Diffusing Lung Capacity | Study notes Medicine

TEST FOR PULMONARY GAS DIFFUSION (DLCO)

Test Gas used in DLCO

Carbon monoxide (CO) - 0.3%

Oxygen (O2) - 21%

Helium (He) - 0.3% (in traditional method they used

10% of helium)

Carbon monoxide - the test gas MOST used in DLCO

Reason why carbon monoxide is used in DLCO

Its transferability / affinity to hemoglobin (210 times

more than oxygen)

Molecular weight is same with oxygen

Advantages of carbon monoxide

% is minimal

can be eliminated after the test

Factors affecting Diffusing Capacity

Ventilation/perfusion relationship.

The gas used to measure DLgas must be capable of two

physiologic actions:

The gas must be capable of diffusing along the A-c

pathway.

The gas must be capable of being transported by

hemoglobin.

NOTE: The test must be fulfilled fast

Indications

Parenchymal lung disease; asbestosis; drug

(amiodarone) & sarcoidosis

Emphysema & cystic fibrosis

Differentiation among chronic bronchitis, emphysema

(decrease DLCO) and asthma (normal DLCO)

Pulmonary involvement in systemic disease

(rheumatoid arthritis, SLE (Systemic lupus

erythematosus))

Cardiovascular diseases (pulmonary hypertension)

Predict arterial desaturation

Disability associated with interstitial lung disease

Increase DLCO

Left to right CV shunt

High altitude

Exercise

Left sided heart failure

Supine body position

Early polycythemia - will increase red blood cells that

affects V/Q relationship

Decrease DLCO - lost of furetion and lost in volume

Emphysema

Pulmonary resection

Asbestosis

Lymphangitic spread in CO

DLCO methods

A. Single Breath Method (Modified Krogh’s Technique) =

DLCOSB

Body Plethysmography device is used (five way

breathing)

TECHNIQUE

CO and tracer gas analysis relatively simple; 10-sec

breath hold

ADVANTAGES:

Does not require the use of invasive measuring procedures.

Analysis of only two gases is required.

Test is easily and rapidly performed and can be

repeated within a reasonably short period of time.

* There should be 4 mins interval between repeats of

procedure

B. Steady State Method = DLCOss

Involves invasive (ABG)

Douglas bag use to collect exhaled air of Px

ADVANTAGES:

Allow a more natural breathing maneuver and allow

for measurements to be made under a greater variety

of clinical conditions (exercise, sleep, anesthesia).

DISADVANTAGES:

More affected by ventilation/perfusion abnormalities

because of the smaller lung volumes used. This can

produce more error than a properly performed DLCO-

SS test.

Different Techniques OF Steady state method

Deadspace-compensated technique

ADVANTAGE

Avoids errors that can occur with end-tidal PACO

measurement.

DISADVANTAGE

Misestimation of VD can result in inaccurate PACO and

therefore inaccurate DLCOSS calculation. This is less of

a problem with testing during exercise where larger

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TEST FOR PULMONARY GAS DIFFUSION (DLCO)

Test Gas used in DLCO  Carbon monoxide (CO) - 0.3%  Oxygen (O2) - 21%  Helium (He) - 0.3% (in traditional method they used 10% of helium) Carbon monoxide - the test gas MOST used in DLCO Reason why carbon monoxide is used in DLCO  Its transferability / affinity to hemoglobin (210 times more than oxygen)  Molecular weight is same with oxygen Advantages of carbon monoxide  % is minimal  can be eliminated after the test Factors affecting Diffusing Capacity  Ventilation/perfusion relationship. The gas used to measure DLgas must be capable of two physiologic actions:  The gas must be capable of diffusing along the A-c pathway.  The gas must be capable of being transported by hemoglobin. NOTE: The test must be fulfilled fast Indications  Parenchymal lung disease; asbestosis; drug (amiodarone) & sarcoidosis  Emphysema & cystic fibrosis  Differentiation among chronic bronchitis, emphysema (decrease DLCO) and asthma (normal DLCO)  Pulmonary involvement in systemic disease (rheumatoid arthritis, SLE (Systemic lupus erythematosus))  Cardiovascular diseases (pulmonary hypertension)  Predict arterial desaturation  Disability associated with interstitial lung disease Increase DLCO  Left to right CV shunt  High altitude  Exercise  Left sided heart failure  Supine body position  Early polycythemia - will increase red blood cells that affects V/Q relationship Decrease DLCO - lost of furetion and lost in volume  Emphysema  Pulmonary resection  Asbestosis  Lymphangitic spread in CO DLCO methods A. Single Breath Method (Modified Krogh’s Technique) = DLCOSB  Body Plethysmography device is used (five way breathing) TECHNIQUE  CO and tracer gas analysis relatively simple; 10-sec breath hold ADVANTAGES: Does not require the use of invasive measuring procedures.  Analysis of only two gases is required.  Test is easily and rapidly performed and can be repeated within a reasonably short period of time.

There should be 4 mins interval between repeats of procedure B. Steady State Method = DLCOss  Involves invasive (ABG)  Douglas bag use to collect exhaled air of Px ADVANTAGES:  Allow a more natural breathing maneuver and allow for measurements to be made under a greater variety of clinical conditions (exercise, sleep, anesthesia). DISADVANTAGES:  More affected by ventilation/perfusion abnormalities because of the smaller lung volumes used. This can produce more error than a properly performed DLCO- SS test. Different Techniques OF Steady state method Deadspace-compensated technique ADVANTAGE  Avoids errors that can occur with end-tidal PACO measurement. DISADVANTAGE  Misestimation of VD can result in inaccurate PACO and therefore inaccurate DLCOSS calculation. This is less of a problem with testing during exercise where larger

tidal volumes make VD a smaller portion of the VT. As a result, VD misestimation produces less error. Estimated-Deadspace (Filey) Technique ADVANTAGE  Provides a more accurate value for VD than does the assumed VD technique. DISADVANTAGE  Requires an arterial blood gas sample. Assumed-Deadspace Technique ADVANTAGE  Avoids the need for arterial blood sampling DISADVANTAGE  Poses greater risk of VD misestimation (although this does not prevent the procedure from being useful for testing during exercise). Alveolar Gas Sampling Technique ADVANTAGE  Avoids errors associated with VD misestimation DISADVANTAGE  Possible error in assuming that PetCO is equivalent to the mean PACO value. This is most likely when VTS are small or uneven or when sampling is done during exercise. C. Rebreathing Method = DLCOrb  There are two rebreathing method techniques: the reservoir-sampling technique and the washout- sampling technique.  Both techniques involve having the subject rebreathe a gas mixture from a bag or balloonlike reservoir.  -The gas mixture used contains 0.3% CO and 10% He with the remaining balance of gas being air.  -The volume of the reservoir is approximately equal to the volume of the subject's FEV₁. ADVANTAGE:  RESERVOIR-SAMPLING TECHNIQUE: In reservoir sampling, the subject rebreathes the gas mixture for a timed period (T_RB) of approximately 30-45 seconds. WASHOUT SAMPLING TECHNIQUE  In washout sampling, rebreathing continues until a gas concentration equilibrium is reached between the reservoir and the subject's lungs. The subject is then switched to inhaling air.  Exhalation washes the gas mixture from the subject's lungs and allows for the concentrations of CO and He to be analyzed.  Rapid- response analyzer systems are used, and the results are recorded  The washout-sampling technique is the DLCO method least affected by ventilation/perfusion abnormalities or by changes in the subject's lung volume at the time of testing. Comparison of DLCO methods Single-Breath Methods  Simplest of the methods in terms of instrumentation and calculations, but it requires the subject to perform a potentially difficult breathing maneuver.  It is moderately affected by ventilation/perfusion abnormalities.  Changes in lung volume at the time of measurement can significantly affect test results. Steady-State Methods  More natural subject breathing is permitted, but the test procedures are moderately complex.  Most likely to be affected by ventilation/perfusion abnormalities. Rebreathing Methods  Least affected by ventilation/perfusion abnormalities.  The required test procedures and instrumentation are the most complex of all the methods. DIFFERENCE OF VALSALVA and MULLER MANEUVER  A Valsalva maneuver reduces pulmonary capillary blood volume and may produce a falsely low DLCO. A Müller maneuver increases pulmonary capillary blood volume and may falsely increase DLCO.

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TEST FOR PULMONARY GAS DIFFUSION (DLCO)