Effect of noninvasive ventilation on the synchrony of the upper airways and inspiration.

Noninvasive ventilation (NIV) can provide ventilatory support in selected
patients with acute respiratory failure, for instance due to acute exacerbation
of COPD and acute heart failure. Advances of noninvasive ventilation compared
to invasive mechanical ventilation include absence of complications associated
with endotracheal intubation, lower risk of pneumonia, lower level or even
absence of sedation and the ability of the patient to verbally communicate.
However, in approximately 30% of patients NIV fails and endotracheal intubation
is needed to provide optimal ventilatory support. Surprisingly, very few
studies have investigated why patients fail on NIV. Clinical observations
indicated that agitation, delirium and most importantly asynchrony between
patient and ventilator play an important role in unsuccessful support with NIV.
The upper airways are bypassed during endotracheal intubation. However, with
NIV the upper airways may play a role in the efficiency of ventilatory support.
In normal breathing the upper airways actively dilate before initiation of
inspiratory flow. This is a highly appropriate response as it prevents
narrowing of the upper airway during inspiration, which would result in
elevated inspiratory resistance. Experiments in newborn lams have shown that
NIV has profound effects on physiology of the upper airways. Positive pressure
during inspiration results in constriction of upper airway muscles in the early
phase on inspiration. This results in elevated upper airway resistance with
lower tidal volume delivered to the lungs. Subsequent studies revealed that
reflexes that mediate this response originate in vagal afferences in located in
the lower airways. From an evolutionary point of view this might be an
appropriate response, as high pressure delivered to the lungs may induce
barotraumas. However, these responses may negatively affect the efficiency of
ventilatory support delivered during NIV. The understanding of upper airway
constriction and dilation during NIV is rudimentary.

The primary objective of this study is to analyze synchrony between ventilator
and upper airways in COPD patients.
Secondary objectives are to investigate whether the level of support and the
triggering mode of noninvasive ventilation induces or influences glottis
behavior.

This study is an observational study.

With the esophageal EMG catheter in situ patients with COPD will be connected
to a ventilator designed for NIV. Different levels of support (5 versus 15
cmH2O) and different modes (pressure support ventilation (PSV) versus NAVA) of
ventilation will be randomized imposed. PEEP will be kept constant at 5 cmH20.

During noninvasive ventilation the following parameters will be monitored:
o Diaphragm EMG and inspiratory time (using esophageal catheter)
o Genioglossus EMG (surface electrodes)
o Opening/closing of vocal cords during respiratory cycle (video laryngoscopy)
o Tidal volume and minute ventilation (plethysmograhy)
o End tidal CO2, (capnography)
o PaCO2 , PaO2 and pH (arterial blood gas)
Safety parameters which will be measured are:
o Peripheral oxygen saturation (pulse oxymetry).
o Heart rate
o Blood pressure
One hour is necessary to apply all 4 modes of ventilation. Including connecting
and disconnecting to the equipment the complete measurement will not exceed 3
hours.

The patients suffering from COPD are submitted to one session (3 hours) of
measurements. To minimize occurrence of complications (e.g. aspiration,
subjects will be asked not to eat 4 hours, and not to drink 2 hours in advance
of the procedure. During this session the subjects receive NIV at different
levels of support. For the patients suffering from COPD, this is part of
regular care and for the healthy subjects there is no considerable risk
involved. Introduction of an flexible bronchoscope to acquire video images may
result in mild discomfort. With the exclusion criteria formulated, the change
of complications caused by the invasive procedures is minimal.