# Step 1 Physiology Formulas High Yield *Most Common

version from 2015-04-26 02:20

## Important formulas

### CV

Cardiac OutputCO = Rate O2 consumption/(art O2 - ven O2)
CO= SV x HR
SV = Stroke volume
HR = Heart Rate
CO = Cardiac output
Mean Arterial PressureMAP= CO x TPR
MAP= 1/3 SBP + 2/3 DBP
MAP = Mean Arterial Pressure
TPR = Total peripheral resistance
SBP = Systolic Blood Pressure
DBP = Diastolic Blood Pressure
Stroke VolumeEDV - ESV
SV = CO / HR
EDV = End diastolic volume
ESV = End systolic volume
Ejection FractionSV / EDV x 100SV = Stroke volume
End diastolic volume
Resistance8ηL ⁄ (πr^4 )η = viscosity
L = Length
Perfusion∆P=Q x R∆P = Change in pressure
Q = Blood flow
R = resistance
Pulse PressurePP = Systolic - DiastolicPP= Pulse Pressure

### Pulm

A - a gradientPAO2 =150 - (PaCO2 / 0.8)
PAO2 = ( 760 - 47 ) x FiO2 - PaCO2 /0.8 (or 1)
PAO2 = Pressure of alveolar O2 gas discovered from this equation
PaO2 = Pressure of asterial O2 (ABG)
PaCO2 = Pressure of arterial CO2 (ABG)
FiO2 = Fraction of inspired O2 (usually 21% change if supplemental O2 is used)

### Renal

Net Filtration Pressure(P_c - P_i ) - (π_c - π_i)P_c = Hydrostatic capillary pressure
P_i = Hydrostatic interstitial pressure
π_c = Osmotic capillary pressure
π_i = Osmotic capillary pressure
Glomerular Filtration RateGFR = K_f (P_gc - P_bs)-(π_gc - π_bs)
GFR= C_inulin =U_inulin × V⁄P_inulin
Creatinine clearance ≈ GFR
K_f = Filtration constant
P_gc = Hydrostatic pressure in glomerular capliiaries
P_bs = Hydrostatic pressure in bowman's space
π_gc = Osmotic pressure in glomerular capillaries
π_bs = Osmotic pressure in bowman's space
C_inulin = Clearance of para-aminohippuric acid (PAH)
U_inulin = Urine concentration of para-aminohippuric acid (PAH)
V = Urine flow rate
P_inulin = Plasma concentration of para-aminohippuric acid (PAH)
Effective Renal Plasma Flow
(renal clearance)
C_PAH = U_PAHx(V/P_PAH)

U_PAH X V / P_PAH
C_PAH = Clearance of para-aminohippuric acid (PAH)
U_PAH = Urine concentration of para-aminohippuric acid (PAH)
V = Urine flow rate
P_PAH = Plasma concentration of para-aminohippuric acid (PAH)
Renal Blood FlowRPF / (1-Hct)RPF = Renal plasma flow
Hct = Hematocrit
Filtration FractionGFR / RPFGFR + Glomerular Filtration Rate
RPF = Renal Plasma Flow
Free Water ClearanceC H_2O = V - C_osm, Where
C_osm = U_osm x V / P_osm
C H_2O = Clearance of water
U_osm = Urine osmolarity
P_osm = Plasma osmolarity
V= Urine Flow Rate
Filtered LoadGFR x PGFR = Glomerular Filtration Rate
P = Plasma concentration
Excretion RateU x VU = Urine concentration
V + Urine flow rate
ReabsorbedFiltered - Excreted
SecretionExcreted - Filtered

Volume of DistributionVd = Dc / CpVd = Volume of Distribution
Dc = Drug concentration
Cp = Concentration of drug in plasma
ClearanceCl = Re / Cp
0.7 x Vd / t1/2
Cl = clearance
Re = Rate of drug elimination
Cp = Concentration of drug in plasma
Vd = Volume of distribution
t1/2 = drug half-life
Loading doseLd = Css x Vd / FVd = Volume of distribution
Css = Concentration at steady state
F = bioavailability of drug
Maintenance doseMd = Css x Cl / FCss = Concentration at steady state
Md= Maintenance dose
Cl = clearance
F = bioavailability of drug
Therapeutic IndexTi = Td50 / Ed50Ti = Therapeutic index
Td50 = Toxic dose in 50% of population
Ed50 = effective dose in 50% of population
Half Life0.7 x Vd / ClVd = Volume of Distribution
Cl = clearance
Half lives1x t1/2 = 50%
2x t1/2 = 75%
3x t1/2 = 87.5%
4x t1/2 = 94%
5x t1/2 ≈ 100%
a drug reaches both steady state and total clearance at ≈ 4x t1/2.