L1 - PHYS - Respiratory Cycle & Mechanics Flashcards
What is the journey of oxygen?
Air (atmosphere) –> Lung and Blood –> Tissues –> Mitochondria
What is Boyle’s Law?
Pressure of gas is inversely proportional to its volume. P1V1=P2V2
How does air passively move into the lungs?
When the lung volume increases, pressure decreases, so air enters.
When lung volume decreases, pressure increases so air exits.
What is PB typically?
760 mm Hg
HOWEVER, we normalize it to 0 cm H2O
What happens when inspiratory muscles contract?
thoracic volume increases
chest wall wants to expand and lungs want to collapse - have interplay
Are lungs and muscles/ribs directly connected?
No lungs and muscles/ribs are NOT directly connected.
This comes into play during inspiration events (contraction of muscles)
Because of the coupling of lungs and chest wall, lungs expand as thorax expands.
What are the Pleural of the Lungs?
The visceral and parietal pleura.
Intrapleural Space
Between the visceral and parietal pleura there is a fluid (parietal fluid) - 5-35 um thick
What is Intrapleural Pressure?
It is less than atmospheric pressure (negative)
Can think of it as intrathoracic pressure - the pressure everywhere in the thorax EXCEPT the lumens of blood vessels, lymphatics, or airways.
What is the unit for respiratory pressures?
cm H2O (NOT mm Hg as in cardio phys)
1 cm H2O is about 1m Hg due to density differences
What is intrapleural pressure (Ppl) at rest?
near -5 cm H2O
What is Ppl (intrapleural pressure) during inspiration?
As volume increases, pressure decreases, so Ppl goes to -8 cm H2O
It becomes more negative
What does Alveolar Pressure (PA) do during inspiration?
PA decreases as thoracic cavity increases in size.
From 0.5 cm H2O to -1 cm H2O
At rest PB=PA = 0 cm H2O
At end of inspiration PA is -1 due to increase in alveolar size which causes air to enter lungs (pressure difference!)
What is Transpulmonary Pressure?
The difference between Pleural Pressure and Alveolar Pressure.
Ptp = Palv - Ppl
5cm H2O at rest
What would happen if Ptp = 0?
Lung collapse
What does the respiratory cycle graph look like for volume changes?
Positive bell curve ranging 0 to +0.5 liters
Increasing during inspiration, decreasing during expiration.
What does the respiratory cycle graph look like for Alveolar Pressure changes?
Looks like an oscillation curve
Decreases then increases during inspiration (0 to -1 cm H2O and then back)
Increases during during expiration (0 to +1) and then decreases back to 0.
What does the respiratory cycle curve look like for the Intrapleural Pressure changes?
a negative bell curve / looks like a U/V
During inspiration it goes more negative from -5 cm H2O to -8 cm H2O
During expiration it increases from -8 back to -5 cm H2O
What does the Air Flow graph look like during the respiratory cycle?
Looks like an oscillation curve
During inspiration it decreases from 0 to -1 then increases back to 0 L/sec.
During Expiration it increases from 0 to +1 and then back to 0 L/sec.
*the convention that inspiration air flow is negative is now important and lost in history
What are the values of the respiratory cycle at rest?
Volume = 0 L
PaO = 0 cm H2O
Ppl = -5 cm H2O
Air Flow = 0 L/sec
What are the values of the respiratory cycle Mid-Inspiration?
Volume - Increasing
Pa - Decreasing
Ppl - Decreasing
Air - flowing INTO the lungs
What are the values of the respiratory cycle at the End of Inspiration?
Volume - reached PEAK increase Tidal Volume, Vt = 500 ml Pa - returned to zero Ppl - decreased to -8 cm H2O Air Flow - ceased (at zero)
What are the values of the respiratory cycle Mid-Expiration?
Volume - Decreasing
Pa - Rises
Ppl - begins to Rise
Air - exits the lungs (goes into positive)
What are the values of the respiratory cycle at the End of Expiration?
Volume - returned to resting (zero)
Pa - decreases to Zero
Ppl - returns to resting (-5 cm H2O)
Air - exited lungs (zero)
*LO, learn to draw graphs
What is Ptp during the Respiratory Cycle?
Ptp values: Rest : +5 cm H20 Mid-Inspiration: +5.5 cm H2O End Inspiration/Start Expiration: +8 cm H2O Mid-Expiration: +7.5 cm H2O Rest: +5 cm H2O
Define Minute Ventilation (VE)
What is the equation?
Volume of air inhaled every minute
VE = VT x frequency
Define tidal volume (VT)
volume of air inhaled and exhaled in single breath
What is the normal minute ventilation value?
7,000 ml/min or 7 L/min
14 breaths per minute (RR)
VT= 500 ml/breath
14x500 = 7,000
What is Dead Space of the lungs?
Regions of the lung that receive air, but not blood so NO GAS EXCHANGE
What are the three types of Dead Spaces?
- Anatomic Dead Space
- Physiologic Dead Space
- Alveolar Dead Space
What is Anatomic Dead Space?
Space in respiratory system other than alveoli
150 lb person = 150 ml of VDS
What is Physiological Dead Space?
Basically alveolar dead space
In healthy persons, physiological dead space is nearly ZERO
What is Alveolar Dead Space?
Alveoli that receive air, but not blood
What is the equation for Physiological Dead Space?
Physiological dead space = VT x [(PaCO2 - PECO2)/ PaCO2]
When does Anatomical Dead Space enter the lungs?
At the end of Inspiration.
Inspired air that fills conducting airways where gas exchange does not occur.
Is there air left in the lungs at the end of expiration?
Yes, Alveolar air from previous breath is left in the conducting airways.
What is the equation for Minute Alveolar Ventilation?
Calculated by subtracting dead space volume from tidal volume.
Valv = VT - VDS
500ml - 150 ml = 350 ml
Minute alveolar ventilation is now alveolar ventilation x frequency
(Vdot)alv = VALV x f
When is it harder to stretch the lungs?
During inhalation at LOW lung volumes.
When the lungs are at LOW VOLUMES, They must work HARD to get a little increase in volume
Also at high lung volumes when nearing TLC
When is it easier to stretch the lungs?
Inhalation at Normal Lung Volumes (quiet breathing)
Once there is a little air in the lungs, a little pressure change will produce a large volume change.
What happens during inhalation at high lung volumes?
As lungs expand toward TLC, it again becomes difficult to stretch.
Small pressure changes produce small changes in volume.
What does the Pressure/Volume Inspiration graph look like?
S shaped curve
What does the Pressure/Volume graph look like during Expiration?
Increases then levels off
What happens when you inflate the lungs with saline rather than air?
Why?
Lungs almost inflate and deflate the same way
The difference is SURFACTANT
It reduces tension in the smallest alveoli more than the larger alveoli
LaPlace’s Law
Contributes to hysteresis - the difference between inspiration and expiration.
What is compliance?
The measure of stretch ability of the lungs
Higher compliance = easier to stretch/open
Calculate = take the slope os the tangent to the pressure/volume curve
Change in volume / change in pressure
When is compliance highest?
During normal breathing range, normal VT
Reduces workload
When is compliance lowest?
At either extreme - when lung volume is too small or too large
Harder work
What is elasticity?
Recoil ability
opposite of compliance
Explain a baby’s first breath in terms of compliance
Prior to first breath, lung volume is very low, so compliance is low and effort/work is high.
No wonder they cry!
What does fibrosis do to compliance?
Lowers compliance, so need more change in pressure required for change in volume.
Occurs during disease, obesity, etc
Usually breath at shallower volume and more frequently
What does age do to compliance?
Compliance increases with age as elasticity decrease with age due to loss of elastin and increased collagen
What does emphysema do to compliance?
Compliance increases as it destroys alveolar septal tissue that normally opposes expansion
What is FRC? (Functional Residual Capacity)
When elastic recoil of lungs and that of chest wall balance each other
What is minimal volume?
What the lungs would shrink to
They want to be smaller
What is Interdependence?
The structural stability of the small airways and alveoli depends on all the connecting airways/alveoli
