Measurement of Lung Diffusion and Cardiac Output with a Single Breath Gas Absorption Method During Graded Exercise Testing: Reference Values for Clinical Testing

ABSTRACT

Measurement of lung diffusion and cardiac output with a single breath gas absorption method during graded exercise testing: reference values for clinical testing.

Objective: The evaluation of ventilation and gas exchange has become a standard part of clinical exercise testing. We sought to assess the practicality of integrating measurements of lung diffusion for carbon monoxide (DLCO) and noninvasive cardiac output (using pulmonary capillary blood flow QC) into our clinical graded exercise tests. Our objective was to define the responses in normal subjects so that impairment could be detected in patients suspected of having pulmonary or pulmonary vascular disease despite normal resting DLCO and QC. We conducted incremental exercise tests on 20 normal volunteers at 6 levels of exercise ranging between rest and 75% of their measured maximum. The investigational method is based on absorption of CO (for DLCO) and acetylene (for QC) into the pulmonary circulation during a single slow exhalation. The subjects averaged 35 years of age with a maximum work capacity of 76% of predicted maximum.

Results: The values increased linearly with workload (QC in L/min = 3.5 + 6.5*VO2 in L/min, and DLCO in ml/min/mmHg = 18.7 + 10.2*VO2 in L/min). From baseline levels the QC increased more than two-fold and the DLCO increased by 50%. The mean deviation of individual measurements from the patient's regressed response was 9.9% and 6.6% respectively.

Conclusions: We found the procedure easy to include in our standard graded exercise protocol and the single breath technique readily performed. Normative values were obtained for measurements expressed as a percentage of individual maximum and as actual VO2. At a moderate level of exercise (VO2 1.0 liter) the DLCO and QC should increase at least 20% and 65% respectively above baseline. Since the response of Qc and DLCO to progressive exercise offers pathophysiological information of clinical interest, its application can now be characterized in patients with different disorders including those with normal resting Qc and DLCO.