Jack Reeves and his science

Respiratory Physiology & Neurobiology 151 (2006) 96–108

Jack Reeves and his science夽 Lorna G. Moore ∗ , Robert F. Grover Colorado Center for Altitude Medicine and Physiology (CCAMP), Campus Box B123, University of Colorado at Denver and Health Sciences Center, 4200 E. 9th Ave., Denver, CO 80262, USA Accepted 15 November 2005

Abstract John T. (Jack) Reeves’ science is reviewed across the 37 years of his research career at the University of Colorado Health Sciences Center, a period which occupied approximately half his remarkable life. His contributions centered on understanding the inter-relatedness as well as the underlying mechanisms controlling the various components of the O2 transport system. We review here his studies on exercise performance; these encompassed about half his scientific output with the other half being devoted to the study of hypoxic pulmonary hypertension. Early studies concerned cardiac output, showing how it was a balance between O2 uptake and O2 extraction, and that cardiac output during exercise at high altitude was reduced, most likely because of decreased plasma volume and left ventricular filling. Jack’s many studies addressed virtually every aspect of the O2 transport system—adding significantly to our understanding of the syndromes of altitude illness, the mechanisms by which ventilatory sensitivity to hypoxia and hypercapnia influenced ventilatory acclimatization, and the contributions of the various limbs of the autonomic nervous system on systemic blood pressure, vascular resistance and substrate utilization. His scientific career ended abruptly in 2004 when struck by a car while biking to work, but his legacy remains in his more than 385+ research articles or chapters, the 40+ fellows he trained, and the countless number of younger (and older) scientists for whom he served as a role model for learning how to scrutinize their data and present their findings in clear and sometimes bold prose. An integral man, he is sorely missed. © 2005 Elsevier B.V. All rights reserved. Keywords: Acute and chronic mountain sickness; Adaptation; Autonomic nervous system; Exercise performance; High altitude; Hypoxia; Lactate

1. Introduction 夽

This paper is part of the Special Issue entitled “New Directions in Exercise Physiology”, guest-edited by Susan Hopkins and Peter D. Wagner. ∗ Corresponding author. Tel.: +1 303 315 4480; fax: +1 303 315 0620. E-mail address: [email protected] (L.G. Moore). 1569-9048/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.resp.2005.11.009

John T. “Jack” Reeves was an integral man—original, unassuming, and highly disciplined. Born in 1928 in Hazard, Kentucky where his father served on the school board, Jack played the country boy, but none of us ever really believed him, despite our pleasure in hearing the tall tales of his

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his output—he was Professor of Medicine/Cardiology, Pediatrics, and Family Medicine with active involvements in Surgery/Emergency Medicine as well. Jack loved science, relentlessly, for the joy of discovery it provided. Here we describe the 37 years of Jack’s scientific career at the University of Colorado, much its early years being spent with Bob Grover and the later years being spent with many of those reading this article, including Lorna Moore. Fig. 1. John T. (“Jack”) Reeves, 1928–2004.

boyhood days. As reflected in his expression (Fig. 1), Jack presented an interesting mixture of intensity and humor, convention and eccentricity, rigor and permissiveness. As Peter Wagner remarked at the 2005 International Hypoxia Symposium honoring him, Jack’s eyes seem to follow one, no matter from what vantage point. Likewise his mouth is at once serious and smiling. An expression he liked to use, Jack too was an enigma wrapped in a mystery. Following his childhood in Hazard, Jack went north, attending the Massachusetts Institute of Technology where he graduated with a B.S. in Biology in 1950. He continued directly to the University of Pennsylvania School of Medicine, receiving his M.D. in 1954. After an internship and residency at Cincinnati General Hospital, Jack came to Denver for specialty training in Cardiology at the University of Colorado (then) Medical Center, staying there 4 years (1957–1961). During this time, Jack and his wife Carol started their family, with the birth of Charlotte and Cathy (their third daughter Beth following in 1967). But importantly for our purposes here, Jack established his association with Bob Grover, an association that laid the foundation for his lifelong research on cardiovascular responses to high altitude. After 4 years in Denver, Jack made a strategic decision: to return to Kentucky and establish himself in his academic career. This was not an “all or nothing” move; he continued to carry out significant research with Bob Grover in Colorado. Jack was at the University of Kentucky for 11 years (1961–1972), including 1 year with Geoffrey Dawes at Oxford University’s Nuffield Institute for Medical Research (1967–1968). In 1972 at Bob Grover’s invitation, Jack returned to Denver where he remained for 33 years, ended by his untimely death in 2004. When he retired officially in 1994–no one really noticed any difference in his work schedule or

2. The early years The year was 1957. When Jack Reeves arrived at what was then the University of Colorado Medical Center to begin his specialty training in cardiology, he was assigned to the cardiac catheterization laboratory under the direction of Bob Grover. Quite literally, this marked the beginning of Jack’s scientific career. Less than a decade earlier, catheterization of the human heart had been shown to be feasible as well as safe by Andr´e Cournand and D.W. Richards. This new procedure opened the possibility for more accurate diagnosis of congenital heart defects. Cardiac catheterization laboratories were established, providing direct measurements of intracardiac pressures and blood flow. −

2.1. The a– v O2 difference: a key for interpreting cardiac output From the outset, Jack applied his scientific training from the Massachusetts Institute of Technology and the University of Pennsylvania’s School of Medicine to the analysis of the data being collected during heart catheterization. He perceived the need for standards of normality against which to compare the measurements from patients with abnormal cardiac hemodynamics. For example, when one measured cardiac output in a patient, how did one decide whether or not it was normal? While it was accepted that cardiac output was related to body size, there was little data to support the concept that cardiac output could be normalized by the use of body surface area, the so-called cardiac index. At that time, cardiac output was measured by applying the Fick principle for O2 . Indicator dilution methods had yet to be perfected, and ultrasonic techniques were still in the future. After passing the tip of a cardiac catheter into the pulmonary artery, and with a rigid

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Cournand needle in a peripheral artery, one could collect simultaneously samples of mixed venous and arterial blood while expired air was collected in a Douglas bag. O2 consumption (V˙ O2 ) was calculated from analysis of the composition of expired air for O2 and CO2 concentration using the micro Scholander technique. The O2 and CO2 content of the blood samples were determined using the van Slyke manometric method. From these data the difference in O2 content between − arterial and mixed venous blood [(Ca − C v)O2 ; often −

abbreviated as “a– v difference”] could be determined ˙ (cardiac output) could then be calculated as and Q − V˙ O2 /(Ca − C v)O2 . Today this appears as a very laborintensive and time-consuming procedure, but in 1957 it was the accepted standard. Jack perceived that this procedure not only yielded measurement of cardiac output but also provided insight into total body O2 transport. Simply relating cardiac output to O2 consumption could be misleading due to the autocorrelation between the two parameters; O2 consumption is not only an independent variable (abscissa) but also a component of the calculated cardiac output (ordinate). Importantly, he realized that it was the magnitude of the whole body’s O2 extraction −

from the arterial blood (a– v difference) that was the index of the adequacy of cardiac output in supplying the O2 needs of the tissues. Jack proceeded to design, execute and publish a series of elegant and now classic papers exploring this fundamental principle. He demonstrated that in normal man during supine rest, the a-v difference remained within narrow limits (40 ± 6 ml/l) over a wide range of −

metabolic rates. Hence, examination of the a– v difference was the key to assessing the normality of cardiac output. A new standard had been established. Widening indicated inadequacy of O2 delivery, i.e. the cardiac output was below normal. Conversely, narrowing indicated the cardiac output was greater than normal (Reeves et al., 1961b). 2.2. The hemodynamic response to exercise How did cardiac output behave when the O2 requirements of the body were extended beyond the resting state? Jack examined this by having his normal supine subjects perform leg exercise on a bicycle ergome-

ter. This required insertion of a simple polyethylene catheter into the femoral vein. Now Jack believed that he should not ask any normal subject to undergo a procedure he himself was unwilling to perform. Therefore Jack’s data appear in this series of publications, and Bob had the honor of placing catheters in Jack’s pulmonary artery and femoral vein. This second catheter permitted examination of blood flow to the exercising −

leg. Jack found that femoral a– v difference increases sharply for mild exercise, and showed smaller further increase during heavier exercise. These responses were reflected by similar, but smaller, increases in total body −

a– v difference. From these findings he inferred that with mild exercise the increase in O2 demands are met primarily by increasing O2 extraction, whereas with heavier exercise, increasing blood flow was chiefly responsible for supplying additional O2 (Reeves et al., 1961c). Since most exercise is performed in the upright rather than supine posture, Jack proceeded to examine circulatory responses in both the total body and the exercising leg upon standing and during treadmill walking (not the stationary bicycle used by most investigators as well as himself in later years). Simply −

by standing, the pulmonary a– v difference widens by 70%, reflecting in a 38% decrease in cardiac output. An increase in vascular resistance in the legs accounted −

for much of this change; the femoral a– v difference increased 200% indicating a marked reduction in leg blood flow. Active walking produced little additional O2 extraction by the leg. All increase in O2 demand was met by progressive increases in leg blood flow. Cardiac output remained consistently lower than during supine exercise requiring comparable O2 consumption. Thus, the major difference in O2 transport between supine and upright exercise occurred in the control of circulation in the legs (Reeves et al., 1961a). 2.3. The hemodynamic response to altitude Having established hemodynamic parameters for normal men at rest and during exercise at low altitude, Jack then proceeded to apply this frame of reference for evaluating humans where the O2 transport system was under stress by the atmospheric hypoxia of high altitude. This endeavor began in 1963 with a chance conversation that Jack and Bob had with David Bruce

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Dill, another true pioneer in studies of environmental stress. Dill pointed out that the summer Olympic Games in 1968 would be held in Mexico City at an altitude of 7400 ft (2240 m), raising concerns about the potential effects of this moderate altitude on athletic performance. Dill was a master at stimulating research, and true to form, he suggested to Jack that this was a subject he might consider investigating. Jack took the bait and together with Bob designed a research project to study track athletes, first at low altitude and then again during a three-week sojourn at 10,150 ft (3100 m) in Leadville, Colorado (Reeves et al., 1967). During treadmill exercise, maximum O2 uptake (V˙ O2 max) was reduced by 25% during the first days after arriving 3100 m, with no change over the subsequent three weeks. Clearly some aspect of O2 transport had been compromised. Their studies revealed a minimal fall in arterial saturation during maximal exertion, implying that blood oxygenation within the lung was not the major limiting factor at this altitude (but possibly could be at higher altitudes). For a given O2 uptake, had cardiac output been reduced? Heart rate was higher at each level of exertion in Leadville but maximal heart rate was not significantly reduced. If cardiac output were indeed reduced, this suggested that a decrease in cardiac stroke volume was not offset by a more rapid heart rate. In fact, earlier investigators had also postulated a decrease in stroke volume at high altitude. Two years later, this hypothesis was tested directly by measuring cardiac output, again by the direct Fick method for O2 . Eight normal subjects performed supine leg exercise at four work loads, first at sea level and then after ten days in Leadville using the same research facility located in the basement of St. Vincents Hospital. For interpretation of the results, the same criteria were applied for the normal cardiac response to supine exercise that Jack had established earlier. At each level of O2 uptake during exercise, the arterio-venous differ− ence in blood O2 content (a– v O2 difference) was wider at high altitude than at sea level, indicating a reduction in cardiac output. Since the heart rate response to exercise was the same at both altitudes, stroke volume had decreased by 10–20%. Erroneously, they postulated at the time that this decrease in stroke volume was the result of a depression of myocardial function by hypoxia (Alexander et al., 1967).

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2.4. What then limits cardiac output at extreme altitude? Fast forward to 1985. Operation Everest II (OE II) was to be conducted under the leadership of Charles Houston, who 40 years previously had conducted OE I. An ambitious series of projects were to be carried out in concert in a large hypobaric chamber during progressive decompression over 40 days to a simulated altitude of 29,000 ft (8800 m), the summit of Mount Everest. Jack and his colleagues were responsible for investigations of O2 transport and myocardial function in the eight research subjects as they adapted to progressively more severe hypoxia. Exercise was performed in the upright posture on a bicycle ergometer with cardiac output measured once again by the direct Fick method for O2 . In contrast with the studies at 3100 m, for a given O2 uptake the a-v O2 difference was no wider than at sea level indicating no reduction in cardiac output. These results were confirmed by simultaneous measurements of cardiac output by thermodilution. However, heart rate was greater at each level of exercise, offsetting a reduction of stroke volume (Groves et al., 1987). Thus, as at 3100 m, a reduction in stroke volume was again observed at these much higher altitudes. The difference in heart rate response may have been due to the difference in posture between upright and supine. The next obvious step in understanding circulatory function at high altitude was to seek the mechanism responsible for the decrease in stroke volume. During OE II, direct measurement by cardiac catheter of ventricular filling pressures (right atrial and pulmonary artery wedge) demonstrated a reduced left ventricular filling pressure during exercise at high altitude. Echocardiography provided supporting evidence for reduced ventricular diastolic volumes (as well as reduced systolic volumes, decreased stroke volumes, but maintained or even increased ejection fractions). It now appeared that the reduced stroke volume resulted at least in part from lower ventricular filling pressures, leading to smaller diastolic volumes as described by the Frank-Starling relationship. These data indicated that ventricular pump function had remained normal even at extreme altitude (Reeves et al., 1987), thereby refuting the earlier speculation of myocardial depression by hypoxia. Additional evidence against depressed myocardial function was obtained from direct measurements of

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coronary blood flow (nitrous oxide) as well as cardiac output (Fick method for O2 ) during exercise at 3100 m (Grover et al., 1976a). In keeping with results from −

a previous investigation at this altitude, systemic a– v difference for O2 widened, cardiac output decreased and stroke volume was smaller at all levels of exer− cise. Coronary a– v difference also widened and coronary blood blow was actually less. Significantly, however, coronary sinus PO2 was preserved at 17–19 Torr under all conditions at both low and high altitude. This implied that myocardial tissue PO2 was also preserved, i.e. that myocardial hypoxia did not develop. Since it now appeared that a lowering of ventricular filling pressure (and not impaired myocardial function) was the primary basis for the reduction in stroke volume at high altitude, what was responsible for this? A decrease in blood volume could be involved. It has long been recognized that upon ascent to high altitude there is a prompt rise in hematocrit resulting from a fall in plasma volume and consequently blood volume (Grover et al., 1998). Hyperventilation resulting in hypocapnia and alkalosis also occur on arrival at high altitude. Reasoning that these two phenomena might be related, Jack Reeves designed an ingenious project to explore this piece of the puzzle. If subjects were exposed to simulated high altitude in a hypobaric chamber, and if hypocapnia and alkalosis could be prevented by adding CO2 to the atmosphere, then decreases in plasma and blood volume might not occur and stroke volume would remain normal. 2.5. Hypocapnia and plasma volume Such a project was conducted in 1974 in collaboration with investigators at the US Army Research Institute in Environmental Medicine (USARIEM) facility in Natick, Massachusetts (Grover et al., 1976b). Normal subjects were exposed to approximately 4300 m for 5 days. For the 5 subjects with supplemental CO2 , PAO2 was 56 Torr with PACO2 held at 41 Torr; for 3 subjects without supplemental CO2 , PAO2 was 57 Torr with PACO2 falling to 27 Torr. If the subjects were allowed to become hypocapnic, stroke volume fell as expected while hematocrit rose implying a decrease in plasma volume. Preventing hypocapnia resulted in maintenance of stroke volume with little change in hematocrit (plasma volume). Jack’s hypothesis proved to be correct.

But a very interesting and significant aspect of O2 transport also emerged. During heavy exercise in the group with supplemental CO2 , arterial O2 tension, content and saturation fell to significantly lower levels than in the hypocapnic group. This implied that impairment of O2 diffusion likely resulted from shortened capillary transit time. In other words, preservation of stroke volume (and pulmonary blood flow) did not enhance systemic O2 transport because the fall in arterial oxygenation cancelled out the benefit of higher blood volume and cardiac output. Indeed, maximal O2 uptake decreased just as much in the CO2 supplemented group (−32%) as in the hypocapnic group (−29%). As Jack would say, “You can’t fool mother nature”.

3. The later years At the time that Jack returned to Colorado in 1972, Bob Grover’s Cardiovascular Pulmonary (CVP) Research laboratory was enjoying unprecedented growth. The emergence of NIH Program Project Grants (PPG) as well as Training Grants and the clearly competitive nature of the research being done at CVP allowed it to capture substantial funding. Following Bob Grover’s retirement, CVP has been able to retain its PPG and training grants for now 33 and 29 years respectively, first under John Weil’s and now Ivan McMurtry’s leadership. Jack’s research during the 1970s, 1980s, and 1990s spanned a broad array of topics (Fig. 2). For Jack, working in these interesting, important areas; interacting with bright, hard-working, and internationally-diverse fellows; presenting results at national or international meetings; and conducting 1st class science around the world was like being a kid in the candy store. But it was not a hedonistic feast; rather, his was a serious, studied inquiry of each of the rich opportunities presented. During these years, Jack’s interests seem to have been less driven by a single, linearly unfolding series of questions than a circle of inter-related themes. The impetus for investigating a particular question was opportunistic, based on the chance constellation of factors that allowed him to move science forward and help a fellow or colleague answer a pressing question. Common to all was his interest in the O2 transport system, its response to high altitude, and the inter-relatedness as well as the underlying mechanisms controlling the

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Fig. 2. Factors bearing on the reduction in exercise performance at high altitude. Cardiac output, in Jack’s view, was determined by a balance between factors that limited a–v O2 extraction and/or served to protect the tissues. Shown are the individual components or systems bearing on cardiac output and exercise performance that Jack investigated. The chronological order of his investigations is shown roughly, in clockwise direction.

various components of the O2 transport system. Here we focus on the unfolding story of what limits exercise performance at high altitude. We leave it to others to summarize the broad range of studies he also conducted concerning the mechanisms, measurement, developmental regulation and species variation in hypoxic pulmonary hypertension. 3.1. Surveying health problems at high altitude In the late 1970s and early 1980s, Jack helped conduct a number of efforts to determine the importance of the various components of the O2 transport system for residents of high altitude. He probed this question from several vantage points. Many of these concerned infants and children, perhaps reflecting his time with Geoffrey Dawes in England. Together with Gene McCullough and Bob Liljegren at the Colorado state health department, Jack demonstrated that slowed growth in the third trimester of pregnancy was responsible for the altitude-associated reduction in infant birth weight pre-

viously reported by John Lichty (Lichty et al., 1957; McCullough et al., 1977). Moreover, when this slowing of growth occurred in newborns born prematurely (the frequency of which was at high and low altitude), such babies were more likely to die from respiratory complications. A second project with which Jack was involved concerned children living at high altitude who were especially susceptible to high altitude pulmonary edema (HAPE) when they returned from a lowaltitude sojourn (Scoggin et al., 1977). These persons had especially brisk hypoxic pulmonary vasoconstrictor responses which suggested, in combination with studies in adults who repetitively developed HAPE plus his earlier work in cattle susceptible to Brisket Disease (pulmonary hypertension and right heart failure), that pulmonary hypoxic vasoconstriction was, in part, genetically determined (Cruz et al., 1980). A third project, initiated by Meir Kryger and John Weil, showed that Leadville residents with chronic

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mountain sickness benefited from treatment with a ventilatory stimulant, medroxyprogesterone (Provera) as the result of improved oxygenation during sleep (Kryger et al., 1978). Collectively, these studies pointed to the importance of the various components of the O2 transport system and especially the lung, not just for immediate but also longer-term survival and reproductive success at high altitude. 3.2. Ventilatory acclimatization Jack’s next series of high altitude studies focused on the lung in general and ventilatory acclimatization in particular. Of course, the rudiments of ventilatory acclimatization had long since been described, prompted in part by Mabel Purefoy Fitzgerald’s pioneering observations in residents of Colorado’s remote mining camps during the early decades of the 20th century (Torrance and Reeves, 2001). But such processes varied among individuals; Jack wanted to know why and how this occurred. An opportunity to investigate these questions was developed in conjunction with Peter Hackett, whom Jack had met in 1977 when Peter was passing through Denver en route to Nepal. Some years previously, Peter and David Shlim had founded the Himalayan Rescue Association at Pheriche (4243 m) in order to provide health care for mountaineers, trekkers as well as Sherpa residing in the Khumbu Valley—Mt Everest Base Camp region of Nepal. Hundreds of trekkers went there, some slowly and some more rapidly by flying to Namche Bazar (2750 m). Peter and Jack reasoned that trekkers could be studied in Katmandu prior to ascent and predictions tested as to the extent to which variation in the hypoxic ventilatory response (HVR) and other characteristics affecting O2 transport predicted the occurrence of acute mountain sickness (AMS). An ambitious field project was carried out, unfortunately in a season marked by relatively few trekkers! Nonetheless, valuable information was gained concerning the role of fluid retention and weight gain in the development of AMS (Hackett et al., 1982)—attributes which could be related to the extent of hypocapnia and the body’s handling of plasma volume and other fluid compartments. Another product was a valuable paper on Sherpa HVR that led to a reassessment of whether or not chronic hypoxia “blunted” HVRs equally in all high altitude residents (Hackett et al., 1980).

Perhaps it was the arduous circumstances of carrying out mechanistic studies in Nepal. Or perhaps it was simply the geographic proximity of Pikes Peak with a well-equipped research laboratory at 4300 m only 100 miles from Denver on (mostly) paved roads. In any event, Jack’s next series of projects dealing with ventilatory acclimatization to high altitude was carried out on Pikes Peak. Variation among individuals in acute HVR, as measured by the progressive isocapnic hypoxia test devised by John Weil, was known to exist. But did such variation influence ventilatory acclimatization? During the summer of 1982, a team assembled under Jack’s leadership carefully dissected the relative roles of several factors affecting ventilation. These studies showed that once acclimatization was achieved, ventilation had risen to the level predicted by the acute HVR. But initially, ventilation was depressed by two factors; the magnitude of the depressant effects of hypocapnia, itself related (inversely) to the hypercapnic ventilatory drive, and the depressant effects of sustained hypoxia (Huang et al., 1984a). Yet a third but this time stimulatory factor, was the betasympathetically mediated rise in metabolic rate. While the rise in metabolic rate did not affect the level of effective alveolar ventilation as measured by the PACO2 , it contributed to the increase in total ventilation (Huang et al., 1984b). Some years later, Jack noted that a fourth factor was also important; the variation in resting ventilation present among individuals while residing at sea level, since sea-level PACO2 related positively to the level of ventilation at high altitude once acclimatization was achieved (Reeves et al., 1993). 3.3. Autonomic nervous system In the late 1980s, Jack’s focus moved to the role of the sympatho-adrenal nervous system. The roots of this interest are obscure but may have stemmed from the classic recognition that this system plays a vital role in the body’s defenses against environmental stress. Perhaps an animated conversation between Jack and Alan Cymerman reinforced the potential importance of this phenomenon as Jack, Lorna and Alan winged their way to Hong Kong to join a group of scientists invited by Dr. Shu-Tsu Hu of the Shanghai Institute of Physiology to give talks about our high altitude studies. (Jack had helped set up this visit by meeting with Dr. Hu and others, including Premier Deng Xiao-Peng,

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in 1980. The trip was to prove valuable for making connections that eventually enabled Lorna Moore to conduct an important series of research studies in Tibet involving Jack and many others). Perhaps, too, Jack’s interests in the autonomic nervous system were reinforced by a conversation with Marsh Tenney about the similarity between the effects of long term high altitude residence and training, given that both led to a diminution in the sympathetic limb and relative dominance of the parasympathetic limb during exercise. In any event, Jack spearheaded important studies in the late 1980s and early 1990s on the roles of the alpha and beta limbs of the sympathetic nervous system (SNS) for altitude acclimatization. In partnership with George Brooks, Gail Butterfield and Bob Mazzeo, studies were conducted in subjects that had been recruited from the San Francisco area, thus avoiding the effects of the moderate altitude of Denver on low-altitude determinations. Rigorous dietary controls were established under Gail’s watchful eye to ensure that no change in energy intake or body weight occurred with high altitude ascent. In a key study, Bob Mazzeo observed that there was a close temporal dissociation in circulating catecholamines; a rise in epinephrine occurred early, followed by an elevation in norepinephrine (Mazzeo et al., 1991; Mazzeo et al., 1995). Different mechanisms were implicated since the rise in epinephrine was likely adrenal in origin whereas the norepinephrine increase likely due to sympathetic stimulation. Elevated epinephrine levels were closely associated with increased heart rate, broncho dilation, and greater reliance on carbohydrates for fuel—all of which would act to increase the efficiency of O2 utilization, although at the cost of increased metabolic rate and lactate production (Reeves, 1993). As ventilatory acclimatization progressed and arterial O2 saturation rose, epinephrine levels fell and norepinephrine rose, leading to constriction of both arteries and veins, a rise in blood pressure and decrease in plasma volume. Supporting increased sympatho-adrenal stimulation was not only a rise in circulating catecholamine levels, but also increased urinary excretion and release across the exercising muscle (Mazzeo et al., 1994b, 1995). But what caused this sympatho-adrenal stimulation? Jack reasoned that O2 sensors were likely involved, but where these were located was unknown. Also unknown were the roles played by the beta and alphaadrenergic limbs of the SNS. This latter was the ques-

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tion that Jack turned to next, evaluating the role of the beta-limb. In 1986, 12 male sea-level residents were treated with either propranolol or a placebo in a double-blinded study and then tested at low (1600 m) as well as at high (4300 m) altitude on top of Pikes Peak. At high altitude, propranolol effectively blocked the rise in resting metabolic rate, implicating betaadrenergic stimulation (Moore et al., 1986). However, ventilatory acclimatization itself was unaffected since PACO2 fell similarly in propranolol and placebotreated subjects. Nor did beta-sympathetic inhibition influence the cardiac output response to exercise or the level of exercise performance (V˙ O2 max) achieved. While blood pressure and heart rate were markedly lower in the propranolol-treated subjects, an increase in stroke volume enabled these healthy young men to achieve similar levels of cardiac outputs and exercise performance. The temporal disassociation between the changes in epinephrine and norepinephrine led Jack, together with George Brooks and Gail Butterfield to hypothesize that early beta-adrenergic stimulation prompted a rise in glycolysis and lactate production after high altitude ascent. Using sophisticated measurements of glucose kinetics, uptake, and oxidation, they were able to show that beta-adrenergic stimulation was responsible for the early rise in lactate and increased reliance on glucose as fuel (Roberts et al., 1996). However, the so-called “lactate paradox” or reduction in arterial lactate levels at a given exercise level following acclimatization, could not be attributed to beta-adrenergic stimulation since the acclimatization-related fall in lactate was similar in the propranolol- and placebo-treated groups (Mazzeo et al., 1994a). Rather, changes in lactate extraction and rising SaO2 were likely responsible (Brooks, 1999). The next series of Pikes Peak studies was a project called “Women at Altitude”, headed by Lorna Moore and Gail Butterfield but involving Jack and many other valued co-investigators. This ambitious 3-year study sought to remedy our relative lack of knowledge about altitude acclimatization in women who, while comprising 51% of the adult population, had often been excluded from earlier investigations or included in too small a number to permit meaningful analysis. Studies were conducted concerning the ventilatory, cardiovascular, erythropoietic, metabolic and autonomic nervous system-related processes of acclimatization (Braun et al., 1998, 2000, 2001; Fulco et al., 2001; Mawson et al.,

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2000; Muza et al., 2001; Reeves et al., 2001; Zamudio et al., 2001). While women were found to resemble men in terms of their ventilatory acclimatization and the altitude-related fall in cardiac output and exercise performance, differences were also apparent insofar as women showed a preference for fat (versus glucose) as fuel and greater preservation of small muscle endurance than was true for men (Braun et al., 2000; Fulco et al., 2001; Muza et al., 2001). However, since women’s alterations in epinephrine and norepinephrine levels were similar to those of men’s (Mazzeo et al., 2001), the opportunity existed to take the next step in exploring the role of the alpha limb of the adrenergic nervous system. In 1998 and 1999, women were studied both at sea level and at 4300 m while being treated with a combined alpha1 and alpha-2 receptor blocker (prasozin) or placebo. Prasozin decreased the rise in blood pressure, implicating alpha-receptor stimulation in the blood pressure rise, but other factors were also involved since some pressure rise nonetheless occurred. Prasozin also reduced the fall in plasma volume by about 2/3rds, implicating venous alpha-adrenergic stimulation as the principal factor in the plasma volume fall. However, the changes in ventilation, cardiac output and exercise (including endurance) performance were unaffected by alpha-adrenergic blockade, suggesting that alphaadrenergic stimulation alone was not responsible for the cardiac output and exercise decline (Tamhane et al., 1999). A difficulty implicit in such studies was that alpha-adrenergic blockade likely prompted compensatory changes in other portions of the SNS, making it difficult to isolate the effects of any one factor alone. 3.4. Acute and chronic altitude illnesses Were another reoccurring theme in Jack’s work. In addition to his late-1970s studies in Nepal concerned with acute mountain sickness, Jack also masterminded a chamber study to assess the influences of increased brain blood flow via measurements of internal carotid artery blood flow velocity. Although marked increases in flow velocity occurred, there were no differences between sick versus well subjects during acute altitude exposure (Reeves et al., 1985). In his later years, Jack played a key role in assembling a consensus group for purposes of better defin-

ing, and ultimately understanding, chronic mountain sickness (CMS). Together with Fabiola Leon-Velarde, Jack helped guide the group through often colorful debates to arrive at a consensus definition and course of study for improving our ability to diagnose and understand this still-enigmatic condition (Leon-Velarde et al., 2005). Key to the definition of CMS was the level of hemoglobin concentration present at a given altitude. Persons with CMS had, by definition, elevated hemoglobin levels, but what were the consequences of this variation in hemoglobin levels at a given altitude, not only with respect to CMS but also for persons in the normal range? At rest, the increase in total red cell mass and consequent rise in hemoglobin concentration had long been thought to be “useful” by increasing the blood’s O2 carrying capacity, O2 content, and thereby offsetting the arterial desaturation. But in a review of literature data carried out with Fabiola, Jack found little evidence to suggest that such secondary polycythemia did indeed improve O2 transport at rest (Reeves and Leon-Velarde, 2004). He had hoped to apply this to an understanding of the contribution of higher hemoglobin levels during exercise when an elderly driver, momentarily blinded by the bright Colorado morning sun, struck him while riding his bicycle to work. The determination of whether increased hemoglobin helps or hinders O2 transport to the working muscle awaits future exploration.

4. Legacy Jack’s legacy is the influence he has had on his fellows, co-workers, and via his publications. Jack worked with persons from many disciplines during his 37-year scientific career at the University of Colorado (and the additional 11 years in Kentucky or England), Jack worked with persons from many disciplines. “Interdisciplinarity” is a new buzzword at NIH and other national agencies; Jack practiced interdisciplinary science for nearly 50 years. The MDs with whom he worked came from anesthesiology, cardiology, pediatrics, pulmonary medicine and surgery; the PhDs from anthropology, biology, engineering, physiology and more. The list of those who published with Jack is long and diverse in terms of disciplinary origin (Table 1). Also impressive is the high proportion who went on to establish distinguished

L.G. Moore, R.F. Grover / Respiratory Physiology & Neurobiology 151 (2006) 96–108 Table 2 Jack Reeves’ publications, 1959–2005

Table 1 Jack’s fellows and co-authors Aldashev Bender Burghuber Doekel Durmowicz Fasules Fedderson Hackett Hiser Hoffman Huang Hyers Kryger Kuriyama Martin McMurtry Mlczoch Moore Morganroth Morrison Newman

Almas Paul Ole Bob Tony Jim Ole Peter Wes Eric Shao-Yung Tom Meir Takayuki Bruce Ivan Johannes Lorna Mel Doug John

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Orton Peacock Redding Rounds Scoggin Selland Shelub Stelzner Stenmark Stevens Sugita Tucker Turkevitch VanBenthuysen vanGrondelle Voelkel Walker Weir Welsh Worthen Zuckerman

Chris Andy Greg Sharon Charlie Mark Irv Tom Kurt Troy Takeshi Alan Darya Karl Albertus Norbert Ben E. Kenneth Carlolyn Scott Brian

scientific careers of their own and who continue to mentor the next generation of scientists in a great many fields. For Jack’s fellows and colleagues, another part of his legacy is the example and instruction he provided for how to focus one’s ideas and be able to describe them in clear prose, backed up graphs or other visually compelling kinds of data. He did this in a distinctive manner. Much was done by quiet observation. Then, often in the setting of the CVP Research lab seminars, Jack would assume his country boy pose (often accompanied by a folk tale of some sort) and ask a penetrating question . . . one that would, at once, summarize the central point and pose the critical issue. This could be intimidating (and often was), but it was always instructive. If the fellow was receptive and Jack sufficiently interested, the conversation would continue. “Show me the data” was the way such a session might start. And then it would progress quickly to where Jack would use his “stubby-pencil” technique for scrutinizing the data, find its hidden meaning, and somehow craft the right story for conveying its message. Jack’s initial graphical presentations were often crude, with hand-drawn wobbly lines, even after he too had become computer savvy. But always the point made was clear and insightful.

Distribution, by decade Total 1960s 1970s 1980s 1990s 2000–2005

N (% total) 385 45 (12%) 85 (22%) 127 (33%), and 2 books 100 (26%), and 7 books 28 (7%), and 2 books

Distribution, by author 1st author 2nd author Last author Other

N (%total) 110 (29%) 39 (10%) 137 (36%) 99 (26%)

Distribution, by topic Altitude, general AMS, HAPE, CMS Autonomic nervous system Cardiac output Chronic lung disease Erythropoiesis Exercise Female hormones, pregnancy, IUGR Fetal/neonatal cardiopulmonary transition Heart failure and treatment Metabolism (glucose, lactate) Miscellaneous Pulmonary hypertension Pulmonary anatomy Systemic circulation, blood flow Techniques Ventilation

% total 4% 6% 3% 3% 3% 0% 6% 2% 3% 3% 3% 3% 44% 3% 3% 4% 6%

The other part of Jack’s legacy is his rich series of articles, some 385 peer-reviewed journal articles or chapters and 11 books (Table 2). This number is likely to grow as several of his projects remain active. The broad topical distribution of Jack’s articles reflects the breadth of his interests; over half are in 14 or more topical areas. The greatest concentration concerns pulmonary hypertension but, as described above, he is equally well known for his contributions to the study of altitude illness, cardiac output and circulatory control, metabolism, and ventilation. Nearly always the scientist, he was also an avid reader and photographer (during one period, chiefly in black and white). He wrote several books; one a little volume called Literary Gems (The Cottage Press, Lincoln Center, MA), a compendium of

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books that he thought should not be missed at any age.

5. Conclusions Jack recognized the interconnectedness of all the components of the O2 transport system. Like Walter B. Cannon, Jack too thought that the “regulating system which determines homeostasis may comprise a number of cooperating factors [which] may be brought into action at the same time or successively” (Reeves, 1993). But Jack yearned to understand the mechanisms responsible for this interrelatedness. Was it the autonomic nervous system? Jack considered that the alpha-adrenergically mediated increase in systemic vascular resistance and decrease in plasma volume could limit cardiac output. Was this to protect the brain from sustained hypoxia? In other words, rather than the reduction in cardiac output being the result of failure in one or more components of the O2 transport system in compensating for the reduced O2 availability at high altitude, perhaps SNS activation served to keep muscle and other organ blood flow in check. Alpha-adrenergic stimulation could prevent most of the fall in plasma volume at high altitude. But neither alpha- nor beta-adrenergic inhibition alone could restore cardiac output and exercise performance at high altitude, hence arguing against either of the two limbs of the sympathetic nervous system – independently – as being responsible. The inter-relatedness of these two limbs was also an issue; if one was blocked, the other may compensate. In addition, the parasympathetic limb of the autonomic nervous system was also likely involved, as suggested by the relative parasympathetic dominance together with greater maximal exercise capacity in Tibetan compared with acclimatized Han (“Chinese”) residents of high altitude (Sun et al., 1990; Zhuang et al., 1993). An alternate explanation is that the limitation in exercise performance at high altitude was due to mechanical factors restricting the rise in ventilation or, as argued by Peter Wagner, O2 diffusion in the lung and working muscle (Wagner, 2000). Jack enjoyed having a riddle with which the best minds of his and the next generation could grapple. As he would say, in trying to solve the riddle, much will be learned. For example, new technologies can be

usefully applied by, for example, employing ‘knock out’ or otherwise genetically modified animals to yield more definitive manipulations of the autonomic nervous system or by probing the genetic variation that exists within and between populations for clues as to the factors responsible for exercise performance differences observed. Jack would be pleased to know that the challenges of high altitude continue to prompt exploration.

References Alexander, J.K., Hartley, L.H., Modelski, M., Grover, R.F., 1967. Reduction of stroke volume during exercise in man following ascent to 3100 m altitude. J. Appl. Physiol. 23, 849–858. Braun, B., Butterfield, G.E., Dominick, S.B., Zamudio, S., McCullough, R.G., Rock, P.B., Moore, L.G., 1998. Women at altitude: changes in carbohydrate metabolism at 4300 m elevation and across the menstrual cycle. J. Appl. Physiol. 85, 1966–1973. Braun, B., Mawson, J.T., Muza, S.R., Dominick, S.B., Brooks, G.A., Horning, M.A., Rock, P.B., Moore, L.G., Mazzeo, R.S., EzejiOkoye, S.C., Butterfield, G.E., 2000. Women at altitude: carbohydrate utilization during exercise at 4300 m. J. Appl. Physiol. 88, 246–256. Braun, B., Rock, P.B., Zamudio, S., Wolfel, G.E., Mazzeo, R.S., Muza, S.R., Fulco, C.S., Moore, L.G., Butterfield, G.E., 2001. Women at altitude: short-term exposure to hypoxia and/or alpha(1)-adrenergic blockade reduces insulin sensitivity. J. Appl. Physiol. 91, 623–631. Brooks, G., 1999. Are arterial, muscle and working limb lactate exchange data obtained on men at altitude consistent with the hypothesis of an intracellular lactate shuttle? Adv. Exp. Med. Biol. 474, 85–204. Cruz, J., Reeves, J.T., Russell, B., Alexander, A., Will, D., 1980. Embryo-transplanted calves: the pulmonary hypertensive trait is genetically transmited. Proc. Soc. Exp. Biol. Med. 164, 142–145. Fulco, C.S., Rock, P.B., Muza, S.R., Lammi, E., Braun, B., Cymerman, A., Moore, L.G., Lewis, S.F., 2001. Gender alters impact of hypobaric hypoxia on adductor pollicis muscle performance. J. Appl. Physiol. 91, 100–108. Grover, R.F., Lufschanowski, R., Alexander, J., 1976a. Alterations in the coronary circulation of man following ascent to 3100 m altitude. J. Appl. Physiol. 41, 832–838. Grover, R.F., Reeves, J.T., Maher JTM, Robert, E., Cruz, J.C., Denniston, J.C., Cymerman, A., 1976b. Maintained stroke volume but impaired arterial O2 ation in man at high altitude with supplemental CO2 . Circ. Res. 38, 391–396. Grover, R.F., Selland, M.A., McCullough, R.G., Dahms, T.A., Wolfel, E.E., Butterfield, G.E., Reeves, J.T., Greenleaf, J.E., 1998. ␤-adrenergic blockade does not prevent polycythemia or decrease in plasma volume in men at 4300 m altitude. Eur. J. Appl. Physiol. 77, 264–270. Groves, B.M., Reeves, J., Sutton, J.R., Wagner, P., Cymerman, A., Malconian, M., Rock, P., Young, P., Houston, C., 1987. Operation

L.G. Moore, R.F. Grover / Respiratory Physiology & Neurobiology 151 (2006) 96–108 Everest II: preservation of cardiac function at great altitude. J. Appl. Physiol. 63, 531–539. Hackett, P., Rennie, D., Hofmeister, S., Grover, R.F., Grover, E.B., Reeves, J.T., 1982. Fluid retention and relative hypoventilation in acute mountain sickness. Respiration 43, 321–329. Hackett, P.H., Reeves, J.T., Reeves, C.D., Grover, R.F., Rennie, D., 1980. Control of breathing in Sherpas at low and high altitude. J. Appl. Physiol. Respir. Environ. Exercise Physiol. 49, 374– 379. Huang, S.Y., Alexander, J.K., Grover, R.F., Maher, J.T., McCullough, R.E., McCullough, R.G., Moore, L.G., Sampson, J.B., Weil, J.V., Reeves, J.T., 1984a. Hypocapnia and sustained hypoxia blunt ventilation on arrival at high altitude. J. Appl. Physiol. Respir. Environ. Exercise Physiol. 56, 602–606. Huang, S.Y., Alexander, J.K., Grover, R.F., Maher, J.T., McCullough, R.E., McCullough, R.G., Moore, L.G., Weil, J.V., Sampson, J.B., Reeves, J.T., 1984b. Increased metabolism contributes to increased resting ventilation at high altitude. Respir. Physiol. 57, 377–385. Kryger, M., McCullough, R., Doekel, R., Collins, D., Weil, J.V., Grover, R.F., 1978. Excessive polycythemia of high altitude: Role of ventilatory drive and lung disease. Am. Rev. Respir. Disease 118, 659–666. Leon-Velarde, F., Maggiorini, M., Reeves, J., Aldashev, A., Asmus, I., Bernardi, L., Ge, R.-L., Hackett, P., Kobayashi, T., Moore, L., Penaloza, D., Richalet, J.-P., Roach, R., Wu, T., Vargas, E., Zubieta-Castillo, G., Zubieta-Calleja G. 2005. Consensus Statement on Chronic and Sub-Acute High Altitude Diseases [Position Paper]. High Alt. Med. Biol. 6, 147–158. Lichty, J.L., Ting, R., Bruns, P.D., Dyar, E., 1957. Studies of babies born at high altitude. Am. J. Diseases Children 93, 666– 669. Mawson, J.T., Braun, B., Rock, P.B., Moore, L.G., Butterfield, G.E., 2000. Women at altitude: energy requirement at 4300 m. J. Appl. Physiol. 88, 272–281. Mazzeo, R., Bender, P., Brooks, G., Butterfield, G.E., Groves, B.M., Sutton, J.R., Wolfel, E.E., Reeves, J.T., 1991. Arterial catecholamine responses during exercise with acute and chronic high altitude exposure. Am. J. Physiol. 261, E419–E424. Mazzeo, R.S., Brooks, G.A., Butterfield, G.E., Cymerman, A., Roberts, A.C., Selland, M., Wolfel, E.E., Reeves, J.T., 1994a. Beta-adrenergic blockade does not prevent the lactate response to exercise after acclimatization to high altitude. J. Appl. Physiol. 76, 610–615. Mazzeo, R.S., Brooks, G.A., Butterfield, G.E., Podolin, D.A., Wolfel, E.E., Reeves, J.T., 1995. Acclimatization to high altitude increase muscle sympathetic activity both at rest and during exercise. Am. J. Physiol. 269, R201–R207. Mazzeo, R.S., Carroll, J.D., Butterfield, G.E., Braun, B., Rock, P.B., Wolfel, E.E., Zamudio, S., Moore, L.G., 2001. Catecholamine responses to alpha-adrenergic blockade during exercise in women acutely exposed to altitude. J. Appl. Physiol. 90, 121–126. Mazzeo, R.S., Wolfel, E.E., Butterfield, G.E., Reeves, J.T., 1994b. Sympathetic response during 21 days at high altitude (4,300 m) as determined by urinary and arterial catecholamines. Metab. Clin. Exp. 43, 1226–1232.

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McCullough, R.E., Reeves, J.T., Liljegren, R.L., 1977. Fetal growth retardation and increased infant mortality at high altitude. Arch. Environ. Health 32, 36–40. Moore, L.G., Cymerman, A., Huang, S.Y., McCullough, R.E., McCullough, R.G., Rock, P.B., Young, A., Young, P.M., Bloedow, D., Weil, J.V., 1986. Propranolol does not impair exercise O2 uptake in normal men at high altitude. J. Appl. Physiol. 61, 1935–1941. Muza, S.R., Rock, P.B., Fulco, C.S., Zamudio, S., Braun, B., Cymerman, A., Butterfield, G.E., Moore, L.G., 2001. Women at altitude: ventilatory acclimatization at 4300 m. J. Appl. Physiol. 91, 1794–1799. Reeves, J., 1993. Sympathetics and hypoxia: A brief overview. In: Sutton, J., Houston, C., Coates, G. (Eds.), Hypoxia and Molecular Medicine. Queen City Printers, Burlington, VT, Chapter 1. Reeves, J, Groves, B.M., Sutton, J.R., Wagner, P.D., Cymerman, A., Malconian, M., Rock, P., Young, P., Houston, C., 1987. OEII: preservation of cardiac function at extreme altitude. J. Appl. Physiol. 63, 531–539. Reeves, J., Leon-Velarde, F., 2004. Chronic mountain sickness: recent studies of the relationship between hemoglobin concentration and O2 transport. High Alt. Med. Biol. 5, 147–155. Reeves, J.T., Grover, R.F., Blount Jr., S.G., Filley, G.F., 1961a. The cardiac output response to standing and treadmill walking. J. Appl. Physiol. 16, 283–288. Reeves, J.T., Grover, R.F., Cohn, J.E., 1967. Regulation of ventilation during exercise at 10,200 ft in athletes born at low altitude. J. Appl. Physiol. 22, 546–554. Reeves, J.T., Grover, R.F., Filley, G.F., Blount Jr., S.G., 1961b. Cardiac output in normal resting man. J. Appl. Physiol. 16, 276–278. Reeves, J.T., Grover, R.F., Filley, G.F., Blount Jr., S.G., 1961c. Circulatory changes in man during mild supine exercise. J. Appl. Physiol. 16, 279–282. Reeves, J.T., McCullough, R.E., Moore, L.G., Cymerman, A., Weil, J.V., 1993. Sea-level PCO2 relates to ventilatory acclimatization at 4300 m. J. Appl. Physiol. 75, 1117–1122. Reeves, J.T., Moore, L.G., McCullough, R.E., McCullough, R.G., Harrison, G., Tranmer, B.I., Micco, A.J., Tucker, A., Weil, J.V., 1985. Headache at high altitude is not related to internal carotid arterial blood velocity. J. Appl. Physiol. 59, 909–915. Reeves, J.T., Zamudio, S., Dahms, T.E., Asmus, I., Braun, B., Butterfield, G.E., McCullough, R.G., Muza, S.R., Rock, P.B., Moore, L.G., 2001. Erythropoiesis in women during 11 days at 4300 m is not affected by menstrual cycle phase. J. Appl. Physiol. 91, 2579–2586. Roberts, A., Butterfield, G., Cymerman, A., Reeves, J., Wolfel, E., Brooks, G., 1996. Acclimatization to 4300 m altitude decreases reliance on fat as a substrate. J. Appl. Physiol. 81, 1762–1771. Scoggin, C.H., Hyers, T.M., Reeves, J.T., Grover, R.F., 1977. Highaltitude pulmonary edema in the children and young adults of Leadville, Colorado. New England J. Med. 297, 1269– 1272. Sun, S.F., Droma, T.S., Zhuang, J.G., Tao, J.X., Huang, S.Y., McCullough, R.G., McCullough, R.E., Reeves, C.S., Reeves, J.T., Moore, L.G., 1990. Greater maximal O2 uptakes and vital capacities in Tibetan than Han residents of Lhasa. Respir. Physiol. 79, 151–161.

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Tamhane, R., McCullough, R., Wofel, E., Hsia, C., Moore, L., 1999. Cardiac output response during acclimatization to high altitude in women. FASEB 13, A784. Torrance, R., Reeves, J.T., 2001. Major breathing in miners: Mabel Purefoy Fitzgerald, an intrepid scientist, visits Colorado’s high mines. In: Reeves, JT., Grover, RF. (Eds.), Attitudes on Altitude. Boulder, Co: Univ of Colorado Press, pp. 59– 87. Wagner, P., 2000. New ideas on limitations to V˙ O2 max. Exerc. Sport. Sci. Rev. 28, 10–14.

Zamudio, S., Douglas, M., Mazzeo, R.S., Wolfel, E.E., Young, D.A., Rock, P.B., Braun, B., Muza, S.R., Butterfield, G.E., Moore, L.G., 2001. Women at altitude: forearm hemodynamics during acclimatization to 4,300 m with alpha1-adrenergic blockade. Am. J. Physiol. Heart Circ. Physiol. 281, H2636–H2644. Zhuang, J., Droma, T., Sutton, J.R., McCullough, R.E., McCullough, R.G., Groves, B.M., Rapmund, G., Janes, C., Sun, S., Moore, L.G., 1993. Autonomic regulation of heart rate response to exercise in Tibetan and Han residents of Lhasa (3658 m). J. Appl. Physiol. 75, 1968–1973.