Equation Review

Question 0

Specificity

Answer 0

Specificity = TN/(TN+FP)

Question 1

Sensitivity

Answer 1

Sensitivity = TP/(TP+FN)

Question 2

Positive predictive value (PPD)

Answer 2

PPD = TP/(TP+FP)

Question 3

Negative predictive value (NPV)

Answer 3

NPV = TN/(TN+FN)

Question 4

Odds ratio

Answer 4

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

*For case-control studies

Question 5

Relative risk

Answer 5

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

Question 6

Attributable risk

Answer 6

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

Question 7

Number needed to treat

Answer 7

1/(absolute risk reduction)

Question 8

Number needed to harm

Answer 8

1/(attributable risk)

Question 9

Body mass index (BMI)

Answer 9

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

Question 10

Hardy-Weinberg equilibrium

Answer 10

p^2 + 2pq + q^2 = 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 = (0.7✖️Vd)/CL

Question 13

Drug clearance

Answer 13

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

Question 14

Loading dose

Answer 14

LD = Cp✖(️Vd/F)

• Cp = target plasma concentration
• F = bioavailability

Question 15

Maintenance dose

Answer 15

MD = Cp✖(️CL/F)

• Cp = target plasma concentration
• F = bioavailability

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 = CO/HR = EDV - ESV

Question 19

Ejection fraction

Answer 19

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

Question 20

Resistance

Answer 20

Resistance = (deltaP)/Q = [8(viscosity)✖️length]/(pi✖️radius^4)

• deltaP = driving pressure
• Q = flow

Question 21

Net filtration pressure

Answer 21

Pnet = [(Pc - Pi) - (oncotic capillary pressure - oncotic interstitial pressure)]

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

Question 22

Renal clearance

Answer 22

Cx = (UxV)/Px

Question 23

Glomerular filtration rate

Answer 23

GFR = (U_inulin✖️V)/P_inulin = C_inulin
GFR = Kf[(Hydrostatic pressure of glomerular capillary - hydrostatic pressure of Bowman's space) - (oncotic pressure of glomerular capillary - oncotic pressure of Bowman's space)]

Question 24

Effective renal plasma flow

Answer 24

ERPF = U_PAH✖️(V/P_PAH) = C_PAH

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

Answer 27

For extracellular pH

pH = 6.1 + log([HCO3-]/0.03PCO2)

Question 28

Physiologic dead space

Answer 28

V_D = V_T✖️[(PaCO2 -PECO2)/PaCO2]

• V_T = tidal volume
• PECO2 = expired air PCO2

Question 29

Pulmonary vascular resistance

Answer 29

PVR = (P_pulm art - P_L atrium)/cardiac output

Question 30

Alveolar gas equation

Answer 30

PAO2 = PIO2 - (PaCO2/R)

• PAO2 = alveolar PO2
• PIO2 = PO2 in inspired air
• PaCO2 = arterial PCO2
• R = respiratory quotient = CO2 produced/O2 consumed (~0.8)