The respiratory function of the blood / by Joseph Barcroft.

  • Barcroft, Joseph, 1872-1947.
Date:
1914
Catalogue details

Licence: Public Domain Mark

Credit: The respiratory function of the blood / by Joseph Barcroft. Source: Wellcome Collection.

    330/344 (page 310)
    Within the last few years a good deal of energy has been expended by the protagonists of each theory; the general motif of which has been to shake confidence in the results obtained by the opposing theory. In so far as I have had an opportunity of seeing the two methods at work on the same individual (and I believe that this test has rarely been performed) the two methods gave an identical result, that being so it seemed to me rather a work of supererogation for the supporters of one method to be so suspicious as to the validity of the other. This however was at or near the sea-level, and it is at great altitudes that the two methods are described as giving most divergent results, the method of Zuntz giving lower readings for the oxygen alveolar air than the method of Haldane and Priestlev We may therefore make some criticisms upon the two methods. (1) There is underlying the method of Zuntz and Loewy, or at all events under¬ lying their application of it, the assumption that the dead space is a constant quantity. This, as Haldane has pointed out, is probably very far from being the case. The respiratory passages, at all events the smaller ones, all have a rich musculature in their walls. They are, in fact, like arteries which admit air instead of blood. The physiology of the bronchial muscles leaves much to be desired. It has mostly been studied from the point of view of asthma, and therefore it is the contraction of the muscles as compared with the normal tone which has claimed attention. It is, how¬ ever, not improbable that our notions about the bronchial muscles are as distorted as those of the arteries would be if we merely considered the changes from the normal arterial tone of the resting organ to that of pathological arterial spasm. In the case of the artery the functional significance of the musculature of the arterial wall is that it can relax to let the organ have the amount of blood which it requires when it is in full activity. There is no reason to doubt that the functional significance of the bronchial muscles is to relax during conditions of exalted respiration and allow perhaps ten times the ordinary quantity of air to pass through the tubes without let or hindrance. When we recollect that the volume of a cylinder increases with the square of its diameter it will be easily seen that the dead space of the lung may increase without difficulty two or three-fold under conditions such as those obtaining at high altitudes, in which the respiration is quicker than usual. Of the mechanism of such dilatation we are in ignorance, it may be medullary ; it may be the effect of changes in the blood*. The neglect of this factor may be one reason why Zuntz’s method diverges from that of Haldane’s at high altitudes. This neglect would tend to make Zuntz and Loewy’s results for the oxygen pressure in alveolar air too low. If however one concedes that the dead space of the lung may be two or three times as great during conditions of deep or rapid respiration, as under ordinary circumstances one must ask oneself whether by a violent deep expiration such as is made for the purpose of Haldane’s alveolar air determinations, it is possible to clear the air space as efficiently as one does under normal circumstances. It would be most desirable that someone should make himself thoroughly con¬ versant with both methods and make a more systematic comparison of the two than has yet been done. * Since this was written the work of Krogh has appeared [Journal of Physiol. Oct. 1913).