How Pulmonary Hypertension is Caused?
Pulmonary hypertension is a pathological condition in which the blood pressure within the pulmonary arteries increases. The patient with pulmonary hypertension present with shortness of breath, dyspnea, fatigue, edema of lower limbs, chest pain, sometimes syncope. Pulmonary hypertension is gradually occurring diseases affecting age group between 25 to 60 years more commonly.
The exact cause of Pulmonary hypertension (PH) is still unknown but there are several risk factor associated with the disease like COPD, Sickle Cell anemia, pulmonary embolism, diseases of right Atrium, mitral valve stenosis. The Mechanism of Pulmonary Hypertension is thought to be due to inflammation of the lungs arteries.
Pathogenesis of Pulmonary Hypertension
Pulmonary Hypertension is multifactorial in Origin. It is often associated with cardiac and pulmonary abnormalities. WHO has classified pulmonary hypertension on the basis of its causes into primary and secondary PH. Primary hypertension is caused due to diseases of the pulmonary arteries while secondary pulmonary hypertension is resulted due to other non-vascular causes.
Classification of Pulmonary Hypertension
WHO group 1- Pulmonary arterial hypertension:
It is caused due to-
- Drug induced.
- Toxin induced.
- Connective tissue disorder.
- Portal hypertension.
WHO Group 1'- Pulmonary veno-occlusive diseases
- Drug and Toxic induced.
- Radiation induced.
- Connective tissue diseases.
WHO Group 1"- Persistent pulmonary hypertension of newborn.
WHO Group 2- Pulmonary Hypertension developing secondary to left heart diseases.
- Valvular heart disease.
- Congenital left/right inflow/outflow track obstruction.
- Congenital cardiac myopathies.
- Congenital pulmonary venous stenosis.
WHO Group 3- Pulmonary hypertension due to Pathology in the lungs:
- Chronic obstructive pulmonary diseases/ COPD.
- Alveolar hypo perfusion.
- Altitude sickness.
- Development abnormalities.
WHO Group 4- Chronic arterial obstruction:
- Pulmonary thromboembolic hypertension.
- Congenital pulmonary arterial stenosis.
WHO Group 5- Pulmonary Hypertension with multifactorial mechanism:
- Chronic hemolytic anemia.
- Glycogen storage disease.
- Thyroid abnormalities.
In the pathogenesis of pulmonary arterial Hypertension there is narrowing of the lumen of arteries going in and out of the lung parenchyma. This results in increased work load on the heart as heart has to pump the same amount of blood through the narrowed lumen. With the course of disease the wall of these arteries becomes harder and stiffer and thicker by the process of fibrosis. Narrowing of the lumen of these arteries is supposed to be due to cumulative effect of processes like vasoconstriction, remodeling of vessels (due to fibrosis, inflammatory mediators). With the passage of time, the arteries become stiffer and thicker due to vascular remodeling. This increases the blood pressure within the pulmonary vessels. This causes increased pressure on the right side of heart. Initially the right side of heart tried to compensate these changes by hypertrophy and increased force of contraction, but these changes fail to cope with the demand and the need of oxygen to the right atrial musculature down not met. So right sided heart failure occurs.
Pulmonary Hypertension due to left heart disease is not due to constriction or endothelial damage to pulmonary vessels. It is due to failure of the pumping action of the right side of heart which causes the pooling of blood in the pulmonary vessels and back pressure in the pulmonary circulatory system.
In Pulmonary Hypertension of lung, hypoxia due to low level of oxygen to the pulmonary vessels there is occurrence of vasoconstriction of the pulmonary vessels. When the hypoxia is extensive and involving a much larger area of the lung parenchyma, there occurs a widespread vasoconstriction of the Pulmonary vascular bed leading to increased pulmonary arterial pressure and sustained high pressure in these vessels causes thickening of the musculature of the same resulting in Sustained pulmonary Hypertension.
Increased arterial pressure in the Pulmonary vascular bed is referred to as Pulmonary Hypertension. In Pulmonary Hypertension there is pathological narrowing and/or stiffening of the pulmonary arterioles or capillaries this causes restrictive flow of blood in arteries and results in increased pulmonary pressure. Long term Pulmonary Hypertension may lead to a right sided heart failure.
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