Equations

Question 1

Sensitivity

Answer 1

sensitivity = TP/(TP + FN) = 1 - FN rate

TP= true positive; FN = false negative

Question 2

Specificity

Answer 2

specificity = TN/(TN + FP) = 1 - FP rate

Question 3

Positive Predictive Value

Answer 3

PPV = TP/(TP+FP)

Question 4

Negative Predictive Value

Answer 4

NPV=TN/(TN+FN)

Question 5

Relative Risk

Answer 5

R=[a/(a+b)]/[c/(c+d)]

Question 6

Attributable Risk

Answer 6

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

*AR - difference in risk between exposed and unexposed groups, or the proportion of disease occurrences that are attributable to the exposure (ie smoking causes 1/3rd of cases of pneumonia)

Question 7

Number needed to treat =

Answer 7

1/absolute risk reduction

*Absolute risk reduction - reduction in risk associated with a treatment compared to a placebo

Question 8

Number needed to harm =

Answer 8

1/attributable risk

Question 9

Hardy-Weinberg equilibrium =

Answer 9

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

• p^2 - frequency of homozygosity for allele p
• q^2 - frequence of homozygosity for allele q
• 2pq - frequency of heterozygosity (carrier frequency)

Question 10

Henderson-Hasselbach equation =

Answer 10

pH = pKa + log [HCO3-]/(0.3XPCO2)

Question 11

Volume of distribution

Answer 11

Vd= (amount of drug in body)/(plasma drug concentration)

Question 12

Clearance

Answer 12

CL = rate of elimination of drug/plasma drug concentration

Question 13

Half-Life

Answer 13

t1/2 = (0.7XVd)/CL

Question 14

Loading dose

Answer 14

LD = Cp X (Vd/F)

• Cp=target plasma concentration
• F=Bioavailability = fraction of administered drug that reaches circulation (if IV, F=100%; if oral, F=% that survives first pass in liver or gut)

Question 15

Maintenance dose

Answer 15

MD = Cp X (CL/F)

Question 16

Cardiac output

Answer 16

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

-AND-

CO = stroke volume X heart rate

Question 17

Mean Arterial Pressure

Answer 17

MAP = CO X total peripheral resistance

-AND-

MAP = 1/3 systolic + 2/3 diastolic

Question 18

`Stroke Volume

Answer 18

SV = end diastolic volume - end systolic volume

Question 19

Ejection Fraction

Answer 19

EF = (Stroke volume/End diastolic volume) X 100

Question 20

Resistance

Answer 20

R = driving pressure / flow

= (8 X viscosity X length) / (pi X r^4)

Question 21

Net filtration pressure

Answer 21

Pnet = [(Pc-Pi) - (rc - ri)]

• Pc=capillary pressure –> pushes fluid out of capillary
• Pi=interstitial fluid pressure –> pushes fluid into capillary
• rc= (r should be sigma) plasma colloid osmotic pressure –> pushes fluid into capillary
• ri= interstitial fluid colloid osmotic pressure –> pushes fluid out of capillary

Question 22

Glomerular filtration rate

Answer 22

GFR= Uinulin X (V/Pinulin) = Cinulin

= (urine concentration X urine flow) / Plasma concentration

• Uinulin = urine inulin
• Pinulin = plasma inulin
• Cinulin = clearance of inulin
• V = urine flow rate

-AND-

GFR = Kf [(PGC - PBS) - (rGC - rBS)]

• GC = glomerular capillary
• BS = Bowman’s space
• rBS - normally equals 0

*** Normal GFR = 100 mL/min

Question 23

Effective renal plasma flow

Answer 23

ERPF = Upah X (V/Ppah) = Cpah

Question 24

Renal blood flow

Answer 24

RBF = RPF / (1-Hct)

Question 25

Filtration fraction

Answer 25

FF = GFR / RPF

Question 26

physiologic dead space

Answer 26

VD = VT X (PaCO2 - PeCO2)/PaCO2