Thorax: first published as 10.1136/thx.15.2.124 on 1 June 1960. Downloaded from Thorax (1960), 15, 124. THE EFFECT OF INTERMITTENT POSITIVE PRESSURE BREATHING ON THE LUNG COMPLIANCE AND INTRAPULMONARY MIXING OF GASES BY PETER A. EMERSON,* G. E. TORRES, AND HAROLD A. LYONS From the Department of Medicine, State University of New York College of Medicine at New York City (RECEIVED FOR PUBLICATION NOVEMBER 4, 1959) Nims, Conner, and Comroe (1955) found that Thus the lower compliance of the whole chest the compliance of the whole chest was smaller in found in anaesthetized as opposed to conscious anaesthetized than in conscious subjects; they subjects may be due to two factors: (1) Because suggested that this was probably due to the the subjects are anaesthetized and paralysed. inability of the conscious subject to relax the (2) Because, as suggested by Howell and Peckett, muscles of inspiration. Howell and Peckett (1957) they are being inflated with intermittent positive confirmed these findings, but pointed out that the pressure and that this results in an abnormal compliance was being measured in different ways. distribution of ventilation and therefore impaired In the conscious subject the inflating mechanism compliance. To simplify the problem we have was the expanding action of the inspiratory compared the compliance and the distribution of muscles, whereas in positive pressure breathing gases in the lungs during normal breathing and the pattern of inflation of the lungs was no longer during intermittent positive pressure breathing in solely dependent on the changing shape of the the same conscious and normal subjects. copyright. thoracic cage. In these circumstances the two components of the thorax, the lungs and thoracic wall with the diaphragm, now represented a single METHODS visco-elastic resistance to the inflating pressure, Advantage was taken of certain characteristics of http://thorax.bmj.com/ and the pattern of inflation of the thorax depended the Bird pressure cycled intermittent positive pressure on the magnitude and distribution of the com- breathing apparatus to study the compliance of the bined resistances and might result in a different lung and the mixing of gases in the lung in six normal distribution of the inspired volume. They subjects and to compare these results with those suggested that positive pressure breathing might obtained during normal breathing. The subjects were trained to relax completely during intermittent positive result in over-distension of some areas of lung and pressure breathing and to allow the work of breathing under-ventilation of others. This would result in to be done for them by the machine; this automatic- a lower effective volume of lung being inflated, ally cycles when a pre-set mouth pressure is reached. and the compliance measured under such circum- All the studies of compliance and mixing were made on September 29, 2021 by guest. Protected stances would be lower than that of the same lung with the subjects in the sitting position as follows: when naturally and evenly inflated by the action of COMPLIANCE.-The intra-oesophageal pressure was of the respiratory muscles. In support this taken as a close indication of the intrapleural pressure theory they quoted their observations (Howell and (Cherniack, Farhi, Armstrong, and Proctor, 1955; Peckett, 1957) of values for lung compliance in 15 Howell and Peckett, 1957). It was recorded by the normal subjects using positive pressure methods. method of Fry, Stead, Ebert, Lubin, and Wells (1952) They drew attention to the larger values obtained using an air-filled intra-oesophageal balloon 16 cm. with normal pressure methods in other patients by long, closed over the end of a 1.0 mm. bore polythene other workers, but when they measured the lung tube which was connected to one side of a differential compliance in the same patients, first with normal Statham gauge. The other side of the Statham gauge pressure methods while conscious and later with was connected to a side outlet of the mouthpiece of a Lilly type pneumotachygraph manometer head positive pressure methods while paralysed and (Lilly, 1950). In this way the pressure difference anaesthetized, the differences were much less than across the lungs (mouth pressure minus intra- they expected (154 ml. conscious, 109 ml. para- oesophageal pressure) was obtained. Flow was lysed, per cm. of water pressure). measured by the pneumotachygraph and the volume *Present address: Westminster Hospital, London. was obtained by electronic integration. The electrical Thorax: first published as 10.1136/thx.15.2.124 on 1 June 1960. Downloaded from POSITIVE PRESSURE BREATHING 125 p v copyright. http://thorax.bmj.com/ (a) (b) FIG. 1.-Records of pressure difference between mouth and oesophagus (P), flow (V), and tidal volume (VT). (a) During breathing at normal pressure; (b) during intermittent positive pressure breathing. signals were amplified and written on a four-channel points B on the pressure and volume tracings for normal breathing and intermittent positive pressure photographic recorder. For the observations made on September 29, 2021 by guest. Protected with normal pressure breathing the mouthpiece was breathing are a measure of the corresponding pressure attached to one end of the pneumotachygraph mano- and volume changes. Ten such measurements were meter head; the other end was open to the atmo- made on each tracing and the means taken. These sphere. For the positive pressure observations the distances multiplied by the calibration factors gave other end of the pneumotachygraph manometer head the actual pressures and volumes concerned, and from was connected to the mouthpiece of the Bird inter- these values the compliance of the lung, in litres per mittent positive pressure breathing apparatus. The centimetre of water pressure, was calculated. Observa- form of the pressure, flow, and volume curves obtained tions were made on each subject during normal in this way is shown for normal breathing in Fig. la, breathing, voluntary hyperventilation, and during and for intermittent positive pressure breathing in intermittent positive pressure breathing at pressures Fig. lb. The tracings during normal breathing are of 5, 10, and 15 cm. of water respectively. These self-explanatory. Points A and C represent points of results appear in Table I. no flow at the end expiratory level. Points B represent MIXING.-The distribution of inspired gases during times of no flow at the maximum inspiratory volume. normal breathing, voluntary hyperventilation, and During intermittent positive pressure breathing the intermittent positive pressure breathing was studied in flow during inspiration is constant until the pressure the same six normal subjects by an open circuit set on the cycling valve is reached; then inspiratory nitrogen washout method; this was also used to flow ceases and after a pause passive expiration estimate the functional residual capacity (F.R.C.) in occurs. The distances between the lines A-C to the each instance. Thorax: first published as 10.1136/thx.15.2.124 on 1 June 1960. Downloaded from 126 PETER A. EMERSON, G. E. TORRES, and HAROLD A. LYONS TABLE I PROCEDURE.-Before and between each experiment LUNG COMPLIANCE (LITRES 'CM. H20 PRESSURE) the whole apparatus was washed out with oxygen MEASURED DURING NORMAL BREATHING, VOLUNTARY from the same cylinder, the unavoidable inert gas HYPERVENTILATION, AND INTERMITTENT POSITIVE PRESSURE BREATHING content of which was known and was in all cases below 0.9%. The nitrogen meter was also calibrated Intermittent Positive Pressure before and between each experiment with oxygen Normal Normal Voluntary Breathing (cm. H20) mixtures of known nitrogen concentration. Each Subject Breathing Hyperven- tilation 15 cm. 10 cm. 5 cm. subject rested for at least 20 minutes before and between each study. At least two studies were made in P. E. 0-274 0-302 0-316 0-325 0 333 T. E. 0-224 0-226 0-137 0-225 0 205 each set of conditions to confirm that the results T. R. 0-119 0-081 0 052 0-067 0-078 obtained for the F.R.C. checked to within 5%. W. B. 0-146 0-126 0-146 0-166 0-135 T. G. 0-140 0-142 0-180 0 152 0-154 Normal breathing was first studied in each subject; R. J. 0-214 0-296 0208 0-207 0-273 normal breathing of atmospheric air was first estab- Mean lished with valves A and B open to the atmosphere values 0-186 0-195 0 186 (Fig. 2). At the end of a normal expiration the valves were closed so that inspiration was from the oxygen-filled gas meter and Douglas bag and expira- The technique and apparatus used for the observa- tion was into the Tissot spirometer. After the start of tions made during normal breathing and voluntary oxygen breathing the end tidal nitrogen concentration fell progressively and these concentrations were hyperventilation were similar to those described by recorded until the end tidal nitrogen concentration of Bouhuys, Hagstam, Lundin By an and (1956). the expired air had fallen to 2% ; valves A and B arrangement of valves the subject inspired from a gas meter and Douglas bag out and were then opened to the atmosphere at the end of a previously washed normal expiration. The volume and temperature filled with oxygen; expiration was a spiro- into Tissot of the expired gas in the Tissot spirometer were meter as shown in Fig. 2. The air at the mouthpiece recorded. was continually sampled by a needle inserted as close Intermittent positive pressure breathing was next to the mouth as possible and leading through a copyright. sampling tube to a nitrogen meter and vacuum pump. studied in the same patient by the arrangement with The concentration of nitrogen in the expired air could the Bird intermittent positive pressure breathing therefore be read on the nitrogen meter dial and apparatus already described.