The elastic pressure‐volume curves of the lungs and thorax of the living rabbit*

Abstract

The usual methods of measuring the mechanical work of breathing, and of analysing it into components corresponding to the viscous resistance of the airways and to the elastic resistance of the expanding airways and alveoli, are based on the work of Bayliss & Robertson (1939). The lungs, in the intact thorax, are inflated with a sinusoidal air flow delivered by a piston pump driven in simple harmonic motion, and the intratracheal pressure and the displacement of the pump are recorded as co-variables. If the viscous pressure is linearly related to air flow and the elastic pressure is linearly related to distension of the lungs, the curve of intratracheal pressure against time will be a sine curve and the dynamic pressure-displacement figure will be an ellipse. The records, from experiments on cats, reproduced in Bayliss & Robertson's paper clearly are not true ellipses. They comment (p. 34 of their paper): 'The distortion from true elliptical form was always observed and it is clear that we are not dealing with a simple visco-elastic system.'Another method of recording was used by Dean & Visscher (1941) to measure the work of breathing in dogs. They ventilated their animals with a sinusoidal air flow, and recorded pump displacement and intratracheal pressure as concurrent curves against time. Some of their intratracheal pressure curves deviated from sine wave form in that the phase of falling pressure was of shorter duration than that of rising pressure. Bernstein (1953a, b) used a similar method of recording, to measure the work of breathing in rabbits, and obtained similarly non-sinusoidal intratracheal pressure curves. When Bayliss & Robertson's published tracings were analysed into their component curves, of intratracheal pressure and pump displacement against time, the pressure curve was found to be distorted from sine wave form in qualitatively the same way as the curves described above.

Mechanical Properties of Lung in Normal Men Over 60 Years Old*

“…Conversely, in lungs with high compliance, slow, deep respiration permits the tidal volume to be distriutited to a larger volume, and C,,.,, rises. This is suggestive of and compatil)le with "recruitment of units" (21,22). A similar but smaller chanige was present ill the young men.…”

Pressure—volume relationships in the chest before and after death

“…In both the rabbits and the cat the 'adapted' P-V curve showed minor departures from linearity, of the type illustrated by Bernstein (1957), over the range of pressure from atmospheric to +20 cm H20. However, the main inflexion of the curve occurred a little below atmospheric pressure, and was not observed by Bernstein, who worked only with positive pressures.…”

“…A second inflexion occurred at pressures in excess of 25 cm H20. If observations cover the full physiological range of pressure, the curve for rabbits thus approaches the sigmoid form previously described for man (Rahn, Otis, Chadwick & Fenn, 1946), and the view of Bernstein (1957), that the sigmoid form is simply an artifact caused by grouping of data, would seem incorrect.…”

Changes in Sedimentation of Surfactant in Ventilated Excised Rat Lungs

“…Ventilation in the resting tidal volume range or below, without an occasional deep breath, leads, in both animals and man, to a fall in pulmonary compliance, to the development of areas of atelectasis, and hypoxemia (1)(2)(3)(4). These changes may be almost completely reversed by a deep inflation.…”