In the portable respiration apparatus, the subject breathes into and out of a confined volume of air that circulates through a series of purifiers which remove the carbon dioxide as fast as formed. As the air passes through the lungs of the subject, oxygen is absorbed from the air, with a consequent gradual decrease in the oxygen content. The decrease in the total volume of the air represents the volume of oxygen consumed.

The portable respiration apparatus consists of a mechanical blower to circulate the air, three bottles which contain purifying material to remove the carbon dioxide and water-vapor, and a spirometer with suitable piping and connections. The spirometer serves the triple purpose of providing (1) a suitable housing for the mechanical blower; (2) a fluctuating factor in the air-circuit to allow for inspiration and expiration, i. e., an expansion chamber; and (3) a measure of the oxygen consumed by means of a direct reading of the level of the spirometer bell at the beginning and end of an experiment.

1 Benedict, Boston Med. and Surg. Journ.. 1918,178, p. 667. The description, together with figures, is in large part reprinted from this article.

After leaving the air-purifying bottles, the air passes through a tube to the mouth of the subject. The expired air, containing carbon dioxide, is drawn through a large-caliber tube to the spirometer, from which it is whirled by the blower through the purifying bottles, and thence returned to the subject for rebreathing. The connections with the subject are shown in figure 2 and the general installation and details of the air-circuit in figure 3.

Fig. 2. - Connections with subject, portable respiration apparatus.

E, second water absorber; W, pipe carrying air to subject; G, pipe conducting expired air from subject to spirometer; V, 3-way valve between air-circuit and mouthpiece; A, hand wheel controlling adjustment of 3-way valve and mouthpiece on extension arm, L; B, hand) wheel permitting the raising or lowering of L on standard, S. The portable nature of the apparatus is indicated by the mounting of base on castors.

Rotary Air-Impeller

The portable respiration apparatus is a recent development of the universal respiration apparatus,1 but has many striking similarities to the early "oxygSnographe" of Fredericq2 and the later device of Krogh.3 In at least one main particular, however, this apparatus differs from the earlier forms in that the air is circulated not by the lungs of the subject, but by an electrically-driven fan. There are no valves to be actuated by the lungs, and the fan does all the work of circulating the air, passing it through the purifying agents, etc. The lungs are thus relieved of the labor forced upon them by many types of respiratory apparatus, and breathing is as free and untrammeled as is possible with any form of breathing appliance. The universal respiration apparatus requires a positive blower for the circulation of the ventilating air current, since considerable pressure is necessary to pass the air through the sulphuric acid used to remove the water vapor, but the absorbents employed in the new apparatus (calcium chloride and soda lime) offer no material resistance; accordingly a small rotary air-impeller may be successfully utilized. For this purpose a small hair-drier is employed which moves a considerable volume of air, but can not give positive pressure. This hair-drier is light in weight and provided with a universal motor so that it can be used with either alternating or direct current.1 The blower must be oiled at least every other day when in constant use. To avoid possible leaks the blower is placed inside the spirometer.

1 Benedict, Deutsch. Arch. f. klin. Med., 1912, 107, p. 156; see also Am. Journ. Physiol., 1909, 24, p. 345. 2 Fredericq, Arch, de Biol., 1882, 3, p. 687; also Elements de Physiologie Humaine, Ghent and Paris, 1888, 2d ed., p. 141. 3 Krogh, Skand. Arch, f. Physiol., 1913, 30, p. 379.

Air-Circuit

By reference to figures 2 and 3, it may be seen that the air leaving the mouth of the subject is drawn along a wide tube, G, enters the spirometer, and is discharged by the air impeller, a, into a calcium-chloride bottle, C, where the water-vapor from the lungs is removed. It then passes through a soda-lime bottle, D, in which the carbon dioxide is absorbed, and next to a second calcium-chloride bottle, E, where the water vapor from the soda lime is absorbed. The air, thus freed from both carbon dioxide and water vapor, is conducted through the tube W to a 3-way valve (V, figure 2) leading to the lungs of the subject.

Fig. 3. - Spirometer and absorbing system of portable respiration apparatus.

G, large-caliber pipe conducting expired air to spirometer; o, air-impeller; C, first water-absorber; D, carbon-dioxide absorber; E, second water-absorber; S, point at which rate of ventilation may be tested by disconnecting coupling; W, pipe conducting purified air to subject; P, pet-cock for introduction of oxygen; T, thermometer for obtaining records of temperature of spirometer. The spirometer bell is counterpoised by the weight, X, attached to silk thread passing over aluminum wheel, Z. Scale on which pointer indicates height of spirometer bell is shown at right of the weight X.

1 The hair-drier, which is manufactured by the Arnold Electric Co., of Racine, Wisconsin, is purchased without switch, heating unit, or handle, and slightly modified by adding a discharge tube to support the drier when in position inside the spirometer.

Unless the volume of respiration is wholly abnormal, the rate of ventilation produced by the blower is sufficient to deliver enough purified air at the junction of the 3-way valve and the main air pipe to supply all that is needed, i. e., approximately 30 liters per minute. If there is unusually rapid and deep inspiration, so that air is, for a moment, drawn back from the spirometer, the extra wide tube, G, provides a minimum resistance between mouthpiece and spirometer.