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UNIT 4 > Respiratory physiology : Ventilation and Gas exchange > Flashcards

Respiratory physiology : Ventilation and Gas exchange Flashcards

1
Q

What are the 2 parts of the respiratory system?

A
  • Conducting system
  • Respiratory zone
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2
Q

How does the cross-sectional area increase as you go down?
What has this got to do with airflow and resistance?

A

> increases due to increasing number of airway structures as we go down the divisions
Resistance to airflow greatest in airways generation 6th to 8th
>Least optimal combination of total airway cross-sectional area and airway radius

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3
Q
  1. What is part of the conducting zone? Why are they known as anatomical dead space?
  2. What is its function?
  3. Is their resistance?
A
  1. -Nasal & oral cavity, pharynx, larynx, trachea, bronchial tree, terminal bronchioles (airway division ~15) - NO RESPIRATION

➢ Distribute air to the lower airways
➢ Warming and humidification
➢ Speech
➢ Removal of pathogens and debris

  1. -Relatively high resistance to air flow (division 1-8)
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4
Q
  1. What is the respiratory zone?
  2. Is their resistance?
  3. What surround the alveoli?
A

1.-Respiratory bronchioles, alveolar ducts, alveoli (airway generation > 15)
-Takes up majority of the human healthy lung

2.Low resistance to airflow despite small diameter due to high cross-sectional area

3.High density of pulmonary capillaries for gas exchange

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5
Q

What is the respiratory membrane made of?
What is its average thickness?
What happens?

A

> EXCHANGE ZONE
1. made of several, thin layers (type I alveolar cells, basement membrane, capillary endothelium

  1. Average thickness: 0.6 micrometres
  2. O2 and CO2 diffuse passively along their concentration gradient across the respiratory membrane
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6
Q

What are the 2 factors lung elasticity is determined by?

A
  1. Anatomical : Collagen + Elastin in lung parenchyma stretch when inflated
    -Contributes to 1/3 of lungs elasticity
  2. By surface tension : force pulling molecules of fluid together at an air-liquid interface!
    > drives fluid to adopt the smallest surface area possible 2/3 of elasticity - promoting collapse of lung, oppose stretching of alveoli
    * SURFACTANT is secreted by type II alveolar epithelial cells to REDUCE surface tension and prevent collapse of smaller alveoli, makes it easier to inflate lungs
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7
Q

What does the elastic recoil of lungs create?

A

-inwardly directed force which opposes expansion of the alveoli

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8
Q
  1. What is lung compliance?
  2. At higher lung volumes what happens?
A
  1. Elasticity of the lung
  2. Lung compliance decreases… greater unit of transpulmonary pressure is needed to distend the lung (shallow gradient)
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9
Q

Why does compliance vary during inspiration and expiration?

A

-Normal inspiration requires greater transpulmonary pressure than expiration > lung less compliant during inspiration
»Rate of extra surfactant molecule reaching the air/liquid interface is smaller than the rate of alveolar surface expansion during inspiration so surface tension increases

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10
Q

Changes in lung compliance can affect ventilation.
What happens when there is an increase or decrease in compliance?

A

↑ compliance > in emphysema, but airway more prone to collapse

↓ compliance > high amount of force needed to stretch / expend the lungs (e.g. lung fibrosis)

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11
Q

Label.

A

1 Basement membrane
2 Type I epithelial cell
3 Endothelial cell
4 Lumen of pulmonary capillary
5 Alveolar space
6 Erythrocyte
7 Respiratory membrane

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12
Q

What are the key structures of the chest wall ?
What is the purpose of pleural fluid? + How much is there?

A

-lubrication to allow repeated movement of lungs in pleural cavity
>15ml

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13
Q

How do you calculate trans pulmonary pressure?
What is its value at rest?

A

PTP =PA –PIP
At rest > PTP = 4 mm Hg

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14
Q

What does changes in lung volume alter?

A
  • alveolar pressure
    > establishing a pressure
    gradient with the atmosphere (Patm) directing airflow
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15
Q

Describe the mechanical aspect of quiet inspiration. (does not use accessory muscles)

A
  1. Brain initiates inspiratory effort and sends motor nerve impulses to:
    >Diaphragm – contracts and flattens
    >External intercostal muscles: contraction moves chest wall upwards and outwards
    • Increase intra-thoracic volume
    • Transient increase in volume of pleural cavity
  1. Intrapleural pressure becomes more negative
  2. Transpulmonary pressure (PTP = PA-PIP) increases > outwardly directed force increases and overcomes the elastic recoil of the lungs
  3. Increase in lung volume
  4. Alveolar pressure (PA) falls below atmospheric
    pressure (Patm) > pressure gradient
  5. Air move by bulk flow into the alveoli

*Steps occurring simultaneously

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16
Q

Describe the mechanical aspect of quiet expiration. (passive)

A
  1. Brain ceases inspiratory effort > no motor signal sent to inspiratory muscles (quiet expiration is a passive process!)
    * Diaphragm and external intercostal muscles relax! chest wall recoils to resting position
    * Reduction of intra-thoracic volume! decrease volume of pleural cavity
  2. Intrapleural pressure becomes less negative
  3. Transpulmonary pressure decreases
  4. Reduction in lung volume due to elastic recoil force of the lungs to a volume where PTP and elastic recoil force are in
    equilibrium
  5. Alveolar pressure (PA) rises above atmospheric pressure (Patm)
  6. Air moves by bulk flow from the alveoli to the atmosphere

*Steps occurring simultaneously

17
Q

What are the 2 ways we create a pressure gradient to generate an air flow to the respiratory zone?
Normal vs artificial

A

➢Lowering alveolar pressure (PA) below atmospheric pressure (Patm) – negative pressure ventilation (= normal ventilation)
➢Increasing pressure in the nose and / or mouth above alveolar pressure (PA) – positive pressure ventilation
(used in artificial ventilation of patient)

18
Q

Change in transpulmonary pressure (PTP) is crucial for ventilation.

Consider what would happen to PTP in those situations:
-Pneumothorax
-Flail chest

A
19
Q
  1. What is partial pressure?
  2. How do we calculate partial pressure?
  3. Why do alveolar PO2 and PCO2 differ to that in atmosphere?
A
  1. pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own.
  2. Partial pressure =
    (% of substance / 100) x (atmospheric pressure = 760mmHg)

3.
- Warming and humidification in conducting airway
- Constant diffusion of respiratory gases through the respiratory membrane
- Partial replacement of alveolar air with each breath (6% alveolar volume)
-Typical values in alveoli are :
pO2 = 100 mmHg
pCO2 = 45 mm Hg

20
Q

How do gas molecules diffuse?

A
  • Gas molecules move rapidly and randomly
  • Net diffusion of gas molecules in one direction occurs from an area of high concentration to an area of low concentration
  • Respiratory gases diffuse passively along their concentration
    gradient at the exchange surface
21
Q

How do respiratory gasses diffuse?

A
  • At the respiratory membrane, gases diffuse passively along their concentration gradient, from high to low concentration
  • Alveolar PAO2 > PvO2 hence O2 diffuses from
    the alveolar air to blood in pulmonary capillaries
    Alveolar PACO2 < PvCO2 so net CO2 diffusion from the capillary blood to the alveoli
22
Q

What determine the rate of diffusion of gases across the respiratory membrane?

A

-Fickes law
* Note: diffusivity of CO2 is 20x greater than O2 = MORE SOLUBLE

23
Q

What does it mean that O2 is perfusion limited?
Why is this a good thing when it comes to exercise?
What happens when there is reduced diffusing capacity?

A
  • Transit time of erythrocytes in pulmonary capillaries at rest: ~0.75 sec
  • After ~ 0.25 sec, blood PO2 has EQUILIBRIATED with alveolar PO2
    > No further net transfer of O2 will occur At normal alveolar PAO2 and cardiac output, O2 diffusion is perfusion limited

*Large safety margin for diffusion:
Exercise: ↑ pulmonary blood flow – erythrocytes may only stay 0.25sec in pulmonary capillary >equilibrium

**Reduced diffusing capacity: equilibrium may be reached AT REST but not during exercise

24
Q

How does the capillary partial pressure of N2O equilibrate compared to P[a]O2 ?

Why is PO2 slower to equilibrate?

A

-Capillary partial pressure of N2O equilibrates much more rapidly

> When oxygen diffuses into the plasma, some of the oxygen binds to Hb in erythrocytes > until Hb is saturated with oxygen so this oxygen doesn’t contribute to the partial pressure
- Hence, more oxygen needs to diffuse in to equilibrate with P[A]O2
- N2O doesn’t have a specific transport protein so can be transported by only dissolving into the blood

25
Q

Is CO2 perfusion limited?

Why does CO2 equilibrate at the same time as O2 despite being 20x more soluble?

A

-CO2 diffusion is perfusion limited at rest

-partial pressure gradient for O2 is much greater (~ 60 mmHg) than that of CO2 (~ 5 mm Hg)

26
Q

How do you calculate Partial pressure of oxygen?

A

20.8 / 100 * atmospheric pressure (760)

27
Q

What is the function of bronchiole circulation?

A
  • Small proportion of left cardiac ventricle (systemic) output
  • Not for gas exchange
  • Provide nutrients to lung tissue
28
Q

What are the specialist tasks of pulmonary circulation?

A

-Allow blood to equilibrate with alveolar gases
-Perfuse each alveolus in proportion to its ventilation

29
Q

What is the structure of pulmonary circulation?

A
  1. Low resistance of pulmonary vasculature> low pressure + high blood flow (Q = ΔP/R)
  2. 1,000 narrow capillaries / alveoli >total exchange surface 50 – 100 m2
  3. Thin walled vessels with few vascular smooth muscles > very distensible
30
Q

How does gravity cause regional variation in pulmonary blood flow?

A

-Greater perfusion of alveoli at the base of the lungs compared to those in the apex

31
Q

What is the V/Q ratio?

What does the ratio provide an indication of?

A

-Ratio between the amount of air drawn into a lung area(ventilation, V) and the amount of blood supplying that area (perfusion, Q)

> indication about the efficiency of respiratory gases exchange in a region of the lung

32
Q

Why are there regional variations in V/Q ratio?

A
  • regional variations in alveolar ventilation and perfusion
    > V/Q < 1 at the base of the lungs
    > V/Q > 1 at the apex of the lungs
    > On average, V/Q ~ 0.9 in the lungs
33
Q

Why are alveoli at the base of the lungs more ventilated than alveoli in the apex?

A
  1. P[IP] is more negative towards the apex of the lungs
  2. As a result, P[TP] is greater at the apex of the lungs so alveoli are stretched more (over-inflated) in the apex
  3. Over-inflated alveoli are less compliant
  4. For the same change in P[IP], increase in alveolar volume is smaller at apex of lungs than base
  5. Hence ventilation will be greater at the base of the lung than at the apex
34
Q

V/Q mismatch : Airway obstruction

-What phenomenon happens?

A
  • LOW V/Q
35
Q

V/Q mismatch: Pulmonary embolism

-What phenomenon happens?

A
  • HIGH V/Q

UNIT 4 (13 decks)

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