title: A simple and portable breathing circuit designed for ventilatory muscle endurance training (VMET).
abstract: BACKGROUND
  Ventilatory muscle endurance training (VMET) involves increasing minute ventilation (V (E)) against a low flow resistance at rest to simulate the hyperpnea of exercise. Ideally, VMET must maintain normocapnia over a wide range of V (E). This can be achieved by providing a constant fresh gas flow to a sequential rebreathing circuit. The challenge to make VMET suitable for home use is to provide a source of constant fresh gas flow to the circuit without resorting to compressed gas.
  
  
  METHODS
  Our VMET circuit was based on a commercial sequential gas delivery breathing circuit (Pulmanex Hi-Ox, Viasys Healthcare, Yorba Linda, CA USA). Airflow was provided either by a small battery-driven aquarium air pump or by the entrainment of air down a pressure gradient created by the recoil of a hanging bellows that was charged during each inhalation. In each case, fresh gas flow was adjusted to be just less than resting V (E). Eight subjects then breathed from the circuit for three 10min periods consisting of relaxed breathing, breathing at 20 and then at 40L/min. We monitored V (E), end-tidal PCO2 (PetCO2) and hemoglobin O2 saturation (SpO2).
  
  
  RESULTS
  During hyperpnea at 20 and 40L/min, PetCO2 did not differ significantly from resting levels with either method of supplying fresh gas. SpO2 remained greater than 96% during all tests.
  
  
  CONCLUSIONS
  Isocapnic VMET can be reliably accomplished with a simple self-regulating, sequential rebreathing circuit without the use of compressed gas.
authors.affiliation: Department of Anesthesiology University Health Network, Toronto, Canada. dahlia.balaban@utoronto.ca
authors.forename: Dahlia Y
authors.initials: DY
authors.lastname: Balaban
authors.forename: Rosemary
authors.initials: R
authors.lastname: Regan
authors.forename: Alexandra
authors.initials: A
authors.lastname: Mardimae
authors.forename: Marat
authors.initials: M
authors.lastname: Slessarev
authors.forename: Jay S
authors.initials: JS
authors.lastname: Han
authors.forename: Greg D
authors.initials: GD
authors.lastname: Wells
authors.forename: James
authors.initials: J
authors.lastname: Duffin
authors.forename: Steve
authors.initials: S
authors.lastname: Iscoe
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fisher
authors.forename: David
authors.initials: D
authors.lastname: Preiss
mesh_terms: D000328:Adult; D001944:Breath Tests; D004867:Equipment Design; D015444:Exercise; D005080:Exercise Test / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010807:Physical Endurance / Q000502:physiology*; D012119:Respiration; D012121:Respiration, Artificial / Q000295:instrumentation*; D012132:Respiratory Muscles / Q000502:physiology*; D012122:Ventilators, Mechanical; D055815:Young Adult