12 IRM equations

Question 1

What is the respiratory quotient?

Answer 1

RQ = V(CO2) / V(O2)

Question 2

What is the relationship between gas flow and speed?

Answer 2

V(dot) = u x A
U = speed
A = Area

Question 3

What is Dalton’s Law?

Answer 3

Px = sum of the pressure of individual gases

Question 4

How would you calculate dead space?

Answer 4

physiological dead space = anatomical dead space + alveolar dead space

Question 5

How would you work out total ventilation?

Answer 5

V(E) = V(T) x f
V(T) = tidal ventilation

Question 6

How would you work out alveolar ventilation?

Answer 6

V(A) = (V(T) - V(D)) x f

Question 7

What is Boyles Law?

Answer 7

P1 x V1 = P2 x V2

Question 8

What is the formula for compliance?

Answer 8

compliance = change in V / change in P

Question 9

What is Laplace’s Law?

Answer 9

P = 2T / r

Question 10

What is Pouisselle’s equation?

Answer 10

flow = change in pressure x pir(4) / 8L x viscosity

Question 11

What is the alveolar gas equation?

Answer 11

P(AO2) = P(iO2) - (P(ACO2) / R)

R = respiratory quotient

Question 12

What is Henry’s Law?

Answer 12

concentration of gas = partial pressure x solubility coefficient

Question 13

What is the diffusibility of a gas?

Answer 13

diffusibiity = V(dot)

V(dot) = d x (A/T) x (P1-P2)

T = thickness
A = total surface area

Question 14

What is the diffusion constant?

Answer 14

D(L) = V / (P1-P2)

Question 15

What is pH equal to?

Answer 15

-log[H+]

Question 16

What is the Henderson - Hasselbach equation?

Answer 16

pH = pK + log[A-] / [HA]

Question 17

What is pK?

Answer 17

negative log of the dissociation constant, [A-] and [HA], ionised and unionised concentrations of buffer

Question 18

What would the henderson hasselbach equation be for a HCO3- buffer?

Answer 18

pH = pK + log[HCO3-] / [PCO2 x solubility]