title: A simple breathing circuit to maintain isocapnia during measurements of the hypoxic ventilatory response.
abstract: We report the development and testing of a simple breathing circuit that maintains isocapnia in human subjects during hypoxic hyperpnea. In addition, the circuit permits rapid switching between two gas mixtures with different partial pressures of oxygen. Eleven volunteers breathed repeated cycles of exposure to air (2 min of 21% O(2), balance N(2)) and hypoxia (2 min of 8.3+/-0.1% O(2), balance N(2)). Hypoxia induced significant increases in minute ventilation, breathing frequency and tidal volume (P < 0.05) that were consistent over repeated cycles of hypoxia (P > 0.1, one-way ANOVA). The system successfully maintained isocapnia in all subjects, with an average change in end-tidal CO(2) of only -0.2 mmHg during hyperventilation in hypoxia (range 0.4 to -0.8 mmHg). This system may be suitable for repeated tests of the hypoxic ventilatory response (HVR) and may prove useful for exploring intra- and inter-individual variability of HVR in humans.
authors.affiliation: Department of Physiological Sciences, University of Stellenbosch, Private Bag X1, Matieland 7206, South Africa. a.fahlman@bham.ac.uk
authors.forename: Andreas
authors.initials: A
authors.lastname: Fahlman
authors.forename: Sue
authors.initials: S
authors.lastname: Jackson
authors.forename: John
authors.initials: J
authors.lastname: Terblanche
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fisher
authors.forename: Alex
authors.initials: A
authors.lastname: Vesely
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sasano
authors.forename: Kathryn H
authors.initials: KH
authors.lastname: Myburgh
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D006985:Hyperventilation / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D010313:Partial Pressure; D012123:Pulmonary Ventilation / Q000502:physiology; D012016:Reference Values; D012119:Respiration; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology; D013990:Tidal Volume; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen