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Everything seems to make sense until you take into account hypoxic pulmonary vasoconstriction.
For the sake of simplicity, imagine one entire lung has either dead space or pulmonary shunting and the other one is normal.
In the case of dead space, the diseased lung will not have any perfusion. All that blood that is supposed to flow through that lung will flow through the normal lung. The normal lung will thus have 2x as much blood flowing through it. As a result, giving a patient in this situation 100% oxygen will benefit them.
In the case of pulmonary shunting, the diseased lung will not have any ventilation. One may argue that both lungs will receive the same amount of blood as usual and thus, giving a patient 100% oxygen in this situation will not benefit them since the normal lung will have 1x amount of blood and will not be able to "extract" any more oxygen from its alveoli than it already does.
However, if you consider the pulmonary vasoconstriction that occurs under hypoxic conditions, all of this seems to stop making sense.
Imagine the patient with pulmonary shunting in one entire lung. One lung is not receiving any ventilation. As a result, would that not cause the vessels in that lung to vasoconstrict and send more blood to the normal lung? And if it does, would 100% oxygen not help this patient if the normal lung will be receiving 2x as much blood (for example) - which is the same scenario in the dead space situation?
Thank you
For the sake of simplicity, imagine one entire lung has either dead space or pulmonary shunting and the other one is normal.
In the case of dead space, the diseased lung will not have any perfusion. All that blood that is supposed to flow through that lung will flow through the normal lung. The normal lung will thus have 2x as much blood flowing through it. As a result, giving a patient in this situation 100% oxygen will benefit them.
In the case of pulmonary shunting, the diseased lung will not have any ventilation. One may argue that both lungs will receive the same amount of blood as usual and thus, giving a patient 100% oxygen in this situation will not benefit them since the normal lung will have 1x amount of blood and will not be able to "extract" any more oxygen from its alveoli than it already does.
However, if you consider the pulmonary vasoconstriction that occurs under hypoxic conditions, all of this seems to stop making sense.
Imagine the patient with pulmonary shunting in one entire lung. One lung is not receiving any ventilation. As a result, would that not cause the vessels in that lung to vasoconstrict and send more blood to the normal lung? And if it does, would 100% oxygen not help this patient if the normal lung will be receiving 2x as much blood (for example) - which is the same scenario in the dead space situation?
Thank you
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