Pulmonary Vascular Physiology Pressure and Hypertension

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Transcript - For Easy Reading!
Hello. In this video, we're going to look at pulmonary circulation and we're also going to talk about the causes of pulmonary hypertension.
So, here we have the heart and the heart has four chambers. Here we have the right side, which is composed of the right atrium and right ventricle. The right side of the heart receives deoxygenated blood from circulation. The right ventricle will then pump this blood through the pulmonary trunk, which will branch into the right pulmonary artery and the left pulmonary artery, before branching even more within the lungs. The lungs will reoxygenate the blood. This newly oxygenated blood will then return back to the heart via the left and right pulmonary vein. The pulmonary veins will return the oxygenated blood to the left atrium. The blood from the left atrium will then join with the left ventricle, before being pumped around the body. Let us now look at the lungs and see the structures responsible for reoxygenating the blood in a little bit more detail.
Here is a cluster of alveolar sacs. Now the alveoli are the ends of the respiratory tract basically. And here is one alveolus. So, you can imagine, here is the pulmonary artery coming from the right side of the heart, bringing in deoxygenated blood - in blue. The pulmonary artery will branch again and again before arriving at these terminal alveoli. The arterial is now a capillary to these alveoli. Here the carbon dioxide from the vessels is absorbed into the respiratory tract and exhaled out, while simultaneously oxygen is inhaled and reoxygenating the blood vessels. The newly oxygenated blood supply will now return to the left side of the heart via the pulmonary venules, which will eventually join with other venules to form the main pulmonary vein. Let's now zoom in and focus on one alveolus. Here is a cross-section of an alveolus, and here is the heart. Again, as we mentioned, the right side of the heart will pump deoxygenated blood through the pulmonary arteries into the lung.
The pulmonary artery will branch until it forms capillaries for each of these alveolus or alveoli in the lung. The blood is reoxygenated. This newly reoxygenated blood will then return to the heart via the pulmonary veins. It enters the left atrium of the heart before going into the left ventricle and the left ventricle will then pump this blood to the systemic circulation through the aorta. When we measure blood pressure, we are actually measuring the systemic circulation pressure really, not the pulmonary circulation pressure. The normal systemic circulation pressure or the normal blood pressure in our body is about a 120 on 80. The pulmonary circulation pressure, on the other hand, is 24 on 12. Another difference between systemic and pulmonary circulation is the response to low oxygen levels. For example, in systemic circulation, a decrease in oxygen supply will cause systemic vasodilation, and this is to increase blood flow and thus hopefully increase oxygen supply to the systemic organs.
However, in the pulmonary circulation, a decrease in oxygen, a decrease in ventilation or supply to the body, means that the pulmonary circulation will constrict. They constrict to compensate for the decrease in ventilation. There is normal blood flow, but poor ventilation. A pulmonary shunt occurs. The volume of blood in the pulmonary vessels at any one time is about one liter, of which less than 100 mills is in the pulmonary capillaries. Pulmonary capillary pressure is about 10 millimeters mercury, whereas the oncotic pressure is 25 millimeters mercury, so that an inward directed pressure gradient of about 15 millimeters mercury keeps the alveoli free of all but a thin film of fluid. When the pulmonary capillary pressure or the pulmonary arterial pressure is more than 25 millimeters mercury, pulmonary congestion and edema result, which really means pulmonary hypertension. Pulmonary hypertension or pulmonary arterial hypertension is when the pulmonary arterial pressure is above 25 millimeters mercury at rest or 30 millimeters mercury on exertion.
When there's a buildup of pressure, let's just say from edema, part of this fluid in the interstitium, the fluid can be drained via the lymphatic system back to the heart. However, oftentimes in pulmonary hypertension, the lymphatic system is not great enough to return the pulmonary vascular pressure back to homeostasis. So what causes pulmonary hypertension? So, now let's briefly talk about pulmonary hypertension and its causes. Before that, we first need to know what four values or factors can influence the pulmonary arterial pressure. These are the cardiac output; the pulmonary artery, and thus the pulmonary arterial pressure; pulmonary vascular resistance; and left atrial pressure, also known as a pulmonary venous pressure. To keep things simple: pulmonary hypertension is when your arterial pulmonary pressure is above 25 millimeters mercury at rest or 30 millimeters mercury with exertion. Now, many things affect your pulmonary arterial pressure and because of this, many things can cause pulmonary hypertension. The pressure of the pulmonary artery is equal to the cardiac output multiplied by pulmonary vascular resistance, plus left atrial pressure. So, basically, any rise in cardiac output, any rise in pulmonary vascular resistance, or any rise in left atrial pressure, will cause an increase in pulmonary arterial pressure, which means will cause pulmonary hypertension.
So let's draw out what each of these mean. Here is the lung which is the alveoli, and here is the right side of the heart which is pumping into the lung deoxygenated blood through the pulmonary artery. The pressure of the pulmonary artery here is the pressure in the pulmonary artery, which again, when high will really tell us if you have pulmonary hypertension or not. The pulmonary artery will branch and form capillaries, supplying each alveoli. Between the alveoli and the capillaries is this space called the interstitium. Cardiac output is the amount of blood pumped by the heart in one minute. Pulmonary vascular resistance is a pressure in the pulmonary circulation. Then the capillaries will form the pulmonary veins and will return oxygenated blood to the left side of the heart. The other important factor affecting pulmonary artery pressure is the left atrium, here where the pulmonary veins drain into. And of course the left side of the heart will pump oxygenated blood to the systemic circulation. This is also your cardiac output from the other side. Now to help diagnose pulmonary hypertension, you really perform a right-sided cardiac catheterization, which if the value is above 25 millimeters mercury at rest, it is diagnostic of pulmonary hypertension. You can also use a transthoracic echocardiogram to help diagnose pulmonary hypertension. The pulmonary wedge pressure can help assess the left side of the heart.
Causes of pulmonary hypertension from the left heart include, mitral valve disease which will increase your left atrial pressure; left-sided heart failure, which will also increase your left atrial pressure, and so increase pulmonary artery pressure, which will then lead to pulmonary hypertension. Hypoxaemia, due to different lung diseases can also cause pulmonary hypertension. These include COPD, interstitial lung disease, obstructive sleep apnea, which all will increase pulmonary vascular resistance. Pulmonary embolism is another important cause. This is where you get occlusion of the pulmonary artery branches and/or capillaries. This will increase pulmonary vascular resistance and so increase pulmonary artery pressure and so will lead to pulmonary hypertension. There are also miscellaneous causes such as granulomas as a result of sarcoidosis or connective tissue disease. They essentially can cause obstruction and reduce profusion to the lungs and so as a consequence, they will sort of increase the pulmonary artery pressure causing pulmonary hypertension.
So, I hope this video on pulmonary circulation and just an overview of the causes of pulmonary hypertension made sense. Hope you enjoyed it. Thank you.
NAssink Transcriptions
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[@hemamalini2003]

Thank you

[@kureha8715]

Thank u very much

[@nicoletta.o]

Congratulations for such a great tutorial ! One addition as others mentioned as well, The definition of pulmonary hypertension is now a *mean* pulmonary artery pressure (mPAP) >20mmHg. Only right heart cath can officially define the presence of pulmonary hypertension. Echo is just used for diagnostic cues. Also, pulmonary arterial hypertension (PAH) is not the same as pulmonary hypertension (PH). PAH is a subtype of PH, classified as Group 1 PH.

[@leandrolima8172]

Congratulations, Mr. Armando Hasudungan, your work in clarifying key points of pathophysiology has brought an enormous contribution to your medical colleagues here in Brazil.

[@mehmet.f]

That was the one of the most successful video about lung physiology! Thank you👏👏

[@SteveHazel]

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thank you.

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Beautiful video. My future patients and I are very appreciative.

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Ur videos are really helpful 👍👍
Waiting for many more lectures...

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Great animation, integration of drawing and commentary: plain, not overly simplistic, easy to folllow

[@hulyaguller4123]

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[@drkamleshdarji]

Such an awesome work..

[@mikefoster3582]

When our author states definition of PHTN, he meant MEAN pressure of 25mmHg....not a peak pressure. Plus, since this video was made, the World Symposium of PHTN 2018 has now adjusted the cutoff to be more likely to be a mean pressure >20mmHg. Always look for the date on videos and articles online as sometimes the information has changed.
Thx for the video. I'm a fan.

[@FedeB932]

Hello, according to the 6th symposium of pulmonary hypertension the new limits are 20 mmHg, since the last 25 mmHg was based on the supposition that the normal pulmonary artery pressure was 25 mmHg, now it is proven that most of the healthy individuals have a mPAP around 14 +/- 3,3 mmHg, having a upper limit at 20 mmHg.

[@sultanaguy08]

Federiking source?

[@paulnewman1061]

@@sultanaguy08 This is the definition based on the recommendations made at the 6th World Symposium on Pulmonary Hypertension in 2019. The US standards will almost certainly follow shortly.
www.ncbi.nlm.nih.gov/pmc/articles/PMC6351336/
www.ncbi.nlm.nih.gov/pmc/articles/PMC6351332/

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Easily got the point
Becos u taught it in diagrammatic
Thank you sir

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Gram negative and gram positive rods

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[@jakepfannenstiel7703]

Great Video. I have a child that is about to *maybe* have her fontan, single ventricle surgery in a couple weeks. I'm trying to explain to my father why any respiratory illness is detrimental to the fontan circulation. QUESTION: Does respiratory illness increase PVR - leading to increased pulmonary arterial pressures? Thanks! (edit: by respiratory illness I mean RSV or seasonal upper respiratory infections)

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[@Be1smaht]

Question: If you have ARDS your wedge pressure is going up and that affects the pulmonary arteriole pressure so why is your PAP not changing inn ARDS?

[@user-lr6xz7pe1c]

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[@linettie71]

I recently got diagnosed with pah
My lung pressure was 80
Can this be fatal

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[@subsdasari]

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