0:00:02.420,0:00:04.810 I want to talk a little bit[br]about the idea of pressure 0:00:04.810,0:00:05.630 and volume. 0:00:05.630,0:00:07.560 And we're actually[br]a clear up some 0:00:07.560,0:00:10.660 misconceptions I think[br]I may have caused. 0:00:10.660,0:00:12.064 I apologize for them. 0:00:12.064,0:00:13.730 But I think this is[br]a good chance for us 0:00:13.730,0:00:15.870 to reflect on the things[br]that we've learned 0:00:15.870,0:00:18.290 and also build up a[br]couple of new ideas. 0:00:18.290,0:00:22.980 So let's draw volume going[br]that way and pressure going up. 0:00:22.980,0:00:25.510 And one of things I[br]want to start with 0:00:25.510,0:00:30.190 was the end systolic[br]pressure volume relationship. 0:00:30.190,0:00:31.780 We drew it something like this. 0:00:31.780,0:00:34.140 So we said this is[br]the relationship 0:00:34.140,0:00:36.740 at the end of systole[br]between the two, 0:00:36.740,0:00:39.070 between pressure and volume. 0:00:39.070,0:00:41.990 And one thing that I wanted[br]to bring up immediately 0:00:41.990,0:00:44.780 was the idea of[br]increasing volume. 0:00:44.780,0:00:48.672 So as I go up to this yellow[br]line, I'm increasing volume. 0:00:48.672,0:00:51.130 And sometimes the way I've[br]drawn that-- actually maybe I'll 0:00:51.130,0:00:54.060 make a little bit of[br]space on this canvas. 0:00:54.060,0:00:56.580 And sometimes the way I[br]draw an increase in volume 0:00:56.580,0:00:58.844 can be a little bit misleading. 0:00:58.844,0:01:00.510 So I've drawn, for[br]example, in the past, 0:01:00.510,0:01:03.450 I've drawn a left[br]ventricle like this. 0:01:03.450,0:01:06.550 And I said well as blood[br]goes into my left ventricle, 0:01:06.550,0:01:08.090 it basically does this. 0:01:08.090,0:01:10.800 You have more and more[br]blood filling up the heart. 0:01:10.800,0:01:13.590 And I've drawn this[br]sort of a picture, 0:01:13.590,0:01:16.210 and it really does tell[br]you about a couple things. 0:01:16.210,0:01:19.580 It tells you that you[br]have filling happening. 0:01:19.580,0:01:21.270 And that part, I'm OK with. 0:01:21.270,0:01:22.720 But the part that[br]I'm not OK with 0:01:22.720,0:01:24.390 is the idea that[br]it basically seems 0:01:24.390,0:01:26.710 like you have a fixed volume. 0:01:26.710,0:01:30.820 It looks like a fixed[br]volume on the heart, 0:01:30.820,0:01:32.360 or the left ventricle anyway. 0:01:32.360,0:01:34.130 And it almost makes[br]it look like you're 0:01:34.130,0:01:36.150 filling up a glass of water. 0:01:36.150,0:01:39.660 Basically, that's kind of[br]what it looks like a glass. 0:01:39.660,0:01:43.400 And really the correct way to[br]think about left ventricular 0:01:43.400,0:01:46.200 filling is a little[br]bit more like this. 0:01:46.200,0:01:49.460 You should be thinking of[br]it more along the lines 0:01:49.460,0:01:52.160 of a picture like this[br]where you basically 0:01:52.160,0:01:56.940 have a smaller volumed the[br]left ventricle filling up 0:01:56.940,0:01:58.310 with blood. 0:01:58.310,0:02:01.590 And over time it kind[br]of feels in completely. 0:02:01.590,0:02:03.302 So it starts out like that. 0:02:03.302,0:02:05.510 And then you add more blood[br]and it becomes like that. 0:02:05.510,0:02:07.660 And then you finally[br]fill it up like that. 0:02:07.660,0:02:09.990 So that would be the[br]more accurate way 0:02:09.990,0:02:12.132 of showing what's going[br]on in the left ventricle. 0:02:12.132,0:02:13.590 And, of course,[br]all three of these, 0:02:13.590,0:02:17.000 then, are the left ventricle[br]at different points in time. 0:02:17.000,0:02:21.320 So this second picture also[br]tells you about filling, 0:02:21.320,0:02:23.930 so you get the idea that[br]blood is filling in the heart. 0:02:23.930,0:02:26.240 But it does a better[br]job of showing you 0:02:26.240,0:02:29.030 that the volume changes. 0:02:29.030,0:02:33.900 The volume of the left ventricle[br]changes, so it's not fixed. 0:02:33.900,0:02:34.740 And that's correct. 0:02:34.740,0:02:36.790 This is the better[br]way of looking at it. 0:02:36.790,0:02:39.410 And kind of an analogy[br]might be a balloon, 0:02:39.410,0:02:43.420 you might think of a balloon[br]for this filling process. 0:02:43.420,0:02:47.560 So I want to be very clear[br]that the left ventricle is not 0:02:47.560,0:02:48.850 like a glass. 0:02:48.850,0:02:50.340 It's like a balloon. 0:02:50.340,0:02:52.610 And that it's not[br]a fixed volume. 0:02:52.610,0:02:54.250 It actually changes. 0:02:54.250,0:02:56.750 So this is probably the more[br]accurate way of thinking about. 0:02:56.750,0:03:00.280 And I apologize for doing[br]this sort of a drawing. 0:03:00.280,0:03:02.190 Truthfully, I didn't[br]mean to confuse anyone, 0:03:02.190,0:03:04.790 but I just want to[br]demonstrate filling. 0:03:04.790,0:03:07.940 And I probably just do it[br]in a quick and hurried way. 0:03:07.940,0:03:09.650 And so I want to[br]clarify that point now. 0:03:09.650,0:03:11.440 So this is what it[br]would look like. 0:03:11.440,0:03:13.330 And actually I could[br]take this a step further 0:03:13.330,0:03:16.120 and say well what[br]if I was to do this? 0:03:16.120,0:03:19.890 What if I was to take a[br]cross section like that, 0:03:19.890,0:03:23.670 cut it with a blade at[br]these three points in time? 0:03:23.670,0:03:25.420 Wouldn't you agree[br]that you would actually 0:03:25.420,0:03:29.230 get an interesting cross[br]section view of it, 0:03:29.230,0:03:31.050 if I was to take[br]it like that and I 0:03:31.050,0:03:33.530 was to erase these top bits out. 0:03:33.530,0:03:35.840 And you were to now[br]look down at the heart, 0:03:35.840,0:03:40.120 you'd basically see kind[br]of an interesting view. 0:03:40.120,0:03:42.660 And I'll actually try to[br]draw that view out for you. 0:03:42.660,0:03:45.160 And it's helpful actually[br]to do it that way. 0:03:45.160,0:03:47.960 And I'll tell you why So[br]this one would basically 0:03:47.960,0:03:50.300 look like this. 0:03:50.300,0:03:54.160 And this one would[br]look like this. 0:03:54.160,0:03:55.900 And this one might[br]look much larger 0:03:55.900,0:03:57.690 than the other two[br]something like this. 0:03:57.690,0:03:59.986 And again this is just[br]looking at a cross section, 0:03:59.986,0:04:01.360 so it's nothing[br]different at all. 0:04:01.360,0:04:04.290 It's just looking at[br]the cut surface of it. 0:04:04.290,0:04:07.420 And all three you'd[br]expect to be full. 0:04:07.420,0:04:10.442 So this is how I'm going[br]to use our diagram. 0:04:10.442,0:04:12.400 I'm actually going to[br]use these kinds of images 0:04:12.400,0:04:15.750 now to show what filling of[br]the left ventricle looks like, 0:04:15.750,0:04:19.160 so we can actually get[br]a real sense for it. 0:04:19.160,0:04:22.420 And you'll see an interesting[br]problem that comes up. 0:04:22.420,0:04:24.240 So let's do that. 0:04:24.240,0:04:25.760 Let's draw a couple[br]of circles here. 0:04:25.760,0:04:28.140 I'm going to draw, let's[br]say, a big circle here 0:04:28.140,0:04:30.050 where it's really large. 0:04:30.050,0:04:32.600 And then let's say the volume[br]is little small at this point. 0:04:32.600,0:04:34.190 So let's draw[br]something like that. 0:04:34.190,0:04:36.440 And the volume is[br]really, really tiny. 0:04:36.440,0:04:38.260 Let's draw something[br]like that over here. 0:04:38.260,0:04:41.410 Now if you have these three[br]volumes, you might say, 0:04:41.410,0:04:44.340 well, OK you've colored them in. 0:04:44.340,0:04:47.250 Well, one thing[br]you'd have to admit 0:04:47.250,0:04:50.990 and you'd realize pretty[br]soon is that at the bottom 0:04:50.990,0:04:53.810 of this curve, you[br]have a small volume, 0:04:53.810,0:04:57.230 but it does take a little bit[br]of blood to fill that volume in. 0:04:57.230,0:04:58.850 When you have zero[br]volume-- like right 0:04:58.850,0:05:01.060 here there's zero[br]blood in there-- 0:05:01.060,0:05:03.777 it would be an empty[br]left ventricle. 0:05:03.777,0:05:06.110 And then you'd actually add[br]a little bit of blood to it. 0:05:06.110,0:05:07.690 Let's say you fill it up. 0:05:07.690,0:05:09.420 Let's say halfway. 0:05:09.420,0:05:11.915 And now you've got a[br]half full ventricle. 0:05:11.915,0:05:14.290 And then you keep doing it[br]and you have a full ventricle. 0:05:14.290,0:05:18.670 So you basically are going[br]this way along the curve. 0:05:18.670,0:05:20.640 But until you have[br]a full ventricle, 0:05:20.640,0:05:23.020 and this is the point, until[br]you have a full ventricle 0:05:23.020,0:05:25.930 you actually don't have[br]any increase in pressure. 0:05:25.930,0:05:28.990 So previously when I drew[br]out the end systolic pressure 0:05:28.990,0:05:32.060 volume relationship[br]with that yellow line, 0:05:32.060,0:05:34.300 I drew it the way[br]you see it now. 0:05:34.300,0:05:37.584 But now I'm telling you that[br]the truth is that it actually 0:05:37.584,0:05:39.250 looks a little bit[br]different, especially 0:05:39.250,0:05:40.730 at the bottom end of this curve. 0:05:40.730,0:05:43.760 So I'm going to erase this[br]and draw it in properly. 0:05:43.760,0:05:46.050 And this is the more accurate[br]way of drawing it in. 0:05:46.050,0:05:48.495 You basically have[br]almost no-- or really no 0:05:48.495,0:05:49.370 increase in pressure. 0:05:49.370,0:05:51.520 I shouldn't say almost no. 0:05:51.520,0:05:55.200 And then once you get[br]to a full ventricle, 0:05:55.200,0:05:57.110 now you start seeing an[br]increase in pressure. 0:05:57.110,0:06:00.190 And really the way that an[br]increase in pressure looks 0:06:00.190,0:06:02.805 is that you have[br]a larger volume. 0:06:02.805,0:06:04.430 And that's what you're[br]starting to see. 0:06:04.430,0:06:06.690 You're start to see[br]that larger volume. 0:06:06.690,0:06:08.440 So even a tiny[br]bit of pressure is 0:06:08.440,0:06:10.800 going to push out on[br]the left ventricle. 0:06:10.800,0:06:13.762 And you'd actually notice that[br]because now it gets larger. 0:06:13.762,0:06:15.970 So the left ventricle actually[br]doesn't change in size 0:06:15.970,0:06:16.862 initially. 0:06:16.862,0:06:19.320 And, finally, when the pressure[br]starts actually mounting up 0:06:19.320,0:06:21.220 it starts changing in size. 0:06:21.220,0:06:23.050 So you can start[br]appreciating why 0:06:23.050,0:06:26.570 I am saying that this first[br]yellow line is incorrect. 0:06:26.570,0:06:29.500 Let me erase it completely[br]so it doesn't distract you. 0:06:29.500,0:06:32.400 So I've drawn out the end[br]systolic pressure volume 0:06:32.400,0:06:35.380 relationship, but what I[br]want to do is now add to it 0:06:35.380,0:06:38.460 our end diastolic pressure[br]volume relationship. 0:06:38.460,0:06:40.430 We know it goes[br]something like that. 0:06:40.430,0:06:42.790 And let me just label[br]it in a yellow color 0:06:42.790,0:06:45.000 just to be parallel. 0:06:45.000,0:06:49.570 So this is our end diastolic[br]pressure volume relationship. 0:06:49.570,0:06:53.681 Now if I was to say, well, what[br]would the cross section look 0:06:53.681,0:06:54.180 like? 0:06:54.180,0:06:56.450 Now let's just kind of[br]choose a couple points 0:06:56.450,0:06:57.570 to say this is this point. 0:06:57.570,0:07:00.960 This is this point like that. 0:07:00.960,0:07:05.030 And if I said what would[br]the same volume look like 0:07:05.030,0:07:07.010 on the other curve, I[br]would have to actually 0:07:07.010,0:07:09.500 just draw a line[br]down and say, OK. 0:07:09.500,0:07:12.170 This is this volume right here. 0:07:12.170,0:07:17.090 And this is this[br]volume down here. 0:07:17.090,0:07:19.950 And along those[br]points-- let me ask 0:07:19.950,0:07:23.320 you just mark it[br]on my other curve. 0:07:23.320,0:07:25.390 Those points would[br]be right there. 0:07:25.390,0:07:27.870 And I actually could just[br]similarly draw them out. 0:07:27.870,0:07:32.050 I could say well[br]this is about that. 0:07:32.050,0:07:35.120 And then the other one looks[br]maybe a little bit larger. 0:07:35.120,0:07:37.330 It would be something like that. 0:07:37.330,0:07:38.800 So these are my two curves. 0:07:38.800,0:07:39.300 Right? 0:07:39.300,0:07:41.591 Now I'm trying to make them[br]look as similar as possible 0:07:41.591,0:07:42.460 to the other ones. 0:07:42.460,0:07:43.970 And I'll fill them in. 0:07:43.970,0:07:47.260 So that's what the volumes[br]would look like at these points. 0:07:47.260,0:07:52.210 So really when you[br]look at the volumes, 0:07:52.210,0:07:53.410 they look about the same. 0:07:53.410,0:07:55.050 They don't look any[br]different at all. 0:07:55.050,0:07:57.590 And so you're left wondering[br]well how in the world is it-- 0:07:57.590,0:07:59.680 and this is actually very,[br]very confusing to think 0:07:59.680,0:08:01.830 about for folks-- how[br]in the world is it 0:08:01.830,0:08:06.390 that the pressure is so darn[br]high on the end systolic curve 0:08:06.390,0:08:09.650 whereas it's low on the end[br]diastolic curve, when they look 0:08:09.650,0:08:10.310 the same? 0:08:10.310,0:08:12.330 They don't look any different. 0:08:12.330,0:08:16.730 And to figure this out-- I think[br]one easy trick I've been using 0:08:16.730,0:08:21.460 is to just imagine what's[br]happening at the muscle level. 0:08:21.460,0:08:24.960 So the muscle cells are kind[br]of contracting and pulling 0:08:24.960,0:08:26.960 in those z-disks. 0:08:26.960,0:08:30.760 At the end of systole, we've got[br]tons of contraction happening. 0:08:30.760,0:08:33.080 And it's happening here too. 0:08:33.080,0:08:38.419 In fact, it's happening at[br]every part of this curve. 0:08:38.419,0:08:40.900 And if I was to try to simplify[br]this, instead of drawing 0:08:40.900,0:08:42.799 hundreds of arrows[br]like this, I could 0:08:42.799,0:08:44.172 do this for every single point. 0:08:44.172,0:08:45.880 So instead of drawing[br]hundreds of arrows, 0:08:45.880,0:08:47.421 you could imagine[br]that I can actually 0:08:47.421,0:08:50.060 connect all these[br]arrows like this 0:08:50.060,0:08:52.480 and that I would have a[br]similar effect if I just 0:08:52.480,0:08:53.910 drew it like this. 0:08:53.910,0:08:57.040 I could simply draw almost[br]like a rope or a band-- 0:08:57.040,0:09:01.290 imagine a band or rope[br]that's pulling and tugging 0:09:01.290,0:09:03.900 this way and this way. 0:09:03.900,0:09:06.130 If I was actually to[br]draw the band like that, 0:09:06.130,0:09:08.280 you could imagine then, it[br]would be the same effect 0:09:08.280,0:09:11.590 as the hundreds of little[br]muscles that are contracting. 0:09:11.590,0:09:13.430 And to take it a[br]step further, you 0:09:13.430,0:09:16.440 could actually even imagine[br]people yanking on that band. 0:09:16.440,0:09:18.840 So this is how I[br]picture it, just 0:09:18.840,0:09:21.300 people yanking on that band. 0:09:21.300,0:09:22.720 These are like two[br]little workers, 0:09:22.720,0:09:26.175 let's say, yanking on[br]the band and pulling it 0:09:26.175,0:09:27.520 in opposite directions. 0:09:27.520,0:09:29.645 And if they were pulling[br]it in opposite directions, 0:09:29.645,0:09:32.150 you basically have what we[br]think of as contraction. 0:09:32.150,0:09:33.860 You could have[br]little workers that 0:09:33.860,0:09:37.800 are basically yanking on all[br]these things, yanking away. 0:09:37.800,0:09:40.400 And by yanking away, what[br]you basically end up with 0:09:40.400,0:09:43.380 is a force of contraction. 0:09:43.380,0:09:46.100 So this is basically how[br]I imagine contraction, 0:09:46.100,0:09:48.620 having workers yanking in[br]two different directions. 0:09:48.620,0:09:51.120 And if you had them going[br]all around the heart 0:09:51.120,0:09:53.300 in every direction you[br]could possibly imagine, 0:09:53.300,0:09:56.270 that is what a contracted[br]ventricle is like. 0:09:56.270,0:09:59.230 And because they're[br]yanking so darn hard, 0:09:59.230,0:10:02.110 because they're pulling[br]so hard on this thing, 0:10:02.110,0:10:03.930 you basically have[br]a lot of increase 0:10:03.930,0:10:07.974 in pressure building up on the[br]inside of these ventricles. 0:10:07.974,0:10:10.390 And you really don't have that[br]happening on the other side 0:10:10.390,0:10:13.730 because on the end[br]diastolic curve-- 0:10:13.730,0:10:15.980 I guess the question is[br]do we have any workers? 0:10:15.980,0:10:16.780 Are they yanking? 0:10:16.780,0:10:18.350 And the answer is no. 0:10:18.350,0:10:20.860 The muscle cells are[br]completely relaxed. 0:10:20.860,0:10:21.940 They're relaxed. 0:10:21.940,0:10:25.390 They're just hanging[br]out and taking a nap. 0:10:25.390,0:10:29.090 You can imagine your workers[br]are really not yanking at all. 0:10:29.090,0:10:31.372 And as a result,[br]you don't have any 0:10:31.372,0:10:32.580 of that increase in pressure. 0:10:32.580,0:10:35.940 You have just a very,[br]very low pressure. 0:10:35.940,0:10:37.789 And so that's the[br]reason you can imagine 0:10:37.789,0:10:39.830 there's a difference, even[br]though the volumes are 0:10:39.830,0:10:42.450 the same, that there's a[br]difference in pressure. 0:10:42.450,0:10:45.010 So final question that plagues[br]a lot of people-- and I'm 0:10:45.010,0:10:46.843 actually going to make[br]a little bit of space 0:10:46.843,0:10:51.224 to answer it-- is so why is[br]their blood in the ventricles 0:10:51.224,0:10:52.140 at the end of systole? 0:10:52.140,0:10:54.910 I mean isn't that the point[br]where all of the blood 0:10:54.910,0:10:57.596 has exited the ventricles[br]and gone into the aorta? 0:10:57.596,0:10:59.220 Why is there any[br]blood in there anyway? 0:10:59.220,0:11:00.990 Shouldn't it be empty? 0:11:00.990,0:11:03.390 And to answer this--[br]to think about this, 0:11:03.390,0:11:05.560 we can actually draw a[br]pressure volume loop. 0:11:05.560,0:11:07.310 I'm just going to[br]draw it in purple just 0:11:07.310,0:11:09.570 to create a little[br]difference in color. 0:11:09.570,0:11:12.260 And let's say that[br]I have contraction 0:11:12.260,0:11:14.230 right here where I[br]have a big purple dot. 0:11:14.230,0:11:15.970 That's where I begin[br]my contraction. 0:11:15.970,0:11:19.740 So I'm going to draw going[br]up from there like that. 0:11:19.740,0:11:24.090 And let's say now my[br]ejection is happening. 0:11:24.090,0:11:27.860 And let's say, just rides[br]over my picture of the worker 0:11:27.860,0:11:28.560 like that. 0:11:28.560,0:11:32.500 Let me actually draw[br]one final volume piece, 0:11:32.500,0:11:34.710 and that would be what[br]is the volume here. 0:11:34.710,0:11:37.020 Because we know that the[br]volume is not changing there, 0:11:37.020,0:11:38.540 it's constant volume. 0:11:38.540,0:11:41.490 And at this point,[br]you begin ejections. 0:11:41.490,0:11:44.240 So this is all ejection. 0:11:44.240,0:11:48.370 I'm going to write ejection on[br]the curvy part of the curve. 0:11:48.370,0:11:51.950 So this is ejection[br]happening right here 0:11:51.950,0:11:53.500 over the hump like that. 0:11:53.500,0:11:56.500 So ejection is happening[br]between my two white lines. 0:11:56.500,0:12:01.500 And here in the vertical part, I[br]could draw a picture like this. 0:12:01.500,0:12:04.330 I could say, well, my[br]heart will be really full. 0:12:04.330,0:12:06.677 So it'll look-- in fact,[br]let me make it bigger. 0:12:06.677,0:12:08.510 My heart is going to[br]be really, really full. 0:12:08.510,0:12:10.970 Let me try to[br]illustrate that nicely. 0:12:10.970,0:12:13.080 So I could have[br]something like this. 0:12:13.080,0:12:15.780 I could have[br]something like that. 0:12:15.780,0:12:19.740 And if my ventricle is that[br]big, if it's that large-- let 0:12:19.740,0:12:21.780 me actually just[br]color it in now. 0:12:21.780,0:12:25.360 Then what's actually happening[br]when I have ejection? 0:12:25.360,0:12:29.250 Well, I'm going to cut[br]and paste this little guy, 0:12:29.250,0:12:33.580 and show you on the top[br]what it would look like. 0:12:33.580,0:12:36.410 So let me just drag this[br]little fella over here. 0:12:36.410,0:12:41.110 And now this, if this[br]is how I start out, 0:12:41.110,0:12:43.714 then when I eject[br]blood, you're basically 0:12:43.714,0:12:45.130 going to have[br]something like this. 0:12:45.130,0:12:49.210 You're going to have an[br]amount that goes away, 0:12:49.210,0:12:50.820 and an amount[br]that's left behind. 0:12:50.820,0:12:54.030 So the amount that's left[br]behind is, of course, the amount 0:12:54.030,0:12:57.580 that I showed you on the side. 0:12:57.580,0:12:58.880 And I'm cutting it out. 0:12:58.880,0:13:01.080 And this doughnut hole[br]shape that's left, 0:13:01.080,0:13:03.620 this is actually[br]our stroke volume. 0:13:03.620,0:13:05.810 This is our stroke volume. 0:13:05.810,0:13:08.930 So you actually do have a lot of[br]blood that goes into the aorta. 0:13:08.930,0:13:11.340 Of course, that's important. 0:13:11.340,0:13:13.690 And you have a little[br]chunk that's left. 0:13:13.690,0:13:18.220 So now you can see that at[br]the beginning of contraction, 0:13:18.220,0:13:21.450 you end up with having[br]a lot of blood here. 0:13:21.450,0:13:23.220 This is where you start. 0:13:23.220,0:13:25.210 And then you lose[br]a lot of blood. 0:13:25.210,0:13:27.070 This is our stroke[br]volume that you lose. 0:13:27.070,0:13:29.660 And then you are left with[br]a little bit of blood here. 0:13:29.660,0:13:32.540 And that's at the end of[br]systole So at the end of systole 0:13:32.540,0:13:35.510 you do have some blood left, but[br]you don't have nearly as much 0:13:35.510,0:13:38.520 as you had when[br]you began systole.