Respiratory physiology Flashcards
Define total lung ventilation
How is it calculated?
Functional significance?
Total rate of air flow in and out of lung during tidal breathing
Tidal volume x respiratory rate
Physiologically insignificant because large percentage of this air flow remains within physiological dead space
Define alveolar ventilation
How is it calculated?
Rate of air flow in and out of gas exchange areas of lung during tidal breathing
Rate of CO2 exhalation / PaCO2 (corrected for units)
Define respiratory dead space
Region in lungs where no gas exchange occurs
What is partial pressure, and what units are used to measure it?
Pressure that a specific gas would exert in the absence of all other gases within a mixture
PP of all gases in a mixture = total pressure exerted by mixture
mmHg and kPa
Average resting O2 consumption
250ml/min
Define tidal volume
Volume of air breathed in and out during normal breathing at rest
Define vital capacity
Volume of air breathed in and out when breathing in and out at maximum capacity
Tidal + Inspiratory reserve + Expiratory reserve
Define Functional residual capacity
How do you measure?
%He1 * (volume of spirometer)
Volume of air remaining in lung after a normal breathe out at rest
Expiratory reserve + Residual volume
Helium dilution
- Known %He dissolved in air chamber of known volume connected to spirometer
- Breathe normally to allow to equilibrate
- Measure new %He
- New volume should be chamber volume + functional residual capacity
%He2 * (volume of spirometer + FRC)
What change generates lung expansion?
Negative intrapleural pressure, drawing air into lung to cause its expansion
What does the lungs compliance curve look like?
At lower lung volumes, smaller transmural pressures are sufficient to increase the lung volume
At higher lung volumes, the size of the transmural pressure required to increase lung volume by the same amount increases
Physical basis of lung compliance curve
- Elastin - Lower compliance at higher volumes due to combined elasticity of elastin molecules found in interstitium
Once stretched fully, elastin becomes highly resistant to further compliance
- Pulmonary surface tension - surface tension enables a fluid to achieve the smallest possible surface area as the molecules attempt to attract one another.
In the alveoli, this translates to collapsing alveolar volumes to decrease surface area.
As lung volumes increase, the resistance to compliance by fluid contributes a significant recoiling force
Hence why type II pneumocytes need to release surfactant to reduce this surface tension
Average intra-pleural pressure? Top and bottom pressures?
- 6cmH2O average
- 10cmH2O top and -2cmH2O bottom
Chest wall compliance description
Chest wall has a tendency to spring outwards
To reduce chest wall volume, negative transmural pressures are required (intrapleural pressure = more positive)
To increase chest wall volume from rest, positive transmural pressure required (intrapleural pressure = more negative)
Why is resting expiration basically passive?
Because during inspiration the lung and chest wall generate an elastic recoiling force which can expire air after inspiration without the need for muscular assistance
What generates the resting negative intrapleural pressure?
Opposing force of lung tending to recoil and the chest wall tending to expand
