Respiratory, Limb Muscle Properties, and Physical Performance in Adult Lung Transplant Recipients

Respiratory and peripheral muscle dysfunction are common in individuals with advanced lung disease awaiting lung transplantation. Muscle weakness, atrophy, and impaired contractile function may contribute to reduced physical performance, frailty, symptom burden, and delayed recovery after transplantation. Although physical function tests provide an overall assessment of performance, they provide limited information regarding specifics of respiratory and limb muscle impairments. Ultrasound imaging is a noninvasive and reliable method to evaluate muscle structure, quality, and contractile function and has been associated with clinical outcomes in several critically ill populations, including prolonged mechanical ventilation, longer intensive care unit (ICU) and hospital stays, and increased morbidity.

The purpose of this study is to characterize respiratory and limb muscle properties before and after lung transplantation and determine how these measures relate to physical performance, patient-reported outcomes, and postoperative recovery. Respiratory muscle function will be assessed using maximal respiratory pressure testing and ultrasound evaluation of the diaphragm and abdominal muscles. Limb muscle function will be assessed using ultrasound imaging and strength testing of the quadriceps muscles. Physical performance, frailty, dyspnea, pain, fatigue, anxiety, and ICU/hospital-related outcomes will also be evaluated.

The central hypothesis of this study is that respiratory and limb muscle weakness, atrophy, and impaired contractile function are associated with poorer physical performance, greater symptom burden, and delayed postoperative recovery after lung transplantation. To test this hypothesis, a prospective observational study of adult lung transplant candidates will be conducted from their hospital admission to their post-operative day 14. Participants will undergo serial ultrasound imaging assessments before transplantation and during the early postoperative period along with symptom questionnaires; while respiratory and limb strength testing, functional assessments, symptom questionnaires will be collected on the first and last day of research visit. Collection of ICU and hospital outcomes will occur from the electronic medical record. The central hypothesis will be evaluated through the following aims:

Aim 1: Evaluate relationships between respiratory strength and ultrasound measurements of contractile dysfunction in candidates awaiting lung transplant.

Aim 2: Characterize the associations between respiratory and limb muscle properties (atrophy, strength), physical performance, and patient-centered outcomes (dyspnea, frailty, pain, fatigue, and anxiety) in pre-lung transplant candidates.

Aim 3: Identify the influence of preoperative respiratory and quadriceps contractile function on the early postoperative mobility progression in lung transplant recipients Aim 4: Determine relationships between postoperative diaphragm dysfunction and functional status at hospital discharge

Inclusion criteria

• 18 years or older.
• Hospitalized as potential candidates for single- or bilateral-lung transplant surgery.
• Hemodynamically stable for out-of-bed mobilization

Exclusion criteria

• Baseline cognitive impairment
• History of previous solid organ transplantation or thoracic surgery
• Existing phrenic nerve lesion
• Lower limb amputation or fracture
• External fixators or open wounds of the lower extremities
• Diagnosed neuromuscular disorder.
• Morbid obesity (body mass index >45 kg/m²).
• Any other medical condition that, in the opinion of the investigators, would make participation unsuitable.