Pulmonary Physiology (Wondisford) - 11/29/16

Question 1

Lung volumes (LITER)

Answer 1

Lung volumes (LITER)

• IRV
  
  • Air that can still be breathed in after normal inspiration
• TV
  
  • Air that moves into lung with each quiet inspiration (typically 500 mL)
• ERV
  
  • Air that can still be breathed out after normal expiration
• RV
  
  • Air in lung after maximal expiration; cannot be measured on spirometry

Question 2

What is a capacity?

Types of capacity (4)

Answer 2

Sum of 2 or more physiologic volumes

• Inspiratory Capacity (IRV + TV)
• Functional Residual Capacity (RV + ERV)
  
  • Volume of gas in lungs after normal expiration; includes RV, cannot be measured on spirometry
• Vital Capacity (TV + IRV + ERV)
  
  • Maximum volume of gas that can be expired after maximal inspiration
  • Usually called FVC (b/c you are forcing the change)
• Total Lung Capacity (IRV + TV + ERV + RV)
  
  • Volume of gas present in lungs after a maximal inspiration
  • Includes RV, cannot be measured by spirometry

Question 3

Physiologic dead space

Answer 3

V_D = V_T x [(PaCO2 - PeCO2)/PaCO2]

“Taco, Paco, Peco, Paco”

(PaCO2 = arterial PCO2, PeCO2 = expired air PCO2)

V_D = physiologic dead space = anatomic dead space of conducting airways + alveolar dead space

• Largest contributor of alveolar dead space = apex of healthy lung
• Volume of inspired air that does NOT take part in gas exchange

Question 4

Physiologic dead space vs. Pathologic dead space

Answer 4

Physiologic dead space

• Approx. equivalent to anatomic dead space in normal lungs

Pathologic dead space

• When part of respiratory zone becomes unable to perform gas exchange
• Ventilated but not perfused

Question 5

Ventilation

Minute ventilation (V_E) vs. Alveolar ventilation (V_A)

Answer 5

Minute ventilation (V_E)

• Total volume of gas entering lungs per minute
• V_E = V_T * RR

Alveolar ventilation (V_A)

• Volume of gas per unit time that reaches alveoli
• V_A = (V_T - V_D) * RR

Normal values:

• RR = 12-20 breaths/min
• V_T = 500 mL/breath
• V_D = 150 mL/breath

Question 6

FEV₁ and FEF_25-75

Answer 6

FEV_{<strong>1</strong>} = volume of air forcibly expelled in 1 sec

FEF_{<strong>25-75</strong>} = mean flow rate (volume/time) over middle half of expiration

• 25 designates that 25% of volume is gone from the lungs
• Slope can be used to calculate how fast air is being expired

Question 7

Answer 7

FEV₁, which is the amount of air forcibly exhaled in first second, = good measure of airflow

When expressed as a % of the forced VC (FVC), can be used to diagnose obstructive diseases (i.e. COPD, asthma)

Normal FEV₁ greater than or equal to 80.

Restrictive lung disease patients demonstrate normal or increased FEV₁%.

FEF_25-75% = another way to estimate flow rate and correlates with FEV₁% and flow volume loop