Glossary of 1 - Physical Aspects of Breathing
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- How many generations does the bifuraction pattern go through? How does the diameter of the airway change through bifurcation?
- *23 generations
*diameter decreases from 25mm to 0.25mm
- What is the action of the diaphragm in inspiration? What percentage of the change in volume of the thoracic cavity is accounted for by the action of this muscle?
- *as it contracts the volume of the thoracic cavity is increased
*accounts for 85% of the volume change
- Contraction of the external intercostals produces what kind of action? When is this used?
- *contraction lifts the ribs upwards and outwards to increase the volume of the thoracic cavity
*used during active inspiration
During normal tidal breathing, expiration is an active process.
- False: it is a passive process.
- What muscles are used to effect active expiration?
- *abdominal muscles
- What is alveolar pressure at end expiration? What is air flow at this point?
- *alveolar pressure is zero
*there is no air flow
- Where is the intrapleural space located? How much fluid in contained in this space?
- *between the outer covering of the lungs and the inner covering of the ribs
*contains ~2mL of fluid
- What is IPP at end expiration? What produces this pressure?
- *-5 cmH2O
*produced by the tendency of the lungs to collapse and the tendency of the ribs to spring outward
- What is IPP during inspiration? What causes this change? How does this affect alveolar pressure?
- *IPP become -8
*an increase in the volume of the thoracic cavity causes this
*alveolar pressure becomes -1
- What is transmural pressure? How can it be calculated?
- *the pressure across the alveolar wall or respiratory membrane
*equal to alveolar pressure minus IPP
- What is transmural pressure at end expiration? During inspiration?
- *end expiration: 0 - (-5) = +5
*inspiration: (-1) - (-8) = +7
- At what point of the respiratory cycle does alveolar pressure reach its peak? IPP?
- *alveolar pressure peaks at mid-inspiration
*IPP peaks at the end of inspiration
Expiration takes twice as long as inspiration during normal tidal breathing.
- This is true and is due to the fact that expiration is a passive process.
- What is a pneumothorax? How can it be caused? What effects does it have?
- *the entry of air into the IP space, thus disrupting the pressure gradient
*trauma (from the outside) or infection (from the inside)
*disruption of the pressure gradient causes lung collapse
- What is tidal volume? What is a normal value?
- *the air moved in and out of the lung during normal breathing
- Give the series of events that leads to development of subatmospheric alveolar pressure.
- 1. Inspiratory muscles contract
2. Thoracic cavity expands
3. IPP becomes more negative
4. Transmural pressure increases
5. Alveolar pressure becomes more negative and air enters.
- What is the inspiratory reserve volume? The inspiratory capacity?
- *IRV = amount of air that can be inspired past tidal volume
*IC = TV + IRV
- What is expiratory reserve volume?
- The amount of air that can be expired past tidal volume.
- What is vital capacity? How can it be calculated?
- *the maximum volume of gas that can be forcibly expired after maximal inspiration
*VC = IRC + TV + ERV
- What is residual volume?
- The amount of air left in the lungs after forcible expiration (i.e. after ERV has been reached)
- What is functional residual capacity? How can it be calculated?
- *volume remaining in the lungs after tidal expiration
*FRC = RV + ERV
- What is total lung capacity? How can it be calculated? What is a normal value?
- *the total volume of the lungs from maximum inspiration to residual volume
*TLC = RV + ERV + TV + IRV
*6L for 70-kg person
- What are two methods of measuring residual volume?
- 1. Helium inspiration method (inaccurate for patients with obstructed airways)
2. Body plethysmograph
- What changes in lung volumes can be expected in patients with obstructive lung disease?
- *FRC and RV are increased
*VC is decreased
*TLC may increase in chronic conditions
- What changes in lung volumes can be expected in patients with fibrotic restrictive lung disease?
- A decrease in TLC, FRC, and RV
- What changes can be expected in patients experiencing restrictive lung function due to obesity?
- *TLC and RV remain constant
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