title: Work of Breathing in Fixed and Pressure Relief Continuous Positive Airway Pressure (C-Flex™): A post hoc Analysis.
abstract: BACKGROUND
  Expiratory pressure relief continuous positive airway pressure (pressure relief CPAP; C-Flex™) causes increases in inspiratory duty cycle and shortening of expiratory time. It has been suggested that these changes are caused by an increase in work of breathing.
  
  
  OBJECTIVE
  We studied the effects of C-Flex on work of breathing and intrinsic positive end-expiratory pressure as compared to fixed CPAP.
  
  
  METHODS
  Work of breathing was analyzed in 24 patients with obstructive sleep apnea during treatment with fixed CPAP and C-Flex with 3 different pressure relief settings in a randomized order during rapid-eye-movement (REM) and non-REM sleep. Work of breathing was assessed on a breath-by-breath basis using a piezoelectric esophageal pressure catheter and a pneumotachograph for measuring airflow.
  
  
  RESULTS
  We found there was no increase in inspiratory work of breathing observed using C-Flex compared to fixed CPAP. Instead, we found a linear decrease in inspiratory work of breathing with increasing pressure relief, with a mean difference of 1.22 J/min between CPAP and maximum pressure release (C-Flex 3; 90% of the value with nasal CPAP); however, the decrease was not statistically significant. The decrease in inspiratory work of breathing associated with C-Flex has a significant inverse correlation with BMI.
  
  
  CONCLUSIONS
  The C-Flex technology does not change work of breathing but shows a tendency towards a reduction of inspiratory work of breathing in patients with a lower BMI using higher C-Flex. The effect is probably caused by diminishing airway resistance generated by the positive end-expiratory pressure. Our findings may lead to additional fields of application of the C-Flex technology, such as chronic obstructive pulmonary disease or muscular dystrophy.
authors.affiliation: Department of Medicine, Pulmonary and Critical Care Medicine, University Medical Center Giessen and Marburg, Philipps-Universität Marburg, Marburg, Germany.
authors.forename: Lukas
authors.initials: L
authors.lastname: Jerrentrup
authors.forename: Sebastian
authors.initials: S
authors.lastname: Canisius
authors.forename: Susanne
authors.initials: S
authors.lastname: Wilhelm
authors.forename: Karl
authors.initials: K
authors.lastname: Kesper
authors.forename: Thomas
authors.initials: T
authors.lastname: Ploch
authors.forename: Claus
authors.initials: C
authors.lastname: Vogelmeier
authors.forename: Timm
authors.initials: T
authors.lastname: Greulich
authors.forename: Heinrich F
authors.initials: HF
authors.lastname: Becker
mesh_terms: D000328:Adult; D000368:Aged; D000403:Airway Resistance; D015992:Body Mass Index; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D015656:Respiratory Mechanics; D020181:Sleep Apnea, Obstructive / Q000628:therapy*