Chest
Volume 81, Issue 4, April 1982, Pages 495-501
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Clinical Significance of Pulmonary Function Tests
Alterations in Gas Exchange Following Pulmonary Thromboembolism

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INTRAPULMONARY SHUNT

Right-to-left intrapulmonary shunts subsequent to pulmonary embolism have been demonstrated both in man and in experimental animals. Wilson et al1 studied 21 patients with angiographically-demonstrated pulmonary emboli while breathing room air and 100 percent oxygen. They found that intrapulmonary shunting accounted for most of the hypoxemia observed in their patients, and this shunting gradually diminished during the first month following embolization. The magnitude of the shunting did not

VENTILATION-PERFUSION INEQUALITY

The development of ventilation-perfusion inequality has also been demonstrated to provide a major contribution to the deranged gas exchange seen following pulmonary embolization. Kafer,9 for instance, studied 21 patients who were felt to have pulmonary thromboembolism on the basis of perfusion lung scan abnormalities. He measured their PaO2 while breathing room air and while breathing 100 percent oxygen and estimated the contribution of V˙A/Q˙ inequality and shunt to each patient's

DECREASED MIXED VENOUS OXYGEN CONTENT

A final element in the pathogenesis of alterations in arterial blood gas tension seen following pulmonary thromboembolism is a decrease in the oxygen content of mixed venous blood. Figure 4 shows that in the presence of V˙A/Q˙ inequality, arterial O2 content falls as the mixed venous oxygen tension falls. In patients with pulmonary thromboembolism, the mixed venous Po2 may fall due to decreases in cardiac output or inability of cardiac output to keep pace with increased tissue oxygen

ARTERIAL BLOOD GAS ABNORMALITIES IN MAN

Arterial hypoxemia is found in most patients who have experienced pulmonary thromboembolization. Figure 6 demonstrates the distribution of arterial partial pressure of oxygen (PaO2) during room air breathing in 54 previously reported patients without underlying lung disease.1, 19,20 All patients had their emboli demonstrated by pulmonary angiography and were studied within three weeks of the first symptoms suggesting pulmonary thromboembolism. Although many factors are likely to have

DEAD SPACE AND EXPIRED Co2 ALTERATIONS IN MAN

The Bohr dead space (VD/VT) as determined from measurement of the partial pressure of CO2 in arterial and mixed expired gas represents the sum of the anatomic dead space and the alveolar dead space. Anatomic dead space is constituted primarily by the large conducting airways and is relatively fixed in size. The alveolar dead space is determined by ventilation to lung units with V˙A/Q˙ ratios greater than the mean for that individual. In normal individuals, these units occur predominantly

SUMMARY

There is a broad spectrum of gas exchange abnormalities that result from pulmonary thromboembolism. The severity and mechanism of these abnormalities are likely to depend upon the size and location of emboli, the presence or absence of preexisting cardiopulmonary disease, and the time elapsed since embolization. Arterial blood gas alterations and changes in expired gas composition reflected in the Bohr dead space and arterial to end-tidal CO2 gradient are neither sufficiently sensitive nor

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