SOME PRACTICAL CONSIDERATIONS OF DYSPNEA

SEYMOUR M. FARBER, B.A., ML)., AND SOL &J,VERMAS, JR., B.A., MA.,* k3-t~ FRAWUSCO, CAJ.IF.

A T THE moment of birth, the human infant is only potentially an air-breath- ing organism. The lungs at this time are airless and immobile, lying in a

chest cage that, is markedly narrow, with t,he sternum depressed and the ribs in close proximity to one another. The critical act of human life is the convulsive expansion of the chest cage within a few moments of birth. This convulsive movement raises the st,ernum, and expands the rib cage upward and outward. The capacity of the thor.ax is thus sharpl,v increased. This increase in volume tends to create a vacuum between the outer pleura, which is adherent to the chest, wall, and the inner pleura, which is adherent to the lungs. The lungs, in turn, resist this tendency to a vacuum by expanding to fill the new space creat,ed. They are able to do this because they themselves can be filled with air drawn in through the mouth. Legally, the child brgins its independc~nt existence when it draws this initial breath.

Maintenance of this existence depends upon the repet,ition of such a thoracic movement at very frequent intervals. The chest cage never again approaches the degree of collapse which is present at birth, although breathing is essentially the alternate expansion and contraction of the chest cage in conjunction with the diaphragm. It will be noted that the lungs do not completely expand at birth; they are gradually expanded by the negative pressures cre.ated by muscular and skeletal changes. For all practical purposes, the lungs can be regarded as passive agents in the act of respiration. The average adult breathes, thus, about 24,000 times a da:-. II’ approxirnatelg 100 of these ventilatory move- ments are consecutively prevented, he will die. If all of them are inhibited to some degree, as in severe dyspnra, he becomes a respiratory cripple.

The importance of the lungs to the maintenance of life depends, of course, upon the fact that all higher organisms from a chemical point of view, are essen- tially oxidizing. The variety of chemical operations that take place in t,he human body is almost infinite, hut basical1.v these reactions are changes in carbon com- pounds which require the presence of free oxygen for them to occur. These chemical reactions, which release the heat and energ>- necessary for life, have as their end product carbon dioxide.

Both the carbon compounds and the free oxygen must be continuously present for life to be maintained. The former are readilp stored by the body until they are required. Human beings can live without food, on the basis of such reserves, for a rather long period of time. The capacity for oxygen storage? on the other hand, is very limited. Outside of the oxygen available in the blood.

From the Division of Medicine, Medical School, ITniversity of California. Read before the Eighth Annual Seminar for the Study and Pmctice of Dental Medicine,

The Desert Inn, Palm Springs, Calif., Oct. 29. 1951. *Dental Student, University of California.

the human body has no means of storing free oxygen beyond the limited c;lpavit > of the lungs. I)eprived of access to this vital element. the human being dies ili about five minutes.

The process by which free oxygen is removed from the air t.o replat~e t 111, waste product,, carbon dioxide, depends finally,+ upon t,hr t+ontinncd operation o! the tllementary laws governing the behavior of gases. ,\ gas is in realit>- a large number of widely spaced molecules movin, u in straight lines at a ver!- hiylr speed. The impact of these molecules upon the walls of a container rxt~rts il measurable pressure; because of their rapid movement this pr’essnrc at 011t’ I~oit~! on the container wall will be equal to the I)ressurc at any other l)oint. ‘l’lll~ most important law, then, is that a gas tends to cliffrise itself exrenly throtlghoti1 every part of an enclosed space.

Furthermore, this is true even when a portion of’ this spats is oceupivcl 1)~. a. liquid. ~lany additional factors enter the theory at this point, esprriall;v ;M concerns the solubility of the gas, but the basic t’acat is ihat the pas nil1 ttvlci to diffuse itself through the liquid as well as 1Irrollgh the spat&v abovtl the litjuiti For instance. if all the free oxygen is removed I’rom a pan of water 1)~ I)oiiittg. and this deoxygynated water is then allowed to stand unc*overed for il whilr. t It< osygen contt~nt will graduall>- be restored. The water will tend to rrahsori~ oxygen until thr pressure of the gas in solution is equal to the prt3siir(l of t-hlx tyig’cn upon the surface of the liquid. If air prrssnrc is irlc*rewst4. the amout~: and, correspondingly, the pressure of the free oyvpcn contained ill thla WI cl’ will he increased proportionately. Blood plasma has thrh same ~)roperty itI Ihi, respect as water; oxygen is readily taken into this mrvlium. A4 furl her Cat>1 regarding the operation of gases must also be noted. 11’ there are two sc~lr~bl~~ gases operating upon a liquid at the same time, they will act indepcntlt~nt ly OI one another. If a pan of water saturated lvith oxygen wore inserted in a vtn; t,ainer contuillinp carbon dioxide., this water would rclrasr osygcn and absorb I 11th (‘0, until both gases have achieved a point oi’ equilibrium between the +zas ill solution and that out of solution. It is by utilizing this basic behavior of YitSt'S

that every higher organism maintains its vital fntlc+ons. Thr blood distributes all the materials rcctnirrd for metabolism, ot’ WLIIW:

however, th(a system of veins and arteries is arranged around the oxygtln-carty- ing capacity of the fluid. The freshly oxygenwtrtl blood passes from thti Im~gs int,o thr arterial system through the left vrntricltl. The arteries eventual I).. 11) a finer and finer division of the vessels. distribute this tts~*gvnatctl blootl illlo the capillary beds of every part of the body, where the basic provess ot’ tncta t)ol- ism takes place. I)uring this metabolism, tha blood loses some of its ox;-grn and picks up CO,. From these capillary beds it is collevtc4 into t,he vvitrs ancl returned to the heart. Here it is directed through the pulmonary ar~rr~’ I>;lt*k into the lungs where it is forced again throuph t~apillary beds. this time to rvstovtx the oxygen lost in metabolism.

These lung capilbaries lie around the finest divisions ot’ the bronchial ttvs. If IW vould follow a moiety of air into the mouth, we should see it rnter itrio the trachea upon inspiration and bc drawn from thenre int,o one ol the larg(‘t bronchi. 111 these larger divisions of the bronchial tree incoming air is \~al*n~t~cl

394 SEYMOUR M. FARBER AND SOL SILVERMAN

and impurities are removed, but their primary function is merely that of pass- ageways. From the major bronchus, the air passes into smaller bronchi, which further subdivide themselves at intervals and grow smaller in diameter. Ulti- mately the inhaled air reaches the point in the bronchial tree at which cartilage is no longer present in the bronchial walls. From this point on, tiny mem- branous sacs a,ppear from time to time openin, w off the bronchiole, until the termination of the whole system is reached. This is a somewhat complicated structure, but essentially it is a whole group of the membranous sacs arranged not unlike a cluster of grapes. In these ultimate structures of the respiratory system the body is able to exchange the waste product, C02, for oxygen.

Such an exchange is possible because of the thinness of the basic membrane. It adequately restrains the denser blood, but it permits a free exchange of gases between the blood and the alveolar air. What happens in this exchange can be shown graphically, with figures representing gas pressure in millimeter of mercury :

OXYGEN: co, :

INSPIRED AIR ALVEOLAK AIR VENOI-S BLOOD ARTERIAL BLOOD

159.00 100 90 0.23 40 260 40

(Since the lungs are not completely emptied and refilled in each respiratory c,ycle, alveolar air, in the deepest part of the lung, shows somewhat different values than the atmosphere.)

In its passage through the lung capillaries, which is estimated to take some- what less than a second, the oxygen pressure of the blood rises from 40 to 90; at the same time CO2 pressure drops from 46 to 40. In the normal individual at rest, for which these figures are calibrated, this represents a condition of equilibrium; the oxygen restored to the blood is equivalent to that consumed by the basic processes of metabolism; CO, is removed at the rate at which it is being formed.

The alveolar membrane must be intact and healthy for this exchange to take place mechanically at an adequate rate. Two other conditions must also exist for effective respiration, however. In the first place, the blood must be driven through the body sufficiently fast to prevent the CO, values from be- coming excessive, and to prevent certain degenerative processes from taking place in the lung. This is a matter largely concerned with the circulatory system and the operation of the heart. The condition which must be met involving the respiratory system requires that the air within the alveoli be regularly replen- ished.

The purpose of breathing is to replenish this air. Normally, only a bout one-fourth of the total amount of air in the lung is expelled with each breath, and an equivalent amount of fresh air is drawn in. Comfort requires that the CO, be maintained at a higher level within the lung than is present in the atmosphere; hence, the air in the interior of the lung is const.antly being mixed with the atmosphere, without being completely replaced by it.

All breathing is initiated and controlled by the respiratory center, lying at the base of the brain above the spinal cord, and operating through the vagus nerve. Quiet breathing is accomplished by light excitation of the intercostal muscles and the diaphragm. The intercostal muscles when stimulated contract

PRACTICAL CONSIDERATIO~P OF DYS1’NF.A :Wl

and slightl,v raise the chest cage; the diaphragm also caontracts, flat~teninx 0~1 t.lle (]iaphragmatic dome. This cnlarpes t,he thoracir cagz’c antI air is dravvn into

the lungs. When the lungs have expanded to a certain point, nerve ending’- wittlin t,he smaller bronchi are stimulated by thr tension in bronchial \\-:ili~, iLfI(i an impttlse is rela,ved to the respiratory center which inhibits the inspirator\- iIn pulse. Xir is exhaled, then, by the simple relaxation of these intercostal mus(*it+ arrd the diaphragm. This whole process is calletl the Hering-Krcuer rifle; i! operates without any external stimuli being applied

If respiration were merely this regular r&x action! human life WOII~~\ be virtually impossible. The slightest activity wo~11c~ increase the oxygen rc- quirements and irreparably destroy the O2 and (‘0, balance of the blood, since (‘0, would accumulate in the alveoli at a constantly increasing rate. .! hcav? meal, which also increases oxygen rcyuirrmenls, would be fatal. It is not rnough that respiration occurs, it must be delicatrly adjtlsted to current bodily IIW~G needs which constantly alter.

There are, as a matter of fact, several ways in which breathing is adjustt~ci

to osygcn requirements. These adjustments, for the most, part, are indirect. h person suRering from a simple l.ack of oxygen, as a mountain climber, 1’01 instance, will increase the depth and the rate of his breathing, but inadrquat~r1.v to this requirements, unless the oxygen lack develops very slowly. He will suffer no acute discomfort that might call attention to his precarious situatio!l.

The most sensitive respiratory controls react not to an oxygen shortage but to minute alterations in the arterial concentration of the CO,, which I-C- maing in the arterial blood. The respiratory center itself, if nourished by this arterial blood, and if this blood has even a very slight increase in CO, content, affects the center directly, setting off an excitative impulse which calls suppt~a- mental muscles into temporary service. Everq’one is avvarc, at one time or another. of t,aking a single deep breath, or several in sncccssion, in the c()nrsc of normal, unconscious respiration. These unconscious, deep breaths arc the means whereby oxygen intake is adjusted to v.ariations in metabolism; thtly arc produced by- the action of CO, directly upon the respiratory center. flowcvcr. ate periods of energetic activity, metabolism takes place at a rate many times that of normal.

The direct, action of the respirat,ory center may still be of importanec, but much more important at such times is the activity of two very small strtlctnrrs lying within the main arterial systems and connected to the respiratory c*cnttlr. One o-f these structures is found in the aortic arch and the other in the tarot- id arteries. Both have a dual function. If there is an increase or c\cc*rcarr in blood pressure in the artery, t,he action of the heart is required to make a major adjustment in the rate and strength of its contractions, and respiratit)n makes less important adjustments on demand. Also, a strong excit,ative impnlsc can be transmitted by these bodies to the respiratory center, if there is a I;!& of oxygen. The excitation of the carotid and aortic bodies by anoxia t~+uits in increased sensitivity of the respiratory center to CO,.

WC ran distinguish two grades of deep breathing. Ilyperpnecl is an in- crease in the rate and depth of hreat,hing which is not apparent to the subject. althongh it may be noticeable to an obscrvcr. An ordinary person will 1101

396 SEYMOUR 31. FARBER AND SOL SILVER>fAN

he aware of an increase in breathing until the rate of pulmonary ventilation (which depends upon the amount of air which is inhaled and exhaled in a minute) is doubled. Dyspnea is breathin g accompanied by a feeling of effort and discomfort. Breathing ordinarily becomes really uncomfortable when pul- monary ventilation is increased four- or fivefold over normal. The point at which the individual becomes acutely uncomfortable is usually called his ’ ‘ dyspnea point. ’ ’

Dyspnen can be, of course, a normal reaction to strenuous activity, or it can be abnormal. It is a, forceful reminder to the individual that he is making an unusual demand upon his respirator- capacity, and that he is consequent13 approaching the point at which the response will be unequal to the demand. Shortly after this point the individual will become unconscious. The closer bodily demands approach the total pulmonary capacity t,he more uncomfortable t,he individual becomes.

Yathologicnl dyspnen will be understood if it is rernembered that dyspnea results from an increased CO, pressure in the art,erirs, and the dyspnea point is that degree of activity at, which the lunps are no longer able to remove CCL from the alveoli fast enough. Dyspnea is p.athological when the normal activity tolerance is decreased hv some organic failure or malfunction.

1. Increased Metabolism.-ln certain pathologic conditions, such as exophthalmic goit,er, basal metabolism is very high. At rest the body requires sometimes two or three times the .amount of osygen that is normal. Conse- quentlp such persons have little capacity for increased activity. Even if the maxirnum capacity of thr respiratory system is normal, it does not provide much of a margin over basic requirements, which arc abnormal.

2. Impaired Rate of Diffusion.-There are many ways in which the total effective membranous area of the lung, through which the gas exchange is made, can be reduced. Any lung infection tends to produce inflammatory changes in and around these membranes and inhibit their function in the infected area. A patient with a massive pneumonia may be dyspneic simply because he has not, enough normal lung tissue properly functioning t,o permit, an adequate aer.ation of the blood. Rarely, the membrane of the pulmonary air sacs will be thickened and impaired for no apparent reason.

3. Air Passage Obstruction.-Likewise, any marked degree of obstruction of the air passages will inhibit the free replacement of alveolar air and produce dyspnea. A paGent with asthma ma!: become dyspneic on slight exertion be- cause even by breathing deeply he is not able to move air through the constricted passages of his bronchial tree fast enough to keep t,he composition of alveolar air within tolerable limits. A tumor or foreign body map act in the same way.

4. Reduced Lung Capacity.-This is the most common cause of dyspnea. It. may come about by an actual reduction in the amount of lung tissue, by disease, or by muscular atrophy of the thoracic cage due to inactivity.

a. In any active case of .tuberculosis it is standard procedure to in- activate the affected part of the lung by collapse therapy. In serious lung con- ditions, such as malignancy or far-advanced tuberculosis, it may be necessary to remove a segment, of a lung, or even an entire lung, surgically. In these in-

PRACTICAI, COSSIDER.\TIOSS OF DYSl’Sl+:.\ :;“,;

I),vspnea is seldom an entirely hopeless wntlition. 13~~11 wherl it irrvol\w irreversible changes in the lungs or circulation. at least some alleviiltiolr 01’ tlw tlisabilit,y is usually possible. It is most important. howvcr, that treatment 11t1 undertaken in the light of the total functioning of the organism, which dcpentlq upon a thorough study of the individual’s dynamic physiology. The dist~.st~ giving rise to t,he condition is the first considtwtion : its effect must he nrinimiz~~l cvert if it is chronic. X weak heart may be beymd (WY. but, its operatiorr van lw

made more efficient by a careful regimen and sgnptomatic drug trwImen~. When the d,vspnea arises from such a contlition, it, is usually automat ica I I> alleviated by an improvement in the primary pathology. If there is in.l’ct~tiori present anywhere in the body it should be rliminatetl OP minimized 1)~ a11t1-

I)iotiw ; any infectious process releases toxic ~)roducts into the bloodst I’PNII ant1 increases the basic demand for oxygen. 11’ such infections are cleart4l up3 tll~ respiratory resrrve of a11 individual is in~~rwsc~rl hy lowerinn his rnin im urn rec~nir~rri~nts.

398 SEYMOUR M. FARBER AND SOL SILVERMAN

Many types of symptomatic treatment are available. Bronchodilators en large the diameter of the bronchi and thus permit freer passage of the air; this is often of considerable benefit. Antihistamines may- give relief if the dyspnea

involves in any way an allergic response. In severe cases, there are intermittent pressure breathing devices available which give considerable symptomatic relief.

The use of pure oxygen, by itself or in conjunction with these intermittent pres-

sure breathing devices, is often helpful. In most instances physical therapy can be of much benefit, if it is undertaken under the direction of a competent therapist skilled in thoracic physiology. The primary object of such therapy is to increase maximum breathing capacity; it is not concerned directly with the underlying pathology. Few individuals normally have at their disposal all the ventilatory capacity of which they are theoretically capable. In all of US, except the trained athlete, the muscles used in respiration are debilitated to a greater or lesser extent by inadequate exercise. This effort of the physical therapist is to make available to the dyspneic patient this undeveloped capacity. The basis of the treatment is a course of carefully planned exercise of the thoracic musculature. Other procedures may supplement the treatment if they suggest themselves. If the diaphragm is markedly depressed, as is commonly found to be the case in emphysema, it can be raised to a functioning position by the periodic injection of air into the peritoneal cavity. Other minor proce- dures may be undertaken from time to time. The object is always to permit a greater degree of expansion and a more efficient operation of the lungs, to com- pensate for the pathology which gave rise to the dyspnea. The relief obtained by this symptomatic treatment is very often striking. At the present time, such a course of exercise is mandatory in a great many hospitals for all patients whose breathing capacity has been markedly diminished by pneumonectomy or other procedures.

This paper, of course, is but a brief review of a complicated subject. Not. many years ago, dyspne.a was regarded as hopeless, an irreversible condition which would inevitably progress to the total incapacity of the patient. We have overcome this prejudice and have already accomplished much in the relief of this chronic and painful condition. It is a rapidly expanding field of clinical research, and further advances can be anticipated with confidence. The .im- portant thing to remember about the condition is that it is not hopeless. If eare- ful therapy is undertaken upon the basis of thorough medical evaluation of the patient’s clinical status, the patient can often be restored to a condition per- mitting at least a moderate amount of normal activity.

References Barach, A. L.: Principles and Practices of Inhalation Therapy, Philadelphia, 1944, J. B.

Lippincott Company. Bard, Philip : MacLeod’s Physiology in Modern Medicine, St. Louis, 1947, The C. V. Mosby

Company. -.

Dorinson, Malvern : Breathing Exercises as an Adjunct in the Treatment of Bronchial Asthma and Pulmonary Emphysema, American Practitioner, vol. 3, no. 9, May, 1949.

Myers, J. A., and McKinlay, C. A.: C Thomas, Publisher.

The Chest and the Heart, Sprmgfield, Ill., 1948, Charles

Richards, D. W., Jr., Barach, A. L., and Cromwell, H. A.: Use of Vaporized Bronchodilator Solutions in Asthma and Emphysema, Am. J. M. SC. 199: 225, 1940.