Pulmonary Equations

Question 1

Lungs as a Circuit

Answer 1

Pulmonary artery pressure - Left atrial pressure = CO X Pulmonary Vascular resistance

PVR

Question 2

LaPlace

Answer 2

Pressure = 2(tension)/radius

Question 3

Dalton’s Formula

Answer 3

Pio2 = (Pb - 47 torr) X Fio2

Question 4

Alveolar Gas Equation

Answer 4

PAo2 = Pio2 - (PAco2/R)

Question 5

Alveolar Ventilation

Answer 5

PaCO2 = VCO2/VA x k

Question 6

Normal pressures

Answer 6

Pb = 760 Torr (630)
Ph2o= 47
Pio2 = 100 torr
PaO2= 90-100 (80-85)
PaCO2 = 40 torr

Hypoxemia:
PAo2

Question 7

O2 solubility

Answer 7

[O2] = ao2 X Pao2

ao2 = o2 solubility coefficient
[o2] = dissolved o2 concentration

Question 8

Content of O2 in blood

Answer 8

CaO2 = SaO2 x [Hb] x 1.39 ml O2/gm Hb

Q is cardiac output
CaO2 is content of O2 in blood
1.39 is mass amount of O2 that a hemoglobin can carry

Question 9

volume of Delivery of O2 in one minute

Answer 9

DO2 = Q x CaO2

Question 10

O2 consumption

Answer 10

CaO2 - CvO2 = (SaO2 - SVO2) x [Hb] x 1.39 ml O2/gm Hb

Question 11

Volume of o2 consumed in 1 minute

Answer 11

VO2 = Q x (SaO2 - SVO2) x [Hb] x 1.39 ml O2/gm Hb

Question 12

A-a gradient

Answer 12

PAO2-PaO2

PAO2 - PaO2 = {[(Pb - PH2O) x FiO2] - PaCO2/R} - PaO2

Less than 10 normally

Question 13

Respiratory acidosis

Answer 13

Compensation rules:
Acutely, for every 10 Torr increase in CO2, pH decreases by 0.08

Chronically, for every 1Torr increase in CO2, HCO3- increases about 0.4 meq/L

Question 14

Metabolic Acidosis (Winter’s Formula)

Answer 14

Expected pCO2 = 1.5[HCO3-] + 8 ± 2

Question 15

Anion Gap

Answer 15

Anion Gap = [Na+] – ([Cl-] + [HCO3-])

Normally 12-14

When elevated it indicates the presence of additional acid which is buffered by bicarbonate and thereby increases the amount of unmeasured anions

Question 16

Metabolic Alkalosis

Answer 16

Compensation rules:

Increase [HCO3-] of 1mEq/L increases PaCO2 by 0.7 Torr

Question 17

Aspiring

Answer 17

ASA causes not only a metabolic acidosis, which
stimulates the respiratory center causing a compensatory respiratory alkalosis; it is
also a direct CNS stimulant leading to a respiratory alkalosis. Notice ASA can
also cause non-cardiogenic pulmonary edema thus could be the explanation for
the increased A-a gradient.