Europ. J. Obstet. Gynec. reprod. Biol., 11 (1981) 435-436 @ Elsevier/North-Holland Biomedical Press

435

CLASSIC ILLUSTRATIONS

25 r

,I”“““““““““’ 30 seco::s 5x7

FIG. 46. Analysis of the effect of asphyxia on

pulse rate. Goat foetus, 123 days. Thick line, vagi intact; A = first gasp. Broken line, vagi cut; B = first gasp. (Bauer.)

Figure taken from: Barcroft, J. (1946): Researches on Prenatal Life, p. 124. Blackwell Scientific Publica- tions , Oxford. Reproduced with the kind permission of Bladkwell Scientific Publishers, Ltd.

Figure 46 is published in the famous book of Sir Joseph Barcroft ‘Researches on Prenatal Life’. This figure carefully analyzed the studies per- formed by D.J. Bauer in the Physiological Laboratory at Cambridge of the slowing of the heart rate produced by clamping the umbilical cord in the fetus. Sir Joseph wrote: “Here again the study centred round tracings of arterial pressure: such tracings showed that shortly after the ligature of the umbilical cord, at or near term, the foetal heart slows. This, of course, is commonplace in obstetric practice, but the cause of the slowing still seemed to demand some investigation - this investigation was initiated in rather a curious way. At a meeting of the Physiological Society I chanced to give a demonstration of the recording of the effect on arterial pressure of tem- porary occlusion of the umbilical cord, and pointed out the bradycardia which took place after the occlusion and was abolished by the ensuing breath. On being asked what the mechanism of this slowing might be, I expressed ignorance (though I had given the matter some thought), at which a member of the Society said: ‘Oh, of course, it’s just asphyxial heart block, there is no

436

more in it than that’. Truth to tell I was just a little nettled by this remark, probably because having given this matter a good deal of thought, I had no reason to suppose that the speaker had given it any, or perhaps because I did not think it good for the Physiological Society that a great man should rap out so ill-considered a statement. However, as the demonstration was at an end, I wheeled the goat and the apparatus straight out of the room, cut the vagi, and repeated the experiment. Here is a graphic record of the two tracings (Figure 46). It is obvious, at least, that the two curves are not the same; in the first the fall is much more rapid than in the second, and that in itself gives some reason for exploring the possibility of a vagus bradycardia in addition to the slowing which must inevitably follow asphyxia as a step on the road to death”.

It is interesting to note that since 1937-1939 when the effects of vagal reflexes on fetal heart rate were demonstrated in experiments performed under anesthesia, with manual compression of the umbilical cord and record- ings on a smoked drum, so much more information has been gained about fetal heart rate and its regulation. This has been due to a number of factors including the development of techniques for the study of the fetus under conditions free from anesthetic and surgical stress, increasingly sophisticated methods for detecting and processing biophysical signals, microtechniques for the measurement of pH, blood gas tensions and other biochemical param- eters. Most of all it has been due to the incresing attention given by both researchers and clinicians to the conditions and afflictions of prenatal life. Here, also, Joseph Barcroft and his close collaborator, D.H. Barron pointed the way: “There are cases, however, about which the last word has not been said, nor the last experiment completed. These I have indicated for the bene- fit of such as may wish to undertake future research”.

T.K.A.B. ESKES Nijmegen