marize the observed effects of the therapeutic applications of compressed and rarefied air, with the indications for the employment of these agents.

4

First, as to the absolute method, the method of Tabarie. In this, it is to be remembered, there is a complete change of pressure, the patient respiring air of the same density as that in which he is immersed. The effects of the compressed air-bath are due both to the physical changes produced in the air itself by the degree of condensation employed (from one-fifth to three-sevenths of an atmosphere excess pressure, with gradual transitions), and to the increased pressure exercised both upon the interior of the thorax and upon the periphery.

Inspiration becomes easier, expiration being slower and more laborious. As a consequence, the respirations are reduced in frequency and increased in depth, and the mobility of the thorax is increased. These effects continuing after a return to ordinary conditions, the ultimate effect is a gain in vital capacity.

The dilatation of the heart is antagonized, but to a less degree than its contractions are aided; for the normal amount of inspiratory negative differentiation can be brought about by increased muscular effort. Arterial bloodpressure is, upon the whole, lowered, so that the pulse becomes smaller and slower; and the blood tends from the superficies, both respiratory and general, to the deeper parts, and to those vessels contained in cavities with rigid and firm walls. There is increased absorption of oxygen and increased tissuechange, therefore increased nutrition and increased excretion. Upon the nervous system the effects are sedative and soporific. Concerning pathological conditions, both pulmonary and cutaneous, it may be noted that hyperæmia is diminished and absorption of effusions and inflammatory new formations, mechanically favored by compression; exactly as a bandage favors the same results.

The therapeutic indications are found in chronic congestive and inflammatory conditions of the skin, acute and subacute inflammations of the air-passages, chronic bronchitis, pulmonary emphysema unaccompanied by cardiac lesion, bronchial asthma, whooping-cough, pleuritic effusions, and the various forms of pulmonary consumption (in which are included the chronic pneumonias and bronchopneumonias), unless contraindicated by the danger of absorption of septic products present in lungs or bronchi, by high daily fever, by softening or excavation of lung-tissue suf

ficient to give rise to danger of rupture or of hemorrhage, or by general tuberculosis. Its especial advantage is to prevent extensive lesion in predisposed subjects with incipient disease. It has also been found useful in anæmia and chlorosis, and in obesity. Some observers commend it in certain cardiac lesions; others prohibit it in all. In the absence of personal experience, I can simply express a theoretical leaning towards the more cautious view. Other contraindications are found in states of the brain, spinal cord, or abdominal viscera, in which an increased supply of blood would be prejudicial.

The action of rarefied air in the pneumatic chambers is generally likened to the effects produced by ascent of mountains or in balloons, but certain differences exist owing to variation of atmospheric conditions in the higher regions. The rarefied air-bath has not been extensively employed in therapeusis, and as the recommendations made are largely based upon theoretical considerations only, I shall abstain from repeating them.

The differential method of pneumato-therapy, is that which is most readily available, most manageable, and, on the whole, most beneficial. Of this I can speak with positiveness, the result of some five years' personal observations. It introduces a new element into our physiological observations, namely, the possibility of facilitating or impeding the performance of both or either of the phases of respiration, together or alternately. It is, then, particularly applicable in the case of patients too weak to respire properly unaided, or in whom pathological conditions oppose one or the other, or both, of the phases of respiration, or in whom the normal respiratory rhythm has become perverted, whether from excess in one direction or from deficiency in the other. It also produces circulatory effects, due to the difference between intra-thoracic and extra-thoracic pressure, — that is, between the pressure upon the heart, pulmonic vessels, and intra-thoracic systemic veins and arteries on the one hand, and upon the peripheral vessels on the other hand.

Atmospheric pressure upon the surface of the body remaining unchanged, increase of pressure upon the pulmonary surface may be obtained, -1. By inspiration of compressed air. 2. By expiration into compressed air. Decrease of pressure upon the pulmonary surface may be obtained, -1. By inspiration of rarefied air. 2. By expiration into rarefied air.

These procedures may be so combined as to maintain the increase or decrease during during the other. All of these combinations were recognized and described by Waldenburg.

Increased pressure facilitates inspiration and impedes expiration. Decreased pressure facilitates expiration and impedes inspiration.

The facilitation of inspiration or of expiration, or of both, is usually the object of treatment; hence inspiration of compressed air, expiration into rarefied air, and the combination of these procedures, are the methods most widely employed. Inspiration of compressed air with expiration into the same medium, which, as pointed out by Dr. Platt, is virtually the method of the pneumatic cabinet, is highly recommended by recent American observers. The effects of these various procedures will vary,-1. With the degree of pressure employed. 2. With the time during which the process is continued; and, therefore, at different periods during its progress. 3. With the amount of voluntary co-operation on the part of the patient. The rationale of these variations being readily understood, and their effect easily deducible from the physiological studies already made, it will only be necessary to give what may be called an average summary under each head. It may first be stated in a general way that the amount of excess or diminished pressure is small, from one-eightieth to one-thirtieth of an atmosphere; much less then, than in the absolute method. The time varies from ten minutes to half an hour or longer, with interruptions. A period of absolute rest should precede, and another follow, each period of

treatment.

Inspiration of Compressed Air.-The excess pressure employed varies from one-eightieth to one-thirtieth of an atmosphere (+9.5 to + 25 mm. Hg.). From fifteen to thirty respirations may be made continuously, and the process repeated after a rest of five or ten minutes. The patient, if able, should stand, and, when necessary, the physician may aid inspiration by pressing the shoulders backward, or assist expiration by compressing the chest. When it is desired to localize or locally increase the effect, the healthy side of the chest (e. g.) may be strapped, or its motion diminished by manual pressure or pressure against a wall, chair-back, or other suitable object.

The effects, which follow from considera tions already detailed, are decrease of muscular exertion necessary for inspiration, dilata

in the penetrating power of inspired air,therefore reopening of air-cells disused from weakness, occluded by the products of secretion and desquamation, or agglutinated from similar causes, and increase in the volume and weight per volume of O brought to and absorbed by the blood; a greater area of blood surface being reached. The subsequent expiration is sometimes slightly retarded, but is deeper, the quantity of air exhaled and of CO, eliminated, being increased. Tidal and complemental air are thus increased, reserve air diminished; the first two quantities and a portion of the third quantity, being added to form what is now virtually an increased volume of tidal air, reaching two hundred cubic inches or even more. Diminished frequency of respiration, increased expansion, ventilation, and gaseous exchange, are therefore the immediate effects; increased vital capacity the ultimate and permanent result. The circulatory effects are those of heightened pressure, — namely, an augmented centrifugal tendency of the blood-current; increased force of the ventricular systole; quickening of the pulmonic circulation, bringing more blood, therefore more corpuscles, more hæmoglobin, in proportion to area, into contact with the increased quantity of O; filling of the systemic vessels, with rise of arterial blood-pressure ; the pulse becoming at first more rapid, afterwards slower, full, and hard. The blood circulates more actively throughout the body, being richer not only in oxygen, but also in nutritive materials, for pressure upon the diaphragm, transmitted to the abdominal viscera, stimulates absorption of chyme; while heightened pressure and augmented volume of blood in the viscera tend to stimulate functional activity. Thus, increased oxidation and tissue-change stimulate appetite and improve nutrition. Passing to effects upon pathological states, pulmonary hyperæmia is relieved; inflammatory products are absorbed; cough and expectoration are at first increased, from dislodgment of accumulated materials, afterwards diminished from relief to irritation and diminution of pathological secretions. Increased ingestion and assimilation repair pathological waste, and the increase in weight sometimes exceeds the previous record in good health. Sleep is promoted; night-sweating is often arrested ; hæmoptysis is sometimes checked.

Expiration into compressed air impedes the act and requires greater muscular exertion. If this be sufficient to overcome the obstruction, the amount of air expelled is increased; otherwise it becomes gradually diminished, and the subsequent inspirations are therefore rendered shallower. In other words, tidal air is

wards impeded from the resistance of the denser outer air. The muscular effort of this phase is thus also increased, and the frequency of respiration, at first heightened by the excitement of impediment, is finally diminished.

ual air gradually encroaches upon reserve air, tidal air, and finally upon complemental air;

ary or residual. The excursions of the diaphragm and thoracic walls become less and less, but at the expense of the contraction, fixed expansion being finally maintained; and if the procedure be pushed to excess with too high a pressure, apnea may result. Pulmonary ventilation is diminished, and gaseous exchange is retarded; the absorption of O by the hæmoglobin being, however, facilitated, although the excretion of CO, is diminished. The effect upon the circulation, is an exaggeration of that produced by inspiration of compressed air, being practically the same as in Valsalva's experiment-depletion of the lungs and heart; over-distention of the systemic vessels, especially the veins. The pulse may disappear from compression of the subclavian artery. Upon pathological conditions, the pressure effects are similar to those already detailed.

Continuous respiration of compressed air, therefore, greatly augments the distention of the thorax and of the lungs, maintaining the patency of the alveoli; and while it diminishes during treatment the volume of air exhaled, the result may nevertheless be properly stated as an increase in vital capacity. The ventilation of the lungs is diminished, but, on the whole, gaseous exchange appears to be slightly increased. There is constantly increasing interference with the dilatation of the heart, and an outward pressure replaces the normal thoracic aspiration of the blood, thus blocking the systemic veins, while at the same time the arteries are distended. Arterial tension, increased at first, soon falls, and the pulse becomes small, slow, and feeble.

Inspiration of rarefied air, which should be conducted against a very small negative pressure, rarely exceeding one-sixtieth of an atmosphere, increases the muscular effort necessary to produce expansion of the chest, and the volume of air needed to supply the proper weight of O. If the requisite effort can be made, there is increase in the elastic tension of the lungs and in the volume of tidal air. If it cannot be made, there is decrease in both these factors. The subsequent contraction of the chest is at first passively facilitated, after

and accumulate within the thorax; but, as there is more blood delivered to the left ventricle, and this can contract with sufficient force to overcome the higher peripheral pressure, the final result is a quickening of the circulation with an increase in the fulness, blood-pressure, and tension of the arteries.

Expiration into rarefied air, conducted with a negative pressure of from one-sixtieth to one-twenty-fourth of an atmosphere, facilitates the contraction of the thorax, exerting a moderate suction-force, and greatly increasing the amount of air expelled from the lungs; thus facilitating the collapse of distended air-vesicles. Subsequent inspirations are rendered easier and deeper; more O-bearing air enters the vesicles; ventilation and gaseous exchange are enormously increased; and the increase in vital capacity is very great. The circulatory effects are similar to those produced by inspiration of rarefied air, but more marked. They vary in different individuals, are evidently different in man and animals, and can be influenced by the manner of subsequent inspiration. While there are conflicting observations as to systemic bloodpressure, there is agreement as to the tendency to pulmonary congestion and the facilitation of cardiac diastole.

The effect of inspiration of compressed air, with expiration into rarefied air, is to increase the efficiency of both processes. The alternate expansion and contraction of the lungtissue stimulates its elasticity. Pulmonary ventilation, both as to interchange of gases and expulsion of effete materials, is vastly augmented. The alternations of opposing circulatory effects relieve hyperæmia wherever present, increase the activity and penetrating power of the blood-current, and stimulate tissue-change and nutrition.

Inspiration of rarefied air, with expiration into compressed air, increases the muscular effort necessary to complete each act, prolongs the respirations, and retards expiration particularly. The alternating centripetal and centrifugal impetus increases the activity of circulation.

Inspiration of rarefied air, with expiration into the same medium (continuous respiration of rarefied air), increases the muscular effort of inspiration, but hastens and facilitates expiration. The centripetal tendency of the blood is maintained during the entire act, and the heart's action is greatly diminished in force and increased in frequency, the general arterial pressure being much lowered.

THE THERAPY closely follows the physiological indications. The degree of usefulness of pneumatic expedients in any given instance will of course vary with the conditions of the case: and proper hygienic, dietetic, and medicinal measures must also be instituted. In pointing out the classes of cases in which pneumato-therapy is useful, I do not wish to be understood as claiming the method to be competent to cure in every instance.

Inspiration of compressed air, and expiration into rarefied air, are the expedients most generally employed, singly or in combination.

Inspiration of compressed air is of benefit in dyspnea, of almost any origin; in laryngeal and tracheal stenosis; in chronic bronchitis; in chronic broncho-pneumonitis; in chronic broncho-pneumonitis verging on tuberculosis; in chronic desquamative pneumonitis; in chronic interstitial pneumonitis; in atelectasis; in chronic pleurisy with effusion; in the dry pleurisy of early phthisis; in phthisis at any stage short of general softening, with one or more large cavities, but particularly in the early stages, when deficient respiration, impaired circulation, anæmia, and malnutritive dyspepsia in a predisposed subject, suggest tuberculosis even in the absence of pronounced physical signs.*

The good results of this procedure in phthisis result not alone from the primary effects already alluded to, -the opening of disused or occluded air-cells, with increased vital capacity, increased pulmonary ventilation, increased activity of circulation, absorption of inflammatory products, relief of congestion, but also secondarily from the increased appetite; relief of cough, with promotion of sleep; and the general stimulus to local and general nutrition, following the systematic pulmonary gymnastics necessitated. In simple anæmia, or chlorosis, without tubercular tendency, the same good effects may be obtained. In asthma,

* It may be remarked here that evidences of pulmonary impairment, indistinguishable by the ordinary methods of physical exploration of the chest, may sometimes be detected during inhalation of compressed air,a fact first published, so far as I am aware, by Dr. J. Solis-Cohen. Vide N. Y. Med. Four., October 18, 1884.

the inspiration of compressed air is also useful, but high pressures are necessary, and must be cautiously employed. I have succeeded in one case, that of a patient who was attacked in my consulting-room, in cutting short a paroxysm by the employment of a pressure of onethirtieth of an atmosphere, steadily maintained for nearly fifteen seconds, the expiratory act being held for the time in abeyance. This expedient, which I believe overcomes spasm by a paralyzing effect upon the bronchial muscles, and by inducing fatigue of the diaphragm, was suggested by the experience of Dr. Monell, who obtained relief in his own person by forced expiration, with his feet braced against the foot-board of his bed, prolonged pause, forced inspiration, pause, and so on. In asthma and emphysema, however, better results are usually obtainable from expiration into rarefied air. In hæmoptysis, good results have been reported from the inspiration of compressed air and its equivalent, - rarefaction of surrounding air in the Brooklyn pneumatic cabinet. Some authors, however, have considered a hemorrhagic tendency as a contraindication to the measure. My own experience leads me to the belief that where there is any weakness of the pulmonary vessels, or any peripheral lesion of hemorrhagic tendency, or where it is inadvisable to increase blood-pressure in the brain, or in the kidneys‡ or other abdominal viscera, the measure is dangerous. In two remarkable instances, elsewhere cited,§ I have, however, been forced to credit it with a tendency to the relief of pulmonary hemorrhage; and this seems to be due directly to the relief of the conditions antecedent to hemorrhage,-namely, pulmonary congestion, with perhaps an exaggerated stasis at one spot, from mechanical obstructions affecting that portion of the circulatory apparatus chiefly. Inspiration of compressed air is also recommended in mitral insufficiency, and in stenosis and insufficiency of the aortic valves. It is theoretically indicated in dilated heart, and with caution in lipocardiac asthma. I have had no experience with it in any cardiac lesion.

Expiration into rarefied air should be combined with the inspirations of compressed air, where it is desired to increase circulatory асtivity and gaseous exchange, or to get rid of

+ N. Y. Med. Record, August 15, 1866. Cited by J. Solis-Cohen, op. cit.

In one of my cases, albuminuria developed during treatment. This may have been merely a coincidence, but at the time I considered it more.

Phila. Med. Times, February 6, 1886, p. 362.