ventilation, perfusion & gas transport in blood

Question 1

what is ventilation ?

Answer 1

air getting to alveoli

Question 2

what is perfusion?

Answer 2

local blood flow

Question 3

what happens to perfusion and ventilation as you move from the top of the lungs to the bottom?

Answer 3

they both decrease

Question 4

where is the lung highly perfused?

Answer 4

the base

Question 5

is pulmonary arterial pressure high or low and what are the systolic and diastolic values?

Answer 5

pulmonary arterial pressure is low
systolic- 25mmHg
diastolic- 8mmHg

Question 6

what mismatch takes place in the apex?

Answer 6

ventilation>perfusion
ratio more than 1
leads to the opposite of a shunt (alveolar dead space)
alveolar PO2 rises- pulmonary vasodilation
PCO2 falls- bronchial constriction

Question 7

what mismatch takes place in the base?

Answer 7

Ventilation

Question 8

what is alveolar dead space?

Answer 8

alveoli that are ventilated but not diffused

Question 9

what is physiologic dead space?

Answer 9

alveolar + anatomical dead space

Question 10

what is a shunt?

Answer 10

when blood is moved from the right side of the heart to the left side without undergoing gas exchange

Question 11

what is the role of respiratory sinus arrhythmia?

Answer 11

to minimise ventilation:perfusion mismatch during the breath cycle.

Question 12

what are the 2 forms in which oxygen travels in the blood?

Answer 12

in solution in plasma 3ml/L

bound to haemoglobin 197ml

Question 13

what % of CO2 is transported in plasma and what % in haemoglobin?

Answer 13

77% in solution in plasma

23% stored within haemoglobin

Question 14

what is the role of haemoglobin in the transport of O2 in the blood?

Answer 14

binds to oxygen

Question 15

why does the shape of the oxyhaemoglobin dissociation curve aid O2 loading in the lungs and unloading in the tissues?

Question 16

what is the main determinant of how much oxygen binds to haemoglobin ?

Answer 16

PaO2 (partial arterial pressure of O2)

Question 17

what is the main determinant of total oxygen content?

Answer 17

How much oxygen binds to haemoglobin, because 97% of oxygen carried in the blood is bound to haemoglobin

Question 18

How much oxygen can bind to haemoglobin is directly determined by…

Answer 18

PaO2, number of red blood cells and amount of haemoglobin in each

Question 19

How much oxygen can bind to haemoglobin is further influenced by…

Answer 19

PaCO2, body temperature, plasma pH and levels of 2,3 DPG.

Question 20

what is anaemia?

Answer 20

any conditions which results in a decrease in the O2 carrying capacity of the blood
eg. iron deficiency, haemorrhage, vitamin B12 deficiency

Question 21

what would happen to PO2 in anaemia?

Answer 21

nothing PO2 is normal despite total blood O2 being low

Question 22

what are the factors that affect the dissociation curve?

Answer 22

1. affinity of haemoglobin for O2 is decreased by a decrease in pH, or/and increase in PCO2, or temperature
2. a rise in pH, or fall in PCO2, or temperature increases affinity or haemoglobin for O2
3. affinity of haemoglobin for O2 decreases by binding of 2-3-DPG

Question 23

what increases in situations associated with low O2 supply and helps maintain O2 release in tissues?

Answer 23

2-3-DPG

Question 24

what does carbon monoxide form when it binds to haemoglobin?

Answer 24

carboxyhemoglobin which has an affinity 250 times greater than O2, this is problematic once dissolved in circulation