Regional Ventilation in the Differential Diagnosis of Pulmonary Embolism

Abstract

In the diagnosis of pulmonary embolism by lung scanning, clinical errors of interpretation may arise. Diseases that affect the distribution of pulmonary blood flow, such as pulmonary emphysema and bronchial asthma, may be confused with pulmonary embolism. With the addition of ventilation studies with 133 xenon to the perfusion scans, distinct differences appear between patients with emboli and those with obstructive lung disease. In patients with pulmonary emboli, ventilation is preserved in the areas of decreased perfusion, whereas patients with obstructive lung disease show both decreased ventilation and perfusion in the affected areas.

Effect of alveolar hypercapnia on regional pulmonary perfusion.

“…Above all, differentiation between vascular and ventilatory factors as a cause of perfusion abnormalities is especially important. In the former a vascular blockade is a major cause, whereas in the latter alveolar hypoxia seems to play a main role in suppressing regional perfusion by hypoxic vasoconstriction (Medina et al 1969;Denardo et al . 1970;Isawa et al 1971a;Moser et al 1971), but the role of alveolar hypercapnia is still debated (Barer et al 1970;Grant et al 1976).…”

Pulmonary embolism: Part 2 Diagnostic methods and management

“…Pulmonary embolism produced perfusion defects unaccompanied by ventilation defects ('mismatches'), whereas most other lung diseases which could cause perfusion defects also caused matching defects in ventilation. 48,49,52,56,63,64 There was awareness that other forms of pulmonary vascular obstruction had a similar effect, but the general view was optimistic.…”

Safe Pulmonary Scintigraphy in the Era of COVID-19

“…The current method of lung scintigraphy for the diagnosis of PE therefore developed into an unusual examination that requires documentation of two disparate physiologic processes, pulmonary perfusion and ventilation, which are then contrasted to arrive at a final diagnosis ( 17 , 18 , 19 ). Perfusion scintigraphy, absent ventilation, can never achieve high specificity for PE.…”