[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:01.96,Default,,0000,0000,0000,,PRESENTER: Hello, and\Nwelcome to Byte Size Med.
Dialogue: 0,0:00:01.96,0:00:05.03,Default,,0000,0000,0000,,This video is on\Nthe breathing cycle.
Dialogue: 0,0:00:05.03,0:00:07.07,Default,,0000,0000,0000,,The breathing cycle\Ninvolves air going
Dialogue: 0,0:00:07.07,0:00:09.32,Default,,0000,0000,0000,,into the lungs during\Ninspiration and air
Dialogue: 0,0:00:09.32,0:00:11.66,Default,,0000,0000,0000,,leaving the lungs\Nduring expiration.
Dialogue: 0,0:00:11.66,0:00:15.45,Default,,0000,0000,0000,,During this cycle, there are\Npressure and volume changes.
Dialogue: 0,0:00:15.45,0:00:18.50,Default,,0000,0000,0000,,In this video, we're going to\Nput pressure and volume together
Dialogue: 0,0:00:18.50,0:00:22.31,Default,,0000,0000,0000,,and see what happens during\None cycle of respiration.
Dialogue: 0,0:00:22.31,0:00:23.97,Default,,0000,0000,0000,,There are three phases.
Dialogue: 0,0:00:23.97,0:00:27.59,Default,,0000,0000,0000,,There's rest where there's\Nno airflow, inspiration
Dialogue: 0,0:00:27.59,0:00:32.70,Default,,0000,0000,0000,,where air enters, and\Nexpiration where air leaves.
Dialogue: 0,0:00:32.70,0:00:34.49,Default,,0000,0000,0000,,Now, we're going to\Nuse this schematic lung
Dialogue: 0,0:00:34.49,0:00:36.23,Default,,0000,0000,0000,,to try and understand it.
Dialogue: 0,0:00:36.23,0:00:38.93,Default,,0000,0000,0000,,The lungs are surrounded\Nby pleural cavities
Dialogue: 0,0:00:38.93,0:00:40.94,Default,,0000,0000,0000,,lined by pleura.
Dialogue: 0,0:00:40.94,0:00:42.98,Default,,0000,0000,0000,,There's an inner\Nvisceral layer, which
Dialogue: 0,0:00:42.98,0:00:44.61,Default,,0000,0000,0000,,is sort of attached\Nto the lungs,
Dialogue: 0,0:00:44.61,0:00:48.21,Default,,0000,0000,0000,,and the outer parietal layer,\Nwhich is towards the chest wall.
Dialogue: 0,0:00:48.21,0:00:51.60,Default,,0000,0000,0000,,Now, the pleural cavity\Nis filled with fluid.
Dialogue: 0,0:00:51.60,0:00:54.74,Default,,0000,0000,0000,,This fluid acts like a lubricant\Nand helps the lungs move
Dialogue: 0,0:00:54.74,0:00:56.66,Default,,0000,0000,0000,,during respiration.
Dialogue: 0,0:00:56.66,0:00:58.89,Default,,0000,0000,0000,,The pressure in\Nthe pleural space,
Dialogue: 0,0:00:58.89,0:01:02.53,Default,,0000,0000,0000,,that's the intrapleural\Npressure, or just simply
Dialogue: 0,0:01:02.53,0:01:04.63,Default,,0000,0000,0000,,pleural pressure.
Dialogue: 0,0:01:04.63,0:01:07.30,Default,,0000,0000,0000,,Now, the air is going to\Nenter through the airways
Dialogue: 0,0:01:07.30,0:01:08.72,Default,,0000,0000,0000,,into the alveoli.
Dialogue: 0,0:01:08.72,0:01:12.92,Default,,0000,0000,0000,,The pressure in the alveoli\Nis the alveolar pressure.
Dialogue: 0,0:01:12.92,0:01:16.12,Default,,0000,0000,0000,,So we've got the pleural\Npressure and the alveolar
Dialogue: 0,0:01:16.12,0:01:17.23,Default,,0000,0000,0000,,pressure.
Dialogue: 0,0:01:17.23,0:01:20.44,Default,,0000,0000,0000,,Now, the difference between\Nthese two pressures--
Dialogue: 0,0:01:20.44,0:01:23.12,Default,,0000,0000,0000,,that is the pressure\Nacross the organ.
Dialogue: 0,0:01:23.12,0:01:25.61,Default,,0000,0000,0000,,That's the transmural pressure.
Dialogue: 0,0:01:25.61,0:01:27.31,Default,,0000,0000,0000,,Since we're talking\Nabout the lungs,
Dialogue: 0,0:01:27.31,0:01:29.60,Default,,0000,0000,0000,,it's the transpulmonary\Npressure.
Dialogue: 0,0:01:29.60,0:01:32.17,Default,,0000,0000,0000,,
Dialogue: 0,0:01:32.17,0:01:34.27,Default,,0000,0000,0000,,The pressures are in\Ncentimeters of water
Dialogue: 0,0:01:34.27,0:01:36.91,Default,,0000,0000,0000,,and are in relation to\Natmospheric pressure.
Dialogue: 0,0:01:36.91,0:01:40.88,Default,,0000,0000,0000,,To understand it, we consider\Natmospheric pressure to be 0.
Dialogue: 0,0:01:40.88,0:01:42.68,Default,,0000,0000,0000,,So that's our\Nreference pressure.
Dialogue: 0,0:01:42.68,0:01:46.06,Default,,0000,0000,0000,,Air moves along a pressure\Ngradient from high pressure
Dialogue: 0,0:01:46.06,0:01:47.36,Default,,0000,0000,0000,,to low pressure.
Dialogue: 0,0:01:47.36,0:01:49.42,Default,,0000,0000,0000,,So that's what drives\Nthe air to move
Dialogue: 0,0:01:49.42,0:01:53.53,Default,,0000,0000,0000,,between the lungs\Nand the atmosphere.
Dialogue: 0,0:01:53.53,0:01:55.46,Default,,0000,0000,0000,,First, let's look\Nat the volumes.
Dialogue: 0,0:01:55.46,0:01:57.37,Default,,0000,0000,0000,,There are four lung volumes--
Dialogue: 0,0:01:57.37,0:02:00.88,Default,,0000,0000,0000,,the inspiratory reserve\Nvolume, the tidal volume,
Dialogue: 0,0:02:00.88,0:02:04.95,Default,,0000,0000,0000,,the expiratory reserve volume,\Nand the residual volume.
Dialogue: 0,0:02:04.95,0:02:07.41,Default,,0000,0000,0000,,The air that enters or\Nleaves the lungs just
Dialogue: 0,0:02:07.41,0:02:09.67,Default,,0000,0000,0000,,while quietly breathing\Nin and breathing out,
Dialogue: 0,0:02:09.67,0:02:12.90,Default,,0000,0000,0000,,that's the tidal volume, which\Nis around 500 milliliters.
Dialogue: 0,0:02:12.90,0:02:16.17,Default,,0000,0000,0000,,So what's left behind after\Nthe tidal volume leaves?
Dialogue: 0,0:02:16.17,0:02:19.81,Default,,0000,0000,0000,,The expiratory reserve volume\Nand the residual volume,
Dialogue: 0,0:02:19.81,0:02:23.29,Default,,0000,0000,0000,,which together form the\Nfunctional residual capacity,
Dialogue: 0,0:02:23.29,0:02:24.28,Default,,0000,0000,0000,,the FRC.
Dialogue: 0,0:02:24.28,0:02:26.64,Default,,0000,0000,0000,,So that is the air\Nthat gets left behind
Dialogue: 0,0:02:26.64,0:02:29.13,Default,,0000,0000,0000,,after quietly\Nbreathing out, and it's
Dialogue: 0,0:02:29.13,0:02:32.50,Default,,0000,0000,0000,,the air that's in the\Nlungs in a state of rest.
Dialogue: 0,0:02:32.50,0:02:35.07,Default,,0000,0000,0000,,So at rest, the\Nvolume in the lungs
Dialogue: 0,0:02:35.07,0:02:37.63,Default,,0000,0000,0000,,is at functional\Nresidual capacity.
Dialogue: 0,0:02:37.63,0:02:42.01,Default,,0000,0000,0000,,During inspiration, 500 mL\Nof air enters the lungs,
Dialogue: 0,0:02:42.01,0:02:46.09,Default,,0000,0000,0000,,and during expiration, that\N500 mL leaves the lungs.
Dialogue: 0,0:02:46.09,0:02:51.12,Default,,0000,0000,0000,,For this to happen,\Npressures have to change.
Dialogue: 0,0:02:51.12,0:02:52.99,Default,,0000,0000,0000,,And now we're going to\Nadd in the pressures.
Dialogue: 0,0:02:52.99,0:02:54.67,Default,,0000,0000,0000,,So let's start at rest.
Dialogue: 0,0:02:54.67,0:02:57.87,Default,,0000,0000,0000,,The volume is at FRC,\Nlike I said before.
Dialogue: 0,0:02:57.87,0:03:00.47,Default,,0000,0000,0000,,The chest wall, it\Nhas a natural tendency
Dialogue: 0,0:03:00.47,0:03:03.80,Default,,0000,0000,0000,,to want to pull outwards,\Nand the lungs have a tendency
Dialogue: 0,0:03:03.80,0:03:05.85,Default,,0000,0000,0000,,to want to collapse inwards.
Dialogue: 0,0:03:05.85,0:03:10.37,Default,,0000,0000,0000,,At this point, these two forces,\Nthey balance each other out.
Dialogue: 0,0:03:10.37,0:03:12.98,Default,,0000,0000,0000,,The pressure in the\Npleural space at rest
Dialogue: 0,0:03:12.98,0:03:16.28,Default,,0000,0000,0000,,is slightly negative at\Nminus 5 centimeters of water.
Dialogue: 0,0:03:16.28,0:03:18.47,Default,,0000,0000,0000,,That keeps the lungs open.
Dialogue: 0,0:03:18.47,0:03:21.41,Default,,0000,0000,0000,,The pressure in\Nthe alveoli is 0,
Dialogue: 0,0:03:21.41,0:03:23.07,Default,,0000,0000,0000,,equal to that of the atmosphere.
Dialogue: 0,0:03:23.07,0:03:25.62,Default,,0000,0000,0000,,Remember, we consider\Nthe atmosphere to be 0,
Dialogue: 0,0:03:25.62,0:03:27.21,Default,,0000,0000,0000,,and that's our reference.
Dialogue: 0,0:03:27.21,0:03:29.04,Default,,0000,0000,0000,,So now there's no gradient.
Dialogue: 0,0:03:29.04,0:03:30.06,Default,,0000,0000,0000,,There's no airflow.
Dialogue: 0,0:03:30.06,0:03:31.92,Default,,0000,0000,0000,,And the system is\Nat equilibrium.
Dialogue: 0,0:03:31.92,0:03:33.82,Default,,0000,0000,0000,,So this is the\Nsituation at rest.
Dialogue: 0,0:03:33.82,0:03:36.74,Default,,0000,0000,0000,,
Dialogue: 0,0:03:36.74,0:03:38.87,Default,,0000,0000,0000,,Now, when inspiration\Nbegins, the diaphragm
Dialogue: 0,0:03:38.87,0:03:40.20,Default,,0000,0000,0000,,is going to contract.
Dialogue: 0,0:03:40.20,0:03:41.94,Default,,0000,0000,0000,,The lungs expand.
Dialogue: 0,0:03:41.94,0:03:45.69,Default,,0000,0000,0000,,And so the alveolar pressure\Nbecomes slightly negative.
Dialogue: 0,0:03:45.69,0:03:49.23,Default,,0000,0000,0000,,It's going to go down to\Nminus 1 centimeters of water.
Dialogue: 0,0:03:49.23,0:03:52.07,Default,,0000,0000,0000,,So now there's a gradient\Nbetween the atmosphere
Dialogue: 0,0:03:52.07,0:03:53.28,Default,,0000,0000,0000,,and the alveoli.
Dialogue: 0,0:03:53.28,0:03:56.58,Default,,0000,0000,0000,,And the alveolar pressure is\Nlower than the atmosphere.
Dialogue: 0,0:03:56.58,0:03:59.79,Default,,0000,0000,0000,,So the air is going\Nto enter the lungs.
Dialogue: 0,0:03:59.79,0:04:02.41,Default,,0000,0000,0000,,The fact that the chest\Nwall is expanding,
Dialogue: 0,0:04:02.41,0:04:05.02,Default,,0000,0000,0000,,that makes the pleural\Npressure more negative.
Dialogue: 0,0:04:05.02,0:04:07.23,Default,,0000,0000,0000,,So it goes down\Nfrom it's negative 5
Dialogue: 0,0:04:07.23,0:04:10.83,Default,,0000,0000,0000,,to minus 7.5\Ncentimeters of water.
Dialogue: 0,0:04:10.83,0:04:13.47,Default,,0000,0000,0000,,At the end of inspiration,\Nthe alveolar pressure
Dialogue: 0,0:04:13.47,0:04:14.98,Default,,0000,0000,0000,,goes back up to 0.
Dialogue: 0,0:04:14.98,0:04:18.69,Default,,0000,0000,0000,,So now 500 mL of air\Nhas entered the lungs,
Dialogue: 0,0:04:18.69,0:04:20.55,Default,,0000,0000,0000,,and the volume in\Nthe lungs would now
Dialogue: 0,0:04:20.55,0:04:23.19,Default,,0000,0000,0000,,include both the functional\Nresidual capacity
Dialogue: 0,0:04:23.19,0:04:25.89,Default,,0000,0000,0000,,and the tidal volume.
Dialogue: 0,0:04:25.89,0:04:28.29,Default,,0000,0000,0000,,Now, unlike\Ninspiration, which was
Dialogue: 0,0:04:28.29,0:04:32.53,Default,,0000,0000,0000,,active from muscles contracting,\Nexpiration is passive.
Dialogue: 0,0:04:32.53,0:04:34.98,Default,,0000,0000,0000,,It's from elastic recoil.
Dialogue: 0,0:04:34.98,0:04:37.56,Default,,0000,0000,0000,,So the alveolar\Npressure now becomes
Dialogue: 0,0:04:37.56,0:04:41.14,Default,,0000,0000,0000,,slightly positive at plus\N1 centimeters of water.
Dialogue: 0,0:04:41.14,0:04:43.75,Default,,0000,0000,0000,,Now you can see that the\Ngradient has reversed.
Dialogue: 0,0:04:43.75,0:04:46.14,Default,,0000,0000,0000,,So air is going to move\Nin the opposite direction.
Dialogue: 0,0:04:46.14,0:04:49.20,Default,,0000,0000,0000,,From high to low pressure,\Nit moves from the lungs
Dialogue: 0,0:04:49.20,0:04:50.97,Default,,0000,0000,0000,,to the atmosphere.
Dialogue: 0,0:04:50.97,0:04:52.74,Default,,0000,0000,0000,,So it leaves the\Nlungs, and what's
Dialogue: 0,0:04:52.74,0:04:55.71,Default,,0000,0000,0000,,left behind is now the\Nfunctional residual capacity
Dialogue: 0,0:04:55.71,0:04:56.67,Default,,0000,0000,0000,,again.
Dialogue: 0,0:04:56.67,0:04:59.63,Default,,0000,0000,0000,,And at the end of expiration,\Nthe pleural pressure
Dialogue: 0,0:04:59.63,0:05:02.70,Default,,0000,0000,0000,,comes back up to minus\N5 centimeters of water.
Dialogue: 0,0:05:02.70,0:05:04.61,Default,,0000,0000,0000,,So now we're at rest again.
Dialogue: 0,0:05:04.61,0:05:07.38,Default,,0000,0000,0000,,So we've completed\None breathing cycle.
Dialogue: 0,0:05:07.38,0:05:09.32,Default,,0000,0000,0000,,And the cycle is\Ngoing to repeat again.
Dialogue: 0,0:05:09.32,0:05:11.90,Default,,0000,0000,0000,,
Dialogue: 0,0:05:11.90,0:05:14.78,Default,,0000,0000,0000,,So this is rest, the\Nphase of inspiration,
Dialogue: 0,0:05:14.78,0:05:16.59,Default,,0000,0000,0000,,and the phase of expiration.
Dialogue: 0,0:05:16.59,0:05:18.33,Default,,0000,0000,0000,,What happened to the volume?
Dialogue: 0,0:05:18.33,0:05:22.22,Default,,0000,0000,0000,,The volume of air that\Nentered, or the volume change,
Dialogue: 0,0:05:22.22,0:05:25.02,Default,,0000,0000,0000,,was from 0 to 500 milliliters.
Dialogue: 0,0:05:25.02,0:05:28.20,Default,,0000,0000,0000,,And then that 500 mL left\Nand it came back to 0.
Dialogue: 0,0:05:28.20,0:05:30.69,Default,,0000,0000,0000,,We're talking about\Na volume change.
Dialogue: 0,0:05:30.69,0:05:34.10,Default,,0000,0000,0000,,The actual volume at rest was\Nthe functional residual capacity
Dialogue: 0,0:05:34.10,0:05:38.50,Default,,0000,0000,0000,,and not 0, but the change that\Nhappened, that was by 500 mL.
Dialogue: 0,0:05:38.50,0:05:41.45,Default,,0000,0000,0000,,
Dialogue: 0,0:05:41.45,0:05:44.00,Default,,0000,0000,0000,,For that 500 mL to\Nenter, what happened
Dialogue: 0,0:05:44.00,0:05:45.69,Default,,0000,0000,0000,,to the alveolar pressure?
Dialogue: 0,0:05:45.69,0:05:49.31,Default,,0000,0000,0000,,It went from 0 at\Nrest down to minus 1,
Dialogue: 0,0:05:49.31,0:05:52.52,Default,,0000,0000,0000,,came back to 0 at the\Nend of inspiration.
Dialogue: 0,0:05:52.52,0:05:56.12,Default,,0000,0000,0000,,Then for the 500 mL to\Nleave, it went to plus 1
Dialogue: 0,0:05:56.12,0:05:59.02,Default,,0000,0000,0000,,and then came back to 0 again.
Dialogue: 0,0:05:59.02,0:06:03.67,Default,,0000,0000,0000,,The pleural pressure went from\Nminus 5 at rest to minus 7.5
Dialogue: 0,0:06:03.67,0:06:06.91,Default,,0000,0000,0000,,at the end of inspiration and\Nthen came back up to minus 5
Dialogue: 0,0:06:06.91,0:06:08.14,Default,,0000,0000,0000,,again.
Dialogue: 0,0:06:08.14,0:06:11.63,Default,,0000,0000,0000,,But there's one more pressure,\Nthe transpulmonary pressure.
Dialogue: 0,0:06:11.63,0:06:15.05,Default,,0000,0000,0000,,It's the alveolar pressure\Nminus the pleural pressure.
Dialogue: 0,0:06:15.05,0:06:17.92,Default,,0000,0000,0000,,So if we take rest,\Nend of inspiration,
Dialogue: 0,0:06:17.92,0:06:20.08,Default,,0000,0000,0000,,and end of expiration,\Nat rest you
Dialogue: 0,0:06:20.08,0:06:23.09,Default,,0000,0000,0000,,can see it's 0 minus of minus 5.
Dialogue: 0,0:06:23.09,0:06:26.06,Default,,0000,0000,0000,,That's plus 5 centimeters\Nof water at rest.
Dialogue: 0,0:06:26.06,0:06:29.60,Default,,0000,0000,0000,,By the end of inspiration,\Nit's plus 7.5.
Dialogue: 0,0:06:29.60,0:06:33.14,Default,,0000,0000,0000,,And then it comes back to plus 5\Nagain at the end of expiration.
Dialogue: 0,0:06:33.14,0:06:36.17,Default,,0000,0000,0000,,So throughout the breathing\Ncycle, it's positive.
Dialogue: 0,0:06:36.17,0:06:39.76,Default,,0000,0000,0000,,As long as the transpulmonary\Npressure remains positive,
Dialogue: 0,0:06:39.76,0:06:41.86,Default,,0000,0000,0000,,the airways stay open.
Dialogue: 0,0:06:41.86,0:06:45.32,Default,,0000,0000,0000,,When the transpulmonary\Npressure becomes negative,
Dialogue: 0,0:06:45.32,0:06:47.65,Default,,0000,0000,0000,,airways collapse.
Dialogue: 0,0:06:47.65,0:06:52.33,Default,,0000,0000,0000,,And that's what happens during\None cycle of respiration.
Dialogue: 0,0:06:52.33,0:06:54.46,Default,,0000,0000,0000,,If this video helped\Nyou, give it a thumbs up,
Dialogue: 0,0:06:54.46,0:06:55.88,Default,,0000,0000,0000,,and subscribe to my channel.
Dialogue: 0,0:06:55.88,0:06:59.16,Default,,0000,0000,0000,,Thanks for watching, and\NI'll see you in the next one.