A simple and portable breathing circuit designed for ventilatory muscle endurance training (VMET)
Received 2 January 2009; accepted 19 July 2009. published online 13 August 2009.
Summary
Background
Ventilatory muscle endurance training (VMET) involves increasing minute ventilation () against a low flow resistance at rest to simulate the hyperpnea of exercise. Ideally, VMET must maintain normocapnia over a wide range of . 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 . 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 , 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.
Conclusion
Isocapnic VMET can be reliably accomplished with a simple self-regulating, sequential rebreathing circuit without the use of compressed gas.
aDepartment of Anesthesiology University Health Network, Toronto, Canada, Department of Physiology, University of Toronto, and Thornhill Research Inc., 70 Peter Street, 2nd Floor Toronto, ON, Canada M5V 2G5
bDepartment of Physiology, Queen's University, 18 Stuart Street, Botterell Hall, Kingston, Ontario, Canada K7L 3N6
ABSTRACT
