CO Diffusion

Measures how well [blank_start]CO[blank_end] can diffuse across the [blank_start]alveolar[blank_end] capillary membrane Measure in mlCO/min/mmHg at STPD (O celcius, 760 mmHg, dry) Normal value = [blank_start]25[blank_end] mLCO/min/mmHg STPD

Factors that affect DLCO: 1. Hb / Hct - DLCO will [blank_start]follow[blank_end] these values, more or less sites available for binding. 2. Alveolar PCO2 - [blank_start]increase[blank_end] in OCO2 will [blank_start]decrease[blank_end] DLCO because PaO2 will be decreased 3. COHb - [blank_start]Increased[blank_end] COHb will [blank_start]decrease[blank_end] DLCO because of back pressure proportionally. 4. Pulminary Capillary Blood Volume - Increase Blood Volume will [blank_start]increase[blank_end] DLCO because of higher Hb volume 5. Body position - Supine will increase DLCO because of [blank_start]increased[blank_end] capillary flow 6. Altitude - [blank_start]Increased[blank_end] altitude will [blank_start]increase[blank_end] 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 [blank_start]smoking[blank_end] for 48 hrs before the test and avoid heavy [blank_start]exertion[blank_end]. DLCO = [blank_start]VCO/PACO[blank_end] = (mL of CO diffusion per min) / (Alveolar Partial Pressure of CO) DLCO will increase 2-3 times during [blank_start]exercise[blank_end] DLCO will [blank_start]decrease[blank_end] with restrictive disease with loss of lung volume. (Pulmonary fibrosis, Sarcoidosis) Emphysema will decrease DLCO because of loss [blank_start]surface area[blank_end]. VQ mismatch and increase distance from terminal bronchiole to AC membrane.

DLCO Troubleshooting 1. A [blank_start]leak[blank_end] will decrease DLCO 2. Unidirectional valves must have [blank_start]low[blank_end] deadspace, low [blank_start]resistance[blank_end], be easy to [blank_start]maintain[blank_end] to prevent leaks/resistance. 3. [blank_start]Polycythemia[blank_end] will increase DLCO to over 100%

DLCO SB Technique 1. Pt exhales to RV then quickly inhales to TLC a mix of [blank_start].3[blank_end]% CO, [blank_start]10%[blank_end] He, [blank_start]21[blank_end]% O2, and [blank_start]N2[blank_end]. Volume must be [blank_start]85[blank_end]% of VC. Pt Hold breath for [blank_start]8[blank_end]-[blank_start]12[blank_end] seconds then exhales quickly. [blank_start]He[blank_end] corrects for CO trapped in [blank_start]RV[blank_end] and is a [blank_start]carrier[blank_end] 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: [blank_start]Fi[blank_end]CO, [blank_start]Fe[blank_end]CO (infrared analyzer), [blank_start]Fi[blank_end]He, [blank_start]Fe[blank_end]He (He analyzer), [blank_start]Inspired[blank_end] and [blank_start]Alveolar[blank_end] volume (Vi, VA) with pneumotach, and [blank_start]breath hold[blank_end] time. [blank_start]CO[blank_end] and [blank_start]He[blank_end] concentrations are used to calculate DLCO (initial CO is .3%) Most [blank_start]common[blank_end] Method. Is fast, easy and simple to calculate

DLCO Single Breath QA Pt should be seated for [blank_start]5[blank_end] minutes before testing and O2 not administered for [blank_start]5[blank_end] minutes before testing Inspired volume should be >[blank_start]85[blank_end]% of SVC Inhalation in [blank_start]2.5[blank_end] - [blank_start]4[blank_end] seconds Exhalation should occur in [blank_start]2.5[blank_end] - [blank_start]4[blank_end] seconds Breath hold time should be [blank_start]10[blank_end] seconds Acceptable efforts within [blank_start]10[blank_end]% of each other. Report [blank_start]mean[blank_end] of [blank_start]2[blank_end] acceptable maneuvers. Wait 4 minutes in between Washout volume is [blank_start].75[blank_end] to 1 liter Sample collection is [blank_start].5[blank_end] - 1 liter

Steady State CO Diffusion (DLCO SS1 - Filey Method): Pt breathes mix of [blank_start].1[blank_end] - [blank_start].2[blank_end]% CO in RA for 5-6 minutes to achieve a steady state. During final [blank_start]2[blank_end] minutes, exhaled gas is collected in neoprene balloon and [blank_start]ABG[blank_end] is drawn. Data measured - [blank_start]Fi[blank_end]CO, [blank_start]Fe[blank_end]CO (infrared analyzer), [blank_start]Fi[blank_end]N2, [blank_start]Fe[blank_end]N2 (N2 analyzer), [blank_start]Exhaled[blank_end] Volume (pneumotach), [blank_start]Pe[blank_end]CO2 (infrared analyzer), [blank_start]Arterial[blank_end] CO2 (severinghaus electrode), [blank_start]Fi[blank_end]O2, [blank_start]Fe[blank_end]O2, mass spec / fuel cell. Simple - can be used for [blank_start]exercise[blank_end] stress testing. Pts with difficulty following instructions or inspiratory obstruction. [blank_start]Pe[blank_end]CO2 and [blank_start]Pa[blank_end]CO2 required for calculation of PACO.

End Tidal CO Diffusion (DLCO SS2): Same as DLCO [blank_start]SS1[blank_end] except the PACO is measured by taking the average [blank_start]PetCO[blank_end] from breath by breath analysis with infrared analyzer. End tidal PetCO is assumed to equal [blank_start]PACO[blank_end] used to calculated DLCO

Assumed VD CO Diffusion (DLCO SS3) Similar to SS1 except FACO is calculated by a formula that assume [blank_start]VD[blank_end] to be 1 mL per lb of body weight Calculated FACO is used to derive [blank_start]PACO[blank_end] for DLCO calculation

Mixed Venous PCO2 Co Diffusion (DLCO SS4): VCO measured using same method as [blank_start]SS1[blank_end] [blank_start]PACO[blank_end] calculated by estimating mixed venous CO2 partial pressure from an [blank_start]equilibration[blank_end] technique AVoids [blank_start]blood[blank_end] draw

Rebreathing CO Diffusion (DLCO RB) Balloon resevoir is filled with [blank_start].3[blank_end]% CO, [blank_start]10[blank_end]% He, and [blank_start]air[blank_end]. Volume is equal to patient's [blank_start]FEV1[blank_end] Pt exhales to [blank_start]RV[blank_end], valve opens and pt rebreathes from balloon for [blank_start]30[blank_end] - [blank_start]60[blank_end] seconds at [blank_start]30[blank_end] breaths per minute. Final [blank_start]He[blank_end], CO, and O2 concentrations are recorded. DLCO is calculated using those gases and breathing time and balloon volume Rarely used because of pt [blank_start]cooperation[blank_end]

Intrabreath CO Diffusion (DLCO IB) Pt inhales to [blank_start]TLC[blank_end] a mix of [blank_start].3[blank_end]% CO, [blank_start].3[blank_end]% CH4, [blank_start]21[blank_end]% O2 and [blank_start]N2[blank_end], then exhales to RV slowly. Infrared analyzers measure [blank_start]Co[blank_end] and [blank_start]CH4[blank_end] Multiple estimates of DLCO made during exhalation. Can be used during exercise testing.

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