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Spontaneous "Second Wind" and Glucose-Induced Second "Second Wind" in McArdle Disease
Oxidative Mechanisms
Ronald G. Haller, MD;
John Vissing, MD, PhD
Arch Neurol. 2002;59:1395-1402.
Background Blocked glycogen breakdown in McArdle disease impairs oxidative as well
as anaerobic metabolism, but the contribution of impaired oxidative phosphorylation
to everyday symptoms of McArdle disease remains poorly defined.
Objective To evaluate the oxidative implications of the spontaneous second wind
and variables that influence the development of this typical feature of McArdle
disease.
Design Assessment of exercise and oxidative capacity ( O2)
before and after the spontaneous "second wind" and with a glucose infusion
after a spontaneous second wind.
Patients Eight patients with complete myophosphorylase deficiency and 1 unique
patient with 3% of normal myophosphorylase activity.
Main Outcome Measures Work capacity, O2, heart rate, cardiac output.
Results All patients with complete myophosphorylase deficiency (1) had low peak O2 (mean ± SD, 13.0 ± 2.0 mL · kg-1·
min-1) in the first 6 to 8 minutes of exercise; (2) achieved
a spontaneous second wind with increased exercise capacity between 8 and 12
minutes of exercise due to a more than 25% increase in peak O2 (16.5 ± 3.1 mL · kg-1· min-1); and (3) with glucose infusion after a spontaneous second
wind, experienced a further more than 20% increase in oxidative capacity (O2, 19.9 ± 3.9 mL · kg-1· min-1). In the patient with residual myophosphorylase, O2 (22.2 mL · kg-1· min-1)
in the first 6 to 8 minutes of exercise was approximately 2-fold higher than
the mean of patients lacking myophosphorylase, and no significant improvement
in exercise and oxidative capacity accompanied prolonged exercise or glucose
infusion.
Conclusions First, the spontaneous second wind and the glucose-induced second second
wind in McArdle disease are due to substrate-dependent increases in muscle
oxidative capacity. Second, by providing glycogen-derived pyruvate, a small
amount of residual myophosphorylase activity normalizes the oxidative deficit
of complete myophosphorylase deficiency and virtually eliminates the spontaneous
second wind and glucose-induced second second wind.
From the Neuromuscular Center, Institute for Exercise and Environmental
Medicine of Presbyterian Hospital, The Veterans Affairs Medical Center, and
The University of Texas Southwestern Medical Center, Dallas (Dr Haller); and
the Copenhagen Muscle Research Center and Department of Neurology, Rigshospitalet,
University of Copenhagen, Copenhagen, Denmark (Dr Vissing).
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