Effects of Continuous Exercise Training at Aerobic Threshold on Ventilation Inefficiency in Chronic Heart Failure
University of Padua and Telematic University Giustino Fortunato of Benevento, Italy
Submission: May 03, 2018;Published: May 11, 2018
*Corresponding author: Stefano Scarpa, University of Padua and Telematic University Giustino Fortunato of Benevento, Italy,
How to cite this article:Stefano S. Effects of Continuous Exercise Training at Aerobic Threshold on Ventilation Inefficiency in Chronic Heart Failure. J Phy Fit Treatment & Sports. 2018; 3(5): 555622. DOI: 10.19080/JPFMTS.2018.03.555622
Chronic Heart Failure (CHF) is a complex syndrome characterised by ventilation inefficiency, as indicated by the increasing of the minute ventilation-carbon dioxide production slope (VE/VCO2). In the present work we investigated the effects of a “low impact” continuative aerobic training on a powerful prognostic indicator as the VE/VCO2 slope in CHF.
Background: Chronic Heart Failure (CHF) is a complex syndrome characterised by ventilation inefficiency, as indicated by the increasing of the minute ventilation-carbon dioxide production slope (the VE/VCO2 slope), and it is correlated with two predominant symptoms: dyspnea and reduced aerobic performance. We investigated how ventilatory efficiency improves (decreasing in the VE/VCO2 slope) after a period of “low impact” supervised continuative aerobic training (SAT) and after a subsequent period of non supervised continuative aerobic “home” training (NST) in CHF patients.
Methods: Individuals with CHF (n = 22) were trained (40 minutes of cycling at the aerobic threshold, 3 times/week) for 8 weeks and continued a non-monitored training for another 8 weeks.
Results: After SAT there was an increasing of peak exercise O2 uptake (pVO2, +7.8%), exercise testing duration (+14.5%), work rate (Watts) corresponding respectively to 2 and 3 mmol/l of blood lactate (respectively +20.2% and +18.4%). After overall training there was a decreasing of the VE/VCO2 slope (-6.5%) and ventilation measured at the maximum work rate in the baseline exercise testing (relative maximal ventilation, -21%).
Conclusion: Low impact training may improve aerobic performance and functional ability. The training increases the pVO2 values and has a positive effect on the powerful prognostic indicator, the VE/VCO2 slope. Finally it has a lot of benefits and helps to guarantee the possibility for an active physical regimen in CHF population in order to maintain all positive effects that exercise produces.
Ventilatory efficiency is commonly assessed by the minute ventilation-carbon dioxide production slope (VE-VCO2) [1-3]. Chronic Heart Failure (CHF) is a complex syndrome characterised by ventilation inefficiency, as indicated by the increased VE/VCO2 slope, correlated with two predominant symptoms: Dyspnea and reduced aerobic performance [3,4]. The VE/VCO2 slope is considered as a powerful prognostic indicator in heart failure population [1,5-11]. Risk of mortality is thought to increased when VE/VCO2 slope values are greater than 45 when it is calculated as the last value of three during the last 30 seconds of exercise  or greater than 34 when it is measured over all the curve [7,11,13] or greater than 32.6 when it is measured excluding ventilatory compensation due to metabolic acidosis .
The increased VE/VCO2 slope in CHF could be explained by the following mechanisms: A large dead space and high values of physiological dead space-tidal volume ratio ; low values of the arterial CO2 partial pressure ; a ventilation-perfusion mismatch [14-16]; a impaired metabolic gas diffusion; abnormalities in endothelial and working muscle function; changes in respiratory musculature with a need of excessive ventilatory effort [2,17,18]; an impaired central and peripheral control of ventilation [19-21].
A study of Guazzi (2004) showed that a regular aerobic exercise training (intensity at 60-80% according to heart rate reserve method) contributes to improve ventilatory efficiency and exercise performance in CHF. A similar exercise program seemed to increase lung diffusion, alveolar-capillary
conductance, pulmonary capillary blood volume, peak exercise
O2 uptake (pVO2), VO2 at anaerobic threshold and decrease the
VE/VCO2 slope . The aim of the present study is to determine
the improvement in ventilation efficiency (decreasing in the
VE/VCO2 slope) and exercise performance after a period of
“low impact” supervised aerobic training (SAT) -intensity
correspondent to aerobic threshold, approximately 60% of
pVO2- and after a subsequent period of non supervised “home”
training (NST) in CHF population.
Twenty-two patients (16 male and 6 female, aged 61.40±7.5)
with symptomatic CHF in a stable condition were enrolled in
this study. CHF was due to either ischaemic (14 patients) or
idiopathic dilated cardiomyopathy (8 patients). The criteria for
their eligibility were: Medically stable heart failure in NYHA
class II-III for at least 3 months before the study, left ventricular
dysfunction with Ejection Fraction 40%, and pVO2 25ml/
kg/min. Exclusion criteria were: myocardial infarction or
unstable angina within the previous 6 months, aortic stenosis,
uncontrolled hypertension, exercise-limiting peripheral
artery disease, de-compensated diabetes mellitus, orthopedic
limitations or any other clinical condition precluding regular
participation in exercise sessions. Patients received standard
medical treatment, and medications remained unaltered
throughout the study. Written informed consent was obtained
from each patient under the supervision of the Local Ethics
Committee, and the investigation conformed to the principles
outlined in the Declaration of Helsinki.
The study was conducted prospectively, without any blinding
procedure, and each patient acted as her/his own control. All
patients received a complete evaluation at the beginning of the
study, after 8 weeks of continuous SAT and again after 8weeks
of the subsequent phase (continuous NST). Each evaluation
included two symptom-limited bicycle exercise tests (one with
gas exchange analysis, one with capillary blood sample collection
for lactate analysis), medical examinations and skinfolds.
The outcome measures for this study were the VE/VCO2 slope,
pVO2(ml/kg/min), relative maximal ventilation (ventilation
measured at the maximum work rate obtained in the baseline
exercise testing), absolute maximal ventilation (ventilation
measured at the maximum work rate obtained in each exercise
testing), dead space-tidal volume ratio, duration of exercise
(min:sec), work rate (Watts), aerobic and anaerobic thresholds
(watts and heart rate values corresponding to respectively
2mmol/l and 4mmol/l of blood lactate concentration), and
anthropometric measurements (height, body weight, body mass
index, 9 skinfolds and 7 body circumferences).
Cardiopulmonary Exercise Test: An incremental upright
cardiopulmonary exercise test was performed on an
electronically braked cycle ergometer (Meditronic M700,
Karlsruhe, Germany). To stabilize gas measurements, patients
were asked to remain still on the ergometer for 3 minutes before
exercising. After a 3minute warm up at a 15Watts workload,
a ramp protocol of 10Watt/min was started and continued
until exhaustion at a constant pedaling rate of 60rpm. A 12-
lead electrocardiogram was monitored throughout the test
(Marquette MAC8, Jupiter Florida) and blood pressure was
measured manually by a cuff sphygmomanometer every minute.
Respiratory gas exchange measurements were obtained breathby-
breath using a computerized metabolic chart (Vmax Sensor
Medics, Yorba Linda, California). Calibrations of volumes and
gases (O2 and CO2) were performed before each test. The mean
oxygen uptake over the last 20 seconds of exercise was pVO2.
Measurements of the VE/VCO2 Slope: Cardiopulmonary
exercise testing also permitted the determination of the VE/
VCO2 slope, relative maximum ventilation, absolute maximum
ventilation and dead space-tidal volume ratio. The VE/VCO2 slope
was measured by linear regression, excluding the non linear
part of the data after the onset of ventilatory compensation for
metabolic acidosis [2,3,22].
Calculation of Aerobic Threshold and Target Heart
Rate: Two days after the cardiopulmonary test, patients
performed a second symptom-limited exercise test on the same
cycle ergometer, starting at a 15Watts workload for 3minutes
followed by a 20Watt increase every 3minutes until exhaustion.
At the end of each 3-minute step, a 20L capillary blood sample
was taken from the ear-lobe for lactate determination using the
enzymatic-amperometric measuring principle (Super GL Dr
Muller Geratebau, Freital, Germany). The target training heart
rate for each patient was determined from the relationship
between lactate concentration and heart rate. The target heart
rate was identified at 2mmol/L of lactate which, in our patients,
corresponded to approximately 60% of pVO2 and to 90% of
anaerobic threshold previously measured by the V-slope method
. This 2mmol/L of lactate workload, determined from the
lactate-workload plot, was named aerobic threshold.
Patients exercised on an upright bicycle ergometer 3 times
a week for 8 weeks. Each session lasted 55minutes, beginning
with a 5-minute warm up at 15Watts followed by 45 minutes
of cycling at the target heart rate and finished with a 5-minute
cool-down at 15Watts. A capillary blood sample was taken from
all patients at least twice during each exercise session to ensure
that the target training intensity corresponding to 2-2.5mmol/L
of lactate was achieved and maintained. In the event of a lower
or a higher lactate concentration, the workload was immediately
adjusted . All sessions were held at the hospital gymnasium
under the supervision of an expert sport scientist.
All data were processed using the SPSS 21.0 program. Age and
anthropometric characteristics are expressed as mean value ±
standard deviation. Comparisons between groups were analyzed
by unpaired t test (2-sided) or Analysis of variance (one-way
ANOVA) for comparisons with >2 subgroups. Bonferroni posthoc
multiple comparisons were performed when appropriate.
The alpha-error probability was set at p<.05 (2-sided).
All 22 patients recruited for the study finished the 8
weeks of SAT without any cardiovascular or muscle-skeletal
complication. At the baseline assessment they showed the
following anthropometric characteristics: weight 83.31±16.3kg,
height 170.1±8.51cm, BMI 28.67±4.07kg/m², muscle mass
40.12±3.02% and fat mass 25.13±5.67%. There were no
significant modifications after the 8 weeks of SAT, while there
was a significant increasing of both muscle mass and fat mass
after 8 more weeks of NST (Table 1).
Anthropometric features at baseline, after 8 weeks of SAT (supervised
aerobic training) and after further 8 weeks of NST (non-supervised
All values are expressed as means ± standard deviations.
Significant differences are denoted with the symbol “*” (p <0.05).
All values are expressed as means ± standard deviations.
Significant differences are denoted with the symbols: “*” for p < 0.001;
“**” for p<0.01 and “***” for p < 0.0005.
For what concerns Cardiopulmonary exercise testing pVO2
changed from a baseline average value of 15.79±3.78ml/kg/min
to 17.03±4.06ml/kg/min (+7.8%, p<0.001) after 8 weeks of SAT
and it decreased again to baseline values after 8 more weeks
of NST (Table 2). The VE/VCO2 slope showed a non significant
decreasing after 8 weeks of SAT, but it significantly decreased
after the 16 weeks of overall training. The baseline average value
was 31.91±6.2. The average value after 8 weeks was 30.86±4.61
and 29.84±4.49 (-6.5%, p<0.05) after 16 weeks (Table 3). The
relative maximal ventilation showed a trend similar to the VE/
VCO2 slope (-21% after 16 weeks of overall training, p<0.0005),
while the absolute maximal ventilation did not show any
significant variation. The dead space-tidal volume ratio showed
a non significant decreasing trend.
All values are expressed as means ± standard deviations.
Significant differences are denoted with the symbols: “*” for p < 0.05;
“**” for p < 0.0005.
All values are expressed as means ± standard deviations.
Significant differences are denoted with the symbol “*” (p < 0.005).
Results originating from Modified Mader testing showed a
significant increasing of the work rate (Watts) expressed at 2
and 3 lactate mmol/l after 8 weeks of SAT in comparison with
baseline values (p<0.005). The elevated values returned to the
baseline values after a further NST (Table 4).
From the analysis of results we observed an increasing in
both exercise performance and functional ability after SAT in
CHF patients. After 8 weeks patients expressed a higher work
rate level and a longer exercise time during Cardiopulmonary
testing. At the same time patients also achieved a decreased
lactate concentration for the same sub-maximal intensity during
Modified Mader testing. Those modifications regressed after
further 8 weeks period of NST.
First of all, we aimed to assess the effects of our “low impact”
training protocol on the VE/VCO2 slope. A previous study had
shown that aerobic high intensity training contributed to the
reduction of the VE/VCO2 slope after a period of 8 weeks and that
the slope regressed to the baseline values after 8 more weeks
of strict de-training . The findings of our exercise protocol
contrasted in part with the findings of the other studies. In our
study the VE/VCO2 slope showed a non significant decrease after
8 weeks of SAT, and a significant decrease after 8 more weeks of
NST (Figure 1). Probably, to see a significant improvement in 8
weeks on this parameter it is necessary to exercise high intensity
training. However, in other studies, it has been observed that
there are not significant difference between an high-intensity
interval training and a continuous aerobic exercise training in
terms of peak heart rate, peak minute ventilation, VE/VCO2 slope
and respiratory exchange ratio, body mass, blood pressure, etc.
The obtained results are also controversial because pVO2
improved after 8 weeks of SAT and seemed to regress at the
baseline values after the second 8 week period while the VE/
VCO2 slope decreased significantly after 16 weeks of overall
training showing a non significant decrease after the first 8 week
period of SAT (Figure 2). A possible explanation might be that
those two parameters depend on different mechanisms and it is
possible that different training intensity versus duration slopes
have different effects on those mechanisms.
Our protocol was characterised by a low impact approach
(~60% of pVO2) during the first 8 week period. We also asked
patients to continue a low intensity training program at home
(NST) during the subsequent 8 weeks of SAT discontinuation.
It is possible that in our study the VE/VCO2 reduction (-6.5%
in 16 weeks) could be explained through an improvement of
lung diffusion and of alveolar-capillary membrane diffusing
capacity . Reduction could also be explained by a reduction of
interstitial pulmonary oedema . We observed an increasing
of both muscle and fat mass for the same body weight that could
be explained by the decrease of body interstitial water. We also
observed a non significant decreasing trend of peak dead spacetidal
volume ratio that could be explained by a redistribution
of the lung blood stream with reperfusion of the previously
excluded alveolar. Finally, an important variable to explain the
VE/VCO2 slope decrease might be the relative decrease of the
maximal ventilation after 16 weeks of overall training.
The CHF patients seemed to prefer low intensity training.
Physical and psychological symptoms, such as dyspnea and
a reduced aerobic performance, created a particular “fear”
towards physical activity, especially when it involved a high
intensity. A “low impact” training has a lot of benefits: it reduces
the onset risk of typical symptomatology, it is safer, it reduces the
number of drop-outs, it is more simple to perform and it could
be easily continued at home or monitored by qualified staff at
fitness centres. For the CHF patients it would be very important
to continue an active physical regimen for the rest of their lives
in order to maintain the benefits that exercise produces .
In the present study we showed that a low impact training
(SAT) could improve aerobic performance, functional ability and
the pVO2 values. A longer period of training (SAT+NST) seemed
to have a positive effect on the powerful prognostic indicator,
the VE/VCO2 slope. Further investigations could lead to a better
understanding of the role that different methods of training
have on the VE/VCO2 in CHF. To achieve an improvement of the
VE/VCO2 using a low impact approach, one probably needs a
longer period of training. New studies might clarify how training
intensity versus duration slope influences or modifies this
prognostic indicator in the CHF population. Though monitored
training (intensity correspondent to 60% of VO2 max) has
faster improvements of some parameters, training with slower
intensity is more tolerated and can be pursued autonomously
and therefore shows long term benefits. In conclusion we see
our results as a partial success considering that although the
importance of exercise training in the cardiovascular disease
population is recognised, only a low rate of CHF patients are
currently involved in exercise rehabilitation programs .
This study offers a contribution in making the data in the
literature more solid. In addition it presents a research and a
training protocol different from all other studies. Considering
also the strong prognostic value of VE/VCO2 slope and its correlation with other indicators [28-32], we can thus receive
important information from our study, also for the prescription
of a low intensity aerobic continuous exercise training to be
carried out at home or in the gym for a lifetime .
The study was held at the sports medicine unit of the
Noale-Venice in collaboration with the University of Padua,
within the project entitled “A multidisciplinary approach to
prevention of cardiovascular disease: Exercise prescription in
the cardiovascular patient”, coordinated by Dr. Patrizio Sarto,
and with the support of CassaMarca Foundation - Treviso and
the Foundation for the research and treatment of cardiovascular