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ESA3 > Resp 4 - Gas Exchange + Lung Mechanics 1 > Flashcards

Resp 4 - Gas Exchange + Lung Mechanics 1 Flashcards

1
Q

Explain why intrapleural pressure is below atmospheric pressure:

A

The lungs and chest wall recoil in opposite directions

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2
Q

What happens to the pleural pressure during inspiration?

A

Decreases as chest wall expands

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3
Q

Define ‘Resting Expiratory Level’:

A

State of equilibrium between lung recoil and chest wall recoil at the end of quiet respiration

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4
Q

Which muscles are involved in inspiration from the resting expiratory level?

A

Contraction of the diaphragm and the external intercostal muscles

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5
Q

Which muscles are involved in expiration from the resting expiratory level?

  • Hint: Passive vs Forced*
A

Passive = Passive recoil of lungs = no muscles involved

Forced = Contraction of the abdominal muscles and internal intercostal muscles

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6
Q

Name the neve which controls inspiration:

A

Phrenic nerve

C3, C4, C5 keeps the diaphragm alive

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7
Q

Name the accessory muscles used in forced inspiration:

A
  • Sternocleidomastoid
  • Scalene
  • Serratus anterior
  • Pectoralis major
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8
Q

Name the accessory muscles used in forced expiration:

A
  • Internal Intercostals
  • External Obliques
  • Internal Obliques
  • Rectus abdominus
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9
Q

Define compliance:

A

The stretchiness of the lungs: ^ stretchy = ^ compliant

Change in volume per unit pressure change

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10
Q

How would abdominal laparoscopic surgery affect the compliance of the lungs?

A

Decrease compliance

- due to increased intra-abdominal pressure

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11
Q

Define surface tension, and how it relates to compliance:

A

Attraction of water molecules to each other

Increased surface tension = decreased compliance

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12
Q

How does surfactant affect surface tension and compliance?

A

Surfactant reduces surface tension, by breaking H-bonds (detergent), therefore increasing compliance

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13
Q

Which cells secrete surfactant?

A

Type II alveolar pneumocytes

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14
Q

What is surfactant made up of?

A

90% phospholipids

10% Surfactant protein A

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15
Q

What is the Law of Laplace?

A

Pressure = (2 x Surface Tension) / Radius of bubble

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16
Q

What prevents small alveoli collapsing into larger alveoli (via Law of Laplace)?

A

Surfactant

17
Q

What is Newborn Respiratory Distress Syndome?

A
  • Cyanosis, grunting, intercostal and subcostal reccesion seen in premature babies < 30 weeks, due to lack of surfactant = high surface tension = tendency of alveoli to collapse
18
Q

Why is most of the resistance to breathing in the upper respiratory tract?

A

As each branching point increases the number of airways in parallel = Decreases resistance

19
Q

Why is the combined resistance of the airways low?

A

Airways are connected in parallel = decreases resistance

20
Q

List the 3 factors affecting the rate of diffusion across the air-blood interphase:

A

1) Area available for exchange (usually ~70m^2)
2) Resistance to diffusion
3) Gradient of partial pressure

21
Q

What is the normal diffusion rate across the air-blood interphase in the lungs?

A

~ 5 L/min

22
Q

What is the distance between the blood and the air in alveoli?

A

~ 0.6 um

23
Q

How does emphysema decrease diffusion between the air and blood interphase in the lungs?

A

Destruction of alveolar walls = large air spaces = decreased total surface area for gas exchange

24
Q

How does pulmonary oedema decrease diffusion between the air and blood interphase in the lungs?

A

Fluid in the interstitium and alveoli increase the length of the diffusion pathway

25
Q

How does interstitial lung disease decrease diffusion between the air and blood interphase in the lungs?

A

Excessive deposition of collagen in interstitial space + thickening of alveolar walls = lengthened diffusion pathway

26
Q

List the 5 layers making up the diffusion pathway at the air-blood interphase in the lungs:

A

1) Alveolar wall
2) Interstitial fluid
3) Capillary endothelium
4) Plasma
6) Red blood cell membrane

27
Q

Why does gas exchange depend on the partial pressure gradient across the diffusion barrier?

A

Gases move down partial pressure gradients

28
Q

Give the normal values of PO2 in:

  • Inspired air
  • Alveolar air
  • Arterial blood
  • Mixed venous blood
A

Inspired air = 20.8 kPa
Alveolar air = 13.3 kPa
Arterial blood = 13.3 kPa
Mixed venous blood = 5.3 kPa

29
Q

Give the normal values of PCO2 in:

  • Inspired air
  • Alveolar air
  • Arterial blood
  • Mixed venous blood
A

Inspired air = 0.04 kPa
Alveolar air = 5.3 kPa
Arterial blood = 5.1 kPa
Mixed venous blood = 6.1 kPa

30
Q

How do we measure diffusion resistance across the air-blood interphase in the lung?

A

TLCO = Transfer Factor for Carbon Monoxide

  • Patient takes 1 deep breath of air, 14% helium and 0.1%CO
  • Collect exhaled air, and calculate how much CO was transferred from alveoli to blood
  • CO used because of very high affinity for Haemoglobin
31
Q

Define anatomical dead space:

A

The volume of the conducting airways (up to and including terminal bronchioles)
Normally ~ 150ml

32
Q

How does adrenaline affect the anatomical dead space in the airways?

A

Increases due to bronchodilation

33
Q

How do we measure the anatomical dead space?

A

Nitrogen washout test

  • Breathe in 100% O2
  • Exhale for as long as possible
  • Should exhale all residual N2 in airways (normal air is 78% N2), indicating how much residual gas sits in airways
34
Q

Define alveolar dead space:

A

The volume of air in the alveoli not taking part in gas exchange

35
Q

Why may some people have more alveolar dead space than others?

A

Some may have dead/damaged/poorly perfused alveoli

36
Q

Define physiological dead space:

A

Anatomical + Alveolar dead space

= The volume of air in the conducting airways and alveoli not taking part in gas exchange

37
Q

Define pulmonary ventilation rate:

A

The total rate of air movement into and out of the lungs
= Dead space ventilation + Alveolar ventilation
= Tidal volume x respiratory rate
~ 750 ml/min

38
Q

How can you calculate dead space ventilation?

A

Dead space volume x respiratory rate

ESA3 (48 decks)

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