This occurs as a Compensatory process perhaps more frequently than is usually supposed. There is evidence to show that in persons who go to reside in high altitudes, the chest increases in size, the greater-requirements of the attentuated air apparently inducing increased respiratory movement and by degrees a permanent enlargement of the lung. It is also probable that in cases of phthisis which recover with loss of a certain portion of lung substance, the loss may be partly made good by a true hypertrophy of the lung, although there is also observed in such cases an emphysema by which the space is filled up without a proper hypertrophy. Hypertrophy in cases of phthisis will be promoted by residence at a high altitude.

An unequivocal compensatory hypertrophy of the lung occurs in consequence of atelectasis. There may be in this case a great enlargement of the expanded lung so as partly to fill the place of the non-expanded part. In such cases there is not probably any numerical increase of lung alveoli, but these are enlarged, their walls expanded, and the capillaries elongated or multiplied.

A case occurred to the author which distinctly manifested the characters mentioned above. The left lung was of very small dimensions, especially the upper lobe, which appeared merely as a membranous structure in which dilated bronchi could be felt. There was no pigment in this lobe, and not a trace of lung parenchyma. The lower lobe contained the ordinary carbonaceous pigment in limited amount, and was greatly reduced in size.

The right lung was of very unusual volume, extending across the middle line, so that its edge reached beyond the left nipple. The enlargement seemed to be due to an addition of lung tissue which threw forward the anterior parts. The supraclavicular part of the lung was normal, and its anterior border indicated the position of the normal anterior margin. Below and beyond this, however, the lung extended into the other half of the chest. This part of the lung had not the appearances of emphysema, but was bulky and consisted of sound pulmonary tissue. The right ventricle of the heart was greatly enlarged, and the pulmonary artery showed a remarkable thickening of its wall, there being scarcely any difference between it and the aorta.

The absence of pulmonary tissue in the upper lobe of the left lung indicated that the collapse had been of long standing, and the entire absence of pigment showed that if not congenital it had occurred in very early life. The enlargement of the right lung was thus compensatory, dating from a period when the organ was in a state of growth. The compensation seems to have been somewhat effective, as the person lived to the age of 46, and it was only during the later months of his life that he suffered from serious dyspnoea, followed by signs of venous engorgement. The remarkable thickening of the pulmonary artery without any appearance of atheroma, also seems to point to a compensatory hypertrophy of the right ventricle during the period of growth, the vessel in its growth accommodating itself to the increased blood-pressure. It may be added that the left pulmonary artery had only about a third of the calibre of the right, but the main bronchus was of equal size on the two sides. A somewhat similar case is described by Recklinghausen.

Literature

Coats, Lect. to pract., 1888; Schuchakdt und Recklinghausen, Virch. Arch., ci., 1885, p. 71.