Respiratory physiology 4

Question 1

Describe the ventilation-perfusion relationship

Answer 1

Ideally match each other but not the same across the whole lung so can get a mis-match
Ventilation is describing the air getting to the alveoli
Perfusion describes the local blood flow
L/min for both

Question 2

Describe ventilation and perfusion at base of lungs

Answer 2

Blood flow is higher than ventilation
This is because arterial pressure exceeds alveolar pressure which compresses the alveoli

Question 3

Describe ventilation and perfusion at the apex of the lungs

Answer 3

Blood flow is lower than ventilation
Because arterial pressure is less than the alveolar pressure which compresses he arterioles
Alveoli compress the vessels in lungs

Question 4

What is the perfectly matched ventilation: perfusion ratio?

Answer 4

1.0
Mismatch1 at base - ventilation<Perfusion< 1.0
Mismatch 2 at apex - ventilation>Perfusion > 1.0

Question 5

What percentage of the healthy lung performs well in matching blood and air?

Answer 5

Over 75%
Majority of mismatch is at the apex
autoregulated to keep ratio close to 1.0

Question 6

Describe what happens when blood flow is more than ventilation

Answer 6

If ventilation decreases in a group of alveoli, PCO2 increases and PO2 decreases.
Blood flowing past these will not be oxygenated
Dilution of oxygenated blood from better ventilated areas
Blood is then shunted from right side to left side of heart without undergoing gas exchange

Question 7

Describe autoregulation when blood flow is more than ventilation

Answer 7

Decreased tissue PO2 around under ventilated constricts their arterioles, diverting blood to better ventilated alveoli.
Increased PCO2 also causes mild bronchodilation

Question 8

Describe autoregulation when ventilation is more than blood flow

Answer 8

Alveolar PO2 rises which causes pulmonary vasodilation
PCO2 falls so there is mild bronchial constriction

Question 9

What is Alveolar dead space?

Answer 9

When ventilation exceeds blood flow so more air that what can participate in gas exchange
Occurs small amount in apex of lungs but can be pathologically in pulmonary embolism

Question 10

Describe the term shunt

Answer 10

Describes the passage of blood through areas of the lung that are poorly ventilated
Is the opposite of alveolar dead space

Question 11

What is anatomical dead space?

Answer 11

Refers to the air in the conducting zone of respiratory tract unable to participate in gas exchange as walls of airways in region are too thick

Question 12

Explain Shunting and dead space on RSA

Answer 12

RSA is respiratory sinus arrhythmia
During inspiration there is increased alveolar dead space
During expiration there is increased shunt
RSA ensures ventilation: perfusion ratio remains close to 1 - increased vagal activity during expiration phase

Question 13

What is physiologic dead space

Answer 13

Alveolar dead space and anatomical dead space

Question 14

What are the 2 forms O2 travels in the blood?

Answer 14

In solution in plasma - 3ml per litre of plasma
Bound to haemoglobin protein in red blood cells - 197ml of O2 out of 200ml

Question 15

How is CO2 transported in the blood?

Answer 15

The bulk of CO2, 77% is transported in solution in plasma due to solubility of CO2
23% is stored within haemoglobin

Question 16

What is the O2 demand of resting tissues?

Answer 16

250ml/min

Question 17

What percentage of arterial O2 is extracted by peripheral tissues at rest?

Answer 17

Only 25% as Haemoglobin and arterial O2 content provide 1000ml/min

Question 18

Describe the structure and function of haemoglobin

Answer 18

Each Hb contains 4 haem groups which each contain one Fe2+ which binds one molecule of O2
Each RBC is packed with O2, just Hb can carry only 4

Question 19

What is the major determinant of of the degree at which Hb binds with O2?

Answer 19

Partial pressure of O2 in the blood which is equal to PP in alveoli

Question 20

Why is partial pressure of O2 in plasma important?

Answer 20

Hb effectively sequesters O2 from the plasma which maintains PP gradient that continues to suck O2 out of the alveoli until Hb becomes saturated

Question 21

How long does it take for Hb to become saturated?

Answer 21

0.25s after contact with the alveoli and the total contact time is 0.75s

Question 22

Explain the oxygen - haemoglobin dissociation curve

Answer 22

Hb is 98% saturated at normal systemic arterial PO2 of 100 mm Hg
Even at PO2 of 60mm Hg there is still 90% saturation
This means there is a normal uptake of O2 by blood when PO2 is relatively reduced
At normal venous PO2 (at peripheral tissues) - 40 mm Hg there is still 75% saturation

Question 23

What is anaemia?

Answer 23

Any condition where the O2 carrying capacity of the blood is compromised
Ex. iron deficiency, haemorrhage or B12 deficiency

Question 24

What would happen to PO2 in anaemia?

Answer 24

Nothing
PO2 is normal despite total blood O2 content being low

Question 25

Is it possible for RBCs to be fully saturated with O2 in anaemia?

Answer 25

RBCs would still be fully saturated with O2 as PO2 is normal The problem could be with Hb deficiency or not enough RBCs

Question 26

What is the effect of pH on the saturation of Hb?

Answer 26

Fallen pH can cause acidosis which causes extra O2 to be given off so tissues receive more - curve fallen Increased pH causes alkalosis which means Hb holds onto O2 more - curve has increased

Question 27

Describe the effect of temperature on the saturation of Hb

Answer 27

An increase in temp. causes the curve to fall - Hb affinity is less for O2 so more given to tissues A decrease in temp. causes the curve to increase - can be dangerous as Hb hangs onto O2 more

Question 28

What effect does conc. of DPG have to Hb saturation?

Answer 28

An increase in DPG conc. causes decrease in curve - saturation decreases No DPG causes increase in Hb saturation More DPG in hypoxia, lung disease, heart disease

Question 29

What is the effect of PCO2 on the Hb saturation?

Answer 29

Increase in PCO2 to 80mm Hg causes decrease in saturation so extra O2 given to tissues Decrease in PCO2 to 20mm Hg causes increase in affinity for O2 so Hb hangs onto O2

Question 30

What is Carbon monoxide?

Answer 30

CO forms from the incomplete combustion of carbon fuel Characterised by hypoxia, anaemia, nausea, headache and cherry res skin and mucous membranes Potential brain damage and death so treatment is 100% oxygen to increase PaO2

Question 31

Explain CO binding to haemoglobin

Answer 31

Is highly toxic CO binds to Hb to form carboxyhaemoglobin with an affinity to O2 x250 more So binds O2 readily and dissociates very slowly

Question 32

What happens to CO2 when it diffuses from the tissues into the blood?

Answer 32

7% remains dissolved in plasma and erythrocytes 23% combines in erythrocytes with deoxyhaemoglobin to form carbamino compounds 70% combines in the erythrocytes with water to form carbonic acid

Question 33

What happens to the carbonic acid formed from CO2 in blood?

Answer 33

Dissociates to yield bicarbonate and H+ ions Most of bicarbonate moves out of erythrocytes into plasma in exchange for Cl- and excess H+ ions bind to deoxyhaemoglobin This is the Cl- shift

Question 34

What is PaO2?

Answer 34

Arterial partial pressure of O2 Refers purely to O2 in solution in plasma and is determined by O2 solubility and partial pressure of O2 in gaseous phase

Question 35

What are the different types of haemoglobin?

Answer 35

92% of Hb is in RBCs in form of HbA Remaining 8% is made of HbA2, HbF and glycosylated Hb Myoglobin is another O2 carrier found in cardiac and skeletal muscle

Question 36

Why does HbF (feotal Hb) and myoglobin have a higher affinity to O2 than HbA?

Answer 36

Is necessary for extracting O2 from maternal/ arterial blood

Question 37

What is hypoxaemic hypoxia?

Answer 37

Most common Reduction in O2 diffusion at lungs due to increased PO2 atmos. or tissue pathology

Question 38

What is Anaemic hypoxia?

Answer 38

Reduction in O2 carrying capacity of blood due to anaemia (RBC loss or iron deficiency)

Question 39

What is stagnant hypoxia?

Answer 39

Heart disease results in inefficient umping of blood to lungs/ around the body

Question 40

What is histotoxic hypoxia?

Answer 40

Poisoning prevents cells utilising O2 delivered to them ex. CO

Question 41

What is metabolic hypoxia?

Answer 41

Oxygen delivery to the tissues does not meet increased O2 demand by cells