Respiratory Physiology Flashcards
How does the intrapleural pressure relate to the atmospheric pressure ordinarily?
Is usually negative with respect to the atmosphere (to draw air in down gradient)
Describe the intrapleural cohesive force
Intrapleural cohesive force is similar to that experienced with a water drop placed between two glass slides – they can slide over each other but cannot separate them, and therefore as the chest wall expands during inspiration, the lung is obligated to follow, so the two structures expand as a single unit
Describe the changes in intrapleural pressure during breathing
Pleural pressure at start of inspiration is slightly negative, intrapleural pressure becomes more negative during expansion of the ribcage and then as intrapleural pressure becomes less negative this leads to quiet expiration (passive)
How can you calculate lung compliance?
Compliance = change in volume/change in pressure
What are surface tension elastic forces?
On the inner surface of the alveoli the water surface is trying to contract which results in the alveoli trying to collapse and forcing air out through the bronchi
What would reduced compliance of the lungs suggest?
A reduced compliance may suggest an increase in fibrous issue in the lung (pulmonary fibrosis), collapse or increase in pulmonary venous pressure
What would increased compliance of the lungs suggest?
Emphysema or age
What is emphysema?
Where there is destruction of the normal lung architecture (including elastic fibres and collagen) so recoil is impaired –> lungs don’t deflate as easily. However, the lung is more easily distended and therefore the compliance of the lung is increased
What does fibrosis in the lungs lead to?
Decreased compliance when the same amount of pressure is applied, and therefore the lungs are harder to inflate
What is a pneumothorax?
If air enters the pleural space
What is infant respiratory distress syndrome?
Developmental insufficiency of surfactant production and structural immaturity in the lungs at birth
How does asthma affect airway resistance?
The contraction of bronchial smooth muscle narrows the airway and increases resistance in response to an allergen
Describe laminar flow
The movement is orderly and streamlined
Describe turbulent flow
Movement is chaotic
Where does almost half of resistance to airflow stem from?
Upper respiratory tract (nose, pharynx and larynx)
