Pulmonary hypertension

Definitions & Key takeaways

Pulmonary hypertension (PH) is a condition characterized by an increase in blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries. It can be due to left heart disease, chronic lung disease, or other conditions that specifically cause pulmonary arterial hypertension. Regardless of the cause, it can complicate right-sided heart failure, what's referred to as cor pulmonale. Symptoms of PH include shortness of breath, dizziness, fainting, and leg swelling. Treatment focuses on the underlying cause and may include supplemental oxygen, and medications like endothelin receptor antagonists and prostacyclins.

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INTRODUCTION0:00–0:14

Pulmonary hypertension refers to increased blood pressure in the pulmonary circulation, more specifically a mean pulmonary arterial pressure that is greater than 25 mmHg.
The pulmonary circulation starts with the right ventricle. From there - blood is pumped into the large pulmonary trunk, which splits to form the two pulmonary arteries – one for each lung.

PHYSIOLOGY0:14–1:16

The pulmonary arteries divide into smaller arteries known as pulmonary arterioles and then eventually into pulmonary capillaries which surround the alveoli - which are the millions of tiny air sacs where gas exchange happens.
At that point, oxygen enters the blood and carbon dioxide enters the alveoli. The pulmonary capillaries drain into small veins that join to form the two pulmonary veins exiting each lung, and these pulmonary veins complete the circuit by delivering oxygen-rich blood into the left atrium.
The blood pressure in the pulmonary circulation is normally much lower than the systemic blood pressure. The normal pulmonary artery pressure is about 25/10 mmHg with a mean arterial pressure of 15 mmHg.

PATHOLOGY1:16–2:50

Pulmonary hypertension most commonly develops as a result of left heart disease. Here the pulmonary blood vessels are normal and undamaged, but the left side of the heart is unable to pump efficiently – for example because of heart failure or valvular dysfunction.
This causes a backup of blood in the pulmonary veins and capillary beds, which can increase the pressure in the pulmonary artery.
Another cause of pulmonary hypertension is chronic lung disease, which typically causes hypoxic vasoconstriction. That’s when some area in the lung is diseased and is unable to deliver oxygen to the blood.
To help adapt to this, the pulmonary arterioles in that area, start to constrict - and this effectively shuttles blood away from those damaged areas of the lung, and towards healthy lung tissue.
But if the problem is widespread, like in individuals with emphysema, the mechanism can backfire. That’s because there’s widespread vasoconstriction of pulmonary arterioles, and that increases pulmonary vascular resistance in general.
Increased resistance makes it hard for the right ventricle to pump out blood – a bit like pushing water through a narrow pipe as opposed to a wider one.
So to make the same amount of blood flow through the pulmonary arterioles, the right side of the heart has to generate increased pressure and that results in pulmonary hypertension.

Chronic thromboembolic pulmonary hypertension2:50–3:34

Another cause of pulmonary hypertension is chronic thromboembolic pulmonary hypertension - which is when there are recurrent blood clots in their pulmonary vessels.
The clots can form because of an underlying clotting disorder, and can embolize or travel to the lungs. The clots can block pulmonary vessels which increases the resistance to blood flow, and they can also endothelial cells in the vessels to release histamine and serotonin, which constricts the pulmonary arterioles.
Together the blockage and the narrowing of the blood vessels causes a rise in the pulmonary blood pressure. One type of pulmonary hypertension is pulmonary arterial hypertension which is when there’s elevated pressure in the pulmonary arterioles, but the pressure in their capillaries and pulmonary veins is still normal.

PULMONARY ARTERIAL HYPERTENSION3:34–5:05

Some congenital heart defects can cause pulmonary arterial hypertension. A long-standing left-to-right cardiac shunt caused by a ventricular septal defect, atrial septal defect, or less commonly, a patent ductus arteriosus can result in pulmonary hypertension and eventual reversal to a right-to-left shunt, which is called Eisenmenger’s syndrome.
Pulmonary arterial hypertension can also be seen in connective tissue disorders like lupus, infections like HIV, thyroid disorders, and inherited genetic mutations.
In these situations, the process begins with damage to the endothelial cells lining the pulmonary arteries. Once that happens, the damaged endothelial cells release chemicals like endothelin-1, serotonin, and thromboxane.
These chemicals make the pulmonary arterioles constrict and cause hypertrophy of the smooth muscle surrounding them. The damaged endothelial cells also produce less nitric oxide and prostacyclin; which have the opposite effect - they make the pulmonary arterioles dilate and inhibit smooth muscle hypertrophy.

COMPLICATIONS5:05–6:20

Regardless of the cause, once there’s pulmonary hypertension, it has important consequences on the lungs and the heart. Fluid can start to squeeze out of the blood vessels in the lungs and can get into the interstitial space.
The presence of excess fluid in the pulmonary interstitium is called pulmonary edema, and it can make it more difficult for gas exchange to happen.
Pulmonary hypertension also makes it a lot harder for the right ventricle to pump blood and over time it hypertrophies. This helps in the beginning, but eventually the muscles of the right ventricle get so bulky that their oxygen demand exceeds the oxygen supply and it can lead to right-sided heart failure.
When chronic lung disease causes right-sided heart failure, it’s called cor pulmonale. Right-sided heart failure causes blood to get backed up in the venous system.
And this leads to elevated jugular venous pressure, fluid buildup in the liver - causing hepatomegaly, and fluid buildup in the legs causing edema.
Also, right-sided heart failure means that the left ventricle receives less blood, and to compensate for that it has to pump harder and faster.

SYMPTOMS6:20–6:45

Pulmonary hypertension can lead to severe shortness of breath. When pulmonary hypertension is caused by left-sided heart failure, there can also be orthopnea which is when the shortness of breath is worse while lying flat.
That happens because lying flat pulls more blood back from the veins into the heart, and extra blood only increases the hydrostatic pressure in pulmonary capillaries.

DIAGNOSIS6:45–7:03

The diagnosis of pulmonary hypertension is usually made with an echocardiogram that shows evidence of increased pressure in the pulmonary arteries and right ventricle.
Follow up tests can be done to identify the underlying cause, for example spirometry can be done to look for chronic lung disease.

TREATMENT7:03–7:27

Treatment for pulmonary hypertension typically involves giving supplemental oxygen. Other treatments are dependent on the underlying cause - if the cause is cardiogenic in nature, medications aimed at boosting the heart’s performance or lowering the blood pressure can be helpful.
In people with pulmonary arterial hypertension, medications like endothelin receptor antagonists and prostacyclins can be given.

Review7:27–8:00

Alright, as a quick recap, in pulmonary hypertension the mean pulmonary arterial pressure is greater than 25 mm Hg. It can be due to left heart disease, chronic lung disease, or conditions that specifically cause pulmonary arterial hypertension.
Regardless of the cause, it can lead to right-sided heart failure which causes physical findings like elevated jugular venous pressure, hepatomegaly, and edema in the legs.