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Formulas Flashcards

1
Q

odds ratio

A

odds of exposure among cases (a/c) versus odds of exposure among controls (b/d)

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

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2
Q

relative risk

A

risk of developing disease in the exposed group divided by risk in the unexposed group

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

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3
Q

relative risk reduction

A

proportion of risk reduction attributable to the intervention as compared to a control

RRR = 1 - RR

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4
Q

attributable risk

A

difference in risk between exposed and unexposed groups

AR = (a/[a + b]) - (c/[c + d])
AR% = (RR - 1)/RR * 100

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5
Q

absolute risk reduction

A

difference in risk (not the proportion) attributable to the intervention as compared to a control

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

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6
Q

number needed to treat

A

number of patients who need to be treated for one patient to benefit

NNT = 1/ARR

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7
Q

number needed to harm

A

number of patients who need to be exposed to a risk factor for one patient to be harmed

NNH = 1/AR

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8
Q

mortality rate

A

number of deaths within a population over a defined period

deaths/1000 people per year

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9
Q

attack rate

A

proportion of exposed people who become ill

(people who become ill)/(total people exposed)

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10
Q

likelihood ratio

A

LR+ = (probability of positive result in a patient with disorder) / (probability of positive result in patient without disorder)
= (sensitivity) / (1 - specificity)
= (TP rate) / (FP rate)

LR- = (probability of a negative result in a patient with disorder) / (probability of negative result in patient without disorder)
= (1 - sensitivity) / (specificity)
= (FN rate) / (TN rate)

LR+ >10 = highly specific test
LR- < 0.1 = high sensitive test

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11
Q

posttest probability

A

posttest probability = posttest odds / (posttest odds + 1)

posttest odds = pretest probability * LR

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12
Q

sensitivity

A

true positive rate; proportion of all people with disease who test positive

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

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13
Q

specificity

A

true negative rate; proportion of all people without disease who test negative

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

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14
Q

positive predictive value

A

probability that a person who has a positive test result actually has the disease

PPV = TP / (TP + FP)

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15
Q

negative predictive value

A

probability that a person with a negative test result actually does not have the disease

NPV = TN / (TN + FN)

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16
Q

standard error

A

SE = SD/(square root of sample size)

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17
Q

statistical power

A

power = 1 - B

B: probability of making a type II error

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18
Q

confidence interval

A

range of values within which the true mean of the population is expected to fall

CI = 1 - a

CI for sample mean = mean +/- Z(SE)

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19
Q

coefficient of determination

A

r^2

20
Q

Michaelis-Menten equation

A

v = Vmax * [S]/(Km + [S])
v = rate of reaction (rate for formation of product)
Vmax = maximum rate achieved
[S] = concentration of substrate
Km = [S] at 1/2 Vmax

21
Q

volume of distribution (Vd)

A

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

compartment = intravascular: low Vd
compartment = ECF: medium Vd
compartment = all tissues (including fat): high Vd

22
Q

clearance (CL)

A

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

Ke = elimination constant

23
Q

half life (t1/2)

A

t1/2 = 0.7(Vd) * CL

(for first-order elimination)

24
Q

loading dose, maintenance dose

A

loading dose = Cp * Vd / F

maintenance dose = Cp * CL * T / F

Cp = target plasma concentration
Vd = volume of distribution
CL = clearance
T = dosage interval (time between doses)
F = bioavailability

25
Q

bioavailability (F)

A

F = (AUC oral * Dose iv) / (Dose oral * AUC iv)

26
Q

therapeutic index

A

TI = TD50/ED50

TD50 = median toxic dose
TD50 = median effective dose

drugs with lower TI values require monitoring: warfarin, theophylline, digoxin, antiepileptic drugs, lithium

27
Q

corrected reticulocyte count

A

also called reticulocyte production index (RPI)

RPI = % reticulocytes * (actual Hct / normal Hct) / maturation time

28
Q

cardiac wall tension

A

wall tension = pressure * radius

wall stress is proportional to (wall tension)/(2*(wall thickness))

29
Q

stroke volume

A

SV = EDV - ESV

30
Q

ejection fraction

A

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

31
Q

cardiac output

A

CO = Q = SV * HR

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

32
Q

pulse pressure

A

PP = systolic blood pressure (SBP) - diastolic blood pressure (DBP)

PP is increased in hyperthyroidism, aortic regurgitation, aortic stiffening, obstructive sleep apnea, anemia, and exercise

PP is decreased in aortic stenosis, cardiogenic shock, cardiac tamponade, advanced HF

33
Q

mean arterial pressure

A

MAP = CO * TPR

MAP = 2/3 DBP + 1/3 SBP = DBP + 1/3 PP

34
Q

resistance (cardio)

A

resistance = driving pressure / Q =
(8(viscosity) * length)/(pi * r^4)

35
Q

capillary fluid exchange (net fluid flow)

A

Jv = Kf[(Pc - Pi) - sigma(pi.c - pi.i)]

36
Q

inspiratory capacity

A

IRV + VT (tidal volume)

air that can be breathed in after normal exhalation

37
Q

functional residual capacity

A

RV + ERV

volume of gas in lungs after normal expiration; outward pulling force of chest wall is balanced with inward collapsing force of lungs

38
Q

vital capacity

A

IRV + VT + ERV

maximum amount of air that can be expired after a maximal inspiration

39
Q

total lung capacity

A

IRV + VT + ERV + RV = VC + RV

volume of gas present in lungs after a maximal inspiration

40
Q

determination of physiologic dead space

A

VD = VT * (PaCO2 - PeCO2)/PaCO2

PaCO2: arterial PCO2
PeCO2: expired air PCO2

41
Q

minute ventilation

A

VE = VT * RR

total volume of gas entering lungs per minute

42
Q

alveolar ventilation

A

VA = (VT - VD) * RR

volume of gas that reaches alveoli each minute

43
Q

pulmonary vascular resistance

A

PVR = (pressure in pulmonary artery - pulmonary artery occlusion pressure)/Q

Q = cardiac output

44
Q

alveolar gas equation

A

PAO2 = PIO2 - PaCO2/RQ
= 150 mm Hg - PaCO2/0.8

45
Q

oxygen content

A

O2 content = (O2 bound to hemoglobin) + (O2 solubilized in plasma) = (1.34 * Hb * SaO2) + (0.003 * PaO2)

SaO2 = percent saturation of arterial blood with O2
0.003 = solubility constant of O2
PaO2 = partial pressure of O2 in arterial blood

Step 1 - Quick Decks (18 decks)

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