Single-breath test in lateral decubitus reflects function of single lungs grafted for emphysema

Abstract

The slope of alveolar plateau for nitrogen derived from the single-breath test is useful to assess the function of bilateral lung grafts, but this technique is not applicable to patients with single-lung grafts due to the confounding influence of the native lung. We tested the hypothesis that the nitrogen slope measured in lateral decubitus with the graft in nondependent position may primarily reflect the distribution of ventilation in this lung. Fifteen patients with single-lung transplantation for emphysema, 10 healthy controls, and 7 patients with advanced emphysema performed single-breath washouts in right and left lateral decubitus; nitrogen slope was measured between 75 and 100% of expired volume. In 10 transplant recipients, the volume of each lung was measured in the two postures by computerized tomography. Nitrogen slope was unaffected by posture in normal controls and emphysema patients. On the other hand, nitrogen slope in transplant recipients was invariably smaller, with the graft in nondependent vs. in dependent position. Values of nitrogen slope with the graft in nondependent position were similar to those obtained in normal controls but significantly smaller than those obtained in emphysema patients. Computerized tomography studies in this position indicated that the volume expired below functional residual capacity was exclusively contributed by the graft. We conclude that, in patients with single-lung transplantation for emphysema, 1) measuring nitrogen slope in lateral decubitus allows to distinguish between the graft and the native lung, and 2) nitrogen slope obtained with the graft in nondependent position reflects ventilation distribution in this lung.

Physiological Measurement of the Small Airways

“…For instance, the weight of the lung is known to produce a positive N 2 phase-III slope due to the greater specific ventilation of the dependent versus the nondependent lung zones and the preferential emptying of the basal lung zones at the beginning of expiration. Hence, depending on whether lung diseases preferentially affect the basal or apical lung zones, the N 2 phase III slope may be affected differently, and one study has elegantly shown how gravity can even be exploited to reveal peripheral lung disease in a part of the lung that is brought into a preferential position along the line of gravity [87]. The vital capacity SBW maneuver is also regularly used to simply determine the closing volume (or closing capacity) as a measure of small airways closure, which can also have a preferential topographical distribution.…”

Gas Mixing in the Airways and Airspaces

“…Timedependent within-breath imaging of ventilation heterogeneity would allow a more rigorous comparison of imaging data with gas mixing indices such as a phase III slope, which depends on both specific ventilation heterogeneity and flow asynchrony. Recently, an elegant example in unilateral lung transplant patients has exploited quasi-static lung volume-dependent CT imaging to demonstrate how flow asynchrony between the native and the transplanted lung translates into different parts of the phase III slope collected at the patient's mouth (141). Applying a similar approach at smaller scales of unit lung volume could enable the quantification of intra-regional ventilation heterogeneity, which is thought to be present in normal human subjects based on indirect measurement.…”

Single-breath test in lateral decubitus reflects function of single lungs grafted for interstitial lung disease

“…Data obtained in the transplant recipients were compared with data obtained in 10 normal subjects and 12 nontransplanted patients with a variety of ILD. The group of healthy controls was the same as that used in our laboratory's previous study (11) and was matched for age and sex with the donors. At the time of studies, all transplant recipients were clinically stable and free of acute infection and rejection.…”

“…However, our laboratory recently showed in patients with single-lung transplantation for emphysema that this limitation can be overcome by performing the test in lateral decubitus (11). When the patient was in lateral decubitus with the graft in the nondependent position, this lung contributed all of the volume expired in the last part of the washout.…”