CO Diffusion

Measures how well can diffuse across the capillary membrane

Measure in mlCO/min/mmHg at STPD (O celcius, 760 mmHg, dry)

Normal value = mLCO/min/mmHg STPD

Factors that affect DLCO:
1. Hb / Hct - DLCO will these values, more or less sites available for binding.
2. Alveolar PCO2 - in OCO2 will DLCO because PaO2 will be decreased
3. COHb - COHb will DLCO because of back pressure proportionally.
4. Pulminary Capillary Blood Volume - Increase Blood Volume will DLCO because of higher Hb volume
5. Body position - Supine will increase DLCO because of capillary flow
6. Altitude - altitude will DLCO because of decreased PaO2
7. Breath Hold Time - Depending on how time is measured, it can increase or decrease DLCO
8. Washout Volume - Volume discarded prior to collecting alveolar sample. is usually 1 liter or less.
9. Alveolar Sampling Technique - Normally .5 - 1 L is collected.

Other DLCO Considerations
No for 48 hrs before the test and avoid heavy .
DLCO = = (mL of CO diffusion per min) / (Alveolar Partial Pressure of CO)
DLCO will increase 2-3 times during
DLCO will with restrictive disease with loss of lung volume. (Pulmonary fibrosis, Sarcoidosis)
Emphysema will decrease DLCO because of loss . VQ mismatch and increase distance from terminal bronchiole to AC membrane.

DLCO Troubleshooting
1. A will decrease DLCO
2. Unidirectional valves must have deadspace, low , be easy to to prevent leaks/resistance.
3. will increase DLCO to over 100%

DLCO SB Technique
1. Pt exhales to RV then quickly inhales to TLC a mix of % CO, He, % O2, and . Volume must be % of VC. Pt Hold breath for - seconds then exhales quickly.
corrects for CO trapped in and is a gas for CO.
1st portion (washout vol) exhaled is discarded (.75 - 1 L, decrease to .5 L if FVC is less than 2L)
Next .5 - 1 L is collected (end tidal or alveolar sample)
Data collected: CO, CO (infrared analyzer), He, He (He analyzer), and volume (Vi, VA) with pneumotach, and time.
and concentrations are used to calculate DLCO (initial CO is .3%)
Most Method. Is fast, easy and simple to calculate

DLCO Single Breath QA
Pt should be seated for minutes before testing and O2 not administered for minutes before testing
Inspired volume should be >% of SVC
Inhalation in - seconds
Exhalation should occur in - seconds
Breath hold time should be seconds
Acceptable efforts within % of each other.
Report of acceptable maneuvers.
Wait 4 minutes in between
Washout volume is to 1 liter
Sample collection is - 1 liter

Steady State CO Diffusion (DLCO SS1 - Filey Method):
Pt breathes mix of - % CO in RA for 5-6 minutes to achieve a steady state.
During final minutes, exhaled gas is collected in neoprene balloon and is drawn.
Data measured - CO, CO (infrared analyzer), N2, N2 (N2 analyzer), Volume (pneumotach), CO2 (infrared analyzer), CO2 (severinghaus electrode), O2, O2, mass spec / fuel cell.
Simple - can be used for stress testing. Pts with difficulty following instructions or inspiratory obstruction.
CO2 and CO2 required for calculation of PACO.

End Tidal CO Diffusion (DLCO SS2):
Same as DLCO except the PACO is measured by taking the average from breath by breath analysis with infrared analyzer.
End tidal PetCO is assumed to equal used to calculated DLCO

Assumed VD CO Diffusion (DLCO SS3)
Similar to SS1 except FACO is calculated by a formula that assume to be 1 mL per lb of body weight

Calculated FACO is used to derive for DLCO calculation

Mixed Venous PCO2 Co Diffusion (DLCO SS4):
VCO measured using same method as
calculated by estimating mixed venous CO2 partial pressure from an technique
AVoids draw

Rebreathing CO Diffusion (DLCO RB)
Balloon resevoir is filled with % CO, % He, and . Volume is equal to patient's
Pt exhales to , valve opens and pt rebreathes from balloon for - seconds at breaths per minute.
Final , CO, and O2 concentrations are recorded.
DLCO is calculated using those gases and breathing time and balloon volume
Rarely used because of pt

Intrabreath CO Diffusion (DLCO IB)
Pt inhales to a mix of % CO, % CH4, % O2 and , then exhales to RV slowly.
Infrared analyzers measure and
Multiple estimates of DLCO made during exhalation.
Can be used during exercise testing.

Membrane Diffusion Coefficient/Factor
Resistance of membrane can be calculayed by performing DLCO at 2 levels of
O2 competes with for , 2 levels of O2 will estimate Hb rate curve.
Back to a point of 0 O2 will identify caused by AC membrane.