visual blackouts and unconsciousness Valsatva maneuver or severe bouts of cough

efforts, particularly with glottis closed (Valsalva maneuver) when because of the large +ve intrapleural pressure the cardiac inflow may be rernarkabty reduced so that cardiac output falls resulting in cerebral ischemia, visual blackouts and unconsciousness Valsatva maneuver or severe bouts of cough may be therefore, dangerous in an old man intrapulmonary pressure As fhe act of inspiration proceeds, the lungs confirms to expand and the intra atveolar irvtrapulmonary) pressure fails In quiet breathing, it may thus become -3 mm Hg As ar of the atmosphere enters (because of the pressure gradient). the negabvity decreases and at the end of the inspration, it is again ob i e. atmospheric During quiet expiration the pressure rises, {maximum +3 mm Hg) but at the end of expiration * is again O In VatsaVa's maneuver, great expiratory efforts are made with the glottis closed, intrapulmonaiy pressure may nse tremendously (say about + 60 mm Hg) This may cause rupture of the atveoli PRESSURE VQLLtoC WTERELATIONSHIP. COMPLIANCE lrutroduciion As The muscles of inspiration contract, the thoracic cage expands, the inrapteurai pressure, that is, the pressure around The lung, falls and the volume of lung increases (fig A 2 1) As already pxplamed in the mechanism of breathing, (he tung expands because it is pulled by the visceral pteura The degree of pull is proportional to the negativity of the plsura! cavity, greater negauvity indicating greater pull 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