At birth, the lungs weigh 60 Gm. (1', oz.), at one year 140 Gm. (4i oz.), at seven years 300 Gm. (9* oz.). Their growth depends princi pally upon the increase in the breadth of the thorax. The lobes of the lungs bear the same relationship as in the adult. As the lungs and dia phragm gradually descend the lungs increase in length, although their lower border remains at the same level with the ribs, coinciding with the adult (Sahli). At the same time with the descent of the thorax and lungs opposite the vertebral column, there also occurs a lowering of the larynx and the trachea, so that in the newborn the bifurcation of the trachea is opposite the third dorsal vertebra and in the adult opposite the fifth (Mehnert).
From the foregoing, it may be reaclily understood, that the arched diaphragm is only on a slightly higher level (estimated according to ribs) than in the adult, but that it is less sloping in its peripheral portions.
Physiology.—The frequency of respiration during rest and sleep may be considered as averaging about : Newborn End of the 1st year 2nd year 5th year 8-10th year 90-45 25 24 20 respirations per minute.
The respiratory frequency is lowest during sleep, is increased on sitting up, especially- by excitement and crying (10-30 respirations), and is decreased by concentrated attention. It. is, therefore, of great advantage, if the respiration can be observed during sleep, the frequency being determined by lightly placing the hand upon the chest.
During the early months and up until the third year, the respira tory rhythm is not always regular, even under normal conditions. This is especially seen in young nurslings during sleep when longer pauses may also occur (Czerny). In older children irregularities of respiration are usually of pathological significance. Infants frequently hold their breath for a long time on auscultation, which is always a proof that no serious disease of the respiratory system is present. During the first years the type of respiration is predominantly diaphragmatic (abdom inal), and only at about the seventh year it is reinforced by an increased participation of the thorax. The type of respiration peculiar to sex be gins to manifest itself at about the tenth year, the abdominal and in ferior costal type being found in males and the superior costal type in females. During the early months of life an inspiratory- recession of the epigastrium is physiological, but later points to disease in the respira tory organs, or to rachitis of the thorax.
We are indebted to the splendid investigations of Gregor for a more accurate knowledge of the mechanism of the infantile respiration. In young nurslings the respiration is diaphragmatic, frequent, and super ficial. An increased demand for oxygen is supplied by an increased fre quency of respiration, to double the usual number. The recumbent posture in which the weight of the intestines presses upon the lungs renders respiration more difficult. In the .seconcl half year and in the second year the capacity for frequent respiration is diminished, and the inspirations become deeper. (Heretofore, the respiratory movement took place almost entirely from its frontal axis; now, however, owing to the broadening of the sides of the chest, and the lowering of the ribs by the completed development of their necks, thus changing the axis di rection backwards, a far greater respiratory capacity is permitted, in addition to elevation of the ribs outwards.) The ability to respire deeply
is increased from the third to the seventh year, thereby causing an in creased capacity of aeration. The frequency of respiration is greatly reduced from the eighth to the fourteenth year, and a diminution of the working capacity is brought about by progressive deepening of the respiration.
Gregor explains very satisfactorily the changes in the mechanism of respiration during infancy. As long as the infant is recumbent the respiration is solely diaphragmatic. Only by raising the body to the up right position, thereby initiating the descent of the anterior chest wall with the thoracic and abdominal organs, the increased thoracic respira tion is brought about. As a matter of fact, the commencement of hold ing the body erect coincides with the blending of the diaphragmatic and thoracic respiration. According to Gregor, two factors are particularly important for normal respiration: the great reduction of the frequency together nith deepening of the respiration at the close of the nursing period. and the tendency to a reduction of the working capacity by reason of the acquired freedom of action* of the depth and volume of respiration after the seventh year. In infants having a tendency to frequent attacks of catarrhal bronchitis, Gregor observed a retarded development of the deep respiratory inovetnents with the associated formation of a rigid and badly poised thorax.
Tbe volume of air of each respiration (at 40-60 respirations during sleep) in the first half year is 27-42 c.c., in the second half year 78 c.c., and towards the end of the first year 136 c.c. (Gregor).
The absolute respiratory volume (expired air in one minute) in creases from 2500 e.c . in the middle of the first year to 5000 c.c. in the eleventh and twelfth year, and does not, therefore, increase correspond ingly with the body weight.
The relative respiratory volume (expired air per kilo and minute), amounts to 330-500 c.c. in the newborn, 563-533 c.c. in the seventh month, and at the end of the second year to 424-32S c.c.
The Chemistry of Respiration.—The insensible perspiration amounts, at first, to about 90 Gni. (3 oz.), at three months to about 200 Gm. (6+ oz.), at six months to 300 Gm. (tn oz.), at one year to 500 Gm. (15 oz.) (Camerer). The excretion of water through the skin and the lungs, calculated according to body weight, is rather higher in the nursing infant than in the adult.
Comparing equal surfaces, the healthy breast-fed infant excretes rather less carbon dioxide than the adult, on the average 113 Gm. carbon clic:6de per day; proportionately to the body surface 13.5 Gm. per hour.
Compared with the breast-fed baby, elimination of carbon dioxide is greater in the bottle baby (17.2 Gm.), partly owing to the greater activity resulting from a large supply of nitrogen with the cow's milk. In comparison with the body weight, infants absorb more oxygen and eliminate more carbon dioxide than adults., less, however, in comparison with the body surface (Rohner, Heubner, Bendix).