Equation Review

Question 1

Sensitivity

Answer 1

Sensitivity = TP / (TP + FN)

Question 2

Specificity

Answer 2

Specificity = TN / (TN + FP)

Question 3

Positive predictive value

Answer 3

PPV = TP / (TP + FP)

Question 4

Negative predictive value

Answer 4

NPV = TN / (FN + TN)

Question 5

Odds ratio (for case-control studies)

Answer 5

Odds ratio = (a/c)/(b/d) = 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

1/absolute risk reduction

Question 9

Number needed to harm

Answer 9

1/attributable risk

Question 10

Hardy-Weinberg equilibrium

Answer 10

p2 + 2pq + q2 = 1

p + q = 1

Question 11

Volume of distribution

Answer 11

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

Question 12

Half-life

Answer 12

t1/2 = (0.693 × Vd) / CL

Question 13

Drug clearance

Answer 13

CL = rate of elimination of drug / plasma drug concentration = Vd × Ke (elimination constant)

Question 14

Loading dose

Answer 14

LD = (Cp × Vd) / F

Question 15

Maintenance dose

Answer 15

MD =(Cp × CL × τ) / F

Question 16

Cardiac output

Answer 16

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

CO = stroke volume × heart rate

Question 17

Mean arterial pressure

Answer 17

MAP = cardiac output × total peripheral resistance

MAP = 2 ⁄3 diastolic + 1 ⁄3 systolic

Question 18

Stroke volume

Answer 18

SV = EDV – ESV

Question 19

Ejection fraction

Answer 19

EF = SV / EDV = (EDV − ESV) / EDV

Question 20

Resistance

Answer 20

Resistance = driving pressure (ΔP) / flow (Q) = (8η (viscosity) × length) / πr4

Question 21

Net filtration pressure

Answer 21

Pnet = [(Pc − Pi) − (πc − πi)]

Jv = net fluid flow = (Kf)(Pnet)

Question 22

Renal clearance

Answer 22

Cx = Ux V / Px

Question 23

Glomerular filtration rate

Answer 23

GFR = Uinulin × V / Pinulin = Cinulin

GFR = Kf [(PGC – PBS) – (πGC – πBS)]

Question 24

Effective renal plasma flow

Answer 24

ERPF = UPAH × (V / PPAH) = CPAH

Question 25

Renal blood flow

Answer 25

RBF = RPF / (1 − Hct)

Question 26

Filtration fraction

Answer 26

FF = GFR / RPF

Question 27

Henderson-Hasselbalch equation (for extracellular pH)

Answer 27

pH = 6.1 + log([HCO3−] / 0.03 PCO2)

Question 28

Winters formula

Answer 28

PCO2 = 1.5 [HCO3–] + 8 +/- 2

Question 29

Physiologic dead space

Answer 29

VD = VT × (PaCO2 − PECO2) / PaCO2

Question 30

Pulmonary vascular resistance

Answer 30

PVR = (Ppulm artery – PL atrium) / cardiac output

Question 31

Alveolar gas equation

Answer 31

PAO2 = PIO2 – PaCO2 / R