![]() 9,11The regional distribution of V is more likely regulated by passive mechanisms, such as variations of alveolar compliance in different parts of the lungs, 12inspiration rate, and regional pleural pressure. 10Raised intrathoracic pressure from continuous positive airway pressure causes a shift in pulmonary blood flow toward dependent parts of the lungs, which may influence V/Q matching. This effect was also observed in healthy volunteers under general anesthesia with mechanical ventilation. 6In addition, human studies have shown that selective nitric oxide synthesis 7and posture 8,9also seem to influence Q with a more uniform distribution in the ventral-to-dorsal direction in prone versus supine position. ![]() Several determinants of regional Q have been reported in animal studies, among them, lung vascular structure, 2differences in vessel conductance between lung regions, 3,4gravity 5and hypoxic pulmonary vasoconstriction. The underlying mechanism of this function is still not fully understood. 1Maintained coordination of regional lung perfusion (Q) and ventilation (V) is crucial for optimal blood oxygenation. ALMOST all forms of general anesthesia, including inhalation anesthesia, are associated with deterioration in pulmonary gas exchange.
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