Mechanics of breathing II Flashcards
What is the speed of the air through the airways proportional to?
→ pressure gradient between atmosphere and lungs
What is the equation for compliance?
→ compliance = Δ volume/ Δpressure
What is compliance?
→How easy it is to get the lungs to expand
What is transpulmonary pressure?
→The force required to expand the lungs
What is the transpulmonary pressure equation?
→Transpulmonary pressure (Ptp) = Alveolar pressure (Palv) - Intrapleural pressure (Pip).
What is the equation for airflow?
→ Pressure / Resistance
What happens as the airway radius decreases?
→The resistance increases and airflow decreases dramatically
What is the Hagen-Poiseuille equation?
→R = 8nl / πr^4
What happens when the lumen diameter increases?
→Increase in luminal area
→Decrease in resistance
→Increase in flow
What happens when the lumen diameter decreases?
→Decrease in luminal area
→Increase in resistance
→Decrease in flow
How does pattern of airflow affect resistance?
→Laminar flow - no resistance
→Turbulent flow - resistance and produces noise (wheezing)
What is FEV 1?
→Forced expiratory volume in 1 second
What is FVC?
→Forced vital capacity
How do you take into account different lung capacities?
→100 x FEV1/FVC = % of total lung capacity an individual can exhale in the first second
→Ratio of volume in 1 second to total capacity.
What happens to FVC and FEV1 in obstructive airway disease?
→The FVC is the same but FEV1 decreases
→Lung capacity is normal
What happens to FVC and FEV1 in restrictive airway disease?
→The FVC is decreased but FEV1 is the same
→Lung capacity decreases
What is the ratio of someone with obstructive airway disease?
→FEV1 ratio is decreased <70%
What is the ratio for someone with a restrictive airway disease?
→The FVC decreases
→The ratio is not affected >70%
What are alveoli lined with?
→Lined with fluid to enable gas exchange (gas molecules dissolve into water before diffusing)
When does surface tension arise?
→When there is an interface between water and air
How does surface tension arise?
→ Generated by H-bonds between the water molecules exerting a collapsing force towards the center of the bubble.
Why do small alveoli empty into larger ones when surfactant is present?
→The inward pressure on the smaller alveolus is much higher so the air gets forced into the larger alveolus.
What is alveolar surfactant secreted by?
→ Type II pneumocytes
What molecules does surfactant contain?
→Surfactant has some molecules that are amphiphatic
What is the purpose of amphiphatic molecules in the surfactant?
→ It disrupts the H-bonding between water molecules and reduces the surface tension.
What happens with an increased concentration of surfactant molecules?
→The surface tension decreases as water molecules do not have space to bond.
What happens with a decreased concentration of surfactant molecules?
→Surface tension increases as water molecules are free to bond.
What does pulmonary surfactant help prevent?
→Alveolar oedema
What does surface tension reduce?
→Reduces hydrostatic pressure produced at the air-liquid interface.
→Fluid is pulled out of the surrounding capillaries and into the alveoli.
When does turbulent air flow occur?
→ Breathing hard
→ Areas of obstruction
Why is an increase in lung compliance bad?
→ Easy to expand the lungs but they cannot recoil
What does a steep gradient mean on the lung compliance graph?
→ The lungs are easier to expand
