In the Bohr equation for physiologic dead space, Vd/Vt = (PaCO2 − PeCO2)/PaCO2. If PaCO2 = 40 mmHg and PeCO2 = 28 mmHg, what is Vd/Vt?

Study for the Respiratory Therapy Test. Use flashcards and multiple choice questions, featuring hints and explanations. Prepare for your exam successfully!

Multiple Choice

In the Bohr equation for physiologic dead space, Vd/Vt = (PaCO2 − PeCO2)/PaCO2. If PaCO2 = 40 mmHg and PeCO2 = 28 mmHg, what is Vd/Vt?

The Bohr equation links the fraction of each breath that's wasted in dead space to the difference between arterial CO2 and the CO2 in the mixed expired gas, normalized by the arterial CO2. Here, subtract PeCO2 from PaCO2: 40 − 28 = 12 mmHg. Divide by PaCO2: 12 / 40 = 0.30. So Vd/Vt = 0.30, meaning about 30% of the tidal volume is dead space. This reflects how much of the inhaled air does not participate in gas exchange because it remains in anatomical and physiologic dead space. If PeCO2 were closer to PaCO2, the dead-space fraction would be smaller; if PeCO2 were much lower, the fraction would be larger.

The Bohr equation links the fraction of each breath that's wasted in dead space to the difference between arterial CO2 and the CO2 in the mixed expired gas, normalized by the arterial CO2. Here, subtract PeCO2 from PaCO2: 40 − 28 = 12 mmHg. Divide by PaCO2: 12 / 40 = 0.30. So Vd/Vt = 0.30, meaning about 30% of the tidal volume is dead space. This reflects how much of the inhaled air does not participate in gas exchange because it remains in anatomical and physiologic dead space. If PeCO2 were closer to PaCO2, the dead-space fraction would be smaller; if PeCO2 were much lower, the fraction would be larger.

More practice questions