Manifestation Miracle

Orthopnea and paroxysmal nocturnal dyspnea occur when recumbency causes redistribution of blood or edema fluid, usually pooled in the lower extremities, into the venous circulation, thereby increasing thoracic blood volume and pulmonary venous pressures. Clinical signs start using the accumulation of interstitial fluid. Physical examination may reveal a third heart sound, but there's a paucity of lung findings in purely interstitial edema.

The earliest sign is frequently a chest radiograph showing an improve in the caliber of the upper lobe vessels ("pulmonary vascular redistribution") and fluid accumulating within the perivascular and peribronchial spaces ("cuffing"). It may also show Kerley B lines, which represent fluid within the interlobular septa.

Pulmonary compliance falls, and also the patient starts to breathe more rapidly and shallowly to minimize the elevated elastic function of breathing. As alveolar flooding begins, there are further decreases in lung volume and pulmonary compliance. With some alveoli filled with fluid, there's an improve within the fraction of the lung that's perfused but poorly ventilated. This shift toward reduced / ratios brings about an improve in A-a PO2, if not frank hypoxemia.