Post-mortem studies of the semistatic volume-pressure characteristics of infants' lungs.

Abstract

Fagan, D. G. (1976). Thorax, 31,[534][535][536][537][538][539][540][541][542][543]. Post-mortem studies of the semistatic volumepressure characteristics of infants' lungs. Semistatic air volume-pressure (V-P) loops were recorded from 172 isolated lungs obtained from infants and children at necropsy. Technically unsatisfactory V-P loop behaviour and the presence of pathological changes led to the exclusion of 98 lungs. A further 10 lungs were excluded as it was decided to study the period of growth up to 90 cm crown-heel length. A total of 64 left lungs remained which were designated 'normal'. Control data were collected in an attempt to quantify the effects of storage and variations in inflation technique. A maximum inflation pressure of +30 cmH2O was used as a standard Pmax. The resulting maximum inflation volume (Vmax) data showed a cubic relation to the crown-heel length which deviated from the values obtained by the use of in-vivo regression equations. The extent and pattern of the deviation suggest that the technical factors are not a major contributory cause, and other explanations are discussed.The low-pressure proportional data from the deflation limb of the V-P curve are plotted against the crown-heel length, and the resulting curve is analysed. There is a sharp fall in the proportion of Vm.a retained in the lung at +5 cmH2O and +2-5 cmH20 with increasing body length, but proportional volume at zero transpulmonary pressure follows the same growth-related pattern as Vmx..The semistatic volume-pressure (V-P) loop obtained by inflating and deflating a lung with air in steps is a well-recognized method of studying the basic pulmonary mechanics of the lung (von Neergaard, 1929;Radford, 1957;Mead, 1961).In its simplest form, the air V-P loop is obtained by inflating and deflating the lung at fixed intervals of either volume or pressure. Time is allowed for equilibration after each change. This technique produces the semistatic loop as opposed to the dynamic loop. It is called semistatic because the stress relaxation curve of the lung is such that no sharp equilibrium point is attainable. The equilibration time of 30 seconds is assumed by most workers to give a good approximation.The deflation limb of the dynamic V-P loop is a measure of the recoil of the lung and the flow capacity of air passages, while the semistatic loop gives a measure of the recoil force of the lungalone.The recoil force of the lung during deflation may be divided into forces due to tissue retractive power and forces due to surface tension. The high-pressure portion of the deflation limb is thought to be controlled by tissue forces, and the low-pressure portion by surface tension forces. The measurement of the semistatic V-P loop gives a measure of the function of both of these elements of the lung's retractive power.Studies of pulmonary mechanics using this technique are mainly performed on experimental animals' lungs as these are the only lungs which can be obtained under strictly controlled conditions. This is highly desirable in or...

Shape changes in static V-P loops from children's lungs related to growth.

“…changes of shape or form of the deflation V-P curve may be occurring in this period as well as the basic fact of a growth-related increase in static recoil at the inflation levels described. This analysis shows that the changes seen in V-P loop shape when plotted in the proportional manner (Fagan, 1969;Havrankova and Kuncova, 1971;Fagan, 1976) are quite consistent with the changes reported by Turner et al (1968), Zapletal et al (1971, and Zapletal et al (1976), whether the index of development chosen is body length, maximum inflation volume, or body weight over the whole of the growth range studied. I am indebted to the Department of Pulmonary Physiology, the Hospital for Sick Children, Toronto, for the use of their facilities, and, in particular, to Dr. A. Mansell for his patient tuition and encouragement, and to D. Pengelly for programming the H-P 9810 A.…”

“…The lungs were inflated and deflated in a stepped manner using fixed pressure intervals to obtain static V-P data. The full details of the methods, population, and controls are described in a previous communication (Fagan, 1976). The standard maximum inflation pressure was +30 cm H20.…”

“…The question whether there is a growth-related shape change in static pulmonary volume pressure (V-P) deflation curves has to some extent been confused by the different methods of data presentation used in human postmortem data (Fagan, 1969;Stigol et al, 1972;Fagan, 1976), animal experiments (Havrankova and Kuncova, 1971), and clinical studies (Turner et al, 1968;Zapletal et al, 1971;Zapletal et al, 1976), and differences in the level of inflation which was regarded as equivalent to in-vivo maximum lung capacity (TLC).…”

“…In this paper the V-P data collected by the methods described in a previous communication (Fagan, 1976) from children's lungs obtained at necropsy, with body lengths ranging from 33 to 168 cm, are analysed by the exponential regression method described by Salazar and Knowles (1964). The results of this analysis are compared with the results from measurement of the same Pst(l) values from the same data displayed graphically.…”

Rate Constant for Forced Expiration Decreases with Lung Growth during Infancy

“…Therefore, more compliant airways in the less mature subject should not contribute to proportionately higher flows in the younger infant. Similarly, limited data on lung elastic recoil pressure in infants suggest lower values in younger infants (9)(10)(11)(12)(13). This would also suggest that the faster rate of emptying in the younger infant should be related to relatively larger airways for the V L that is to be emptied.…”