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)
Describe the changes in alveolar pressure during a normal breathing cycle
Begins at zero when there is no airflow (same as atmospheric), during inspiration it becomes slightly negative to draw air in, and then slightly positive during expiration to force air out
What is functional vital capacity (FVC)?
Amount of air which can be forcibly exhaled from the lungs after taking the deepest breath possible
What is tidal volume?
Normal volume of air breathed in/out
What is residual volume (RV)?
Amount of air left after maximal expiration
What is functional residual capacity (FRC)?
Volume of air present in the lungs at the end of passive expiration; ERV + RV
What is expiratory reserve volume?
Amount of additional air that can be forced out
What is inspiratory reserve volume?
Amount of extra air that can be inhaled
How do you calculate inspiratory capacity?
Tidal volume + inspiratory reserve volume
How do you calculate vital capacity?
Inspiratory reserve volume + expiratory reserve volume + tidal volume
How do you calculate total lung capacity?
Inspiratory reserve volume + expiratory reserve volume + tidal volume + residual volume
What is forced expiratory ratio 1 (FEV1)?
Maximum exhalation volume in 1 second
What is the anatomical dead space?
Volume of air in the mouth, pharynx, trachea and bronchi up to the terminal bronchioles
What is the physiological dead space?
Anatomical air space + alveolar dead space; in health individuals there should only be anatomical dead space, but with age or disease, alveolar dead space appears
Define alveolar ventilation
The portion of the total ventilation that reaches the alveoli and participates in gas exchange.
How do you calculate alveolar ventilation?
Alveolar ventilation (ml/min) = pulmonary ventilation (ml/min) – dead space ventilation (ml/min)
