title: A study of cardiorespiratory dynamics with step and ramp exercise tests in normoxia and hypoxia.
abstract: The ability of the cardiorespiratory system to adapt to the demands of increased exercise intensity was studied under the effects of hypoxia with two different submaximal cycling exercise protocols. A step transition in work rate from 25 W to 105 W and a ramp increase in work rate from a baseline of 25 W with a slope of 40 W.min-1 were used. Eight healthy male subjects each completed maximal exercise tests to exhaustion, as well as six repetitions of the step and the ramp, during normoxia and during hypoxia (FIO2 = 14%, balance N2). VO2 was measured breath by breath and cardiac output (Q) was estimated beat by beat by impedance cardiography. Kinetic analyses of the VO2 and Q data were performed to obtain the gain and the total lag time. With hypoxia, the gain of the VO2 response was no different from normoxia, at 10.6(SEM 0.1) ml.min-1.W-1, but total lag time increased from 23.0(2.2) s to 32.5(2.6) s (p less than 0.05). In contrast, with ramp exercise there was a significant reduction in the gain or slope of the VO2 response from 9.4(0.2) ml.min-1.W-1 in normoxia to 9.0(0.1) ml.min-1.W-1 in hypoxia, while total lag time was no different between normoxia and hypoxia, at 19.7(3.3) v 21.4(2.9) s. Both the gain and total lag time of the step tests were significantly different from the ramp test. Kinetics of Q during the step transition did not differ between normoxia and hypoxia, at 26.5(2.3) v 31.0(4.9) s, respectively (NS).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Kinesiology, University of Waterloo, Ontario, Canada.
authors.forename: P C
authors.initials: PC
authors.lastname: Murphy
authors.forename: L A
authors.initials: LA
authors.lastname: Cuervo
authors.forename: R L
authors.initials: RL
authors.lastname: Hughson
mesh_terms: D000328:Adult; D005080:Exercise Test / Q000379:methods; D006321:Heart / Q000503:physiopathology*; D006334:Heart Function Tests; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008168:Lung / Q000503:physiopathology*; D008297:Male; D012129:Respiratory Function Tests