title: Gas exchange responses to constant work-rate exercise in patients with glycogenosis type V and VII.
abstract: During constant work-rate exercise above the lactic acidosis threshold, oxygen consumption fails to plateau by 3 minutes, but continues to rise slowly. This slow component correlates closely with the rise in lactate in normal subjects. We investigated if oxygen consumption during constant work-rate exercise could rise after 3 minutes in the absence of a rise in lactate. We studied five patients with McArdle's disease, one patient with phosphofructokinase deficiency and six normal subjects. Subjects performed two 6-minute duration constant work-rate exercise tests at 40 and 70% of peak oxygen consumption. During low-intensity exercise, oxygen consumption reached steady state by 3 minutes in both groups. Lactate rose slightly in control subjects but not in patients. During high-intensity exercise, oxygen consumption rose from the third to the sixth minute by 144 (21-607) ml/minute (median and range) in control subjects and by 142 (73-306) ml/minute in patients (p = not significant, Mann-Whitney U test). Over the same period, lactate (geometric mean and range) rose from 2.68 (1.10-5.00) to 5.39 (2.70-10.00) mmol/L in control subjects, but did not rise in patients (1.20 [0.64-1.60] to 0.70 [0.57-1.20] mmol/L). We conclude that the slow component of oxygen consumption during heavy exercise is not dependent on lactic acidosis.
authors.affiliation: Department of Medicine, Royal Victoria Hospital, Belfast, Northern Ireland.
authors.forename: Hean-Yee
authors.initials: HY
authors.lastname: Ong
authors.forename: Conor S
authors.initials: CS
authors.lastname: O'Dochartaigh
authors.forename: Sharon
authors.initials: S
authors.lastname: Lovell
authors.forename: Victor H
authors.initials: VH
authors.lastname: Patterson
authors.forename: Karlman
authors.initials: K
authors.lastname: Wasserman
authors.forename: D Paul
authors.initials: DP
authors.lastname: Nicholls
authors.forename: Marshall S
authors.initials: MS
authors.lastname: Riley
mesh_terms: D000140:Acidosis, Lactic / Q000378:metabolism / Q000503:physiopathology; D000328:Adult; D016022:Case-Control Studies; D004837:Epinephrine / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology; D005260:Female; D006012:Glycogen Storage Disease Type V / Q000378:metabolism / Q000503:physiopathology*; D006014:Glycogen Storage Disease Type VII / Q000378:metabolism / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D019289:Pyruvic Acid / Q000378:metabolism
chemical_list: D019344:Lactic Acid; D019289:Pyruvic Acid; D009638:Norepinephrine; D004837:Epinephrine