Carbon monoxide partial pressure in tissue of different animals

ESYIROXMENTAL

Carbon

RESEARCH

Monoxide

3, 30*%2-509

Partial

Presslure

M. GOTHERT, Institute

(1970)

of Pharmacology,

F.

in Tissue

Animals

AND G. MALORNY

LUTZ,

University

of Different

of

Hamburg,

Received February

5, 1970

Hamburg,

Germairy

A pneumoperitoneum of nitrogen was set to rabbits, guinea pigs, and rats, and the CO partial pressure was measured in this tissue model of the animals, breathing 86, 300, 700, and 1000 ppm CO. After diffusion equilibrium had been reached, we ohtained the following results: ( 1) the CO partial pressure in tissue is only 42-691 of the CO partial pressure in the inspired air; (2) the percentage CO partial pressure in tissue compared with the CO partial pressure in the inspired air is lower, the higher the CO content of the inspired air; (3) the CO partial pressure in tissue of a species of animal is lower, the higher the CO affinity of hemoglobin. These results can be explained by the competition of CO and 0, for the receptor hemoglobin. The CO partial pressure in tissue is influenced decisively by the different CO and 0: affinities of hemoglobin.

In a previous study Giithert and Malorny (1969) reported on measurements of the carbon monoxide partial pressure in the tissue of rabbits. One of the most important results was that the less affinity the hemoglobin of individual animals has for carbon monoxide, the higher the CO partial pressure in the tissues, once diffusion equilibrium has been achieved. In this study the results obtained with rabbits shall be proved by further experimental data. The main point will consist of the comparison of some animal sp:lcies whose hemoglobin molecules show significant difference in affinity to carbon monoxide. Exact statements about the inhibitory action of carbon monoxide on the acti\.ity of enzymes in tissue call for precise estimation of CO partial pressure in tissw. The possibility of such a mechanism in addition to inhibition of oxygen transport by hemoglobin must be considered because of experimental results obtained with animals and human beings. Thus, Malorny et al. (1963) observed physical and psychological decrease of efficiency by very low CO concentrations as observed at working places and in traffic. Schulte (1963) as well could prove a significant reduction of psychological efficiency of men breathing 100 ppm CO. hlETHODS

R!r measuring the concentration of gas in a bubble injected into tissue the partial pressure of gas in tissue can be analyzed. Once diffusion equilibrium has been achieved the partial pressure measured in this gas bubble coincides with that in the tissue (Loeschke, 1956). For our experiments WC used 32 rabbits, 12 guinea pigs, and 3 rats. One day before the experiment we set a pneumoperitoneum of nitrogen. During the experiment we put the animals into an experimental box of 0.24 m3. A membrane pump continuously perfused this box with air containing constant amounts of 303

304

CijTHERT,

LUTZ,

AND

MALORNY

carbon monoxide. These investigations were performed with S6, 300, 700, and 1000 ppm CO in the inspired air. At certain times samples of gas of maximum 50 cI11” were taken from the pneumoperitoneum and samples of blood were drawn from an ear vein or the heart. Samples of expired air were collected in respiratory bags. Carbon monoxide hemoglobin was analyzed by the method of Fretwurst and Meinecke ( 1959 ) . The CO concentration in the inspired air was continuously controlled by the ultrared gas analyzer URAS 1 (produced by Hartmann and Braun, Frankfurt/M. ). The CO concentrations in the pneumoperitoneum as well as in the expired air were measured with the ultrared gas analyzer UNOR 2 (firm: Maihak, Hamburg) and transformed into partial pressures. These transformations into partial pressure were based upon the following conditions: body temperature, pressure, saturated with water vapor. All these values of partial pressure refer to dry gas after transformation. RESULTS

As Table 1 shows, the partial pressure of CO in the pneumoperitoneum first reaches equilibrium after approximately 15 hr breathing a constant mixture of CO and air. Even in equilibrium this intraperitoneal CO concentration attains a significantly lower level than in inspired air. TABLE INCREASE

OF CO

CONCEXTRATION

IN

1

PNEUMOPERITONELM

ppm

lkration Before eXpOSUlY ppm

CO ip

~1Mean

-

with

standard

11 RAHBITS

1OOO

BREATHING

of exposure

(hours)

~.

0

values

OF

co”

2

.i

s

I.?

134 --+ “2

341 + 4:;

406 *46

*47

2.5

460 551

1.533

deviations.

Table 2 indicates that equilibrium of COHb in blood is already attained after 90 minutes, After 2 hours the CO concentration in expired air reaches the same value as in inspired air and remains constant until the end of the experiment. ‘I’ABI,l~: IK(:REASE

1000

Before CXpOS~llY

n 11

7

‘ii, COHb

ppm

(1 Xean

1.i

0. 3

CO in the expired air values

with

2

ANI) CO CONCENTRATION IN EXPIREI) AIR OF

OF COHb

standard

3~0.6 3 271

l-1.6

+3.0 ml +70

deviations.

ppm

R.srts1w

BREATIIIN(;

coa 1 )Ilritl,ion

of csposure

:
60

‘)‘I ‘J I-..

+2.2 w4 f66

3s

(minutes) no

1

50.0 987 f4;,

38.9

11.6 995 It- 30

120 28.S

* 3 .i 1008 + 19

CARBON

hIONOXIDE

IN

30s

TISWE

In Fig. 1 the pneumoperitoneal CO concentration in equilibrium expressed in percentage of the CO concentration in inspired air of rabbits and guinea pigs is plotted against the CO concentration in inspired air. These percentages are also rclc\rant to the corresponding partial pressures in inspired air and tissue. As shown in this figure the CO partial pressure in tissue of these animals exposed to S6 up to 1000 ppm CO amounts only to 42-69% of the CO partial pressure in inspired air. The higher the partial pressure in inspired air, the lower is the prxrccntn,~e of the CO partial pressure in tissue. ‘!. cc IP 100

*.

4

‘.

’ 1. ’

\

‘\

rabbit ’ ‘I.

\ -0,

50 I

’

,guinea .

‘. pig

--OS

. ‘x

---a

01 0

500

1000 Ppm CO in

FIG. breathing

1.

Percentage CO concentration different CO concentrations,

insplr.oir

in the pneumoperitoneum of rabbits and guinea related to the CO concentration in inspired air.

pigs

Figure 8 shows the dependence of the mean CO partial pressure in tissue on the COHb value for rabbits, guinea pigs, and rats exposed to different CO partial pressures in inspired air. All the given values represent results obtained in equilibrium of diffusion. The left curve shows this dependence for all CO concentrations up to 1000 ppm in inspired air of rabbits, the right one this relation in guinea pigs. This curve of the guinea pigs runs in the range of higher COHb concentrations as indication of a higher CO affinity to hemoglobin but lower CO partial pressures in tissue. For the rat these experiments were made only under the influence of 700 ppm CO in inspired air. The straight lines connect the mean values of rabbits, guinea pigs, and rats exposed to the same partial pressure in inspired air. The straight lines clearly indicate that the CO partial pressure in tissue of the different species

306

GijTHERT,

LUTZ,

AND

MALORNY

:pn ( i-p. 500

nmHg l@?O Ppm

iJ

:o

1.p

0.708mmHg

I /

I

\

I

0.3

400

/ /

/

robbIt

300

/’

0.2

/ / / 2co

3.1

100 / /

66 PDrnd OCEJm,m g

/’

/A / O/

0 10

FIG. 2. Dependence of the CO guinea pigs, and rats are breathing once diffusion equilibrium achieved.

20

30

40

‘/. COHb

partial pressure in tissue on the COHb value different carbon monoxide partial pressures.

when rabl>its, Mean values

of animals attains the higher values, the lower the COHb value, i.e., the less the affinity of hemoglobin to carbon monoxide: Hemoglobin of guinea pigs and rats has a higher affinity to carbon monoxide than the hemoglobin of rabbits; guinea pigs and rats breathing the same CO partial pressure have a significantly lower CO partial pressure in tissue than rabbits. Moreover, this figure indicates that the straight lines run steeper when the animals are exposed to higher CO concentrations.

The distribution of carbon monoxide between blood and tissues is mainly influenced by the following factors (Rieders, 1965) : (1) the blood supply of the different tissues; (2) the ability of CO to diffuse across membranes into other tissues; and (3) their ability to take up CO either by combination or by solution. Moreover, one would suppose that the carbon monoxide partial pressure in all organs perfused with blood attains the same value as in alveolar air, when

CARBOX

hIONOXIDE

IS

TISSUE

307

equilibrium of diffusion is reached after breathing a constant mixture of CO and air for a long time. This supposition results from the fact that carbon monoxide is neithrr produced cndogcnously in amounts worth mentioning nor does it enter irrcversiblc reactions in the organism. On thr contrary, our rxpcriments ha1.c proved that this supposition is wrong. The CO partial pressure in tissue is in fact only 4%-69% of the CO partial pressure in inspired air, The CO partial pressure in the alveolar air in equilibrium attains the same value as in the inspired air if this air at body temperature is saturated with water vapor. Table 2 proves this statement because in equilibrium the CO concentration in expired air equals the CO value in inspired air. The comparatively low CO partial pressure in tissue can be explained by the compc~tition bctwecn carbon monoxide and oxygen for the receptor hemoglobin in blood, as shown by Giithcrt and Malorny (1969). This competition depends upon the law of mass action corresponding to the eqnation ( 7 )IIl) + I,( )1 ~0,111, + I’(Y). (I 1 7’1~1 oqnilibriuni

constant

of this reaction

is identical to the relative affinity constant of hemoglobin to CO and 0,. The hemoglobin in arterial blood is saturated \vith oxygen ar~cl carbon monoxide corresponding to the mentioned equilibrium. When the blood is passing through thct capillaries this equilibrium is disturbed by thr delivc>ry of oxygen to the tisSII(‘S (Riinder and Kirw, 1955). Part of thr ,small amount of the carbon monoxide tlissoIvcd in plasma is bound to hcwoglobin. Thus, the CO partial pressure in ITJ~IIS blood and tissue is lower than in arterial blood and in alveolar air. This proved the experimental results obtain4 with rabbits. The CO partial pressure $0 ill \~nous blood inflwncin g dwisively the CO partial pressure in tissue ( hlalorny and Schniewind, 1961) could be calculated after having introduced that mc~nsrwc~d values in tissue or vc~nons blood into Eq. (2). As an example, for rabbits breathing 0.212 Torr (300 ppm) CO a partial pressure of 0.135 Torr in tissue, \\XS nwasurcd correspondin (r closelv, to the c&dated value of 0.112 Torr t Giithcrt and Malorny, 1968). l\Iorco\w, it follows from the application of Eq. (2) to the conditions in venous blood and tissw that the CO partial pwssurc in tissuck is invcrscly proportional to the, affinity of hemoglobin to carbon nionosidc. The higher affinity the hemoglobin of individual animals has for carbon monoxide. the lower the CO partial prcwln7~ in tll(, tissues. Also this dc~pcntlcwcc~ found in csperiinrmts can thus 1~1 c>zplainc-d bv the la~v of mass action. This relation is not only cvidcnt when c>wIuatillg the individual analysts of rabbits bllt also \\rhcn the mean valncs of tliff(lrc,nt animal species arc compared with coach other. Finallp. it can ho be csplainc~d Lvh?; the pcrcent:lge of the CO partial prcssurc in tissw is less, the’ higher the, CO partial prc’ssurcl in the inspired air. \T$~JI IwcXthinS nlixturrs of carbon inonosidc and air two gases colllpctc for tlic s;ttnc rtwJl,tor in l~lood \vhich alrcwly nVould 1,~ saturatc;d colllpl(~tcly in the prescnccs of olrl\. ow component. that is. osygcn. In that cxr, hon.cw7, ltc~nioglol~in c0n-k

308

GijTHERT,

bines only partly the equation

with

LUTZ,

oxygen, partly

AND

with

MALORNY

carbon

monoxide,

corresponding

to

The arterial CO and O2 partial pressures are almost completely identical to those in the pulmonary alveoli no matter what partial pressures are breathed. The arterial saturation of hemoglobin with carbon monoxide, however, is lower when breathing a mixture of carbon monoxide and air compared with a hypothetic case, in which carbon monoxide alone would be breathed with the same partial pressure. This “deficit of saturation” increases absolutely and relatively with rising CO partial pressure in inspired air. In venous blood the partial pressures of CO and 0, together no longer suffice to saturate the hemoglobin completely. lrnder these conditions so much of the excess CO physically dissolved in plasma will he bound to hemoglobin until the venous CO partial pressure corresponds to the CO saturation of hemoglobin. Because of the high binding capacity of hemoglobin for carbon monoxide compared to the physical solubility,’ actually only the CO partial pressure changes while, on the other hand, there is only a very slight increase of the COHb value not mcasurablc with the method of Frctwurst and Meinccke ( 1959). The “deficit of saturation” described above increases relatively, the higher the CO partial pressure in inspired air; inversely the perccntagc CO partial pressure in venous blood and tissue related to the CO partial prcssurc in the higher this CO partial pressure in ininspired air attains the lower values, spired air ( compare Fig. 1) . This relation is clearly demonstrated by the law of mass action after transforming equation (2) in the following way: /(IOHb] = --I(),H}>]

l’(‘O

p0.’ K .

( 1)

With this formula the venous CO partial pressure can be calculated which is almost completely identical to the CO partial pressure in tissue. The CO partial pressure is proportional to the COHb concentration. The COHb value is relatively decreasing if the CO partial pressure in inspired air is increasing: in this case, too, the percentage pC0 in tissue related to the CO partial prcssurc in the inspired air has to decrease. Therefore, the CO partial pressure in tissue is decisively influenced b,r the competition between CO and 0, for the receptor hemoglobin as well as by the affinity of hemoglobin to CO and 0,. REFERENCES A., Zellatmung

BLNDER,

FRETWURST,

Bestimmung 1 The monoxide

KIESE, M. (1955). Die Bedeutung der Wirkung des Kohlenosyds auf die fiir die Kohlenoxydvergiftung. Klin. Wochensch. 33, 152. K. H. ( 1959). Eine neue Methode xllr quantitatixen F., AKD MEINECKE, des CO-Hboglobins im Blut. Arch. Z’oxikd. 17, 273.

AND

Bunsen solubility in water at 39O

coefficient (ml (body temperature

gas/ml liquid/760 mm of rabbits and guinea

Hg pressure) for pigs) is 0.01795.

carbon

CARHOX

hlONO;YIDE

IN

TISSUE

309

Xl., AND ~IALOHNI., G. ( 1969). Zur \‘erteilung van Kohlenoxid z\\~ischcn Blut und Gewebe. AI&. Toxikol. 24, 260. Loescxrs~. H. ( 19.56). ither die Diffusion von Gas in mit Gas untersiittigte Liisuugen nlit Dnrchrechnung biologischer Beispiele. Z. Natrtrforsch. llb, 61:;. ~IALORNY, G., AST) SCHNIEWIX,,, II. ( 1961). iibcr tlic Diffusion van Kohlenoxyd und Saurrstoff in vivo. Z. Biol. 112. -468. hI.wzu