Respiratory System Physiology - Ventilation and Perfusion (V:Q Ratio) Physiology

hello in this video we're going to talk about pulmonary circulation and we will also talk about ventilation and perfusion so first of all ventilation is essentially the amount of air traveling into your alveoli ready for gas exchange perfusion is the amount of blood flow going into the alveoli and thus prepared for gas exchange as well ventilation is abbreviated V and perfusion is abbreviated Q a simple concept to understand is that the lung is divided into three zones the so called ventilation perfusion ratio is higher at the apex of the lung on the top towards the base of the lung the ventilation perfusion ratio is decreased the ventilation here again is the amount of air coming into the lungs specifically into the alveoli ready for gas exchange the perfusion is a blood flow to the lungs to the alveoli and thus ready for gas exchange the average ventilation perfusion ratio is 0.8 0.8 really means that there is more perfusion more blood flow to the lungs to the alveoli than there is ventilation but fun fact through the lungs perfusion and ventilation differ different lung diseases can also further affect the ventilation perfusion ratio also known as the VQ ratio let's now try to understand the concept of ventilation and perfusion and why they differ in different zones of the lungs so here we have two lungs the heart pumps deoxygenated blood through the pulmonary artery into the lungs in the upright position the upper portion of the lungs are well above the level of the heart and the base of the lungs are at or below it this has important implications on the perfusion as well as the ventilation because as you can imagine when standing up gravity will affect how much blood goes to different areas in the lungs so as mentioned the lungs can be divided into three zones as you can imagine blood traveling to this zone on the top at the apex of the lung will be decreased because of gravity there's decreased perfusion at the apex perfusion here is represented by Q remember this means that the blood flow to the base of the lungs will have increase in perfusion so the Q is increased thus we can say that at the apex of the lung we have wasted ventilation all the gas that goes to the alveoli is not exchanged efficiently because there is less perfusion whereas at the base of the lungs we have wasted perfusion there is a lot of blood flow to this area but not as much ventilation not as much gas going into these alveoli funfact like perfusion ventilation is actually higher at the base of the lungs than at the apex of the lungs just important to keep note that both ventilation and perfusion is actually greater at the base of the lung so let's look at another representation here because the apex of the lung sits well above the heart you have larger alveoli there is reduced pulmonary intravascular pressure because of less blood flow to this area less blood flow means less perfusion in the apex you also have less ventilation occurring because of your large alveoli but despite the reduced ventilation the perfusion is far more reduced here and so you actually have wasted ventilation which means you have a lot of gas a lot of oxygen to offer but not enough red red blood cells around as you go to the base of the lungs your alveoli becomes smaller the size difference is in alveoli from the apex to the base of the lung is attributed to the difference in intrapleural plush pressure which we won't actually talk about here you have more blood flow to the base of the lungs as mentioned and so you have more profusion at the base of the lungs you also have more ventilation because the small alveoli are able to expand more at the base the ventilation increase is not as much as the increase in perfusion and thus the ventilation perfusion ratio is lower here thus we can create a ventilation perfusion ratio using this concept so at the base of the lung you have good ventilation and great profusion for the apex you have not-so-good ventilation and pretty bad perfusion this is again in an upright position and these differences in VQ ratio is thought to be primarily due to gravity but also other factors play a role including different diseases if this concept of different ventilation perfusion is still confusing let's take another look at it and introduce pressures again you have two lungs each lung can be divided into three zones the pulmonary artery brings blood to the lungs the pulmonary artery pressure P small a here brings blood to the alveoli the alveoli have their own pressure represented as P capital a gas exchange occurs between the pulmonary vessels and alveoli then the pulmonary vein will return this newly oxygenated blood to the heart the pulmonary vein pressure here is represented by P small V so now let's introduce the three zones again at the apex of the lung you have large alveoli you have a large alveolar pressure blood flow to the apex is less so pulmonary arterial pressure here is normally just sufficient to maintain perfusion but if pulmonary artery pressure is reduced or if alveolar pressure is increased some of these capillaries collapse under these circumstances no gas exchange actually takes place in the affected alveoli and they become part of the physiological dead space easy to remember that in zone 1 alveolar pressure is highest followed by pulmonary artery pressure but normally in healthy adults pulmonary artery pressure will be just higher in order to maintain the blood flow then pulmonary vein pressure is obviously lowest thus in zone 1 perfusion is crap in the middle portion of the lungs the pulmonary artery pressure exceeds the alveolar pressure perfusion is good and so ventilation is good finally towards the base of the lung alveolar pressure decreases and pulmonary blood flow increases as the arterial pressure increases in the lower portion of the lungs alveolar pressure is lowest in the pulp in the pressure in all parts of the pulmonary circulation again recapping the apex of the heart focusing on the pulmonary artery pressure if this drops no gas exchange takes place you thus have physiological dead space let's look at the pulmonary blood flow in more detail here's the right side of the heart which pumps deoxygenated blood to the lungs the lungs can be divided into three zones gas exchange occurs in the lungs then the pulmonary vein will return the newly oxygenated blood to the left side of the heart to the middle zone of the lung perfusion is good ventilation is good however remember perfusion to the apex of the lung is poor you have decrease in Q ventilation is lower at the apex of the lung but not as bad as perfusion at the apex of the law thus VQ ratio is high here as you go to the base of the lung ventilation increases but perfusion increases a lot more so your VQ ratio will decrease at the base of the law so in summary your ventilation the amount of gas you breathe in increases from the apex of the lung to the base of the lung but your profusion the amount of blood flow going to your lungs going to your alveoli increases a lot more from the apex of the lung to the base of the lung and so your v2 ratio decreases from the apex of the lung to the base of the lung so I just want to talk about one more thing about venous return to the left side of the heart I wanted to introduce the waterfall effect whereby the height does not actually influence blood flow so here looking at an example distance as in the height as in towards the apex and blood flow we would assume that blood flow coming from the apex would be highest but just like the waterfall the height of the waterfall has no influence on flow so in summary your ventilation the amount of gas you breathe in increases from the apex of the lung to the base of the lung but your perfusion the amount of blood flow going to your lungs going to your alveoli increases a lot more from the apex of the lung to the base of the lung and so your v2 ratio decreases from the apex of the lung to the base of the lung again ventilation is the amount of gas oxygen coming into your alveoli ready for gas exchange and perfusion is the amount of flow to the lungs the red blood cells to the lungs ready for gas exchange and the average VQ ratio through the whole lung is about 0.8 the VQ ratio can change drastically depending on diseases so let's take a look at some examples here so here again is your heart the right side of your heart will pump blood to your lungs through the pulmonary arteries here in blue the blood will go to the alveoli eventually gas exchange occurs and new oxygenated blood will go back to the heart if you the pulmonary veins colored here in red now in different diseases ventilation and perfusion gets messed up imagine you breathe air in to your alveoli this is ventilation normal VQ ratio is about 0.8 which really means you have a higher perfusion than ventilation on average in pneumonia for example where you have consolidation you have decrease in ventilation you don't get enough gas moving into your alveoli as a consequence your ventilation perfusion ratio is low similarly if you have mucus thickening and build up along the Airways like in COPD you get reduced gas coming into your alveoli and so you have reduced ventilation thus your VQ ratio is decreased another example of a decrease in VQ ratio is in pulmonary edema when you have fluid overload in your lungs this results in reduced ventilation there is reduced gas travelling into your alveoli where gas exchange should take place and so you can see spectrum of VQ mismatch whereby on the left side your ventilation is decreased so does your VQ ratio on the very end of the spectrum on the left side you can have one area of the lung where the ventilation is zero which would mean that in this area the VQ ratio is zero when this happens this is called absolute physiological shunt or absolute pulmonary shunt where you have perfusion without ventilation with this scenario you can imagine no oxygen is coming into the alveoli so you get net low oxygen levels leaving the pulmonary system and you still have all that carbon dioxide because you cannot breathe it out you have perfusion but no ventilation now back to COPD we mentioned how mucus buildup causes reduced ventilation but in COPD you can also get destruction of the pulmonary capillaries supplying the alveoli and so when this happens you get a reduced perfusion because you are destroying the blood flow to the alveoli so I mean in COPD like in many other lung diseases it's a fine balance of reduced ventilation and reduced perfusion reduced perfusion in COPD occurs more in late stages of the disease as the vq ratio spectrum moves more to the right your VQ ratio increases it increases until the middle when you get our ventilation and perfusion ratio about 1 which is ideal here you get enough air entering the alveoli and you're getting enough blood flow to the alveoli in real life the average humans as mentioned have a VQ ratio of 0.8 however as a spectrum of VQ ratio moves to the right you have an increase in VQ ratio which means you really have a decrease in perfusion you have a decrease in blood flow to the alveoli the example of this is a damaged to the capillaries as seen in late COPD another good example is pulmonary embolism where a clot occludes the pulmonary capillary or artery causing reduced perfusion which will subsequently increase the VQ ratio causing a mismatch when the perfusion to an area of the lung is so low the number could really be anything because it will depend on the top value which is ventilation when perfusion is zero to an area of the lung the area is called an absolute dead space which really means that gas is actually entering the alveoli but does not participate in gas exchange and so this space is dead space the trick here for example is dead space because air flows through here but the trachea does not participate in gas exchange so I hope this video on ventilation perfusion makes sense thank you for watching you

Channel: Armando Hasudungan

Views: 664,470

Keywords: ventilation perfusion mismatch, ventilation perfusion physiology, V/Q mismatch explained, V/Q ratio, pulmonology, V/Q mismatch in COPD, V/Q ratio tutorial, lung physiology, pulmonary system ventilation, respiratory system physiology, respiratory system pressure and ventilation, medicine

Id: -mL_NQ3pKnA

Length: 15min 0sec (900 seconds)

Published: Tue Mar 20 2018