out in the high-altitude chamber at Rochester and led to high- altitude expeditions in the Rocky Mountains with A. Otis, S. M. Tenney, R. S. Stroud, and H. Bahnson, and in Peru with T. Velasquez and A. Hurtado. At Buffalo these carried me into the high-pressure chambers with E. Lanphier and to the diving Ama of Korea with S. K. Hong, and in Japan with T. Yokoyama. With W. Garey I went to the Amazon to study acid-base balance in the electric eel, and during the last decade, with C. V. Paganelli and many others, I have explored strange islands in Alaska, Mexico, the Marshall and Midway Islands of the Pacific, and Spitsbergen in the high Arctic to study diffusive gas transport in eggs of various native birds."

The names of many of Rahn's associates and disciples can be found in his complete bibliography. Something of the range and variety of his investigations, however, is evident from the account given above. Rah's friends know that it is both high professional competence and unusual breadth of interest that intensify the "soft blue light' of his halo.

Selected Publications

1. Rahn, H., A. B. Otis, L. E. Chadwick, and W. O. Fenn. The pressure-volume diagram of the thorax and lung. Am. J. Physiol. 146: 161-178, 1946.

2. Rahn, H. A concept of mean alveolar air and the ventilation-blood flow relationships during pulmonary gas exchange. Am. J. Physiol. 158: 21-30, 1949.

3. Rahn, H., and W. O. Fenn. A Graphical Analysis of the Respiratory Gas Exchange: the O2-CO2 Diagram. Washington, DC: Am. Physiol. Soc., 1955.

4. Farhi, L. E., and H. Rahn. A theoretical analysis of the alveolar-arterial O2 difference with special reference to the distribution effect. J. Appl. Physiol. 7: 699-703, 1955.

5. Klocke, F. J., and H. Rahn. The arterial-alveolar inert gas ("N2") difference in normal and emphysematous subjects, as indicated by the analysis of urine. J. Clin. Invest. 40: 286-294, 1961.

6. Rahn, H. Aquatic gas exchange: theory. Respir. Physiol. 1: 1-12, 1966.

7. Rahn, H. Gas transport from the external environment to the cell. In: Development of the Lung, edited by A. V. S. de Reuck and R. Porter. London: Churchill, 1966, p. 3-23.

8. Howell, B. J., F. W. Baumgardner, K. Bondi, and H. Rahn. Acid-base balance in cold-blooded vertebrates as a function of body temperature. Am. J. Physiol. 218: 600-606, 1970.

9. Rahn, H., and O. Prakash (Editors). Acid-Base Regulation and Body Temperature. Dordrecht, Holland: Martinus Nijhoff, 1985.

10. Rahn, H., and C. V. Paganelli. Transport by gas-phase diffusion: lessons learned from the hen's egg. Clin. Physiol. Oxf. 5 (Suppl) 3: 1-7, 1985.