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Barosaurus and its circulation

SIR,-Dr Choy and Dr Altman postulate that some dinosaursmight have had multiple hearts (Aug 29, p 534), and I had

independently reached the same conclusion. In response to thisproposal, Professor Millard and colleagues (Oct 10, p 914) suggestthat estimates of the arterial pressure necessary to perfuse the headshould be based on a heart-to-head height of only 8 m, rather thanthe 12 m of Choy and Altman, which would give a mean systemicarterial pressure of 740 mm Hg. La Place’s law indicates that thepressure generated by the heart is directly proportional to theventricular wall thickness. Thus, to generate a pressure nine timeshigher than that of a whale of similar mass (to support this 8 mpressure head in the dinosaur), the left ventricle of a sauropod heartwould have been about 90 cm thick. If it is further assumed that theheart was spherical and that the density of the sauropodmyocardium was similar to that of mammals, a sauropod heartwould have weighed about 7-3 tonnes and would have had adiameter of about 2-3 m. A heart of this size would be intrinsicallyinefficient, and is unlikely in view of the fact that the total weight ofTyrannosaurus rex was probably about 7 tonnes.Millard et al argue further against multiple hearts on the grounds

that they would "probably create non-continuous blood flow at thebrain" and that there would be "risks of damage or interruption ofblood flow during activities such as combat, mating, and falling tothe ground from syncope", without saying why this might be so.There is indeed no reason why the flow resulting from multiplehearts in series should be less continuous than the flow from a singleheart, and many contemporary animals including the hagfish, thegiant Brazilian earthworm, and many insects function well withmultiple perfusion organs. Dr Rewell (Oct 10, p 914) points out thatsyncope would be disastrous for the dinosaur if the ensuing rapidloss of consciousness resulted in a "spectacular cervical

dislocation", as it does in giraffes.As have others before them, Millard et al suggest that the

problem of cerebral perfusion of barosaurus may have beenameliorated if these giant animals lived partly submerged in water.Although this strategy may have relieved their cardiovascular

system of the pressure problem, the mechanical work of breathingwhile the torso was submerged by several metres makes this optionhighly unlikely.The alternative possibility that the blood flow between the heart

and the brain operated as a siphon, which would reduce the pressurerequired and therefore the size of the heart, can be rejected on thegrounds that the pressure at the top of a siphon is usuallysub-atmospheric, and a siphon would therefore be unable to perfusetissues of the head exposed to atmospheric pressure, such as thesense organs.

I therefore agree with Choy and Altman’s educated guess that thegreat sauropods may have managed the difficulty of perfusing abrain located at the top of a high column by means of (probablymultiple) pulsatile organs with their associated valves, in theirnecks. This arrangement would enable non-cranial circulation totake place at a moderate pressure. If the auxiliary hearts wereindependently controlled to regulate the blood pressure to the head,they would also reduce the large compensatory changes in arterialpressure that would inevitably occur when the animal lowered itshead to drink or feed. It is even possible that the additional heartsevolved from, or into, carotid sinuses.

Department of Physiology,University of Adelaide,5001 Adelaide, South Australia JAMES M. DENNIS

SiRj—Dr Choy and Dr Altman propose that the sauropoddinosaur barosaurus had accessory hearts to pump blood up its erectneck, but Professor Millard and colleagues regard these as

unnecessary, and say that a more tenable proposition "is thatbarosaurus was amphibious and supported its neck partly oroccasionally in water". However, the current consensus, based onevidence such as the foot skeleton, narrow chest, and erect stance, isthat sauropods were primarily terrestrial, like, for example,elephants.l-3 The long neck was used for gathering food, like the

An elasmosaur.

The long neck poses problems for its respiratory physiology Courtesyof Leicestershire Museums, Arts and Records Service.’ 7

elephant’s trunk and giraffe’s neck. The neck was a highly refinedcantilever beam of great strength and lightness, counterbalanced bythe tail. It did not need support in water; Choy and Altman’s figs 2and 3 show the weightsaving hollowed structure of the cervicalvertebrae, and the split neural spine housing a massive nuchalligament. 3

Alexander has shown that barosaurus could not use the neck as asnorkel to breathe while standing on the bottom in deep water.3This would, of course, compensate precisely for the pressure causedby the column of blood within the neck, easing cardiovascularproblems, but the water would cause an overpressure of about80 kPa-ie, about 8 tonnes-weight per square metre-crushing thelungs inwards. I suspect that even if the muscles were strong enoughto resist this pressure and even to inspire, water pressuretransmitted through the blood would tend to rupture the

pulmonary capillaries.The same difficulty was shared by another group of bizarrely

long-necked extinct reptiles, the elasmosaurid plesiosaurs. Thesefish-eating and cephalopod-eating marine reptiles include somewith necks 6 m long on a total body length of almost 13 m (figure).’Respiratory physiologists may also like to contemplate the dilemmaof the optimum diameter of the tracheal lumen. The larger thelumen, at least underwater, the more buoyancy is provided tocompensate for the nose-heaviness induced by the dense muscle andbone of the long neck, but the greater the stagnant air volume withinthe trachea. This last would be a drawback if the elasmosaur, likemany marine mammals, surfaced only briefly, taking one or twobreaths before submerging. Presumably the elasmosaur had hugelungs, breathed several times, or both. The almost universalpresence of stomach stones, apparently for ballast,s would

compensate for the large lungs. Perhaps the elasmosaur was a fairlylethargic ambush predator, hovering in the water, taking its timeover surfacing to breathe, and catching prey by darting out its longneck rather than swimming after it.6

Leicestershire Museums, Arts and Records Service,Leicester LE1 6TD, UK MICHAEL A. TAYLOR

1. Bakker RT. Ecology of the brontosaurs. Nature 1971; 229: 172-74.2. Coombs WP. Sauropod habits and habitats. Palaeogeogr Palaeoclimatol Palaeoecol

1975; 17: 1-33.3. Alexander RMcN. Dynamics of dinosaurs and other extinct giants. New York,

Columbia University Press, 1989: 167.4. Welles SP. Elasmosaurid plesiosaurs with description of new material from California

and Colorado. Mem Univer Calif 1943; 13: 125-254.5. Taylor MA. Plesiosaurs: rigging and ballasting. Nature 1981; 290: 628-29.6. Massare JM. Swimming capabilities of Mesozoic marine reptiles: implications for

method of predanon. Paleobiology 1988; 14: 187-203.7. Taylor MA, Martin JG. Big mouths and long necks: the plesiosaurs, fossil

sea-monsters of ancient times. Leicester: Leicestershire Museums, Arts andRecords Service, 1990: 24.

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SIR,-Dr Choy and Dr Altman’s speculation, we suggest, isformulated on a misconception. Their hypotheses, as well as thoseof others,1,2 are based on the assumption that the circulatory systembehaves like an open system. In such a system the blood is raised

from a lower to a higher gravitational potential energy and on returnto the heart it acts as a free falling liquid. Therefore, in a creature inan upright position, the greater the vertical distance between theheart and the head, the greater the pressure required to pump theblood up to the brain. To provide evidence that their assumption iscorrect, they report the high mean aortic pressures (about 250 mmHg) measured in the giraffe;3 "the nearest living model of thelong-necked dinosaur". This implies that the pressure

requirements of sauropods are rooted in the firm foundation ofbiophysical principles. We disagree.By contrast with an open system, the circulatory system is a

closed pump-driven circuit-ie, one in which the liquid (blood) in acontainer (heart) is driven and returned to its original level through atube system (arteries and veins) without being exposed to theambient atmosphere above the original level." A critical point in thedesign of the circulatory system is that the liquid does not return byfree fall in air or become exposed to atmosphere above the originallevel. The mechanical advantage of such a closed system in relationto gravitational effects is similar to the operation of a siphon.5Unfortunately, this analogy may be misinterpreted because it

suggests that siphon flow takes place within the circulatory system.In closed systems, siphon flow does not occur, and it is the

counterbalancing of gravitational pressures within the arterial andvenous circuits that eliminates the additional energy needed toovercome gravity. The pressure that must be developed by the heartwill be a balance between the output and the resistance of the entirecircuit.

It can be argued that the circulatory system is composed ofcollapsible tubes, especially veins, which alter the physics of thecirculatory system. However, just as in rigid tube systems, liquidflow in collapsible tube systems cannot result from differences ingravitational potential energy. Liquids fall when there is no

opposing force to support the liquid. In the circulatory system, theblood is contained within the heart and vessels, which constitutesthe supporting force. In any closed system fluid flow must occur bya pump mechanism, but this should not imply that gravitationalforces cannot influence the cardiovascular system. Gravity exertsconsiderable effects on venous return, cardiac output, blood flow

distribution, vascular pressures, and fluid balance. However,gravity does not induce flow of blood within the vascular circuit.For example, if the pumping actions of the heart are suddenlystopped, blood will cease to circulate. Under these conditions,repeatedly changing the vertical orientation from horizontal tovertical will not restore the circulation. To assume, as Choy andAltman do, that the cardiovascular system is analogous to an opencircuit and to present hypotheses based on this assumption isfallacious.The pressure requirements for pumping blood up to the brain in

long-necked long-bodied animals are appealing and provideentertaining speculation. However, the basic assumptions are notconstructed on a firm foundation. As stated by Burton,s within thecirculatory system of vertebrates the heart does not have to expendenergy to raise blood up to the head; it has only to provide sufficientperfusion pressure to overcome the total resistance of the vascularcircuit and supply enough blood to meet the metabolic needs of thetissues.

Department of Ecology and Evolutionary Biology,University of California,Irvine, California 92717, USA JAMES W. HICKSDivision of Physiology,School of Medicine,Creighton University Omaha, Nebraska HENRY S. BADEER

1. Hohnke LA. Haemodynamics in the sauropoda. Nature 1973; 244: 309-10.2. Seymour RS. Dinosaurs, endothermy and blood pressure. Nature 1976; 262: 207-08.3. Goetz RH, Warren JV, Gauer OH, et al. Circulation of the giraffe. Circ Res 1960; 8:

1049-58.4. Hicks JW, Badeer HS. Gravity and the circulation: "open" vs. "closed" systems. Am J

Physiol 1992; 31: R725-32.5 Burton AC. Physiology and biophysics of the circulation. 2nd ed. Chicago: Year Book,

1972: 98-120.

Harm done through treatment of childhoodcancers

SIR,-In your Sept 26 editorial you ask "how can we assess theharm done through the treatment of childhood cancer?" We canstart by being aware of the sort of harm that can be done, and then byasking appropriate questions of the people most able to answerthem.

I answer your question as a survivor of childhood cancer who hastaken up a career in medicine. The illness itself was bad enough butI believe that I suffered unnecessary psychological and emotionalstress because doctors and nurses refused to answer my questions orenter into any discussion with me about my illness. Attitudes have

changed over the past 20 years, but I feel that my experience maystill be relevant.At age 12 I developed paravertebral neuroblastoma. After an

extensive laminectomy and decompression, my parents were toldthat there was "not much expectation of life". I was keen to knowwhat was going on but when I asked questions the responses wereno answer, lies, or I would be told not to ask questions. I wonderedwhat was wrong with asking questions. I felt that to confront

problems and to seek to overcome them was a healthier responsethan to give up. I am glad to see that Greer et al’s work on fightingspirit’ supports my intuition. But one nurse told me that it waschildish to ask questions-that shut me up for quite a long time.

I could make no sense of the medical and nursing stafl’s sbehaviour and I was plagued by insecurity and self-doubt until Ibecame a medical student, obtained my notes, and found that thedoctors and nurses had felt compassion but clearly could not bringthemselves to show it. Whatever the intentions of my doctors and

nurses, the effect of their attitude was to teach me that to feelemotion was childish and therefore that emotion along withaspirations of recovery and self-improvement should be

suppressed.It is easy to succeed as a medical student or doctor if one is good at

suppressing emotion, but this caused me considerable conflict; andhow best to respond to emotional distress in patients is still difficultfor me. Do I follow my instincts or my training? The harder I look atthis dilemma, the more I realise how inadequate my training hasbeen in equipping me to deal with the many aspects of care forpatients. Naysmith et aP have described the long-termpyschological sequellae in survivors of adult cancer. Additionaldifficulties can reasonably be expected in those of us who weretreated during our formative years.To answer your question therefore, we can: ask the right

people-ie, the patients, survivors, and relatives, as well as theirattendants; ask open questions and do not administer pre-arrangedquestionnaires which determine the agenda and limit the scope ofthe response; and be prepared for the release of powerful emotion.

11 Parkway,Shenfield,Brentwood, Essex CM15 8LH, UK ERIC J. WATTS

1. Greer S, Morris T, Pettingale KW. Psychological response to breast cancer: effect onoutcome. Lancet 1979; ii: 785-87.

2. Naysmith A, Hinton JM, Meredith R, et al. Surviving malignant disease:

psychological and family aspects. Br J Hosp Med 1983; 30: 22-27.

Volunteering for researchSIR,- Your Oct 3 editorial refers to the lack of data about why

patients do or do not participate in clinical trials. We have beeninterested in this issue with respect to patients with HIV infectionand have conducted a survey with a self-administered questionnairein 133 outpatients.Of the 73 patients who were participating in clinical trials, 67%

indicated that they had entered a trial mainly to improve theirhealth, and a further 34% specifically stated that their participationin a trial gave them a chance of receiving a cure for HIV or AIDS.Whether these results represent optmism about the agents beingassessed on the part of a special group of patients, or the failure ofpatients’ advisers to explain properly the intrinsic therapeuticdilemma in such trials is uncertain. However, the increase in use ofdetailed information sheets and the requirement for the patient to