Glossary of 3 - Resistances to airflow
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- Give the basic equation for resistance.
- R = change in P/flow
- What two factors complicate the calculation of resistance in the lungs?
- 1. Bifurcation of airways
2. Flow varies between turbulent and tolerant.
- What is the calculation for pressure in laminar flow? Turbulent flow?
- 1. Laminar: P = VR
2. Turbulent: P = VR^2
- Why is a greater pressure required to drive turbulent air at a given velocity? Where in the respiratory tree is the greatest pressure required?
- *eddies and vortices dissipate driving force
- What type of flow exists in the bronchioles - laminar or turbulent?
- Why does resistance decrease with successive airway generations?
- The aggregate cross-sectional area increases.
- What happens to flow with successive airway generations? Of what benefit is this? What is a drawback of this?
- *Flow decreases
*low flow facilitates diffusion in the alveoli
*low flow may complicate diagnosis of obstructive disease in the small airways
- Describe the relationship between resistance and lung volume. What is resistance like during expiration? During inspiration?
- *resistance is inversely related to lung volume
*during inspiration, when volume is at its highest resistance is lowest
*during expiration when volume is at its lowest, resistance is at its highest
- Why does resistance change with lung volume?
- As lung volume increases, airway diameter increases thus reducing resistance.
- What are two strategies used by asthmatics to increase flow?
- 1. Breathing through pursed lips to create back pressure that holds airways open
2. Breathing off the top of the lungs to maintain high lung volume
- What powers expiration during the effort-independent phase?
- Elastic recoil
- At end inspiration, what keeps the alveoli from collapsing?
- Transmural pressure created by alveolar pressure of 0 and IPP of -8.
- What marks the transition between effort-dependent and effort-independent expiration?
- The collapse of small airways.
- What increases IPP during forced expiration? What effect does this have on pressure within the lungs?
- Muscular compression - abdominals and internal intercostals. This creates a pressure gradient between the alveoli and atmosphere allowing air to flow out.
- What is the Z point? Where is it located during effort-dependent expiration?
- *the point where transmural pressure is zero
*in the cartilagenous airways
- What happens when the Z point moves distally into the smaller (non-cartilagenous) airways?
- Negative transmural pressure results in the collapse of these airways.
- What keeps some small airways and alveoli open during expiration?
- Structural interdependence.
- Describe the appearance of the flow-volume curve for patients with obstructive lung disease?
- *lower peak flow
*higher peak volume
- What offsets the large resistance created by turbulent air flow in the large airways?
- Large pressure drop.
- What is one factor that makes resistance in small airways dynamic?
- Dynamic compression.
- What is FEV-1? What is normal for this value?
- The volume of air expired over the first second of a forced expiration. Normal is 4L or 80% of FVC.
- What is FEF(25-75%)? What is normal for this value?
- *the flow between 75 and 25% of the FVC.
*normal is 3.5L/sec
- Describe the changes in FVC, FEV-1, and FEV-1/FVC in patients with obstructive disease.
- *all values decrease as less air is able to be expired
- Describe the appearance of the flow-volume curve for patients with restrictive lung disease.
- *decreased peak flow
*decreased peak volume
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