Pulm Equations Flashcards
Pulmonary Compliance
a. Delta volume / delta pressure
b. Delta volume / (PA – End inspiration Pip) – (PA – Pre inspiration Pip)
c. Units = L/cmH2O
Total Compliance
a. Delta volume / delta pressure (using PB instead of Pip)
b. Delta volume / (PA from end inspiration – 0mmHg) – (PA from pre inspiration – 0mmHg)
c. Units = L/cmH2O
PB in this equation will always be 0mmHg, regardless of altitude
Total Compliance (W/ Chest Wall Compliance)
a. 1/total = 1/pulm compliance + 1/CW compliance
b. Units = L/cmH2O
FRC w/ Advanced Spirometry
a. Concentration1 x Volume1 = Concentration2 x (Volume2 + FRC)
b. Units = L
Volume 2 may also be volume 1 depending on whats given
VT
a. VT = VD + VA
b. Tidal volume = ventilation dead space + alveolar ventilation
c. Units = mL or L
VA
VA = (VE - VD) x
Units = L/min
Bohr Equation- Determining Dead Space
VD = VT x (PACO2 – PECO2) / PACO2
OR
VD = VT x (FACO2 - FECO2) / FACO2
c. Units = mL or L
Partial Pressure of Inspired Gas
a. PI gas = PI gas x (PB – water vapor pressure)
c. Units = mmHg
Inspired gas is what goes into the alveoli and mixes with current gases in lung
New alveolar CO2 or O2 based on changed in ventilation
a. New PACO2 = Old PACO2 x (VA-old / VA-new)
b. New PAO2 = PIO2 – (New PACO2 / (V/Q) Ratio) + F correction factor
c. PIO2 = FIO2 x (PB – water vapor pressure)
d. Units = mmHg
Pulmonary Vascular Resistance
a. PVR = (MPAP – MLAP) / Blood flow
b. Units = mmHg/L/min (this gives us PRU)
c. Multiply by 80 → If converting PRU to dyne·s/cm⁵ (standard vascular resistance conversion).
Multiply by 1333 → If converting only mmHg to dyne/cm², often used when calculating resistance from pressure and flow separately.
MAP
a. diastolic pressure + 1/3(systolic – diastolic)
b. Units = mmHg
Fick, Solving for VO2
a. VO2 = Qt x (CaO2 – CvO2)
b. VO2 = Total amount of O2 absorbed by the body per minute.
c. Qt = Cardiac out in L/min or mL/min
d. CaO2 = total arterial oxygen content
e. CvO2 = Mixed venous oxygen content
f. Units for CaO2 and CvO2 = mL/dL
Fick, Solving for CO
a. Qt = VO2 / (CaO2 – CvO2)
b. Qt = Cardiac out in L/min or mL/min
c. Units for CaO2 and CvO2 = mL/dL
Partial Pressure of Expired CO2
PECO2 = PACO2 (1-VD/Vt)
Partial Pressure of Expired O2
PEO2 = [(VD/Vt) x PIO2] + [(1-VD/Vt) x PAO2]
Concentration of Alveolar Gas
FA[gas] = PA[gas] / PB
**What happens if there is a change in volume? **
Calculate the new PA of the gas prior to using this equation
Concentration of Expired Gas
FE[gas] = PE[gas] / PB
Dissolved O2 Content- Arterial & Venous
0.003mLO2/mmHg/dL x PAO2
0.003mLO2/mmHg/dL x PvO2
Oxygen Carrying Capacity
1.34mL O2/g Hb/ dL blood
1.34mL O2 x Hb in grams
Bound O2 Content (Arterial and Venous)
(1.34ml x Hb in grams) (Hb Saturation)
Hb Saturation
(O2 Bound / O2 Carrying Capacity) x 100
Calculating FRC from N2 Washout
- Determine average FeN2:
FeN2 =
(Vol. per breath x [N2] per expired breath) + (Vol. per breath x [N2] per expired breath) + (continue pattern for each breath) / Total exhaled Volume - Determine volume of N2
VN2 = Entire Volume Exhaled x FeN2 in decimal form (where FeN2 is the average fraction of expired N2) - Determine FRC:
FRC= VN2/ Initial [N2] (initial [N2] is assumed to be 75% unless otherwise stated)
Resistance (Series vs Parallel)
Series: Rtotal= R1 + R2 +…
Parallel: 1/R. Total = 1/R1 + 1/R2 + …
Alveolar Pressure
PA = PIP + PER
