Equations

Question 1

Sensitivity

Answer 1

TP/(TP + FN)
1 - FN rate
Screening

Question 2

Specificity

Answer 2

TN/(TN + FP)
1 - FP rate
Confirmation

Question 3

Positive predictive value

Answer 3

PPV = TP/(TP + FP)
High pretest probability = high PPV
Proportion of positive test results that are true positive

Question 4

Negative predictive value

Answer 4

NPV = TN/(FN + TN)
High pretest probability = low NPV
Proportion of negative test results that are true negative

Question 5

Odds ratio (for case-control studies)

Answer 5

(a/c) / (b/d) = ad / bc
Odds that group with the disease (cases) was exposed to a risk factor (a/c) divided by odds that group without disease (controls) was exposed (b/d)

Question 6

Relative risk (for cohort studies)

Answer 6

[a/(a+b)] / [c/(c+d)]
Risk in exposed/Risk in unexposed
Risk of developing disease in exposed group divided by risk in unexposed group
21
If prevalence is low, RR ~ OR

Question 7

Attributable risk

Answer 7

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 equation

Answer 10

p^2 + 2pq + q^2 = 1

p + q = 1

Question 11

Volume of distribution

Answer 11

Vd = amount of drug in body/plasma drug concentration

Question 12

Half-life

Answer 12

t1/2 = (0.693 x Vd) / CL

Question 13

Drug clearance

Answer 13

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

Question 14

Loading dose

Answer 14

LD = (Cp x Vd) / F

Question 15

Maintenance dose

Answer 15

D = (Cp x CL x tau) / F

Question 16

Cardiac output

Answer 16

CO = rate O2 consumption/(arterial O2 content - venous O2 content)
CO = SV x HR

Question 17

Mean arterial pressure

Answer 17

MAP = cardiac output x total peripheral resistance
MAP = CO x TPR
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

R = (Driving pressure [Change in P]) / (Flow [Q])
R = (8 x viscosity x length) / (pi x r^4)

Question 21

Net filtration pressure

Answer 21

Pnet = [(Pc - Pi) - (pic = pii)]
Jv = net fluid flow = Kf x Pnet

Question 22

Renal clearance

Answer 22

Cx = UxV/Px

Question 23

Glomerular filtration rate

Answer 23

GFR = Uinulin x V/Pinulinin = Cinulin
GFR = Kf [(Pgc - Pbs) - (pigc - pibs)

Question 24

Effective renal plasma flow

Answer 24

ERPF = Upah x 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-]) / (0.03Pco2)

Question 28

Winters formula

Answer 28

Pco2 = 1.5 [HCO3-] + 8 +/- 2

Question 29

Physiologic dead space

Answer 29

VD = VT x (PaCO2 - PECO2) / PaCO2

Question 30

Pulmonary vascular resistance

Answer 30

PVR = (P pulm artery - P L atrium) / cardiac output

Question 31

Alveolar gas equation

Answer 31

PAO2 = PIO2 - PaCO2/R