title: Bench experiments comparing simulated inspiratory effort when breathing helium-oxygen mixtures to that during positive pressure support with air.
abstract: BACKGROUND
  Inhalation of helium-oxygen (He/O2) mixtures has been explored as a means to lower the work of breathing of patients with obstructive lung disease. Non-invasive ventilation (NIV) with positive pressure support is also used for this purpose. The bench experiments presented herein were conducted in order to compare simulated patient inspiratory effort breathing He/O2 with that breathing medical air, with or without pressure support, across a range of adult, obstructive disease patterns.
  
  
  METHODS
  Patient breathing was simulated using a dual-chamber mechanical test lung, with the breathing compartment connected to an ICU ventilator operated in NIV mode with medical air or He/O2 (78/22 or 65/35%). Parabolic or linear resistances were inserted at the inlet to the breathing chamber. Breathing chamber compliance was also varied. The inspiratory effort was assessed for the different gas mixtures, for three breathing patterns, with zero pressure support (simulating unassisted spontaneous breathing), and with varying levels of pressure support.
  
  
  RESULTS
  Inspiratory effort increased with increasing resistance and decreasing compliance. At a fixed resistance and compliance, inspiratory effort increased with increasing minute ventilation, and decreased with increasing pressure support. For parabolic resistors, inspiratory effort was lower for He/O2 mixtures than for air, whereas little difference was measured for nominally linear resistance. Relatively small differences in inspiratory effort were measured between the two He/O2 mixtures. Used in combination, reductions in inspiratory effort provided by He/O2 and pressure support were additive.
  
  
  CONCLUSIONS
  The reduction in inspiratory effort afforded by breathing He/O2 is strongly dependent on the severity and type of airway obstruction. Varying helium concentration between 78% and 65% has small impact on inspiratory effort, while combining He/O2 with pressure support provides an additive reduction in inspiratory effort. In addition, breathing He/O2 alone may provide an alternative to pressure support in circumstances where NIV is not available or poorly tolerated.
authors.affiliation: Medical Gases Group, Air Liquide Santé International, Centre de Recherche Claude-Delorme, Jouy-en-Josas, France. andrew.martin@airliquide.com
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Martin
authors.forename: Ira M
authors.initials: IM
authors.lastname: Katz
authors.forename: Katharina
authors.initials: K
authors.lastname: Jenöfi
authors.forename: Georges
authors.initials: G
authors.lastname: Caillibotte
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
authors.forename: Joëlle
authors.initials: J
authors.lastname: Texereau
mesh_terms: D000328:Adult; D000388:Air; D000403:Airway Resistance / Q000502:physiology; D001187:Artificial Organs; D006371:Helium; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008168:Lung / Q000502:physiology*; D008170:Lung Compliance / Q000502:physiology; D008173:Lung Diseases, Obstructive / Q000503:physiopathology*; D010100:Oxygen; D016544:Patient Simulation; D011175:Positive-Pressure Respiration; D015656:Respiratory Mechanics / Q000502:physiology
chemical_list: D006371:Helium; D010100:Oxygen