. The comparative physiology of respiratory mechanisms. Respiration. 84 RESPIRATORY MECHANISMS The sudden rise in blood lactic acid just after the dive might indicate a suspension or at least a great reduction in blood flow through the muscles during the dive, and the most interesting and probably the most important adjustment tak- ing place in diving is the extreme slowing of the heart rate observed by several authors and amply confirmed by Scho- lander. The electrocardiogram shown in Fig. 49 illustrates. Fig. 49. Electrocardiographic record of seal before, during, and after dive. (Scholander
. The comparative physiology of respiratory mechanisms. Respiration. 84 RESPIRATORY MECHANISMS The sudden rise in blood lactic acid just after the dive might indicate a suspension or at least a great reduction in blood flow through the muscles during the dive, and the most interesting and probably the most important adjustment tak- ing place in diving is the extreme slowing of the heart rate observed by several authors and amply confirmed by Scho- lander. The electrocardiogram shown in Fig. 49 illustrates. Fig. 49. Electrocardiographic record of seal before, during, and after dive. (Scholander.) the point. The rate drops from 120 per min. to about 10. With such a very slow pulse blood pressure cannot possibly be kept up unless the peripheral circulation is largely suspended, and there is reason to believe (Irving, 1938) that at least in muscles and perhaps also in many internal organs the arteries are closed down. A corresponding bradycardia during diving has been observed also in the beaver and in diving birds (Irving, Scholander) but not so far in whales, where a mechan- ism for shunting blood through the retia mirabilia is suggested by studies made by Eriksson in Scholander's laboratory. We know from Barcroft's admirable book The Architecture of Physiological Function that it is the central nervous system which requires oxygen at a fairly high tension to work properly while all other organs are very resistant, and we may reason- ably assume therefore that during diving the blood circu- lation and oxygen supply are reserved mainly for the brain and medulla. The mechanisms for prolonged diving turn out to be closely related to those allowing man to contract a large oxygen debt. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Krogh, August, 1874-1949. Philadelphia, University of Pennsylvania pres
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