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.
