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BMS 264: Biomedical Physiology > Lecture 19: Ventilation, Lung Measurements And Disease > Flashcards

Lecture 19: Ventilation, Lung Measurements And Disease Flashcards

0
Q

Factors affecting pulmonary ventilation.

1. Lung compliance

A

Compliance describes how easily the lungs can be stretched.
The change in lung volume resulting from a given change in pressure.
Healthy lungs have a high compliance:
-this means lungs stretch easily
-smaller changes is Ptp to bring in given volume of air
-less work is required to attain a certain lung volume

Dependant on:
A) stretchability/ elasticity of the tissues in the lungs and thoracic cage
B) alveolar surface tension

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1
Q

What are the factors affecting pulmonary ventilation?

A
  1. Pressure gradient
  2. Lung compliance
  3. Airway resistance
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2
Q

What are some pathological tissue changes that may change compliance?

A

Fibrosis:
Damage to lung tissue by bacteria (eg tuberculosis) or irritants (asbestos)
-tissue death leads to scar tissue (abnormal formation of fibrous connective tissue)
-“stiffer” therefore reduced compliance

Emphysema:

  • cigarette smoke leads to backdown of alveolar walls
  • increased compliance (like floppy balloon) but reduced elastic recoil
  • also having airways narrowing
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3
Q

Tell me about surface tension and compliance?

A

Premature infants often have inadequate production of surfactant. How does this effect compliance?
Decrease lung compliance? Or increase

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8
Q

Factors effecting pulmonary ventilation
2. Resistance
Tell me about it

A

Resistance is a force that opposes air flow

  • increased resistance requis a greater pressure gradient to produce same flow.
  • gas molecules encounter resistance when they collide with the wall of the airway
  • most important factors for airways resistance is the radius of the airway.

Total airway resistance:

  • due to extensive branching, especially in respiratory zone, total airway resistance is low.
  • radius and resistance in trachea and bronchi is fairly constant (effect of cartilage) -can change with disease
  • changes in airway resistance occur mainly due to changes in radius of the bronchioles (memba smooth muscles in wall not cartilage)
  • radius of bronchioles change due to:
    • passive forces
    • active forces (ANS and local mediators)
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9
Q

Tell me the factors affecting resistance of bronchioles?

A
  1. Passive forces:
    - change to bronchiolar radius with each breath, increased transpulmonary pressure during inspiration pulls bronchioles open and decreases resistance.
    - decreased tp pressure during expiration allows to return to normal and increase in resistance.
    - forced expiration causes even greater increase in resistance
  2. Active changes to bronchiolar resistance.
    - relaxation/ contraction of bronchiolar smooth muscle, altering radius
    - long term variations in airway resistance
    - under control of ANS and local mediators eg CO2” histamine, etc
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10
Q

Describe the autonomic control of airway diameter

A

Sympathetic:
-nerve releases Ach to nicotonic Ach receptor which releases adrenaline ➡ beta adrenergic receptor➡ bronchiolar relaxation

Parasympathetic:
Nerve releases Ach➡ attaches to nicotonic Ach receptor ➡ causes release of more Ach ➡ causing bronchiole constriction

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11
Q

Increased resistance in disease
Eg asthma
Tell me how it works

A
  • short term and reversible
  • bronchiole inflammation, smooth muscle contraction, increased mucus production
  • decreased airway radius so increased resistance
  • increased resistance means larger pressure gradient needed to create normal airflow
  • most difficulty during expiration
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12
Q

Increased resistance in disease

Eg Emphysema

A
  • smoking leads to inflammation: excess mucus, edema (fluid accumulation) and constriction of bronchiolar smooth muscle
  • this leads to narrowing of the airways and increased resistance
  • also increased compliance due to breakdown of the alveolar walls
  • exhalation is difficult die to loss of elastic recoil and passive narrowing of airways
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13
Q

Respiratory measurements: Lung volumes and capacities.
Spirometry to assess pulmonary function.
Describe how the test is done and why

A
  • non invasive pulmonary function test
  • measures volume of air moving into and out of lungs
  • a typical spirometry recording involves?
    • a few quiet breaths
    • maximal inspiration
    • maximal expiration
  • can help to diagnose and distinguish between pulmonary disease
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14
Q

What is the tidal volume?

A

Volume of air that moves in and out of the lungs during a single quiet breath (unforced breath)

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15
Q

Inspiratory reserve volume (IRV)

A
  • max volume that can be inspired after the end of a normal inspiration
  • measures how much extra air you can breathe in by forced inspiration
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16
Q

Expiratory reserve volume (ERV)

A
  • max volume that can be expired after the end of a normal expiration
  • measures how much extra air you can breathe out by forced expiration
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17
Q

Residual volume (RV)

A

-volume of air remaining in lungs after maximum expiration

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18
Q

Inspiratory capacity (IC)

A

-lung capacities are the sum of 2 or more lung volumes
-maximum volume of air that can be inspired at the ends of resting expiration
IC= Vt + IRV
Tidal volume

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19
Q

Vital capacity (VC)

A

-maximum volume of sit that can be expired following a maxi al inspiration
VC=Vt + IRV + ERV
Slide 31

20
Q

Functional residual capacity

A

-volume of air remaining in the lungs at the end of a tidal (quiet) expiration
FRC= ERV + R
Slide 31

21
Q

Total lung capacity

A

Total volume of air in the lungs at the end of maximal inspiration.
TLC= Vt + IRV + ERV + RV
Slide 32

22
Q

There is a summary of lung volumes and capacities on slide 34 that you could learn

A

Summary

23
Q

How would you expect these volumes and capacities to change in:
A) fibrosis eg tuberculosis
B) conditions with low surfactant

A

A) fibrosis eg tuberculosis

  • reduced compliance, therefore difficulty expanding lungs
  • VC and TLC are low

B) low surfactant

  • increased surface tension ➡ reduced compliance and difficulty expanding lungs
  • VC and TLC are low

These are examples of restrictive lung disease

24
Q

How would you expect these volumes and capacities to change in:
A) asthma
B) emphysema

A

A) asthma:

  • narrowing of airways, especially during expiration, makes it difficult to exhale
  • air gets trapped in the lungs
  • RV and ERV decreases
  • TLC may increase later in the disease as lungs over inflate

Emphysema?
-loss of elastic recoil and narrowing of airways, especially during expiration, make it difficult to exhale and air gets trapped in lungs
RV and FRC increase
-VC and ERV decrease

These are examples of obstructive lung disease

25
Q

What is the difference between restrictive and obstructive lung disease?

A 
Restrictive: 
Cause- decreased ability for lungs to expand due to damage to lungs, pleura or thoracic wall 
⬇VC and ⬇TLC
-decreased lung compliance 
Eg fibrosis, low surfactant

Obstructive lung disease:
-narrowing of airways, causing obstruction to flow
-difficulty expiring, lungs over inflate
⬆RV and ⬆FRC
-increased resistance
Eg asthma and emphysema

26
Q

Assessing flow rate

Slide 38

A

Check it ouuut

27
Q

Ventilation rate

Respiratory ventilation = airflow per minute

A

-we can define different ventilation rates depending on which part of the respiratory system we are talking about
Minute ventilation: total volume of air entering or leaving the lungs per minute
Deadspace ventilation: volume of air inspired per minute that DOES NOT take part in gas exchange
Alveolar ventilation: volume of air that reaches the alveoli per minute (GAS EXCHANGE)

28
Q

Minute ventilation (Ve)
Total volume of air breathed per minute
How to calculate it?

A 
Ve= Vt x f
Vt= tidal volume 
F= respiratory frequency (=breath/min)
29
Q

Dead space ventilation.

Describe and calculate. Two types

A

The volume of air inspired per minute that DOES NOT participate in gas exchange.

  1. Anatomical dead-space
    - air in airway that does not participate in gas exchange eg URT, trachea, bronchi, bronchioles
  2. Alveolar dead-space:
    - dead space within alveoli
    - ventilated alveoli that are poorly perfused
  3. Equipment/mechanical dead space
    - dead space caused by respiratory equipment eg face mask, snorkeling, tubing
30
Q

Alveolar ventilation

A 
The volume of air that reaches the alveoli every minute 
Va= Vt-Vd x f
Vt= tidal volume 
Vd= dead space volume per breath 
F= breaths per min

BMS 264: Biomedical Physiology (33 decks)

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