Ventilation Flashcards
What lung volume is represented when forces inflating and deflating the lungs are equal? What phase of the respiratory cycle does this occur?
Balance between forces is seen at the end of quiet inspiration, dorce is required to displace this equilibrium to produce inspiration. Respresented by the functional residual capacity (resting volume of the lungs)
What keeps the lungs from collapsing away from the chest wall?
The lungs and thorax form a mechanical system. Elastic forces tending to collapse the lung are balanced by the elastic recoil in the thoracic cage and diaphragm trying to expand the chest. The two opposing forces create a negative intrapleural pressure. The pressure gradient between the outside and inside of the lungs ensures that the lungs are held partially expanded in the thorax.
Describe the differences between the first and twelfth rib and how this affects respiration
The first rib is fixed during respiration by scalenes which help keep the thorax in a fixed position, while the 12th rib is ‘floating’ and not attached to the sternum. Durign inspiration the itnercostal muscles expand the upper ribs forwards (pump-handle) and the lower ribs move upwards and outwards (bucket handle).
Which parts of the lung expand the most during inspiration?
Expansion is determined by compliance. Compliance is greatest at lower lung volumes and smallest at higher volumes
The lung volume in the base of the lung is less because it is compressed relative to the apex, therefore it has a greater initial compliance than the apex. The base of the lung will therefore expand more than the apex.
What are the muscles involved in inspiration?
Scalenes (fix the thorax)
Intercostals
Diaphragm
What are the accessory muscles involved in forced expiration?
Abdominal muscles
Intercostals
Pectoralis major
Latissimus dorsi
Sternocleidomastoid
How is the respiratory pattern of a patient with a low cervical spinal injury different from a patient with low thoracic spinal injury
Injuries between C4-T6 will leave the person able to breathe on their own via the diaphragm, however, the intercostals may be weak or paralysed. Coughing is impaired because there is not enough abdominal movement to clear their airways on their own.
Injuries between T6 and T12 do not normally affect breathing, but ability to cough will be impaired. It is only with injuries below T12 that normal breathing and cough reflexes are preserved.
How do you calculate compliance of the lung?
Change in volume/ change in pressure
Name three roles of surfactant
Reduces the work of breathing by reducing the surface tension in the lung and increasing lung compliance
Reduces the likelihood of tissue fluid transudation Has antioxidant activity
Surfactant proteins (SP-A, SP-D) act as opsonins and can activate macrophages and neutrophils
How does the lung volume change in a patient with fibrosis of the lung? How does this affect ventilation?
In diseases that cause fibrosis, scar tissue replaces normal interstitial tissue in the lung. As a result the lungs become stiffer and compliance decreases. Elastic recoil is increased so greater force is required on inspiration but once inflated recoil is rapid.
Factors that affect lung compliance
Actual lung volume
Diameter of the alveoli
Content of the alveoli
Integrity of surfactant production
Resistance of the airways
Character of air flow
How does the lung volume change in a patient with emphysema of the lung? How does this affect ventilation?
In patients with emphysema, the compliance of the lung is increased, and it becomes more easily distended. This is due to desctuction of the normal lung architecture. Impaired elastic recoil means that the lungs do not deflate easily and there is air-trapping. Vital capacity is decreased.
Functional residual capacity
The volume remainign at the end of quiet (passive) expiration. (Not all the air in the lungs is breathed out)
Residual volume
After forced expiration, a portion of the functional residual volume will be eliminated (expiratory resever volume) but a fraction will always remain (residual volume)
Inspiratory reserve volume
The lung volume at the end of inspiration is not maximal and can be divided further by actively increased = IRV
