Diaphragm dimensions after single-lung transplantation for emphysema

Diaphragm and Lung Transplantation

Mutual interactions between the diaphragm and lung transplantation (LTx) are known to exist. Before LTx, many factors can exert notable impact on the diaphragmatic function, such as the underlying respiratory disease, the comorbidities, and the chronic treatments of the patient. In the post-LTx setting, even the surgical procedure itself can cause a stressful trauma to the diaphragm, potentially leading to morphological and functional alterations. Conversely, the diaphragm can significantly influence various aspects of the LTx process, ranging from graft-to-chest cavity size matching to the long-term postoperative respiratory performance of the recipient. Despite this, there are still no standard criteria for evaluating, defining, and managing diaphragmatic dysfunction in the context of LTx to date. This deficiency hampers the accurate assessment of those factors which affect the diaphragm and its reciprocal influence on LTx outcomes. The objective of this narrative review is to delve into the complex role the diaphragm plays in the different stages of LTx and into the modifications of this muscle following surgery.

Change in diaphragmatic morphology in single-lung transplant recipients: a computed tomographic study

Introduction: The influence of lung disease on the diaphragm has been poorly studied. The study aimed to evaluate the diaphragm morphology (height and thickness) in single-lung transplantation (SLTx), using computed tomography (CT), by assessing the evolution of the hemidiaphragm of the transplanted and the native side. Methods: Patients who underwent single lung transplantation in our center (Marseille, France) between January 2009 and January 2022 were retrospectively included. Thoracic or abdominal CT scans performed before and the closest to and at least 3 months after the surgery were used to measure the diaphragm crus thickness and the diaphragm dome height. Results: 31 patients mainly transplanted for emphysema or pulmonary fibrosis were included. We demonstrated a significant increase in diaphragm crus thickness on the side of the transplanted lung, with an estimated difference of + 1.25 mm, p = <0.001, at the level of the celiac artery, and + 0.90 mm, p < 0.001, at the level of the L1 vertebra while no significant difference was observed on the side of the native lung. We showed a significant reduction in the diaphragm height after SLTx on the transplanted side (-1.20 cm, p = 0.05), while no change on the native side (+0.02 cm, p = 0.88). Conclusion: After a SLTx, diaphragmatic morphology significantly changed on the transplanted lung, while remaining altered on the native lung. These results highlights that an impaired lung may have a negative impact on its diaphragm. Replacement with a healthy lung can promote the recovery of the diaphragm to its anatomical morphology, reinforcing the close relationship between these two organs.

Lung transplantation and lung volume reduction surgery

Since the publication of the last edition of the Handbook of Physiology, lung transplantation has become widely available, via specialized centers, for a variety of end-stage lung diseases. Lung volume reduction surgery, a procedure for emphysema first conceptualized in the 1950s, electrified the pulmonary medicine community when it was rediscovered in the 1990s. In parallel with their technical and clinical refinement, extensive investigation has explored the unique physiology of these procedures. In the case of lung transplantation, relevant issues include the discrepant mechanical function of the donor lungs and recipient thorax, the effects of surgical denervation, acute and chronic rejection, respiratory, chest wall, and limb muscle function, and response to exercise. For lung volume reduction surgery, there have been new insights into the counterintuitive observation that lung function in severe emphysema can be improved by resecting the most diseased portions of the lungs. For both procedures, insights from physiology have fed back to clinicians to refine patient selection and to scientists to design clinical trials. This section will first provide an overview of the clinical aspects of these procedures, including patient selection, surgical techniques, complications, and outcomes. It then reviews the extensive data on lung and muscle function following transplantation and its complications. Finally, it reviews the insights from the last 15 years on the mechanisms whereby removal of lung from an emphysema patient can improve the function of the lung left behind.

Asymmetrical action of the canine diaphragm after single-lung inflation

Single-lung transplantation (SLT) in patients with emphysema leads to a cranial displacement of the diaphragm on the transplanted side and a shift of the mediastinum toward the transplanted lung. The objective of the present study was to assess the effect of unilateral lung inflation on the mechanics of the diaphragm. Two endotracheal tubes were inserted in the two main stem bronchi of six anesthetized dogs, and radiopaque markers were attached along muscle fibers in the midcostal region of the two halves of the diaphragm. The animals were then placed in a computed tomographic scanner, the left or the right lung was passively inflated, and the phrenic nerves were stimulated while the two endobronchial tubes were occluded. As lung volume increased, the fall in airway opening pressure (ΔPao) in the inflated lung during stimulation decreased markedly, whereas ΔPao in the noninflated lung decreased only moderately ( P < 0.001). Also, the two hemidiaphragms shortened both during relaxation and during phrenic stimulation, but the ipsilateral hemidiaphragm was consistently shorter than the contralateral hemidiaphragm. In addition, the radius of curvature of the ipsilateral hemidiaphragm during stimulation increased, whereas the radius of the contralateral hemidiaphragm remained unchanged. These observations indicate that 1) in the presence of unilateral lung inflation, the respiratory action of the diaphragm is asymmetric; and 2) this asymmetry is primarily determined by the differential effect of inflation on the length and curvature of the two halves of the muscle. These observations also imply that in patients with emphysema, SLT improves the action of the diaphragm on the transplanted side.

Transplantation in Chronic Obstructive Pulmonary Disease

Lung transplantation is a surgical option for patients who fail optimization of medical treatment for the severe symptoms that result from COPD. This review will discuss patient selection, transplant listing, and the surgical technique for transplantation in COPD. Furthermore, it will describe transplant outcomes and its effects on recipient survival, pulmonary function, exercise capacity, respiratory muscle function, and quality of life. The respective roles of transplantation and lung volume reduction surgery as therapies for advanced disease will be outlined.

Matching donor to recipient in lung transplantation: How much does size matter?

OBJECTIVE

The impact of size matching between donor and recipient is unclear in lung transplantation. Therefore, we determined the relation of donor lung size to 1) posttransplant survival and 2) pulmonary function as measured by forced expiratory volume in 1 second.

METHODS

From 1990 to 2006, 469 adults underwent lung transplantation with lungs from donors aged 7 to 70 years. Donor and recipient total lung capacities were calculated using established formulae (predicted total lung capacity), and actual recipient lung size was measured in the pulmonary function laboratory. Disparity between donor and recipient lung size was expressed as a ratio of donor predicted total lung capacity to recipient predicted total lung capacity-the predicted total lung capacity ratio-and predicted donor total lung capacity to actual recipient total lung capacity-the actual total lung capacity ratio. Survival was measured by multiphase hazard methodology and repeated measures of National Health and Nutrition Examination Survey-normalized forced expiratory volume in 1 second analyzed by temporal decomposition.

RESULTS

Predicted total lung capacity ratio and actual total lung capacity ratio ranged widely, from 0.55 to 1.59 and 0.52 to 4.20, respectively. Overall survival was unaffected by predicted total lung capacity ratio (P = .3) or actual total lung capacity ratio (P = .5). Patients with emphysema and an actual total lung capacity ratio of 0.67 or less or 1.03 or greater had higher predicted mortality (P = .01). During the first posttransplant year, forced expiratory volume in 1 second increased and then gradually declined. Predicted total lung capacity ratio and actual total lung capacity ratio had a small impact on forced expiratory volume in 1 second, primarily in the late phase after transplant in a disease-specific manner.

CONCLUSION

Size matching between donor and recipient using predicted total lung capacity ratio and actual total lung capacity ratio is an effective technique. Wide discrepancies in lung sizing do not affect overall posttransplant survival or pulmonary function. Therefore, a greater degree of lung size mismatch can likely be accepted, thereby improving patients' odds of undergoing transplantation.

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

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.

Mechanics of Respiratory Muscles in Single-Lung Transplant Recipients

BACKGROUND

Emphysema and pulmonary fibrosis force the patients to breathe at an abnormal lung volume, which alters the lengths of the respiratory muscles and thereby their work capability is reduced. After single-lung transplantation, muscle function is restored on the side of the transplant but it may be asymmetric to that on the side of the native diseased lung.

OBJECTIVE

Investigating the hypothesis that single-lung transplantation induces mechanical asymmetry of the respiratory muscles on the two sides.

METHODS

Simultaneously noninvasive measurements of inspiratory and expiratory mouth pressure, airflow rate and electromyography signals from the sternomastoid, external intercostal, rectus abdominis and external oblique muscles were acquired during different breathing maneuvers. The study group included 10 single-lung transplant recipients (5 with pulmonary fibrosis and 5 with emphysema) and 10 healthy controls.

RESULTS

Analysis of the finding shows a significant lower global strength of the respiratory muscles of single-lung transplant recipients compared to that of healthy subjects. No significant difference in the EMG signals of respiratory muscles was found either between the different groups or between the sides of the transplant and the native lung in the patient groups. Both single-lung transplant recipients and healthy subjects demonstrated high EMG activity of the inspiratory muscles during inspiration at different breathing efforts.

CONCLUSION

Patients after single-lung transplantation have lower respiratory muscle strength than healthy subjects, but apparently normal electrical activity. The lower global respiratory muscle strength emphasizes the importance of their rehabilitation before and after single-lung transplantation.

Effects of single-lung inflation on inspiratory muscle function in dogs

After single-lung transplantation (SLT) for emphysema, a hyperinflated (native) lung operates in parallel with a normal (transplanted) lung. The interpulmonary distribution of the changes in pleural pressure (DeltaP(pl)) during breathing, however, is unknown. To approach the problem, two endotracheal tubes were inserted in the right and left main stem bronchi of anaesthetized dogs, one lung was passively inflated, and the values of inspiratory DeltaP(pl) over the two lungs were assessed by measuring the changes in airway opening pressure (DeltaP(ao)) in the two tubes during occluded breaths. With single-lung inflation, DeltaP(ao) decreased in both lungs, but the decrease in the inflated lung was invariably larger than in the non-inflated lung; when transrespiratory pressure in the inflated lung was set at 30 cmH(2)O, DeltaP(ao) in this lung was 27.7 +/- 2.0% of the value of functional residual capacity (FRC), whereas DeltaP(ao) in the non-inflated lung was 74.4 +/- 4.5% (P < 0.001). This difference was abolished after the ventral mediastinal pleura was severed. The ribs in both hemithoraces were displaced cranially with inflation, such that the displacement in the contralateral hemithorax was 75% of that in the ipsilateral hemithorax, and parasternal intercostal activity remained unchanged. These observations suggest that in patients with SLT for emphysema (1) the inspiratory DeltaP(pl) over the transplanted lung are greater than those over the native lung and (2) this difference results primarily from the greater pressure-generating ability of the inspiratory muscles, in particular the diaphragm, on the transplanted side.

Breathing power of respiratory muscles in single-lung transplanted emphysematic patients

Single-lung transplantation may induce asynchronous performance between the respiratory muscles of the chest. The objective of this study was to investigate the influence of a single transplanted lung on respiratory muscle mechanics. The force and power of the sternomastoid, external intercostal and external oblique muscles were evaluated throughout a range of respiratory maneuvers in emphysematic patients with a single transplanted lung and compared with that of healthy subjects. A significant differences was observed between the force, work and power of the muscles on the two sides of the chest in emphysematic patients (P<0.05). The control group demonstrated higher averaged maximal force, work and power. The total work done during either inspiration or expiration by the external intercostal and external oblique muscles on the side of the transplanted lung were higher compared with that of the native lung side and compared with the control group. The asynchrony between the lungs after single-lung transplant leads to asynchronous muscle force and work and lesser muscle strength compared to healthy subjects.

Ventilation asymmetry after transplantation for emphysema: role of chest wall and mediastinum

After single-lung transplantation for emphysema, the hyperinflated native lung and the graft have different extents and rates of inflation and emptying. This requires that breathing produces asymmetrical expansion of the chest wall, displacement of the mediastinum, or both. In a first study in four seated transplant recipients, we measured the volumes of the two hemithoraces with optoelectronic plethysmography. Functional residual capacity and total lung capacity were identical on the native and transplanted sides, and changes in chest wall volume during CO(2)-induced hyperpnea and FVC maneuvers were similar on both sides. Studies with computerized tomography in three of these patients and in four additional patients in supine posture indicated that the mediastinum was shifted toward the graft at functional residual capacity and total lung capacity. The mediastinum moved toward the native lung during tidal and full inspiration and toward the graft during tidal and forced expiration; additional studies with fluoroscopy showed qualitatively similar changes in upright posture. In summary, the two hemithoraces assume identical static volumes and show similar volume changes during CO(2)-induced hyperpnea and FVC maneuvers in patients with single-lung transplantation for emphysema; displacement of the mediastinum accommodates part, if not all, of the unequal lung volumes and asymmetrical ventilation.

[Surgery for emphysema: recent advances]

INTRODUCTION

The treatment of chronic obstructive pulmonary disease has progressed considerably over the past 40 Years but, for most patients with advanced disease, medical management does not often produce more than limited benefits, particularly in terms of quality of life.

STATE OF ART

Over the last decade the surgical treatment of emphysema, which was previously limited to bullectomy, has seen important developments: for carefully selected patients lung Volume reduction surgery and lung transplantation now offer the possibility of real symptomatic improvement and even prolonged survival. Thanks to the thousands of patients who have received these treatments our understanding of the pathophysiological mechanisms, surgical techniques, risks and benefits, medium and long-term results, and selection criteria has improved considerably.

PERSPECTIVES AND CONCLUSIONS

This review summarises the most important aspects of these developments and discusses the role of Volume reduction and lung transplantation in the treatment of advanced emphysema.

Disorders of the respiratory muscles

The act of breathing depends on coordinated activity of the respiratory muscles to generate subatmospheric pressure. This action is compromised by disease states affecting anatomical sites ranging from the cerebral cortex to the alveolar sac. Weakness of the respiratory muscles can dominate the clinical manifestations in the later stages of several primary neurologic and neuromuscular disorders in a manner unique to each disease state. Structural abnormalities of the thoracic cage, such as scoliosis or flail chest, interfere with the action of the respiratory muscles-again in a manner unique to each disease state. The hyperinflation that accompanies diseases of the airways interferes with the ability of the respiratory muscles to generate subatmospheric pressure and it increases the load on the respiratory muscles. Impaired respiratory muscle function is the most severe consequence of several newly described syndromes affecting critically ill patients. Research on the respiratory muscles embraces techniques of molecular biology, integrative physiology, and controlled clinical trials. A detailed understanding of disease states affecting the respiratory muscles is necessary for every physician who practices pulmonary medicine or critical care medicine.

Virtual tools for imaging of the thorax

Helical computed tomography (HCT) allows for volume acquisition of the entire thorax during a single apnoea. Combination of HCT acquisition with synchronous vascular enhancement gives rise to HCT angiography (HCTA). In the last decade, HCT and HCTA have revolutionized the diagnosis of thoracic diseases, modifying many diagnostic algorithms. Because HCT provides for a true volume acquisition free of respiratory misregistration, three-dimensional (3D) rendering techniques can be applied to HCT acquisitions. As these 3D rendering techniques present the HCT information in a different format to the conventional transaxial CT slices, they can be summarized as virtual tools. The purpose of this review is to give the readers the most important technical aspects of virtual tools, to report their application to the thorax, to answer clinical and scientific questions, and to stress their importance for patient management, clinical decision making, and research.

Effects of lung volume reduction surgery for emphysema on diaphragm dimensions and configuration

Part of the functional benefit provided by lung volume reduction surgery (LVRS) may be related to improvement in respiratory muscle function resulting from changes in diaphragm dimension and configuration. To study these changes, we obtained 3D reconstructions of the muscle using spiral computed tomography in 11 patients with severe emphysema before and 3 mo after surgery, and in 11 normal subjects matched for sex, age, height, and weight. Bilateral LVRS was performed by thoracoscopy in eight patients and by sternotomy in three patients. Acquisitions were made in the supine posture at relaxed FRC, midinspiratory capacity, and TLC. On average, LVRS produced a 51 +/- 11% increase in FEV(1) and a 30 +/- 4% decrease in FRC. The total surface area of the diaphragm (A(di)) and of the zone of apposition (A(ap)) at FRC increased by 17 +/- 4% and 43 +/- 8%, respectively, but the surface area of the dome did not change. Compared with the values recorded in the normal subjects, postoperative values of A(di) and A(ap) at FRC were reduced by 11% (p < 0.05) and 24% (p < 0.005), respectively. The curvature of the dome increased at TLC in the left sagittal plane, but was otherwise unaffected by the procedure. We conclude that LVRS substantially increases A(di) and A(ap), but does not significantly improve diaphragm configuration at FRC.

Lung transplantation for chronic obstructive pulmonary disease

Lung transplantation is able to provide dramatic gains in pulmonary function to patients with advanced pulmonary emphysema. At the present time, however, transplantation is available to a strictly defined pool of candidates, and outcomes are limited by numerous respiratory and nonrespiratory postoperative complications. Further progress is needed in expanding the supply of donor lungs, minimizing perioperative complications, and optimizing postoperative immunologic management.