Effects of inspiratory and expiratory positive pressure difference on airflow dynamics during sleep

We measured theeffects of dissociating inspiratory and expiratory positive pressure(PI andPE, respectively) on theinspiratory flow limitation pattern and on genioglossus (GG) activityin nine sleep apnea patients. Measurements were made at two different levels of PI with stepwiseincreases in PE. Flow-limitedbreaths were observed during each recording session. In six of ninesubjects, maximal inspiratory flow (I_max)was correlated with the difference betweenPI andPE (correlations were negativein 5 subjects, positive in 1 subject). In three other patients,I_maxwas not influenced by the amount of pressure difference. A positiverelationship between tonic and/or phasic GG electromyographicactivities and PI-PEdifference was observed at least at onePI level in all patients. Thiscorrelation was observed independently of the presence or absence ofany relationship betweenI_maxand the amount of pressure difference. Our results suggest thatincreasing thePI-PE difference (i.e., decreasingPE) may be associated with asignificant worsening in inspiratory flow limitation and that theI_max-pressure difference behavior is not dependent on the GGelectromyographic-pressure response.