Vol.3, No.8, 477-481 (2011)
doi:10.4236/health.2011.38078
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Health
Using of spectral analysis of heart rate variability for
increasing reliability of bicycle ergometry results
Vladimir Ivanovich Gridnev, Anton Robertovich Kiselev, Olga Mikhailovna Posnenkova,
Vladimir Alexandrovich Shvartz
Centre of New Cardiological Informational Technologies, Saratov Research Institute of Cardiology, Saratov, Russia;
Received 18 November 2010; revised 25 April 2011; accepted 18 June 2011.
ABSTRACT
The aim was to study the suitability of the heart
rate variability (HRV) spectral parameters for
evaluations of bicycle ergometry results in
coronary heart disease (CHD) patients. Methods.
Our study included 243 male CHD patients aged
49±8 years. The coronary atherosclerosis was
assessed by coronary angiography. T he results
of bicycle ergometry, Doppler echocardio-
graphy and HRV spectral analysis were also
analyzed. The duration of each stage of bicycle
ergometry was 3 min, the initial load value was
25 W. Dynamic load continued until the patient
had reached 75% of heart rate from his maximal
age level. The maximal level of load achieved
(i.e. load tolerance) was taken into conside-
ration. We calculated sensitivity (Se), specificity
(Sp), likelihood ratios of positive (LR+) and
negative (LR–) bicycle ergometry results. Re-
sults. All patients had similar clinical chara-
cteristics. LR+ become maximal under the
moderate load tolerance. LR- are maximal in the
CHD patients with high load tolerance. Thus, the
excessiveness of false-negative results of bi-
cycle ergometry is in CHD patients with high
load tolerance. Reliability of results of bicycle
ergometry increased under using assessments
of low-frequency (LF) range power of HRV
spectrum. Conclusions. Thus,the using of LF
range power of HRV spectrum increases relia-
bility of bicycle ergometry (or other load tests)
results in CHD p atients.
Keywords: Heart Rate Variability; Bicycle
Ergometry; Coronary Heart Disease
1. INTRODUCTION
Submaximal exercise tests are most frequently used in
diagnosis of coronary heart disease (CHD). But the sen-
sitivity (Se) and specificity (Sp) of these kind of tests are
limited [1]. Defining the conditions under which exer-
cise tests may produce both true and false results, is an
important task of applied cardiology.
It was shown that the heart rate variability (HRV) pa-
rameters turned out to be sensitive indicator of a myo-
cardial and coronary status in CHD patients [2,3]. The
model of heart control based on a baroreflex feedback
loop [4-8] has great importance for researches of auto-
nomic heart control. This model explains an origin of
low-frequency (LF) component of HRV [9-15]. Thus, LF
range of HRV spectrum is of the interest for evaluation
of autonomic heart control in CHD patients during load
tests.
The aim was to study the suitability of HRV spectral
parameters for evaluations of bicycle ergometry results
in CHD patients.
2. METHODS
2.1. Subjects
The study was approved by the Ethics Committee of
the Saratov Research Institute of Cardiology in Saratov,
Russia, and informed consent was obtained from all par-
ticipants. Our study included 243 male CHD patients
aged 49 ± 8 years. 132 CHD patients had acute myocar-
dial infarction six months prior to the start of the study.
Pathological Q-wave on electrocardiogram (ECG) was
observed in 67 CHD patients. Angina pectoris of I-II
functional classes was observed in 86 CHD patients and
120 CHD patients had angina pectoris of III-IV func-
tional classes. 59 CHD patients had arterial hyperten-
sion.
We excluded from the study CHD patients with renal
pathology, valves heart disease, rhythm and conduction
disorders hindering the HRV analysis.
2.2. Measurements and Protocol
The coronary atherosclerosis was assessed by selec-

V. I. Gridnev et al. / Health 3 (2011) 477-481
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
478
).
tive coronary angiography in all CHD patients. The se-
verity of coronary atherosclerosis was assessed in ac-
cording with the degree of maximal stenosis of coronary
arteries (no less 75%). Bicycle ergometry results, Dop-
pler echocardiography results and HRV spectral analysis
were also estimated.
Systolic and diastolic sizes of heart left ventricle,
ejection fraction of the left ventricle (EF), the velocity of
circumferential fiber shortening (Vcf), isovolumetric
relaxation time (IRT) and the condition of the left ven-
tricle local contractility were determined by Doppler
echocardiography.
Bicycle ergometry were performed by stepwise in-
creasing load under electrocardiography (ECG) moni-
toring. The initial load was 25 W. Bicycle ergometry
continued till each CHD patient reached 75% of maxi-
mal heart rate level [16]. In case of ST segment depres-
sion no less 2 mm in one ECG lead during bicycle er-
gometry, this load test results were considered to be po-
sitive. Bicycle ergometry result was considered negative
if CHD patient either reached 50% of maximal heart rate
level at the highest point of load or performed load of no
less 150 W during 3 minutes without any criteria of test
cessation. CHD patients with other causes of test cessa-
tion were not included in this study. The maximal level
of load achieved (i.e. load tolerance) was assessed. All
CHD patients have stopped the treatment with nitrates
(24 hours prior) and beta-blockers (3 - 7 days prior) be-
fore bicycle ergometry.
ECG recorded during 3 min both for rest and load of
25 W during bicycle ergometry. ECG signal was sampled
at 250 Hz and digitized at 14 bits. For further analysis
were only ECG and PPG records without artifacts, ex-
trasystoles and considerable trends were left. ECG signal
had been recorded between 13 and 15 hours.
2.3. Statistical and Data Anal ysis
Spectral characteristics of HRV were calculated using
parametric method of spectrum estimation based on 14
order autoregression model construction. High-frequency
(HF) range, 0.15 - 0.4 Hz, and LF range, 0.04 - 0.15 Hz,
of HRV were analysed [17].
Sensitivity (Se), specificity (Sp), likelihood ratios of
positive (LR+) and negative (LR-) bicycle ergometry
results were estimated.
For a statistical analysis the software package Statis-
tica 6.1 was used. We apply the Shapiro–Wilk test to
check whether the HRV spectral data are approximately
normally distributed. Since these data occur to be non-
normal their further analysis was carried out using non-
parametric statistical methods. To compare the variables
we used the Mann–Whitney test. Continuous variables
are reported as medians (Me) with inter-quartile ranges
(25%, 75%). Categorical data are presented as frequen-
cies and percentages. The obtained estimations were
considered statistically significance if P < 0.05.
3. RESULTS AND DIS CUSSION
CHD patients have been classified in two groups, ac-
cording to bicycle ergometry results:
 First group included 125 CHD patients (aged 50 ± 7
years) with positive bicycle ergometry results,
 Second group included 118 CHD patients (aged 47 ±
8 years) with negative bicycle ergometry results.
It was shown that both CHD patient’s groups had
similar clinical characteristics (age, sex, frequency of
myocardial infarction, arterial hypertension, EF, systolic
and diastolic sizes of heart left ventricle, etc.
The group of CHD patients with positive bicycle ergo-
metry results differed from the group with negative re-
sults in following characteristics: 1) less load tolerance
by 36% (P < 0.001); 2) more clinically severe angina
pectoris: 56% of CHD patients had III-IV functional
class of angina and only 30% patients had angina of I-II
functional class (versus 36% and 42% respectively in
CHD patients with the negative bicycle ergometry re-
sults).
For the further analysis all CHD patients were divided
into three groups according to the load tolerance level:
low level (<75 W), moderate level (75 - 125 W), high
level (>125 W). It is theoretically supposed that the
load tolerance correlates with coronary atherosclerosis
degree. These groups of patients had similar clinical
characteristics. Frequency of positive bicycle ergometry
results was greater in group of CHD patients with low
load tolerance in comparison with other groups (P =
0.003). Angina was principal cause of bicycle ergometry
cessation in the group of patients with low tolerance.
Frequency of ECG ischemic changes was greater in the
group of CHD patients with high tolerance (77%) than in
groups with moderate (64%) and low (41%) tolerance
levels.
Frequency of significant coronary arteries stenosis
decreased reliably under increase of the load tolerance in
these patients groups (Table 1). In the group of CHD
patients with high load tolerance, frequency of signifi-
cant coronary arteries stenosis decreased 1.7 times (р <
0.001) in compare with the group with low tolerance,
and it decreased in 1,5 times (р = 0.02) in group with
high tolerance compared with group of patients with
moderate tolerance (р = 0.03). It is shown that Se of bi-
cycle ergometry worsens under the decrease of load tol-
erance in CHD patients (Table 1).
Spectral analysis of HRV for the rest and load of 25 W
displayed reliable differences between the groups of
CHD patients with positive and negative bicycle er-

V. I. Gridnev et al. / Health 3 (2011) 477-481
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
479
Ta b le 1 . Coronary atherosclerosis in CHD patients with diffe-
rent load tolerance. Dependence of bicycle ergometry sensitiv-
ity (Se) and specificity (Sp) from load tolerance in these pa-
tients.
Indices
Low tolerance
level
(<75 W)
n = 54
Moderate
tolerance level
(75 - 125 W)
n = 113
High
tolerance level
(>125 W)
n = 59
Coronary artery
stenosis,
% of CHD patients
78 71 47
Se, % 93 69 29
Sp, % 25 79 81
gometry results (Figure 1). CHD patients with negative
test results had level of autonomic heart control differing
from CHD patients with positive results in presence of
similar clinical and instrumental status and coronary
atherosclerosis. LF and HF ranges power of HRV spec-
trum was greater in CHD patients with the negative bi-
cycle ergometry results than in other groups.
Load tolerance and HRV spectral parameters corre-
lated with negative bicycle ergometry results under rest
in CHD patients; multiple correlation coefficient was
0,41 (р = 0,004). In group of CHD patients with positive
test results there was no correlation between the HRV
spectral parameters and load tolerance (P = 0.26).
These distinctions of LF range became a basis for im-
provements of diagnostic effectiveness of bicycle ergo-
metry. Using the load of 25 W allows supposing auto-
nomic heart control to be in some functional activity.
This fact is a way of condition standardization for using
of HRV spectral analysis. Three ranges of LF power
were chosen in all CHD patients. They were the follow-
ing for the rest: <200 ms2, 200 - 400 ms2, >400 ms2. And
they were the following for 25 W load: <75 ms2, 75 -
150 ms2, >150 ms2. The range intervals correspond to
33% and 66% percentiles of values in the sample of the
examined patients, i.e. about one third of all CHD pa-
tients are presented in each group. It is shown that bicy-
cle ergometry is of the most diagnostic value under LFrest
> 400 ms2 and LF25 W >150 ms2. In these cases, sum of
Se and Sp is maximal (Figure 2). Thus, for increase a
reliability of bicycle ergometry in CHD patients It is
possible to use LF range spectral power, it is applied
especially for positive bicycle ergometry results (Figure
3). This concerns both standard bicycle ergometry pro-
cedure and analysis of bicycle ergometry results taking
into account load tolerance (Tables 2 and 3). Positive
results of bicycle ergometry in CHD patients are more
reliable under moderate load tolerance and LF25 W >
150 ms2. Otherwise a diagnostic effectiveness of bicycle
ergometry decreases. Reliability of negative bicycle er-
gometry results is maximal under high load tolerance,
independently of LF range power of HRV spectrum.
Figure 1. HRV indices in CHD patients with positive
and negative bicycle ergometry results in rest (a) and
load of 25 W (b).
Figure 2. Assessments of Se and Sp of bicycle er-
gometry in CHD patients based LF range power in
rest (a) and load of 25 W (b).

V. I. Gridnev et al. / Health 3 (2011) 477-481
Copyright © 2011 SciRes. http://www.scirp.org/journal/HEALTH/
480
Figure 3. Likelihood ratio (LR) of standard procedure of bicycle ergometry results interpretation and likelihood ratio
(LR) of complex assessment of bicycle ergometry results (tolerance level and the power of LF range of HRV spec-
trum) under the rest and 25 W loading. (a) LR(+) under rest; (b) LR(+) under 25 W loading; (c) LR(–) under rest; (d)
LR(–) under 25 W loading.
Table 2. Likelihood ratio (LR) the bicycle ergometry results in
CHD patients for the LF range spectral power of HRV under
the rest.
Probability of false-negative bicycle ergometry out-
comes keeps on the level of standard procedure of test-
ing results evaluation. It follows from this that any nega-
tive test result is characterized by low reliability and thus
could not be used for the assessment of the severity of
coronary pathology. It agrees with the European Asso-
ciation of Cardiology data showing that probability of
CHD in a 65 years patient with true angina is more, then
75% even if the bicycle ergometry showed a negative
result [18]. At the same time, the reliability of positive
bicycle ergometry results could be assessed taking into
consideration the load tolerance and the spectral power
in LF range of HRV. As a criterion of the diagnostic
value of the test results the likelihood ratio (LR) index
could be used. This index gives direct knowledge of the
probability of CHD in the presence of a positive or nega-
tive physical load test outcome. In the clinic of Saratov
Institute of Cardiology LR+ values no less then 5 were
used as a threshold for the positive result of exercise
testing and LR– values less then 0.2 were used for the
negative one. In the case of exceeding the likelihood
ratio threshold values it is possible to consider that an
exercise test result reliably conform to the clinical pic-
ture of illness. Otherwise, if LR values do not exceed the
threshold ones, then a stress test result could be consid-
ered unreliable.
Load tolerance (W)
LF range spectral
power, ms2 <75 75  125 >125
Positive result of bicycle ergometry
<200 ms2 3.1 8.6 3.9
200  400 ms2 2.5 6.9 3.2
>400 ms2 5.3 14.5 6.6
Negative result of bicycle ergometry
<200 ms2 0.2 0.2 0.4
200  400 ms2 0.2 0.2 0.5
>400 ms2 0.2 0.2 0.4
Table 3. Likelihood ratio (LR) of bicycle ergometry results in
CHD patients for the LF range spectral power of HRV under
25 W loading.
Load tolerance (W)
LF-range spectral
power, ms2 <75 75  125 >125
Positive result of bicycle ergometry
<75 ms2 2.3 6.3 2.9
75  150 ms2 4.1 11.2 5.1
>150 ms2 5.8 15.8 7.2
Negative result of bicycle ergometry
<75 ms2 0.2 0.2 0.4
75  150 ms2 0.2 0.2 0.5
>150 ms2 0.2 0.2 0.4
Openly accessible at

V. I. Gridnev et al. / Health 3 (2011) 477-481
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
481
The approach offered allows to determine bicycle er-
gometry result reliability in cases of positive or negative
results of the test individually in each patient and de-
crease possibility of diagnostic mistakes. Limitations of
the method offered for CHD diagnostics are initial heart
rate increase (heart rate more then 100 beats per minute)
and impossibility to obtain suitable for the spectral an-
alysis bicycle ergometry rhythmograms due to noise and
artifacts presence.
4. CONCLUSIONS
Thus, the analysis of spectral power of LF range of
HRV allows to advance diagnostic value of bicycle er-
gometry results in CHD patients. It is necessary to use a
complex assessment of bicycle ergometry results taking
into account the load tolerance level and a power of LF
range of HRV spectrum. Combined use of the load tol-
erance and LF range spectral power levels (in rest and
during 25 W loading) the validity of an individual exer-
cise raises 2 - 3 times (in particular, bicycle ergometry)
test result compared with standard procedure of the bi-
cycle ergometry results analysis in CHD patients.
Table 2 can be used for preliminary assessment of the
bicycle ergometry results especially in CHD patients
with low levels of LF range spectral power (<400 ms2).
Further the obtained value of likelihood ratio can be
specified with the help of Tab le 3. Table data are con-
structed for CHD patients with hemodynamically sig-
nificant atherosclerotic stenosis at least one coronary
vessel (stenosis degree >50% according to data of coro-
narography).
REFERENCES
[1] European Society of Cardiology (1993) Guidelines for
cardiac exercise testing: ESC working group on exercise
physiology, physiopathology and electrocardiography.
European Heart Journal, 14, 969-988.
[2] Porta, C. and Bernardi, L. (2001) Interaction between
respiration, autonomic function, and respiratory pattern
inheart failure. New possibilities of rehabilitation inter-
vention. Italian Heart Journal, 2, 624-627.
[3] Juhani, K.E., Marku, J.I., Heikki, V.H., et al. (1993) Re-
sponses of heart rate variability to coronari occlusion
during coronari angioplasty. American Journal of Cardi-
ology, 72, 1026-1030.
doi:10.1016/0002-9149(93)90857-9
[4] De Boer, R.W., Karemuker, J.M. and Stracker, J. (1986)
On the spectral analysis of blood pressure variability.
American Journal of Physiology, 251, 685-687.
[5] De Boer, R.W., Karemuker, J.M. and Stracker, J. (1985)
Relationships between short-term blood pressure fluctua-
tions and heart variability in resting subjects. II: A simple
model. Medical & B iological Engineering & Computing,
23, 359-364. doi:10.1007/BF02441590
[6] De Boer, R.W., Karemuker, J.M. and Stracker, J. (1985)
Relationships between short-term blood pressure fluctua-
tions and heart variability in resting subjects. I: A spectral
analysis approach. Medical & Biological Engineering &
Computing, 23, 352-358. doi:10.1007/BF02441589
[7] De Boer, R.W., Karemuker, J.M. and Stracker, J. (1987)
Hemodynamic fluctuations and baroreflex sensitivity in
humans: A beat-to-beat model. American Journal of
Physiology, 253, 680-687.
[8] Madwed, J.B., Albrecht, P., Mark, R.G. and Cohen, R.J.
(1989) Low-frequency oscillation in arterial pressure and
heart-rate: A simple computer model. American Journal
of Physiology, 256, 1573-1579.
[9] Pagani, M. and Malliani, A. (2000) Interpreting oscilla-
tions of muscle sympathetic nerve activity and heart rate
variability. Journal of Hypertension, 18, 1709-1719.
doi:10.1097/00004872-200018120-00002
[10] Sleight, P., La Rovere, M.T., Mortara, A., et al. (1995)
Physiology and pathophysiology of heart rate variability
in humans: is power spectral analysis largely an index of
baroreflex gain? Clinical Science, 88, 103-109.
[11] Richter, D.W. and Spyer, K.M. (1990) Cardiorespiratory
control. Oxford University Press, New York.
[12] Cevese, A., Grasso, R., Poltronieri, R. and Schena, F.
(1995) Vascular resistance and arterial pressure low-fre-
quency oscillations in the anesthetized dog. American
Journal of Physiology, 268, 7-16.
[13] Whittam, A.M., Claytont, R.H., Lord, S.W., et al. (2000)
Heart rate and blood pressure variability in normal sub-
jects compared with data from beat-to-beat models de-
veloped from de Boer’s model of the cardiovascular sys-
tem. Physiological Measuremen, 21, 305-318.
doi:10.1088/0967-3334/21/2/310
[14] Bernardi, L., Passino, C., Spadacini, G., et al. (1997)
Arterial baro-receptor as determinants of 0.1 Hz and res-
piration-related changes in blood pressure and heart rate
spectra. IOS Press, Amsterdam.
[15] Simon, C.M. (2002) Neural influeces on cardiovascular
variability: Possibilities and pitfalls. The American
Physiological Society, 282, 6-20.
[16] Andersen, K., Shephard, R., Denolin, H., et al. (1979)
Fundamentals of exercise testing. WHO, Geneva.
[17] American Heart Association (1996) Heart rate variability.
Standarts of measurement, physiological interpretation
and clinical use. Circulation, 93, 1043-1065.
doi:10.1161/01.CIR.93.5.1043
[18] European Society of Cardiology (1997) Management of
stable angina pectoris: Recommendations of the task
force of the European Society of Cardiology. European
Heart Journal, 18, 394-413.