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In some cases the cardiac dilatation affected the whole organ with tolerable uniformity.
In other instances the auricles and the ventricles were unequally affected, sometimes the auricles
and sometimes the ventricles being more readily influenced. Occasionally the left auricle
became very prominently distended. The distension of the auricles may, in some cases, be in
part a secondary change. Their dilatation may be brought about or contributed to by a pre--
ceding distension of the ventricles, whereby the auricles are rendered unable to discharge their
contents in a normal manner, and so become distended. But in all probability the auricular
dilatation is partly a primary change caused by the direct influence of chloroform, and not
simply by the obstacle to their emptying themselves offered by the presence of an already
existing ventricular distension. The fact that the auricles sometimes become affected much
more readily and extensively than the ventricles supports this conclusion.
The cardiac dilatation that occurs from the influence of chloroform is independent
of any distinct change in the rate of the heart's action. There is no slowing, or indeed any
c h a r a n c t e r i s t i c a l t e r a t i o n o f r h y t h m . T h e r a t e o f a c t i o n c o m m o n l y r e m a i n s u n i m p a i r e d , e v e n
when all the chambers of the organ have become greatly distended. When the dilatation has
become extreme the heart fails in its function at the central organ of circulation. Though
it continues to Contract rhythmically, its action is feeble and entirely ineffective , and its cavities
remain gorged with blood. In this condition evidenee of rhythmic movement may still be
obtained in the intact animal by passing a needle through the chest wall into the heart (as was
done in many of the experiments of the Second Hyderabad (Chlorofont. Commision).
Relation between Dilatation of the Heart and the Fall of Blood-pressure. —The occurrence
of cardiac dilatation from chloroform is usually associated with a marked fall of blood-pressure.
Now, a fall of blood-pressure involves various changes, nutritive and mechanical, in the heart;
as already mentioned, there is a diminished resistance to the ventricular systole and a lessened
b l o o d s u p p l y t h r o u g h t h e c o r o n a r y a r t e r i e s . B u t i t c a n b e c l e a r l y s h o w n t h a t t h e c a r d i a c
dilatation above described is not due to the occurrence of a fall of blood-pressure and the
changed conditions of heart action dependent on that fall.
T h e a m o u n t o f d i l a t a t i o n i s n o t a l w a y s p r o p o r t i o n a t e t o , a n d d o e s n o t a l w a y s r u n p a r a l l e l w i t h , t h e
f a l l o f b l o o d - p r e s s u r e . S o m e t i m e s t h e r ei
s a
m a r k e d
l o w e r i n g o f t h e b l o o d - p r e s s u r e
with little or no cardiac dilatation; while, on the other hand, dilatation not infrequently begins
before the fall of blood-pressure has commenced, and, indeed, even during the temporary rise
o f p r e s s u r e w h i c h s o m e t i m e p r e c e d e s a m a r k e d f a l l . A g a i n , a t o t h e r t i m e s d i l a t a t i o n o c c u r s i n m a r k e d d e g r e e w h e n t h e f a l l o f p r e s s u r e i s b e i n g r e c o v e r e d f r o m . w h e n t h e p r e s s u r e h a s
risen to some extent, and is still rising.
Further, cardiac dilatation may, though rarely, be induced in a pronounced degree by
the influence of chloroform without any approciable change in the blood-pressure.
Causation of the Cardiac Dilatation.—Many years ago it was shown that chloroform in
considerable strength is able in certain circumstances to cause contraction of small arteries;
this would lead to an increased resistance to the outflow of blood from the large vessels.
Hence, the possible influence of chloroform upon the pulmonary vessels has to be considered