ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

Effective Date: 2017 Version #2

Chapter 10

Procedure Name: Single-Breath Carbon Monoxide Uptake in the Lung (Diffusing Capacity [D l CO ], Transfer Factor [T l CO ])

Purpose or Principle The diffusing capacity of the lung for carbon monoxide (Dl CO

), also referred to as the transfer factor of the lung for

carbon monoxide (Tl CO ), is used to evaluate the transfer of gas from the alveolar air spaces into the pulmonary capil- laries. It can be measured when known and very low concentrations of carbon monoxide (CO) are inspired. The rate of CO disappearance is calculated from the ratio of the CO concentrations of the inspired and expired gas and then expressed as a function of the driving pressure (ml CO/min/mm Hg). This can be expressed in the equation below: D L CO = ˙ V CO / P A CO − PC CO Where: V˙ co is the uptake of CO in ml of CO at STPD conditions per minute Pa CO is the average partial pressure of CO in alveoli P C CO is the average partial pressure of CO in the pulmonary capillary plasma Because hemoglobin (Hb) has a very high affinity for CO, the partial pressure of CO in the plasma ( P C) can be considered zero when the carboxyhemoglobin (COHb) concentration is low (1 to 3%). The equation then becomes: D L CO = ˙ V CO /P A CO Thus, all physiologic methods of assessing Dl CO involve two steps: (1) measuring the rate of CO uptake, and (2) estimating CO driving pressure (1). Carbon monoxide uptake is usually measured as the product of a concentration change over time multiplied by alveolar volume (Va); CO driving pressure is calculated by multiplying the inhaled CO concentration times the ratio of inspired volume (Vi) to the Va, and the barometric pressure.

The 10-second, single-breath breath-holding technique is the most widely used. It was introduced by Marie Krogh (2) in 1915, and later refined by Forster and coworkers (3), Ogilvie and coworkers (4), and McGrath and Thomson (5). Two alveolar gas sampling techniques following the 10-second, single-breath have emerged: ( 1 ) an © 2016 AmericanThoracic Society www.thoracic.org

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