Preoperative Inspiratory Muscle Training

Highly active muscles such as the diaphragm are particularly sensitive to both disuse and training. For example, diaphragm fibers of controlled mechanically ventilated young adults atrophy by more than 50% within 36 hours of complete inactivity, and mechanical ventilation (MV) initiates signaling pathways within the first several hours of inactivity that promote progressive diaphragmatic fiber dysfunction. The investigators have shown that widespread atrophy signaling begins in the operating room during cardiac surgery, after only a few hours of MV. In addition to this fiber atrophy, MV leads to significant declines in the strength of the diaphragm, which can lengthen the time it takes to wean from MV. The clinical occurrence of early onset, progressive contractile dysfunction is defined as ventilator-induced diaphragmatic dysfunction (VIDD). VIDD is regarded as a primary contributor to difficulties with weaning from MV.

Conversely, the investigators have shown that IMT increases the pressure-generating capacity of the diaphragm and inspiratory synergist muscles, and facilitates weaning in patients with VIDD. Preoperative IMT for as little as 1-2 weeks reportedly increases inspiratory muscle strength. IMT prior to cardiothoracic surgery has been shown to reduce post-operative pulmonary complications such as atelectasis, pneumonia, or delayed ventilator weaning. Additionally, strength gains associated with preoperative IMT are associated with shorter ICU and hospital lengths of stay, which may potentially offer a cost benefit.

Unfortunately, very little is understood about the neuromuscular adaptations and signaling mechanisms that contribute to these IMT clinical advantages. A particularly novel aspect of this project is it will be the first study of the mechanisms that contribute to diaphragm strengthening. A greater understanding of these mechanisms may help future investigators to develop more efficient exercise prescriptions to offset MV use in cases such as surgery, and it may help identify molecules and exercise that could protect the diaphragms of individuals who cannot exercise in advance, as in the case of acute infections that compromise breathing.

The overall objective of this study is to investigate diaphragm neuromuscular remodeling associated with pre-operative, telehealth delivered IMT, compared with relaxation breathing training (RLX). Guided RLX exercises have been shown to improve post-operative pain perception and modestly lower systolic blood pressure in hypertensives but are not thought to significantly alter diaphragm strength.

Forty adult volunteers will receive either IMT (n=20) or RLX training (n=20) for 2-4 weeks prior to elective cardiothoracic surgery and undergo breathing performance tests before and after the training period. A full thickness biopsy (approximately 6mm x 20 mm) from the right ventral costal diaphragm will be acquired as soon as the diaphragm is exposed during surgery. Additionally, a biopsy from the pectoralis major will be obtained and used as a non-exercised control muscle. Histological and RNA sequencing analyses will be performed to examine the mechanisms that contribute to neuromuscular adaptations to training.