Physio - Pulm Function Tests

Question 1

How do we determine lung volumes and capacities from spirometry? What cannot be determined from spirometry?

Answer 1

Spirometry

Normal Values:

• Tidal volume (Vt) = 0.5
• Total lung capacity (TLC) = 6.0
• Residual volume (RV) = 1.2
• Vital capacity (VC) = 4.7
• Functional residual capacity (FRC) = 2.4

What cannot be determined…

• RV
• TLC
• FRC

Break down:

• Vital capacity (VC) = Inspiration capcity (IC) + expiratory reserve volume (ERV)
  
  • IC = inspiratory reserve volume (IRV) + Vt
• TLC = VC + RV

Question 2

Explain and apply methods for determination of functional residual capacity (FRC) and residual volume (RV).

Answer 2

Basics:

• Spirometry cannot measure RV & FRC

2 Methods to Calculate:

• Helium dilution
  
  • does NOT include volume of gas trapped in lungs
    
    • small airways closed
    • poorly/non-ventrilated alveoli
• Whole body plethysmography
  
  • includes trapped gas volumes

Question 3

Pulmonary functions tests (PFTs) vs. Spirometry

Answer 3

Pulmonary Function Tests (PFTs)

• Assessment of lung function
  
  • done at LARGE lung volumes & exhalation
• Employ maximal expired effort & volume

FEV = Force expiratory volume

• measured in 1st second

PEFR = Peak expiratory flow rate

Question 4

Effort‐dependent vs. effort‐independent portions of forced exhalation

Answer 4

Effort‐dependent

• occurs at initial stage of exhalation

Effort‐independent

• outward movement of gas become effort-independent
  
  • mainly attributable to smaller airways

Question 5

What is Obstructive lung disease?

Answer 5

Obstructive lung disease

• Partial blockage of airway lumen
• Thickening of airways
  
  • ie: ↓ airway diameter
• Loss of traction on airways
  
  • ie: airway collapse more easily

Types of Obstructive Lung Disease:

• Chronic obstructive lung disease (COPD)
  
  • Emphysema
  • Chronic bronchitis
• Asthma

PFT of Obstructive Lung Disease:

• ↓ forced expiratory volume in 1st second
• ↓ forced vital capacity
• ↓ FEV1/FVC

Question 6

Emphysema

Answer 6

Basics:

• Destruction of alv walls –> enlargement of air spaces distal to terminal bronchioles
  
  • greater SA = less ventilation/perfusion
• Narrowing of small airways & thinning/atrophy of walls

Results:

• ↑ lung compliance
• ↑ airway resistance (esp during expiration)
• ↑ RV & TLC
• Pronounced V/Q inequalities!
  
  • alv to arterial O2 difference of varying magnitudes

Question 7

What are the complications of Asthma?

Answer 7

Basics:

• Hypertrophy of bronchial smooth muscle
  
  • increased reactivity to stimuli
• Widespread narrowing of airways
  
  • inflammation of airways
  • mucosal edema

Results:

• ↑ mucus production
  
  • mucus plugs airways/traps pathogens
  • mucosal edema = ↓ diameter of airway
• trouble breathing air in & out

Treatment:

• beta2 agonist = albuterol
  
  • opens up airway & improve ventilation (broncodilation)
• corticosteroids = anti-inflammatory
  
  • improve ventilation
  • ↑ expression of beta2 receptors

Question 8

What is Restrictive Lung Disease?

Answer 8

Restrictive Lung Disease

• Expansion of lung = restricted
  
  • due to:
    
    • alteration of lung parenchyma
    • disease of pleura/chest wall
    • neuromuscular apparatus

Types of Restrictive Lung Disease:

• Diffuse interstitial pulmonary fibrosis
• Sarcoidosis
• Extrinsic allergic alveolitis
• Pneumothorax
• Pleural effusion
• Poliomyelitis, ALS, MG

PFT of Restrictive Lung Disease:

• ↓ vital capacity & ↓ FRC
• Airway resistance = NOT ↑ relative to lung vol.
• Pronounced ↓ in FVC
  
  • w/ accompanying ↓ in FEV1
• FEV1/FVC% = ↑ (compared to normal)
  
  • values are closer together

Question 9

Obstructive vs. Restrictive

Answer 9

Question 10

Summary of Obstructive & Restrictive Lung Disease

Answer 10

Question 11

What causes Hypoxemia?

Answer 11

Basics:

1. Hypoventilation
   
   • decreased alv ventilation
   • ideally want it ~100 mmHg
     
     • ↓ in alveolar P_O2
     • ↑ alveolar P_CO2
   • causes:
     
     • depression of CNS centers for breathing
     • damage to phrenic motorneurons
     • problems w/ respiratory muscles
     • obstruction of upper airways
2. Diffusion impairment
   
   • P_AlvO2 – P_end‐capO2 > 0 mm Hg
   • alteration in diffusion barrier
     
     • thicker barrier or fewer alv
   • Fick’s law of diffusion
     
     • V_gas α (P1‐P2)(A)(Sol)/(T)(MW)
     • we would change (P₁-P₂) of O2 to compensate
   • Fibrosis = major factor
3. Shunt
   
   • poor alveolar ventilation
   • blood passing thru pulm circulation & doesnt see alveoli
     
     • example: collapsed lung
       
       • blood flow but no reoxygenation
   • causes:
     
     • extreme V/Q inequalilties
     • AV fistula
     • Septal defects
     • Patent ductus arteriosis
4. Ventilation-Perfusion inequalities
   
   • ​most common cause
   • V_A/Q inequality = modest​, then (Alv-A) O2 difference can be easily corrected

Note:

• All corrected w/ supplemental O2 EXCEPT - shunt

Question 12

How can we assess pulmonary function?

Answer 12

Flow curves:

• amt of air exhaled in 1st second = FEV₁
  
  • normal FEV₁/FVC = 0.8
  • 80% of capacity we get rid of w/in 1st sec
• amt of air exhales btw 25% - 75% of different btw TLC & RV

Flow vs Volume Curves:

• peak expiratory flow rate = PEFR
  
  • shape of expiratory curve