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Department of Medicine, University of California, San Diego, La Jolla, California 92093-0623
Submitted 19 February 2003 ; accepted in final form 28 April 2003
To determine the effect of age on quadriceps muscle blood flow (QMBF), leg
vascular resistance (LVR), and maximum oxygen uptake
(Q
O2 max), a
thermal dilution technique was used in conjunction with arterial and venous
femoral blood sampling in six sedentary young (19.8 ± 1.3 yr) and six
sedentary old (66.5 ± 2.1 yr) males during incremental knee extensor
exercise (KE). Young and old attained a similar maximal KE work rate
(WRmax) (young: 25.2 ± 2.1 and old: 24.1 ± 4 W) and
Q
O2 max
(young: 0.52 ± 0.03 and old: 0.42 ± 0.05 l/min). QMBF during KE
was lower in old subjects by
500 ml/min across all work rates, with old
subjects demonstrating a significantly lower QMBF/W (old: 174 ± 20 and
young: 239 ± 46 ml · min1 ·
W1). Although the vasodilatory response to
incremental KE was
142% greater in the old (young: 0.0019 and old: 0.0046
mmHg · min · ml1 ·
W1), consistently elevated leg vascular
resistance (LVR) in the old,
80% higher LVR in the old at 50% WR and
40% higher LVR in the old at WRmax (young: 44.1 ± 3.6
and old: 31.0 ± 1.7 mmHg · min ·
ml1), dictated that during incremental
KE the LVR of the old subjects was never less than that of the young subjects.
Pulse pressures, indicative of arterial vessel compliance, were
36%
higher in the old subjects across all work rates. In conclusion, well-matched
sedentary young and old subjects with similar quadriceps muscle mass achieved
a similar WRmax and
Q
O2 max during
incremental KE. The old subjects, despite a reduced QMBF, had a greater
vasodilatory response to incremental KE. Given that small muscle mass
exercise, such as KE, utilizes only a fraction of maximal cardiac output,
peripheral mechanisms such as consistently elevated leg vascular resistance
and greater pulse pressures appear to be responsible for reduced blood flow
persisting throughout graded KE in the old subjects.
vascular resistance; quadriceps; pulse pressures; O2 conductance
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