Term
| Determinants of Viscosity of Air |
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Definition
1) radius
2) velocity
e.g. large airways, big radius, big velocity = more turbulent
e.g. small airways, small radius, small velocity = more laminar |
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Term
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Definition
2rvd/n
where: r = radius; v = velocity; d = gas density; n = gas viscosity
(higher the number, more turbulent the flow) |
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Term
| Characteristics of Laminar Flow |
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Definition
- where: small peripheral airways
- flow: get more flow for a given pressure than turbulent flow
- definition: when the streamlines in fluid or gas are well defined
- flow velocity profile: parabolic
- flow directly proportional to pressure difference
- energy required: minimum (proportional to the pressure) |
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Term
| Characteristics of Turbulent Flow |
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Definition
- where: central large airways
- flow: streamlines become mixed up
- factors: occurs when flow is high and diameter is large
- flow velocity profile: blunt
- pressure difference is equal to the square of the flow
- less energy efficient
- less change in flow for a larger pressure drop |
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Term
| Calculate the overall pressure drop of the respiratory system. |
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Definition
| Pressure drop = [flow in laminar pathways * laminar constant] + [flow in turbulent pathways squared * turbulent constant] |
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Term
| How do airways change from mouth to alveoli? |
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Definition
- pathways increase in number
- velocity decreases, individual radius decreases
- cross-sectional area of the airway gets larger
- flow will be laminar, despite the fact that the surface area will be so large because of the greatly decreased velocity
- flow becomes more and more laminar |
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Term
| Resistance (series and parallel) |
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Definition
- the energy cost of flow
- resistance = pressure difference/flow or R = 8nL/(pi)r^4
- in series -- Rtotal = R1 + R2 + R3...
- in parallel -- 1/Rtotal = 1/R1 + 1/R2 + 1/R3... |
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Term
| Determinants of Resistance |
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Definition
radius - if you decrease the radius by half you increase the resistance 16-fold
length - if you increase length by 2 you increase resistance by 2 |
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Term
| What determines Pulmonary Resistance? |
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Definition
5/6 due to airway resistance = loss of energy as air flows through the airways
1/6 due to tissues resistance = loss of energy dissipated as fibres and molecules move past each other |
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Term
| Difference between static transpulmonary pressure and dynamic transpulmonary pressure |
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Definition
- transpulmonary pressure = the pressure gradient between the mouth and the plural space
- increase the Raw (airway resistance component)
- Raw = the resistance from the mouth to the alveoli
- in dynamic states the Ptp = (Pao - Palv) + (Palv - Ppl) as there is a pressure difference between the mouth and the alveoli
- in static states the Ptp = Palv - Ppl as at stasis the pressure at the mouth and the pressure in the alveoli are the same |
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Term
| Describe the respiratory cycle during normal tidal breathing. |
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Definition
1) inspiratory muscles contract (expanding the thorax) making a negative pressure in the plural space.
2) alveolar pressure becomes less than atmospheric pressure
3) gas moves into the lungs (due to the negative pressure gradient)
4) inspiratory muscles relax, elastic recoil of the lungs and chest wall make the alveolar pressure positive (by making the plural pressure positive) so that gas moves out of the lungs (down the pressure gradient) |
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Term
| Describe the link between lung volume and airway resistance. |
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Definition
- lung volume increases, airways are pulled open
- alveolar attachments on the membranous bronchioles that tether and pull the airways open and decrease the airway resistance
- lung volume increases so tension increases pulling the airways more open and decreasing resistance |
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Term
| What are the determinants of Maximum Flow? |
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Definition
1) resistance of the airways to airflow (increase resistance, reduce flow)
2) elastic recoil of the lungs (decrease elastic recoil, reduce flow)
3) expiratory muscles (reduce muscles structure, reduce flow) |
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Term
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Definition
| once flow reaches a certain maximum, no matter how hard the expiratory muscles push, flow will not increase |
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Term
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Definition
| An index of obstruction (normal = 0.8 or 80%) |
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Term
| Effort dependant Region versus Effort indépendant région |
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Definition
EDR = the first two thirds of the expiratory flow volume loop (during forced manoeuvre) where muscular effort effects the flow rate
EIR: the last third, where matter how much effort you make you cannot increase the flow rate |
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Term
| Choke Points (aka Equal Pressure Point) and Flow Limitation |
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Definition
- increasing intrathoracic pressure compresses airways
- choke points are transient narrowings of the airways that are dependent on the lung volume
- occurs when the pressure outside the tube exceeds the pressure inside the tube (e.g. plural pressure exceeds alveolar pressure) which causes a negative transmural pressure
- at this point, the airway is no longer able to resist the plural pressure
- at high lung volumes, there is more recoil pressure which = more flow
- at low lung volumes, recoil pressure falls = low volume, forces pulling open the airways are lower, increases airway resistance, decreases maximal flow
- now the driving pressure is no longer the plural pressure but the elastic recoil of the lung and the pressure gradient between the alveolus and the point of the flow limitation |
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Term
| Effects of low volume and low elastic recoil on the choke points and flow |
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Definition
- if you have a lower elastic recoil, you will have a higher tendency to collapse sooner (or meet your choke point sooner)
- if you have a lower volume you will have a tendency to collapse sooner (or meet your choke point sooner) |
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