airway resistance / obstruction Flashcards
what is the pressure gradient in the respiratory system?
- the difference in pressure of the alveoli and the atmospheric pressure
what equation is relavent to the pressure gradient?
pressure gradient = resistance x flow
therefore, if the pressure gradient P= R x F, what is the resistance equal to (as an equation)?
- R= delta P divided by flow
what is a low airflow rate called?
- laminar flow - ie the air flow runs parallel through the airway
what are higher airflow rates called ?
turbulent flow
what 3 main factors determine airway resistance?
- air viscosity - if it increases, resistance increases
- airway length - longer airways have higher airway resistance
- radius - the largest effect
what effect does a decreased radius have on the resistance of the airway?
- a decreased radius causes an increase in resistance
what effect does an increased radius have on the resistance of an airway?
- it lowers the resistance
what does poiseuilles law state?
- states that the flow of fluids is related to a number of factors including viscosity (n), radius (r), the pressure gradient (P) and the length (l)
at resting rate, what is the flow rate like in normal lungs?
predominantly laminar flow
what is the flow rate like in normal lungs during exercise?
- transitional flow ie
- laminar flow in small airways
- turbulent flow in certain regions such as branch points and large airways
what 2 factors affect the probability of a turbulent flow rate occuring?
- increasin radius
- increasing velocity
how does the resistance change along the airway?
from the trachea- lower resistance - down to the alveoli - higher resistance
what are the major sites of resistance in the respiratory system?
- larger airways and medium sized bronchioles
what structures of the respiratory system contribute little to total resistance?
- small bronchioles down to terminal bronchioles
why does the **total airway resistance decline with increasing lung volume?
- because the airways distend as the lungs inflate and wider airways have less resistance
how does bronchilar diameter change with decreasing or increasing lung volume?
- bronchial diameter increases with increasing lung volume
- bronchiolar diameter decreases with decreasing lung volume
what type of tissue specifically regulates bronchial smooth muscle?
- airway smooth muscle - regulates airway diameter by bronchoconstriction and bronchodilation
Describe the autonomic effects on smooth muscle in the airways
ie what effect do they have - constriction or dilation and what happens to the airway diameter and resistance
- parasympathetic stimulation causes bronchoconstriction - reducing airway diameter and increasing airway resistance
- sympathetic stimulation causes bronchodilation of smooth muscle which increases the airway diameter and decreaes airway resistance
what is dynamic compression of the airways?
- occurs when the** intrapleural pressure equals or exceeds the alveolar pressure **which causes dynamic collapsing of the lung
- it is termed dynamic as the given **transpulmonary pressure **(pressure between alveoli and intrapleural) **varies **based on different factors
in what type of situations can dynamic compression of airways occur?
- forced expiration - when the intrapleural pressure is greater than the ATM pressure
- also seen in diseases like COPD- wheezing sound during expiration
why are the airways compressed during forced expiration?
- as the intraplueral pressure is highly positive
- this positive pressure is exerted on all the airway regions and airway begins to collapse
what is the equal pressure point and what happens above this point??
- the point at which the pressure inside the airway equals the pressure outside (intrapleural pressure)
- above this point, there is a tendancy for airway collapse
Describe factors (seen in diseases) that enhance dynamic airway collapse
- increased small airway resistance - eg in asthma and chronic bronchitis
- increased compliance- eg in emphysema
what effect does an increased compliance (eg during emphysema) have on inspiration and expiration?
- during inspiration, the lung is much easier to inflate and dynamic collapse is not a problem here
- during expiration - there is dynamic airway collapse - as it causes a forced expiration - using the muscles which creates a positive pressure and collapse
what is chronic bronchitis histoogically associated with?
- thickening of the airway wall with encroachment into the lumen
how does chronic bronchitis affect the radius and resistance of the airway?
as chronic bronchitis is associated with thickening of the airway wall, there is a reduced lumen radius and increased resistance
why does asthma cause increased airway resistance?
- as there is excessive bronchial smooth muscle contraction
how can we test for increased airway resistance?
doing clinical pulmonary function tests - checking forced vital capacity (FVC - sum of lung volumes) and FEV1(forced expiration volume)
what are obstructive diseased characterised by & give a clinical example?
- airway obstruction / narrowing
- difficulty expiring air
- eg COPD and asthma
what are restrictive diseases characterised by & give a clinical example?
- reduced compliance ie ability to expand lungs
- ie difficulty to get air into the lungs
- eg pulmonary fibrosis
how if FVC, FEV1 and FEV1/FVC affected by obstrutive lung disease?
ie are they reduced / normal etc
- FVC - same or can be slightly reduced
- FEV1 - reduced
- FEV1/FVC - reduced
how is FVC, FEV1 and FEV1/FVC affected by restructive lung diseases?
ie are they reduced or normal
- FVC - reduced
- FEV1- reduced
- FEV1/FVC - normal
