Gaseous Diffusion

Question 1

What is dead space?

Answer 1

Airway volume with no gas exchange

Question 2

What is anatomical dead space?

Answer 2

All except the alveolar and respiratory bronchioles

Question 3

What is physiological dead space?

Answer 3

All except the alveolar and respiratory bronchioles as well as areas where gas exchange is dysfunctional

Question 4

What is barometric pressure?

Answer 4

Sum of all the partial pressures of each gas including water vapour

Question 5

What happens to barometric pressure at altitude?

Answer 5

Reduced, fraction of oxygen does not change but pressure does

Question 6

What is Pb?

Answer 6

Barometric pressure

Question 7

What does the partial pressure of a gas in a liquid depend on?

Answer 7

The conc of the liquid

the solubility of a gas in the liquid

Question 8

Can solubility be increased?

Answer 8

No, it is a constant

Question 9

What does water vapour pressure depend on?

Answer 9

Temperature (mainly) and saturation

Question 10

Why is the water vapour pressure constant in the lungs?

Answer 10

The alveolar air temperature is constant at 37 degrees (Water vapour pressure, 6.3kPa, 47mmHg)

Question 11

What is the main determinant of alveolar PO2?

Answer 11

Oxygen inspired and how much CO2 there is

Question 12

Alveolar Gas Equation

Answer 12

Inspired Oxygen - (Arterial CO2 divided by R)

Question 13

What is the pressure gradient driving diffusion for alveolar-capillary membrane?

Answer 13

Alveolar (Pa) - Mean Pulmonary Capillary (Pc)

Question 14

Examples of reduction in surface area of the alveolar capillary gas exchange surface:

Answer 14

Emphysema
Lung resection- lung removal
Decreased venous return (heart failure)

Question 15

Examples of increase in thickness of barrier membrane (larger diffusion distance):

Answer 15

Interstitial/alveolar fibrosis
Collagen Vascular Diseases
Congestive Heart Failure

Question 16

What is the diffusion constant directly proportional to and inversely proportional to?

Answer 16

Direct: Solubility
Inversely: Molecular Weight

Question 17

What happens to CO2 if ventilation is reduced?

Answer 17

Increase

Question 18

What do you use to measure blood capillary O2?

Answer 18

Carbon monoxide

Question 19

Why is carbon monoxide used as a surrogate marker for the diffusion capacity?

Answer 19

Haemoglobin has approx 240 times more affinity for CO than for O2

Question 20

What is cyanosis?

Answer 20

The bluish or purplish discolouration of the skin or mucous membranes due to the tissues near the skin surface having low oxygen saturation

Question 21

What is peripheral cyanosis?

Answer 21

Reduced blood flow to a region resulting in hypoxic tissue causing a bluish grey tinge to extremities.
Respiration is ok, arterial o2 content is ok

Question 22

What are the causes of peripheral cyanosis?

Answer 22

cardiovascular shock
Low temp
Reduced cardiac output
Poor arterial supply

Question 23

What is central cyanosis?

Answer 23

Arterial hypoxaemia (reduction in O2 content)
Buccal mucosa and lips are best to spot this

Question 24

What are the causes of central cyanosis?

Answer 24

Chronic Respiratory Disease

Right to left (heart) shunts

Question 25

What is the Haldane Effect?

Answer 25

At any given PCO2 the quantity of CO2 carried is greater in partially deoxygenated blood (Venous) than in oxygenated blood (Arterial)

Question 26

Why does the haldane effect occur?

Answer 26

Hb forms carbamino compounds more readily when deoxygenated ( can carry more CO2)
Hb binds to H+ better when deoxygenated (increases CO2 carriage)

Question 27

What is hyperventilation?

Answer 27

Over-ventilation in proportion to metabolism

lead to a lowering of arterial PCO2 below normal= hypocapnic

Question 28

Whta is Hypoventilation?

Answer 28

Under-ventilation in proportion to metabolism

Results in higher arterial PCO2 levels= hypercapnic