H. T. Edwards

Studies in muscular activity: VII. Factors limiting the capacity for work

IN a dog the energy reserve consists chiefly of carbohydrate and fat. For their utilization oxygen must be supplied and carbon dioxide eliminated. The maximum over-all efficiency is probably from 20 to 30 p.c., most of the energy appearing as heat. Hence, if a constant body temperature is to be maintained, provision must be made for heat dissipation. The experiments to be described indicate that, by suitably varying the conditions, inadequacy in any one of the three factors, fuel supply, oxygen supply or heat dissipation, may limit the capacity for work. In our experiments these three taken singly, or in combinations, are of primary importance, although factors of secondary importance no doubt exist. Two dogs were trained to run on a motor-driven treadmill. Most of the experiments were carried out on Joe, an immature male of the foxterrier type weighing 13 kg. Additional experiments were carried out on another dog, a mature female of the Irish terrier type and of the same weight. With the exception of a few early experiments the grade 1 was 17-6 p.c. The rates and other experimental conditions will be given in detail below. Observations were made of: (a) heart rate, using a cardiotachometer previously described; (b) rectal temperature either with a thermocouple during exercise or with a clinical thermometer after it; (c) room temperature; (d) blood lactic acid by the method of Friedemann, Cotonio and Schaffer [1927]; (e) blood sugar by the method of Folin and Malmros [1929]; and (f) morphologicalproperties2 of the blood. Notes were made of the dogs behaviour, particularly during the onset of exhaustion. The nomenclature of Campos, Cannon, Lundir

Properties of the blood of the skate (Raia oscillata).

In the acid range, carbon dioxide pressure has almost no effect on affinity of skates whole blood for oxygen. In the physiological range the effect is appreciable but still only one-half as great as in man. No difference was discerned between the carbon dioxide dissociation curves of oxygenated and of reduced blood. This was partly due to the facts that the hemoglobin concentration is one-fourth as great as in man and that the carbonic acid-combining capacity (when pCO2 = 40 mm.) is less than in man.The effect of temperature on the oxygen dissociation curves is identical with that found by Brown and Hill (1923) for human blood but somewhat different from that found by Redfield and Florkin (1931) for Urechis blood.The buffer value of plasma proteins is about twice as great, per unit weight, as that of human plasma proteins. Since the concentration f protein in skates plasma is one-third to one-half as great as in human plasma, it follows that the buffer value of plasma of the two species is about the sam...

On the partial pressures of oxygen and carbon dioxide in arterial blood and alveolar air

EVER since the work of Haldane and Priestley(l) (1905) on the pressure of C02 in alveolar air, and that of Krogh(2) (1910) on the mechanism of gas exchange in the lung, it has been generally believed that the partial pressure of C02 is the same (to a close approximation) in arterial blood and alveolar air. The relation, however, of the partial pressure of oxygen in alveolar air to that in the arterial blood has not been determined with the same accuracy. This uncertainty is due in part to the dispute concerning the role played by the lungs in oxygen transfer, in part to difference of opinion regarding the mechanics of pulmonary ventilation, and also to lack of precise knowledge of the facts. It is the purpose of this paper to present data with reference to gas exchange in the lung. Our experiments have been performed on normal men while they were breathing air or low oxygen mixtures.

A study of leukocytosis in exercise

SummaryHard muscular work is accompanied by a leucocytosis in normal individuals and trained athletes, the leucocytosis in football players often showing an increase of between 200% and 300%. The magnitude of leucocytosis is related to both the duration and the intensity of work. Excitement alone will not cause a leucocytosis. Intense exertion of short duration produces a lymphocytosis which is followed by a polynuclear stage if the work is continued for a long enough time. The average recovery curve exhibits no appreciable drop in leucocyte count during the two hours following a football game unless the player lies down immediately after leaving the field. The absolute lymphocyte count falls rapidly for an hour or more after the player leaves the game. The rapidity of the leucocyte changes, the evidence against leucocytolysis and the absence of an appreciable increase in theSchilling-Torgau “band-form” cells all point toward a storage phenomenon. The bone marrow, spleen, liver, lungs, and organs of internal secretion must be considered as possible reservoirs, although no definite statement can yet be made as to the relative importance of each. The fact that lactic acid, blood sugar, blood pressure, body temperature, and capillary dilation can be ruled out as separate variables directly related to leucocytosis in exercise points toward a stimulus perhaps more complicated than has yet been studied. Any explanation of leucocytosis in exercise involving only a simple physical mechanism cannot at present be considered adequate.

Analysis of recovery from anaerobic work

SummaryRecovery processes have been studied in severe work of uniform intensity continuing from a minimum of 5 seconds to a maximum of 106 seconds. The work was largely anaerobic, requiring the accumulation of an oxygen debt, the magnitude of which was approximately a linear function of time.The rate of removal of lactic acid is a logarithmic function of time; the rate varies somewhat from time to time and from one person to another. In the type of activity studied the lactic acid accumulated is proportional to the duration of work. The total oxygen debt as well as the lactacid debt being proportional to duration of work, it follows that the so-called alactacid debt is also proportional to the duration of work. In other words, the lactacid debt and the alactacid debt in such activity are contracted concurrently.The oxygen intake in recovery may be analyzed into a rapid process nearly complete in 5 minutes which pays the alactacid debt, a process about 1/20th as rapid which pays the lactacid debt, and finally an increase in resting metabolism which decreases in a linear fashion until the pre-exercise level is reached. The excess R. Q for the entire process of work and recovery probably lies within the range 0,9 to 1,0.

Renal function in exercise

where U ~urine nitrogen in mg. %, V = ccm of urine per minute, and B ---blood urea nitrogen in rag. %. Cm is used when V is above the augmentat ion limit of 2 ecru per min. The per cent of average normal Cm is obtained, as developed by the above authors, by dividing the absolute Cm value the mean normal Cm, 75, and multiplying by 100. Similarly the per cent of average normal C~ is obtained by dividing the absolute Cs by 54 and multiplying by 100. The urea clearance values presented here are in terms of per cent of average normal Cs or Cm, and unless qualified the word clearance in this paper will have tha t meaning. Some efforts have been made to record kidney function in exercise. Addis and Drurff 2 in 1923 reported the u r e a clearance ratio,

Respiratory responses to changes in air density

SummaryThe use of a 4 to 1 mixture of helium and oxygen in maximal work does not increase the capacity for transporting oxygen nor greatly modify the heart rate. It does favor the elimination of carbon dioxide. It is associated with the same increase in lactic acid but at the same time it favors the elimination of carbon dioxide; accordingly the change in pH is smaller.