Although single breath helium (He) dilution measurement (VASB) is currently used in pulmonary function laboratories to assess functional alveolar volume and diffusing capacity for carbon monoxide, the extent to which VASB reflects ventilatory and thoracic volume has not been prospectively determined in emphysema. We hypothesized that VASB underestimates rebreathe helium dilution volume (VARB), and plethysmographic volume (VApleth) as clinical and physiologic severity of emphysema increases.

VASB, VARB, and VApleth were measured in 52 consecutive stable outpatients with clinical and radiographic emphysema. Thirteen patients with an obstructive ventilatory defect without emphysema (OVD) and 18 normal controls were similarly studied. All subjects underwent spirometry followed by whole body plethysmography and He dilution volume measurements; VASB and VARB order was randomized.

Inclusion Criteria:

• All outpatients between the ages of 18 and 81 years referred to the Columbia University Medical Center Pulmonary Diagnostic Unit between 1/18/06 and 7/30/07 for full pulmonary function evaluation, and with an obstructive ventilatory defect on spirometry, were considered eligible.

Exclusion Criteria:

• Patients who did not want to undergo the re-breathe diffusing capacity testing
• Patients who could not give informed consent;and
• Patients who were too physically compromised to undergo full testing including the re-breathe maneuver as deemed by our technicians.

This is a prospective trial in all outpatients with emphysema referred for full pulmonary function testing to the pulmonary diagnostic unit.