Therapeutics Pulmonary Lubsch Flashcard

Primary function of the respiratory system is to maintain normality of arterial blood gases (PaO2 and PaCO2) through:

  • Alveolar ventilation
  • Pulmonary perfusion
  • Gas transfer across alveolar-capillary membrane
  • Ventilation-perfusion matching

Procedures for PFT: Arterial Blood Gases

  • pH and pCO2 are most important
  • pO2 — pulse oximeter is most accurate way to get oxygen saturation
  • HCO3-

Procedures for PFT: Carbon Monoxide Diffusion Capacity (DLCO)

  • Marker of gas diffusion across the alveolar-capillary membrane
  • Reduced in situations where impairment of gas transfer exists (COPD, Interstitial lung disease)
  • Can differentiate between astham and COPD
  • Not clinically used — too expensive, not practical

Procedures for PFT: Gas Dilution or Washout Technique

  • Either closed circuit helium dilution or open-circuit nitrogen washout to measure lung volume
  • Extrapolates lung volumes – what comes in vs what comes out

Procedures for PFT: Body Plethysmography

AKA Body Box

  • Can get any lung measure you could possibly want!
  • Patient sits in chamber and pressure is manipulated
  • Important test for total lung capacity

Procedures for PFT: Peak Expiratory Flow (PEF)

  • Same as Peak Flow Meter
  • Maximal level on forced expiration
  • Not for diagnosis

Procedures for PFT: Spirometry

  • Most clinically useful for diagnosis and monitoring
  • Measurement of the movement of air into and out of the lungs during various breahting maneuvers
  • Measures Vital Capacity, Inspiratory Reserve Volume, Tidal Volume, and Expiratory Reserve Volume
  • Residual Volume MUST BE calculated

Inspiratory Reserve Volume
Amount of air inhaled over and above normal tidal volume after a normal tidal inspiration
Tidal Volume
Volume of air inhaled or exhaled during normal breathing
Expiratory Reserve Volume
Amount of air that can still be expired by forceful expiration after the end of a normal tidal expiration
Residual Volume

  • Volume of air remaining in the lungs at the end of the maximal exhalation
  • Must be calculated

Obstructive Pulmonary Diseases: Effects on Spirometry Volumes

IRV – decreased

TV – same to increased

ERV – decreased

RV – increased

IC – decreased

FRC – increased

VC – decreased

TLC – same, sometimes increased



Restrictive Pulmonary Diseases: Effects on Spirometry Volumes

IRV – decreased

TV – same to decreased

ERV – decreased

RV – decreased

IC – decreased

FRC – decreased

VC – decreased

TLC – decreased


Forced Vital Capacity
The VC performed at maximal efforts
Forced Expiratory Volume

  • Measured after maximal inhalation then exhalation
  • Results in a flow volume curve

Forced Expiratory Volume in 1 second

  • Amount of air moved over 1 second (most important for PFT)
  • Used to diagnose most obstructive pulmonary disease
  • Used to predict response to bronchodilators


Flow Volume Loop

  • Term used to describe the graph resulting from plotting the FVC against the FEV1
  • FEV1 should be at least 75-80% of FVC — if not, some obstructive disease exists

The most sensitive way to measure obstruction is:
Characteristics of Flow Volume Curve: Obstructive

Shape – Concave

FVC – Same

FEFmax – Same

FEV50 – Increase

Characteristics of Flow Volume Curve: Restrictive

Shape – Convex or “same”

FVC – Decreased

FEFmax – Same or decreased

FEV50 – Decreased

Restrictive Defect vs Obstructive Defect


  • Overall decrease in lung volumes without reduction in airflow
  • Hallmark: reduction in TLC
  • Decreased VC may also be seen and is sometimes more clinically useful


  • Reduction in airflow through the conducting airways due to a decrease in diameter, loss of integrity, or reduction in elastic recoil
  • Hallmark: reduction in FEV1

Diseases Associated with Obstructive Defect

  • Asthma
  • COPD
  • Presence of tumor or granuloma
  • Presence of foreign body that mechanically obstructs bronchi
  • Bronchiolitis
  • Cystic Fibrosis

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