Lecture 3 - Pulm Disease

Pulmonary Function Tests

  • To diagnose obstructive and restrictive lung disorders

  • Obstructive - occur in the airway

  • Restrictive - occur in the alveolus

Lung Volumes and Capacity

  • Inspiratory Reserve Volume (IRV) - 1500 cc

  • Tidal Volume (TV) - 500 cc

  • Expiratory Reserve Volume (ERV) - 1500 cc

  • Residual Volume (RV) - 1500 cc

  • Inspiratory Capacity (IC)

    • IRV + TV

  • Vital Capacity (VC)

    • IRV + TV + ERV

  • Total Lung Capacity (TLC)

    • IRV + TV + ERV + RV

The Aging Lung

  • RV increases

  • ERV decreases

  • IRV decreases

  • VC decreases

  • FRC decreases

  • > 80% is considered normal

  • < 80% shows impairment in lung function

Obstructive Lung Diseases

  • Airway obstruction causes an INCREASE IN RESISTANCE

    • Asthma

    • COPD (emphysema, chronic bronchitis)

    • Bronchiectasis

Restrictive Respiratory Disease

  • Compliance of the lung is REDUCED

    • Increases the stiffness of the lung and limits expansion

  • INTRAPULMONARY - Interstitial Lung Disorders

    • Excessive fibrous / connective tissue deposits in lungs

      • Lung injury —> scar tissue formation —> lung stiffness

        • Compliance decreases

    • Due to…

      • Irritant inhalation

      • Autoimmune dysfunction

      • Idiopathic pulmonary fibrosis

      • Hypersensitivity pneumonitis

    • Leads to decreased ventilation (harder to breathe)

      • Hypoxemia

      • V/Q mismatch

  • EXTRAPULMONARY - Chest Wall Restrictions

    • Work of breathing increases and ventilation decreases

      • Hypoventilation, hypercapnia, hypoxemia

      • Impaired lung defenses

    • Due to…

      • Chest wall deformities

      • Fat overlaying chest muscles in very obese patients

      • Neuromuscular diseases

      • Diaphragmatic paralysis

      • Respiratory depression

      • Pleural effusions

    • Dyspnea

    • Susceptible to lower respiratory tract infections

    • Overtime, can lead to respiratory failure

Lung Volumes / Gas Distribution

  • Obstructive Pattern:

    • Trouble exhaling

    • Diaphragm down

    • RV increases with little or no change in VC - AIR TRAPPING

      • Increased RV, FRC, RV / TLC

      • Decreased VC, IRV, ERV

    • TLC increased proportional to TV - HYPERINFLATION

  • Restrictive Pattern:

    • Everything does DOWN (TLC, FRC, RV, VC, VT)

Pulmonary Physiology

Lung Mechanics

  • Obstructive:

    • FEV1 = lower

    • FEV1 / FVC < 0.70 (70%)

Lung Volume

  • Total Lung Volume (TLV):

    • Volume in air in lungs at full inspiration

  • Functional Residual Capacity (FRC):

    • Volume in lungs at resting expiration

  • Residual Volume (RV):

    • Volume in lungs at full expiration

  • NOT MEASURED WITH SPIROMETRY

Airflow

  • Forced Vital Capacity (FVC):

    • Volume of air exhaled from full inspiration to maximal full expiration

  • Forced Expiratory Volume in 1 Sec (FEV1):

    • Volume exhaled in 1 second

  • FEV1 / FVC:

    • Fraction of FVC exhaled in 1 second

    • Normal: airway disorders, asthma, chest wall disorders

    • Decreased: interstitial disorders, COPD, bronchiectasis

FEV1 / FVC

  • Indicates what percentage of the total FVC was expelled from the lungs during the first second of forced exhalation

  • Important in the diagnosis of obstructive and restrictive diseases

    • NORMAL = 0.80

    • OBSTRUCTIVE = < 0.70

    • RESTRICTIVE = 0.80

  • Improved with meds —> Asthma

  • No improvement —> COPD or Bronchiectasis

Flow-Volume Loop

  • Air Flow vs. Volume

    • Graphic representation of the inspiratory and expiratory maneuvers

  • OBSTRUCTIVE: concave loop

  • RESTRICTIVE: narrow loop

Asthma

  • Obstructive

  • Peak expiratory flow reduced

    • Maximum height of the loop is reduced

  • Airflow reduces rapidly with the reduction in lung volumes

    • Airways narrow

    • Loop become concave

  • Concavity may be the indicator of airflow obstruction

    • May be present before the change in FEV1 or FEV1 / FVC

Emphysema

  • Airways may collapse during forced expiration

    • Destruction of supporting lung tissue

    • Very reduced flow at low lung volume

    • Dog-leg appearance to the flow volume curve

  • No improvement after meds or treatment

Diffusing Capacity

  • How well O2 moves in and out of the lungs

    • Getting O2 into alveoli

    • Getting O2 from alveoli to capillary

  • Depends on…

    • Vital capacity (VC): how much air enters the lungs

    • Ventilation relative to perfusion

    • Alveolar-capillary surface area

  • Single-Breath Carbon Monoxide Diffusing Capacity (DLCO)

    • Low DLCO, Normal Spirometry

      • Pulmonary Vascular Disease

      • Anemia

      • Chronic Pulmonary Embolism

      • Pulmonary Hypertension

    • Low DLCO with Restriction

      • Interstitial Lung Disease

    • Low DLCO with Obstruction

      • Emphysema

    • Normal DLCO with Restriction

      • Chest Wall or Neuromuscular Dysfunction

PFT Patterns of Impairment

Obstruction

  • Normal or big lungs

  • Low flow

  • FVC = normal or low

  • FEV1 = low

  • FEV1 / FVC = low (< 0.70)

  • TLC = normal or high

  • RV = high

  • DLCO = normal or low

Restriction

  • Small lungs

  • Normal flow

  • FVC = low

  • FEV1 = low

  • FEV1 / FVC = normal or high (> 0.80)

  • TLC = low

  • RV = low

  • DLCO = low