This study is investigating the normal range of maximal diaphragm thickness during a sniff inspiratory manoeuvre using ultrasound in healthy subjects stratified by age and gender.

Diaphragm dysfunction is associated with poor clinical outcomes in critically ill patients but is difficult to diagnose. Traditionally, diaphragm function is measured by evaluating inspiratory muscle strength via maximal inspiratory pressure (MIP). However, this technique relies on a volitional maximal effort and can be challenging for patients to perform.

An alternative to measuring inspiratory muscle strength is the sniff inspiratory pressure approach. During short, sharp sniffs, the diaphragm is maximally activated.

Currently, there are no reported values of the normal range of maximal diaphragm thickness during a sniff maneuver. This study will define the normal range of values for sniff maximal diaphragm thickening fraction, maximal thickening against an occluded airway, and diaphragm thickening during resting tidal breathing in healthy subjects.

Inclusion Criteria:

• Over 18 years of age

Exclusion Criteria:

• Antecedent history of neuromuscular or cardiorespiratory disease

Healthy adult subjects with no antecedent history of neuromuscular or cardiorespiratory disease.

Currently, there is no plan to make data IPD available to others.