Key Equations

Question 1

Sensitivity

Answer 1

Sensitivity= TP / (TP+FN)

Question 2

Specificity

Answer 2

Specificty = TN / (TN + FP)

Question 3

Positive predictive value

Answer 3

PPV = TP / (TP + FP)

Question 4

Negative predicitve value

Answer 4

NPV = TN / (TN + FN)

Question 5

Odds ratio (for case-control studies)

Answer 5

Odds ratio = ad / bc

Question 6

Relative risk

Answer 6

Relative risk = [a / (a + b)] / [c / (c + d)]

Question 7

Attributable risk

Answer 7

Attributable risk = [a / (a + b)] - [c / (c + d)]

Question 8

Number needed to treat

Answer 8

NNT = 1 / absolute risk reduction

Question 9

Number needed to harm

Answer 9

NNH = 1 / attributable risk

Question 10

Body mass index

Answer 10

BMI = weight in kg / (height in meters)²

Question 11

Hardy-Weinberg equilibrium

Answer 11

p² + 2pq + q² = 1

p + q = 1

Question 12

Volume of distribution

Answer 12

V_d = amount of drug in the body / plasma drug concentration

Question 13

Half-life

Answer 13

t_1/2 = (.7 x V_d) / CL

Question 14

Drug clearance

Answer 14

CL = rate of elimination / plasma drug concentration = V_d x K_e (elimination constant)

Question 15

Loading dose

Answer 15

LD = C_p x (V_d / F)

C_p = plasma drug concentration; F = bioavailablity

Question 16

Maintenance dose

Answer 16

MD = C_p x (CL / F)

C_p = plasma drug concentraion; F = bioavailabilty; CL = clearance

Question 17

Cardiac output

Answer 17

CO = rate of O₂ consumption / (arterial O₂ content - venous O₂ content)

CO = stroke volume x heart rate

Question 18

Mean arterial pressure

Answer 18

MAP = cardiac output x total peripheral resistant

MAP = ²/₃ diastolic + ¹/₃ systolic

Question 19

Stroke volume

Answer 19

SV = CO / HR = EDV - ESV

Question 20

Ejection fraction

Answer 20

EF = SV / EDV = (EDV - ESV) / EDV

Question 21

Resistance

Answer 21

Resistance = driving pressure (delta P) / flow (Q) = [8n(viscosity) x length] / [πr⁴]

Question 22

Net filtration pressure

Answer 22

P_net = [(P_c - P_i) - (π_c - π_i)]

J_v = net fluid flow = K_f x P_net

Question 23

Renal clearance

Answer 23

C_x = U_x V / P_x

C = clearance of x; P = plasma [x]; U = urine [x]; V = urine flow rate

Question 24

Glomerular filtration rate

Answer 24

GFR = U_inulin x V / P_inulin = C_inulin

GFR = K_f [(P_GC - P_BS) - (π_GC - π_BS)]

Question 25

Effective renal plasma flow

Answer 25

ERPF = U_PAH x (V / P_PAH) = C_PAH

Question 26

Renal blood flow

Answer 26

RBF = RPF / (1 - Hct)

Question 27

Filtration fraction

Answer 27

FF = GFR / RPF

Question 28

Henderson-Hasselbalch equation (for extracellular pH)

Answer 28

pH = 6.1 + log ( [HCO₃^-] / 0.03 x Pco₂)

Question 29

Physiologic dead space

Answer 29

V_D = V_T x [(Paco₂ - P_Eco2) / Paco₂]

Question 30

Pulmonary vascular resistance

Answer 30

PVR = (P_{pulm artery} - PL atrium) / CO

Question 31

Alveolar gas equation

Answer 31

P_AO2 = P_IO2 - (P_aCO2 / R)