Complete Text (Part 3)

of increased negative pressure in the thorax, causing increased flow of blood into the heart; (2) difference of atmospheric pressure level in the pulmonary artery and vein, causing an increased flow of blood out of the heart. At the beginning of expiration the sudden con- traction of the lung-capillaries causes a momentary FUNCTIONAL DIAGNOSIS 29 rise in pressure, which is quickly overwhelmed by a reversal of the conditions described under (1) and (2) in the previous paragraph, producing a distinct fall in pressure. Respired Air. — The air respired by the lungs is classified in various fractions of its volume accord- ing to their exchange under various physiological conditions. The classification is as follows: Tidal Air. — The amount of air breathed in and out during a normal respiration. Complemental Air. — The amount of air that can by forced inspiration be taken in in excess of the tidal air. Supplemental Air. — The amount that can by forced expiration be expelled in excess of tidal air. Residual Air. — The amount which remains in the lungs even after the supplemental air is expelled. Minimal Air. — The small amount which is cap- tured by the collapse of the small bronchi in an ex- posed and collapsed lung. A lung that has once breathed never thereafter becomes entirely airless; it always retains the minmial air even after death. Vital Capacity is the term used to express the amount of air that a person can inspire and expire, and is, of course, equal to the tidal air plus the com- plemental and supplemental. Pressure Conditions of Oxygen in Respiration. — The pressure of the atmosphere is equal to a column. of mercury 760 mm. high, and is expressed as 760 30 FUNCTIONAL DIAGNOSIS mm. Hg. According to the law of partial pressure of gases, the oxygen in the atmosphere, forming one-fifth of its volume, exerts one-fifth of its pres- sure — i. e., 152 mm. Hg. This pressure determines the point of equilibrium at which oxygen is held in solution or dissociable combination by a liquid in the presence of atmospheric air. At this pressure, the hemoglobin of the blood is saturated with oxy- gen and as long as the oxygen-pressure in the atmos- phere is maintained the oxygen equilibrium between the blood and the air is maintained at saturation point. If the proportion of oxygen in the atmos- phere is increased the equilibrium is disturbed and oxygen flows from the air to the blood (to the limit of absorption by the plasma) ; if the proportion of oxygen in the atmosphere is diminished the equilib- rium is disturbed the other way, and oxygen flows from the blood to the air. The same condition ob- tains if for the air is substituted another environ- ment containing a more or less pressure of oxygen. The blood at the surface of the lungs is practically under 152 mm. Hg. oxygen pressure (i. e., one-fifth atmospheric pressure.) In its course along the ar- teries this oxygen pressure is gradually lowered as it comes into contact with greater and greater areas of tissue devoid of oxygen. By the time it reaches the capillaries the oxygen pressure has come down to 76 mm. Hg. In its passage through the capillaries, where this low pressure area is greatly increased, the oxygen pressure is rapidly reduced, and the oxygen FUNCTIONAL DIAGNOSIS 31 just as rapidly given off to preserve the oxygen equilibrium. When it reaches the lungs again, with very little oxygen in it, it is suddenly subjected once more to an oxygen pressure of 152 mm. Hg. and sat- urated with the gas. Difference of Pressure at Lungs. — Experiment shows that the relative pressures of oxygen in the alveolar air, where the exchange is made, and the venous blood that is brought to the lungs by the pul- monary arteries are as follows: Alveolar air — 83 to 129 mm. Venous blood — 40 mm. ■ It is evident that the exchange takes place from the air toward the blood. Insufficient Oxidation. — It will be readily seen that any diminution in the oxygen pressure at the lungs will result in an abnormally small impartation of this gas to the venous blood, and consequently in poor oxygenation of the tissues. This may occur either from (a) poverty of the surrounding air in oxygen or (b) any condition of the respiratory mech- anism which tends to rarify the air as it enters the lungs — e. g., stenosis of the trochea or bronchi — causing undue negative pressure during inspiration ; or emphysema, in which the inspired air is continu- ally diluted by an excess of residual air. Chemical and Physical Changes in Respired Air. — Expired air differs chemically from inspired air in having lost a part of its oxygen and acquired 32 FUNCTIONAL DIAGNOSIS carbon dioxid. This is indeed the chief end of res- piration, the carrying of oxygen to the blood and the removal of carbon dioxid. The proportion of gain and loss depends, of course, upon the character of the inspired air, depth of inspiration, etc. Under normal conditions, however, the exchange is about as follows: C0 2 Insp 'd. Bxp'd. OLost. Gained. Oxygen 21 16 .05 Carbon dioxid. ... 00.4 4.5 .04 79 79 . . It will be seen that more oxygen is lost than is represented by the carbon dioxid which replaces it. The excess oxygen is utilized in oxydizing hydro- gen in the body to form water. Physically the expired air differs from inspired air in being warmer (equal to body temperature) and saturated with water vapor from the lung sur- face. This loss of heat and water is a subsidiary function of respiration in regulating the tempera- ture and moisture of the body. Pressure Conditions of Carbon Dioxid. — The par- tial pressure of carbon dioxid in the atmosphere, on the other hand, is only four-hundredths of the atmospheric pressure, or 30.4 mm. Hg. At this pres- sure the blood contains 38 per cent by volume of car- bon dioxid. During the passage of the blood through the arteries and capillaries, the carbon dioxid pres- FUNCTIONAL DIAGNOSIS 33 sure increases, just as the oxygen pressure decreases, and carbon dioxid flows to the blood, taking the place of the oxygen which under decreased pressure has passed to the tissues. "When the blood reaches the lungs again, containing 45 per cent of carbon dioxid, it is suddenly subjected to the low C0 2 pres- sure of the atmosphere, and parts with enough to adjust C0 2 equilibrium with the atmosphere. Difference of Pressure at Lungs. — The relative pressures of carbon dioxid in the alveoli and in the venous blood are as under : Venous blood — 45 mm. Alveolar air — 28 to 41 mm. Showing an inevitable exchange in favor of the air. Insufficient Decarbonization. — Any increase of C0 2 pressure in the alveoli will, of course, result in an in- sufficient diffusion of this gas from the blood. ^ ^ -y Pressure Condition of Nitrogen. — Experiment has shown the amount of nitrogen in arterial blood and in venous blood to be the same — namely, 1.7 per cent — and as this quantity corresponds with the co- efficient of absorption of nitrogen for blood at body temperature — i. e., the amount absorbed by 1 ce. at a pressure of 1 atmosphere — it may safely be con- cluded that nitrogen enters into merely physical so- lution in the blood, in accordance with Dalton's law, and plays no part in the respiratory function. Internal Respiration. — It is, of cource, in the tis- sues supplied by the blood that the exchange of 34 FUNCTIONAL DIAGNOSIS gases which constitutes respiration actually takes place. In the tissues surrounding the capillaries C0 2 is being rapidly formed by metabolism, and the C0 2 pressure is therefore high. Oxygen, on the contrary, is being constantly utilized for carbo-hydrate com- pounds (too stable to be dissociated) and pressure is therefore low. In the blood, as it enters the capil- laries, the pressure conditions of the two gases are the reverse of this — hence the flow of oxygen to the tissues and of carbon dioxid to the blood. Both of the exchanges take place through the plasma of the blood and the surrounding lymph. C0 2 Narcosis. — Any interference with the process of respiration, unless compensated for, will ulti- mately result in an accumulation of C0 2 in the tis- sues to an extent which will render them inert and unable to perform their proper functions. This con- dition is known as C0 2 Narcosis, and is the cause of death in all diseases which kill by impeding res- piration. "• -W *m Variations in Respiratory Frequency. — From what has gone before it is evident that the rapidity of res- piration may be modified by either one of two gen- eral conditions : (1) By any condition influencing the expansion and recoil of the lungs, acting as a stimulant of the accelerator or depressor nerves of the lungs. (2) By any condition influencing the quantity of FUNCTIONAL DIAGNOSIS 35 carbon dioxid in the blood, acting as a direct stimu- lant of the respiratory centre. Physiological variations are probably rarely, if ever, primarily due to the first of these groups of conditions, as it is hard to conceive of any set of normal conditions which could directly cause an ex- aggerated or diminished expansion of the chest. The pathological conditions which influence this feature of respiration are described elsewhere. The latter group includes (a) varying degrees of metabolism and consequent variations in carbon dioxid production, (b) conditions influencing the gaseous exchange in the lungs or tissues, and thus influencing the quantity of C0 2 in the blood, (c) the velocity and pressure of the blood, and its oxygen- carrying power. These influences may all be, and continually are, exerted in varying degree in the ordinary course of physiological activity, causing continual variations in the frequency of respiration, which are familiar to everyone. The increased frequency of breathing during mus- cular exercise, the diminished frequency during rest and sleep, the increased rate under vitiated atmos- pheric conditions and decreased rate under pure air, the differing effects of heat and cold, hunger and sa- tiety, are well-known phenomena. Of these, the in- fluences of metabolism, and especially muscular ex- ercise, where C0 2 is very rapidly produced, are the most common. It is a well-known fact that the respiration is 36 FUNCTIONAL DIAGNOSIS relatively rapid in infancy, 35 to 40 per minute, gradually diminishing in frequency until in adults it remains pretty constant at 18 to 24 per minute. This is doubtless due in large measure to the rela- tively smaller available lung capacity in children, which increases in greater ratio than the growth of the body; and to the relatively greater metabolic activity of the tissues in childhood consequent upon growth. Fevers. — Undoubtedly the increased freqneucy of respiration in fevers, as already explained, is largely due to accumulation of carbon dioxid. Pleurisy causes rapid respiration because the lim- ited expansion of the time chest due to the pain sets in motion the reflex mechanism of the vagus accel- erators. Pneumonia, phthisis, etc., exhibit rapid breathing because of the small amount of available lung area, operating both by way of the vagus and by the accu- mulation of C0 2 in the blood. In hydro and pneumothorax the movements of the lungs are limited by the pressure in the thorax ; here both the vagus reflex and the excess C0 2 in the blood operate to increase the frequency of respiration. In emphysema and atelectasis the excess C0 2 ap- pears to be the causative factor. In paralysis of the phrenic nerves (innervating diaphragmatic respiration) or paralysis of the costal nerves (innervating thoracic respiration) the expan- sion of the thorax is much limited, hence the pul- FUNCTIONAL DIAGNOSIS ^7 monary branch of the vagus is stimulated and the group of motor nerves which are intact call their mechanism into increased play to compensate for the inactivity of the other group. ■V -U «!■ Modified Variations. — Many of the causes of in- creased respiratory frequency only manifest them- selves when some extra demand is made upon the respiration, such as exertion, which in health would not embarrass the breathing at all. Especially is this the case in those conditions where it depends upon an insufficient oxidation and compensated heart lesions. In chronic lesions which would otherwise tend to induce rapid breathing the process may be so grad- ual that the system adapts itself to the disability. In tuberculosis, for example, the lessened lung area is frequently offset by the reduction of body weight, thus lessening the necessity for oxygen and C0 2 elimination. C0 2 Narcosis. — In all those cases where increased frequency is caused by accumulation of C0 2 in the blood, this condition if prolonged sufficiently to in- duce C0 2 narcosis will eventually slow the respira- tion. Brain Compressions and Toxemias produce a di- minuation in the frequency of respiration. 38 FUNCTIONAL DIAGNOSIS Variations in Rhythm are also quite common in health. It is difficult to assign any definite or single explanation for the physiologic irregularities that are frequently seen, sometimes even in sleep, espe- cially among children and nervous people. It is highly probable that they depend largely upon cen- tral and reflex disturbances of the inhibitory and accelerator factors of the nervous mechanism, of the same kind, only differing in degree, as those inhibi- tions of the centre which arise from powerful emo- tions and cause prolonged variations in rapidity. Cheyne-Stokes Breathing is the most notable ex- ample of pathological abnormality in respiratory rhythm. In this type of breathing there is a rapid cresendo and diminuendo, both as to frequency and depth, the paroxysms lasting from thirty seconds to a minute, and intervened by a pause in respiration. The cause of the phenomenon is unknown, but it doubtless has its explanation in some disturbance of the central nervous system. It is usually of grave import. In children, however, it occasionally occurs physiologically during sleep. Cabot describes a very irregular gasping respira- tion, accompanied by a nodding of the head, "the chin being thrown quickly upward at each inspira- tion, and falling slowly during expiration," which he attributes to nervous dissociation, and regards as a precursor of death. This is seen in Uremia, and certain Diseases of the Brain. FUNCTIONAL DIAGNOSIS 39 Asthma is a common illustration of disturbed rhythm; the exciting cause is usually reflex, as de- scribed under Reflex Inspiration. Variations in Amplitude or Depth are quite com- mon within physiological limits, depending upon practically the same conditions that determine the rapidity of the process. 40 FUNCTIONAL DIAGNOSIS THE VASCULAR SYSTEM. General. The Circulation. — The blood of the body is con- tained in a closed set of tubular vessels, through which it is propelled by the beat of the heart; the coats of the vessels are muscular, elastic, and micro- scopically permeable. The blood leaves the ventricle of the heart by one artery of large lumen (aorta), which, in its passage to the peripheries, subdivides continually into more numerous arteries of less cali- ber but of a constantly increasing total capacity. At the peripheries the arteries quite suddenly subdivide into innumerable capillaries, of very small caliber, which with equal suddenness widen out again into the veins, and these, by a reverse progression to that of the arteries, viz., by coalescence into a less and less number of veins of increasing caliber, finally unite in two large veins (venae cavae) and empty again into the heart. The vessels lie in numerous planes, changing with the various movements and postures of the body, and their contents are of course subject to the influences of gravity. This combination of conditions gives rise to all the dy- namic and static phenomena of the circulation. If to the above set of premises we add that the blood carries oxygen and nourishment to the tissues, removes waste gases and products, and equalizes the heat of the body, and that the muscular features of the system are under the control of various nerve FUNCTIONAL DIAGNOSIS 41 centers and fibers, we have the data for the physio- logical rationale of the vascular function. The Blood. — Histologically the blood consists of a fluid (plasma) in which are floating cellular bodies known as the corpuscles. These comprise — (1) Red Corpuscles. (2) White corpuscles. (3) Blood plates. Of these the white corpuscles are the only true cellu- lar structures, with nuclei and stroma. The red cor- puscles contain nuclei at the early stages of develop- ment of the fetus, but they disappear at the seventh month. In certain conditions of excessive formation of red corpuscles in the blood — e. g., after excessive hemorrhage — these nucleated red corpuscles may be seen in goodly numbers. The blood plates are homo- geneous, elliptical bodies, whose only function, so far as known, is to assist in coagulating the blood. Reaction and Specific Gravity. — The normal re- action of the blood is alkaline, due no doubt to the preponderance of carbonate of potassium and phos- phates in the plasma. This alkaline reaction is a necessary factor in the maintenance of life. Specific gravity is about 1060, that of the corpuscles being greater than that of the plasma; the red corpuscles have the greatest specific gravity. •m •m ■!• Red Corpuscles. — Chemically the properties of the blood resolves itself into a study of the properties of the red corpuscles, as they are the only specialized 42 FUNCTIONAL DIAGNOSIS constituent of the blood, whose chemistry plays an important part in the physiology of the circulation. The red corpuscles are by far the most numerous of the microscopic elements of the blood. Separately their color is a pale yellow, but in large numbers they give