Pulmonary Equations

Question 1

Inspiratory Reserve Volume

Answer 1

Additional air to be breathed in after normal inspiration

Question 2

Tidal Volume

Answer 2

Air that moves into lung with ea quiet inspiration

Normal = 500 mL

Question 3

Expiratory Reserve Volume

Answer 3

Air to be breathed out after normal expiration

Question 4

Residual Volume

Answer 4

Air left in lung after max expiration

CANNOT be meas by spirometry

Question 5

Inspiratory Capacity

Answer 5

TV + IRV

Question 6

Functional Residual Capacity

Answer 6

RV + ERV

Volume of gas in lung at end of expiration

Airway and alveolar pressure both = 0

Inward pull of lungs = outward pull of chest wall

Question 7

Vital Capacity

Answer 7

TV + IRV + ERV

Question 8

Total Lung Capacity

Answer 8

IRV + TV + ERV + RV

Question 9

Physiological Dead Space

Answer 9

VD = VT x (PaCO2 - PeCO2)/PaCO2

PeCO2 is expired air PCO2

Question 10

Minute Ventilation

Answer 10

VE = VT x RR

Question 11

Alveolar Ventillation

Answer 11

VA = VE - VD (minute ventilation - dead space)

VA = (VT-VD) x RR

Question 12

Oxygen Content of Blood

Answer 12

O2 Content = (1.34 x Hb x SaO2) + (.003 PaO2)

AKA amount bound to Hb + amount dissolved

**Anemia/ polycythemia changes Hb but not SaO2 while CO poisoning dec O2 sat

Question 13

O2 Delivery

Answer 13

O2 Delivery = CO x O2 Content

Question 14

Diffusion Equation

Answer 14

Vgas = A x D X (change in P / T)

A - area
T - alveolar wall thickness
D - diffusion coefficient of gas

Question 15

Pulmonary Vascular Resistance

Answer 15

PVR = (P pulm artery - P L atrium) / CO

Question 16

Alveolar Gas Equation

Answer 16

PAO2 = PIO2 - (PaCO2/R)

= 150 - PaCO2 / .8 at sea level and room air

PA - alveolar
PI - inspired air
R - respiratory quotient (CO2 prod / O2 consumed)

Question 17

A-a Gradient

Answer 17

PAO2 - PaO2

Normal = 10-15 mmHg

A-a gradient is inc in shunt, V/Q mismatch or fibrosis that impairs diffusion

Question 18

V/Q by Lung Zone

Answer 18

Apex - ventilation > perfusion

Base - perfusion > ventilation

**Both ventilation and perfusion are greater at bases but perfusion fluctuates more so larger dec in perfusion at apex than ventilation

Question 19

Law of Laplace

Answer 19

Pressure = 2T / r

T - surface tension
r- radius

**So alveoli with same surface tension but smaller radius would have more pressure and thus lose air and collapse BUT surfactant preferentially dec surface tension more and more as alveoli gets smaller to prevent collapse