Oxygen consumption is increased relative to work rate in patients with McArdle's disease.
BACKGROUND
Patients with McArdle's disease suffer exercise incapacity as a result of myophosphorylase deficiency, and for a given work rate have excessive circulatory and ventilatory responses. We hypothesized that the rate of increase of oxygen consumption with work rate (DeltaVO2-DeltaWR slope) would also be elevated in such patients as a result of these excessive responses.


METHODS
Five patients with McArdle's disease and five matched controls carried out a maximal incremental cardiopulmonary exercise test. Controls then carried out a second test matched to the maximal test of a paired patient. Venous blood was sampled at rest, peak exercise and recovery.


RESULTS
During the matched test, the DeltaVO2-DeltaWR slope was higher in the patients than in the controls [19.9 (15.0-24.6) vs. 11.7 (9.2-13.5) mL min(-1) W(-1); mean (range); P = 0.022], and the peak-achieved VO2 was also greater in the patient group [1201 (890-1575) vs. 918 (599-1248) mL min(-1); P = 0.003]. A similar pattern was observed for heart rate [173 (165-182) vs. 108 (105-134) b.p.m.; P = 0.001] and plasma norepinephrine levels [12.6 (9.2-19.9) vs. 2.9 (2.2-4.9) nmol l(-1); P = 0.003].


CONCLUSIONS
There is an increased rate of rise in VO2 relative to work rate during exercise in patients with McArdle's disease. There is also a greater rise in catecholamines, which may be the result of a physiological response to substrate starvation, and is likely to contribute to the increase in VO2.
O'Dochartaigh
C S
CS
Department of Medicine, Royal Victoria Hospital, Belfast, Northern Ireland.
Ong
H Y
HY
Lovell
S M
SM
Riley
M S
MS
Patterson
V H
VH
Young
I S
IS
Nicholls
D P
DP
D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D004837:Epinephrine / Q000097:blood; D005080:Exercise Test / Q000379:methods*; D005260:Female; D006012:Glycogen Storage Disease Type V / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology*; D012129:Respiratory Function Tests / Q000379:methods
D009638:Norepinephrine; D004837:Epinephrine