Pulm/Renal - Physiology - Equations Flashcards
For what calculation is this equation used?
Describe the terms.
The shunt equation: the percentage of shunted pulmonary blood
Cc’O2 — the ideal oxygen amount extracted into the blood
CaO2 — the amount in the pulmonary venous blood
CvO2 — the amount in the mixed venous blood
For what calculation is this equation used?
Describe the terms.
The alveolar gas equation: to calculate the pO2 in the alvelous (or the FiO2 to get it back to a certain paO2).
PAO2 — Alveolar partial pressure of oxygen
FiO2 — Inspired fraction of oxygen (0.21)
PB — atmospheric pressure (760 mmHg)
PH2O — water pressure (47 mmHg)
PACO2 — Alveolar partial pressure of carbon dioxide
R — a constant (0.8)
For what calculation is this equation used?
Describe the terms.
The Bohr Equation (dead space ratio): Deadspace : total ventilation
VD / VT — ratio being solved
PaCO2 — arterial partial pressure of CO2
PECO2 — expired partial pressure of CO2
For what calculation is this equation used?
Describe the terms.
PA = Pip + Pelastic
Intraalveolar pressure: external pressure acting on the alveolus
PA — total pressure on the alveolar wall
Pip — intrapleural pressure (often a negative value)
Pelastic — pressure created by elastic recoil of the lung
Given a PaO2, what else can be calculated using the equation below?
The A-a gradient
(by calculating PAO2)
For what calculation is this equation used?
Describe the terms.
Fick’s Law: the rate of diffusion.
VX (with a dot above the V) — volume flow being solved
A — surface area of alveoli
D — diffusion constant
T — thickness of alveolar-capillary interface
(Px1 - Px2) — pressure differential
Which pulmonary equation can be rearranged to give the DLCO equation?
Fick
Which equation is this?
The DLCO equation
What equation is this?
Rewrite it in the pulmonary format.
The Henderson-Hasselbalch equation
Fill in the blank for oxygen bound to hemoglobin:
___ mL O2 / g hemoglobin
1.34
Fill in the blank for oxygen dissolved in the blood:
___ mL O2 / 100 mL blood / mmHg pO2
0.003
How much oxygen is found bound to hemoglobin in one dL?
How much oxygen is found dissolved in one dL of blood?
20.1 mL / dL
1.34 mL O2 / g hgb * 15 g hgb / dL blood
0.3 mL / dL
0.003 mL O2 per 100 mL blood / mmHg pO2 * 100 mmHg paO2
What equation is used to calculate total ventilation?
What equation is used to calculate alveolar ventilation?
Respiratory rate * tidal volume
Respiratory rate * (tidal volume - dead space)
What equation is used to calculate an anion gap?
Anion gap = (Na+ + K+) - (Cl- + HCO3-)
Via what equation is renal clearance measured?
Clearancex = Urine flow * Urinex / Plasmax
What equation would you use to calculate this patient’s GFR?
GFR = Urine flow * UrineCreatinine / PlasmaCreatinine
(1440 mL/day / 24 hours/day / 60 min/hour) * 100 mg/dL / 1 mg% = 100 mL /min
What equation would you use to calculate this patient’s filtered load of urea?
Filtered Load of urea = GFR * PlasmaUrea
100 mL/min * 0.005 mM/mL = 0.5 mM/min
What equation would you use to calculate this patient’s urea excretion?
Urea excretion = Urine flow * UrineUrea
1 mL/min * 0.220 mM/mL = 0.22 mM/min
What equation would you use to calculate this patient’s net urea reabsorption?
Net urea reabsorption = Filtered - Excreted
0.5 mM/min - 0.22 mM/min = 0.28 mM/min
What equation would you use to calculate this patient’s fractional excretion of urea?
Fractional excretion of urea = Excreted / Filtered
0.22 mM/min / 0.5 mM/min = 0.44 = 44%
