Diaphragm electromyography to estimate breathing effort and fatigue : a physiological study

The respiratory muscles drive ventilation. Normally, there is a tight
correlation between the ventilatory demands of the body and the work of
breathing. Respiratory failure occurs when the respiratory muscles are unable
to meet the demands of the body. Mechanical ventilation (MV) is lifesaving in
these situations by taking over (part of) the work of breathing. Most patients
can be extubated quickly after treatment of their disease. However, up to 40%
of all patients have difficulties getting of the ventilator (weaning failure).
Recent studies have shown that respiratory muscle dysfunction is a mayor
contributor to weaning failure. If there is little to no activity of the
respiratory muscles during MV (over-assistance) atrophy and contractile
dysfunction can occur. If activity of the respitatory muscles is excessive
(under-assistance), it can lead to fatigue and inflammation of the respiratory
muscles. Both processes result in weakness and dysfunction of the respiratory
muscles, which in turn leads to prolongation of ventilator dependency, creating
a vicious circle. It is therefore important to maintain adequate levels of
activity during MV.
This is only possible if the activity of the respiratory muscles is regularly
assessed with dedicated measurements. These measurements are currently
technically challenging and difficult to interpret, and are thus are seldom
performed in clinical care. Developing more practical techniques to reliably
measure respiratory muscle activity during MV can benefit many critically ill
patients.
In this study, we examine whether the electrical activity of the diaphragm can
give a reliable prediction of muscle activity. If this is fthe case, then this
new method can improve monitoring and management of criticially ill patients on
MV, potentially leading to improved outcomes and reduced healthcare costs.

1). Develop a model in which the electrical activity of the diaphragm (EAdi)
is used to predict the transdiaphragmatic pressure (Pdi)
2) Assess to which degree this model is accurate in estimation Pdi-derived
parameters (such as work of breathing and pressure-time product).

Physiological proof-of-concept study

A stepwise inspiratory threshold loading protocol. During this protocol Pdi,
EAdi and other physiological parameters are collected with a dedicated
measurement set-up and stored offline for further analysis. See protocol
section 8.3 'study procedures' on page 14 for more information, such as a
flowchart with all study procedures per subject.

The stepwise inspiratory loading protocol is comparable to exerting vigorous
exercise, such as cycling or sprinting. There are no risks associated with an
exercise protocol if the subjects are in good health. We will employ a
screening protocol to assess the physical condition of the subjects (medical
history related to exercise, physical examination and EKG). The increased
levels of physical activity and breathing through a pneumotach can feel
uncomfortable to the participants. The subjects are given time to get
comfortable with the measurement equipment and techniques. The participants can
rest with unloaded breathing during the first protocol. The investigators will
provide explanation and coaching before and during the study to further reduce
physical and psychological burden.
Placement of a nasogastric tube is uncomfortable, but is generally not
perceived as painful. Risks are negligible if high-risk groups are excluded.
The research team has extensive experience with the placement of the
nasogastric tubes. There is no risk or burden after the tube is in situ.
Magnetic stimulation of the phrenic nerve is a non-invasive measurement that is
not painful. The technique is used in regular care for specific groups of
critically ill patients. The research team has experience with the technique.
There are no risks associated with the technique if risk groups are excluded.
Test subjects can get used to the sensation of magnetic stimulation prior to
the loading protocol by receiving a number of low intensity stimulations.
In conclusion, the risks of participation are negligible. The physical and
psychological burden is moderate, and will be limited where possibleby good
preparation, coaching and explanation by the researchers.






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