Given the difficulty of diagnosing early-stage pulmonary arterial hypertension (PAH) due to the lack of signs and\nsymptoms, and the risk of an open lung biopsy, the precise pathological features of presymptomatic stage lung\ntissue remain unknown. It has been suggested that the maximum elevation of the mean pulmonary arterial pressure\n(Ppa) is achieved during the early symptomatic stage, indicating that the elevation of the mean Ppa is primarily driven\nby the pulmonary vascular tone and/or some degree of pulmonary vascular remodeling completed during this stage.\nRecently, the examination of a rat model of severe PAH suggested that the severe PAH may be primarily determined\nby the presence of intimal lesions and/or the vascular tone in the early stage. Human data seem to indicate\nthat intimal lesions are essential for the severely increased pulmonary arterial blood pressure in the late stage\nof the disease.\nHowever, many questions remain. For instance, how does the pulmonary hemodynamics change during the\ncourse of the disease, and what drives the development of severe PAH? Although it is generally acknowledged\nthat both pulmonary vascular remodeling and the vascular tone are important determinants of an elevated pulmonary\narterial pressure, which is the root cause of the time-dependent progression of the disease? Here we review the\nrecent histopathological concepts of PAH with respect to the progression of the lung vascular disease.
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