title: Spontaneous breathing of heliox using a semi-closed circuit: a bench study.
abstract: BACKGROUND
  The use of helium-oxygen mixture (heliox) for ventilation has an advantage in patients with obstruction of the airways. The physical properties of helium enable an easier gas flow through the airways; this enables easier breathing for the patient when compared to standard ventilation of air. A high cost of heliox falls within the factors that limit the use of heliox in clinical practice. At present, heliox is administered by use of an open circuit. The aim of this study is to propose a way of heliox administration that reduces heliox consumption but does not affect the positive heliox effects upon the airway resistance.
  
  
  METHODS
  To minimize consumption of heliox, a semi-closed circuit has been designed. The circuit is a modification of an anesthetic circuit composed of parts with the lowest possible resistances. As any circuit has its own resistance, the evaluation of its possible negative effect upon the work of breathing of patients with exacerbation of chronic obstructive pulmonary disease (COPD) has been conducted.
  
  
  RESULTS
  A semi-closed circuit for heliox administration has been constructed and evaluated. The intrinsic resistance of both the inspiratory and expiratory limbs of the circuit is less than 140 Pa.s/l. This resistance does not represent a significant workload for a patient with COPD exacerbation whose airway resistance is 10 to 20 fold higher.
  
  
  CONCLUSIONS
  The designed semi-closed circuit offers a potential benefit of heliox in patients with COPD exacerbation.
authors.affiliation: Czech Technical University in Prague, Faculty of Biomedical Engineering, Kladno - Czech Republic. roubik@fbmi.cvut.cz
authors.forename: Karel
authors.initials: K
authors.lastname: Roubík
authors.forename: Roman
authors.initials: R
authors.lastname: Zazula
authors.forename: Adéla
authors.initials: A
authors.lastname: Strnadová
authors.forename: Vladimír
authors.initials: V
authors.lastname: Zábrodský
authors.forename: Antonín
authors.initials: A
authors.lastname: Spálený
authors.forename: Martin
authors.initials: M
authors.lastname: Müller
authors.forename: Jan
authors.initials: J
authors.lastname: Chlumský
authors.forename: Tomáš
authors.initials: T
authors.lastname: Tyll
mesh_terms: D000280:Administration, Inhalation; D000403:Airway Resistance; D000764:Anesthesia, Closed-Circuit / Q000295:instrumentation*; D004867:Equipment Design; D045853:Exhalation; D006371:Helium / Q000008:administration & dosage*; D006801:Humans; D001239:Inhalation; D008422:Materials Testing; D010100:Oxygen / Q000008:administration & dosage*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000628:therapy*; D012121:Respiration, Artificial / Q000295:instrumentation*; D012122:Ventilators, Mechanical; D014939:Work of Breathing
chemical_list: D006371:Helium; C038949:heliox; D010100:Oxygen