Pulm Eq and values Flashcards
Equation for Transpulmonary pressure PTP
PTP = Plung - PIP
difference between:
air pressure in the lung and
the intrapleural pressure in the water in the intrapleural space
Equation for compliance C
C = ΔV / ΔP
LaPlace’s Formula
P= 2 x T /r
surface tension creates a tendency for small alveoli to empty their air down the pressure gradient into larger ones, leading to the collapse of the small ones.
Eq for air Flow in airways
Flow = ΔP/R
Flow is proportional to P difference
Is Resistance directly proportional or inversely proportional to radius?
R = 1/r^4
inversely
Eq for minute ventilation
- typical rates?
Minute Ventilation = Tidal Vol (TV) x Breathing rate (RR)
0.5 L/breath x 12 breaths/min = 6L
Eq for Vital Capacity (VC)
VC = TLC - RV
The volume of air exhaled after a maximal inspiration followed by a maximal expiration
Winter’s formula
pCO2 = (1.5 * HCO3-) + 8 ±2
Calculation of the A-a gradient
Alveolar gas equation to estimate PAO2:
PAO2 = [(Pb-PH2O) x FiO2] -PaCO2/R
In Denver P AO2 = [(630-47)0.21)] -PaCO2/0.8
PAO2 - PaO2
How do we calculate PIO2?
what is normal PIO2 at sea level and denver?
PIO2 = (PB – 47 Torr) × 0.21
150 Torr - sea level
120 Torr - denver
Alveolar ventilation equation
PACO2 = V˙ CO2/ V˙ A * k
V˙ CO2 is the quantity of CO2 produced in one minute
V˙ A is the quantity of alveolar ventilation in one minute
Because PACO2 is essentially equivalent to PaCO2, one can also substitute PaCO2 for PACO2 in the equation.
*note: this is the Rate limiting step dictating how much CO2 is removed
CaO2 equation
CaO2 = (SaO2 × [Hb] X 1.39)
- total concentration of oxygen, including hemoglobin-bound and freely dissolved
components. but we ignore that last part bc its so tiny
Hypoxemia values
The definition of hypoxemia is a PaO2
Equation for PAP
PAP = CO* PVR + LAP
Just move the equation around.
There are 3 things that go into PAP, so it makes sense that there are 3 ways that PAP can be affected
