The structural alterations of the heart that occur in emphysema are the results, more or less directly, of the mechanical conditions involved in the disease. Earliest in the sequence of changes affecting this organ are non-compensative hypertrophy and dilatation of its right chambers; and by some writers it has been maintained that the alterations due to emphysema are found only on this side of the organ. This, however, has been completely disproved by extended observations, and it has been shown that left hypertrophy and dilatation, while not such direct consequences of emphysema as the corresponding changes on the right side, are yet frequently encountered, and are plainly due to the disease in the lungs.
The hypertrophy and dilatation of the right chambers of the heart are easily understood when it is considered that the constant pressure of the enlarged air-vesicles of the emphysematous lungs interferes more and more with the circulation through the pulmonary capillaries, and that there is thus a constant impediment to the onward course of the blood from the pulmonary artery, and a continuous backward pressure within the right ventricle and auricle. The effort to overcome this pressure leads to hypertrophy, and ultimately, as this effort is less and less effective, to dilatation of the right chambers.
It would appear as though the readiness with which the alterations on the right side of the heart may be explained has led, if not to their being more frequently observed, yet at any rate to their being more emphasized, than are the corresponding changes on the left side. Some writers have referred only to those on the right side, giving the correct explanation of them, but making no mention of the similar condition on the other side. Thus, Rokitansky6 refers to the obstruction to the circulation occasioned by the expansion of the air-cells in pulmonary emphysema as one of the causes of dilatation of the right ventricle and auricle, but says nothing of similar changes on the left side. Other pathologists, however, as Lebert and Gairdner, have shown that at least in long-standing emphysema the left side is also not infrequently involved in disease.
6 Path. Anat., vol. iv. p. 130.
What explanation, then, is to be given of those changes in the left chambers which, if less frequent than hypertrophy and dilatation on the right side, are yet certainly not uncommon? Evidently, they cannot be referred to obstruction in the pulmonary circulation; for this, while producing backward pressure into the right compartments, must, on the contrary, lessen the amount of blood received by the left chambers, which therefore have no excessive labor thrown upon them from this cause, and so cannot become hypertrophied in such a manner.
The explanation is probably to be found partly, as suggested by Waters,7 in the altered position of the heart occasioned by the emphysema, and partly in the remora of the venous circulation.
7 Diseases of the Chest, p. 152.
There are thus two factors to be considered, the first of which applies to the right heart as well as to the left. As to this first, the more extensive the emphysema the greater is the degree of displacement that the heart undergoes; and as the normal position of the ventricles with reference to the arteries emanating from them offers the easiest course to the blood-currents, any departure from this position causes an embarrassment, and consequently increased labor, in the left chambers as well as the right; hence one explanation of the hypertrophy on both sides. As to the second factor, the obstruction to the general capillary circulation necessitates an increased effort of the left ventricle to overcome it; and so, as far as it is concerned, another cause of hypertrophy is in operation.
It is frequently observed in advanced emphysema that there is a marked disproportion between the forcible heart-beat and the feeble radial pulse, the former being due to the hypertrophy, and the latter to the small amount of blood received and propelled by the heart.
Besides these changes in the size of the heart and the thickness of its walls, constituting hypertrophy or dilatation as the case may be, a displacement of the entire organ is a not uncommon consequence of emphysema. The direction of this displacement may vary, so that it may be either directly backward, the heart being overlapped by the distended lung, or it may be downward or to the right of the sternum. A much greater degree of displacement of the heart may result from the pressure of pleural effusion than from emphysema of the lung; but when due to pleurisy it is generally of shorter duration and admits of perfect restoration, whereas when caused by emphysema it is usually permanent. The writer has at present under his care a case of extreme displacement of the heart to the right, the apex-beat being felt and seen to the right of the sternum; but in this patient, while extensive supplementary emphysema of the left lung, due to the almost complete incapacitation of the right lung, has probably had a share in causing the displacement, yet a more important cause of it has been contraction of the right side of the chest, the result of absorption of an old pleural effusion which has left the lung bound back and adherent. This case closely resembles one reported by Stokes as presenting "the singular phenomenon of the displacement of the heart to the right side, consequent on the removal of an effusion of the right side."8