Stumbling Over a Bias
What Happens to Spinal Fluid pH at High Altitude?

JOHN W. SEVERINGHAUS

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I have agreed to retell an altitude study my coauthors and I published 36 years ago in anecdotal rather than SC (Scientifically Correct) prose for this series. The article was: "Respiratory control at high altitude suggesting active transport regulation of CSF pH", in J. Appl. Physiol 1963;18:1155-1166 by J. W. Severinghaus, R. A. Mitchell, B. W. Richardson, and M. M. Singer. We made the first measurements of human cerebral spinal fluid (CSF) pH during acclimatization to high altitude to understand respiratory control. We concluded that, since during hypoxic hyperventilation, spinal fluid shifted less in an alkaline direction than blood, the blood-brain barrier must regulate brain extracellular fluid (ECF) pH.

We knew that the immediate fall of Pa_CO2 at high altitude cancels most of the hypoxic (carotid body) ventilatory drive. It was not known why breathing slowly rises over hours to days, raising the blood oxygen and reducing blood CO₂ and stays high for a few days after descent, as first shown by Charles Houston and Richard Riley, during World War II. Renal correction of respiratory alkalosis was too slow.

At the NIH in 1954-57, my associate Freeman Bradley and I had developed electrodes to measure blood pH, PCO₂ and PO₂, the first "blood gas apparatus." We were looking for uses, or as the Danish poet, mathematician and philosopher Piet Hein later wrote in his "Grooks":

Solutions to problems are easy to find;

The problem's the great contribution.

But what is truly an art is to wring from your mind

A problem to fit your solution.

In 1957, shortly after I completed my anesthesia residency at Iowa City with Stuart Cullen, Julius Comroe persuaded Cullen to move to University of California at San Francisco (UCSF) by persuading the chief of surgery to let anesthesia be an independent department. I agreed to come along to the new Cardiovascular Research Institute (CVRI). I shared a laboratory with Robert Mitchell, a pulmonary internist studying patients with chronic obstructive pulmonary disease (COPD). He wanted to find a way to stimulate their breathing, improve their oxygenation and reduce their very high PCO₂ values. In COPD patients he found normal spinal fluid pH with high CSF bicarbonate concentration. He was able to stimulate breathing to normal levels for about 1 day in 2 patients by reducing CSF bicarbonate concentration. Comroe proscribed further tests in patients because when he was at Penn injection of saline into CSF had been followed by convulsions. Mitchell showed, in dogs, that the blood-brain barrier was essentially impermeable to bicarbonate ion. Thus, acidifying blood did not help COPD patients. Clearly, the control of breathing and CO₂ must lie within the brain, where spinal fluid acidbut not blood acidcan stimulate ventilation.

In Goettingen, Germany, physiologist Hans Loeschcke was also searching for the respiratory CO₂ chemoreceptors in or near the fourth ventricle. We persuaded him to join Bob in San Francisco for about two months of collaborative research. In the last experiment before Hans left, by injecting acidified CSF from the rear, through catheters passed ventrally, they observed a much greater respiratory response. Devising a new ventral surgical approach to the brain stem, Mitchell then located and characterized the now classical medullary ventral surface CO₂ chemo-sensing regions as ECF pH sensors. Hyperventilation occurred when the surface was touched with filter paper wet with acidified CSF. Topical local anesthetics of this area minimized the ventilatory response to inhaled CO₂. Electrical stimulation of the surface caused hyperventilation. The relationship between PCO₂ and pH depends on CSF and ECF bicarbonate concentration. The question then was what controlled CSF HCO₃.

Ralph Kellogg, a physiologist at UCSF, had studied sleep at high altitude. When I described the problem at lunch one day, he suggested the possibility that the blood-brain barrier regulated brain ECF pH. For me this was a great "Aha," and led to our plan to sample human CSF during acclimatization at altitude. The idea appealed especially to me as an avid backpacker and (nontechnical) mountain climber, a passion acquired at age 17 on a one month pack trip in the High Sierra.

In the early 1950s, Professor Nello Pace, Kellogg, and other physiologists at UC Berkeley had assembled a large Navy surplus Quonset "hut" at 3,810 m (12,470 ft) in the White Mountains, east of the Sierra, near the ancient Bristlecone pines. They named the laboratory for Joseph Barcroft (1872-1947), the Cambridge high altitude physiologist. By 1960, the Barcroft lab was not only heated, electrified and plumbed, but had a library, billiards table, and a cook.

Anesthesiologists consider spinal taps routine, so we enlisted as subjects two anesthesiology research fellows, Burt Richardson and Morley Singer, and Mitchell and myself. We did sea level controls, packed up our home made blood gas apparatus, and in early July 1962, with two technicians, the team, in 2 UCSF station wagons, drove 400 miles, across the Sierra, past Bishop, up Westgard Pass and started up the 30 mile dirt road through limber pines, junipers, and bristlecones in a snow storm. At 9,500 ft, in the late afternoon, in 6 inches of new snow, Bradley and I, in a station wagon heavily loaded with 3 H-sized (large) cylinders of oxygen and the apparatus, slid off the edge, almost overturning, and hung, perched at about 45 degrees. Since the others had preceded us, we held little hope of being rescued that night.

Within minutes, however, an elderly photographer pulled up, driving his 1935 coupe. He had been unable to find a place to turn around in the snow and was too scared to drive further. In trade for a lift, I offered to drive his car, despite my post- spinal tap headache, and offered him a night's lodging at Crooked Creek, the half way station at 10,500 ft altitude, still 10 miles farther up.

With helpers from that lab, we took a big surplus Navy truck with winch down to our stranded wagon, but weren't able to pull it back up on the road. Rescue the next day required equipment and men from Bishop. They dragged the wagon up to the roadway, undamaged. The road was blocked by drifted snow at 11,500 ft on the side of Sheep Mountain. We hand-shoveled a passage. Effort before acclimatization often causes acute mountain sickness (AMS), and may have affected us, but no pulmonary edema resulted, and by the end of Day 2 we were all safely in the Barcroft Labs. We may have had impaired ability to reason, resolve, and act on first arrival at Mt. Barcroft. Nevertheless, we proceeded with the experiments.

The blood gas apparatus at that time consisted of Leland Clark's 1956 oxygen electrode mounted in a cuvette with stirring paddle, my modification of the CO₂ electrode described by Richard Stow in 1954, and a McInnes Belcher pH electrode designed about 1930 fitted into a small stirred 37° C water bath. We brought compressed gas cylinders of known CO₂ composition and several pH buffers checked against materials from the National Bureau of Standards.

We took turns doing the spinal taps on each other, lying on an army surplus cot, on one side, resting for about 15 min first with sterile drapes, needles, syringes, local anesthetic, gloves, etc. in UCSF operating rooms. There were no problems with sampling. To minimize headache known to be caused by leaking CSF we used 25 gauge needles. Because I was unusually prone to these headaches, I was usually studied at bedtime, in my bed, staying flat the rest of the night. All these precautions only prevented a headache once for me, on a night when I slept prone with a pillow under my stomach to elevate my lumbar spine. Lumbar punctures were scheduled on Days 1, 2, 4 and 8 at altitude. Unfortunately we had to cancel two studies on Days 1 and 4, excusing those with spinal tap headaches or with AMS.

Pa_CO2 fell as expected, making arterial blood significantly alkaline. CSF pH was only slightly higher at altitude than at sea level. Bicarbonate ion concentration fell faster and farther in CSF than in blood, and in proportion to the fall of Pa_CO2.

I too boldly reported confirmation of our hypothesis that active transport slowly restored CSF pH to normal, although our data showed no significant decrease with time. (It just never was found high.) This proved to be incorrect. Burt Forster, Jerry Dempsey and Lou Chosy, and Richard Weiskopf, Ronald Gabel and Vladimir Fencl, showed that CSF in most subjects rises significantly more than we reported, and often continues to rise over several weeks. Forster and colleagues showed this could be due to gradually increased sensitivity of the carotid body peripheral chemoreceptors.

What caused me to misinterpret and misunderstand our evidence, and why did CSF pH values rise so little? Had we missed something by omitting samples on Days 1 and 4 in two of the four subjects? Four was too small a number of subjects and samples considering the needed precision of pH measurement. The sea level CSF pH average may have been erroneously high because one of the four samples was noted (in the report) to have had an air bubble. We did not know, at that time, that the central chemosensitivity was so great that a change of pH of less than 0. 01 unit sufficed to permit the slow fall of Pa_CO2. Or did my hypothesis, in some still unknown way, bias my reading and interpretation of the CSF and blood data? I had not then learned the investigator's mantra: "Try to disprove your own hypothesis."

I chose this first attempt to study CSF in humans acclimatizing to altitude for a memoir because it yielded results that were misinterpreted, and because in my inadequate understanding of the complexity, I claimed to have found evidence of active transport by the blood-brain barrier and a resulting correction of CSF alkalosisa still unfalsified and unproved hypothesis. Wallace Fenn once wrote, "Any investigation, no matter how well done, could be improved upon if repeated." But none of my subsequent altitude studies provoked as much controversy or valuable challenging research. Piet Hein gets the last word:

Our choicest plans have fallen through

Our airiest castles tumbled over

Because of lines we neatly drew

And later neatly stumbled over.

	Footnotes

Correspondence and requests for reprints should be addressed to John W. Severinghaus, M.D., Dept. of Anesthesiology and Cardiovascular Research Institute, University of California Medical School, Box 0542, UCSF, San Francisco, CA 94143-0542. E-mail: jws{at}itsa.ucsf.edu