The diaphragm in man : a record of our present knowledge of its development, relationships, structure, and mode of action / by J.F. Halls Dally.

  • Dally, John Frederick Halls, 1877-1944.
Date:
[1908?]
Catalogue details

Licence: In copyright

Credit: The diaphragm in man : a record of our present knowledge of its development, relationships, structure, and mode of action / by J.F. Halls Dally. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    53/58 (page 211)
    in the costo-vertebral and diaphragmatic directions. The essential differences between deep and quiet breathing are (a), that the lower half of the thorax does not expand to anything like the extent of the upper half, in the lowest portion ex- panding even less than in quiet breathing, and (b) that in the latter part of the act the abdominal wall ceases to advance and then actively recedes, under these circumstances the abdominal muscles actiug as antagonists to the powerful spinal muscles in keeping the centre of gravity vertically above the point of support. Thus it is that the thoracic cavity enlarges chiefly in its upper part through elevation of ribs rather than by descent of diaphragm. The traction of this muscle upon the lower ribs overcomes their property of elevation, but the slight reduction in size of the thorax produced by this constriction is more than counterbalanced by the diaphragm’s greater de- scent. Constriction takes place only during forced breathing(^°°), and undue narrowing is resisted by the downward pull of the abdominal muscles on the ribs and the downward push of the abdominal viscera. In rapid deep breathing the intercostal spaces tend to be sucked in. The important action of the fibres passing obliquely upwards from the seventh costal car- tilage and attached to the pericardium and central tendon behind the xiphoid in pulling downwards the lung on the right side and the heart and lung on the left, has been touched upon by Sibson 4, In Forced Expiration.—In this act the abdominal muscles play the chief part. The first event is relaxation of the diaphragm and pericardium, this being followed almost immediately by recession of the abdominal wall, changes taking place in thorax and abdomen similar to those which occur in quiet breathing. To these are superadded a vigor- ous contraction of the abdominal musculature, which has the effect of thrusting upwards the abdominal viscera after the relaxed diaphragm within the hollow of the thorax, and of pulling downwards the sternum and lower set of ribs, thus lessening the vertical, antero-posterior, and trans- verse thoracic diameters. Simultaneously, forcible lowering of the ribs as a whole is caused by strong contraction of the internal intercostals, and the whole of the extraordinary muscles of expiration are brought into play with resulting further depression of ribs and shoulder-girdle, forward move- ment of the vertebral column, and compression of the ab- dominal viscera, in which latter function the levator ani is an essential auxiliary.