Cowbird Research and Measuring Pulsatile Diffusing Capacity

Richard W. Hyde

Pulmonary and Critical Care Unit, University of Rochester Medical Center, Rochester, NY

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In the early 1960s, I was a newly minted research fellow in the Department of Physiology of the Graduate School of Medicine at the University of Pennsylvania. Subsequent events led me to indulge in cowbird research that appeared in the "JCI" (Menkes HA, Sera K, Rogers RM, Hyde RW, Forster RE II, DuBois AB. Pulsatile uptake of CO in the human lung. J Clin Invest 1970;49:335-345). This paper extended the earlier concept of pulsatile pulmonary capillary blood flow to include pulsatile pulmonary diffusing capacity.

One fall morning when I entered the Physiology offices, an excited executive secretary said "I thought a tramp was coming into the office but at the last minute, thank goodness, I decided not to call the campus police! We are having a visit from the famous Dr. Roughton." His customarily ruffled tweeds were in greater disarray than usual after the overnight flight from England. Dr. F. J. W. Roughton was indeed famous for his work with in vitro hemoglobin reaction rates with carbon monoxide (CO), CO₂ and O₂ as well as the identification of red cell carbonic anhydrase. He had worked closely with my chief mentor, Dr. Robert E. Forster. I asked Bob "How does Dr. Roughton now spend his time as a senior professor?" He replied, "He does cowbird research. He lays innovative scientific eggs in other people's nests and comes back in a year or two to check up on his fledglings." Several days later, Dr. Roughton departed for La Jolla, California, presumably to lay another egg in Pete Scholander's nest.

Cowbird research: What a marvelous way to be an investigator! You avoid cantankerous respiratory gas mass spectrometers whose maintenance proved to be a formidable task for a junior research fellow. I promised myself to keep my eyes open for opportunities to do this type of research.

An ongoing dispute in the early 1960s about the pulsatile nature of pulmonary capillary blood flow led me to cowbird research. Grant Lee and Arthur DuBois in our physiology department had measured the "instantaneous" rate of uptake of a breath of nitrous oxide from the alveoli with a body plethysmograph. They found blood flow to be five-fold greater during systole than diastole. This finding was challenged by a group of New York City investigators using similar methods but supported by measurements performed by Karl Wasserman and Julius Comroe in San Francisco.

Several years later, Bob Forster and I were developing a method to measure the degree of uneven distribution of pulmonary CO diffusing capacity (DL_CO) to pulmonary capillary blood flow using short breath holds of 6% CO. I thought it might be possible to add support to the Philadelphia claim for pulsatile pulmonary capillary blood flow by showing that CO uptake and DL_CO were also pulsatile by measuring the instantaneous uptake of a breath of CO during short breath holds with the body plethysmograph. Unfortunately, at normal alveolar oxygen tensions, uptake of an inspired breath of CO by the lungs shifts the oxygen dissociation curve to the left. This shift of the curve lets an equal amount of oxygen come off the Hgb molecule and obliterates any pressure change in the body plethysmograph from the CO uptake. This interest in CO led me to read Roughton's chapter entitled "Transport of O₂ and CO₂" published in the Handbook of Physiology in 1964. Roughton plotted the oxygen dissociation curve with pO₂ against oxygen content instead of the usual O₂ saturation for different carboxyhemoglobin (COHb) concentrations. The curves looked peculiar below a pO₂ of 40 mm Hg. The multiple O₂ dissociation curves at different COHb concentrations converged into a single line. Several days later, while repairing the mass spectrometer, it suddenly occurred to me this meant that if a breath is held after an inspiration of CO at an alveolar pO₂ of 40 mm or less, the CO entering the blood would not release O_2, and you should be able to measure instantaneous CO uptake with the body plethysmograph.

I presented this idea to Bob Forster and after our usual heated but friendly debate, we agreed it should work. If you inhaled 2% CO and held your breath at an alveolar pO₂ of about 35 mm Hg, CO uptake would be diffusion-limited and the lung would take up roughly 2 ml of CO per second.

Next, I met with my other mentor, Dr. Arthur DuBois, by then the world-renowned expert on whole body plethysmographs. After I finished my presentation, he had his usual period of silence, accompanied by inquisitive frowning and roving eye movements that could be misinterpreted as indifference. By that time, our shared research projects had taught me not to interrupt his silence because he was analyzing the idea at a level of sophistication far beyond my talents. Interruption would lead to a painful analysis of your nervous ramblings and an unproductive meeting. Several minutes later it was obvious he understood what I had told him. He responded that the standard 600 liter plethysmograph had insufficient sensitivity to measure the uptake of 2% CO. Even if you reduced the size of the plethysmograph to 150 liters, the resulting four-fold increase in the signal would be insufficient.

I was disappointed by my failure to lay a fertile cowbird egg in Arthur's nest that included some very capable fellows namely, Harold Menkes and Bob Rogers.

But several days later, Harold burst into the laboratory and enthusiastically reported, "Arthur has the solution! If you breathhold in a water-filled plethysmograph, the gas volume is reduced to the subject's resting lung volume, giving a signal gain of more than a hundred fold!" The egg had hatched. Arthur and his crew took on the formidable task of designing a water-filled body plethysmograph. They let the totally immersed subject initially breathe through a valve system connected to the room while another valve let the water flow in and out of the plethysmograph with each breath through an ingenious stand-pipe system. Closing the valves after inspiring 2% CO at an alveolar O₂ tension of 35 mm Hg lets the subject take up the CO at a total gas volume of only 3 to 4 liters. Theoretically, the signal would increase over 100 fold compared with the standard air-filled plethysmograph. However, much fussing was required to obtain sufficient gain. For example, the plethysmograph had to be mounted on springs and dampers to minimize signal noise transmitted from trolley cars rumbling up and down Spruce Street.

Other problems were political. One day the plethysmograph was over-filled and the stand-pipe flooded the laboratory. An appreciable amount of water leaked into the clinic one floor below and stopped all visits. Multiple meetings with deans, administrators, hospital engineers, and housekeeping finally let Arthur's crew proceed with the experiments. Five normal subjects including Arthur, Harold, and myself produced satisfactory data. Bob Rogers served as the life guard because his ruptured ear drum prevented him from going underwater. Only once did a subject make an emergency exit and the system worked smoothly. We joked that if you could learn the necessary maneuvers, and not drown, you were entitled to be a co-author of the paper! CO uptake proved to be pulsatile, with a five-fold gain between systole and diastole. This dramatic pulsatility of CO uptake during the cardiac cycle was interpreted to reflect pulsatile DL_CO and pulmonary capillary blood volume.

I had moved to Rochester, NY, while the manuscript was under review, but Arthur sent me the reviews and his team's responses. In the diagram of the water-filled plethysmograph, someone had placed a small fish blowing out a few bubbles so the reader would know the plethysmograph was filled with water. DeWitt Goodman, the JCI reviewing editor, wrote "Incidentally one of the editors wondered how much of a contribution the fish made to the measurements?"

Arthur responded, "The name of the fish was "Matsya." He was protecting the man in the water. The earliest reference I could find was, "The Four Vedas," written by Brama at the time of creation, and revised by Vyasa about 3,000 B.C. . . . . . . . Matsya, the fish, preserved Manu, the ancestor of the human race, during a universal deluge. In this way Manu was able to complete his experiment and submit a paper ("manuscript") to the JCI . . . . . . "

Enclosed to Dr. Goodman were two pages from "The Age of Fables, or Beauties of Mythology" by T. Bulfinch, published in 1899.

Another reviewer wrote, "Reference 21 (which referred to a Federation Proceedings abstract by Sol Permutt) should be changed to the complete paper published in the recent book on pulmonary circulation from The Chicago Symposium of 1968, edited by Fishman and Hecht." Arthur responded, "We prefer to keep the reference to Permutt's more recent abstract in Federation Proceedings. This presentation was made before a scientific society. A publication in a symposium is not considered to be a "complete paper," and its citation as "scientific evidence" is of dubious validity. Otherwise, we might be publishing our present manuscript in a symposium instead of submitting it to the tender mercies of the editors of the JCI." Sol Permutt's abstract remained in the published paper and the fish stayed in the plethysmograph.

What did the above events teach me? I experienced the ecstasy of discovery that kept me hooked into a career of investigation. I certainly learned not to be obsequious in response to editors but apply humor and well referenced responses! By good fortune, I chose a laboratory with loyal and cooperative mentors who tolerated my missteps and took time to guide me. I also learned to develop efficient ways of good communication with my mentors. Different people need different approaches. With Arthur DuBois it took me at least a year to learn to keep quiet and let his analyses proceed uninterrupted. Interaction with Bob Foster required "Hegelian dialecticism." One proceeded from argument to counter argument that led to synthesis of good ideas. Trainees who did not argue fell by the wayside. And finally was the importance of taking advice carefully when given. When I moved to Rochester, one mentor said "if you want to continue a career in investigation, avoid committees. When appointed, be slightly disruptive but not disloyal so you don't get invited back. Committees can consume all your energy and even turn you into a dean or something worse." The advice was taken and neither I nor my mentor have become deans.

	Footnotes

Correspondence and requests for reprints should be addressed to Richard W. Hyde, M.D., Pulmonary and Critical Care Unit, Box 692, University of Rochester Medical Center, Rochester, NY 14642-8692. E-mail: richard_hyde{at}urmc.rochester.edu

Acknowledgments: Arthur DuBois, Bob Forster, Mark Frampton, and Bob Rogers reviewed the manuscript and provided helpful recollections and advice. Where memories differed, I have given you the more colorful version at the possible expense of accuracy.