SFP: ventilation and pressure gradients Flashcards
What is ventilation
The process of bringing in fresh air and removing stale air
What is atmospheric pressure
0 cmH2O
PA is…
Alveolar pressure
Pa is…
Pressure in artery
Is intrapleural pressure positive or negative
Negative; this creates a vacuum
What is the formula for the pressure gradient across the lung
PL = PA – Pip
(alveolar pressure minus intrapleural pressure)
What is the formula for pressure gradient across the chest wall
PW = Pip – Pb
(intrapleural pressure minus atmospheric pressure)
What is the formula for trans airway pressure
Pta = Paw – Ppl
(airway pressure minus intrapleural pressure)
What is the formula for trans respiratory pressure
Ptr = PA – Pb
(alveolar pressure minus atmospheric pressure)
What is the function of the negative pressure in the intrapleural space
It helps keep the lungs open and keeps the chest wall in; without the negative pressure, the lungs would want to recoil and collapse and the chest wall wants to expand
Give the atmospheric, intrapleural, and alveolar pressures at end expiration
0, -5, 0
Give the atmospheric, intrapleural, and alveolar pressures during inspiration
0, -7, -2
Give the atmospheric, intrapleural, and alveolar pressures at end inspiration
0, -8, 0
Give the atmospheric, intrapleural, and alveolar pressures during expiration
0, -6, +2
What is tidal volume
The volume of air you move in and out during one breathing cycle
What is the formula for minute ventilation
Minute ventilation = tidal volume x frequency
Describe movement of CO2 seen in alveolar air sampling
During inspiration, no movement of CO2 is seen. At the very start of expiration, the air exiting is fresh air from the dead space, so no CO2 is seen. As expiration continues, CO2 movement rises and eventually plateaus. As inspiration begins again, movement of CO2 declines
What is end tidal? What is it reflective of
The value of partial tension of gas just prior to inspiration; The amount of CO2 in the alveolus
What is normal end tidal value?
40
What is alveolar dead space
Alveolar air not participating in gas exchange due to inadequate vascular perfusion
What is anatomical dead space
Areas where no gas exchange occurs
Is height or weight a better indicator of lung size and dead space
Height
What is physiological dead space
The total wasted ventilation. It is the sum of anatomical and alveolar dead space
What is the Bohr equation
VD = [(PACO2 – PECO2)/(PACO2)] x VT
