what is a Pulmonay embolism?

[osborne10]

what effect does a PE have on the oxygen levles within the body and the blood pressure in the pulmonary artery?

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[campbellking]

Patients with a P.E. become hypoxic (oxygen levels in the body are reduced) due to the mismatch between ventilation and perfusion. Ventilation of the lung will continue in an area with there is no circulation. Not sure about the pressure in the pulmonary artery.

[Clanad]

Although initial abnormal physical findings may be absent in most patients with pulmonary embolism (PE) and its cousin, the equally serious deep vein thrombosis (DVT), arterial hypoxemia (reduced oxygen in the blood) typically occurs with diminished arterial O2 saturation. Hypoxemia is due to right-to-left shunting in areas of partial or complete atelectasis ( the collapse of part or all of a lung by blockage of the air passages)not affected by embolization. Pulmonary hypertension results from increased pulmonary vascular resistance. Consequently, the right ventricle must generate higher pulmonary arterial pressure to maintain normal cardiac output. Although some degree of pulmonary hypertension can occur after any PE, significant pulmonary hypertension (> 25 mm Hg mean pressure) usually occurs in a previously healthy lung only when > 30 to 50% of the pulmonary arterial tree is occluded. Higher pressures more commonly occur in patients with preexisting cardiopulmonary disease than in those without.
(Source: The Merck Manual)