Vascular Disease



well welcome back this session is devoted to diseases of the pulmonary circulation and here's a list of the topics that we're going to cover I'm going to spend most of my time on pulmonary edema and pulmonary embolism and we'll look more briefly at pulmonary hypertension and then finish with a few words about cor pulmonale and arterial venous malformation now pulmonary edema is a very important topic it's not a disease in its own right but it accompanies many forms of lung and heart disease and it can be lethal and so it's important that we understand the pathophysiology of this condition and it's defined if you like as an abnormal accumulation of fluid in the extravascular spaces and tissues of the lung that's a fancy way of saying that the fluid should be in the pulmonary capillaries and if it leaks out then that's probably edema so let's start with our old friend here the electron micrograph of a pulmonary capillary here's the lumen here of course and that's where the fluid should be but it can either leak into the interstitial space or even into the alveolar space and that of course is pulmonary edema now let's look at the components of the blood gas barrier which of course are important in maintaining the integrity of the barrier and its function and here we see a very high power view of a section of the barrier we've actually seen this before now this is the the slide we saw just previously and it's been turned on its side and the microscopist has chosen an area of the blood gas barrier there and enormously magnified it here and I can see and maybe you can that the bar here is only 0.4 of a micron so we're at a very high magnification and we can see very clearly the ultra structure of the alveolar epithelium here the extracellular matrix and the capital e endothelium here and at first sight these cellular layers don't look all that different in this particular image the endothelium is a little bit thicker than the epithelium and it contains more vesicles but basically the two cell in the layers look rather similar however this is misleading because their functions are very different their permeability is a completely different the capillary endothelium is highly permeable to water solutes ions and even some proteins as we'll see some albumin can move through the capillary endothelium but by contrast the alveolar epithelium is extremely important solutes ions proteins in fact the epithelium actively pumps water from the alveolar space into the interstitial using a sodium potassium ATPase pump so the epithelium is in the business of keeping the alveoli dry of course it's true that there is a thin layer of surfactant on the RVL epithelium but this pump actively transports water from the alveolar space into the indecision now the reason why the functions of these two layers are so different perhaps can be illustrated if we look at the intercellular junctions of the two layers here we see an intracellular junction of the capillary endothelium and you can see that it's made of two cells just buttered together and it's easy to imagine that materials can move fairly easily from the capillary lumen into the interstitial here by contrast if we look at the intracellular junction for the epithelium we see it's completely different it's a bit like two layers of velcro stuck together it's long as you can see and very looks very tight and that is consistent with what I indicated before and that is that the permeability of the alveolar epithelial layer is is very very tight its impermeable to water to solutes ions or proteins as I said and it actively pumps water from the alveolar space into the interstitial now we can't get very far with a discussion of pulmonary edema before we come across the Starling equilibrium and this is shown here this is a cartoon showing the alveolar wall here with the alveolar gas on both sides of it here and a pulmonary capillary in the alveolar wall and the forces tending to move the fluid out of the capillary are the hydrostatic pressure in the capillary minus the hydrostatic pressure in the interstitial PC minus P sub I okay those forces are opposed by the colloid osmotic forces in particular the colloid osmotic pressure indicated by the Greek letter pi colloid osmotic pressure in the capillary minus the colleague colloid osmotic pressure in the interstitial so you've got these two sets of forces now there's one complicating factor here and that's indicated by the the Greek letter Sigma here if the capillary endothelium were truly semipermeable that is to say it didn't allow any of the protein to move out of it then Sigma would be one the forces would be just a simple subtraction that forces but in fact the capillary endothelium is partly permeable to protein now what kinds of what proteins are we talking about here in terms of osmotic pressure well you may remember back from your physical chemistry that osmotic pressure is determined by what's called colligative properties that means the number of particles and the number of particles of albumin the number of molecules of albumin it's much greater than that for up for globulin because although the concentrations of the two sets of proteins are not all that different albumin is a much smaller much lower molecular weight and so there are very much greater number of albumin particles and so it's the albumin that's chiefly responsible here now it turns out that the as I said the endothelium is partly permeable to albumin and that's why we have doing to include this Sigma factor here Sigma is called the reflection coefficient it's a measure of the ability of the capillary endothelium to prevent the passage or reflect the albumin molecules as they bump against the interior of the capillary wall here so the complete equation is shown down here it's the forces tending to move the fluid out minus the forces tending to move the fluid in but indicate we have an indication here of the reflection coefficient and then the constant here is called the filtration coefficient now that's a very important equation in principle in practice it's it's it's somewhat limited because we're rather ignorant of some of the values here let's look at them the capillary hydrostatic pressure we believe is probably about halfway between the pulmonary arterial and venous pressures in in fact there's some evidence that much of the pressure drop in the pulmonary circulation is in the capillary bed also there is a substantial difference in capillary from the top to the bottom of the lung because of the hydrostatic gradient the hydrostatic pressure in the interstitial space is not known with any accuracy although some there are some measurements that suggest that it's very low maybe less than atmospheric pressure the colloid osmotic pressure in the blood is known 25 to 28 millimeters of mercury but the colloid osmotic pressure in the interstitial fluid is is uncertain the value of Sigma is about 0.7 and the net result of all this is that there is a continuous small loss of fluid from the interior of the capillary into the interstitial space probably only about the the lymph lymph flow from the lung thought to be about 20 mils per hour it's a relatively small amount but it's a continuous loss of fluid from the capillary into the interstitial space now that's a very important point because what that in what that means is that whenever we disturb the equilibrium here for example we raise the pressure and the pulmonary capillary we're going to increase the amount of fluid coming out of the capillary and that's nicely shown by an experiment that was done a few years ago where the lymph flow from the lung was measured in an animal preparation and this is lymph flow here and mils per unit time and here's ours along this axis here and at this point these are the control measurements here and at this point there was an infusion made of both of either say line or dex dextran and you can see that immediately there was an increase in limb flow and that indicates as we said before that whenever you raise the capillary pressure fluid moves out of the capillary you can see that the increase lasted much longer for dextran than for say line and that's because when the ceylon was infused it very quickly moved out of the circulation into the interstitial fluid res dextran having a much larger molecule remained in the circulating blood volume for a much longer time now that's an interesting point and there's a historical point here that I'm just going to make briefly and that is that when I was a medical resident admittedly a very long time ago we believed that the capillary pressure in the lung could be raised to quite high levels big for any edema occurred and the reason why that we made that why we believed that why I was taught that is that we saw patients with mitral stenosis which was a relatively common disease in those days who had very high pulmonary capillary pressures but no evidence of alveolar edema now the mistake that we made or mistake that was made was that we did not recognize interstitial edema by edema we meant alveolar edema and but we now know that that was a misconception and that as soon as the pressure rises in the pulmonary capillary the amount of lymph flow increases now let's talk about the two stages of pulmonary edema first of all we've got the normal situation here and you can see the artist is very nicely drawn a capillary we've got the thick side of the blood gas barrier here and the thin side here and he's put in the pressures responsible for the movement of fluid and under normal conditions as we've seen a small amount of fluid moves out of the capillary finds its way through the interstitial of the alveolar wall and eventually ends up in the peri vascular and peri bronchial spaces of the lung which is where the lymphatics are located and eventually the fluid moves out of the lung as limp now suppose we raise the pressure inside the pulmonary capillary in that case we're going to increase the rate of egress of fluid and actually the artist has drawn a slightly thicker but gas barrier here which is exactly what happens on the thick side the blood gas barrier expands somewhat as the fluid moves out now we see the fluid moving through the interstitial and we get these cuffs of fluid around the small arteries veins and Airways and that's called interstitial Idina at that stage there is no deema fluid in the in the alveoli but then later if we raise the palm of the capillary pressure even more we increase the rate at which the fluid moves out and now some fluid may spill over into the alveolar spaces what exactly causes the fluid to spill over is not fully understood but I suppose that if the pressure in the interstitial rises high enough then we're going to damage the alveolar epithelium and fluid is going to move out I believe that whenever we have alveolar edema there is damage to the alveolar epithelium and part of the evidence for that is that the our beloved Luud always contains red blood cells so that suggests that the barrier is damaged and as we said before the normal barrier is very empowered so that makes a lot of sense so you get both alveolar oedema now and of course interstitial edema as well now how does the fluid move out of the lung well it moves along what's called the interstitial of the lung here's a very old diagram but it's quite useful because it shows the interstitial of the lung the peri vascular and peri bronchial spaces and you can see the lymph glands here and that's the way the fluid moves out of the lung and here's a nice image of a small pulmonary vein and if we look closely we can see the potential peri vascular space it's very small normally doesn't contain anything at all it's a bit if you like like the potential intrapleural space which contains essentially nothing under normal conditions this is the peri vascular space and it that it will contain fluid if there is interstitial edema and I'll just remind you as we talked about in the session on the pulmonary circulation in the respiratory physiology series that there are two types of blood vessels in the lung there are the alveolar vessels which are mainly the capillaries exposed to alveolar pressure and there are the extra Arbela vessels which on the one hand are being pulled open by the radial traction of the lung parenchyma around them because these vessels are running in the parenchyma in the avila tissue and on the other hand they tend to close because they've got elastic tissue in the wall and also smooth muscle with tone so the caliber of these vessels is determined by a balance between those two forces and I think you can see that the pressure in this very vascular space is going to be low it's rather like the sump of a car engine where the oil collects the that's this is a sort of sump if you like of the lung and that's the reason why if we get interstitial edema we get a cuff of edema fluid around in a small blood vessel in this case in fact two of them here or a small airway get these Perea vascular cuffs so that's what happens in industry flow Deema interstitial edema does not cause much change in pulmonary function as we'll see in a moment and it's actually difficult to identify in a patient it's difficult to know whether a patient's got interstitial edema and the people who are going to tell us how the radiologists because they are able to pick up signs of interstitial edema these are called septal lines and they are horizontal white short lines here perpendicular to the pleural surface and here are a few examples here these are formed by the edema of the inter lobular septa the thickened interlocutor septa now I'm sure you're not going to be very impressed by that radiological appearance so if you're in doubt the best thing is to ask a friendly radiologist to help you alveolar edema of course is quite different here is an example of early alveolar edema electron micrograph and you can see the capillaries here and some edema fluid around them here the capillaries incidentally don't detain red cells because this preparation was made by by fixing the lung by infusing fixative through it and here's a light micrograph showing much well-developed alveolar edema and you notice that the alveoli are rather full of edema fluid or empty and in other words the our VL I thought fill in a sort of quantum fashion and they're either full they're not there's no edema fluid at all and of course you can also understand that this kind of condition is going to be very serious for the lung it's going to impair gas exchange because we had blood flow through some of these edema Demeter's areas of course that's going to represent a shunt and cause hypoxemia it's very easy to pick up our bailar edema on the chest radiograph and here's a rather florid example here but it's usually easy to pick it up you've got this bilateral shadowing here sometimes people refer to this as a bat swing or a butterfly wing appearance and it's usually quite easy to pick up our velar edema now let's talk about the pathogenesis of pulmonary edema and I'm going to do that by using the Starling equilibrium and the commonest cause of pulmonary edema is an increase in pulmonary capillary pressure and examples of that would be myocardial infarction with a heart attack the left ventricle fails to pump the blood as it should there's an increase in left atrial pressure palm Levinas pressure and therefore capillary pressure and there may be very severe edema fact the patient may cough up large volumes of pink frothy sputum and he may in fact he may drown at his own edema so myocardial infarction can be an example another example is hypertensive live in particular failure in systemic hypertension the left ventricle can often just cope with the increased after load for a period and then suddenly it'll fail and you can get a foramen and pulmonary edema a very different situation is mitral stenosis where the narrowing of the valve the stenosis occurs over many months or even years and therefore the the fluid coming out of the capillary of course increases over this time but there's no alveolar edema however there's extensive interstitial edema and the reason why there's no alveolar edema is not fully understood but apparently what happens is there is an increase in the number and the caliber of the lymphatics in this condition and that prevents and that allows the edema fluid to be removed from the lot transfusion overload which sometimes occurs during an over-enthusiastic transfusion in the intensive care unit is another cause and a rather unusual disease pulmonary veno occlusive disease where the veins are diseased is also an example now the second most important cause probably is increased capillary permeability and that's where the capillary wall is abnormal and therefore the filtration for coefficient increased Sigma is decreased in other words much more easy for the proteins to get across and there's a change also in the colloid osmotic pressure of the interstitial fluid which gets more protein and there are a number of causes of that including inhaled or circulating toxins an important cause is toxic gases chlorine gas for example every now and again somebody is exposed to chlorine gas in an industrial setting and develops hominid edema a very important cause is the adult respiratory distress syndrome where and we'll be talking about that later on when we talk about respiratory failure and in that condition there is a big increase in capillary ability which causes demon to occur radiation of the lungs and other cause of increased capillary permeability of course if you're radiating a breast cancer you try to protect the lung but sometimes the protection is not adequate and where the lung is radiated you tend to get a Deemer oxygen toxicity where a patient in the intensive care environment is given too high concentration of oxygen for too long a period can cause pulmonary edema and one of the important features of edema caused by damage to the capillary wall that is a high permeability edema is that the edema fluid has a high protein concentration whereas in the previous type of edema that is just an increase in pulmonary pressure itself Parmalee hydrostatic pressure the filtration characteristics of the of the capillary are preserved and the protein and the edema fluid has a relatively low protein concentration however I should say that that is the classical view and we're now beginning to realize that if you raise the the pressure in the pulmonary capillaries initially you get a low permeability edema but if you raise it high enough you damage the walls of the capillaries and therefore you can get an increased capillary permeability so there is actually a spectrum of types of edema when you raise the pressure in the pulmonary capillaries another possible cause is a decreased interstitial hydrostatic pressure now whether that is really the cause or not is a little bit iffy but it is certainly true that if you have a long standing pleural effusion or a pneumothorax where the lung is collapsed at a very low volume and you rapidly expand it you can get edema on that side and this is a unilateral pulmonary edema very unusual if you see unilateral pulmonary edema you raise your eyebrows because that's something unexpected but that can occur in this situation whether this kind of edema is really caused by a reduced interstitial hydrostatic pressure is uncertain because there are some there's some evidence that the edema fluid is with a high permeability type and therefore the capillaries are damaged a decreased colloid osmotic pressure is usually not a cause of edema in its own right but it can certainly exaggerate any other cause that's present and this can occur for example with saline / transfusion which can occur in the intensive care unit for example or in diseases where there is high Pope wrote anaemia they would be a diseases liver diseases and renal diseases couldn't cause hypo Prout anaemia lymphatic insufficiency is a rather uncommon cause but does occur in silicosis for example the silica particles are very toxic they're picked up by the macrophages which enter the lymphatics perhaps and the macrophages die and they they plug up the lymphatic so that sometimes occurs lymphangitis carcinomatosis where you get where you get carcinoma cells plugging up the lymph vessels is another example and lung transplantation you get probably edema but and of course there are no lymphatics that that are transplanted but there it's an immutable problem probably there are some courts some types of edema where the the the the cause is uncertain and I'm going to say a few words about one of those that's high altitude pulmonary edema because it's a very interesting topic and it's certainly been sorted out in the last few years turns out that when people go to high altitude they may develop high-altitude pulmonary edema it's actually a potentially lethal condition and incidentally the the treatment is to come down as quickly as possible but the cause of this high-altitude pulmonary edema has been a mystery because although we know that there's a strong association with a high pulmonary artery pressure then the wedge pressure is normal in other words there's no left ventricular failure so it's not live in tricular failure so why would a high Parmalee artery caused by the hypoxic pulmonary vasoconstriction why should that cause pulmonary edema and a very important and rather enterprising experiment was done a few years ago when actually a couple of friends of mine went to high altitude set up a clinic very hot at a very high altitude and treated patients with Parmelee edema as they came down as they came down these climbers would say you know can you help me with my probably demon they would say yes I can but do you mind if I bronchoscope you first said they bronchoscope these people at an altitude of about I can't remember exactly 14,000 feet or so in this tent and what they found was something very important that the edema fluid was of the high permeability type with a very high concentration of large molecular weight proteins and here's an example of the data they showed his cape here high altitude pulmonary edema very high protein concentration see a log scale here in a RDS which we often think of is the best example of high permeability edema the protein concentrations are really not quite as high and here we are at sea level and acute mountain sickness here so what this meant was that that for some reason when the the pulmonary artery pressure was high the capillaries had damage to their walls or some cavities now how could there be because we we believe that the constriction of hypoxic pulmonary vasoconstriction is upstream of the capillaries and then it transpired that there's evidence that the hypoxic pulmonary vasoconstriction is uneven and that where there is constriction of the smooth muscle the capillaries are protected of course from the high poly artery pressure but where there is no constriction the capillaries exposed and that they their walls are damaged and in fact if in animal preparations you raise the capillary pressure to an unphysical aaja Clee high level is the capillary here the alveolar space here this is the the alveolar wall here you can see that what hit is the wall of the capillary I should say here you can see a break in the capillary endothelial and that's an example of the of the ultra structural changes that occur under these conditions why do the capillaries break because the stress in the wall becomes so high remember that the blood gas barrier the wall of the capillary is fantastically thin and therefore an increase in pressure in this very thin wall is going to cause an extremely high stress it's laplace s formula and that's one reason why the stress increases the other is that if you go to an abnormally high lung volume you can also increase the stress now let's move on and talk about the clinical features of pulmonary edema and one of the most important features is Tiffany a shortness of breath all patients with Prom Leah Dima a short of breath they also have orthopnea in other words when they lie supine the shortness of breath is greater and they may develop what's called paroxysmal nocturnal dyspnea where they wake up in the night feeling desperately short of breath and that's probably because they slip down it's probably because the fluid collects in the lung as they slip down from their pillows cough is seen in pulmonary edema and initially it may be dry but then the patient may cough up pink frothy sputum pink because the alveolar edema always contains red blood cells frothy because of the surfactant if you listen in to the chest you can hear crepitations crackles on auscultation tickly at the lung bases and as we've seen the radiograph shows septal lines in interstitial edema and blotchy shadowing in alveolar edema the reason for the dista is not fully understood but very likely it's the juxtaposition the alveolar wall which becomes a dimittis and they presumably are stimulated by this and they caused this rapid shallow breathing the dysphoria now interstitial edema has very little effect on pulmonary function there's a little bit of evidence that lung compliance is reduced the evidence is not all that strong but probably the lung becomes a little bit stiffer but there is evidence that both airway resistance and vascular resistance are increased and probably this is because of the perivascular and peribronchial cuffing that we saw earlier on and here's a diagram just showing how this could occur here you've got a potential peri vascular or peri bronchial space this is either a blood vessel on the airway it doesn't matter and you've got the radial traction pulling it open and now if you get a deal a fluid filling this potential space here because that's where the cap where the lymphatics run then you get a reduction in the lumen of the of the blood vessel or the airway and that causes either an increased vascular resistance or an increased airway resistance now our villa edema causes much bigger much bigger changes in pulmonary function in fact dramatic changes the first thing that happens or one of the things that happens is that the lung compliance is reduced the length becomes very stiff and you'll find that in patients for example with a RDS the adult respiratory distress syndrome you meet large pressures to expand the lung because of the edema fluid airway resistance is increased partly because of the mechanism I just described but also because there's a lot of edema fluid in the Airways themselves gas exchange is seriously compromised there's always severe hypoxemia due to both a shunt as we saw if you have blood flow through those on those alveoli that are filled with fluid of course that's a shunt and that's part of the ventilation perfusion the quality typically there's no co2 retention the pco2 is normal possibly because of stimulation by those juxta capillary receptors pulmonary vascular was sensors increased as I indicated earlier on now that's what I'm going to say about pulmonary edema let's shift now to pulmonary embolism which is another very important disease and one of the reasons why it's important is that it's very frequently overlooked you've got to have a high level of suspicion of pulmonary embolism under a number of circumstances of course as we'll see if we've got a massive embolism there's no problem there but many patients with Tom knee embolism the diagnosis is missed the Communist cause is that there are venous thrombosis and these are detached and they move up into the lung you can also get thrombi in the pelvic area and also the right heart particularly with atrial fibrillation there can be emboli in the right heart mostly it's venous thrombi that are responsible for embolism but occasionally you can have fat air even amniotic fluid that can cause embolism now what's the pathogenesis of the thrombosis that occurs initially and eventually causes the embolism or may cause the embolism well there are three the there are three categories one is stasis of blood and that can caused with immobilization for example a frequent cause is a is a patient who has broken a leg for example and is in a long plaster and the leg is immobilized and that tends to cause the venous thrombosis in the leg venous obstruction is another case if you're wearing something tight that obstructs the leg or if the leg is up against a an obstruction of some kind and incidentally immobilization and venous obstruction can possibly occur during long flights in the economy section of an aircraft although there is some question about that but it makes sense that that's a lot of immobilization and they can be Venus obstruction against the chair gets the seat and that could cause it other causes of stasis or heart failure and also dehydration there can be an increased coagula ability of the blood that occurs in some diseases sickle-cell disease it occurs for example polycythemia can cause this in fact at high altitude when you get polycythemia there's a concern about pulmonary embolism malignancies can do this oral contraceptives can and unfortunately there's no really reliable test of this increased coagula bility and finally you can get an abnormality of the vessel wall Proma can do this if the leg is banged in a football mattress on thee and inflammation can cause it although when you've got information then the the clot the thrombosis tends to adhere to the vessel wall it's less likely to cause an embolism as I said length from BOCES is often unsuspected there may be a bit of swelling there may be a bit of local tenderness and if you dorsiflex the ankle pull the ankle up sometimes there is pain in the calf and that is some evidence and there are techniques venography radioactive fibrinogen impedance plethysmography that can help in the diagnosis of a thrombosis when the embolism actually occurs the thrombus has swept up into the palm the artery it usually doesn't completely block the artery but it certainly causes a great deal enormous reduction in blood flow of course distal to the embolic area it may deplete the surfactant in the embolize region of lung and that can cause some atelectasis you know surfactant is turned over very rapidly so if the surfactant is depleted then you can get local electus in people used to talk about infarction maybe that does occur from time to time but probably what we see is really atelectasis in this region of the lung remember that the bronchial circulation is always available even if the pulmonary circulation is obstructed the eventual fate of emboli if the patient survives is that they're removed by lytic components in the blood and it's very remarkable that after several weeks several weeks following an embolus there may be no evidence of obstruction at all now the clinical picture of pulmonary embolism depends very much on the size of the emboli and I'm going to look at three sizes medium-sized massive emboli and very small emboli and maybe a medium-sized and balaiah one of the commonest kinds those are the kinds you get when a patient is put into bed following an accident with a long splint or something like that immobilized and the patient suddenly develops some kind of pulmonary problem and you need to be suspicious of prominent embolus otherwise you're going to miss it occasionally the patient will have pleuritic pain and disappear well the pleuritic pain of course is obviously out that's going to give a suggestion that they have a net embolus there may be a cough with blood-stained sputum sometimes there's a mild increase in temperature occasionally there's a pleural friction rub that you can hear by auscultation but if the patient develops a pleural effusion this will go away the radiograph is often normal but occasionally you can see an area of reduced vascular markings now it's going to be a very good chest x-ray to show that but sometimes that can be seen and the key thing is an abnormal lung scan the the the gold standard is angiography that angiography is invasive and often is not required if the lung scan is clearly diagnostic and here's an example of a lung scan showing multiple pulmonary emboli here's a scan following I think the inhalation of radioactive xenon in this case sharing normal ventilation throughout both lungs but now look at what happens when you inject a radioactive albumin then you find that there it's a tremendous reduction in blood flow at the apex and vase and the left lung here and there are clearly and normal areas on the right lung here as well so this patient has multiple pulmonary emboli massive emboli occasionally occur and that's a very different clinical picture there's sudden hemodynamic collapse because the connect output is greatly reduced there's shock pallor maybe central chest pain loss of consciousness there's systemic hypotension the pulse is rapid and weak they're signs of right ventricular failure the neck veins are engorged the ECG shows right ventricular foot strain and there's a fairly high fatality rate occasionally with a massive embolus a it's possible to do emergency surgery and remove the embolus but the death rate with this condition is high repeated small emboli is a different kind of clinical picture these are frequently unrecognized in fact I would say generally unrecognized what I would say and the pulmonary capillary bread is gradually obliterated by these small emboli and often the presenting problem is evidence of pulmonary hypertension patient may have dis Mir on exertion occasionally you can you can feel a right ventricular heave because of enormous increase in because of the right ventricle hypertrophy as a loud pulmonary ii sound and the ECG and radiograph confirmed the right ventricular hypertrophy so these patients sometimes come along with unexplained pulmonary hypertension and the answer turns out to be repeated embolism a word or two about pulmonary function in embolism of course the Pommery circulation has a la Reserve and and small emboli therefore are not recognized in terms of functional changes you know you can you can remove one lung from a normal subject with with normal lungs and there's no essentially no increase in pulmonary artery pressure at rest on exercise there will be an increase but but the the homily section has a large reserve because of the abilities of the capillaries to recruit and and distend occasionally we see pulmonary edema with poly embolism it's not common and if it occurs it's presumably because of the same mechanism that I referred to in high altitude problem the edema that is to say if you get a very high pulmonary artery pressure in the non embolize region of the lung then the homily the the homily pressure the capillary pressure increases and causes edema the embolized region may develop atelectasis as said before because of surfactant depletion in fact if you do experiments in animals where you you embolize the region of the lung then after a couple of days you can see atelectasis also immediately after the embolic event you can see an increase in local airway resistance that's caused apparently by the low pco2 in the embolized area because there's so little blood flea they're acting directly on the smooth muscle but this is apparently not seen in humans because one of the features of pom the embolism of the of the the scan for Parmalee embolism is that there is a mismatch between the blood flow and the ventilation and that's an important diagnostic point because if the patient has an area of emphysema for example both the ventilation and the blood flow will be done so this occurs in in animals as acute wood I could increase in airway resistance but apparently does not occur in humans although of course in humans we're always looking at the event much later hours later so perhaps that's the reason gas exchange is impaired in pulmonary embolism you get hypoxemia because uh ventilation/perfusion inequality and you can get a shunt with large emboli possibly because of edema and here are a couple of distributions they're pretty remarkable that anyone was able to make these measurements these are distributions of inhalation of effusion ratios in two cases of massive pulmonary emboli and you can see several things first of all the distributions are cosa grossly abnormal large amount of ventilation to high viq units that's the embolized area being ventilated that's dead space and in fact they measure the dead space here and it's very very high as you can see but in addition to that there are large shunts the shunt here is 20% of the cardiac output here 39 percent of the cardiac output so of course these patients have very very serious lung disease and pretty remarkable that they were able to measure these distributions now let's say just a few words about pulmonary hypertension and here's a classification that's often given it can be caused by an increased level pressure for example in mitral stenosis see the atria left atrial pressures increased therefore poorly venous pressure and therefore pulmonary artery pressure is increased and perhaps I should have said pulmonary hypertension here of course means an abnormally high pulmonary artery pressure normal value of about 15 millimeters of mercury and that's the definition of pulmonary hypertension the increased blood flow can cause an increased pulmonary artery pressure that can occurs on exercise a lot of people don't realize that if a normal subject exercises at a high level this is substantial increase in pulmonary artery pressure family vascular resistance can increase as a result of either vasoconstriction as in our villa hypoxia we mentioned the increase in pulmonary artery pressure at high altitude for example obstructive as in thromboembolism of course and obliterated as an emphysema where many of the capillaries are destroyed primary pulmonary hypertension is a relatively uncommon disease but recently there's been much more interest in this its causes is says here uncertain I would say in most cases unknown although in some instances there is a genetic component and that's something that's been described relatively recently as I said occasionally it's due to repeated small emboli the the population that in which this is mostly seen a women between 20 and 40 years of age you get dis earlier on exertion and sometimes syncope because the cardiac output is is reduced there are signs of right ventricular hypertrophy because of the hypertension the increase in right heart sometimes vasodilator drugs such as sildenafil can help and this is one of the reasons why there's so much interest in the disease at the moment in spite of it being a rather uncommon disease that there's a lot of interest by the pharmaceutical interesting industry and finding new drugs that are going to help because the prognosis of this condition is is poor and it would be very important to try and find ways of helping these patients if the cause is repeated emboli occasionally these can be removed by surgery and that's important here's an example of an abnormal pulmonary artery in primary pulmonary hypertension looks terrible doesn't it it's called a plexiform lesion there's an increase in smooth muscle here the media's increased the intimus increased obviously a very dramatic change in the pathology of the artery cor pulmonale we won't dwell on this it's defined as right heart disease secondary to lung disease and we've mentioned it already in the context of COPD and in interstitial fibrosis the pulmonary hypertension is caused by AB literation of the capillary bed occurs in both COPD and in diffuse interstitial primary fibrosis or toxic vasoconstriction and possibly polycythemia in patients with COPD who develop increased hematocrit's there's a question as to whether this is really right heart failure because actually the heart is operating high on the Starling curve and the pot and the cutting output can be increased on exercise but that that's not so important finally let's a word or two about arterial venous malformation this is an abnormal communication between a branch of a pulmonary artery and a vein it's something you're born with and many of the patients have other evidence of vascular abnormalities teal inject disease of the skin or mucous membranes sometimes as a family history of this condition if you've got a large communication of course you've got a substantial amount of pulmonary arterial blood mixed venous blood joining the pulmonary venous blood that's a shunt and that can cause hypoxemia it's one of the classical causes of hypoxemia caused by shunt sometimes a bruit can be heard over the lesion by auscultation finger clubbing occurs and now it's possible in some of these patients to to obstruct the shunt by inserting a blocking device and wires and that can be done and that's useful so that's all I'm going to say about the disease diseases of the primary circulation they're very important particularly Parmalee edema and and pulmonary embolism are particularly important and I'll leave it there hope to see you next time

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