Mechanics of ventilation Flashcards
What is Boyle’s law?
At a fixed temperature; the pressure and volume of an ideal gas are inversely proportional
What muscles of respiration are used in inspiration?
Diaphragm, external intercostal muscles, scalenes - when upright
What are the muscles of respiration used in expiration?
None, it is a passive process. There is elastic recoil in the lungs.
Name some accessory muscles
Sternocleidomastoid, scalene muscles, pectoralis minor, trapezius, transversus thoracis, subcostal muscles, serratus posterior groups
What muscles are used in forced expiration?
Abdominal muscles contract which increases abdominal pressure and expels air.
What is lung volume?
The amount of air moved with respiration
What does lung volume depend on?
Inspiratory effort, expiratory effort, lung capacity
What is lung capacity related to?
Age, sex, height and ethnicity
What parameters make up the total lung capacity (TLC)?
TV/IRV/ERV/RV
What 3 things affect lung compliance?
1) Elastic tissues of the lung - elastin and collagen fibres help with recoil
2) Elasticity of thorax
3) Surface tension
What is the equation for lung compliance?
Compliance = change in volume / change in pressure
What is Laplace’s Law?
P=2T/r
Collapsing pressure = 2(surface tension)/radius of the sphere. A smaller alveolus is more likely to collapse than a bigger alveolus.
What is surfactant?
Produced by type II pneumocytes. Lipoprotein with hydrophobic and hydrophilic segments. Produced at 24 weeks gestation.
Reduces surface tension so alveoli is less likely to collapse.
What 4 factors determine airway resistance?
1) Lung volume - obstructive and restrictive diseases
2) Bronchial muscle smooth tone - autonomic nervous system
3) Altered airway calibre
4) Change in density and viscosity of inspired gas
What is the approximate intrapulmonary pressure?
760mmHg or 0mmHg (since it is equal to atmospheric pressure)
