Lecture 3 - Méchanics of breathing Flashcards
What is Boyle’s law
Boyle’s Law: P1V1 = P2V2
How does inspiration and expiration lead to gas exchange
Inspiration and expiration leads to lung volume change, changing the alveolar pressure, causing bulk flow of air into the lungs and alvoli, allowing for gas exchange
After inspiring or expiring and after gas flow, pressure equilisation occurs
Remember, Air moves down pressure gradients from high to low pressure
Describe the physiological changes seen on inspiration that leads to air moving into the lungs
Diaphragm and external intercostal muscles contract, increasing thoracic volume. The lungs will expand, increasing their volume (& decreasing pressure) - causes air to move down it’s pressure gradient into the lungs.
Describe the physiological changes seen on expiration that leads to air moving out of the lungs
The respiratory muscles relax, diaphragm moves upward, theres a decrease in thoracic volume and hence lung volume. This increases alveolar pressure, causing air to move out of the lungs.
Also take about changes in thoracic volume before changes in lung volume, then go onto alveolar pressure
Why is the intrapleural space pressure negative (-5cmH2O)
The lung has a tendency to recoil inwards, whilst the chest has a tendency to expand outwards - they are pulling away from each other and this creates a negative intrapleural pressure (just means it’s less than PATM).
Describe the process of inspiration (include Pip, and transpulmonary pressure)
During in inspiration the diaphragm and external intercostal muscles contract, increasing the volume of the thorax. This makes intrapleural pressure more substmospheric to -8cmH2O, and increases transpulmonary pressure (diff. between intrapleural pressure and alveolar pressure).
This causes the lungs to expand, making alveolar presure subatmospheric - causing air to flow into alveoli.
How is expiration mainly passive at rest?
There is elastic recoil from the elastic elements in the lung.
This recoils the lung back to resting volume (FRC), increasing alveolar pressure, causing air exhalation.
We can use accessory muscles to assist this in forced expiration to generate more pressure e.g. abdominal muscles.
When is there a fall in intrapleural pressure, and what does this equate to?
Fall in intrapleural pressure during inspiration equates with work done to move air.
What is compliance? And what factors affect compliance
Is a measure of the elastic properties of the lung
CL varies with:
- Lung volume - as the lung is stretched it gets harder to stretch, and disease may cause it due to loss of elastic tissue.
- Age - lungs become more compliant (but chest wall becomes more stiff)
- Influenced by alveolar surface tension - controlled by surfactant
What proportion of compliance is determined by surface tension?
2/3’s
How does surface tension occur in the lungs, and why do we need surfactant?
The fluid lining the alveoli exert surface tension, causing them contract and resist expansion.
We overcome this by type II pneumocytes producing surfactant, which breaks up water moleucules by reducing attractive forces of hydrogen bonding to reduce surface tension - this increases lung compliance
If we didn’t have surfactant then we wouldn’t be able to expand our lungs.
What equation describes airways resistance
Where is the main area of airways resistance?
The bronchi are the main area of airways resistance due to the reduced cross sectional area.
Most of the resistance to air flow occurs in the upper airway and the first 6 divisions of the airway.
Smaller airways contribute very little to air ways resistance due to much larger cross-sectional area
