Equations Flashcards

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1
Q

Sensitivity

A

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

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2
Q

Specificity

A

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

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3
Q

Positive predictive value

A

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

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4
Q

Negative predictive value

A

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

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5
Q

Odds ratio (for case-control studies)

A

(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)

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6
Q

Relative risk (for cohort studies)

A
[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
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7
Q

Attributable risk

A

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

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8
Q

Number needed to treat

A

1/absolute risk reduction

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9
Q

Number needed to harm

A

1/attributable risk

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10
Q

Hardy-Weinberg equation

A

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

p + q = 1

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11
Q

Volume of distribution

A

Vd = amount of drug in body/plasma drug concentration

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12
Q

Half-life

A

t1/2 = (0.693 x Vd) / CL

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13
Q

Drug clearance

A
CL = rate of elimination of drug/plasma drug concentration 
CL = Vd x Ke (elimination constant)
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14
Q

Loading dose

A

LD = (Cp x Vd) / F

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15
Q

Maintenance dose

A

D = (Cp x CL x tau) / F

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16
Q

Cardiac output

A
CO = rate O2 consumption/(arterial O2 content - venous O2 content)
CO = SV x HR
17
Q

Mean arterial pressure

A
MAP = cardiac output x total peripheral resistance
MAP = CO x TPR
MAP = 2/3 diastolic + 1/3 systolic
18
Q

Stroke volume

A

SV = EDV - ESV

19
Q

Ejection fraction

A

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

20
Q

Resistance

A
R = (Driving pressure [Change in P]) / (Flow [Q])
R = (8 x viscosity x length) / (pi x r^4)
21
Q

Net filtration pressure

A
Pnet = [(Pc - Pi) - (pic = pii)]
Jv = net fluid flow = Kf x Pnet
22
Q

Renal clearance

A

Cx = UxV/Px

23
Q

Glomerular filtration rate

A
GFR = Uinulin x V/Pinulinin = Cinulin
GFR = Kf [(Pgc - Pbs) - (pigc - pibs)
24
Q

Effective renal plasma flow

A

ERPF = Upah x V/Ppah = Cpah

25
Q

Renal blood flow

A

RBF = RPF/(1 - Hct)

26
Q

Filtration fraction

A

FF = GFR/RPF

27
Q

Henderson-Hasselbalch equation (for extracellular pH)

A

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

28
Q

Winters formula

A

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

29
Q

Physiologic dead space

A

VD = VT x (PaCO2 - PECO2) / PaCO2

30
Q

Pulmonary vascular resistance

A

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

31
Q

Alveolar gas equation

A

PAO2 = PIO2 - PaCO2/R