space Now if a lung is stiff. a greater (more man usual) amourt of negativity

Therefore, ultimately the expansion or the lung is proportional to the increase of the negatrvity of the intrapleural space Now if a lung is stiff. a greater (more man usual) amourt of negativity wril be required to expand the lung This interrelationship between the pressure surrounding the lung and the volume of the lung is called compliance In plan words, compliance means the distensibility Imagine the following sequence of events which normally occurs Inspiration begins intrapleural pressure fads 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