Respiratory System Lec 4+5 Flashcards
Discuss pressure changes during breathing
Quiet breathing = intra alveolar pressure changes by 1 mmHg from AP
So while exercise the inspiratory pressure can reduce by 30 mmHg
And the expiration pressure can reach 100 mmHg during straining with close glottis
The transpulmonary pressure (pressure across the barrier between lung walls and pleural cavity) must always remain positive under normal conditions, if it becomes negative the lung will collapse due to elastic properties of the lung
Explain how you measure ventilation
Spirometry
Subject breathed into spirometer during quiet breathing or with max effort
You can do static or dynamic measures of breathing
- static = lung volumes and capacities check up
- dynamic = rates (how fast can u blow out), volumes under forced ventilation
What are the normal lung volumes and capacities that are usually checked for
Tidal volume = 500 mL
Inspiratory reserve volume =3000 mL
What’re the major measurements that are done for a dynamic measurement (ie. forced expiratory test)
FVC (forced vital capacity) = total volume of air expelled from lungs (with maximum force)
FEV1 (Forced expiratory volume in one sec) = volume of air (in L) expired in 1 sec (first sec)
FEV1/FVC (FEV1%) = normally greater than 80%
Why do we need force when breathing?
To over come:
Elastic recoil of lungs and thoracic wall tissue (compliance) during inspiration
Surface tension created by fluid layer lining the inner surface of the alveoli during inspiration (compliance)
Resistance to airflow in airways during both inspiration and expiration (resistance)
Frictional resistance created by deformation of the lung and thoracic wall tissue as it is deformed during inspiration (resistance)
HOWEVER THESE FACTORS ARE MINOR AND SO THE WORK OF BREATHING IS LOW (ONLY 3% EXPENDITURE OF ENERGY AT REST)
What is meant by the compliance of the lungs?
A measure of the effort required to stretch or inflate the lungs
What factors affect the complicance of the lungs?
Pulmonary elastic properties
- increased with high lung volumes
Alveolar surface tension
- fluid film lining of internal alveolar walls which squeezes the alveolus aiding with recoil, thus resisting expansion.
- Reducing lung compliance during inspiration
- La Place’s law = collapsing pressure increases with reduced radius, and low lung volumes
What happens when compliance of lungs decrease?
This would increase the effort in ventilation because a greater charge in pressure would be required to stretch the lung (more effort)
Explain what’s a restrictive airway disease?
Caused by low lung compliance (reduced lung inflation), which causes both FVC (reduced much more) AND FEV1 to decrease
STIFFER LUNGS
Whatre the major causes of restrictive airways disease?
Pulmonary fibrosis
-normal lung tissue replaced by scar tissue
Eg. Asbestosis
Infant respiratory distress syndrome
- lack of surfactant
What determines airway resistance mathematically?
Radius of airways key indicator
F =🔺P/R
F= airflow 🔺P= change in pressure (intra alveolar P and atmospheric) R= resistance to flow (greater the resistance, the lower the force)
Resistance is usually so low that a very small pressure gradient will be enough for normal air flow
IAP is usually the same as AP but differs by like 1 unit
Explain the mechanics of airway resistance during exercise
During exercise ventilation is increased hence the sympathetic NS causes the activation of adrenaline which causes bronchodilation, ensuring minimal resistance
Reasons for airway resistance
Bronchocontriction can be cold induced or occur with asthma and COPD (narrowed lumen of bronchioles)
Explain the impact to expiration and inspiration when there’s increased airway resistance
Expiration is more affected than inspiration
Inspiration = the bronchioles (that lack cartilage ring) are held open by the trans mural pressure
Expiration = the bronchioles are restricted causing increased effort (expiratory pressure) and can lead to the collapse.
Ie. asthmatic pt. Finds it hard to expire and this leads to wheezing
Ie. normal pt. Only at High force expiration and very low volumes can lead to collapse of small airways and air outflow if halted
What’s obstructive airway disease?
Very similar to restrictive airway disease (relevant to surface tension and pulmonary eleastic properties) where the total volume air expired is greatly decreased (FVC) (ratio is higher) whereas, in obsfrguve airway disease we find that the FVC is only reduced a little bit
Therefore the ratio between FEV1:FVC would be very low (less than 70%)
Eg. Asthma, COPD (smoking Tb)
How can you treat obstructive airway disease?
- bronchodilators (acute) = vetalin (beta receptor agonist)
- corticosteroids (long term) = reduce inflammation
Explain the energy expenditure relevant to quiet breathing
Only requires 3% of total energy expenditure.
Quiet breathing allows 500 mL (TV) of air to enter and leave the lungs (inspire and expired), but not all of the 500 mL will empty each time and so the lung volume (TV) remains in the mid range.
HENCE COMPLIANCE IS HIGHEST DURING QUIET BREATHING and so energy is minimised
However, this energy percentage can be increased by decrease in compliance and increase in resistance (like when doing exercise)
What’s tidal volume
Amount of air that enters the nose and mouth per breath, and it’s measured by measuring the volume of air that has been expired
Explain the relation between tidal volume and alveolar volume to anatomical dead space and alveolar ventilation
TV is the amount of volume of air that enters the nose and mouth right, and it’s said that the same amount leave and enter so 500 mL of air
But the TV is not the air available for gas exchange, cause like 150 ml of the conducting part of the airways are the dead space and no gas exchange occurs here
It’s the alveolar volume of air (fraction of TV) that reaches the alveoli (respiratory portion) that allows for gas exchange to occur
How do you calculate the alveolar volume
AV = TV - Volume of deadspace
This determines the efficiency of breathing
So like with each breath, you take in 350 mL of air that reaches the respiratory zone
How do you measure ventilation in terms of rate (ie. per unit time) during a normal tidal volume? Normal quiet breathing
Ve (total pulmonary ventilation ie. the amount of air you are breathing in per unit time)
So Ve = TV x F (respiratory frequency)
So if F = 12 breaths per min and TV = 500 mL per breath
Then Ve = 500 x 12 = 6000 mL/min
Va (alveolar volume) rate = F x (TV- deadspace)
So Va = 12 x (500-150) = 4200 ml per min
How do you measure ventilation in terms of rate (ie. per unit time) during a low tidal volume? Short rapid breaths
TV= 300 mL now (lowered) F = 20 breathes per min (compensated)
Ve = 300 x 20 = 6000 ml per min (no change)
BUT
Va = 20 x (300-150) = 3000 ml per min
This shows that the Va is more affected as it’s reduced by 30% that reaches the alveoli
How do you measure ventilation in terms of rate (ie. per unit time) during a high tidal volume? Long slow breaths
TV = 1000 ml F = 6 b/min
Ve = 1000 x 6 = 6000 ml/min (NO CHANGE)
BUT
Va = 6 x (1000-150) = 5100 ml/min
Here, the Va has increased by 20%
THIS SHOWS US THAT CHNAGIGN THE WAYS YOU BREATHE WILL DRastically AFFECT THE ALVEOLAR VOLUME.
What factors effect rate of gas diffusion between the alveoli and the blood capillaries
- thickness of alveolar capillary boundary (usually 0.2-0.5 microm)
- surface area available for diffusion
- partial pressure gradient of oxygen gas between alveoli and capillary blood
