![]() ![]() Depending on the disease condition, additional mechanisms that can contribute to an elevated physiological dead space measurement include shunt, a substantial increase in overall V'A/Q' ratio, diffusion impairment, and ventilation delivered to unperfused alveolar spaces. The volume of air that participates in gas exchange because it is in contact with perfused alveoli is the alveolar ventilation (V A V E V D physiological). For the range of physiological abnormalities associated with an increased physiological dead space measurement, increased alveolar ventilation/perfusion ratio (V'A/Q') heterogeneity has been the most important pathophysiological mechanism. Physiological dead space may be increased with lung disease, due to an increase in the alveolar component. Although a frequently cited explanation for an elevated dead space measurement has been the development of alveolar regions receiving no perfusion, evidence for this mechanism is lacking in both of these disease settings. In this lesson, investigate dead space in more detail to. An elevated physiological dead space, calculated from measurements of arterial CO2 and mixed expired CO2, has proven to be a useful clinical marker of prognosis both for patients with acute respiratory distress syndrome and for patients with severe heart failure. Physiological dead space includes anatomical dead space and dead space in the lungs where gas exchange should occur but does not.
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