Air is normally pumped in and out of the lungs by the muscles that contribute to inhalation and exhalation, called the respiratory muscles. The abdominal muscles help by forcing air out of your lungs during exhalation; whereas the diaphragm, the main muscle used for breathing, contracts to get air into the lungs during inhalation. With mechanical ventilation, respiratory muscles are able to rest and recover while the breathing machine takes over; however, this may cause respiratory muscle weakness. Patients who develop weakness of these muscles may require more assistance from the ventilator and take longer to recover their ability to breathe without assistance. The impact of this phenomenon on long-term outcomes is uncertain.

The RESPIRE study is designed to characterize how respiratory muscles change during mechanical ventilation and to evaluate the impact on long term quality of life. An additional objective of this study is to examine novel measures obtained from automated functions of a ventilator, that may better predict success from weaning from mechanical ventilation.

Previous work has established that diaphragm atrophy during mechanical ventilation is associated with adverse clinical outcomes. Abdominal muscles, which are engaged during breathing also undergo atrophy during mechanical ventilation. However, the relationship between these muscles and how they relate to long term function status is known and warrants further investigation.

Mechanical ventilation is a life-saving technique in patients with respiratory failure, however reasons why some patients require long term ventilation and are unsuccessful from weaning from ventilators are not fully elucidated. Respiratory muscle dysfunction as a result of mechanical ventilation is only recently being understood. Diaphragm atrophy is associated with adverse clinical outcomes, but the same is unknown if this holds true with abdominal muscle atrophy. Properly understanding the natural progression of diaphragm and abdominal muscle atrophy and dysfunction, and how they relate to each other, is critical to identifying markers or factors that may put particular patients at risk for long durations of mechanical ventilation and adverse clinical outcomes.

This study will provide important insights into the relationship between inspiratory and expiratory muscle function, and the evolution of functional impairments in critical care patients undergoing weaning from invasive mechanical ventilation. Further understanding of the pathophysiological processes of how these muscle groups interact in this context is important in moving forward with potential therapeutic strategies aimed at mitigating injury.

Cases Inclusion Criteria:

• Adult patients ≥18 years of age undergoing invasive mechanical ventilation in the ICU for any reason within 36 hours of intubation

Control condition A Inclusion Criteria:

• Non-invasively ventilated patients in the ICU within 36 hours of initiating non-invasive ventilation

Control condition B Inclusion Criteria

• Non-ventilated patients admitted to the ICU receiving no respiratory support or oxygen therapy alone, including high flow nasal cannula

Exclusion Criteria:

• Patients expected to be extubated within 24 hours of screening for eligibility
• Patients who have already undergone a SBT at time of screening
• Patients with a previously diagnosed neuromuscular disorder
• Patients receiving long-term invasive mechanical ventilation (prior to current hospitalization)
• Patients who have required previously (during current hospitalization) a period of invasive ventilation in ICU of more than 24 hours
• Patients who have previously been enrolled in the study
• Patients for whom post-hospital follow-up may be challenging, e.g. those who reside overseas or who have no fixed address

Patients will be enrolled in the Medical-Surgical ICU at Toronto General Hospital.