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ED Primary Exam > Week 15 Physiology - Respiratory Physiology II > Flashcards

Week 15 Physiology - Respiratory Physiology II Flashcards

1
Q

How does regional perfusion of the lung differ from top to bottom?

A

Blood flow decreases almost linearly from base to apex (when standing)

Due to gravity and the effect of hydrostatic pressure on lung, hydrostatic pressure can exceed perfusion pressure (approx 23mmHg)

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2
Q

Ventilation vs perfusion ratios at apex, middle, and base:

A

Apex: ventilation > perfusion (high VQ ratio) —> Zone 1

Middle: V/Q = 1 (no mismatch) –> Zone 2

Base: Perfusion > Ventilation (low VQ ratio) –> Zone 3

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3
Q

What is the mean arterial pulmonary pressure?

A

15mmHg

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4
Q

How can alveolar ventilation vary with the same minute volume but different tidal volumes?

A

Due to role of dead space.

RR 30 + Tidal volume 200mL = minute volume of 6 L
RR 10 + tidal volume 600mL = minute volume of 6L

However alveolar ventilation = (tidal volume - dead space) x respiratory rate

Therefore with a 150mL dead space, per breath alveolar ventilation would be only 50mL as opposed to 450mL per breath.

When extrapolating to a minute of these breaths, Vt of 200mL = alveolar ventilation of 1500mL vs Vt of 600mL = 4500mL

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5
Q

What are the metabolic functions of the lung?

A

Fibrinolytic system
Activation of Angiotensin I to Angiotensin II
Inactivates prostaglandins, bradykinin, adenine nucleotides, serotonin, noradrenaline, acetylcholine
Removes leukotrienes

Synthesises prostaglandins, histamine, kallikrein, collagen, elastin, surfactant (compromised of phospholipids)

Produces and secretes IgA

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6
Q

Why does the alveolar gas equation exist/why care?

A

Alveolar O2 is not directly measurable, but it is the main driving force behind diffusion of O2 into capillaries and supplying tissues with O2. Need to find variables that are directly measurable, to allow indirect way of calculating.

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7
Q

What is alveolar gas equation?

A

PAO2 = PiO2 - (PACO2/R)

       = 0.21 x (760-47) - (PACO2 / R )
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8
Q

What is PAO2?

A

Alveolar concentration of oxygen

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9
Q

What is PiO2?

A

Oxygen percentage x (barometric pressure - water vapour pressure)

= 0.21 x (760-47)

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10
Q

What is R?

A

Respiratory quotient (CO2 production / O2 consumption)

(0.8 in normal western diet)

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11
Q

What generally occurs with increasing altitude?

A

With fixed FiO2, increasing altitude will decrease partial pressure of inspired O2, and will lead to decreased alveolar oxygen

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12
Q

What are the different causes of hypoxia?

A
  1. Low PO2 in arterial circulation caused by lung disease/hypoventilation/increased altitude/mismatch
  2. Reduced O2 carrying capacity of blood (anaemia, CO poisoning)
  3. Reduction in tissue blood flow, generalised = shock state, local may be thrombus/embolism
  4. Inability of tissues to utilise delivered O2 (i.e. cyanide poisoning)
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13
Q

In what type of hypoxia will O2 administration not help?

A

In shunt: there is no perfusion to the ventilated area, and so increasing O2 will not improved oxygenation

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14
Q

What is more of an issue for gas diffusion, CO2 elimination, or O2 delivery?

A

CO2 diffuses 20x faster than O2, so CO2 elimination is generally less issue than O2 delivery

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15
Q

What is lung compliance?

A

Change in volume / change in pressure

Normal compliance 200mL/cm H20

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16
Q

What factors can reduce lung compliance?

A

Pulmonary fibrosis
Alveolar oedema
Atelectasis
Increased pulmonary venous pressure
Pneumothorax
High standing diaphragm (i.e. laparoscopic surgery)

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17
Q

What factors can increased lung compliance?

A

Emphysema
Normal ageing lung

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18
Q

When is compliance higher, inspiration or expiration?

A

Expiration

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19
Q

What cell produce surfactant?

A

Type II Pneumocytes

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20
Q

What is the function of surfactant?

A

Reduce alveolar surface tension to increase compliance, reduce work of expanding alveoli, improves stability, assists with keeping alveoli dry

21
Q

What affect does blood flow have on surfactant production?

A

Reduced blood flow = reduced surfactant production

22
Q

What role do bronchial arteries have?

A

Helps supply O2 to conducting airways and pleura, as well as hilar lymph nodes

23
Q

What is a normal right ventricular pressure?

A

25mmHg

Pulmonary artery pressure approximately 24 mmHg
Pulmonary capillaries approximately 8mmHg

Left atrium approx 5mmHg

24
Q

Describe hypoxic vasoconstriction:

A

In response to low alveolar O2, active process of shunting blood away from poorly ventilated areas of lung.

Unknown mechanism, but is independent of CNS control.

25
Q

Why is hypoxic vasoconstriction important at birth?

A

As foetus, very high pulmonary vascular resistance to assist with shunting of maternal oxygenated blood to heart and bypassing pulmonary circulation

26
Q

What are the two ways O2 is transported in blood?

A
  1. Bound to Hb
  2. Dissolved in plasma
27
Q

What is Henry’s law, and how does it relate to O2 transport in blood?

A

Amount of gas dissolved is proportional to the partial pressure of the gas surrounding the liquid.

If PAO2 100mgHg, dissolved O2 = 0.3mL / 100mL blood

28
Q

What is heme?

A

Iron-porphyrin compound joined by 4 polypeptide chains (the alpha and beta haemoglobins)

29
Q

What state has a greater affinity for O2, ferrous or ferric iron?

A

Ferrous (Fe2+)

30
Q

How is CO2 transported in blood?

A
  1. Dissolved as CO2
  2. Dissociated as HCO3-
  3. In combination with proteins as carb amino compounds
31
Q

What is the equilibrium equation for CO2 dissolving into blood?

A

CO2 + H20 –> H2CO3 –> H+ and HCO3 -

32
Q

What is the difference between formation of carbonic acid in plasma vs inside RBC?

A

RBC has carbonic anhydrase which catalyses this reaction.

It still occurs in plasma, but much slower.

**Second reaction/dissociation is enzyme independent and occurs rapidly

33
Q

What happens to the HCO3- in RBCs?

A

Move out of cell into plasma, but the H+ gets trapped.

*To maintain electrical electroneutrality, Cl- shifts into RBC –> increased osmolar content of RBCs after passing through capillary beds

34
Q

What is the role of carbamino compounds?

A

Formed by combination of CO2 with terminal amine groups of blood proteins, most importantly globin portion of haemoglobin

Happens without enzyme, reduced Hb can more readily transport CO2 (facilitated by unloading of O2 in peripheral tissues)

35
Q

What percentages of CO2 is transported via each method in venous blood?

A

60% as HCO3-
30% as carbamino compounds
10% as CO2 dissolved in plasma

36
Q

What is the major difference in transport of CO2 in arterial blood?

A

90% via HCO3- due to decreased Hb affinity/capacity for CO2 in its non-reduced form whilst it is carrying O2

37
Q

What is SaO2?

A

Saturation of haemoglobin, expressed in the formula:

SaO2 = HbO2 / total O2 carrying capacity of Hb

38
Q

What is the general arterial SaO2 with a PO2 of 100mmHg?

A

97.5%

39
Q

What is the general SaO2 of venous blood, with a PO2 of 40mmHg?

A

75%

40
Q

Regarding O2 dissociation curve, what does a RIGHT shift refer to, and what can cause this?

A

Right shift = decreased O2 affinity for Hb. **You give with your right hand!

Low pH
Increased PCO2
Increased temperature
Increased 2,3 DPG

41
Q

Regarding O2 dissociation curve, what does a LEFT shift refer to, and what can cause this?

A

Left shift, increased O2 affinity for haemoglobin

High pH
Decreased PCO2
Decreased temperature
Carbon monoxide

42
Q

What point on the O2 dissociation curve signals the end of the plateau phase?

A

PO2 50mmHg, which roughly has SaO2 80%

43
Q

What is the p50 regarding O2 dissociation curve?

A

Point at 50% SaO2, which generally correlates with PO2 of 27mmHg.

44
Q

What is the Bohr effect?

A

The decrease in the oxygen affinity of haemoglobin in the presence of low pH or high CO2W

45
Q

What is the Haldane effect?

A

Deoxygenated blood increases its ability to carry CO2 (via H+ reduction of Hb)

46
Q

Describe the pulmonary circulation:

A

Blood flows from RV via pulmonary valve into the pulmonary trunk, which bifurcates to R + L pulmonary arteries.

These undergo several branches to eventually form capillaries which contact the alveolus, and then venues –> pulmonary veins which drain directly into the left atrium.

**Bronchial arteries come from T3-T8 level fro thoracic aorta, supplying trachea, bronchi, aorta via vaso vasorum

47
Q

What is paradoxical diaphragmatic movement?

A

Unilateral diaphragmatic paralysis, causing paradoxical elevation of the diaphragm with downwards excursion of the unaffected side due to fall in intrathoracic pressure

48
Q

What are the muscles of inspiration?

A

Most important = diaphragm, along with external intercostal muscles (bucket handle movement)

Accessory muscles of inspiration = scalene muscles, sternomastoids (raising the sternum)

49
Q

What are the muscles of expiration?

A

Normally passive effect of diaphragmatic relaxation during quiet breathing.

Most important muscles of expiration are abdominal wall muscles: rectus abominus, external and internal obliques, transverse abdominus, and internal intercostal muscles.

ED Primary Exam (46 decks)

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