Dulness on percussion, varying in degree and extent with the number of affected lobules and their nearness to each other, is a very constant sign of collapse; but it must be kept in mind that if the collapsed lobules are disseminated or central the dulness may be hardly observable. Sometimes there is difficulty in detecting dulness, because from the bilateral character of the bronchitis the collapse of lobules may take place in about equal degree on both sides, so that one side cannot be contrasted with the other. Ordinarily, however, there is a difference in the degree of dulness between the two sides, because the affection is more extensive in one than in the other; and in general the loss of resonance over the collapsed lobules is determinable without comparison of the two sides. Not uncommonly, patches of dulness are found with intervals of comparatively clear resonance.
On auscultation the respiratory sounds are feeble or entirely absent in an area in which a number of adjacent lobules are involved together in collapse.
When a considerable part of a lobe is affected, bronchial breathing may sometimes be heard, but this is in general less marked than the degree of dulness and the amount of condensation would lead the examiner to expect, because the breathing is too feeble to give rise to the vibrations necessary for the production of this sign.
An important indication of lobular collapse is the rapidity with which the signs just described are developed; a part or parts of the lung which had been clear on percussion and normal in respiratory character becoming in a day, or sometimes in a few hours, dull and nearly silent to the ear. This very suddenness with which the physical signs are developed in a case of bronchitis or catarrhal pneumonia in a child points very plainly to the occurrence of collapse of the lung.
PATHOLOGY.—The pathological appearances in collapse of the lung vary according to the extent of tissue involved in the change, and also according to the cause which has induced it. In the disseminated lobular form which is due to bronchitis the collapsed portions are chiefly seen on the surface and at the margins of the lung, and they extend more deeply into the organ as it becomes more involved in the atelectatic condition. On the surface or on a section the collapsed patches are depressed somewhat below the surrounding parts and are of a darker hue, so that they are readily seen as dark-red or purplish spots surrounded by the lighter healthy tissue. The contrast is sometimes enhanced by the fact that the non-collapsed parts are even paler than natural from the vicarious emphysema that has been established in them.
The consistence of the affected part varies in different cases. If the change has occurred without previous congestion, the texture may be somewhat flaccid; but if there has been hyperæmia, the part will be leathery, non-crepitant, and resisting pressure. If no crepitation can be detected the part will sink in water from the complete expulsion of air from the affected lobules. A cut surface is smooth and does not present the granular appearance of a hepatized lung, nor can exudation-matter be pressed or scraped from it.
The collapsed lobules may be made to swell up and resume their normal appearance and rosy color by forcing air with a blowpipe into the bronchus leading to them. This is so generally true, at least, that it has been regarded as a certain test by which to discriminate between atelectasis and pneumonic consolidation when there may be a doubt at a post-mortem examination as to which condition exists. In general, the attempt to inflate will succeed when the air is directed into a collapsed lobule; but the test is of less value than it was once held to be because it has been shown, on the one hand, that lobules which have been collapsed for some time will not always expand under the inflating force, and, on the other, that in recent catarrhal pneumonia the alveoli may for a time still be inflated with air.
Meigs and Pepper, while stating that in general the results of the attempt to produce inflation are altogether different in the two conditions, yet hold, in accordance with Gairdner's teaching, that "partially pneumonic lung may be inflated when the affection is recent and combined, as it frequently is, with bronchitic collapse; while in the latter lesion—i.e. collapse of lobules—in its purest forms complete inflation is often very difficult or impossible after the collapsed state has been of some duration."3
3 Diseases of Children, p. 143, 4th ed.
Nevertheless, the test is of value when applied along with others; for, as stated by J. Lewis Smith, "the inflated pneumonic lung is more solid and resisting when pressed between the thumb and fingers than is the collapsed lung."4