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

OR = (a/c) / (b/d) = ad / bc

Question 6

Relative risk

Answer 6

RR = (a/(a+b) / (c/(c+d)

Question 7

Relative risk reduction

Answer 7

RRR = 1 - RR

Question 8

Absolute risk reduction

Answer 8

ARR = (c/c+d) - (a/a+b)

Question 9

Number needed to treat

Answer 9

NNT = 1/ARR

Question 10

Number needed to harm

Answer 10

NNH = 1/AR

Question 11

Hardy-Weinberg equilibrium

Answer 11

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

Question 12

Volume of distribution

Answer 12

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

Question 13

Half-life

Answer 13

t1/2 = 0.693 x Vd / CL

Question 14

Drug clearance

Answer 14

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

Question 15

Loading dose

Answer 15

LD = Cp x Vd / F

Question 16

Maintenance dose

Answer 16

D = Cp x CL x tau / F

Question 17

Cardiac output

Answer 17

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

OR

CO = stroke volume x heart rate

Question 18

Mean arterial pressure

Answer 18

MAP = cardiac output x total peripheral resistance

OR

MAP = 2/3diastolic + 1/3systolic

Question 19

Stroke volume

Answer 19

SV = EDV - ESV

Question 20

Ejection fraction

Answer 20

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

Question 21

Resistance

Answer 21

Resistance = driving pressure (ΔP) / flow (Q) = 8η (viscosity) x length / πr^4

Question 22

Capillary fluid exchange

Answer 22

Jv = net fluid flow = Kf[(Pc-Pi) - ς(πc - πi)]

Question 23

Renal clearance

Answer 23

Cx = UxV/Px
Cx: clearance of X (mL/min)
Ux: Urine concentration of X (mg/mL)
Px: Plasma concentration of X (mg/mL)
V: Urine flow rate (mL/min)

if Cx > GFR: net tubular secretion of X
if Cx < GFR: net tubular absorption of X
If Cx = GFR: no net secretion or reabsorption

Question 24

Glomerular filtration rate

Answer 24

GFR = [Xurine]*V /[Xplasma]
GFR = excretion rate/plasma concentration

Question 25

Effective renal plasma flow

Answer 25

eRPF = CPAH = [PAHurine] * V/ [PAHplasma]

Question 26

Renal blood flow

Answer 26

RBF = RPF / (1 - Hct)

Question 27

Filtration fraction

Answer 27

FF = GFR/RPF

Question 28

Henderson-Hasselbach equation (for extracellular pH)

Answer 28

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

Question 29

Winters formula

Answer 29

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

Question 30

Physiologic dead space

Answer 30

Vd = Vt x (Paco2 - Peco2) / Paco2

Question 31

Pulmonary vascular resistance

Answer 31

PVR = (Ppulm artery - P L. atrium) / Cardiac output

Question 32

Alveolar gas equation

Answer 32

PAO2 = PIO2 - (PaCO2/R)

Question 33

Normal GFR

Answer 33

~ 100 mL/min

Question 34

Urine anione gap

Answer 34

Na + K - Cl

Question 35

Plasma anion gap

Answer 35

Na - Cl + HCO3