 FEV1 by FEC ratio is a marker for differentiating between obstructive and restrictive lung diseases. Before we proceed, you should remember that the main problem in obstructive lung disease is in expiration, basically problem in moving the air out of lungs, while in restrictive lung disease there is restriction to lung expansion, so main problem is getting the air into the lung, so problem is in the inspiration. So with this concept, let's try to understand FEV1 by FEC ratio. So by the way, what is this FEV1 and FEC? Well, FEC is forced vital capacity and FEV1 is forced expiratory volume in first second. So let's try to understand their meaning. See, to determine forced vital capacity and FEV1, we have to connect the patient to the spirometer. Now we will discuss more about the analogue kind of spirometer, however these days everything can be done digitally. But anyways, so for determining forced vital capacity, what we do is, we ask the person to fill his lungs completely by taking maximum inspiration while obviously he is connected to the spirometer. So he will draw in air from the spirometer. Now when that happens, when the patient draws in the air, the spirometer bell actually goes down because the volume in the spirometer is decreasing, so the top bell will go down and this will cause the movement of the marker of the spirometer to go up. So if initially say suppose it is somewhere here, then the marker will go up and we will get a straight line and this straight line we will get because the spirometer right now is not moving. Now once he fills his lungs completely, what will happen that he will not be able to draw any more air. So when that point is reached, we ask them to exhale maximally and forcefully. So as much forcefully and as much fast he can do that, he is asked to exhale out the air and immediately we start the spirometer at a speed of 20 millimeter per second. So because the spirometer is now moving, we will get a line like this in the spirometer and he is exhaling out, isn't it? So the air is going back into the spirometer and the drum of the spirometer will go up and hence the marker will go down. So we will get this kind of line. Fine. Now for complete evaluation of FEV1 and FVC, it is important that you continue to record this till the time he is exhaling or maximum up to six seconds. Now with the graph obtained, we determine FEV1 by FVC ratio. See from here to here is the total volume which is exhaled. So that is forced whiter capacity. So forced whiter capacity is defined as the amount of air which can be exhaled out after maximum inspiration and here because it is forced, so the amount of air which can be exhaled out forcefully after maximum inspiration. Now the spirometer chart which is there, actually it is already calibrated means it has some lines like this and the distance between lines represents 500 ml. So we can actually determine how much total volume of air has been exhaled out by just counting these lines. So here if we count, so this is 500 ml, this is 500 ml, so here it is coming to till here 4000 ml and say suppose this is approximately 200 ml, right? So 4200 ml. Fine. Now let's determine FEV1. So FEV1 we said is forced expiratory volume in first second. So in first second how much air he is exhaling out that is FEV1. So for that we should know the speed of his spirometer. So here we said that speed of his spirometer is 20 millimeter per second. So here basically with the speed we can determine the distance which the graph will move in one second. So that is 20 millimeter per second, so it is moving 2 centimeter in one second. So what we do is to mark this time on the graph we use a scale, mark it as 2 centimeter. From the point the person has started exhaling, right? So this much is representing one second. Now if we drop a perpendicular from the point of start of exhalation to this one second, this much will be the volume which is exhaled in first second, right? So here again by counting the lines we can determine how much it is coming. So it is coming to say 3800 ml. With these values let us now calculate FEV1 by FEC ratio. So just divide 3800 ml with 4200 ml and it comes to 0.90. Now normally greater than 80 percent of forced vital capacity is exhaled in first second. So here it is coming to 0.90. So that is if we express in percentage it comes to 90 percent. So in this case yes obviously it is normal. But clinically if the value is less than 0.7 it signifies obstructive lung disease. So as we said that in obstructive lung disease problem is in exhalation, right? So like if we allow him to exhale as much as possible for long duration then total volume of air which is exhaled that is the FEC it will be normal. But the volume which is exhaled in first second forcefully and maximally it will be less because actually the person is exhaling very slowly, okay? So this FEV1 will be less. So the problem is basically in exhalation. Hence the value of FEV1 FEC ratio is going to decrease. So graphically if we draw this it will be like this because he is exhaling slowly and hence the ratio FEV1 by FEC ratio will decrease. Now in restrictive lung disease what will happen? In restrictive lung disease the person is not able to fill his lungs completely. So this line which we are seeing it will go till here and then the graph will be something like this, okay? So basically FEC has decreased and when FEC decreases what happens at FEV1 also decreases proportionately. It's like if a tank is filled less then the speed of water moving out of that will also be less isn't it? So FEV1 also be proportionately less. So in restrictive lung disease if we see the ratio wise FEV1 FEC then the denominator is less, FEC is less and FEV1 also decreases proportionately. So it will be normal or sometimes even increase if this FEC decline is too much then this ratio may be increased as well. So basically to diagnose restrictive lung disease we need to look at the individual value of FPC and fundamentally we have to look at the values of static lung volumes and capacities in which we will see that there is decrease in vital capacity, decrease in residual volume and decrease in functional residual capacity. Okay, before finishing let's try to solve one question on FEV1 by FEC ratio. So suppose the forced vital capacity is 2500 ml and FEV1 is 2200 ml for a 35-year-old male and if we calculate FEV1 by FEC ratio it will come to 2200 divided by 2500 so it comes to 0.88. So the ratio is normal. So definitely it is not obstructive lung disease but is it actually normal? Well look at the individual values of FPC and FEV1. See FEC is definitely decreased normally for an adult male it is around 4500 ml so that means FPC is less. Hence it is basically restrictive lung disease where FEC has decreased and FEV1 has also decreased proportionately causing the ratio to remain normal. So that's all for FEV1 by FEC ratio. I just want to bring to your notice with this that if you want to solve more clinical based question more thinking applied questions on practical physiology then you can get our book on practical physiology where we have given lot of thinking and analytical questions for minds to actually think and apply their knowledge in physiology. Okay, thanks for watching the video. If you liked it do press the like button share the video with others and don't forget to subscribe to the channel Physiology Open. Thank you.