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Diffusing Capacity

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Diffusing Capacity RET 2414 Pulmonary Function Testing Module 4.0 Diffusing Capacity Single Breath Method (DLcosb) (Modified Krogh Technique) DLco measures the ... – PowerPoint PPT presentation

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Title: Diffusing Capacity


1
Diffusing Capacity
  • RET 2414
  • Pulmonary Function Testing
  • Module 4.0

2
Diffusing Capacity
  • Single Breath Method (DLcosb)
  • (Modified Krogh Technique)
  • DLco measures the transfer of a carbon MONOXIDE
    (CO) across the alveolocapillary membranes

3
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)

4
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

5
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)

6
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

7
Diffusing Capacity
  • DLcosb

8
Diffusing Capacity
  • DLcosb
  • DLcosb is then calculated as follows
  • DLcosb VA x 60 x Ln FACO0
  • (PB 47) x (T) FACOT

NOT !
MEMORIZE !
9
Diffusing Capacity
  • DLcosb
  • Average DLcosb value
  • 25 ml CO/min/mm Hg (STPD)

10
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)

11
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

12
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

13
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

14
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

15
Diffusing Capacity
  • DLcosb
  • Significance and Pathology
  • Decreased in
  • Restrictive Lung diseases
  • Asbestosis
  • Berylliosis
  • Silicosis
  • Idiopathic pulmonary fibrosis
  • Sarcoidosis
  • Systemic lupus erythematosus
  • Scleroderma

16
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

17
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

18
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

19
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

20
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

21
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

22
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

23
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
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