Diaphragmatic Electromyographic Evaluation Of Upper Airway Resistance With OSA

Background:Patients with respiratory diseases (e.g. COPD) may develophypoventilation during sleep which could be due to increased upper airwayresistance or reduction of neural respiratory drive. Few methods areclinically available to distinguish hypoventilation due to increased upperairway resistance from that due to reduction of neural respiratory drive.Obstructive sleep apnea is a common disease which is characterized withincreased upper airway resistance and could be an idea model to develop amethod to differentiate upper airway resistance from reduction of neuralrespiratory drive. Upper airway resistance (R) can be defined as R=(pressure at hypopharynx-atmosphere)/flow. Because atmosphere pressureoutside the nose is zero therefore the above function could be simplifiedas R=pressure at hypopharynx/flow. Because pressure at hypopharynx couldbe difficult to measure during sleep and pressure at hypopharynx relates toesophageal pressure (Pes), therefore the above function could be furthersimplified as R=Pes/flow. It has been reported that there was a goodrelation between Pes and diaphragm EMG, the purpose of the present study isto determine whether the ratio of diaphragm EMG to airflow could be reliablyquantify upper airway resistance.Methods:Sixteen patients with OSA were recruited in the study. Fullpolysomnography was performed including EEGs (C3A2, C4A1) EOGS (LOC, ROC),chin EMG, oxygen saturation, snoring and airflow from pnenmotachgraphy connecting to full face mask. We also recorded the diaphragm EMG and Pes froma diaphragm function catheter. Data were recorded during wakefulness,stable breathing, snoring and hypopnea events during sleep stage2. More than120respiratory cycles were analyzed.Results:We found that there was a good relation between Pes and diaphragmaticEMG and upper airway resistance increases from wakefulness to sleep duringstable breathing and further increases during snoring and hypopnea events.There are significantly differences in upper airway resistance duringwakefulness, stable breathing, snoring and hypopnea during stage2sleep andwere (arbitary unit)1.5±0.4,2.3±0.6、3.1±1.0、5.3±1.2respectively.Conclusion:We conclude that diaphragm EMG combined with recording airflowcould be used to quantify upper airway resistance.