title: Comparing and characterizing transient and steady-state tests of the peripheral chemoreflex in humans.
abstract: What is the central question of this study? We aimed to characterize the cardiorespiratory and cerebrovascular responses to transient and steady-state tests of the peripheral chemoreflex and to compare the hypoxic ventilatory responses (HVRs) between these tests. What is the main finding and its importance? The cardiovascular and cerebrovascular responses to transient tests were small in magnitude and short in duration. The steady-state isocapnic hypoxia test elicited a larger HVR than the transient 100% N(2) test, but the response magnitudes were correlated within individuals. The transient test of the HVR elicits fewer systemic effects than steady-state techniques and may have greater experimental utility than previously appreciated. Carotid chemoreceptors detect changes in arterial PO(2) and PCO(2), eliciting a peripheral chemoreflex (PCR). Steady-state (SS) hypoxia tests using dynamic end-tidal forcing (DEF) have been used to assess the hypoxic ventilatory response (HVR) but may be confounded by concomitant systemic effects. Transient tests of the PCR have also been developed but are not widely used, nor have the cardiovascular and cerebrovascular responses been characterized. We characterized the cardiorespiratory and cerebrovascular responses to transient tests of the PCR and compared the HVR between transient and SS-DEF tests. We hypothesized that the cardiovascular and cerebrovascular responses to the transient tests would be minimal and that the respiratory responses elicited from the transient and SS-DEF tests would be different in magnitude and not well correlated within individuals. Participants underwent five consecutive trials of two transient tests [three-breath 100% N(2) (TT-N(2)) and a single-breath 13% CO(2), in air] and two 10 min SS-DEF tests [isocapnic (SS-ISO) and poikilocapnic (SS-POI) hypoxia]. In response to the transient tests, heart rate, mean arterial pressure and the middle and posterior cerebral artery blood velocity increased (all P < 0.01), but responses were small (all <10%) and transient. Although the TT-N(2) and SS-POI tests elicited similar HVR magnitudes, they were not well correlated within individuals (r = 0.064, P = 0.79). The TT-N(2) test elicited a smaller HVR than the SS-ISO test, but they were correlated within individuals (r = 0.57, P = 0.008). Given that the transient tests exploit the temporal domain of the peripheral chemoreceptors and have minimal cardiovascular and cerebrovascular confounders, we suggest that they may have broader utility than previously appreciated.
authors.affiliation: Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada.
authors.forename: Jamie R
authors.initials: JR
authors.lastname: Pfoh
authors.affiliation: School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Tymko
authors.affiliation: Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada.
authors.forename: Maria
authors.initials: M
authors.lastname: Abrosimova
authors.affiliation: Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada.|School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Lindsey M
authors.initials: LM
authors.lastname: Boulet
authors.affiliation: School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Glen E
authors.initials: GE
authors.lastname: Foster
authors.affiliation: School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Bain
authors.affiliation: School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Philip N
authors.initials: PN
authors.lastname: Ainslie
authors.affiliation: Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Craig D
authors.initials: CD
authors.lastname: Steinback
authors.affiliation: Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada.
authors.forename: Christina D
authors.initials: CD
authors.lastname: Bruce
authors.affiliation: Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada.
authors.forename: Trevor A
authors.initials: TA
authors.lastname: Day
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000502:physiology; D002628:Chemoreceptor Cells / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000097:blood / Q000503:physiopathology; D008297:Male; D010100:Oxygen / Q000097:blood; D010525:Peripheral Nerves / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen