0:00:00.000,0:00:02.375 0:00:02.375,0:00:03.000 So here we are. 0:00:03.000,0:00:04.790 We have our two[br]lungs and the heart. 0:00:04.790,0:00:06.430 I'm just going to[br]quickly label stuff. 0:00:06.430,0:00:09.287 We've got our right and left[br]lung, and we've got our heart. 0:00:09.287,0:00:10.745 And I want to make[br]sure I label all 0:00:10.745,0:00:12.450 of the four chambers[br]of the heart. 0:00:12.450,0:00:15.440 I've taken away a[br]lot of the vessels. 0:00:15.440,0:00:17.600 I just want to focus[br]on a couple of things 0:00:17.600,0:00:21.630 here-- mainly, the blue[br]blood vessel coming off 0:00:21.630,0:00:24.040 of the heart-- the one I've[br]drawn in blue-- which I'm 0:00:24.040,0:00:26.480 going to label here as[br]the pulmonary artery. 0:00:26.480,0:00:30.390 Remember, again, arteries[br]go away from the lungs. 0:00:30.390,0:00:33.630 So this is our pulmonary[br]artery, even though it's 0:00:33.630,0:00:36.580 got deoxygenated blood in it. 0:00:36.580,0:00:39.080 A little counterintuitive,[br]but I think you got it now. 0:00:39.080,0:00:41.970 So this is our pulmonary[br]artery, and it's 0:00:41.970,0:00:44.320 going to the left[br]and right lungs. 0:00:44.320,0:00:48.120 And if we assume that there's,[br]let's say, 5 liters of blood 0:00:48.120,0:00:49.694 flowing through the[br]heart per minute, 0:00:49.694,0:00:51.110 that means that 5[br]liters are going 0:00:51.110,0:00:53.490 to go through this vessel. 0:00:53.490,0:00:55.840 And some of that is[br]going to go to the right, 0:00:55.840,0:00:58.880 and some is going[br]to go to the left. 0:00:58.880,0:01:01.440 Let's say I told you that[br]2 and 1/2 liters goes 0:01:01.440,0:01:03.620 to the left lung per minute. 0:01:03.620,0:01:05.110 Let's just assume that. 0:01:05.110,0:01:07.240 Then you know that[br]the other half 0:01:07.240,0:01:09.960 of that 5 liters-- the rest[br]of it, 2 and a 1/2 liters-- 0:01:09.960,0:01:11.290 must also go to the right. 0:01:11.290,0:01:13.780 Because whatever[br]goes into this tube-- 0:01:13.780,0:01:16.130 almost like a straw--[br]on one end has 0:01:16.130,0:01:17.900 got to come out[br]on the other end. 0:01:17.900,0:01:20.260 So you just, basically,[br]add up what's exiting. 0:01:20.260,0:01:22.560 And it's got to equal[br]what's entering. 0:01:22.560,0:01:24.840 So here we have[br]the idea of flow. 0:01:24.840,0:01:26.980 And we've talked about[br]flow in other videos, 0:01:26.980,0:01:28.770 but basically, I just[br]want to restate it. 0:01:28.770,0:01:31.170 It's a volume over[br]a period of time. 0:01:31.170,0:01:33.680 And in this case, we're[br]using liters over minutes. 0:01:33.680,0:01:35.940 But really any kind of[br]volume over time you 0:01:35.940,0:01:37.790 could describe as blood flow. 0:01:37.790,0:01:40.600 Now, let's say that a[br]tragic event occurs, 0:01:40.600,0:01:45.860 and I end up having[br]a surgery to my lung. 0:01:45.860,0:01:47.770 Let's say underneath[br]this yellow line 0:01:47.770,0:01:51.430 is my lower lobe and[br]above it is my upper lobe. 0:01:51.430,0:01:54.640 Let's say my lower lobe,[br]it needs to be removed. 0:01:54.640,0:01:56.790 It's a pretty drastic[br]thing to have happen, 0:01:56.790,0:01:59.160 but let's say this[br]is what happens. 0:01:59.160,0:02:02.810 What would change in[br]terms of my blood flow? 0:02:02.810,0:02:05.120 Well, the thing that[br]is going to change 0:02:05.120,0:02:08.910 is my resistance[br]is going to change. 0:02:08.910,0:02:10.090 Let's think about it. 0:02:10.090,0:02:12.790 Before I had this surgery,[br]I had a certain amount 0:02:12.790,0:02:15.170 of resistance in[br]this blood vessel 0:02:15.170,0:02:17.254 and also some resistance[br]in this blood vessel. 0:02:17.254,0:02:18.670 And let's say it's[br]about the same, 0:02:18.670,0:02:20.590 just to kind of[br]make things easy. 0:02:20.590,0:02:22.810 Let's say the resistance[br]was about the same. 0:02:22.810,0:02:25.280 So again, I had a surgery. 0:02:25.280,0:02:32.430 And before they removed the[br]lower lobe-- just to make sure 0:02:32.430,0:02:35.140 we are clear on what[br]this surgery was-- so 0:02:35.140,0:02:36.260 removed the lower lobe. 0:02:36.260,0:02:38.890 0:02:38.890,0:02:42.020 So before the surgery-- I'll[br]write "before" up here-- 0:02:42.020,0:02:43.440 what was the resistance? 0:02:43.440,0:02:47.570 Well, the resistance I[br]was facing was-- remember, 0:02:47.570,0:02:49.600 we have a branch here. 0:02:49.600,0:02:52.000 So we have to add up[br]the total resistance. 0:02:52.000,0:02:53.300 You remember how to do this. 0:02:53.300,0:02:56.320 Total resistance--[br]I'll call it R total-- 0:02:56.320,0:03:02.310 equaled 1 divided by[br]1 over R-- because we 0:03:02.310,0:03:05.620 said that's what the resistance[br]is right there-- 1 over R 0:03:05.620,0:03:09.962 plus 1 over R. And that second[br]one is because of this guy. 0:03:09.962,0:03:11.170 So we just kind of add it up. 0:03:11.170,0:03:12.003 And I would say, OK. 0:03:12.003,0:03:17.730 Well, that's equal to[br]1 over 2 divided by R. 0:03:17.730,0:03:19.690 And I can flip the[br]whole thing around. 0:03:19.690,0:03:26.260 And I get R divided by[br]2 or 1/2 R. So this is 0:03:26.260,0:03:27.652 my total resistance-- 1/2 R. 0:03:27.652,0:03:30.110 It's a little counterintuitive--[br]the fact that you actually 0:03:30.110,0:03:33.810 have half of the resistance[br]just because you have a fork. 0:03:33.810,0:03:36.100 The fork in the road--[br]meaning this fork right 0:03:36.100,0:03:40.380 here-- offers you a chance[br]to go one of two ways. 0:03:40.380,0:03:42.900 And as a result, the[br]resistance falls in half. 0:03:42.900,0:03:45.620 So after my surgery,[br]what was my resistance? 0:03:45.620,0:03:48.090 Well, in my surgery, this[br]all kind of went away. 0:03:48.090,0:03:49.780 This is now all gone. 0:03:49.780,0:03:53.060 Because my surgery removed the[br]lower lobes, this is now gone. 0:03:53.060,0:03:55.490 So what is my new R total? 0:03:55.490,0:03:57.260 Well, if I had to[br]calculate it again, 0:03:57.260,0:03:58.680 I would say, OK, R total. 0:03:58.680,0:04:00.320 In this case, it's[br]actually really easy 0:04:00.320,0:04:02.440 because it's just[br]whatever's left. 0:04:02.440,0:04:06.120 In this case, the total[br]is going to be just R. 0:04:06.120,0:04:12.770 So really, my resistance[br]went from half R to R. 0:04:12.770,0:04:16.240 And so my resistance really,[br]by removing the lower lobe, 0:04:16.240,0:04:16.959 it doubled. 0:04:16.959,0:04:18.834 My resistance went much higher. 0:04:18.834,0:04:20.500 So this is the first[br]interesting point-- 0:04:20.500,0:04:23.350 that by having a[br]half a lobe removed, 0:04:23.350,0:04:24.785 my resistance went way up. 0:04:24.785,0:04:27.690 So on this side, my[br]resistance after the surgery 0:04:27.690,0:04:29.650 is much higher[br]than it used to be. 0:04:29.650,0:04:31.890 Now, remember this[br]flow-- 5 liters a minute. 0:04:31.890,0:04:34.040 Now, you still have that[br]much blood coming in, 0:04:34.040,0:04:37.427 but now there's extra[br]resistance on the left side. 0:04:37.427,0:04:38.760 So what's the blood going to do? 0:04:38.760,0:04:40.580 Well, it's going to[br]say, well, why would I 0:04:40.580,0:04:42.570 go that way when[br]I can go this way? 0:04:42.570,0:04:44.990 So more of the blood's[br]going to kind of go this way 0:04:44.990,0:04:48.350 because there's more[br]resistance on the left side. 0:04:48.350,0:04:51.300 And so I can actually--[br]I don't know exactly what 0:04:51.300,0:04:54.370 the amount of flow would be--[br]but I can kind of take a guess. 0:04:54.370,0:04:57.410 And I would say, well, my guess[br]is that the flow will be lower. 0:04:57.410,0:04:59.770 So I'm actually going[br]to redo these numbers. 0:04:59.770,0:05:01.700 I'm going to give[br]you new numbers. 0:05:01.700,0:05:05.620 And let's say the new flows--[br]I'll write them in green-- 0:05:05.620,0:05:09.080 are going to be 3 liters a[br]minute and 2 liters a minute. 0:05:09.080,0:05:11.260 They still have to add[br]up to 5, of course. 0:05:11.260,0:05:12.690 That's not changed. 0:05:12.690,0:05:15.570 But you have more blood[br]going to the right lung. 0:05:15.570,0:05:17.650 So here let me[br]introduce another word. 0:05:17.650,0:05:19.470 So we've talked[br]about flow, but now 0:05:19.470,0:05:20.982 let me talk about perfusion. 0:05:20.982,0:05:23.440 And sometimes people actually[br]think they're the same thing. 0:05:23.440,0:05:26.740 They sometimes will use[br]them kind of synonymously. 0:05:26.740,0:05:30.790 But really, perfusion[br]is volume over time. 0:05:30.790,0:05:33.500 And so, so far you're thinking,[br]well, it is about the same. 0:05:33.500,0:05:39.190 But actually, it's all[br]divided by amount of tissue. 0:05:39.190,0:05:41.110 And when I say amount,[br]I could do either 0:05:41.110,0:05:44.880 be talking about a volume of[br]tissue or a weight of tissue. 0:05:44.880,0:05:47.250 So amount of tissue. 0:05:47.250,0:05:50.030 Just to kind of make this[br]a little bit more concrete, 0:05:50.030,0:05:54.240 I'm going to assume that I'm[br]going to use 100 grams here. 0:05:54.240,0:05:55.170 And that's often used. 0:05:55.170,0:05:55.810 Not always. 0:05:55.810,0:05:57.210 Sometimes you'll[br]see other units. 0:05:57.210,0:05:59.900 But I'm going to[br]use 100 grams here. 0:05:59.900,0:06:03.140 So let's now think about[br]this entire scenario 0:06:03.140,0:06:04.980 with the new numbers--[br]2 liters a minute 0:06:04.980,0:06:07.716 and 3 liters a minute--[br]in terms of perfusion. 0:06:07.716,0:06:08.590 What would that mean? 0:06:08.590,0:06:12.510 Well, let's say I[br]weigh out my two lungs. 0:06:12.510,0:06:15.580 And here I only have an upper[br]lobe on my left side left. 0:06:15.580,0:06:20.950 So let's say that[br]weighs half a kilogram. 0:06:20.950,0:06:23.700 And let's say, on the right[br]side, I've got 1 kilogram. 0:06:23.700,0:06:25.600 Let's say this is 1 kilogram. 0:06:25.600,0:06:27.930 These are the weights[br]of my two sides. 0:06:27.930,0:06:31.400 And to figure out perfusion,[br]then all you really are doing 0:06:31.400,0:06:34.370 is taking the flow-- because[br]remember, this whole chunk, 0:06:34.370,0:06:36.780 this whole part right[br]here is just flow-- 0:06:36.780,0:06:39.140 and dividing it by[br]the amount of tissue. 0:06:39.140,0:06:41.460 So I could figure out[br]perfusion pretty easily. 0:06:41.460,0:06:42.240 I could say, OK. 0:06:42.240,0:06:44.970 Well, on the right side--[br]let's do right side first-- 0:06:44.970,0:06:48.160 I've got 3 liters a minute. 0:06:48.160,0:06:51.120 I'm going to write that[br]as 3,000 milliliters, 0:06:51.120,0:06:53.750 just to make it a[br]little easier to see. 0:06:53.750,0:06:57.700 3,000 milliliters per[br]minute divided by-- I 0:06:57.700,0:07:02.290 said 1 kilo, which is[br]the same as 1,000 grams. 0:07:02.290,0:07:03.810 So what does that[br]turn out to be? 0:07:03.810,0:07:06.720 If I'm going to use 100 grams[br]as my denominator, I could say, 0:07:06.720,0:07:09.600 well, that's-- let's[br]see, 0s cancel. 0:07:09.600,0:07:16.940 So I've got 300[br]milliliters per minute 0:07:16.940,0:07:21.800 per 100 grams of lung tissue. 0:07:21.800,0:07:23.491 And so this is for[br]the right side. 0:07:23.491,0:07:25.490 And I could do the same[br]thing for the left side. 0:07:25.490,0:07:27.740 I could say, well, what would[br]it be for the left side? 0:07:27.740,0:07:32.570 It would be-- I've[br]got 2,000 milliliters. 0:07:32.570,0:07:33.960 We said 2 liters. 0:07:33.960,0:07:37.720 And of course, the 2 and 3 I[br]was just kind of estimating. 0:07:37.720,0:07:40.770 But we'd have to[br]actually measure 0:07:40.770,0:07:43.290 to see what the actual flow is. 0:07:43.290,0:07:45.480 But here I've got 500 grams. 0:07:45.480,0:07:51.160 And so that works out[br]to 400 milliliters 0:07:51.160,0:07:55.792 per minute per 100 grams. 0:07:55.792,0:07:58.250 So what I wanted to show you[br]is an interesting thing, which 0:07:58.250,0:08:00.900 is that you can actually[br]have, on the one side-- 0:08:00.900,0:08:03.240 if I said which side,[br]the right or the left, 0:08:03.240,0:08:07.910 after my surgery, which[br]side has more blood flow? 0:08:07.910,0:08:10.450 Well, then, this side[br]has more blood flow. 0:08:10.450,0:08:13.640 The right side has more flow. 0:08:13.640,0:08:18.339 But if I said which[br]one has more perfusion, 0:08:18.339,0:08:19.880 well, it turns out[br]that actually that 0:08:19.880,0:08:22.940 left upper lobe is actually[br]getting more perfusion. 0:08:22.940,0:08:25.590 So just because one[br]side has more flow 0:08:25.590,0:08:27.885 doesn't necessarily mean[br]that it has more perfusion. 0:08:27.885,0:08:29.510 Oftentimes that is[br]the case because you 0:08:29.510,0:08:32.070 can see how closely flow[br]and perfusion are related. 0:08:32.070,0:08:35.159 But it just depends[br]on exactly what 0:08:35.159,0:08:37.760 the weight is for the tissue. 0:08:37.760,0:08:39.299 Kind of a classic[br]example of this 0:08:39.299,0:08:42.330 I'm going to write out over here[br]that you might hear people talk 0:08:42.330,0:08:45.000 about sometimes is-- if[br]you say this side is high 0:08:45.000,0:08:48.550 and this side is low-- let's[br]do flow and perfusion-- 0:08:48.550,0:08:50.649 they'll say, well,[br]if you have flow 0:08:50.649,0:08:52.690 and you're trying to talk[br]about different organs, 0:08:52.690,0:08:55.800 one of the organs with the[br]highest flow in the body 0:08:55.800,0:08:57.390 would actually be your liver. 0:08:57.390,0:08:59.380 This is, let's say, your liver. 0:08:59.380,0:09:00.900 This is your liver. 0:09:00.900,0:09:03.600 And then, with a little[br]bit less blood flow 0:09:03.600,0:09:06.230 would be your kidneys. 0:09:06.230,0:09:09.290 This would be your[br]kidneys, let's say. 0:09:09.290,0:09:10.730 I'll write K for kidney. 0:09:10.730,0:09:12.355 Or actually, I guess[br]I'll spell it out. 0:09:12.355,0:09:13.410 I have enough space. 0:09:13.410,0:09:16.420 And then, something[br]that has almost no flow 0:09:16.420,0:09:19.720 relative to the other[br]two would be bones. 0:09:19.720,0:09:21.830 And actually, compared[br]to this, if you 0:09:21.830,0:09:25.300 were to now talk[br]about perfusion, 0:09:25.300,0:09:27.160 it would actually looks[br]slightly different. 0:09:27.160,0:09:31.010 So for perfusion-- using[br]these same three organs-- 0:09:31.010,0:09:33.690 if I was to kind of rank[br]them based on which one gets 0:09:33.690,0:09:36.390 the most perfusion[br]or blood perfusion, 0:09:36.390,0:09:38.110 the kidney actually[br]does the best. 0:09:38.110,0:09:41.392 So here you have to take a[br]certain amount of tissue. 0:09:41.392,0:09:42.850 And it's got to be[br]the same amount. 0:09:42.850,0:09:45.400 So I'm just imagining if I[br]took a little chunk of kidney 0:09:45.400,0:09:46.420 tissue. 0:09:46.420,0:09:47.795 And if I did the[br]exact same thing 0:09:47.795,0:09:50.830 and I took a little[br]chunk of liver tissue. 0:09:50.830,0:09:52.330 And this is kind[br]of the way to think 0:09:52.330,0:09:54.496 about it is that, if you[br]want to balance things out, 0:09:54.496,0:09:56.720 you've got to take the[br]exact same amount of tissue. 0:09:56.720,0:09:59.700 In this case, it would[br]be 100 grams, let's say. 0:09:59.700,0:10:02.497 Maybe these boxes are[br]100 grams of tissue. 0:10:02.497,0:10:03.830 It would be something like this. 0:10:03.830,0:10:05.120 And this would be the bone. 0:10:05.120,0:10:08.380 So the liver ends up[br]not doing as well. 0:10:08.380,0:10:11.280 It gets a little[br]bit less perfusion 0:10:11.280,0:10:13.300 in terms of 100 grams. 0:10:13.300,0:10:15.100 The kidney does a[br]little bit better 0:10:15.100,0:10:16.410 when it comes to perfusion. 0:10:16.410,0:10:18.184 And the bones-- the[br]sad, little bones-- 0:10:18.184,0:10:19.850 they actually don't[br]get much blood flow. 0:10:19.850,0:10:23.130 And even if you do it[br]by 100 grams of tissue, 0:10:23.130,0:10:25.609 they actually don't get[br]much perfusion either. 0:10:25.609,0:10:27.650 So this is kind of another[br]way to think about it, 0:10:27.650,0:10:29.066 and you might hear[br]these examples. 0:10:29.066,0:10:31.550 So I wanted to give[br]them to you here.