Early detection of upper airway obstructions by analysis of acoustical respiratory input impedance |
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Authors: | S Reisch H Steltner J Timmer C Renotte J Guttmann |
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Institution: | (1) Section of Experimental Anaesthesiology, Clinic of Anaesthesiology, University of Freiburg, Freiburg, Germany, DE;(2) Center of Data Analysis and Model Building, University of Freiburg, Freiburg, Germany, DE;(3) Faculté Polytechnique de Mons, Laboratoire d'Automatique, University of Mons, Mons, Belgium, BE |
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Abstract: | Repetitive occurrence of partial or total upper airway obstruction characterizes several respiratory dysfunctions such as
the obstructive sleep apnea syndrome (OSAS). In OSAS patients, pharyngeal collapses are linked to a decrease in upper airway
muscle activity during sleep which causes decreased upper airway wall stiffness. Continuous positive airway pressure (CPAP)
is recommended as the treatment of choice. Advancements in CPAP therapy require early detection of respiratory events in real
time to adapt the level of the applied pressure to airway collapsibility. The forced oscillation technique (FOT) is a noninvasive
method which reflects patients' airway patency by measuring respiratory impedance. The aim of this study was to evaluate by
a mathematical model of the respiratory system if FOT can provide an early detection index of total or partial upper airway
obstruction. Furthermore, the simulation should suggest which characteristic features are relevant for early apnea detection
in measured clinical data. The respiratory system has been treated as a series of cylindrical segments. The oropharynx analog
of the model allows simulation of upper airway collapse, mimicking the situation in patients with OSAS. We calculated the
input impedance for different degrees of upper airway obstruction ranging from unobstructed airways to total occlusion. Furthermore,
we simulated different upper airway wall compliances. We compared the simulation with real data. The results of the study
suggest that FOT is a valuable tool for assessing the degree of upper airway obstruction in patients with OSAS. Especially,
the phase angle of the impedance seems to be a potentially useful tool for early apnea detection by assessing the upper airway
wall collapsibility.
Received: 23 July 1998 / Accepted in revised form: 26 January 1999 |
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