Effect of lung transplant and volume reduction surgery on respiratory muscle function

Abstract

Lung transplantation and lung volume reduction surgery have opened a new therapeutic era for patients with advanced emphysema. In addition to providing impressive clinical benefits, they have helped us better understand how the chest wall and respiratory muscles adapt to chronic hyperinflation. This article reviews the effects of these procedures on respiratory muscle and chest wall function. Inspiratory (including diaphragm) and expiratory muscle strength are often close to normal after unilateral and bilateral transplantation, although some patients have marked weakness. After bilateral transplantation for emphysema, graft volume is normal at full inflation but remains greater than normal at end expiration, which results from structural changes in the chest wall. In contrast, patients with unilateral transplantation have a reduction in graft volume at full inflation. The mediastinum is displaced toward the graft at end expiration, which reduces the surface area of the diaphragm on the transplanted side, and it moves toward the native lung during tidal and full inspiration and toward the graft during tidal and forced expiration. Lung volume reduction produces an increase in contractility, length and surface area of the diaphragm, and increases its contribution to tidal volume; at the same time, neural drive to the muscle and respiratory load are reduced, such that diaphragm neuromechanical coupling is improved. Diaphragm configuration and rib cage dimensions are only minimally affected by the procedure. Single-lung transplantation and lung volume reduction favorably impact on the disadvantageous size interaction by which the lungs are functionally restricted by the chest wall in emphysema.

Respiratory Muscle and Lung Function in Lung Allograft Recipients: Association with Exercise Intolerance

“…In the present study, sniff Pdi did not differ between LTRs and controls, and values in LTRs were even higher than previously reported [14]. This finding is not inconsistent with diaphragm dysfunction in LTR: while lung transplantation, especially if bilateral, leads to reduced lung volume and enhanced inflatability of the lung during the sniff maneuver [14,37], inspiratory strength may be shifted to near-normal values by compensatory activation of other inspiratory muscles.…”

Breathing pattern and chest wall volumes during exercise in patients with cystic fibrosis, pulmonary fibrosis and COPD before and after lung transplantation

“…Several factors contributing to the reduced exercise performance have been discussed, including cardiovascular and muscular deconditioning due to inactivity34 and intake of immunosuppressive agents 35. Additionally, it has been reported that patients transplanted for diseases that produce chronic hyperinflation, such as CF and emphysema, may have preoperative structural changes in rib cage shape that persist in part after transplantation and lead to persistent increases in functional residual capacity and residual volume 36. These alterations, when still present after transplantation, might contribute to decreased exercise tolerance.…”

Respiratory muscle fiber remodeling in chronic hyperinflation: dysfunction or adaptation?

“…However, whether diaphragm fiber lengths physically shorten by deletion of sarcomeres in series in chronically hyperinflated humans has never been clearly established, in part because of the difficulty in accurately measuring sarcomere length in vivo, at FRC. It is a critically important problem to understand because of the obvious implications for lung volume reduction surgery, as discussed in the accompanying review in this series (19). Some studies have measured human diaphragm length using computed tomography, coupled with three-dimensional modeling, e.g., Ref.…”