We assessed the test-retest variability of central and peripheral respiratory chemoreflex characterization by Duffin's modified rebreathing method and explored whether signal averaging of repeated trials improves confidence in parameter estimation. Over four laboratory visits, 13 participants (mean ± SD age, 25 ± 5 years) performed six repetitions of modified rebreathing in isoxic-hypoxic conditions [end-tidal P O 2 (P ET,O 2 ) = 50 mmHg] and isoxic-hyperoxic conditions (P ET,O 2 = 150 mmHg). End-tidal P CO 2 (P ET,CO 2 ), P ET,O 2 and minute ventilation ( VE ) were measured breath-by-breath, by gas analyser and pneumotachograph. The VE versus P ET,CO 2 relationships were fitted with a piecewise model to estimate the ventilatory recruitment threshold (VRT) and the slope above the VRT ( VE S). Breath-by-breath data from the three within-and between-day trials were averaged using two approaches [simple average (fit then average) and ensemble average (average then fit)] and compared with a single-trial fit. Variability was assessed by intraclass correlation (ICC) and coefficient of variance (CV), and the minimal detectable change was computed for each approach using two independent sets of three trials. Within days, the VRT and VE S exhibited excellent testretest variability in both hyperoxic conditions (VRT: ICC = 0.965, CV = 2.3%; VE S:
During incremental exercise, the ventilation (V̇E) versus carbon dioxide production (V̇CO2) relationship exhibits a double‐linear response with an inflection of slope at the transition from hyperpnea to hyperventilation (i.e., respiratory compensation point (RCP)). Whether peripheral or central chemoreflexes contribute to the hyperventilatory response to incremental exercise remains undetermined. This study tested the hypothesis that peripheral and not central chemoreflex sensitivity would relate to the magnitude of the V̇E‐V̇CO2 slope above RCP and that neither would relate to the sub‐RCP V̇E‐V̇CO2 slope. Seven healthy, caffeine‐free males (age: 27±5 years) performed a ramp‐incremental test to exhaustion on a cycle ergometer, during which ventilation and gas exchange were measured by metabolic cart. The V̇E‐V̇CO2 slope above and below RCP were determined by linear regression from the estimated lactate threshold to RCP, and from RCP to end‐exercise, respectively. On four separate days, 12 modified rebreathing tests were performed: six in isoxic‐hyperoxia (PO2=150 mmHg) and six in isoxic‐hypoxia (PO2=50 mmHg). Using ensemble‐average data, central chemoreflex sensitivity was measured as the mean hyperoxic V̇E versus end‐tidal partial pressure of carbon dioxide (PETCO2) slope (in L∙min‐1∙mmHgPETCO2‐1) and the peripheral chemoreflex sensitivity was determined from the difference of hypoxic and hyperoxic slopes. The mean V̇E‐V̇CO2 slopes above and below RCP were 35.0+3.7 (range: 28.3‐39.9) and 61.8+9.2 (range: 51.9‐78.3), respectively. Mean peripheral and central chemoreflex sensitivities were 1.6±1.3 L∙min‐1∙mmHgPETCO2‐1 (range: 0.1‐3.7) and 4.1±2.1 L∙min‐1∙mmHgPETCO2‐1 (range: 2.3‐8.4), respectively. Peripheral chemoreflex sensitivity did not relate to V̇E‐V̇CO2 slope below (r=0.44, p=0.32) or above (r=‐0.02, p=0.96) RCP. No relationships were found between central chemoreflex sensitivity and V̇E‐V̇CO2 slope below (r=0.06, p=0.90) or above (r=0.04, p=0.93) RCP. These preliminary observations suggest that neither central nor peripheral chemoreflex sensitivity factor into the magnitude of the hyperpneic or hyperventilatory response to incremental exercise.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.