Effect of A Slow Ramp Rate on Exercise Testing: A Healthy Volunteer Study-Juniper Publishers
Authored
by Julian Martin Brown
Introduction
Submaximal exercise testing is now used routinely to
assess fitness for surgery. The anaerobic threshold determined by
expired gas analysis during ramped exercise predicts surgical morbidity
and mortality [1]. Cycle ergometry with a ramped protocol is typically
used but there is little standardisation of protocols. A comparison
between 20,30,50 and 100 watts per minute increments [2] showed no
difference in anaerobic threshold and VO2 max but lower ramp increments
were not tested. In another study comparing 10,30 and 50 watts per
minute anaerobic threshold was unchanged but “VO2 peak” was reduced with
a 10 watts per minute protocol [3]. Using a running treadmill test V
Vucetić et al. [4] showed differences in peak running speed using
different ramp rates but no difference in VO2max or AT. Ramp rates of 6
watts per minute and 12 watts per minute have been compared using arm
crank ergometry, yielding higher end exercise lactate and VCO2 [5,6]. To
date ramp rates below 10 watts per minute have not been compared using
cycle ergometry. We investigated the difference between a 3 watts per
minute and 20 watts per minute in healthy volunteers.
Methods
Participants
8 non-elite experienced cyclists were tested on two
occasions using cycle ergometry. The subjects were all experienced
non-competitive cyclists with a mean age of 40 years, mean height 180 cm
and mean weight 77kg. The study was approved by the Local Research and
Ethics Committee.The study was performed in accordance with the
Declaration ofHelsinki and the Ethical Standards in Sport and Exercise
Science Research [7]. Subjects were asked to refrain from strenuous
exercise in the 24 hours prior to each test. Tests were carried out in
random order with a minimum of 3 days interval.Subjects were blinded to
the study protocols.
Protocol
Tests were carried out on a Zan 200 metabolic cart
(NSpire). Subjects were monitored throughout with continuous ECG and
pulse oximetry. Subjects warmed up for 3 minutes at 100 Watts and then
started one of two incremental ramp tests. Fast ramp (FR) incremented at
20 watts/ minute and Slow Ramp (SR) incremented at 3 watts/minute.
Twenty minutes into the
SR subjects were allowed to drink briefly whilst continuing to
exercise. Tests continued until subjects were unable to continue
due to exhaustion.
All data were analysed off line by a clinician experienced at
interpreting exercise tests, blinded to the study protocol. The
“V-slope” method was used to determine anaerobic threshold.
Statistical analysis
The results are expressed as mean (+/- standard deviation).
All calculations were carried out in an Excel Spreadsheet with
internal statistical package. Atwo-tailed paired t test was used
to compare differences between means for AT, VO2 max and the
ratio of AT to VO2 max. P values are quoted with significance
assumed to be a P value less than 0.05.
Results
Maximum power was significantly higher for FR than for
SR. Mean AT was lower for FR (37.6 (7.1) ml/min/kg) than the
slow ramp (43.1 (4.2) ml/min/kg) (p= 0.07). Conversely mean
VO2 max was higher for the fast ramp (54.6 (3.2) ml/min/kg)
than the slow ramp (52.6 (4.3) ml/min/kg) (p=0.28). Mean ratio
between AT and VO2 max was significantly lower for the slow
ramp (9.46 (3.9) than the fast ramp (16.9 (6.52) (p = 0.02).
Discussion
Our study showed that a slow ramp rate (3 watts/minute)
gave significantly different results for peak power and the ratio
of anaerobic threshold to VO2max compared to faster ramp (20
watts / minute).
We showed a non-significant reduction in VO2 max for
the
slower ramp which confirms the findings of Weston at 10 watts/
minute [3]. Our anaerobic threshold appeared higher (nonsignificant)
in contrast with others [2,3]. Using arm ergometry
there was no difference in VO2 peak but a higher VCO2 at VO2
peak [5,6]. We showed a significant difference in the ratio of AT
to VO2 using a slow ramp test. We used a very slow ramp (3 watts
per minute) which has not been previously tested. This very
slow ramp rate has two potential effects which higher ramps
may not achieve. Our subjects exercised for 40 minutes allowing
them to potentially “warm up” effectively but also allowing them to
potentially fatigue by the end of the test. We are undertaking
further research to determine if a long sub maximal “warm up”
prior to testing accounts for the differences seen. Our subjects
were relatively young fit experienced cyclists. Further research
would be required to quantify these changes in older less fit
subjects. For clinical testing using cardiopulmonary testing the
values obtained may be used to guide treatment or surgery.
Ramp rates may need to be adjusted objectively to standardise
interpretation of results.
Summary
Our study has shown that the ramp rate used during
exercise testing can influence the values obtained. Clinical use
of cardiopulmonary exercise testing should be standardised as
it may influence the values and hence surgical risk prediction.
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