One obvious cause of a reduction in the pulmonary vascular bed is surgical resection. Even if a pneumonectomy is performed, however, the increase in pulmonary artery pressure is only 5-8 mm Hg provided that the remaining lung is normal. Much greater increases in pressure are seen if the remaining lung is affected by disease. A reduction in the area of perfused vascular bed is also produced by pulmonary embolism. This may result from thromboemboli, amniotic fluid, tumour, fat, or gas bubbles. As the normal pulmonary circulation has a low resistance, thromboembolism leads to little increase in pressure until at least 60% of the pulmonary vessels have been occluded. If, however, pulmonary hypertension is already present (for example, from previous embolisation), right heart failure may be induced by a relatively small embolus. It has been suggested that the release of serotonin (5-hydroxytryptamine) or other endogenous substance may accentuate the hypertension resulting from the obstruction, but there is little evidence that this occurs in humans. Pulmonary embolism results in perfusion defects on the lung scan, and ventilation of these areas of lung increases the alveolar component of dead space. Arterial hypoxaemia is almost invariably present and is caused mainly by an increase in right to left shunt. This could be the result of right to left shunting through a patent foramen ovale, the redistribution of blood flow to collapsed areas of lung, or to the presence of a high pressure pulmonary oedema.
Amniotic fluid embolism typically occurs during or shortly after labour and is commonly fatal. It is believed that the lethal effects of amniotic fluid
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...