Pulmonary Gas Exchange

Question 1

When is airflow turbulent?

Answer 1

Passing uneven surfaces/bifidcations (at branches and irregularities in the airways). Especially in the upper respiratory tract.

Question 2

What is laminar air flow and where does this occur?

Answer 2

When its in straight lines, easy flow through. Mainly in tubular structures, eg bronchi down to cebntri-acinar region of perhiperal part of lung

Question 3

What is the centriacinar region of the peripheral part of the lung

Answer 3

The area around the terminal bronchiole and 1st respiratory bronchiole. Big change in flow laminar to turbulent.

Question 4

What is the “blood-air barrier”?

Answer 4

Basicallly the alveolar pneumocyte to the endothelial cell.

Question 5

What is FIO2

Answer 5

The fraction on inspired air that is oxygen (eg. of air we breathe is 21%)

Question 6

Hb leave lungs with what saturation and why?

Answer 6

98% oxygen saturation, because Hb is very efficient in picking up oxygen

Question 7

Is it common or rare for CO2 transfer to be affected by disease and why?

Answer 7

Rare, due to the extremely high solubility of CO2 it can easily continue to equilibrilate (usually)

Question 8

Normal PaO2 and PaCO2 (kPa)

Answer 8

PaO2 = 10.5 - 13.5kPa
PaCO2 = 4.8 - 6.0kPa

Question 9

Type 1 vs Type 2 resp failure

Answer 9

Type 1 = hypoxia (PaO2 less than 8kPa) - PaCO2 normal or low

Type 2 = PaCO2 = >6.5kPa (O2 usually low)

Question 10

4 mechanisms of abnormal pulmonary gas exchange

Answer 10

ventilation/perfusion mismatch (V/Q)
shunting
diffuse impairment (interstitial lung diseases)
Alveolar hypoventilation

Question 11

v/q =? and what is normal v/q ratio?

Answer 11

Ventilation/perfusion ratio
Usually:
4L/5L = 0.8

as ventilation is approx 4L/min and perfusion is approx 5L/min.

Question 12

low/high v/q commonest cause of hypoxeimia?

Answer 12

Low (reduction in ventilation)

Question 13

will O2 help fix v/q mismatch?

Answer 13

Help. Usually the mismatch isn’t throughout the whole lung and so the increased oxygen won’t help the areas that are already performing well but by increasing the concentration of oxygen in areas with v/q mismatch it means that the haemoglobin are able to become more saturated with oxygen.

Question 14

What is Shunt?

Answer 14

When blood goes from right ventricle to left atrium with NO opportunity for gas exchange (without contacting ventilated alveoli)

Question 15

Normal % shunt?

Answer 15

2-4% in a normal person

Question 16

What can cause shunts more?

Answer 16

AV malformations (Arteriovenous malformation) - when the artery just turns into the vein and back to the heart
Congenital Heart disease
Pulmonary disease (eg. complete consolidation of the lung in pneumonia)

Question 17

Do shunts improve with o2? Why?

Answer 17

No, because the blood still isn’t going past any opportunity for ventilation, and the blood leaving normal lung is already saturated with 98% O2.

Question 18

Pneumonia, why hypoxaemia?

Answer 18

Severe bronchopneumonia/lobar pattern with large areas of consolidation - get shunting

Bronchitis/Bronchopneumonia (Areas not fully consolidated) - decreased ventilation/perfusion ratio

Question 19

When does shunting occur in pneumonia?

Answer 19

When there has been large areas of consolidation

Question 20

What is hypoventilation?

Answer 20

When there is low ventilation, so not enough fresh air getting to the alveolar.

Question 21

Hypoventilation leads to what type of resp failure why?

Answer 21

Type 2,

CO2 still able to diffuse across, not enough fresh air coming into/leaving alveolar, so increase in PA CO2. Therefore decreasing the gradient for CO2 and leading to PaCO2 increasing. Due to the increased PACO2, the PAO2 will fall, and so will the PaO2.

The decrease in PaO2 can be corrected by raising FIO2.

Question 22

Hypovention improve with O2?

Answer 22

Yes

Question 23

Hypoventilation, why???

Answer 23

Usually affects ALL of the lngs.

Upper airway/tracheal obstruction

Skeletal - mechanical problems - chest wall damage
Muscular - eg paralysis/diaphragmatic damage
Neuro - ig nerve damage/CNS malfunction - eg Opiate posioning/COPD not responding - hypoxic drive

Question 24

What is a characteristic feature of opiate/herrorin overdose?

Answer 24

Suppresses the CNS and can lead to sometimes fatal alveolar hypoventilation

Question 25

COPD desensitised to what??

Answer 25

The increase in CO2 , therefore lives at a higher PaCO2 and lower level of PaO2 as reliant of hypoxic drive from peripheral chemoreceptors

Question 26

COPD patient hypoxaemia, why??

Answer 26

V/Q mismatch - airway obstructio (+/- bronchopneumonia)
Diffusion impairment (loss of alveolar surface area in emphysema
Alveolar Hypoventilation -reduced respiratory drive
Shunt - Only during acute exacerbation if pneumonia is enough

Question 27

What does gas diffusion depend on? And what can impair it?

Answer 27

Pressure of the gas - impaired diffusion if low pressure of gas
Thickness of membrane - thicker interstitium impairs diffusion
Surface area available - less surface area impairs diffusion

Question 28

why co2 easier diffusion? What effect does this have when there is impairment?

Answer 28

Greater solubility. It means when there is impairment, the PaCO2 may remain normal whilst PaO2 drops.

Question 29

What effect does diffusion impairment have on the time taken to adequately saturate the haemoglobin?

Answer 29

Increase

Question 30

Equilibration usually takes how long in normal cells? (length of time for Hb to become fully saturated)

Answer 30

0.25 seconds

Question 31

How long is capillary transit time?

Answer 31

0.75s at rest

Question 32

In disease how long may it take to get equilibrated?

Answer 32

More than 0.25s, up to and over the 0.75s threshold of time the Hb has going past the alveoli

Question 33

What happens to capillary transit time during exercise?

Answer 33

Decreases

Question 34

Increasing O2 conc has what effect on time taken to equilibrate?

Answer 34

Decreases