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2. HDS Pulmonary > Pulmonary Mechanics and PFTs > Flashcards

Pulmonary Mechanics and PFTs Flashcards

1
Q

Functional Residual Capacity

Characteristics

A
  • “Resting” position of lungs and chest wall
    • Inward elastic recoil of lungs = outward forces of chest wall
  • Where breathing begins
  • Volume where gas exchange mostly occurs
  • Buffers changes in PO2 and PCO2 that occurs with alveolar ventilation
    • Prevents wide pH swings
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2
Q

Inspiratory Muscles

A
  • Diaphragm
    • ↑ vertical volume of chest cavity
    • ↑ AP diameter ⇒ bucket-handle effect
  • External intercostals
    • Raises rib cage
    • ↑ AP diameter
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3
Q

Accessory Respiratory Muscles

A

Sternocleidomastoid and strap muscles

Raises rib cage

↑ AP diameter

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4
Q

Normal Tidal Breathing

A
  1. Start at FRC
  2. Inspiratory muscles ↑ thoracic volume above FRC
    • Pleural pressure ⇒ ⊖
    • Alveolar pressure ⇒ ⊖
    • Inspiration by negative pressure
  3. Relaxation of inspiratory muscles
  4. Elastic forces passively return lung/chest wall back to FRC ⇒ expiration
    • Expiratory muscles used for cough, exercise, respiratory distress
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5
Q

Lung Compliance

A

Compliance = ∆V / ∆P

  • High compliance @ low to moderate lung volumes
  • Low compliance @ very high volumes or when lungs deflated
  • Max compliance @ FRC
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6
Q

Lung Recoil

A

Due to:

  • Elastic and collagen fibers of the lung
  • Surface tension
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7
Q

Pulmonary Mechanics

Effects of Emphysema

A
  • Secretion of proteases, elastases, etc ⇒ destruction of elastic and collagen fibers
    • High compliance ⇒ easy to inflate
    • Low elastic recoil ⇒ low flow during expiration
    • Equal pressure point moves into the lung
      • Can lead to collapse of airway
  • “Paper bag” model
  • Leads to obstructive lung disease
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8
Q

Pulmonary Mechanics

Effects of Bronchitis and Asthma

A
  • Bronchitis
    • Airway narrowing due to inflammation
  • Asthma
    • Airway narrowing due to inflammation & bronchoconstriction
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9
Q

Pulmonary Mechanics

Effects of Interstitial Lung Disease

A
  • ↑ Collagen or fibrotic tissue
    • Low compliance ⇒ hard to inflate
    • High elastic recoil ⇒ high flow during expiration
  • Ex. pulmonary fibrosis
  • Model ⇒ rubber band around the chest
  • Result ⇒ Restrictive lung disease
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10
Q

Obstructive vs Restrictive

Pulmonary Changes

A
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11
Q

Pulmonary Function Tests

A
  • Spirometry
  • Lung volume studies
  • Diffusion capacity
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12
Q

PFT

Indications

A
  • ID cause of dyspnea
    • Obstructive vs Restrictive
    • Detect/assess reversible airway diseases
    • R/O pulmonary cause of dyspnea
  • Measure effect of disease on pulmonary function
  • Follow course of disease progress or treatment
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13
Q

Spirometry

A

Measurement of lung volumes as a means of detecting disease.

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14
Q

Tidal Volume

(TV or VT)

A

Volume inspired with a normal tidal breath.

Normal ~ 5 ml/kg ideal body weight

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15
Q

Residual Volume

(RV)

A

Volume remaining after a maximal expiration

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16
Q

Inspiratory Reserve Volume

(IRV)

A

Max volume that can be inhaled above an inhaled tidal volume.

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17
Q

Expiratory Reserve Volume

(ERV)

A

Max volume that can be exhaled below FRC.

18
Q

Lung Capacities

A

Defined as one or more lung “volumes”

19
Q

Inspiratory Capacity

(IC)

A

Max volume inspired from resting volume @ FRC.

IC = VT + IRV

20
Q

Vital Capacity

(VC)

A

Max volume that can be exhaled after a maximal inspiration.

VC = IRV + VT + ERV

21
Q

Functional Residual Capacity

(FRC)

A

Volume remaining in the lung after a normal expired tidal volume.

FRC = RV + ERV

22
Q

Total Lung Capacity

(TLC)

A

Max volume that the lungs can contain.

TLC = VC + RV

TLC = FRC + IC

23
Q

Slow Vital Capacity

A

VC measured with a slow expiratory maneuver

24
Q

Forced Vital Capacity

A

VC performed with a maximal forced exhalation

25
Q

Combined Vital Capacity

A

Calculated by adding inspiratory capacity to expiratory reserve volume

26
Q

Inspired Vital Capacity

A

VC calculated by measuring complete inhalation from RV

27
Q

FEV-1

A

Volume of gas exhaled over 1 sec during the performance of a forced expiration

28
Q

FEV-1%

A

FEV-1% = ( FEV-1 / FVC ) x 100

• FEV-1% ≤ 70 or lower limit of normal ⇒ obstruction

29
Q

FEF 25-75%

A

Average rate of flow during the middle half of the volume expired during forced expiration.

  • Measure of small airways obstruction when FEV-1% is normal
  • May be the first signs of COPD
30
Q

Peak Flow

A

Max flow obtained during FVC maneuver.

• Tangent of volume-time curve at start of flow

31
Q

Peak Expiratory Flow

Meters

A
  • Measures initial flow from a forced expiration
  • Provides info about daily variability
  • Used to detect early signs of deterioration in asthma
  • Can be repeated without triggering bronchospasm
  • Portable, inexpensive, and reproducible
32
Q

Bronchodilator Response

A

A positive response defined as any of the following:

  • 12% improvement in FEV-1 and at least 200 cc absolute value improvement
  • 12% improvement in FVC and at least 200 cc absolute value improvement
  • 30% improvement in REF 25-75%
33
Q

Pharmacological

Bronchoprovacation Testing

A
  • Non-specific ⇒ produces rxn in most people
  • Agents
    • Methacholine
    • Histamine
    • Carbachol
    • Specific challenge testing ⇒ oral ASA or inhaled antigen
  • Start with low doses (0.03 mg/ml)
    • Double until concentration > 16 mg/ml or FEV-1 ↓ ≥ 20%
  • If there is < 20% ↓ FEV-1 @ 16 mg/ml ⇒ asthma unlikely
34
Q

Cold Air

Bronchoprovocation Testing

A
  • Inhalation of dry 32°F air
  • Sensitivity overlaps methacholine
    • Neither is 100% sensitive
  • May be more sensitive and specific for exercise induced asthma
35
Q

Exercise Challenge

Bronchoprovocation Testing

A
  • Less sensitive than methacholine
  • More specific at detecting exercise induced asthma
  • 20% ↓ FEV-1 at 5-30 mins post-exercise ⇒ positive
36
Q

Helium Dilution Method

A

Pt inhales a known [He] at end of forced expiration.

[He] determined after air allowed to equilibrate with lungs.

Can be used to calculate residual volume.

C1 x V1 = C2 x (V1 + FRC)

37
Q

Body Box Method

A
  • Patient placed in a closed box
  • Inhalation taken at pressure valve starting from FRC
    • V1 = FRC
    • V2 = V1 + ∆V
    • Pressure in box ↑
    • Pressure at valve ↓
  • Based on Boyle’s Law ⇒ P1V1 = P2V2
    • P1V1 = P2(V1 + ∆V)
    • P1 and P2 are measured
    • ∆V can be calculated from change in box pressure
38
Q

Obstructive Lung Disease

PFT Changes

A
  • FEV-1 < 80% predicted
  • ↔︎ or ↓ FVC
  • FEV-1% < 70% or 75% predicted

Obstructive lung disease defined by FEV-1% < 70%.

39
Q

Obstructive Diseases

A
40
Q

Restrictive Lung Disease

PFT Changes

A

Spirometry suggestive but not diagnostic of restriction.

↓ FEV-1

↓ FVC

↔︎ or ↑ FEV-1%

Restrictive diseases defined by ↓ TLC.

41
Q

Restrictive Diseases

A
42
Q

Summary

A
  • Narrowed airways or overly compliant lungs ⇒ obstruction
  • Interstitial disease or other processes reducing compliance ⇒ restriction
  • Spirometry ⇒ accurate assessment of obstruction
  • Lung volumes ⇒ denies presence of restriction
  • Presence of restriction or obstruction on PFTs may give clues to etiology of pulmonary sx

2. HDS Pulmonary (28 decks)

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