Pulmonary membrane diffusing capacity and capillary blood volume measured during exercise from nitric oxide uptake

Area of Science:

• Physiology
• Pulmonary Medicine
• Respiratory Physiology

Background:

• The alveolar-capillary membrane's diffusing capacity is crucial for gas exchange.
• Lung diffusing capacity for carbon monoxide (DLCO) is a standard measure, but its interpretation can be complex.
• Pulmonary capillary blood volume (Vc) is another key parameter in assessing lung function.

Purpose of the Study:

• To validate lung diffusing capacity for nitric oxide (DLNO) as an index of alveolar-capillary membrane conductance during exercise.
• To compare DLNO with DLCO and pulmonary membrane diffusing capacity for carbon monoxide (DMCO).
• To compare pulmonary capillary blood volume (Vc) calculated using two distinct methods.

Main Methods:

• 12 healthy volunteers (aged 23-79) underwent simultaneous measurements of DLCO, DLNO, cardiac output (c), and lung volume at rest and during graded exercise using a rebreathing technique.
• Pulmonary membrane diffusing capacity and Vc were calculated using the Roughton and Forster method (DLCO at varying PAO(2)) and a method utilizing DLNO and DLCO, assuming negligible nitric oxide (NO) erythrocyte resistance.
• DLNO was assumed to approximate pulmonary membrane diffusing capacity for nitric oxide.

Main Results:

• DLNO demonstrated a linear increase from rest to exercise, with age, cardiac output, and lung volume being significant determinants.
• The DLNO/DLCO ratio averaged 3.98 ± 0.38, and the DLNO/DMCO ratio averaged 2.49 ± 0.28, independent of exercise intensity.
• Estimates of pulmonary membrane diffusing capacity and Vc derived from the two methods showed a strong correlation, and changing PAO(2) did not affect DLNO.

Conclusions:

• DLNO serves as a direct measure of pulmonary membrane diffusing capacity.
• DLNO enables the estimation of Vc within a single exercise rebreathing maneuver.
• The DLNO-DLCO rebreathing technique is clinically applicable for investigating pulmonary microvascular regulation.