Equations Flashcards
Sensitivity
Sensitivity = TP / (TP + FN)
Specificity
Specificity = TN / (TN + FP)
Positive predictive value
PPV = TP / (TP + FP)
Negative predictive value
NPV = TN / (TN + FN)
Odds ratio (for case-control studies)
Odds ratio = (a/c)/(b/d) = ad / bc
Relative risk
Relative risk = [a / (a + b)] / [c / (c + d)]
Attributable risk
Attributable risk = [a / (a + b)] - [c / (c + d)]
Number needed to treat
1 / absolute risk reduction
Number needed to harm
1 / attributable risk
Body mass index
BMI = weight in kg / (height in meters)^2
Hardy-Weinberg equilibrium
p^2 + 2pq + q^2
p + q = 1
Volume of distribution (Vd)
Vd = amount of drug in body / plasma drug concentration
Half-life
t1/2 = 0.7 x Vd / CL
Drug clearance (CL)
CL = rate of elimination of drug / plasma drug concentration CL = Vd x Ke (elimination constant)
Loading dose
LD = Cp (plasma concentration) x (Vd / bioavailability)
Maintenance dose
MD = Cp (plasma concentration) x CL
Cardiac output
CO = rate of O2 consumption / (arterial O2 content - venous O2 content) CO = SV x HR
Mean arterial pressure
MAP = CO x TPR MAP = 2/3 diastolic + 1/3 systolic
Stroke volume
SV = CO / HR SV = EDV - ESV
Ejection fraction
EF = SV / EDV EF = (EDV - ESV) / EDV
Resistance
Resistance = [driving pressure (change in P)] / flow (Q) Resistance = [8n (viscosity) x length] / (pi x r^4)
Net filtration pressure
Pnet = [(Pc - Pi) - (pi c - pi i)] Jv = net fluid flow = Kf x Pnet
Renal clearance
C = (U x V) / P
Glomerular filtration rate
GFR = Uinulin x V/Pinulin = Cinulin GFR = Kf [Pgc - Pbs) - (pi gc - pi bs)]
Effective renal plasma flow
ERPF = Upah x (V / Ppah) = Cpah
Renal blood flow
RBF = RPF / (1 - Hct)
Filtration fraction
FF = GFR / RPF
Henderson-Hasselbalch equation (for extracellular pH)
pH = 6.1 + log ([HCO3] / 0.03 Pco2)
Physiologic dead space
Vd = Vt x [(PaCO2 - PeCO2) / PaCO2]
Pulmonary vascular resistance
PVR = (Ppulm artery - Pleft atrium) / CO
Alveolar gas equation
PAO2 = PIO2 - (PaCO2 / R)
