Lecture 19: Ventilation, Lung Measurements And Disease Flashcards
Factors affecting pulmonary ventilation.
1. Lung compliance
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
What are the factors affecting pulmonary ventilation?
- Pressure gradient
- Lung compliance
- Airway resistance
What are some pathological tissue changes that may change compliance?
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
Tell me about surface tension and compliance?
Premature infants often have inadequate production of surfactant. How does this effect compliance?
Decrease lung compliance? Or increase
Factors effecting pulmonary ventilation
2. Resistance
Tell me about it
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)
Tell me the factors affecting resistance of bronchioles?
- 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 - 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
Describe the autonomic control of airway diameter
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
Increased resistance in disease
Eg asthma
Tell me how it works
- 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
Increased resistance in disease
Eg Emphysema
- 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
Respiratory measurements: Lung volumes and capacities.
Spirometry to assess pulmonary function.
Describe how the test is done and why
- 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
What is the tidal volume?
Volume of air that moves in and out of the lungs during a single quiet breath (unforced breath)
Inspiratory reserve volume (IRV)
- 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
Expiratory reserve volume (ERV)
- 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
Residual volume (RV)
-volume of air remaining in lungs after maximum expiration
Inspiratory capacity (IC)
-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
Vital capacity (VC)
-maximum volume of sit that can be expired following a maxi al inspiration
VC=Vt + IRV + ERV
Slide 31
Functional residual capacity
-volume of air remaining in the lungs at the end of a tidal (quiet) expiration
FRC= ERV + R
Slide 31
Total lung capacity
Total volume of air in the lungs at the end of maximal inspiration.
TLC= Vt + IRV + ERV + RV
Slide 32
There is a summary of lung volumes and capacities on slide 34 that you could learn
Summary
How would you expect these volumes and capacities to change in:
A) fibrosis eg tuberculosis
B) conditions with low surfactant
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
How would you expect these volumes and capacities to change in:
A) asthma
B) emphysema
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
What is the difference between restrictive and obstructive lung disease?
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
Assessing flow rate
Slide 38
Check it ouuut
Ventilation rate
Respiratory ventilation = airflow per minute
-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)
Minute ventilation (Ve)
Total volume of air breathed per minute
How to calculate it?
Ve= Vt x f Vt= tidal volume F= respiratory frequency (=breath/min)
Dead space ventilation.
Describe and calculate. Two types
The volume of air inspired per minute that DOES NOT participate in gas exchange.
- Anatomical dead-space
- air in airway that does not participate in gas exchange eg URT, trachea, bronchi, bronchioles - Alveolar dead-space:
- dead space within alveoli
- ventilated alveoli that are poorly perfused - Equipment/mechanical dead space
- dead space caused by respiratory equipment eg face mask, snorkeling, tubing
Alveolar ventilation
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
