l e the negahvty nses) 4 lung expands Clearly, therefore, compliance indicates the strechatufty of the lung Compliance is defined as the volume 0f expansion of the lung per unit change of pressure, that is dV/d P, vvnfiere V and P indhcate volume of the lung and ntrapteural pressure (Ppl)respectively and A = the difference In noimal heathy young adults the value of compliance is about 0-2 l/cmH20 This means that per every cm fall in inirapleural pressure, the expansion of the lung is 0-2 1 It can be defined in another way also, viz the shrinkage of lung volume per every cm of H2Onse of irtrapleural pressure [Note. AV = expansion or shnnkage of volume] Compliance can be defined in another way But before that, the term Trans pulrnorTary pressure' (Ptp). should be explained in fig 4 2 11he lung and pleura! cavity are shown schematically The lung may be visualized bag
situated a closed pleura! cavity it the inraalvenlar pressure is say 761 mm
Hg (ib, +! mm Hgl and the mTrapleurai pressure is755mmHg(ie,-5 mm hg), then the transpulmoary pressure (Ptp) is (761 - 755)OrBmmHg ObviOusV greater the Ptp, greater wll be volume of the lung But depenoing on the stretchabilityr differeni lungs will have different values at a given Ptp Compliance of the lung therefore is AV/Ap where P is the transpufmonary pressure The pressure volume curve Compliance in an ntact man can be measured clinically The principle, in short, of this measurement, is as foflows Irtrapleural pressure is recorded and simultaneousty the lung volume is also recorded The person, now, partially inspires (or expires) and stops in the midway making no further inspiration or expiration His intrapieurai pressure and the lung volume are again recorded at this point A series of such observanons are made and the graph plotted (figure A 22) ( HYPERUl*: http //Fig 4 2 2 Compliance ) of lung, the hysteresis loop (descnption in the text) The intrapleural pressure is recorded by placing a balloon m the esophagus as mentioned above The subject breathes from a spirometer The volume of ar that has entered from a spircrneter [thus which can be measured due to the expansion of the lung must be the volume of expansron of the lung In this way the values of v and P are obtained This curve therefore denotes the Interrelationship between the intrapleural pressure (PpL)and the volume of lung Such a pressure volume curve is also called a compliance curve The following features of the compliance curve (fig 4 22)should be noted 1 it is not linear In the lower left portion of the curveL smail changes in P (PPl) causes greater changes of V In plain words lungs become less stretchable when they are already expanded Not much an, therefore, enters the lungs at the terminal part of a very forcible inspiration Beyond 1 liter volume. inspiratory efforts fail to cause air entry m me lung 2 The ascending and me descending Lmbs of the
situated a closed pleura! cavity it the inraalvenlar pressure is say 761 mm
Hg (ib, +! mm Hgl and the mTrapleurai pressure is755mmHg(ie,-5 mm hg), then the transpulmoary pressure (Ptp) is (761 - 755)OrBmmHg ObviOusV greater the Ptp, greater wll be volume of the lung But depenoing on the stretchabilityr differeni lungs will have different values at a given Ptp Compliance of the lung therefore is AV/Ap where P is the transpufmonary pressure The pressure volume curve Compliance in an ntact man can be measured clinically The principle, in short, of this measurement, is as foflows Irtrapleural pressure is recorded and simultaneousty the lung volume is also recorded The person, now, partially inspires (or expires) and stops in the midway making no further inspiration or expiration His intrapieurai pressure and the lung volume are again recorded at this point A series of such observanons are made and the graph plotted (figure A 22) ( HYPERUl*: http //Fig 4 2 2 Compliance ) of lung, the hysteresis loop (descnption in the text) The intrapleural pressure is recorded by placing a balloon m the esophagus as mentioned above The subject breathes from a spirometer The volume of ar that has entered from a spircrneter [thus which can be measured due to the expansion of the lung must be the volume of expansron of the lung In this way the values of v and P are obtained This curve therefore denotes the Interrelationship between the intrapleural pressure (PpL)and the volume of lung Such a pressure volume curve is also called a compliance curve The following features of the compliance curve (fig 4 22)should be noted 1 it is not linear In the lower left portion of the curveL smail changes in P (PPl) causes greater changes of V In plain words lungs become less stretchable when they are already expanded Not much an, therefore, enters the lungs at the terminal part of a very forcible inspiration Beyond 1 liter volume. inspiratory efforts fail to cause air entry m me lung 2 The ascending and me descending Lmbs of the
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