Term
| What are the 3 major determinants of pO2 & pCO2 balance |
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Definition
1) Ventilation
- Breathing delivers oxygen to and removes carbon dioxide from the alveoli
- Regulated by Medullary center that receives input from cortex and peripheral receptors
2) Ventilation-Perfusion matching
- Each alveolus receives a volume (V) and blood flow (Q) each minute, and V/Q determines PAO2 and PACO2 of alveolar gas (if V/Q increases, PaO2 falls and PaCO2 rises).
3) Diffusion
- Oxygen and CO2 move between alveoli and pulmonary capillary blood along a partial pressure gradients (CO2 from blood to alveoli and O2 from alveoli to blood) |
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Term
| What happens when ventilation exceeds blood flow to a given alveolus? |
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Definition
If V/Q >1, PaO2 falls and PaCO2 increases, since more gas (O2) is reaching each alveolus than blood (CO2)
- less CO2 can be removed |
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Term
| What resisting factors must be overcome for ventilation to occur? |
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Definition
1) Elastic Recoil
- inversely related to lung Compliance
- Determined by balance between transpulmonary pressure (PL= Palv- Ppl) and the gradient across the chest wall (Pw= Ppl-Patm)
2) Viscous forces
- Arise during inspiration and expiration because of gas flow
- Pressure gradient= 8VnL/(pi)r^4 is required to overcome these forces (MOST DEPENDENT on airway size) |
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Term
| Describe the basic pressure-volume relationships of the respiratory system. How do these relationships relate to the pressure of elastic recoil? |
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Definition
Transmural pressures are generated by elastic recoil of lungs and chest wall and are calculated by subtracting pressure "outside" from pressure "inside" each structure.
1) Transpulmonary Pressure (PL)= Palv-Ppl
2) Gradient across chest wall (Pw)= Ppl- Pabs
Palv is estimated by Pao and Ppl is estimated by Pes, so
P (respiratory system)= PL + PW or Pao
The pressure of the respiratory system at any volume is therefore simply the pressure at the AIRWAY OPENING. |
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Term
| What is meant by "Functional residual capacity" (FRC) and "Total Lung Capacity" (TLC)? |
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Definition
1) FRC is volume remaining in the lungs at the end of passive expiration (inward and outward recoil are exactly balanced).
Since Prs= 0 (Palv-Pbs= 0), it resquires no muscle activity to maintain this volume, so it is the resting position of the respiratory system.
**Different from Residual Volume, which is the volume left after active expiration**
2) TLC is volume present after maximal inspiration, when combined elastic recoil of lungs and chest is balanced by maximum pressure generated by inspiratory muscles |
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Term
| What is the pulmonary vital capacity (VC)? |
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Definition
TLC-RV
In other words, it is the volume of gas that be exhaled after maximal inspiration with maximal expiratory effort. |
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Term
| How does pulmonary compliance relate to elastic recoil? |
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Definition
| Inversely, since a high compliance means a small change in volume for a given change in pressure, which would be a small amount of recoil. |
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Term
| What are the 2 basic mechanisms that generate elastic recoil? |
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Definition
Remember, recoil is approximated by the difference in pressure in the alveoli and body space, or the Pressure at an open airway.
1) Tissue forces (chest wall)
- tissue properties
2) Surface forces (surfactant on lungs)
- Surface tension decreases alveolar volume and increases internal pressure (P= 2T/r)
- Surface tension increases in a size-dependent manner to prevent alveolar collapse on expiration from huge recoil forces. |
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Term
| What does a reduced airway size have to do with viscous forces resisting airflow? |
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Definition
Remember, viscous forces dominate in the upper airways and first 6 segments, where resistance is highest (lowest SA)
Pressure gradient required to overcome viscious forces is determined by flow rate (V), viscosity (n), length (l) and radius ^ 4 (r).
If radius is cut in half, pressure required to overcome viscous forces increases by 16! |
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Term
| Why do viscous forces decrease with airway size? |
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Definition
Majority of viscous fore contributed by upper airway and lower airway in first six generations.
Remember, a smaller radius means that more pressure must be exerted to overcome viscous force.
However, since airways continue to branch, airflow slows at each branching point, leading to a decreased viscous force. |
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Term
| How does resistance relate to viscous force of resistance in terms of pulmonary air flow? |
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Definition
Just as elastic recoil is expressed in terms of compliance, viscous force is represented as resistance, where
R= deltaP/V (flow rate)
R= 8nL/(pi)r^4
Depending on length and radius ans well as viscosity of gas flowing through. |
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Term
| How does the diaphragm increase the volume of the lungs? |
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Definition
2 ways
1) Contracts, flattening from its normal dome-shaped configuration and increasing the volume of the thorax and lungs, and decreasing volume of abdominal cavity
2) As abdominal volume falls, intra-abdominal pressure increases, pushing lower ribs out and further increasing lung volume |
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Term
| What is responsible for the pressure gradient between the mouth and alveoli upon inspiration? |
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Definition
1) Diaphragm increases volume of lungs faster than they can fill, so alveolar pressure falls.
2) This "negative pressure" decreases as air enters the lungs, returnig to zero at the end of inspiration. |
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Term
| What happens to intrapleural pressure, alveolar pressure and airflow as lung volume changes? |
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Definition
1) Inspiration (increased lung volume)
- Intrapleural pressure decreases
- Alveolar pressure decreases then increases to baseline
- Airflow increases then falls to baseline
2) Expiration
- Intrapleural pressure increases
- Alveolar pressure increases then decreases to baseline
- Airflow decreases then increases to baseline. |
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Term
| How are viscous forces overcome during passive expiration so that the lungs return to their equilibrium volume? |
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Definition
| Elastic Recoil alone provides the pressure gradient to overcome the viscous forces. |
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Term
| How is additional pressure provided to augment flow and shorten expiratory time during exercise? |
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Definition
Active expiration depends upon "Starting volume" and depends entirely upon lung elastic recoil.
During active expiration (as opposed to passive expiration), pleural pressure becomes positive.
1) >85% of vital capacity, increasing effort increases expiratory flow
2) <85%, expiratory flow cannot be ramped up |
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Term
| What is the "Equal Pressure Point"? |
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Definition
EPP is point where pressure inside and outside of the airways becomes equal (airway pressure is equal to pleural pressure).
Beyond the EPP, the airway collapses, so flow is driven by Pressure Differential between ALVEOLUS and EPP (choke point), NOT the mouth
Remember, Alveolar Pressure= Elastic recoil + Ppl
So, expiratory pressure gradient is equal to lung elastic recoil pressure (so volume determines maximum expiration) |
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Term
| What is the basic anatomical structuring of a lung? |
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Definition
1) Lobes
- physically separated and covered by visceral pleura
2) Segments
- Separated only by visceral pleura
3) Lobules
- 1 TBL and 1 Pulmonary artery per lobule
4) Acinus
- 1 RBL per acinus |
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Term
| What is the major determinant of PAO2 and PACO2? |
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Definition
| Ventilation:Perfusion matching. |
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Term
| Explain the basic static pressure-volume relationship in expiration and inspiration in terms of elastic recoil forces on the chest wall and lungs. |
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Definition
In these experiments, subjects took a breath and exhaled against a closed shutter, in order to measure how much P it takes to keep lungs inflated at a given volume (elastic recoil).
At FRC, lungs exhibit inward elastic recoil force (they want to contract, and chest wall exhibits outward elastic recoil force (it wants to expand).
PL + Pw= 0
1) Inspiration
- As Vt is reached, inward recoil force on lungs increases further and outward recoil force on chest becomes 0.
- As VC is reached, inward recoil force is present on BOTH lungs and chest wall
2) Expiration
- At RV, both chest wall and lungs exhibit outward elastic recoil (they both want to expand). |
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Term
| Why does pleural pressure increase during inspiration with the static pressure-volume curves, and actually decrease in real life? |
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Definition
In the static experiments, people are relaxing their lungs against a closed shutter. The parietal pleura is pressing on the visceral pleura, which cannot shrink against the closed shutter, pressure increases.
Measurements are made with esophageal balloons (Pe) and at the open airway (Pao).
In real life, the visceral pleura of the lungs "tug" on the parietal pleura of the chest wall, creating negative pressure between the 2 surfaces, |
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Term
| What does compliance have to do with the PV curve? |
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Definition
It is the slope of the static PV curve!
Compliance is highest at FRC, which indicates elastic recoil is lowest, so it is easiest to breathe around FRC! |
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Term
| How is surfactant similar to soap? |
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Definition
Soap disturbes interactions between water molecules that create surface tension.
Surfactant generates some ST, but reduces it relative to H2O alone.
It 1) reduces ST (relative to water) and 2) Equalizes P between different sizes of alveoli (small alveoli enable more surfactant-surfactant interactions, which reduce ST further)
Remember, P= 2T/r, so T is proportional to Pr. As radius decreases, pressure should increase. HOWEVER, surfactant exhibits size-dependent non-linear viscoelasticity, equalizing Pressure between different sized alveoli. |
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Term
| What does sucking through a straw have to do with imagining frictional forces that must be overcome during ventilation? |
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Definition
Approximated by Resistance, which is
R= 8nL/(pi)r^4
Thinking of the straw, smaller, longer straws with thicker drinks take more pressure to drink from (the radius is the MAJOR factor) |
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Term
| What are the elastic forces that are acting on the chest wall and lungs at FRC? |
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Definition
At FRC, pressure in the respiratory system (Pao) is zero, which means PL + PW must = 0.
Therefore, elastic forces acting on the chest (Pw) and lungs (PL) must cancel out.
There is slight outward recoil force chest wall and slight inward recoil force on the lungs (-5 and + 5 respectively). |
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Term
| What is "expiratory flow limitation"? |
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Definition
It is a normal restriction where lung volume cannot decrease below RV, because expiratory muscles cannot compress ribs further.
Remember, at a low starting volume, increasing effort will not increase expiratory flow because of EPP.
Therefore, expiratory flow limitation is determined by starting volume (recoil force) |
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Term
| How does Partial Pressure differ from concentration? |
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Definition
partial pressure is number of gas particles of a given species relative to total # of particles above and below solution.
concentration depends on solubility and is determined by number of dissolved gas molecules in liquid. |
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