Ventilation Flashcards
How does elastic recoil within the lung occur?
Thoracic cavity has a negative pressure relative to the atmosphere, the lung is an elastic tissue and tries to collapse - the lungs are bound by the ribs, sternum and diaphragm which are under tension and try to spring out
What is compliance?
(Equation)
Compliance = Change in Volume/Change in Pressure
If a small change in pressure leads to a alrge change in volume, the tissue has hogh compliance such as the lungs or veins
Are the movements of the lungs passive or dynamic?
Passive - resulting from forces external to the lungs
The respiratory muscles provide these forces
What is the role of the diaphragm in inspiration? how does this change during exercise?
Raises pressure within the thoracic cavity (increasing volume) this pressure wants to equalise so air from the atmosphere enters
In exercise the external intercostal muscles and scalene muscles act as accessory muscle
How is expiration a passive process and explain this
Passive as there are no muscles involved - diaphragm nd other muscles simply relax. Lowering the pressure in the thoracic cavity decreading volume meaning air has to leave and pressure becomes negative compared to the atmosphere
What is elastic resistance in regards to lung tissue?
a.k.a. Compliance
What is surface tension in the respiratory system?
Resistance from the surface forces of the alveolar gas-liquid interface
How is elastic recoil obtained in alveolar walls and the airways?
Lots of collagen and elastin fibres meaning that the lung is able to return to its resting volume after distension
Where are the surface tension forces within the lung?
Surface tension forces are only exhibited on the gas-liquid/gas-exchange surface of the alveoli
How are small alveoli adapted not to collapse due to surface tension?
Alveoli interconnected via proes/septae so due to surface tension we might expecyt smaller alvoli to collapse as there is more pressure and large alveoli to expand but we dont as the lung produces surfactant to reduce surface tension produced by type II epithelial cells surrounding type I alveoli
How does surfactant prevent alveolar collapse?
Surfactant is a polar phospholipid - the head of surfactant is polar and they repel each other on the surface of the alveolus preventing collapse
Therefore, surfactant works to increase compliance and reduce work of expanding in the lungs as well as promoting stability of each alveolus
How does infant respiratory distress syndrome occur? How is it treated?
Lck of surfactant production for the alveoli - causing: stiff lungs with low compliance, atelectasis, alveoli filled with transudate
Treated with synthetic surfactant
What are the factors determining airway resistance?
- Lung volume
- Contraction of bronchial smooth muscle
- Density and viscosity
- Tissue resistance
How do we work out pulmonary resistance (total resistance)?
Total resistance = Airway Resistance + Tissue Resistance
