Mechanics of breathing Flashcards
Describe the relationship between air flow in expiration and inspiration and alveolar pressure
Expiration= positive air flow Inspiration= negative air flow
Graph of air flow vs time and alveolar pressure vs time looks like -sinx.
Negative air flow and alveolar pressure in inspiration.
Positive air flow and alveolar pressure in expiration
What is the relationship between alveolar pressure and alveolar volume?
Palv directly proprtionate to 1/alvolar V
Palv= elastic recoil pressure+ pleural pressure
Distending pressure increases alveolar volume leading to decrease in Palv = INWARD AIRFLOW
Elastic recoil decrease in alveolar volume leading to increase Palv = OUTAWRD FLOW. THIS IS PASSIVE
Describe distending pressure
It is the transpulmonary pressure (Ptp)
Ptp= Palv - Ppl
Ppl is the inward force of the lungs and the outward force of the chest a.k.a INTRAPLEURAL PRESSURE
How is transpulmonary pressure generated (Ptp)?
By inspiratory muscles
Diaphragm is main muscle of inspiration. Accessory muscles include external intercostals and sternocleidomastoid and scalene muscles.
When the diapragm is flattened, the radius of lung increases leading to decreased pressure force inside lung to generate breath
Where is intrapleural pressure highest? Why?
Ppl is more -ve at the top as the alveoli are larger, less compliant and so less ventilation
What is compliance? Describe compliance in lung and chest wall
Compliance refers to the distensibility of a chamber due to changes in transmural pressure
In the lung this is the relationship between the change in lung volume and intrapleural pleasure (Ptp=Palv-Ppl). In the curve lung volume vs transpulmonary pressure, the curve is steepest when lung volume is around 40%. The lungs are less compliant at high volume
In the chest wall this is the relationship between the change in lung volume and transmural pressure (P=Ppl-Patm). The curve %Vital capacity against ins/expiration is signed shape. The steepest bit= most compliant and it occurs just before expiration.
What is FRC?
Functional residual capacity- the amount of air at end of expiration.
What is hysteresis?
The transpulmonary pressure vs Volume curve of inhalation is different from the Pressure vs Volume curve of exhalation, the difference being described as hysteresis. Lung volume at any given pressure during inhalation is less than the lung volume at any given pressure during exhalation.
Which cells produce pulmonary surfactant?
What is its role?
Type 2 alveolar cells
It reduces surface tension, thus increasing lung compliance
Premature babies (less than 30weeks) have not made enough surfactant and are at risk of infant respiratory distress syndrome.
Prevents atelectasis by supporting uniform
What is atelectasis?
A complete or partial collapse of a lung or lobe of a lung develops when the tiny air sacs (alveoli) within the lung become deflated.
What is breathing?
Overcoming recoil pressures and airway resistance
In large vessels, or where blood is high in viscosity, turbulent flow may occur. Turbulent flow resistance is greater than laminar flow resistance
When you decrease the radius of a blood vessel, you increase the resistance by a factor of 4.
Terminal airways are in parallel so resistance is low as 1/Rt= 1/R1 + 1/R2 + 1/R3
