Gaseous Exchange: Oxygen

Question 1

Regarding dead space (true or false):

Physiological dead space = alveolar minute ventilation - alveolar dead space

Answer 1

False. Physiological dead space is the combination of alveolar dead space and anatomical dead space.

Question 2

Regarding dead space (true or false):

Dead space includes alveoli that are perfused but not ventilated

Answer 2

False. Alveoli that are perfused but not ventilated contribute to shunt, not dead space.

Question 3

Regarding dead space (true or false):

In an adult, anatomical dead space ≈ 150 ml

Answer 3

True

Question 4

Regarding dead space (true or false):

AMV = (TV-DSV) x RR

Answer 4

True

Question 5

Regarding dead space (true or false):

Dead space contains gas with a carbon dioxide concentration of 5%

Answer 5

False. Dead space gas is not taking part in gas exchange, therefore is the same as atmospheric gas.

Question 6

Regarding V/Q ratio (true or false):

It is increased as the shunt fraction increases

Answer 6

False. Increasing shunt means more areas are perfused but not ventilated, causing a decrease in V/Q ratio.

Question 7

Regarding V/Q ratio (true or false):

It is unaffected by normal pulmonary shunt

Answer 7

False. All areas where ventilation and perfusion are not perfectly matched contribute to changes in V/Q ratio.

Question 8

Regarding V/Q ratio (true or false):

It is normally = 0.8

Answer 8

True

Question 9

Regarding V/Q ratio (true or false):

It can be calculated using the alveolar air equation

Answer 9

False. The alveolar air equation estimates the partial pressure of oxygen in the alveoli, not the V/Q ratio.

Question 10

Regarding V/Q ratio (true or false):

Increased scatter may affect the A-a O2 gradient

Answer 10

True

Question 11

Regarding O2 transport in the blood (true or false):

PO2 depends on the amount of O2 bound to Hb

Answer 11

False. Oxygen bound to Hb does not contribute to the partial pressure of the gas in blood. Only dissolved oxygen is relevant.

Question 12

Regarding O2 transport in the blood (true or false):

Each Hb molecule can bind four O2 molecules

Answer 12

True

Question 13

Regarding O2 transport in the blood (true or false):

Hb binds O2 more avidly at lower a pH

Answer 13

False. At lower pH, oxygen binds less avidly to Hb, aiding the delivery of unbound oxygen at the metabolically active tissues.

Question 14

Regarding O2 transport in the blood (true or false):

The Bohr effect refers to the effect of temperature on the Hb-O2 dissociation curve

Answer 14

False. The Bohr effect refers to the effect of pH, not temperature, on the Hb-O2 dissociation curve.

Question 15

Regarding O2 transport in the blood (true or false):

In the lungs the Hb-O2 dissociation curve is shifted to the left

Answer 15

True

Question 16

Regarding tissue oxygen delivery (O2) (true or false):

Tissue oxygen delivery depends on the transfer of oxygen from the atmosphere to the blood within the alveoli, and on the volume of blood perfusing the tissues

Answer 16

True. DO2 is calculated from the product of blood oxygen content and cardiac output.

Question 17

Regarding tissue oxygen delivery (O2) (true or false):

Given a blood oxygen content of 20 ml/100 ml of blood, and a cardiac output of 5 L/min, the tissue oxygen delivery would be 2500 ml/min

Answer 17

False. In this case the DO2 would be:

DO2 = blood O2 content x cardiac output

= 20 (ml/dl) x 10 x 5 (L/min)

= 1000 ml/min

Question 18

Regarding tissue oxygen delivery (O2) (true or false):

At tissue pH the affinity of Hb for oxygen is operating at the shallow part of the O2 dissociation curve.

Answer 18

False. At tissue pH the affinity of Hb for oxygen is operating at the steep part of the O2 dissociation curve.

Question 19

Regarding tissue oxygen delivery (O2) (true or false):

Small changes in PO2 result in large changes in Hb O2 saturation

Answer 19

True. Small changes in PO2 result in large changes in Hb O2 saturation, releasing oxygen from the Hb to the plasma and helping to maintain the partial pressure gradient for oxygen and transfer to the tissues.