Diffusion Conductance Formula in Pulmonary Physiology

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What units are used to report Dlco?

Milliliters of CO/minute/millimeter of mercury at 0°C, 760mm Hg, dry (STPD)

What does Dlco stand for?

Diffusing capacity of the lungs for carbon monoxide

What factors affect the uptake of CO by Hb?

Reaction rate (θ) and pulmonary capillary blood volume (VC)

What does STPD stand for?

Standard temperature, pressure, dry Signup and view all the answers

All methods for determining DLCO are based on the following equation:

DLCO = VCO / (PA CO - PaCO ) Signup and view all the answers

What is the conversion factor from DLCO SI units to mm Hg?

2.986 Signup and view all the answers

How should the subject position themselves before conducting a DLCO maneuver?

Have the subject sitted upright with feet flat on the floor and adjust the mouthpiece to the proper height. The mouthpiece should rest on top of the tongue. Have the subject gently bite down with his or her teeth and seal lips firmly around the mouthpiece. Emphasize the need for tight lips without a leak. Place the nose clip securely. Signup and view all the answers

What is the key instruction regarding the mouthpiece during a DLCO maneuver?

Seal lips firmly around the mouthpiece Signup and view all the answers

What is the recommended breathing pattern before starting a DLCO maneuver?

Breathe quietly for several breaths and then empty completely to residual volume, then inhale rapidly as much as possibly and hold the breath. Signup and view all the answers

How long is the wait period required between DLCO maneuvers?

4 minutes Signup and view all the answers

What is the equation for diffusion conductance across alveolocapillary membrane ?

1/DLCO = 1/Dm + 1/(hb reaction rate)xVc x D Signup and view all the answers

What is the unit used to express DLCO in SI units?

mmol/min/kPal Signup and view all the answers

What is VCO in the context of DLCO measurement?

Milliliters of CO transferred per minute (STPD) Signup and view all the answers

What are the conditions for VA in relation to the largest VA from other acceptable maneuvers?

Within 200mL or 5%, whichever is greater Signup and view all the answers

What is the recommended range for BHT (Breath Hold Time)?

Between 8 and 12 seconds Signup and view all the answers

How long should total exhalation last?

4 seconds or less Signup and view all the answers

What is the minimum recommended interval between repeated tests?

4 minutes Signup and view all the answers

In a normal subject, how should the TLC-VA relationship be?

Remarkably close or the same Signup and view all the answers

How many single breath maneuvers should be performed at most?

Five Signup and view all the answers

What is the maximum allowable difference for duplicate determinations in alveolar gas analysis?

Within 2mL/min/mm Hg or 0.67mmol/min/kPa Signup and view all the answers

What needs to be done before obtaining an alveolar gas sample in Dlcosb systems that use RGA technology?

Dead space gas needs to be washed out Signup and view all the answers

What is the advantage of multigas analysis in Dlco gas analysis?

CO and CH4 are measured rapidly and continuously Signup and view all the answers

What method should be used to measure the breath hold time (BHT) in Dlco calculations?

Jones and Meade method Signup and view all the answers

What should be done to correct gas volumes for Dlco calculations?

Correct from ATPS (ambient temperature, ambient pressure, and saturated to with water vapor) STPD Signup and view all the answers

Why is it important to watch the patient carefully during Dlcosb effort?

To detect Valsalva or Müller maneuvers Signup and view all the answers

What is used to absorb carbon dioxide (CO2) during gas analysis?

Ba(OH)2 (baralyme) or NaOH (sodium hydroxide, soda lye) Signup and view all the answers

How should the anatomic dead space (VD) be calculated?

Anatomic dead space should be calculated as 2.2mL per kilogram of ideal body weight. Signup and view all the answers

What is the acceptable timing accuracy required for measurememnt of the BHT in Dlco calculations?

Within 100msec over a 10-second interval (1%) Signup and view all the answers

What is the maximum inspiratory pressure allowed in a demand-flow system to maintain a flow of 6L/sec?

Less than 10cm H2O Signup and view all the answers

Why is it important to ensure linearity within 0.5% of full scale in gas analysis systems?

To avoid more than a 0.5% error when analyzing a known gas concentration Signup and view all the answers

Explain how the concentration of CO at the beginning of the breath hold (FACO 0) is calculated.

FACO 0 = FICO x (FAtracer / FItracer) Signup and view all the answers

What is the formula to calculate DLCOsb (single breath diffusion capacity for carbon monoxide)?

DLCOsb = (VA x 60) / ((PB-47) x T) x Ln(FAO 0 / FAOT) Signup and view all the answers

How is the alveolar volume (VA) calculated for the single-breath dilution of the tracer gas?

VA = (VI - VD) x (FItracer / FAtracer) x STPD correction factor Signup and view all the answers

Explain the physiological significance of KCO in the context of Dlco/VA.

KCO reflects physiology better than Dlco/VA because KCO is not constant as VA changes. Signup and view all the answers

Why is the term KCO recommended for reporting instead of Dlco/VA by the ATS-ERS Standardized Pulmonary Function Reporting statement?

The misinterpre- tation that Dlco/VA “corrects” Dlco for reduced VA is physiologically incorrect because Dlco/VA is not constant as VA changes Signup and view all the answers

What is the formula to measure KCO?

log [FACO 0 / FACO T] / BHT Signup and view all the answers

Describe the simplification of the single-breath method that avoids analyzing absolute gas concentrations.

Ln(FAtracer/FACOT); FAtracer = fraction of tracer in alveolar gas, equal to FACO 0; FAcoT = fraction of CO in alveolar gas at end of breath hold Signup and view all the answers

This process of conductance across the membranes to hemoglobin can be divided into two components. What are them?

Membrane conductance (Dm) and the chemical reaction between CO and Hb Signup and view all the answers

What Dm stands for?

Dm reflects the process of diffusion across the alveolocapillary membrane. Signup and view all the answers

Uptake of CO by Hb depends on (2)?

the reaction rate (θ) and the pulmonary capillary blood volume (VC) Signup and view all the answers

Because little or no CO is normally present in pulmonary capillary blood, the pressure gradient causing diffusion is basically the alveolar pressure (PAco). (T or F?)

True Signup and view all the answers

Inspiration from RV to TLC should be rapid and should occur in less than ?

4 seconds Signup and view all the answers

How much should be VI in DLCO manouvre?

VI ≥ 90% of largest VC in the same test session. or VI ≥ 85% of largest VC in the same test session and VA within 200 mL or 5% (whichever is greater) of largest VA from other acceptable maneuvers Signup and view all the answers

Criteria for acceptability - comments about breath holding time

BHT should be between 8 and 12 seconds, with no evidence of leaks or of Valsalva or Müller maneuver. Signup and view all the answers

Criteria for Acceptability - How should be the exalation after the breath holding time?

Exhalationshouldberapid,withtotalexhalation lasting 4 seconds or less, with appropriate clearance of Vd and proper sampling/analysis of alveolar gas. Signup and view all the answers

No more than x single-breath maneuvers should be performed. What is x value?

5 Signup and view all the answers

The VA is consistent with the clinical presentation. Explain

In a normal subject, the TLC–VA relationship should be remarkably close, if not the same, and TLC performed by any method in any disease state should be larger than VA. Signup and view all the answers

Criteria for acceptability - How should the results of DLCO be reported?

The average of two or more acceptable tests should be reported. Duplicate determinations should be within 2mL/min/mm Hg (0.67mmol/min/kPa). Signup and view all the answers

CRITERIA FOR ACCEPTABILITY How inspiration from RV to TLC should be?

Should be rapid and should occur in less than 4 seconds. Signup and view all the answers

CRITERIA FOR ACCEPTABILITY Before measuring values, system must have passed?

calibration and quality control procedures Signup and view all the answers

When the VA is used to calculate the ratio of Dlco to lung volume (Dl/VA), how is it normally expressed ?

In BTPS Signup and view all the answers

In a “classic system,” a discrete sample of alveolar gas is collected after a suitable washout volume has been discarded. What volume?

750–1000mL Signup and view all the answers

In rapid gas analyzer (RGA) systems, which have a 0% to 90% response time of ≤ 150 ms, continuous gas analysis occurs. Is a fixed washout or sample volume required in this sistems?.

No, A fixed washout volume is not required Signup and view all the answers

The expiratory sample is analyzed to obtain the fractional CO and tracer gas concentrations in alveolar gas, FA COT (where T is the time of the breath hold), and FA tracer, respectively. (T or F?) What must be determined as well?

The concentration of CO in the alveoli at the beginning of the breath hold (FA CO 0). Signup and view all the answers

HOw is the FA CO 0 calculated?

It is calculated as follows: FA CO 0 = F1CO × (FAtracer/ Ftracer) Where: FAco0 = fraction of CO in alveolar gas at beginning of breath hold (time = 0) F1CO = fraction of CO in reservoir (usually 0.003) FAtracer = fraction of tracer in alveolar gas sample FItracer = fraction of tracer in inspired gas (varies with tracer gas used) Signup and view all the answers

The change in tracer gas concentration reflects the dilution of the inspired gas by the gas remain- ing in the lungs (i.e., RV). What is this change used for?

To determine the CO concentration at the beginning of the breath hold before diffusion from the alveoli into the pulmonary capillaries. Signup and view all the answers

How is the Dlcosb (single breath) calculated ? (equation)

DLCOsb= V A×60 /((PB –47)×(T)) x Ln FA CO 0/ FA COT Where: VA = alveolar volume, mL (STPD) 60 = correction from seconds to minutes PB = barometric pressure, mm Hg 47 = water vapor pressure at 37°C, mm Hg T = breath-hold interval, seconds Ln = natural logarithm FA CO 0 = fraction of CO in alveolar gas at beginning of breath hold F co T= fraction of CO in alveolar gas at end of AT breath hold Signup and view all the answers

VA may be calculated from the single-breath di- lution of the tracer gas. What is the equation?

VA = (V I − V D ) x (FI Tracer/FA Tracer) x STPD correction factor Where: VI = volume of test gas inspired, mL VD = dead space volume (anatomic and instrumental), mL FAtracer = fraction of tracer in alveolar gas sample FItracer = fraction of tracer in inspired gas (depends on tracer used) Signup and view all the answers

Note that the VA, usually expressed in body tem- perature, pressure, and saturation (BTPS) units, but for DLCO sc calculation it must be converted to?

STPD for the single-breath calculation. Signup and view all the answers

The dilution of tracer gas is used twice in the calculus of the DLCOSB. For what?

<ul> <li>To determine the CO concentration at the beginning of the breath hold.</li> <li>To determine the lung volume (i.e., VA) at which the breath hold occurred.</li> </ul> Signup and view all the answers

What is Kco?

the rate constant for carbon monoxide up- take from alveolar gas and the “measured” alveolar volume (VA). Signup and view all the answers