Royal Army Medical Corps training pamphlet / War Office.

Date:
1944
Catalogue details

Licence: Public Domain Mark

Credit: Royal Army Medical Corps training pamphlet / War Office. Source: Wellcome Collection.

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    Each beat of the heart forces blood into the capillaries of the lungs, where it comes into close contact with air. The air extracts carbon dioxide from the blood, while the blood extracts oxygen from the air; and in this way the blood is both purified and refreshed. This can only happen, however, if the air in the lungs is frequently changed. Some people can hold their breath for a minute or two, but by the end of this time the air in their lungs is exhausted : it will provide no more oxygen and accept no more carbon dioxide. The craving for new air then becomes so great that respiration has to start again. 56. Description of respiration.—A complete respiration consists in (a) imspivation of air into the lungs, followed immediately by (b) expiration of air from the lungs, followed by (c) a pause. In a healthy person at rest, a complete respiration takes place 14-18 times a minute; but the rate is increased during exertion and in many diseases. At each respiration, air is drawn into the lungs by expanding the chest, and is then expelled by contracting the chest. The muscle that plays the greatest part in expanding the chest Fic. 21.—DurRiInG INSPIRATION (LEFT) THE RIBS ARE RAISED, AND THE DIAPHRAGM BECOMES FLATTER, THE CHEST CAVITY THUS ENLARGES. DURING EXPIRATION (RIGHT) THE RIBS FALL INWARDS, THE DIAPHRAGM RISES, AND AIR IS DRIVEN OUT OF THE LUNGS. In this drawing the changes of shape and position have been greatly exaggerated. cavity is the midriff or diaphragm which forms the partition between the chest and abdomen (Fig. 20, lower drawing), When not in action it is arched upwards ; but during inspiration it contracts and becomes flatter, thus pushing the abdominal organs downwards and enlarging the chest cavity from above downwards. Other muscles raise the ribs and at the same time carry the sternum upwards and forwards, making the chest broader from side to side and deeper from front to back. In Fig. 21