Group 1 patients are those with pulmonary arterial hypertension (PAH). This is due to increased pulmonary vascular resistance. PAH may be idiopathic, hereditary, drug-induced, or associated with other diseases.
Idiopathic pulmonary arterial hypertension (IPAH) is the most common type. It occurs sporadically.
Hereditary (or familial) PAH is often associated with a mutation in bone morphogenetic protein, receptor type 2 (BMPR2). This subtype of PAH is inherited in an autosomal dominant fashion.
Bone morphogenetic protein receptor type 2 (BMPR2) normally inhibits vascular smooth muscle proliferation. The loss-of-function mutation seen in hereditary PAH causes increased cellular proliferation thus increasing pulmonary vascular resistance.
Group 2 patients are those with left heart disease. Left heart disease can cause pulmonary hypertension due to pulmonary vessel congestion or increased pulmonary blood floow. Left heart disease includes valvular heart disease, systolic/diastolic dysfunction, and left-to-right shunts. Treatment focuses on improving comorbid conditions.
Patients are classified in group 3 if their pulmonary hypertension is due to chronic lung disease or hypoxia. Over time, hypoxic pulmonary vasoconstriction causes descruction of the vascular bed and smooth muscle hypertrophy. Since the total cross-sectional area of pulmonary capillaries decreases, pulmonary pressures increase.
Chronic obstructive pulmonary disease (COPD) is a common cause of PH.
Obstructive sleep apnea (OSA) is another cause of PH. Repetitive nocturnal oxygen desaturation results in the same hypoxic vasoconstriction as seen in COPD that over time will increase pulmonary vascular resistance.
Group 4 patients have chronic or recurrent pulmonary embolisms. The persisent obstruction of pulmonary vessels causes increased pulmonary vascular resistance.
Group 5 PH patients have multifactorial or unique etiologies such as metabolic systemic, or hematologic disease. End-stage renal disease or extraluminal compression from a mass can also result in PH.
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