DLCO can be affected by valsalva maneuver

The two major determinants of carbon monoxide uptake by the lungs (Dlco) are alveolar-capillary membrane properties (diffusion properties and surface area – Dm) and pulmonary capillary blood volume coupled with the reaction rate of CO binding to hemoglobin (thetaVc). These determinants are roughly equal in importance and are mathematically expressed as 1/Dlco = 1/(thetaVc) + 1/Dm.

1DLCO=1θVc+1Dm\frac{1}{DLCO}=\frac{1}{\theta V_c}+\frac{1}{D_m}

During Dlco testing, an expiratory effort against a closed glottis (Valsalva maneuver) increases intrathoracic pressure creating a decrease in pulmonary capillary blood volume (Vc). Dlco has been shown to drop up to 30% under these circumstances. This is important to remember during Dlco testing and patients should be encouraged to relax during the breath-hold rather than push against the closed test valving.

In a normal seated subject, gravity produces a relative hypo-perfusion of apical lung regions – so called “West zone 1” regions. This is increased during the Valsalva maneuver as described above. In contrast, maneuvers that increase Vc and reduce zone 1 conditions (eg assuming the supine position, increasing pulmonary capillary blood flow with exercise, reducing intrathoracic pressure with an inspiratory effort against a closed glottis (Mueller maneuver) will increase Dlco.1

Footnotes

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