Pulmonary Equations Flashcards
Inspiratory Reserve Volume
Additional air to be breathed in after normal inspiration
Tidal Volume
Air that moves into lung with ea quiet inspiration
Normal = 500 mL
Expiratory Reserve Volume
Air to be breathed out after normal expiration
Residual Volume
Air left in lung after max expiration
CANNOT be meas by spirometry
Inspiratory Capacity
TV + IRV
Functional Residual Capacity
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
Vital Capacity
TV + IRV + ERV
Total Lung Capacity
IRV + TV + ERV + RV
Physiological Dead Space
VD = VT x (PaCO2 - PeCO2)/PaCO2
PeCO2 is expired air PCO2
Minute Ventilation
VE = VT x RR
Alveolar Ventillation
VA = VE - VD (minute ventilation - dead space)
VA = (VT-VD) x RR
Oxygen Content of Blood
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
O2 Delivery
O2 Delivery = CO x O2 Content
Diffusion Equation
Vgas = A x D X (change in P / T)
A - area
T - alveolar wall thickness
D - diffusion coefficient of gas
Pulmonary Vascular Resistance
PVR = (P pulm artery - P L atrium) / CO
Alveolar Gas Equation
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)
A-a Gradient
PAO2 - PaO2
Normal = 10-15 mmHg
A-a gradient is inc in shunt, V/Q mismatch or fibrosis that impairs diffusion
V/Q by Lung Zone
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
Law of Laplace
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
