Question

The total amount of O₂ carried by the circulation to the tissues/min. (oxygen delivery or total available oxygen) 

A. Normally equals the rate of O₂ consumption by the body/min. 

B. Is normally more than 95 per cent combined with hemoglobin. 

C. Must fall by about half if hemoglobin concentration is halved. 

D. Is more closely related to P_O2 than to percentage saturation of the blood with O₂. 

E. Must double if body oxygen consumption doubles.

Answer 1

A. False At rest, O₂ consumption (about 250 ml/min) is about 25 per cent of the total available. 

B. True All but 3 of the 200 ml/l is combined with hemoglobin, the rest is dissolved. 

C. False In anaemic hypoxia, cardiac output rises to compensate for the reduced oxygen content per litre of blood. 

D. False If P_O2 falls by 25 per cent from normal, there is relatively little change in the blood oxygen content. 

E. False The extraction ratio rises as oxygen consumption rises, e.g. during exercise.