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Lots of talk about funny hemoglobin and ‘happy hypoxic’ people with #COVID19. I think we can explain everything using plain old pulmonary physiology. Let’s dive into hypoxic pulmonary vasoconstriction (HPV) and hypoxic ventilatory drive (HVD) and try to make sense of this...
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Normally, different areas of the lung receive different amounts of ventilation. The lungs are able to sense oxygen levels and adjust smooth muscle tone to modulate blood flow. This process is hypoxic pulmonary vasoconstriction (HPV), reviewed here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5310129/
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To understand why HPV is important, imagine a simple two alveoli model of the lung. Normally oxygen content (CaO2) and saturation (SpO2) increase as blood crosses the alveolar capillaries. This brings the oxygen level from venous SpO2 of 70% up to an arterial SpO2 of 100%.
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What happens if one alveolus is filled with fluid? Deoxygenated blood would go through the pulmonary vasculature without picking up any oxygen. This is Shunt.
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