Tidal air is that which is taken in and given out with each quiet respiration. It is equal to 20 cubic inches (500 c.c.). Complemental air is that which can be forcibly inspired over and above that taken in at a normal respiration. It is equal to 100-130 cubic inches (1500 c.c.). Vital capacity is the volume of air which can be forcibly expelled after the deepest possible inspiration. It reserve air + tidal air + complemental air=230 cubic inches (3800 c.c.). These numbers were obtained by Hutchinson by means of the instrument he invented and called the spirometer, a special form of gasometer adapted for the purpose. The above numbers are averages. Varying conditions which modify the vital capacity are height (one inch in height increasing it by eight cubic inches); weight (when the weight exceeds the normal by seven per cent. each kilogramme of increase diminishes the vital capacity by 2-3 cubic inches); age (after 35 it gradually diminishes); sex (in a man and woman of the same height the ratio is 10 : 7); position and diseases. The frequency of quiet respiration varies with age; the following average numbers are given by Quetelet in newborn children, 44; at the age of five, 26; at the age of fifteen to twenty, 20; twenty to twenty-five, 18; twenty-five to thirty, 16; thirty to fifty, 18 respirations per minute. Hutchinson gives 16-24 respirations per minute as the average of 2000 observations. The total air respired in the twenty-four hours = 11 Oxygen taken in in the twenty-four hours=744-516,500 c.c. The excess of oxygen absorbed over carbonic acid expired is thus 61,000 cubic centimetres in the day; most of this combines with hydrogen to form water, and a small quantity is contained in urea, uric acid, &c. Dumas gives the total quantity of carbon exhaled in carbonic acid as 8 oz. in the twenty-four hours; E. Smith as 7-11 oz. The aqueous vapour averages between 350 and 500 grammes. But this is very variable, the chief factor in the variation being the See Ranke, Grundriss d. Physiol. d. Menschen, p. 353, Leipzig, 1868. quantity already present in the inspired air which is dependent on climate, temperature, &c. The effects of varying circumstances on Respiration Many circumstances affect the respiratory exchanges, particularly with reference to the carbonic acid: such as state of rest or activity, food, day and night, sleep, sex, age, mode of respiration, season of year, alterations of atmospheric pressure, &c. Age.-Until the body is fully developed the carbonic acid given off increases with age; as the bodily energies decay it diminishes. Hence the oxygen absorbed is relatively greater than the carbonic acid given off. The absolute amount of carbonic acid given off is less in children than adults, but in relation to body weight a child gives off twice as much as an adult. The following table is taken from Landois and Stirling's Physiology: Sex.-After the eighth year males give off about one third more CO, than females (Andral and Gavarret). At puberty the difference may rise to one half. Pregnancy increases the output of carbonic acid. Temperament.-Energetic muscular people absorb more oxygen and excrete more carbonic acid than less active persons of the same weight. Day and Night.-C. Schmidt' was the first who found that the output of carbonic acid during the night is diminished. Pettenkofer and Voit arrived at the same result. The cause is that during sleep the respiratory, like all the other functions of the body, is less active than in waking hours. The influence of light in increasing the output of carbonic acid has been investigated by numerou experimenters, and appears to be explicable on the supposition that muscular movements are more active in the light than in the dark, or during sleep. Hibernation.-Respiration is enormously diminished, and the exchange of gases is carried out by diffusion and the cardio-pneumatic movements. The carbonic acid given off falls to, the oxygen taken in to of what they are during active life (Valentin). The body weight may increase through the relative excess of oxygen; and according to Regnault and Reiset a small quantity of atmospheric nitrogen is also absorbed. 1 Bidder and Schmidt, Die Verdauungssäfte und der Stoffwechsel, Milan and Leipzig, 1852, p. 867. ? Moleschott (Chem. Centralbl. 1872, No. 49), Pott (Habilitationsschrift, Jena, 1875), Pflüger and v. Platen (Pflüger's Arch. xi. 272). See also p. 211. Surrounding temperature.-The temperature of cold-blooded animals rises and falls with that of the atmosphere, and the amount of chemical, including respiratory, activity varies similarly. Moleschott states that a frog at 39° C. excretes three times as much carbonic acid as when the temperature was 6° C. In warm-blooded animals, however, the body temperature remains constant amid the variations of that of the surrounding air. As the atmospheric temperature diminishes, the processes of oxidation within the body are necessarily increased; this is brought about by a reflex nervous mechanism; the increase of chemical changes produces an increased amount of heat, so as to keep the body temperature up to the normal level. The reverse processes obtain when the atmospheric temperature increases (Lavoisier,' Sanders-Eyn,2 Vierordt, Colasanti,' Theodor,' Voit," Page'). The following is the mean result of 21 experiments by Colasanti on guineapigs: Page experimenting on dogs found that there is a temperature of the surrounding medium at which the carbonic acid is at a minimum (about 25° C.); below this temperature the quantity of carbonic acid discharged increases as the temperature falls; above this the discharge also increases, and at abnormally high temperatures (40°-42°) the increase may be very rapid. Fever.-In fever the body temperature is raised, and this brings with it, as in cold-blooded animals, an increase of chemical activity. In Page's experiments with the high temperatures just mentioned, the body temperature of the animal, as well as that of the air, was raised. The following were the results obtained by Pflüger and Colasanti in guineapigs: Liebermeister has made similar observations in cases of typhoid and intermittent fever in human beings. It will be sufficient to quote one example; this shows how, in the quickly succeeding phases of an attack of ague, the output of carbonic acid and the production of heat run parallel. Handbuch der Path. u. Therap. d. Fiebers, Leipzig, 1875, pp. 327-340. Leyden and Frankel' have made similar observations. Other pathological conditions have not been so fully worked out as fever; it may, however, be stated that diseases of the lungs which diminish their capacity for respiratory purposes necessarily lead to a diminished respiratory exchange. In such cases, as well as in cases of obstructive disease of the respiratory passage. the inspiration of compressed air would be of great benefit. In the normal condition the blood takes from compressed air very little more oxygen than at the ordinary barometric pressure; this is because the gas in the blood is chiefly in a state of chemical union with hæmoglobin, not in a condition of simple solution (see further under Gases of the Blood). But when the volume of the lungs is diminished the hæmoglobin is unable to get all the oxygen necessary to form a due quantity of oxyhæmoglobin; but air occupying the same volume, but containing a greater supply of oxygen, i.e. compressed air, would obviously correct this. Food. In inanition the output of carbonic acid and the intake of oxygen both diminish, especially the former, and thus the respiratory quotient falls (0-75) (Bidder and Schmidt, Pettenkofer and Voit, Regnault and Reiset); a small quantity of atmospheric nitrogen is absorbed (Regnault and Reiset). An increase of respiratory activity occurs after meals, especially about an hour after the chief meal (Vierordt). Substances rich in carbon (starches and fats) cause an increased excretion of carbonic acid. A purely carbohydrate diet is only compatible with life for a short time; but during this time the respiratory quotient rises to unity, or almost so; this is because the hydrogen of the food is already fully oxidised, hence the oxygen inspired has virtually only carbon to combine with (Regnault and Reiset). Substances which are oxidisable, like sodic lactate, glycerine, &c., when injected into the blood stream cause an increase of the oxygen taken in and the carbonic acid given out (Ludwig and Scheremetjewsky). Alcoholic drinks (especially brandy, whisky, and gin-E. Smith), tea and ethereal oils diminish the output of carbonic acid (Prout, Vierordt). Muscular Activity.-Muscular contraction causes a great increase in the output of carbonic acid, and in the intake of oxygen, but especially in the former, so that the respiratory quotient, CO2, rises. This was originally pointed out by Lavoisier, but has been more especially worked out by the researches of Ludwig and Sczelkow. If the venous blood leaving a muscle during rest be examined and compared with that which leaves the muscle during activity, it will be found that in the latter case the carbonic acid in the blood will be more increased and the oxygen more diminished than in the former. A few examples from these experi ments are given in the following tables : 1 Centr. med. Wiss. 1875, No. 39. 2 Wien. Akad. Sitzungsber. xlv. (1862) If the expired air be analysed instead of the blood gases, analogous results are obtained. The following example is taken also from Sczelkow's work. Rabbits were the animals employed : The following example is from experiments on human beings : : Experiments on man by Vierordt, Speck, and Pettenkofer and Voit, and on horses by F. Smith,' all gave the same result. In curare poisoning, where the muscles are inactive, there is much diminished respiratory exchange of gases (Zuntz).2 The increase of the gaseous exchanges during forcible respiration is partly explicable by the increase of muscular work. Increased work of the involuntary muscles also produces the same result. The stomach and intestinal tract have been investigated in this direction (v. Mering and Zuntz,3 A. Loewy1). Loewy's experiments were carried out both on rabbits and men; when the activity of the intestinal tract is increased by saline purges, there is a rise in the respiratory gaseous exchanges. No doubt this increased metabolism is due to the activity both of the muscular tissue and the glands of the intestine, but probably the former is the more important factor concerned. This subject is of practical interest, as, therapeutically, the cures of Carlsbad, Marienbad, &c., consist in increasing the activity of the alimentary canal by means of saline purgatives. 1 Journ. of Physiol. xi. 65. Zuntz and Lehmann (Zeitsch. f. wiss. handwirthsch. 1889 Journ. of Physiol. xi. 396) have also made similar experiments with horses. 2 Pflüger's Archiv, xii. 522. 3 Ibid. xv. 634; xxxii. 173. 4 Ibid. xliii. 515. |