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