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A research into the physiology of the pulmonary circulation

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McDowallRJS_1921redux.pdf (11.83Mb)
Date
1921
Author
McDowall, Robert John Stewart
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Abstract
 
 
The following concluding remarks are perhaps not strictly relevant in connection with the pulmonary circulation, but as they contain a new aspect s or rather a revival of old conceptions based on more modern knowledge they have been considered worthy of inclusion.
 
At an early date Poiseuille suggested that such rhythmic movement indicated a propulsive force and it may be so in some of the invertebrates in which the heart is but little differentiated. It seems however more justifiable to consider such rhythmic action as a remnant of the lower and simpler vascular systems which in the higher animals has been adapted for use in connection with the heart.
 
It has been shown that the arteries have an inherent rhythm of their own and also that arteries respond by contraction to a dilating force. One cannot avoid noting the analogy that the ventricles of the heart have a rhythm of their own yet beat more rapidly as a result of stimulation from the sino- auricular node - in mammals by way of the auriculoventricular bundle. If the conducting fibres be severed, e.g. by a ligature - in the frog at the sino-auricular junction - the ventricle may after a period of stoppage resume contraction and almost certainly if a second ligature be tied at the auriculo-ventricular junction. This latter fact has been generally considered due to a distension of the ventricle or a stretching of its fibres.
 
It would not therefore be considered an impossible hypothesis to suggest that something similar occurs in relation to the arteries, in some animals at least, namely that the smooth muscle of arteries contracts normally in response to the pulse wave. It may be that this is just sufficient to counteract the distending influence of the pulse wave and assists in storing up the heart's energy - a process hitherto ascribed purely to the elastic tissue of the vessel walls, and it may be noted that in this very connection Lister remarked upon the very slight apparent change of calibre of human arteries in comparison to the pulse wave and suggested the influence of the muscular tissue apart from its mere elasticity. If such a hypothesis be allowed it is easy to go a step further and suggest in asphyxial or anaemic conditions of the bulbar centres the regulating action of the vasomotor centre becomes upset, the synchronism between the heart and arteries becomes abolished and waves (llaube Hering) appear in tracings of the blood pressure similar to those which are found in the perfusion experiments described above.
 
If such autochtonicity is present it is justifiable to assume that the activity may be tonic as well as rhythmic, indeed the existence of tonic as well as rhythmic waves has been indicated above. Such activity would therefore account for the recovery of vascular tone which it is well known succeeds its loss after cutting of the spinal cord; a fact hitherto attributed to subsidiary vasomotor centres in the spinal cord.
 
The fuller knowledge of the physiology of the blood -vessels and their associated ganglia will in the process of time gradually solve the many interesting problems which beset alike the scientist and clinician.
 
URI
http://hdl.handle.net/1842/35231
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