The Skodaic resonance is a remarkable tubular quality of resonance heard on percussion when the effusion extends up to the fourth rib or beyond it, nearly filling the pleural cavity. It is a high-pitched, long vibration, semi-tympanitic sound, rarely absent when, from an effusion, the lung is retracted to a very small size, but still contains some air. It is most frequently found anteriorly under the clavicle, near the sternum, because to that point the lung withdraws as long as it has any retractility left. If the air be forced out of the lung by pressure, this sound is no longer heard. Flint called this peculiar tympanitic sound, heard above the level of the fluid in pleurisy, by the descriptive name vesiculo-tympanitic resonance. The vesicular, though feeble, is combined with the tympanitic quality, and the intensity of the resonance is abnormally increased. This subclavicular tympanitic sound is not peculiar to pleurisy. It exists in pneumonia preceding hepatization, and was noticed by Hudson, Graves, and Williams before Skoda called attention to it in pleurisy. Skoda's explanation of this phenomenon is now generally accepted—namely, that it comes from diminished tension of the lung-tissue, caused by diminution in the quantity of air, and consequently relaxation of lung-tension. The residuary air in the alveoli does not mix properly with the tidal column: it is indeed pent up by the narrowed diameter of the minute bronchi. Thus it becomes surcharged with carbonic-acid gas; this relaxes the air-sacs and lessens their tension. In fact, the percussion sounds are invariably tympanitic when the parietes of the organ which contains air are not stretched. When they are firmly stretched, the sound elicited by percussion becomes less and less tympanitic, and finally dull: such, we know, is the case in striking a drumhead. The chief characteristic of the sign relates to the quality of the sound; the resonance is nearly devoid of vesicular quality. A resonance absolutely non-vesicular is always tympanitic (Flint). This tympanitic sound is so constant under the clavicle that although it may be from other causes, its appearance would lead us to suspect effusion, especially in children. It is not only at the apex, but wherever the lung shrinks from pleuritic exudation and loses in tension, the percussion sound has the tympanitic quality. We find it occasionally near the sternum, and sometimes in sacculated effusions we observe it in different parts of the thorax. Traube, and subsequently Fraentzel (Ziemssen's Cyc.), called attention to the fact that sometimes a long expiration would cause a temporary abolition of this tympanitic sound at the apex. Their explanation is that the sound is heard over the compressed lung. Garland urges that this explanation cannot be a satisfactory one, for a certain amount of pulmonary expansion is essential to the production of tympanitic resonance.
This exaggerated resonance elicited by percussion has received its name from the eminent German who wrote so much about it; but it did not escape the accurate ear of the discoverer of percussion, Avenbrugger, who clearly defined the subclavicular tympanitic resonance in pleurisy.33 Skoda's sign, however, is not unique, for observation proves, when the lung is contracted with fluid below, that there are several varieties of resonance. Notta,34 who was not aware of Skoda's ideas, describes the sound as hydroaérique where the lung is above the level of the fluid. Roger,35 who called especial attention to Skoda's views, admitted that there were several varieties of tympanitic resonance heard above the fluid. He compares them to those heard on percussing over the stomach of the cadaver. Woillez36 describes five varieties or types of sonorousness, according to their intensity, their tone, and their quality. He noticed these under the clavicle at different points above the liquid—ordinarily on the level of the second or the third rib. (1) The most common and the best defined was a short sound, dry and superficial; the tone of this was acute, with exaggeration of intensity. Williams37 in 1841 called attention to these peculiarities. With this variety we frequently have a reverberation, pointed out by Stokes in 1837—a cracked-jar sound more or less marked. Woillez noticed this variety in 11 of his 82 cases; of this number 9 were in pleurisy of left side. (2) There was exaggeration of intensity or tympanism with a grave tone: 7 of Woillez's cases showed this variety, of which 6 were on left side. (3) A subclavicular resonance, unnaturally acute, but with exaggerated intensity. (4) Exaggeration of intensity, with equal tone on both sides; only 2 patients out of 82 showed this variety. (5) Exaggerated abnormal resonance, more acute than healthy side, and with normal fulness of sound. These are all modifications of percussion sounds elicited in pleurisy and other pathological physical conditions resembling it, where there are variations of tension together with other modification of the structure of the lung. The bruit de pôt fêlé is sometimes clearly marked, as it is also in hepatization of lung.
33 Avenbrugger, Ouv., ed. de Corvisart, 1808, Paris.
34 Arch. gén. de Méd., 1850, t. xxii.
35 Ibid., 1852, t. xxix.
36 Mal. Aig. des Org. Resp., Paris, 1872.
37 The Path. and Diagnosis of Dis. of the Resp. Organs, 1841.
Traube's Semi-lunar Space.—There is a point on the left side where we find normally a vesiculo-tympanitic sound, first pointed out by Traube and enforced by Fraentzel. It is situated at the anterior base of the left side, and is of a half-moon shape. It is bounded inferiorly by the margin of the thorax, and superiorly by a curved line whose concavity is turned downward. It begins in front, below the fifth or sixth costal cartilage, and extends backward along the margin of the chest as far as the top of the ninth or tenth rib. Its greatest breadth is from four to four and a half inches. This tympanitic sound is caused by the air in the stomach, which lies well up against the diaphragm. When the stomach is pushed down by the falling of the diaphragm, from excessive fluid, the tympanitic sound disappears. The value of this semi-lunar space in the diagnosis of pleuritic effusions has been variously estimated. Fraentzel considers it of great significance in the differential diagnosis between pleurisy and pneumonia; Ferber and Garland do not. Weil suggests that the area of this space may be diminished by filling the stomach and colon with solid or fluid food. Garland shows that as the diaphragm's depression depends upon the excess of fluid overcoming the lifting force of the lung, we may have, with a vigorous, unimpaired lung, a large amount of effusion in the pleural cavity, yet the resonance of the semi-lunar space may remain tympanitic. The condition of this semi-lunar space is of most diagnostic value in extensive left-sided effusions. The more the diaphragm is pressed down by the effusion, the smaller becomes the space of tympanitic resonance. It may gradually disappear altogether.
Auscultatory percussion may sometimes be advantageously employed to detect fluid in the pleura, especially in the younger subjects, for intercostal fluctuation may frequently be appreciated when we press carefully with the palm or surface of the finger between the ribs while the percussion shock is applied to another part of the same side. If we auscultate with a stethoscope, the chest extremity of which is made to fit in between the ribs, while another person percusses the chest, we can sometimes detect the fluctuation within the cavity of the chest.
We thus see that in the diagnosis of pleuritic effusions percussion is very valuable, perhaps the most valuable of the physical signs. We must not, however, forget that its significance may deceive us if the fluid is prevented from gravitating by pre-existing adhesions, or if it is encapsuled between the diaphragm and lung or between the lobes. Cases occasionally occur where, from fibrinous bands, the fluid is kept in the posterior part of the thorax, consequently there is pronounced clearness and fulness in front. Percussion does not enable us to diagnose the consistence of the contents of the pleura, or its nature, whether it be fibro-serous or purulent. To do this we must resort to Bacelli's method, or, still better, to exploratory punctures by the hypodermic syringe.