No abstract

Mass loading of the thorax in four normal conscious subjects and in six anesthetized paralyzed subjects transposed the thoracic volume-pressure curve to higher levels on the pressure axis without greatly affecting the slope of its linear portion. This effect is similar to that produced by forward acceleration and snorkel breathing. Mass loading the lower thorax produced a greater effect than mass loading the upper thorax. Mass loading the abdomen flattened the slope of the linear portion of the thoracic-volume pressure curve both in conscious subjects and in anesthetized paralyzed subjects, the effect resembling that of elastic loading which also flattened the thoracic volume-pressure curve. The shape of the total respiratory static volume-pressure curves in six of ten excessively obese subjects resembled that produced by thoracic mass loading in normal subjects. Five patients with the obesity-hypoventilation syndrome had curves suggesting a combination of elastic and mass loading or alternatively, abdominal mass loading. At any lung volume, the total transrespiratory static pressure is made up of a volume-dependent elastic component and a volume-independent gravitational component. The latter is approximately 5 cm H2O in the supine adult male of normal weight. thoracic compliance; total respiratory compliance; gravitational effects on thorax; respiratory compliances in obesity Submitted on January 6, 1964

Total respiratory inertance may be defined as that component of the total impedance to breathing that relates to acceleration of respiratory gas and of all tissue elements (lungs, rib cage, diaphragm, and abdominal contents) that move during respiration. It is expressed in units of pressure required to overcome this inertial component of the total impedance and produce air flow acceleration of 1 L per second per second. Thus its units are centimeters H2O per liter per second2. Intuitively, one would suspect that the inertance of the chest and the abdomen should be increased in severely obese subjects. In investigations of total respiratory mechanics in excessively obese persons, we made measurements of total respiratory inertance. In addition, we attempted to separate the total respiratory inertance into its gas and tissue (including lung tissue, chest wall, and abdominal) components in three normal and three excessively obese subjects. These data form the substance of this report.Inertance data on the normal human respiratory system were first published by DuBois, Brody, Lewis, and Burgess (1) in 1956. These authors, assuming that the respiratory system behaves mechanically as a simple or "lumped" physical system, determined the total compliance and the natural frequency of the respiratory system. They then calculated the total inertance of the respiratory system by using the simple physical relationship by which the natural frequency of a system may be predicted if its elastic and inertial characteristics are known: fn = 1/274 1/jI *C, where fn is the natural frequency, I is the total inertance, * Submitted for publication July 5, 1962; accepted November 21, 1963. Supported in part by National Institutes of Health grant H5124.and C is the total compliance. Their estimated value for total respiratory inertance was 0.0058 cm H20 per L per second2, a value which, though measurable, is small enough to be neglected in normal subjects at ambient pressures and at the air flows and accelerations usually encountered. These authors pointed out that the respiratory system is more than critically damped, necessitating that the natural frequency be determined by examining the phase relationship between sinusoidal waves of driving pressure and the resulting oscillations of air flow. Estimates of natural frequency made in this way, together with measurements of the total respiratory compliance, constitute the data from which inertances were calculated in the present study. MethodsOf the 22 subj ects studied, 8 were normal laboratory personnel of normal weight, and 14 were excessively obese persons varying in weight from 250 to 407 pounds. Of the obese subjects, 9 were otherwise normal except for slight arterial hypoxemia in 2; their Pco%'s were normal. The remaining 5 subjects had the obesity-hypoventilation syndrome, although Pco2 values were normal in 3 at the time these studies were performed.The total respiratory compliance was measured by a modification of the method of Heaf and Prime (2), in which steady negative p...

Pathological changes in lung tissue following chest wall irradiation have been adequately documented in the past (1-5). However, pulmonary function has not been systematically studied. Published studies (6-9) are incomplete and the findings complicated by the original disease. In view of this and because of a desire to determine the amount of radiation which might safely be administered to the chest, a systematic study was undertaken in dogs. The results of this study follow. METHODSPulmonary function and vascular resistance were evaluated in dogs before and after irradiation to the chest. All studies were performed under pentobarbital anesthesia. Two different irradiation schedules were utilized. Eight dogs received a calculated dose of 1,000 to 2,900 roentgens (r) to the mid-chest in a single exposure. No animal survived longer than two and one-half months. For practical reasons, it was not feasible to study resistance and function in the same animal. Therefore, resistance was evaluated in the first five animals within 24 hours of irradiation. Diffusing capacity, functional residual volume and compliance were determined in the remaining three animals at two to three week intervals. In order to effect a longer period of survival, seven animals were irradiated under a second schedule consisting of a dosage of 200 to 300 r to each side of the chest repeated at weekly intervals up to a total calculated mid-chest dose of 3,000 to 4,800 r. Three of these animals survived longer than six months. Diffusing capacity, functional residual volume and compliance were determined at two to three month intervals following onset of irradiation. Vascular studies were also conducted in four animals at the time of the final evaluation. 4 Clinical Investigator of the Veterans Administration.All irradiation was given with 260 KV. peak equipment (filter, one-half mm. Cu, 1 mm. Al, half-value layer 1 mm. Cu; target-skin distance, 50 to 70 cm.) with the animals under pentobarbital anesthesia. Field size included the chest from xiphoid to lower neck.Compliance. Values for total thorax, lung and chest wall compliance were obtained by the static method (10) with the animals anesthetized and curarized. A cardiac catheter, with a latex condom secured to the terminal 5 inches, was introduced well into the thoracic portion of the esophagus (11, 12). The catheter was marked at the level opposite the incisors, so that it could be placed in the same position in subsequent tests. A cuffed endotracheal tube was positioned within the trachea and sealed by inflation of the cuff. Muscle paralysis was obtained by the intravenous injection of approximately 6 ml. of a 0.01 per cent solution of succinyl-choline. Respiration was maintained artificially with a mechanical respirator, except during evaluation of the pressure-volume relationships. Air was introduced into the tracheal cannula until pressure in the cannula reached a pre-selected level. In order to minimize variations due to hysteresis, inflation time for a given volume was maintained approxima...