Europ. J. appl. Physiol. 34, 1--10 (1975) 9 by Springer-Verlag t975

Influences of Exercise and Endurance Training on the Oxygen Dissociation Curve of Blood under in rive and in vitro Conditions* ** Dieter BSning, Ursula Schweigart, Ulrich Tibes, and Bernd H e m m e r Physiologisehes Institut der Deutschen Sporthoehsehule K61n Received November 19, 1974

Abstr~t. In experiments with graded exercise of 15 men (6 untrained, 3 semitrained, 6 endurance-trained) the trained subjects showed a massive shift to the right of the in rive O~ dissociation curve (ODC) of femoral venous blood. At a saturation of 20 to 25 % (18 mkp/sec) Po2 was about 9 mm ttg higher for the trained than for the untrained group. The following factors play a role: I. The 2,3-diphosphoglycerate [2,3-DPG] concentration was increased by 15 to 20 % in the trained group which explains about 2 mm Itg of the difference in Po2. 2. Exercise acidosis in the femoral venous blood depends to a large extent on CQ in the trained, but on lactic acid in the untrained group. At low saturations the CQ-Bohr effect increases sharply thus having a greater importance in the trained subjects. This factor can explain about 2 mm Itg of the difference. However, influence of chloride and 2,3-DPG on the Bohr effect must be taken into consideration. 3. Since the large ODC-shift to the right of the trained group was not reproducible under in vitro conditions, it is suggested that a rapidly decaying unknown substance accounts for the remaining difference in Po~. Key words: Oxygen Dissociation Curve -- Exercise -- Physical Fitness -- 2,3-Diphosphoglycerate. E n d u r a n c e training induces a decreased blood flow to the working muscles at a given oxygen consumption (Grimby et al., t967; Varnauskas et al., t970). As a consequence oxygen extraction in the tissue capillaries is enlarged (Varnauskas et al, t966; E k b l o m et al., t968; D e t r y et al., t 9 7 i ; Shappell et al., 1971). Since the hemoglobin concentration does not increase in trained m a n (Kjellbcrg et al., 1950), blood can only deliver more oxygen under two conditions: either the capillary P % m u s t decline or the oxygen dissociation curve (ODC) m u s t be shifted to the right. The first possibility m a y be excluded, for femoral venous Po~ was found to be at least as high in trained as in untrained subjects at the same work rate (Doll and Keul, 1968). A right shift of the ODC can be caused by elevated temperature, b y acidosis or b y an increasing a m o u n t of phosphorus compounds in the red cells, especially 2,3-diphosphoglycerate (2,3-DPG). The temperature dependent right shift of the ODC is p r o b a b l y reduced in physically fit subjects since b o d y temperature at a given oxygen consumption decreases during endurance training ( W y a d h a m and Strydom, 1972). * A preliminary report was presented at the 39th meeting of the German Physiological Society, Erlangen, 1972. ** Supported by Deutsche Forsehungsgemeinschaft B e 360/2.

2

D. BSning et al.

D u e to a less severe exercise acidosis a t equal loads in t r a i n e d as c o m p a r e d w i t h u n t r a i n e d s u b j e c t s (Doll a n d Keul, i968; Tibes et al., 1974) a larger B o h r effect seems u n l i k e l y in t h e former group. R e c e n t results, however, d e m o n s t r a t e an o x y g e n a t i o n - l i n k e d v a r i a t i o n of t h e B o h r coefficient which q u a n t i t a t i v e l y differs d e p e n d i n g on w h e t h e r fixed acid or CO 2 is used ( G a r b y et al., i972; Meier et al., t974). A small increase of [2,3-DPG] during exercise or p h y s i c a l t r a i n i n g was f o u n d b y several a u t h o r s ( E a t o n et al., 1969; F a u l l m e r et al., ~[970; S h a p p e l l et al., t971) b u t could n o t be confirmed b y others ( D e m p s e y et al., t 9 7 i ; H a s a r t et al., t973). The h a l f s a t u r a t i o n pressure a t p i t 7.4 (Ps0, 7.4), i n d i c a t i n g t h e position of t h e ODC, was either n o t m e a s u r e d or no significant change could be o b s e r v e d u n d e r in vitro conditions. H o w e v e r , when m e a s u r e d in vivo, a large d i s p l a c e m e n t to ~he r i g h t of t h e ODC was f o u n d in exercising subjects which could n o t e n t i r e l y be e x p l a i n e d b y t e m p e r a t u r e a n d B o h r effects (Sproule a n d Archer, t959; Sproule et al., i960). Since a t t h a t t i m e t h e i m p o r t a n c e of 2,3-DPG a n d t h e v a r i a b i l i t y of t h e B o h r coefficient were n o t known, t h e findings h a v e to be r e i n v e s t i g a t e d . To clarify t h e effects of a c u t e a n d chronic exercise on t h e o x y g e n d i s s o c i a t i o n curve we d e c i d e d to u n d e r t a k e s i m u l t a n e o u s in vivo a n d in vitro e x p e r i m e n t s in t r a i n e d a n d u n t r a i n e d subjects.

Methods Seven experiments were per;ormed with six untrained male subjects (UT: 25.2 years + 4.9 SD, t77.8 cm _+ 6.0 SD, 69.6 kg -- 8.5 SD) and six experiments with highly endurance trained male athletes (TI~: 23.7 + 3.3 years, 179.7 + 4.2 cm, 75.4 + 5.2 kg) participating regularly in competitions (rowing, cycling, long distance running, decathlon). Three other subjects (three experiments) ranged between both groups (sere• ST: 28.3 + 3.2 years, 177.5 • 5.0 cm, 75.5 • 4.9 kg). This classification was checked by measuring heart rate and acid-base status during exercise. All subjects were nonsmokers. For additional information see elsewhere (Tibes et at., 1974). After a 20 min control period the subjects exercised on a bicycle ergometer (pedalling frequency 60/min) with the load increasing every 10 to 15 rain (Table 1). At rest and at each work rate femoral venous blood (10 ml each) was collected into heparinized syringes by means of an indwelling catheter. Oxygen pressure Po, (Clark electrode) and acid-base status (Siggaard-Andersen, 1964) were measured at 37 ~ immediately after sampling, the oxygen saturation So.~ (Siggaard-Andersen, 1964, modified for whole blood) at room temperature within 30 rain. The C02-equilibration line was corrected for So2 according to B~rtschi et al. (1970). All these values (P%, Pco,, So~, pH) are called in rive data in the following. In samples 2, 4, 7, and 8 [2,3-DPG] in red cells was determined enzymatically (Krimsky, t970) after centrifugation under oil at 0 ~ In the same samples So2 (sixfold) and pH were measured after 15 rain equilibration in spherical tonometers (4.23 % 02, 6.25 % C02, 37 ~ yielding 50 to 60 % saturation (in vitro data). These determinations lasted not longer than t hr 30 rain after collection of blood. Samples not immediately used were stored at + 4 ~ Po2 was corrected to p i t 7.4 and 40 mm Itg Pc% by use of Bohr coefficients referring to either respiratory or nonrespiratory acidification as well as to oxygen saturation (Meier et at., 1974). A nonrespiratory pH difference is indicated by the shift of the equilibration line in the pH -- log Pco2 diagram along the pH axis. Pairs of corrected Po2 and of measured So2 were used to determine ODCs and Psos for standard conditions (Pso denotes Ps0, ~,4,4o in this paper) by means of a blood gas calculator (Severinghaus, 1966). Analysis of variance (Keller, 1955~ was applied to test significance.

Oxygen Dissociation Curve during Exercise Table t. Experimental schedule Control period Sample no. Work rate (mkp/sec) Time (rain) UT Sampling time (rain) ST TR

Work period

1

2

0

0

0--20 9.0 19.0 9.7 20.0 9.2 19.2

3 4

4 8

21--30 29.0 29.7 29.2

31--40 39.3 40.0 39.2

5 t2

6 t8

7 t8

8 24

41 - 5 0 49.3 50.0 49.2

51 - 5 8 55.5 57.7 57.5

59--66 62.3 65.8 65.8

67--74

73.3

S02 (%) 80

70

q1

60

50so 2

(O/o)

:i

40"

6O

,I

30-

++'-b

50 4O

4"

3O 20"

10

15

20

2

30

35

'

ho Po2

10

-,)(

;

,b

2;

(ram Hg)

3b

4o ~2 (ml/m~n.kg)

Fig. 2

Fig. 1

Fig. 1. Relation between oxygen saturation (So2) and oxygen pressure ( P @ at 37 ~ in femoral venous blood during rest and exercise. Means and standard errors of the means. 9 U T (6 experiments), + ST (3 experiments), x TI~ (5 experiments). For the reason of clearness SE is not drawn for the ST Fig. 2. Relation between oxygen saturation (Sos) in femoral venous blood and oxygen uptake ( ~ ) during rest and exercise. Means for 7 experiments in UT (O) and 6 experiments in TR ( x ) Results

1. The in vivo Oxygen Dissociation Curve T h e m e a n v a l u e s o f a c t u a l So~ a n d P o , in f e m o r a l v e n o u s b l o o d for all g r o u p s a r e d e p i c t e d in Fig. I. D u e ~o t e c h n i c a l errors d u r i n g d e t e r m i n a t i o n o f Po~ t h e

UT TR

UT TI~

UT TI~

pttb~ooa

Pco~ (ram Hg)

Standard[•C03- ] (meq/1)

23.7

24.5

41,0 44.2

• 0.6 _+ 0.4

+_ 3,0 + 0.8

7,405 +_ 0.035 7,380 .+ 0,015

t

0

S a m p l e no.

Work rate (mkp/see)

24.3 23.7

41.7 42.2

• 0.5 • 0.5

• 1.7 • 0.9

7.410 • 0.020 7.390 + 0.015 .

0

2

23.4 23.1

51,5 48.3 • 0.3 +_ 0.4

+ 2,0 • 1.9

7,330 • 0.025 7,365 + 0,025 . .

4

3

23.2 22.6

54.8 52.9 • 0.5 • 0.3

+_ 1[,5 + 1.4

7.320 +_ 0 . 0 i 5 7.330 + 0.020 .

8

4

22.3 22.7

55.0 57.3 • 0.8 • 0.3

+ 2.8 _+ 0.7

7.320 +_ 0.025 7.310 . + 0.015

t2

5

19.5 22.3

57.6 63.6

+_ 0.8 • 0.5

_+ 3.2 • 1.9

7.250 +_ 0.025 7,280 + 0.020 .

18

6

.

18.4 2J.7

59.0 59.6

4= 1.0 • 0.3

• 3.6 • 2.2

7,225 +_ 0.055 7.285 + 0.025

18

7

T a b l e 2. A c i d - b a s e - s t a t u s in f e m o r a l v e n o u s blood. M e a n s ~ ~,nd s t a n d a r d errors o f t h e m e a n s (SE) 8

21.1

69.7

• 0.8

+_ 3.8

7.230 + 0.055

24

r-

:

~. 0~ c~

O:

Oxygen Dissociation Curve during Exercise

5

so 2

(%)

/ /

80'

70

sO.

//I

50

/

'~

/ "/

//// /

/./

/ I~

•

9

~

20 // //x "x IC10_.A_ 15 2~0 2;. 30 3; .'~O i5{mmHg) PO2 Fig. 3. Relation between So, and Po~ (corrected to pH 7.4 and Pco~ 40 mm Hg) in femoral venous blood. Experiments and symbols like Fig. ~. Curves are standard O2-dissociation curves according to Severinghaus (7966) for the resting values (drawn curves UT, dashed curves TI~)

results of one trained and one untrained subject were discarded. Control values of saturation scatter between 70 and 80 % for the untrained and between 60 and 70 % for the trained while oxygen pressure oscillates around 40 m m Hg. During exercise Po~ and So S decline progressively with increasing work rate. The most striking result is the distinctively higher oxygen pressure during exercise in the trained group as compared to the untrained (P < 0.001). The differences increase to approximately 9 m m ttg at a S% of 20 to 25 %. The values of the ST lie in between the other groups. The oxygen saturations of the trained and untrained groups differ clearly at rest (P < 0.001), but only slightly during exercise. This can be explained b y ~ tendency co a smaller oxygen uptake at equal work rates in the T R (Fig. 2) and thus is in accordance with the introduction.

2. The in vivo Importance o/the Bohr Effect Table 2 contains acid-base data of U T and TR. Under resting conditions the femoral venous p H is decreased in the T R as compared with the U T (P < 0.01). At equal load p H fulls to lower levels in the untrained than the trained group but finally reaches the same value at the corresponding highest work rate. Trained subjects, however, exhibit a mainly respiratory acidosis whereas the untrained produce comparibly more fixed acid.

D. B6ning et al. Table 3. P50 (pH 7.4, 40 mm Hg Pco~) after in vitro equilibration (2 + SE) Sample no. Work rate (mkp/sec) Ps0 in vitro

(ram Hg)

2 0

4 8

7 I8

8 24

UT n=7

25.2 _+ 0.5

25A • 0.9

26.7 i 0.9

n.s.

ST n=3

27.6 i 0.4

28.7 • 1.3

29.6 + 1.0

n.s.

TR n=6

27.4 • 0.5

28A +_0.3

28.4 _+0.7

28.9 • 0.8

Significance level P

P < 0.0i

Fig. 3 shows means of corrected P% (pH 7.4/40 m m Hg Pco2) and of So S. Additionally, standard oxygen dissociation curves are constructed through the resting values by use of the blood gas calculator (Severinghaus, t966). During exercise the corrected in vivo values deviate to the right from their correspouding curves. While the deviation amounts to not more than 3 m m Kg in the UT, it reaches 6 m m Hg ia the TR (P < 0.01). The differences in Po~ between UT and T R remain approximately as great as before the Bohr-correction with the exception of the highest work rates. I n the last sample the Bohr effect increases P % in the UT (~8 mkp/sec, p H 7.225) by 3.7 and in the TI~ (24 mkp/see, p H 7.230) by 5.5 m m Hg. By applying a constant Bohr coefficient of - - 0.48 marked differences arise only on the last exercise step : in the UT Po~ (pit 7.4) is higher by 0.3, in the TR, however, b y 1.5 m m Hg than with use of saturation dependent coefficients. 3. The Hall Saturation Pressure Pso

The half saturation pressures in vivo) are 25.8 m m Hg +_ 0.8 SE the trained group. The significant exercise as can be seen in Fig. 3. rest.

of the in vivo standard ODCs in Fig. 3 (Ps0 in the untrained and 3i.7 m m Hg + 0.4 SE in difference (P < 0.0i) increases further during The value for the ST is 29.3 • 1.4 m m Hg at

Table 3 contains the half saturation pressures determined after in vitro equilibration (1)50 in vitro). There are also differences between UT and TI~ (P < 0.00i) which, however, amount only to 2 m m Hg. For the U T in vivo and in vitro Ps0 approximately coincide at rest; the small increase during exercise is similar for both conditions (see also Fig. 3). I n vitro half saturation pressures of TR and ST (Table 3) are distinctively lower than the in vivo values. The difference between Ps0 in vivo and Ps0 in vitro of the TI~ amounts to 4,3 m m Hg (P < 0.025) already at rest when only small Bohr-corrections are necessary.

During exercise the t.5 m m t t g increase of Ps0 in vitro is significant (P < 0.0i) in the T R but small when compared to the 3 to 6 m m Hg right shift of the in vivo curve.

Oxygen Dissociation Curve during Exercise Table 4.2,3-diphosphoglycerate concentration in the red cells (~?+ SE) Sample no. Work rate (mkp/sec) 2,3-DPG mmol/1

UT n=7 TI~ n=6

2 0

4 8

7 18

8 24

4.03 _+0.26

3.95 _+0.37

4.08 + 0.29

n.s.

4.80 +_0.22

4.53 _+0.16

4.55 _+0.11

5.34 _+0,44 n.s.

Significance level P

4. The 2,3-DPG Concentration in the Erythrocytes Throughout the experiment [2,3-DPG] is at least by 0.5 mmol/l red cells higher in the TR than in the UT (P < 0.001, Table 4). During exercise 2,3-DPG remains almost constant. The increase in the TR at the highest load (n = 4) is due to a single extreme value. For the ST there exist no complete measurements.

Discussion The results demonstrate that physical training leads to the expected right shift of the ODC. The in rive shift in the TR is so pronounced that it not only induces an enhanced oxygen extraction bat also an increase of femoral venous P%. This suggests a considerably improved oxygen diffusion from the capillaries to muscular mitoehondria. Several factors may account for this effect of physical training. Firstly, the 2,3-DPG concentration in the TR is about 20% higher than the UT. According to data of Duhm (1971) the in vitro differences of 1)50 between UT and TR can be fully explained by the [2,3-DPG] increase whereas this is not possible fbr the three times larger in vivo difference. A small dependence of 2,3-DPG on physical training was also observed by Shappell et al. (1971). p H in blood is known to be most influential on the 2,3-DPG metabolism (/.i. Astrup et al., i970; Duhm and Gerlach, 1971). Due to the more frequently arising exercise acidosis as well as to the higher [I-I+] at rest (Table 2) pH might be decreased in training subjects on the average. Therefore one should expect a decrease of [2,3-DPG]. Decisive for this, however, is only a p H change within the red cells. Surprisingly no considerable difference of pHErv between UT and TR exists under resting conditions (unpublished results). This partly depends on the l0 % lesser saturation in the TR yielding a priory increase of 0.007 units (Duhm and Gerlach, t97t) due to the Doanan effect. Further, inorganic phosphate enhances the 2,3-DPG synthesis (Astrup et al., 1970; Liehtman et al., 197t); possibly this is the crucial factor since its resting concentration is increased by 20% (Tibes et al., t974) as well as that of 2,3-DPG in the trained group. During acute exercise [2,3-DPG] generally remains constant, similarly as described by Shappell et al. (197i) and Dempsey et al. (t97t). Thus, this phosphorus compound can not directly cause the additional in vivo right shift of the ODC in the working subjects.

8

D. B6ning r al.

Secondly, femoral venous Po~ is elevated b y the Bohr effect which is more pronounced in the T R than in the U T at high work rates. This results from the finding t h a t at low oxygen saturations the C02-induced Bohr effect increases sharply whereas the lactic acid induced one simultaneously decreases (Meier st al., 1974). The p i t fall during exercise is mainly caused b y CO 2 in the T R ; the UT, however, produce a large amount of lactate. The quantitative contribution of the Bohr effect to the Po~ difference between TI~ and U T accounts for not more than 2 m m Hg thus being of the same order of magnitude as the 2,3-DPG effect. The so far described factors can not sufficiently explain the large differences between the ODCs of T R and U T at rest and especially during exercise. Influences of temperature must be excluded since p H and Po~ were always measured at 37 ~ So s remains almost constant under anaerobic conditions (Severinghaus, 1966). Further, a possible different behaviour of pttEry and pHelasma has to be considered. Such differences are, however, only small (unpublished results), their influence on the Bohr effect can be neglected. Erythrocytic hemoglobin and cation concentrations which possibly play a role for oxygen binding (Waldeck and Zander, 1969; Bellingham et al., t97t) show no differences between all groups at rest and during exercise (B6ning st al., t972). This does not hold for chloride which is increased by work acidosis and for 2,3-diphosphoglycerate. Both substances enlarge the Bohr effect (de Bruin et al., 1974; Bauer, 1969; Siggaard-Andersen, 1971) and surely influence the displacement of the ODC during exercise. They cannot, however, explain the in v i v o - - i n vitro Ps0 difference in the T R at rest since p H deviations from 7.4 are only small. Therefore one m a y suggest an unknown substance in the T R shifting the ODC which rapidly decays in vitro. Some evidence for the existence of unknown factors which influence oxygen binding is also presented in a paper of Shappell st al. (i970). Red cell A T P is of questionable effect since no increase could be detected after physical training (Shappell st al., t97t). As to whether substances like adrenaline, noradrenaline or acetylcholine are involved awaits further elucidation. Acknowledgements. The authors thank D. Fotescu, M. D., for catheterization of the femoral vein, Miss Ch. Pieritz and Mrs. H. Ringelmann for technical assistance. We are also indebted to all test subjects.

tteferenees Astrup, P., R6rth, U., Thorshauge, C.: Dependency on acid-base-status of oxyhemoglobin dissociation and 2,3-diphosphoglycerate level in human erythrocytes. IL In vivo studies. Scan& J. clin, Lab. Invest. 26, 47--52 (t970) Bartschi, F., ttaab, P., Held, D. 1~.: Reliability of blood Pco~-measurements by the COselectrode, the whole-blood (Cco,)/pH method and the Astrup method. Resp. Physiol. 10, 121--t3~ (1970) Bauer, C.: Antagonistic influence of CO~ and 2,3-diphosphoglycerate on the Bohr-effect of human haemoglobin. Life Sci. 8, I04t--1064 (1969) Bellingham, A. J., Defter, J. C., Lenfant, C. : Regulatory mechanisms of hemoglobin oxygen affinity in acidosis and alkalosis, g. clin. Invest. 10, t00--106 0971) B6ning, D., Schweigart, U., Tibes, U., ttemmer, B. : In vlvo and in vitro investigations on the oxygen dissociation curve of blood of trained and untrained subjects during exercise. Pflfigers Arch. 882, Suppl. R 78 (1972) de Bruin, S. H., l~ollema, It. S., Janssen, L. H. M., van Or, G. A. g.: Tile interaction of chloride ions with human hemoglobin. Biochcm. biophys. Res. Commun. ~8, 210--215 (t974)

Oxygen Dissociation Curve during Exercise

9

Dempsey, J. A., Rodriguez, J., Shahidi, N. T., Reddan, W. G., McDougall, J. D.: Muscular exercise, 2,3-DPG and oxy-hemoglobin affinity. Int. Z. angew. Physiol. 80, 34--39 (1971) Detry, J~-M. R., Rousseau, M., Vandenbroucke, G., Kusumi, E., Brasseur, L. A., Bruce, 1~. A. : Increased arteriovenous oxygen difference after physical training in coronary heart disease. Circulation 44, 109--1t8 (1971) Doll, E., Keul, J.: Zum Stoffwechsel des Skelettmuskels. IX. Sauerstoffdruck, Kohlensguredruck, pH, Standardbicarbonat und base excess im ven6sen Blut der arbeitenden Muskulatur. Untersuchungen an I-Iochleistungssportlern. Pflfigers Arch. ges. Physiol. 301, 214 229 (1968) Duhm, J.: Effects of 2,3-diphosphoglycerate and other organic phosphate compounds on oxygen affinity and intracellular p i t of human crythrocytes. Pfliigers Arch. 826, 3 4 1 - 356 (1971) Duhm, J., Gerlach, E. : On the mechanisms of the hypoxia-induced increase of 2,3-diphosphoglycerate in erythrocytes. Pfliigers Arch. 326, 254--269 (197'1) Eaton, J. W., Faulkner, J., Brewer, G. J. : ~esponse of the human red cell to muscular activity. Proc. Soc. exp. Med. 132, 886--887 (1969) Ekblom, B., Astrand, P.-O., Saltin, B., Steuberg, J., Wallstr6m, B.: Effect of training on circulatory response to exercise. J. appl. Physiol. 24, 518--528 (1968) Faulkner, J., Brewer, G., Eaton, J.: Adaptation of the red blood cell to muscular exercise. In: G. J. Brewer, ed., Red cell metabolism and function. Advances in experimental medicine and biology, Vol. 6, pp. 213--225. New York-London: Plenum Press t970 Garby, L., Robert, U., Zaar, B. : Proton- and carbaminolinked oxygen affinity of normal human blood. Acta physiol, scand. 84, 482--492 (1972) Grimby, G., H~ggendal, E., Saltin, B.: Local Xenon clearance from the quadriceps muscle during exercise in man. J. appl. Physiol. 22, 305--310 (1967) Hasart, E., Roth, W., Jagemann, K., Pansold, B.: 2,3-Diphosphoglyceratkonzentration in Erythrocyten und k6rperliche Belastung. Med. Sport 13, 112--118 (1973) Kjellberg, S. R., Rudhe, M., Sj6strand, T.: Increase of the amount of hemoglobin and blood volume in connection to physical training. Acta physiol, scand. 19, 146--151 (1950) Koller, S.: Statistische Auswertung der Versuchsergebnisse. In: Handb. Physiol. Pathol. Chem. Anal., K. Lang, E. Lehnartz, eds., Vol. 2, pp. 93t--1036. Berlin-G6ttingen-tteidelberg: Springer 1955 Krimsky, I. : D-glycerate-2,3-diphosphat. In: H. U. Bergmeyer, Methoden der enzymatischen Analyse, 2. Aufl., Vol. II, pp. 1397--1399. Weinheim (Bergstr.): Verlag Chemie 9970 Lichtman, M. A., Miller, D., Cohen, J., Waterhouse, C.: Reduced red cell glycolysis, 2,3-diphosphoglycerate and adenosine triphosphate concentration, and increased hemoglobinoxygen affinity caused by hypophosphatemia. Ann. intern. Med. 74, 562--568 (1971) Meier, U., B6ning, D., Rubinstein, H. J. : Oxygenation dependent variations of the Bohrcoefficient related to whole blood and erythrocyte pH. Pfliigers Arch. 849, 203--213 ('[974) Se,cringhaus, J. W.: Blood gas calculator. J. appl. Physiol. 21, t108--1146 (:1966) Shappel], S. D., Murray, J. A., Bellingham, A. J., Woodson, R. D., Detter, J. C., Lenfant, C. : Adaptation to exercise- role of hemoglobin affinity for oxygen and 2,3-diphosphoglycerate. J. appl. Physiol. 30, 827--837 (1971) Slmppell, S. D., Murray, J. A., Nasser, M. G., Wills, R. E., Torrance, J. D., Lenfant, C. J.: Acute change in hemoglobin affinity for oxygen during angina pectoris. New Engl. J. Med. 282, 1219--1224 (t970) Siggaard-Andersen, 0. : The acid-base-status of the blood, 2nd ed. Copenhagen: Munksgaard 1964 Siggaard-Andersen, O. : Oxygen-linked hydrogen ion binding of human hemoglobin. Effects of carbon dioxide and 2,3-diphosphoglycerate. I. Studies on erythrolysate. Scand. J. clin. Lab. Invest. 27, 351--360 (t971) Sproule, B. J., Archer, R. K.: Changes in intravascular temperature during heavy exercise. J. appl. Physiol. 14, 983--984 (1959) Sproule, B. J., Mitchell, J. H., Miller, W. E.: Cardiopulmonary physiological responses to heavy exercise in patients with anemia. J. clim Invest. 39, 378--388 (1960) -

-

iO

D. BSning et al.

Tibes, U:, Hemmer, B., Schweigart, U., BSning, D., Fotescu, D.: Exercise acidosis as cause of electrolyte changes in femoral venous blood of trained and untrained man. Pflfigers Arch. 347, 145--158 (1974) Vamauskas, E., Bergmann, H., Houk, P., Bjoerntop, P. : Haemodynamic effects of physical training in coronary patients. Lancet 1966 II, 8--t2 Varnauskas, E., Bjoerntop, P., Fahlen, M., Prerovsky, I., Sternberg, J. : Effects of physical training on exercise blood flow and enzymatic activity in skeletal muscle. Cardiovasc. Res. 4, 418--422 (1970) Waldeck, F., Zander, R. : Lagever~nderungen der Sauerstoffbindungskurve in Abh~ngigkeit von den intraerythroeyt~ren Kationen- und tI~Lmoglobinkonzentrationen. Klin. Wschr. 47, t068--i078 (1969) Wyndham, C. H., Strydom, N. ]3.: KSrperliche Arbeit bei hoher Temperatur. In: W. Hollmann, ed., Zentrale Themen der Sportmedizin, pp. 131--150. Berlin-Heidelberg-New York: Springer 1972 Priv.-Doz, Dr. Dieter BSning Physiologisches Institut der Deutschen Sporthochschule KSln D-5000 KSln 41 Carl-Diem-Weg Federal Republic of Germany