Gas exchange — Flashcards

Flashcard 151: In exercise, O2 exhibits _____-limited gas exchange

Answer: perfusion

Extra: O2 is perfusion-limited in both resting and exercise states in healthy individuals at sea level. It becomes diffusion-limited in conditions like pulmonary fibrosis or during exercise at high altitude where the partial pressure gradient is reduced.

Flashcard 152: How does **resin T3 uptake (RT3U)** (a measure of TBG saturation) change with pregnancy or OCP use?

Answer: Decreased

Extra: Pregnancy and OCP use increase **estrogen**, which stimulates the liver to increase production of **thyroid-binding globulin (TBG)**. Because there are now significantly more TBG binding sites available while the amount of free hormone remains relatively stable (due to feedback), the **percentage of TBG saturation** (measured by **resin T3 uptake**) **decreases**.

Flashcard 153: The lung diffusing capacity (DL) can be measured with _____ because it is exclusively diffusion-limited

Answer: carbon monoxide (CO)

Flashcard 154: The approximate Po2 in inspired, humidified air (PIO2) at sea level is _____ mmHg

Answer: 150

Flashcard 155: _____ emboli present with joint and muscle pain ('bends') and respiratory symptoms ('chokes')

Answer: Gas

Flashcard 156: _____ is the total volume of the lungs that does not participate in gas exchange

Answer: Physiologic dead space

Flashcard 157: The partial pressure of oxygen in the venous blood (PvO2) is normally approximately _____ mmHg

Answer: 40

Flashcard 158: When patients have diseased lung tissue (e.g. fibrosis/emphysema) O2 transfer becomes _____-limited

Answer: diffusion

Flashcard 159: In _____-limited gas exchange, the gas does not equilibrate by the time blood reaches the end of the capillary

Answer: diffusion

Flashcard 160: N2O exhibits _____-limited gas exchange

Answer: perfusion