The use of mechanical ventilation (MV) to replace spontaneous breathing has been associated with respiratory muscle dysfunction and lung injury from positive pressure. While using MV in an intensive care unit setting, the diaphragm is unloaded, potentially resulting in early development of diaphragmatic atrophy in as early as 18 hours of complete diaphragm inactivity. These changes in muscle properties result in a decrease in the force generating capability of the muscle, ultimately resulting in difficulty to restore spontaneous breathing and a subsequent prolonged weaning process or failure. A prolonged weaning period is associated with longer duration of MV, which may result in a cascade of further diaphragm dysfunction, weakness, and injury.

Stimulation of the phrenic nerves to produce diaphragm contraction and activity is a possible mechanism to reduce MV related diaphragm dysfunction. Two promising studies have shown the potential of repetitive phrenic nerve stimulation on inducing diaphragm activity in human subjects with trains of pulses via both cervical and bilateral phrenic nerve stimulation. However, neither study provided optimal stimulation settings. As such, the primary purpose of this study is to investigate the optimal settings for noninvasive phrenic nerve stimulation to induce diaphragm contraction.

Inclusion Criteria:

• Informed Consent as documented by signature
• Age: 18 - 35 years
• Non-smoking
• Healthy
• Able to communicate in English
• Normal lung function
• Normal Body mass index between 18.5 and 24.9 kg/m2
• Willingness to adhere to the study rules

Exclusion Criteria:

• Acute illness or chronic conditions affecting sleep or the performance of the respiratory, cardiovascular, neuromuscular, gastrointestinal or muscle system
• Women who are pregnant or breast feeding or have the intention to become pregnant during the course of the study
• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant
• Known or suspected non-compliance, drug or alcohol abuse
• Intake of medication affecting sleep or the performance of the respiratory, cardiovascular or neuromuscular system or gastrointestinal or muscle system
• Presence of cardiac pacemaker, implanted defibrillators or implanted neurostimulators
• Any metal or electronics inside of the body
• History of seizures or epilepsy
• Tattoos on the stimulation sites
• Previous enrolment into the current study