Ventilation and perfusion Flashcards

1
Q

What is the usual value of tidal volume?

A

500ml

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2
Q

How do you calculate minute ventilation?

A

Tidal volume x respiratory rate

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3
Q

What is the typical value of minute ventilation?

A

6-8 L/min at rest

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4
Q

Define anatomical dead space.

A

Volume of air in the conducting airways

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5
Q

What is the typical value of anatomical dead space?

A

150mls

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6
Q

Define physiological dead space.

A

The total volume of air that does not participate in gas exchange

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7
Q

Give the calculation for physiological dead space.

A

Physiological dead space = anatomical dead space + alveolar dead space

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8
Q

Define hyperventilation.

A

An increase in the rate and depth of breathing

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9
Q

Describe how increased alveolar ventilation affects the partial pressure of CO2 in the alveoli, and how this would affect diffusion of CO2 from the blood.

A

When alveolar ventilation increases, it helps remove CO2 from the alveoli and brings in more oxygen.

Removing CO2 reduces the partial pressure of CO2 in the alveoli. This lowers alveolar pCO2 which increases the pressure gradient between the alveoli and the blood.

With a greater pressure gradient, CO2 will diffuse more easily from the blood into the alveoli to be exhaled.

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10
Q

What are some common causes of low V/Q ratio?

A

Airway obstruction such as asthma or pneumonia

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11
Q

What could be a cause of high V/Q ratio?

A

Pulmonary embolism

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12
Q

The respiratory control centre is in which area of the brain?

A

Medulla

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13
Q

The brainstem responds to changes in the lungs via which 2 mechanisms?

A

Change in lung volume via mechanoreceptors

Change in blood gas composition via chemoreceptors

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14
Q

The central chemoreceptors are located in which area of the medulla?

A

Ventral surface of the medulla

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15
Q

What 2 things do the central chemoreceptors respond to and how?

A

Directly to changes in pH of CSF

Indirectly to changes in arterial pCO2

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16
Q

Which 2 areas are the peripheral chemoreceptors located?

A

Carotid bodies – at the bifurcation of the common carotid artery

Aortic bodies – in the aortic arch

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17
Q

What 3 things do the peripheral chemoreceptors respond to?

A

Arterial pO2

Arterial pCO2

Arterial H+ and thus pH

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18
Q

The peripheral chemoreceptors respond dramatically when pO2 is below what value?

A

Respond dramatically when pO2 <8kPa

19
Q

How do the peripheral chemoreceptors signal for a change in ventilation?

A

Signal to the respiratory control centre to modulate ventilation via the vagus nerve and glossopharyngeal nerve

20
Q

Which 2 mechanisms do the lungs use to prevent a large increase in pressure when blood flow increases?

A

Capillary distension

Capillary recruitment – previously closed capillaries open up to accommodate more blood flow

21
Q

What if the action of thromboxane A2 in the lungs?

A

Vasoconstrictor

22
Q

What is the action of prostacyclin in the lungs?

A

Vasodilator

23
Q

What effect does O2 have on pulmonary arteriole smooth muscle?

A

Relaxes pulmonary arteriole smooth muscle

24
Q

What is the normal V/Q value?

25
Q

Describe what a shunt is and what value V/Q ratio this would lead to.

A

An area of lung with perfusion but no ventilation, resulting in a V/Q ratio of zero

26
Q

Describe what dead space is and what value V/Q ratio this would lead to.

A

An area of lung with ventilation but no perfusion, resulting in an infinite V/Q ratio

27
Q

In which area of the lung is perfusion greater, apex or base? Why?

A

Base, due to the vessels at the base having less gravity to work against

28
Q

In which area of the lung is ventilation greater, apex or base? Why?

A

Base

Due to gravity, the intrapleural pressure at the apex of the lung is more negative compared to the base. This means the alveoli at the apex are more expanded at rest. In contrast, alveoli at the base are relatively compressed. Since the alveoli at the apex are already more expanded, they are less compliant and don’t expand as much as we inhale. The alveoli at the base, being less expanded to start with, are more compliant and can expand more with each breath. As a result, a larger proportion of inhaled air goes to the base of the lungs, making ventilation greater there

29
Q

Are gravitational effects greater on ventilation or perfusion?

30
Q

How does V/Q ratio change as you move from the apex to the base of the lung?

A

V/Q is high at the apex of the lung and low at the base of the lung

31
Q

Describe why other areas of the lung can’t compensate when certain areas of the lung have a low V/Q ratio, for example in pneumonia?

A

In areas with a normal V/Q ratio, the haemoglobin quickly becomes saturated with oxygen, meaning increased ventilation will not increase the oxygen content of the blood

32
Q

What is the last structure of the conducting airways?

A

Terminal bronchioles

33
Q

What is the first structure of the respiratory airways?

A

Respiratory bronchioles

34
Q

What type of epithelium are type I pneumocytes?

A

Simple squamous

35
Q

Give the equation for calculating alveolar ventilation.

A

Alveolar ventilation = (tidal volume - dead space volume) x respiration rate

36
Q

Why can chronic hypoxia result in right sided heart failure?

A

Due to hypoxic pulmonary vasoconstriction - low PAO2 induces pulmonary vasoconstriction, which increases pulmonary vascular resistance and pulmonary arterial pressure, causing pulmonary hypertension

37
Q

What will happen to PAO2 if ventilation increases but perfusion remains constant?

A

PAO2 increases as more fresh air enters the alveolus

38
Q

What will happen to PACO2 if ventilation increases but perfusion remains constant?

A

PACO2 decreases as more CO2 is removed

39
Q

What will happen to PAO2 if perfusion increases but ventilation remains constant?

A

PAO2 will decrease as more blood passing by carries away more oxygen

40
Q

What will happen to PACO2 if perfusion increases but ventilation remains constant?

A

PACO2 will increase as more CO2 from blood enters alveolus but constant ventilation means it is not expelled

41
Q

Describe the partial pressure of O2 and CO2 in a blood vessel leaving a shunt area.

A

Low O2
High CO2

42
Q

In which part of the lung is V/Q ratio highest, apex or base?

43
Q

What form of oxygen is proportional to the partial pressure of oxygen in the blood (PaO2)?

A

Oxygen dissolved in the plasma