9.1 Mechanical properties of Lung and Chest Wall Flashcards
Where is airway flow the highest?
Over the vocal cords and decays from here and the biggest velocity is at about the 3rd birfurcatuin
What kind of flow is at the voal cords and in airways?
Turbulent over vocal cords and laminar in airways
What are the determinants of airway resistance?
Viscosity, length and radius (under laminar conditions)
Define laminar flow
occurs when a fluid flows in parallel layers with no disruption between the layers
Define turbulent flow
Flow with no organisation
Define transitional flow and when does it occur?
When there is a combination of laminar and turbulent flow and this arises at the birfucation points (laminar until the bifurcation points when it becomes turbulent)
During forced inspiration what keeps the small airways open?
positive transmural pressure
What factors modulate airway resistance and what is the result of these factors?
NEURALLY MEDIATED
Parasympathetic: bronchial constirction and mucous production increases
Sympathetic: B2 action (smooth muscle relaxation, secretion decreases)
Paco2 increase: local airway dilation
P aco2 decrease:local airway constriction
What is static compliance and how is it measured?
When there is no flow and there is a fixed volume
what is actually measured is the total compliance
what static compliance changes occur in emphysema and pulmonary fibrosis?
emphysema: large compliance at FRC with loss of recoil
Fibrosis: reduced compliance at FRC and too much recoil
What is dynamic compliance?
The change in lung volume during cyclic breathing
Compliance changes in emphysema
High static compliance, loss of recoil (has to actively breathe out)
Compliance changes in asthma
Increase in compliance (large expiratory work)
Compliance changes in respiratory distress syndrome
Low static and dynamic compliance
Compliance changes in pulmonary fibrosis
will have to work much harder to breathe out but this work will be saved it will be easier to breathe in
What is Laplace’s law and how does this explain why it is harder to blow up a small lung
P=2t/r
A higher pressure is needed to maintain stability in smaller alveolus
How do alveoli overcome Laplace’s law?
they are interdependent: physically interconnected with each other and lined with surfactant
What is the role of surfactants?
To reduce the surface H2O and hence the surface tension: it is an attractive source of surface molecules that tends to minimise surface area
what cells produce surfactant?
Alveolar type 2 cells
What happens to surfactant during inspiration?
As alveolar surface increases and [surfactant] decreases, surfcatant from micelles recruited to surface
What happens to surfactant during expiration?
Alveolar surface decreases, [surfactant] is higher and surfactant then reforms micelles
What happens in rapidly expanding alveoli?
[surfactant] decreases - calcium decreases - ventilation decreases
What happens in slowly expanding alveoli?
[surfactant] increases - calcium increases - ventilation increases
