Sonographic assessment of diaphragm function during inspiratory loading.

In spite of the growing evidence that diaphragm weakness develops in
mechanically ventilated patients and contributes to weaning failure, the
respiratory muscles are poorly monitored in the ICU. Therefore, diaphragm
dysfunction is usually unrecognized and only becomes apparent when a patient
fails to wean from mechanical ventilation. An important reason for poor
monitoring of the diaphragm is that current state of the art techniques for
monitoring are cumbersome in clinical routine due to their invasiveness and
susceptibility to interference. An ideal assessment of diaphragm function
should be available at bedside, fast and easy to acquire and allow standardized
quantification. In contemporary intensive care, sonography is ubiquitously
available as a non-invasive diagnostic tool, but current diaphragm sonographic
methods sample only a small section of the diaphragm and show a low specificity
in identification of weaning failure. A relatively new sonographic approach,
known as speckle tracking sonography, is a promising technique already used in
cardiac sonography that allows quantification of muscular deformation and
displacement.

We hypothesize that speckle tracking sonography of the diaphragm is a potential
non-invasive method to evaluate diaphragm function.
The objective is to evaluate whether speckle tracking sonography of the
diaphragm gives a good representation of diaphragm function in a model of
inspiratory loaded breathing.

Prospective observational study.

Placement of the double balloon EMG catheter is not painful, but can be
discomfortable for the subject. Also, the presence of the catheter throughout
the experiment can cause discomfort for the subject. In contrast to electrical
stimulation, magnetic stimulation is not painful, because it does not induce
high currents in the skin. Due to this wider field of stimulation,
co-contraction of upper limb muscles may occur with magnetic stimulation of the
phrenic nerve. This co-contraction could be encountered as uncomfortable by the
subject. Therefore, stimulation intensity is gradually increased to let the
subject get acquinted with the stimulus intensity.
Both placement of the esophageal catheter and cervical magnetic stimulation
have been performed in previous study carried out by the current investigators.
Sonography of the diaphragm induces neglectable load for the subject; the
subject will hardly feel the positioning of the measuring instrument.
The risk of complications due to procedures in this study is minimal. Healthy
subjects are measured, which makes the risk even less: muscle contractility is
not harmed. On the other hand, this research is of great clinical importance.
In current clinical practice, there is no quick and noninvasive method
available to measure strength or fatigue of the diaphragm, although this is a
very important measure during weaning from the ventilator.
When the clinician knows why someone cannot wean from the ventilator, the
underlying problem can be solved much more quick and effective and possibly the
duration of mechanical ventilation can be decreased.
Both placement of the esophageal catheter and cervical magnetic stimulation
have been performed in previous study carried out by the current investigators.