Dynamics-Scharf Flashcards
What is the difference between statics and dynamics?
Statics: Pressure-Volume properties, No airflow Dynamics: Pressure-Flow properties, during airflow
How does flow relate to pressure, conductance and resistance?
=P/R or PxG (conductance)
Which regions are laminar vs turbulent?
Laminar flow in small airways
How do turbulent laminar flow relate to viscosity and density?
Laminar flow resistance depends on viscosity not density. Turbulent flow depends on density not viscosity.
Equation for Reynold’s number
Re= 2rvd/η where v is velocity, d is density and η is viscosity
quation for pressure change in laminar flow
Δ P = R X V (Pressure drop is proportional to the flow down the tube.)
quation for pressure change in turbulent flow
Δ P = K X V^2 (Pressure drop is proportional to the square of the flow down the tube).
What components of pressure do the lungs need to overcome across the airways? Graphs of inspiration and expiration.
Elastic pressure and flow/resistive pressure. Elastic force would be a linear decrease in pressure but extra (more negative) pressure needs to be generated to make flow move overcoming resistance. Extra pressure not needed on the way out.
How does lung inflation affect intraalveolar and extraalveolar vessels?
As the lung inflates – it applies positive pressure in intra-alveolar airways (and blood vessels), and negative pressure to extra-alveolar airways (and blood vessels)-Resistance decreases as lung volume increaswes and conductance increases linearly with lung volume.
What controls airway resistance/conductance?
Lung volume (asthmatics compensation for increased resistance)
Airway smooth muscle tone
- Autonomic control
- Sympathetic
- Beta = dilate
- alpha = constrict
- Parasympathetic = constrict
- Sympathetic
- Nonautonomic, noncholinergic nerves
Airway mucous secretion
Inflammation
Autonomic influences
Airway wall edema
Flow regime
Turbulent flow specific
Gas density: gas compression (e.g. diving), gas mixture (He/O2 vs. N2/O2-lower density lowers resistance)
Dynamic airway compression (increased pleural pressure relative to airway pressure-coughing compresses airways)
Flow limitation
Plot of pneumotachograph
Use spirometry to measure airflow volume vs flow. Experiment: blow out into spirometer at different efforts: A = maximum, D = less, B = poor effort, C = start from volume lower than TLC. Line 1 = effort dependence of maximum flow rates at HIGH lung volume. Line 2 = effort independence of maximum flow rates at LOW lung volume.
Different lung volumes plotted on pressure vs effort
Here we plot flow against pleural pressure (a measure of expiratory effort) at 3 different lung volumes. Note that at LOW and MID lung volumes, past a certain effort point increasing effort (pleural pressure) does NOT lead to increased flow. Flow is LIMITED. These curves are called isovolume pressure-flow curves. At lower volume there is effort independence of flow rates.
What is the effect of lung volume reduction surgery?
Improved pulmonary function, restored effort independence after effort dependence across all volumes in emphysema.
How is transpulmonary pressure calculated?
Alveolar pressure-Equal pressure point pressure (EPP). EPP is the point where pleural pressure is equal to airway pressure on the way to the mouth.
How is the flow related to the equal pressure point?
Flow= Transpulmonary pressure/Upstream resistance. Not dependent on how much pleural pressure is applied. Upstream is airway resistance. Increased airway resistance leads to decreased flow.
Graph of elastic and resistive properties and work
AEC = elastic recoil
ABC = actual inspiratory PV tract. The extra pressure between B and E is due to flow resistance. OABCD = total Work
OAECD = elastic work
ABC = resistive work
AFC is expiratory PV path. Energy is stored in inspiration and recovered in expiration and dissipated as heat.
If breathe through a straw, will not change elastic properties but will move resistive pressure curve to the right to increase work.
