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Physiology

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Respiration

Question
1 out of 16
 

Gas used to measure diffusion capacity of lung (AIIMS NOV 2010)


A CO
B NO
C CO2
D O2

Ans. A CO

I. Carbon monoxide (CO) is taken up by hemoglobin in the red blood cells at such a high rate that the partial pressure of CO in the capillaries stays very low and equilibrium is not reached in the 0.75 s the blood is in the pulmonary capillaries.

II. Therefore, the transfer of CO is not limited by perfusion at rest and instead is diffusion limited.

III. The diffusing capacity of the lung for a given gas is directly proportionate to the surface area of the alveolocapillary membrane and inversely proportionate to its thickness.

IV. The diffusing capacity for CO (DLCO) is measured as an index of diffusing capacity because its uptake is diffusion-limited.

V. DLCO is proportionate to the amount of CO entering the blood (VCO) divided by the partial pressure of CO in the alveoli minus the partial pressure of CO in the blood entering the pulmonary capillaries.

VI. The normal value of DLCO at rest is about 25 mL/min/mm Hg. It increases up to threefold during exercise because of capillary dilation and an increase in the number of active capillaries.

Respiration Flashcard List

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