hello everyone welcome today we're going to talk about mechanics of breathing and compliance so in the mechanics of breathing let's first talk about the muscles that are involved in inspiration and expiration so among the muscles of inspiration the most important muscle is diaphragm so suppose this is your abdomen and thoracic cavity and those are your diaphragms so whenever the diaphragm contracts they push the abdominal content downwards and increase the volume in the thoracic cavity and also they lift the ribs upward and outward so ultimately increasing the volume of the thoracic cavity this is the main mode of respiration during quiet breathing and whenever someone is exercising or someone in is in respiratory distress he uses external intercostal and accessory muscles to help him breathing more and the muscles of expiration are actually normally not used because commonly expiration is passive and the passivity is actually due to the elastic elasticity of the lung ancestral system which helps to return it to resting state after inspiration and you can only use experity muscles during exercise or when the air resistance is increased because of disease like asthma and the muscles that you can use for forceful expiration are abdominal muscles and also the internal intercostal muscles now let's talk about the very important point in respir system which is compliance of the respiratory system so compliance actually described by the following equation which is compliance equals to volume change divided by the change in pressure so C is compliance V is volume and PRI pressure compliance actually tells you how well the voluming lungs or lung gestal system compliance to changes in pressure or how well the volume changes with changes in pressure so it actually describes that distance ability of the lungs and the chest wall and it is the slope of the pressure volume curve so if we put some carve here like this is the here is the volume and here is the pressure and if we put a graph and if we want to see the change of volume and change along with change of pressure the curve may be like this or maybe like this so This curve has a higher compliance because it is steeper and this curve is has a lower compliance because it is not steep it is a bit flatter in comparison to this curves so compliance is actually the change in volume for a given change in pressure and the pressure refers to transoral or transpulmonary pressure and transp pressure is actually the pressure difference across pulmonary structures so here we can see the compliance of the lungs so this is the volume and this is the pressure suppose we are increasing the pressure from zero and it will actually causes the volume to increase so you will have a curve here like that and the compliance is actually steepest in this this area so in the middle range of pressure the compliance is highest so actually for compliance the most important pressure is transoral pressure and transoral pressure is actually the Alvar pressure minus intraoral pressure if the pressure outside the lungs meaning the interpal pressure is negative the lungs will expand and lung volume increases this occurs during inspiration so when you are inspiring you are pull pulling your diaphragm downwards and also you're increasing the volume in your chest wall system it increases the pressure incre increas the negative pressure inside the uh inside the inside your plal cavity which causes which causes the lungs to expand and causes inspiration and if the pressure outside the lungs is positive the lungs collapse and the lung volume decreases these kind of things occur during neumotorax in the middle range of pressure the compliance is greatest and the lungs are most distensible and at high expanding pressure the complex is lowest so the volume doesn't change much with the pressure and the lungs are less distensible and the carve will flatten so here we can see the compliance of the lung testal system so this blue carb represents the compliance of the chest wall system this red curve represents the compliance of the lung system only and the green curve represents the lung and chest wall system as you can see here the chest wall carve is flat uh steeper and the long curve is steeper but the L chest curve is actually a bit flatter uh in comparison to chest only or lungs only so in those curves you can see see the changes in the volumes according to changes in trans organ static pressure so whenever the pressure changes the volume changes too and the intersection where I put a dot here is is the functional residual capacity and in the line of functional residual capacity the compliance of the lung testal system has the Steep portions steep portion so the compliance is greatest at the functional residual capacity and in case of functional resal capacity the chest wall system have has a negative pressure and the lung system has a positive pressure this causes this causes a net zero pressure in the lungs or in the lung gestal system so in due to this net zero pressure there is no movement of air into lungs or out out to out out from lungs so here you can see from the previous picture that the compant of the lung and chestal system is actually less than than that of the compilance of lung alone or the chestal alone and at rest which identify the field circle at the center of the cares which is this so at rest this is the F FRC so at rest the lung volume is at functional resal capacity and the pressure in the AR and lungs equal to the atmospheric pressure which is zero and under those equilibrium conditions there is a collapsing force in the lungs and an expanding force on the chest wall so here this is the force which is trying to collapse the lungs which is the positive pressure and this is the pressure which is trying to expand the lung which is the negative pressure and at the functional residual capacity those two forces are equal and opposite so as you can see this is the negative press and this is the positive pressure both of them are equal and they're opposite so that's why the combined lung chest wall system neither wants to collapse or neither expans so it remains in the same situation and as the there is a positive pressure in the lung system and the negative pressure in the chest wall system in between the lung and chest wall you have the plural cavity so that's why interpolar pressure is negative in our subatmospheric if you in produce a inside your inter space which is called neumotorax the interpolar pressure becomes equal to atmospheric pressure and that's why the lungs will collapse which is their natural tendency and the chest wall Will Spring outward which is their natural tendency and this is this point is very important to remember compliance is decreased in ponary fibrosis because palmary fibrosis causes the causes diffuse fibrosis in different areas of the lung and the AAS cannot expand as well as they should in case of pneumonia the ARs cannot expand because of infection in case of pulmonary Eda the arrows cannot expand well because there is fluid in the spaces so the fluid actually is preventing the arrows to expand and and actually in empis normal aging the compx increases the compx increase in empis normal aging is due to the decrease elastance of the lungs and the lungs actually is not that elastic uh which is as a oos to normal people or as opposed to younger people so here we have a practice problem so the lung and chestal compliance carves for a heal individual are shown on the slide below so here you can see the lung and chestal comp curves so this is the chestal comps the black one and the black one here is the lung compliance and the blue one is the combined lung chestal system now the question is which of the following is a best estimate of the interpolar pressure at the point on the graph marked by the the Red Dot so what is the Red Dot so as you can see the Red Dot in the Red Dot the negative pressure or the chest compliance and the positive pressure of the lung complex are equal and opposite so this is actually the functional residual capacity and in case of functional residual capacity the interp pressure is negative because the two forces are opposite and they are creating a negative pressure inside the plal cavity and it is about -5 CM water so that's the answer we have another practice problem here a 63-year-old male with recent history of Mard infection presents to the emergency room because of an increasing shortness of breath and cough physical examination reveals cracks at the base of the lungs bilaterally and S3 on cardiac osculation his oxygen saturation is low now which of the following is most likely accounts for this patients disia so what is the most likely cause of of this patients dis here there are multiple options I'm picking the right one here you can pause if you want so the most important cause of this patients disia here is decreased lung compliance why so first of all what is the diagnosis in this patient this patient has a previous ma infection which damaged his heart walls or ventricular walls and this leads to formation or this leads to development of the heart failure which is evidenced by the shortness of breath Cal and crackles in lung bases and also S3 in cardia osculation so this patient actually has acute L ventricular failure and in case of acute left ventricular failure the L the heart cannot pump the blood out of the lungs that's why the blood actually accumulates in the lungs which then extravasates and then this this Blood goes into inside your Alvi also the fluid portion also goes into the intertial space and when the fluid portion goes into the interstitial space and Alvi the Alvi cannot expand as well as it should so the compliance of the respiratory system actually decreases so decreasing lung compliance is the cause of disia in a patient with lvf leading to pulmonary edema we have another practice problem here here we have a 43-year-old patient presenting to your office with Chief complaints of disnea and the carve Below in Black represents the pressure volume relationship in this patient's lung tissue and the blue carve represents a normal pressure volume relationship so this is the normal one which is a steeper one and we have an abnormal one which is the flatter one now which of the following is the most likely cause of this patient symptom so you can pause here and you can pick your answer I'm going to the answer directly so here the diagnosis is pulmonary fibrosis why is so first look at the volume and pressure curves so in the volume and pressure carves you can see that the normal curve is steeper and the patient carve is flatter so there is actually a decrease in compliance so the as the curve is flatter there is decrease compliance and among the conditions presented here the most important cause of decrease compliance is palmary fibrosis so that's all from me today thanks all for watching my 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