Resistance to Air Flow Flashcards
Airflow in the trachea and bronchi is (laminar or turbulent)
Turbulent
Airflow in the small airways (bronchioles) is (laminar or turbulent)
Laminar
If you half the radius of an airway, the resistance changes how?
Resistance increases 16x (greater contact with walls) (inversely proportional to the 4th power)
Resistance is inversely proportionally to the ______ power of the radius
4th
Total airway resistance is highest in the…
Segmental bronchi
Total airway resistance decreases as you go towards ______
alveoli (may be individually smaller, but have tremendous total cross-sectional area)
Resistance to airflow is increased during (expiration or inspiration)
Expiration
Why is flow rate asymmetrical during expiration?
Flow rate is high at high lung volumes, but declines rapidly as the lung empties and airways are compressed (effort independent limitation)
What does effort-independent mean in context to expiration?
With forced expiration, there is a point where more force can’t increase flow rate because you begin to compress airways
What prevents non-cartilaginous airways from completely collapsing during the effort-independent phase of forced expiration?
alveolar interdependence and tethering of small airways by alveolar walls (synergistically keeping each other open)
An example of a pulmonary disease characterized by the destruction of lung tissue, and thus decreased alveolar interdependence and tethers
Emphysema
Coping strategies for obstructive lung diseases (to help prevent airway collapse)
- Exhale slowly (airflow is less turbulent therfore less resistance)
- Breath at high lung volumes (keeps the airway more open)
- Create backpressure via pursed lips (keeps the airway more open)
Obstructive flow-volume curves have what kind of appearance?
“scooped out” (premature collapse of airway)
Common test/measurement for pulmonary function
Spirometry
the volume of air expired in the 1st second of a maximal expiration
Forced Expiratory Volume 1 (FEV1)
rate of flow during the middle portion of the expiration; has greater representation for air flow through the small airways, as flow is entering the effort independent phase of expiration
FEF 25-75%
Why do patients with obstructive lung disease have a low FEV1 value?
their lungs have low elastic recoil and small airways lack tethers and/or are occluded by mucus plugging and edema. As a result, small airway collapse occurs early
During the effort-independent phase of forced expiration, air flow is driven mainly by…
elastic recoil of the lung
Minute Ventilation = ?
Tidal volume x Resp. Rate
Airflow in airways is analogous to the flow of electrical current but is more complex because of three reasons:
- Airway diameter shrinks with each generation but dichotomous branching pattern increases airway number and cross sectional area.
- Airway caliber (diameter) changes as the lung inflates and deflates.
- Resistance is dependent on the radius and the airflow pattern.
Resistance depends on the airflow because the interaction of the flowing gas with the tube wall consumes energy and cause _________ down the length of the tube.
pressure drop
Under laminar flow conditions, the pressure drop is ___________ to flow rate
directly proportional
Under turbulent flow conditions, the pressure drop is _________ to _______ of flow rate
directly proportional; square
Airflow in the bronchial tree (branching point) is
transitional
Flow rate is largely determined by
resistance
Resistance is largely determined by
radius
Resistance to airflow is critically determined by
airway caliber
- which is NOT static!
Poiseuille’s Law only applies to what airflow pattern?
laminar
How much resistance do small airways contribute to the overall lung resistance?
very small
Bronchioles and small airways are called _________ since disease must become well advanced before it is detected.
silent zone
________ are lower in both obstructive & restrictive lung disease.
peak flows
Restrictive flow-volume curves do not have “scooped out” appearance, why?
FRC decreases due to fibrosis but elastic coil is still intact, the effort independent phase of later expiration is normal.
What is the normal FEV1 in healthy young adults?
generally >80%
Why do patients with restrictive lung disease have a low FEV1 value?
their lungs have reduced compliance, making them harder to fill and easier to empty
*smaller amount of air in lung to begin expiration with
Why do patients with restrictive lung disease have a normal FEV1/FVC ratio?
Since both of their FEV1 and FVC are low but their difference is small, the ratio looks normal.
