Carátula del artículo
Acute Response to Aerobic Exercise on Autonomic Cardiac Control of
Patients in Phase III of a Cardiovascular Rehabilitation Program Following
Coronary Artery Bypass Grafting
Bruno Bavaresco Gambassi
Universidade Ceuma, Brazil
Fabiano de Jesus Furtado Almeida
Universidade Ceuma, Brazil
Universidade Federal do Maranhão, Brazil
Universidade Estadual do Maranhão, Brazil
Ana Eugênia Araújo Furtado Almeida
Universidade Ceuma, Brazil
Daniela Alves Flexa Ribeiro
Universidade Ceuma, Brazil
Rômulo Sérgio Araújo Gomes
Universidade Federal do Maranhão, Brazil
Luiz Filipe Costa Chaves
Universidade Ceuma, Brazil
Thiago Matheus da Silva Sousa
Universidade Ceuma, Brazil
Vinicius José da Silva Nina
Universidade Federal do Maranhão, Brazil
Universidade Federal do Maranhão, Brazil
Brazilian Journal of Cardiovascular Surgery, vol. 34, no. 3, pp. 305-310, 2019
Sociedade Brasileira de Cirurgia Cardiovascular
Received: 20 August 2018
Accepted: 17 March 2019
Funding
Funding source: Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e
Tecnológico
Contract number: 01019/13
Funding statement: Financial support: This study was funded by the Fundação de
Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão
(FAPEMA). APP-Universal 01019/13.
INTRODUCTION
Heart rate variability (HRV) reflects the variation in time between each heartbeat,
indicating the ability of autonomic cardiac control to respond to multiple
physiological stimuli, such as metabolic and mechanical alterations[1,2]. This process results from the interaction between stimuli
traveling via afferent pathways and responses to the efferent
pathways[1,2].
Any negative changes in the interaction between the central and peripheral nervous
systems (afferent and/or efferent pathways) decrease HRV, thus impairing autonomic
cardiac control and increasing the risk of cardiac death[3-6]. In this sense, Kleiger et al.[6] have demonstrated a strong
relationship between mortality risk and impaired autonomic cardiac control in
patients after acute myocardial infarction. Additionally, Quintana et
al.[7] have found
out that patients who had nonfatal infarction and cardiac events (death or
revascularization) presented lower HRV when compared to patients without these
conditions.
On the other hand, the practice of physical exercise may be used as an effective
non-pharmacological strategy to increase HRV[8,9]
and consequently reduce the aforementioned risks[3-6]. Although Bilińska et al.[10], Takeyama et al.[11], and Wolszakiewicz et
al.[12] have
demonstrated positive effects of physical exercise on autonomic cardiac control in
patients after coronary artery bypass grafting (CABG), few studies to date have
focused on this topic[13].
Additionally, after assessing a review study carried out by Almeida et
al.[13], we noticed
the paucity of research involving HRV, exercise, and patients undergoing CABG. Since
many health professionals work with this population, they must resort to the few
published relevant studies to prescribe the safest and most effective training
protocol. As such, further studies on this topic are needed. Thus, the aim of the
present study was to investigate the acute response to aerobic exercise on the
autonomic cardiac control of patients undergoing CABG.
METHODS
Patients
This is an experimental study, with pre and posttreatment tests designed for one
group. Using a convenience sampling, we recruited patients from the cardiac
rehabilitation program at the Department of Cardiac Surgery of the University
Hospital of Federal University of Maranhão (HUUFMA), President Dutra Unit, São
Luís, MA, Brazil. All patients signed an informed consent form after being
properly instructed about the study proposal, the procedures they would have to
undergo, and their potential risks and benefits.
The inclusion criteria were: patients who underwent a successful CABG (no
complications during surgery and/or in the following weeks), with normal
ejection fraction (>50%), Class I (according to New York Heart Association),
who participated in phases I and II of cardiac rehabilitation, not using any
beta blockers (e.g., atenolol), and having no impairment in the
musculoskeletal system.
Patients were excluded if they had a clinical diagnosis of diabetes mellitus
(uncontrolled), hypertension (uncontrolled), physical discomfort at any stage of
the study and/or any reaction to the tests (nausea, dizziness, discomfort,
feeling faint, tachycardia, excessive sweating), and if they failed to attend
the scheduled sessions.
The study sample consisted of eight patients (five males and three females) with
mean age of 58.6±7.7 years and mean body mass index of 26.7±3.5
kg.m2 (Table 1).
Table 1
Study patients' clinical profile (N=8).
Data are expressed as mean ± standard deviation or absolute
values and percentages. F=female; M=male
Procedures
From the first to the fourth visit to the laboratory, anthropometric measurements
were carried out, and participants were familiarized with the assessment
procedures and the exercise protocol on the cycle ergometer. In the following
week, evaluations were undertaken, and the exercise protocol was started.
Anthropometric Measurements
Total body mass in kilograms (kg) and height in centimeters (cm) were measured
using an anthropometric scale (PL-200, Filizola S.A. Pesagem e Automação, São
Paulo, SP, Brazil), with an accuracy of 50 g and 0.1 cm, properly calibrated
(NBR ISO/IEC 17025:2005). Body mass index was determined by body mass (kg)
divided by the square of height (m2).
Experimental Protocol
All patients underwent an aerobic exercise session (AES) on the cycle ergometer.
The session consisted of the following:
Five minutes of low-intensity warm-up (ranging from 7 to 9 CR-10 [Borg
scale]);
25 minutes of moderate-intensity exercise (resting heart rate +30 beats and
ranging from 11 to 13 CR-10 [Borg scale]);
Five minutes of low-intensity exercise (ranging from 7 to 9 CR-10 [Borg
scale])[14,15].
Assessment of Heart Rate Variability (Autonomic Cardiac Control)
To assess HRV, participants remained in a supine position with 30-degree head
elevation for 20 minutes. Electrocardiographic signal (protocol with three
derivations) was collected from 600 Hz sample rate to obtain beat-to-beat
intervals (R-R interval). This assessment was performed before, after one hour,
and after 24 hours of the exercise session.
At the end of the examination, the series of R-R intervals were extracted in text
format through the Kubios HRV Standard software for Windows (Kubios Oy, Kuopio,
Finland, Release 3.1.0) to obtain the variables related to time and frequency
domain measurements of HRV.
The following variables were selected for time domain measurements:
Root mean square of successive RR interval differences (rMSSD) (ms)
(parasympathetic component);
Percentage of successive RR intervals that differ by more than 50 ms (pNN50) (%)
(parasympathetic component).
The following variables were selected for frequency domain assessment:
High frequency (HF) (ms2) (0.15 to 0.4 Hz; parasympathetic component);
Low frequency (LF)/HF ratio (sympathetic and parasympathetic components with a
predominance of the sympathetic component).
The frequency domain measurement of HRV was performed using Fast Fourier
Transform (FFT) in intervals of five minutes, with an interpolation of 4 Hz and
50% overlap.
Statistical Analysis
Descriptive statistical analysis was performed using Prism software (GraphPad
Inc., San Diego, CA, USA, Release 7.0.0). Normality of data was tested using the
Shapiro-Wilk test. Comparisons between the means of the different times of
evaluation (baseline, one hour, and 24 hours) were undertaken by repeated
measures analysis of variance (ANOVA) along with Dunnett post-hoc test. All
measurements were two-tailed, and P-values were calculated with
significance levels set at 5%. Cohen’s effect size (ES) d was
calculated to determine the magnitude of the difference between the variables.
An ES between 0.20 and 0.49 was considered small, if between 0.50 and 0.79 it
was moderate, and an ES ≥ 0.80 was considered the largest magnitude of
effect[16].
RESULTS
Significant changes in autonomic cardiac control were observed after one AES.
Significant differences were found in the time domain, with positive changes in
rMSSD (one [P=0.017] and 24 hours [P=0.007]
post-session) (Figure 1 and Table 2). In frequency domain, we found a
significant difference in HF (ms2) (one hour [P=0.048]
post-session) (Table 2). The LF/HF ratio
reached statistical significance only after 24 hours (P=0.018)
post-session (Figure 1 and Table 2). Additionally, the largest ES was
observed only for the LF/HF ratio at one (d=-0.8) and 24 hours
(d=-1.3) post-session.
Fig. 1
Changes in root mean square of successive RR interval differences
(rMSSD) (ms), high frequency (HF) (ms2), and low frequency
(LF) indexes for each participant before (baseline), after one hour, and
after 24 hours of the exercise session.
Table 2
Comparison between autonomic cardiac control measurements at baseline and
at one hour and 24 hours after AES (N=8).
* Significant differences between baseline and one hour after exercise;† Significant difference between baseline and 24 hours after exercise. AES=aerobic exercise session; HF=high frequency; LF/HF ratio=ratio between low and high frequency components; pNN50=percentage of successive RR intervals that differ by more than 50
ms; rMSSD=root mean square of successive RR winterval differences SD=standard deviation
DISCUSSION
The main finding of the present study lies in the improved autonomic cardiac control
in patients undergoing CABG. This was demonstrated by increased vagal modulation
(rMSSD [ms] [one hour, P=0.017; and 24 hours,
P=0.007], HF [ms2] [one hour,
P=0.048]), and key changes in the LF/HF ratio (24 hours,
P=0.007) after one AES.
In a recent review study, Almeida et al.[13] have investigated the benefits promoted by different
physical exercise programs after CABG and found only two randomized controlled
trials with autonomic variables investigated. These authors pointed to two
studies[10,17], demonstrating the benefits of
exercise training in the standard deviation of NN intervals (SDNN) index and heart
rate (HR) recovery, respectively. Additionally, in a non-randomized controlled
trial, Wolszakiewiczet al.[12] have also found improved HRV in patients after CABG.
Given the above, we may say that, in the last 10 years, research associating physical
exercise, HRV, and patients after CABG have been underexplored in the relevant
literature. In earlier studies (>10 years), some researchers have demonstrated
positive effects of exercise in autonomic parameters (heart rate recovery) of
patients after CABG[18,19].
However, it is still unclear whether the heart rate recovery has a significant
prognostic value for patients after CABG. Thus, further studies about autonomic
cardiac control assessed by HRV measurement after exercise training are
required.
In this context, the present study evaluated the acute response to aerobic exercise
on the autonomic cardiac control of patients undergoing CABG. The largest ES was
observed for the LF/HF ratio at one (d=-0.8) and 24 hours
(d=-1.3) after AES when compared to baseline. The findings of
the present research may have important clinical implications, since higher HRV
levels are associated with improved autonomic cardiac control and lower risk of
cardiac death. Therefore, the improvements in HRV brought about by the study
protocol (aerobic exercise) may reduce the odds of poor outcomes in patients
undergoing CABG. In this sense, further randomized controlled trials (chronic
intervention) are needed to support our findings.
On the other hand, some studies involving other populations and different
intensities, volumes, and types of training would seem to call our findings into
question. In this sense, some research studies have highlighted a reduction in HRV,
following acute physical exercise[20-23].
According to Michael et al.[24], when assessing autonomic cardiac control responses to
exercise practice, it is important to analyze how the variables (volume and
intensity) are handled and the exercise modality used. Additionally, it seems that
the effects of exercise on HRV also depend on how much autonomic cardiac control is
committed (i.e., level of the impairment caused by chronic
degenerative diseases)[8,25-28]. As such, professionals in the
area of cardiac rehabilitation should always bear in mind that acute exercise
practice exerts stress on the organism, requiring a balanced prescription between
workout and recovery. When the stimulus is adequate in relation to the rest period,
we expect recovery and/or that the patients have exercise-related beneficial effects
on autonomic cardiac control. In this sense, corroborating our findings, Francica et
al.[29] have
demonstrated positive effects on HRV in poststroke individuals 20 minutes after the
end of exercise test.
In view of the above, the recommendations of the American College of Sports
Medicine[15],
followed in the present study, may be considered fully adequate for the population
of our study, since the physical stress was not severe enough to prevent recovering
of the autonomic cardiac control after 35 minutes of the exercise. In addition,
improved HRV was demonstrated after aerobic exercise with moderate volume and
intensity as mentioned above. In line with our study, Michael et
al.[30] have also
demonstrated a rapid reactivation of vagal HRV measurements/values, with a recovery
to baseline within 5-10 minutes after exercise practice in the intensity of the
first ventilation threshold. According to these authors, exercise above this
intensity may result in delayed vagal HRV recovery.
Limitations
The absence of a control group, the lack of randomization, and the small sample
size may be considered limitations. However, given the limited number of
published researches involving HRV, exercise, and patients undergoing CABG, our
findings may encourage further studies on this topic.
CONCLUSION
The practice of (acute) aerobic exercise improved autonomic cardiac control in
patients undergoing CABG. However, further randomized controlled trials using the
same exercise modality and population of the present study should be undertaken with
stricter control of variables (internal and external validity) to lend support to
our findings.
ACKNOWLEDGMENTS
Fabiano de Jesus Furtado Almeida and Vinicius José Nina are grateful to the Fundação
de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão
(FAPEMA).
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Notes
Notes
Financial support: This study was funded by the Fundação de Amparo à Pesquisa e
ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA). APP-Universal
01019/13.
This study was carried out at the Universidade Federal do Maranhão (UFMA), São
Luís, MA, Brazil.
Conflict of interest declaration
No conflict of interest.
Author notes
Correspondence Address: Vinicius José da Silva Nina,
https://orcid.org/0000-0003-3017-7459, Hospital Universitário da Universidade
Federal do Maranhão (HUUFMA), R. Barão de Itapari, 227 - Centro, São Luís, MA,
Brazil. Zip Code: 65020-070, E-mail:
rvnina@terra.com.br
