Diffusing Capacity

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Diffusing Capacity

• RET 2414
• Pulmonary Function Testing
• Module 4.0

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Diffusing Capacity

• Single Breath Method (DLcosb)
• (Modified Krogh Technique)
• DLco measures the transfer of a carbon MONOXIDE
  (CO) across the alveolocapillary membranes

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Diffusing Capacity

• DLcosb
• CO combines with Hb 210 times more readily than
  O2
• DLco is expressed as
• ml of CO/minute/mm Hg (STPD)
• STPD (0? C, 760 mm Hg, Dry)

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Diffusing Capacity

• DLcosb
• Procedure
• Unforced exhalation to RV
• (limited to 6 seconds)
• Rapid inhalation of a diffusion gas mixture to
  TLC (from spirometer/demand valve/reservoir)
• 0.3 CO
• 10 He (tracer gas)
• 21 O2
• Balance Nitrogen

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Diffusing Capacity

• DLcosb
• Procedure
• Breath hold at TLC for 10 /- 2 seconds
• Rapid exhalation
• (should not exceed 4 sec)
• Alveolar gas is collected after a washout volume
  (0.75-1.0 L) has been discarded
• (If VC is lt2.0 L, washout volume may be reduced
  to 0.50L)

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Diffusing Capacity

• DLcosb
• Procedure
• Sample gas volume should be 0.50 1.0 L
• (If VC lt1.0L, a sample of lt0.50L can be analyzed
  if deadspace volume has been cleared)
• Sample is analyzed for the fractional CO and He
  (tracer gas) concentration
• Change in He concentration reflects dilution by
  gas in lungs at RV
• This change is used to determine the initial CO
  concentration

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Diffusing Capacity

• DLcosb

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Diffusing Capacity

• DLcosb
• DLcosb is then calculated as follows
• DLcosb VA x 60 x Ln FACO0
• (PB 47) x (T) FACOT

NOT !
MEMORIZE !
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Diffusing Capacity

• DLcosb
• Average DLcosb value
• 25 ml CO/min/mm Hg (STPD)

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Diffusing Capacity

• DLcosb
• Pretest Patient Preparation
• Should refrain from
• Smoking for at least 24 hours prior to testing
• Consuming alcohol 4 hours prior to test (will
  reduce DLco)
• Strenuous exercise before testing (effects
  pulmonary capillary blood volume)
• Eating for at least two hours prior to testing
  (digestion effects pulmonary capillary blood
  volume)

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Diffusing Capacity

• DLcosb
• Pretest Patient Preparation
• Should sit for at lest 5 minutes before test
  (effects pulmonary capillary blood volume)
• Supplemental O2 should be discontinued at least
  five minutes prior to testing

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Diffusing Capacity

• DLcosb
• Acceptability Criteria
• Volume-Time tracing should show smooth, rapid
  inspiration (lt4 sec) from RV to TLC
• Expiration should be rapid but not forced 4
  seconds or less

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Diffusing Capacity

• DLcosb
• Acceptability Criteria
• Dead space washout should be 0.75 1.00 L (0.5 L
  if VC is less than 2.0 L)
• Alveolar sample volume should be 0.5 to 1.0 L
• Inspired volume should be at least 85 of
  previously recorded best VC

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Diffusing Capacity

• DLcosb
• Acceptability Criteria
• Breath hold time should 10 sec /- 2 sec (No
  Valsalva or Mueller maneuver)
• The average of two or more acceptable test should
  be reported. Duplicate determinations should be
  within 10 of highest value or 3 ml CO/min/mm Hg

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Diffusing Capacity

• DLcosb
• Significance and Pathology
• Decreased in
• Restrictive Lung diseases
• Asbestosis
• Berylliosis
• Silicosis
• Idiopathic pulmonary fibrosis
• Sarcoidosis
• Systemic lupus erythematosus
• Scleroderma

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Diffusing Capacity

• DLcosb
• Significance and Pathology
• Decreased in
• Inhalation of toxic gases (alveolitis)
• Loss of lung tissue
• Space occupying lesions (tumors)
• Pulmonary edema
• Lung resection
• Radiation therapy (fibrotic changes)
• Chemotherapy

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Diffusing Capacity

• DLcosb
• Significance and Pathology
• Decreased in
• Emphysema
• Chronic Bronchitis , Asthma (may or may not be
  decreased)
• DLco sometimes used to differentiate between
  emphysema and chronic bronchitis

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Diffusing Capacity

• DLcosb
• Significance and Pathology
• In patients with COPD, DLco less than 50 of
  predicted is accompanied by O2 desaturation
  during exercise
• Low resting DLco (lt50 - 60 of predicted) may
  indicate the need for assessment of oxygenation
  during exercise

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Diffusing Capacity

• DLcosb
• DL/VA
• DLco is directly related to lung volume in
  healthy individuals
• DL/VA is approximately 4-5 ml CO
  transferred/minute/liter of lung volume

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Diffusing Capacity

• DLcosb
• DL/VA
• DL/VA is useful in differentiating between
  restrictive and obstructive disease
• Obstruction Low DL/VA ratio
• Restriction DL/VA Ratio is preserved

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Diffusing Capacity

• DLcosb
• DLco is affected by
• Hemoglobin (Hb)
• Corrections for Hb concentrations should be
  applied
• Low Hb reduces DLco
• High Hb elevates DLco
• Carboxyhemoglobin (COHb)
• Corrections for COHb should be applied
• High COHb reduces DLco

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Diffusing Capacity

• DLcosb
• DLco is affected by
• Alveolar PCO2
• Increased PCO2 elevates DLco
• Hypoventilation
• Pulmonary capillary blood volume
• Increased blood volume causes increased DLco
• Mueller maneuver
• Increased cardiac output
• Decrease pulmonary capillary blood volume causes
  decreased DLco
• Valsalva maneuver

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Diffusing Capacity

• DLcosb
• DLco is affected by
• Altitude above sea level
• High altitude increases DLco
• Poor inspiratory effort during testing
• If less than 85 of VC will decrease DLco