Downloaded from https://academic.oup.com/ptj/article/48/5/455/4638136 by guest on 29 September 2021 RESTRICTIVE LUNG DISEASE WARREN M. GOLD, M.D. RESTRICTIVE LUNG DISEASE is a These disorders can be divided into two pattern of abnormal lung function defined by groups: extrapulmonary and pulmonary. a decrease in lung volume (Fig. I).1,2 The In extrapulmonary restriction, an abnormal total lung capacity is decreased and, in severe increase in the stiffness of the chest wall (kypho­ restrictive defects, all of the subdivisions of the scoliosis) restricts the lung volumes, as does total lung capacity including vital capacity, respiratory muscle weakness (poliomyelitis or functional residual capacity, and residual vol­ muscular dystrophy). These extrapulmonary ume are decreased. In mild or moderately se­ causes of pulmonary restriction are treated vere restrictive defects, the residual volume may be normal or slightly increased. CLINICAL DISORDERS CAUSING TABLE 1 RESTRICTIVE LUNG DISEASE CAUSES OF RESTRICTIVE LUNG DISEASE Restrictive lung disease is not a specific clin­ I. Extrapulmonary restriction 3 ical entity, but only one of several patterns of A. Chest wall stiffness (kyphoscoliosis) B. Respiratory-muscle weakness (muscular dystrophy)4 abnormal lung function. It is produced by a C. Pleural disease (pneumothorax)5 number of clinical disorders (see Table 1). II. Pulmonary restriction A. Surgical resection (pneumonectomy)6.7 Dr. Gold: Director, Pulmonary Laboratory and Re­ B. Tumor (bronchogenic carcinoma or metastatic tumor)8 search Associate in Cardiology (Pulmonary Physiology), C. Heart disease (hypertensive, arteriosclerotic, rheu­ Children's Hospital Medical Center; Associate in Pedi­ matic, congenital)9 atrics and Tutor in Medical Science, Harvard Medical 10 11 School, Boston, Massachusetts. D. Pneumonia (viral, bronchial, lobar) . Presented at the Symposium on Chest Disorders in Chil­ E. Granulomatous disorder (sarcoidosis, tuberculosis, dren. fungal infections)12 This work was done during the tenure of an Advanced F. Pneumoconiosis (silicosis, asbestosis)13-14 Research Fellowship of the American Heart Association. G. Diffuse interstitial fibrosis (Hamman-Rich syndrome)15 This work was supported in part by Grant HE-10436 H. Collagen disease (lupus erythematosis, scleroderma)16 from the National Heart Institute of the National Institute I. Atelectasis 17>19 of Health. Volume 48 / Number 5 455 Lung Volumes Normal Restrictive Lung Disease Downloaded from https://academic.oup.com/ptj/article/48/5/455/4638136 by guest on 29 September 2021 Fig. 1. A normal spirogram (left) is depicted in relation to the total lung capacity (TLC), vital capacity (VC), junctional residual capacity (FRC=ERV 4- RV), inspiratory capacity (IC), expiratory reserve volume (ERV), and residual volume (RV). A spirogram of the type observed in restrictive lung disease is superimposed on the normal TLC (right). Note the dif­ ference in pattern of respiration (rapid and shallow). RESTRICTIVE LUNG DISEASE PATHOPHYSIOLOGY OF RESTRICTIVE LUNG DISEASE separately in this symposium.18 Any disorder Lung Volumes of the pleural space (pleural effusion, pneumo­ The vital capacity (the maximum volume thorax, or fibrothorax) can also lead to a loss of air expired after a maximum inspiration) is of lung volume. always decreased in restrictive lung disease. Pulmonary restriction includes any disorder However, this test of lung volume depends on which causes an actual loss of lung tissue the effort and co-operation of the patient. (tumor, pneumonectomy), loss of air-contain­ Furthermore, it may be abnormally decreased ing alveoli (pulmonary edema or pneumonia), if the residual volume is abnormally increased or loss of lung distensibility (fibrosis, sarcoid­ (hyperinflation) secondary to airway obstruc­ osis, collagen disease). This pattern may tion. It is important, therefore, in the physio­ also result from any of the disorders that pro­ logic diagnosis of pulmonary restriction to duce obstructive airway disease (asthma, measure the total lung capacity (Fig. 2). In bronchitis, cystic fibrosis) when complicated most pulmonary laboratories, this measure­ by atelectasis. The role of the physical ther­ ment is made by a gas dilution method such apist is so important in the treatment of atelec­ as the open-circuit N2 washout method illus­ tasis that this condition is also considered trated in Figure 2, or by a plethysmographic separately in this symposium.10 method. 456 PHYSICAL THERAPY >r 0 Liters Room Air Downloaded from https://academic.oup.com/ptj/article/48/5/455/4638136 by guest on 29 September 2021 30 Liters Cone. = 4% Fig. 2. There are several methods of determining the volume of gas which cannot be expired, but most laboratories use an open-circuit N2 washout method. The volume of gas in the lungs is unknown. When the patient breathes room air, however, this gas is known to contain 80 per cent N2. The amount of N2 in his lungs is determined by washing all the N2 out of the lungs with N2-free 02. The patient inspires 02 and expires through a suitable valve system into a Nz- free spirometer (previously flushed with 02) where the volume and N2 concentration of the expired gas is measured. At the beginning of the test all the N2 is in the lungs (grey circles); at the end of the test all the N2 is in the spirometer which contains 30,000 ml of gas and N2 conc. — 4 per cent. The spirometer contains 0.04 X 30,000 ml •=. 1200 ml N2. All this N2 came from the lungs; since 1200 ml N2 existed in the lungs as 80 per cent N,, then the volume 80 of gas in the alveoli at the start of the test was 1200 X JQQ — 1500. Corrections must be made in this volume for small amounts of N2 in the 02 which the subject inspires and for the blood and tissue N2 washed out during the procedure. Volume 48 / Number 5 457 RESTRICTIVE LUNG DISEASE must be applied to them sufficient to overcome the force with which the springs recoil.* If a second set of stiffer springs is stretched, they Lung Elastic Recoil generate an even greater recoil force. To Many of the disorders listed in Table 1 not stretch these "stiff" springs to the same length only cause a loss of lung volume, but also alter as the "normal" springs, a much greater force the distensibility of the lungs; the lungs be­ must be applied than was used with the come stiffer than normal.20 The process of "normal" springs. lung inflation is analogous to stretching a set The parenchyma of the lung behaves like of springs (Fig. 3). If the "springs" in Figure a set of springs tending to recoil to its resting 3 are stretched from their rest length (Li) to length (Fig. 4). Stretching the "lung springs" a greater length (L2), they tend to recoil to their resting length with a certain force (F= * An elastic material returns to its original form when Downloaded from https://academic.oup.com/ptj/article/48/5/455/4638136 by guest on 29 September 2021 the force distorting it is removed. The stretching force recoil force). To stretch the springs, a force on a set of springs is therefore called an elastic force. "Normal" Springs "Stiff" Springs /VM /W\A, < L, 4 •< Lji »' B. Length F, F. Force £ Fig. 3. (A) Comparison of "normal" and "stiff" springs. Rest length = Lx, stretched length = L2; recoil force of "normal" springs = F,, recoil force of stiff springs = Fs. (B) Length-force relationships of "normal" and "stiff" springs. To stretch the "stiff" springs a distance equal to the normal springs requires a greater force. Note that the slope of the stiff spring line is decreased compared to the slope of the normal line. 458 PHYSICAL THERAPY A. "Normal" B. Stiff IWWV W\AA/1 PAPP v PAPP ; V, rAA/W/n 5 p; AAAAA AAAAAAA VWW\A PAPP v, PAPP- : V2 Downloaded from https://academic.oup.com/ptj/article/48/5/455/4638136 by guest on 29 September 2021 Q\ '5 P' LA/WWV 2 •WWV\J Volume Pressure Fig. 4. (A) ELASTIC RECOIL PRESSURE OF THE LUNG. The lung is represented by a bellows with a "springs" in its walls. The elastic recoil pressure (P) generated by these lung springs is measured by the manometer in the tube leading to the bellows. The applied pressure (Papp) is supplied by a piston in the tube. Vi and V2 are two different lung volumes, Pt and P2 are the corresponding recoil pressures. The stiff lungs on the right generate a greater-than-normal recoil pressure P' at any lung volume. (B) ELASTIC RECOIL CURVE OF THE LUNG. Volume is on the ordinate and pressure on the abscissa. Note that the stiff lung requires a greater pres­ sure to distend it to the same volume as the normal lung. The slope of the pressure-volume , change in volume . ....... , curve or lung compliance (C = —2—: ) is diminished in the stiff lung. L change in pressure produces a volume change and generates a may be applied by a ventilator, or by the pressure which makes the lung recoil to its anesthesiologist's hand on the anesthesia bag. resting volume. The magnitude of this elastic Many of the disorders listed in Table 1 change recoil pressure depends on the volume of air the distensibility characteristics of the lung so put into the lung. The more the lung is dis­ that it becomes stiffer than normal (Fig. 4). tended, the greater the recoil pressure generated This means that the elastic recoil curve of the by the "lung springs." To distend the lung, lung is altered (shifted to the right and below a pressure must be applied that is sufficient to the normal range) so that at any given volume, overcome this recoil pressure. This applied the "stiffer" lung requires a greater than pressure is usually produced by the muscles normal pressure to produce a comparable de­ of respiration, but in the patient, this pressure gree of distention or volume.