RECORD OF MEDICAL SCIENCE.
ANATOMY AND PHYSIOLOGY.
Impulse of the healthy heart. By O’Bryen Bellingham, M. D.—The
impulse of the heart accompanies the sys ole of the ventricles and the
first sound of the organ, and has its cause in the apex of the heart
coming in contact with the parietes of the thorax between the cartilages
of the fifth and sixth left ribs. The mechanism by which the impulse
is produced, was long a disputed point, and various have been the the-
ories advanced by physiologists to explain it: even the period of the
heart’s action at which it occurs has been the subject of difference of
opinion.
Thus it was at one time maintained that the impulse occurred during
the diastole of the ventricles ; and this opinion appeared to derive con-
firmation from the fact that when the heart of the frog is exposed
(which will continue to pulsate for a considerable time after being laid
bare,) the ventricle, during its diastole, is seen to expand, and to ap-
proach the parietes ; while during the systole the apex is simply ap-
proximated to the base. In this animal, therefore, the heart approaches
the parietes during the diastole, not during the systole of the ventricle,
and any impulse which is given, must be at the period of the ventricular
systole. An experiment was performed by Oesterreicher, which con-
sisted in removing the heart of the frog from the body, and laying
upon it a substance sufficiently heavy to press it flat, anil yet so small
as not to conceal the heart from view. He states that during the sys-
tole of the ventricle the weight was raised, but that during its diastole
the heart remained flat. This experiment has been quoted by Muller
and others, to prove that the diastole of the ventricles is not a muscular
act, in ignorance, apparently, of the foregoing peculiarity in the action
of the heart in this animal. In warm blooded animals, however, ex-
periments and observations repeated over and over again have proved
that the impulse occurs at the period of the ventricular systole, and
that it is due to the apex of the heart coming in contact with the pari-
etes of the chest.
Mechanism by which the impulse of the heart is produced.—It will
not be necessary to delay to notice the various theories which have
been advanced in order to explain the mechanism by which the impulse
of the heart is produced: the majority of these are founded on errone-
ous views. It will be sufficient to observe, that during the ventricular
systole, the walls of the ventricle become more convex upon the surface,
the apex of the heart describes a spiral motion from behind forwards,
and from right to left: in describing this spiral movement, the apex
glides obliquely upon the pericardium, is approximated to the base,
comes in contact with the parietes of the thorax in the intercostal space
between the cartilages of the fifth and sixth ribs, and thus causes the
impulse. Indeed, this part of the heart is naturally so close to the pa-
rietes of the chest, that no tilting forward of its apex is necessary to
produce the slight shock felt at this period.
It was the received opinion until within a few years, that during the
diastole of the ventricles, the heart receded from the parietes of the
chest, and that the impulse was produced by a blow or shock given to
the ribs by its apex, during the systole. Harvey, Haller, Senac, Hun-
ter, may be quoted as authorities for this theory. The experiments
which have been performed upon animals of late years, and the exami-
nation of the action of the organ in cases of ectopia of the heart, have,
however, shown that this theory has no foundation, and that the heart
“does not suffer any changes in consequence of its own efforts (ex-
clusive of the movements of the lungs and diaphragm) except in its
shape and size, in the thickness and tension of its parietes, and in the
capacity of its cavities,” which are quite sufficient to produce the
slight shock felt when the hand is laid on the parietes of the chest.
M. Ritter has recently advanced this as a novel doctrine, in ignorance
probably of the results of the experiments of the “ Committees of the
British Association.” His experiments are entirely corroborative of
those previously made. “ The portion of the heart’s surface (he ob-
serves) which is in immediate relation to the walls of the chest is at
all times in close contact with them; and it is impossible that in any
of its motions it can act so as to withdraw itself from the thoracic walls
or so as to leave a space between them.” Being thus fixed, therefore,
it follows that, when the heart contracts and assumes a more globular
form, it will exert its distending force on the yielding intercostal spaces
against which it rests, and will thrust them forwards, so as to produce
the impulse. This distending force cannot be exerted with any effect
against the unyielding ribs or their cartilages ; and consequently the
impulse is not perceived by the finger placed over the cartilages of the
fourth, fifth, or any other rib. If the impulse was caused by an actual
stroke or blow of the heart against the walls of the chest, it would be
perceived on these parts and on the sternum as clearly as it is in the
intercostal spaces, and every person would feel the impulse of his own
heart, just as a pregnant woman feels any violent movements made by
the foetus in utero.”
Sound sometimes produced by the impulse of the healthy heart.—Al-
though in the healthy subject, when the circulation is tranquil, and the
heart’s action is normal, no sound is produced by the impulse, yet it
occasionally happens, that when the same heart is excited to increased
action,- in other words, when palpitation ensues, whether the cause
be mental emotion or corporeal exertion, but particularly the former,—
the apex of the heart does come in contact with the ribs, the patient
feels the blow or shock produced by the impulse of his own heart, and
this is accompanied by sound, which of course will be heard at the
period of the first sound of the heart, and will modify it in a certain
degree, or add to it. Under such circumstances, the first sound of the
heart becomes loud and ringing, and in diseased states it is sometimes
so intense as to be audible without applying the stethoscope, and may
be heard at a short distance from the patient. This point will be again
alluded to when we come to consider the abnormal conditions of the
heart.
Seat of the impulse of the heart.—The point at which the impulse of
the heart is felt in the healthy male, is the intercostal space between
the cartilages of the fifth and sixth ribs upon the left side, to the sternal
side of the nipple, and about two inches below this point. In the fe-
male, owing to the habitual wearing of slays, the impulse is usually
a little higher up—viz. between the cartilages of the fourth and fifth
left ribs ; and in the latter months of pregnancy, for an obvious reason,
it is perceived still higher up, and the apex is pushed more to the left
side.
The impulse of the healthy heart is naturally slight; it is more
marked in the erect than in the recumbent position, because in the latter
position, the heart, by its own weight, recedes slightly from the parietes
of the chest. For the same reason the impulse becomes more distinct
if a person leans forward, and more indistinct if he lies upon his
right side. In the erect posture, the impulse is said to be slightly lower
than in the recumbent posture, but the difference, if any, is very trifling.
In very fat persons the impulse is scarcely perceptible to the eye or
hand. In very lean persons it is very obvious to both. When the
lungs are largely developed, they will overlap the heart more than usual;
when the lungs are small, less of the heart will be covered by these
organs : in the latter case, therefore, the impulse will be better marked
than in the former.
Alteration of the impulse in inspiration and expiration.—In inspira-
tion, particularly on a full inspiration, the impulse of the apex of the
heart will be felt lower down than natural, as low as between the
cartilages of the sixth and seventh ribs, or in the epigastrium, between
the line of the xyphoid cartilage. This is partly owing to the con-
nection of the heart with the lungs, and partly to the connection of the
pericardium with the diaphragm. On a full inspiration the lungs ex-
pand from above downwards, as well as from before backwards; and,
.according to Dr. Sibson, from the manner in which the pulmonary
veins are joined to the left auricle, the heart is drawn down by the
descent of the lungs. The principal cause of this descent of the heart
in inspiration, appears to lie rather in the intimate connection of the
pericardium with the central tendon of the diaphragm ; as the latter
descends it must bring with it the heart; and from the connection of
the inferior or ascending vena cava with the diaphragm, it must follow
the movements of the latter, and draw down the right auricle. On a
full inspiration, the impulse, in addition to being lower down, will be
less marked than natural, because the lungs, when fully inflated, meet
so as almost to cover the heart, and prevent its apex from coming in
contact with the parietesof the thorax.
On a forced expiration, on tl|e other hand, owing to the ascent of the
diaphragm, the impulse of the heart is felt higher up—viz. on a line
with the space between the cartilages of the fourth and fifth ribs on the
left side: it is likewise more marked than natural, because the heart is
less covered by lung. The point at which the impulse of the heart is
felt, is altered in some diseases of this organ, or of the lungs or pleura,
as well as in diseases of the abdominal viscera. These matters will,
however, be considered when we come to describe the diseased states
of the heart.
Double, impulse of the healthy heart.—The impulse of the healthy
heart has been almost always described as single; Magendie, however,
who attributes the first sound of the heart to the shock of the apex
during the ventricidar systole, lays it down that the second sound
is due to the shock given by the ventricles to the parietes of the thorax
during their diastole. “ The ventricles in dilating (he observes) in a
great measure under the influence of the rapid influx of the blood,
give a shock to the anterior parietes on the right side of the thorax, and
thus produces the second clear sound.” Dr. Sibson, in his valuable
essay upon the “ Changes in the Situation of the Internal Organs,” ob-
serves:—“A second impulse is often felt in persons whose lungs are
diminished, and whose great vessels come close to the sternum. This
is synchronous with the second sound, and must, I conceive, be due to
the sudden springing forwards of the walls of the right ventricle after
the systole.” In the year 1848, in a communication upon the sub-
ject of “ Aneurism of the Aorta,” made to the Surgical Society of Ireland,
I called attention to the fact that the impulse of the healthy heart, when
the organ is acting vigorously, is double, not single.
The impulse of the healthy heart, I observed upon that occasion,
has been always described as single, just as that of aneurism of the
arch of the aorta was supposed to be. If we carefully examine this
organ, however, when it is beating vigoroursly, we shall find that a
second but slighter impulse is perceptible, which quickly succeeds the
Other; andon applying the stethoscope we shall find that this second
impulse accompanies the second sound of the heart: it appears as if
the agency which gives rise to the second sound was capable of com-
municating a distinct sensation to the hand or stethoscope.
In the healthy heart the second impulse is scarcely felt, unless the
organ beats vigorously; when the ventricles are somewhat hypertro--
phied, and their cavities somewhat dilated, the second impulse becomes
better marked ; when this has arrived at an extreme degree, it becomes
very evident, and constitutes then the “ back stroke of the heart,” or
the diastolic impulse. This diastolic impulse, except in cases of dis-
ease, is never so strong as to be perceptible to the eye, but is readily
distinguished when the ear is applied to the stethoscope laid upon the
praecordial region. It is perceived at the same part of the chest as the
systolic impulse, and is more marked, the larger the surface of the
heart uncovered by lung, and the stronger the action of the organ.
With respect to the cause of the diastolic impulse, Dr. Sibson observes
—“ The second or diastolic impulse, which is felt between the second
and third, and sometimes between the first and second costal cartilages,
is neither more uor less than a sign that the upper part of the right
ventricle, and the origin of the pulmonary artery, over which it is felt,
are in contact with the walls of the chest.’’ “This diastolic impulse,
which is synchronous with the second sound, is a physiological, not a
pathological phenomenon, and is due to the sudden return forward of
the walls of the right ventricle, and of the origin of the pulmonary
artery, immediately after the systole; the parts in question then im-
pinge with a short sharp tap on the left second and third costal carti-
lages, and on the space between them.”
When describing the motions of the heart, we saw that during ven-
tricular diastole, the apex of the heart recedes from its base; the
organ becomes elongated, the ventricles increase in all their dimensions,
and the hand grasping the heart, is forcibly opened. Now, when we
consider how closely the anterior surface of the ventricular portion of
the heart lies to the parietes of the thorax, there is no difficulty in
understanding how an impulse may be communicated during this
movement, equally as during the ventricular systole ; it appears only
surprising that it should have been so very generally overlooked.—Lon-
don Med. Gaz.