Methodological factors in measuring heart rate-based indices and effect of exercise-based cardiac rehabilitation on mortality predictors: from athletes to patients
- Autores: Agustín Manresa Rocamora
- Directores de la Tesis: Francisco J. Vera García (dir. tes.), Manuel Moya Ramon (codir. tes.)
- Lectura: En la Universidad Miguel Hernández de Elche ( España ) en 2021
- Idioma: español
- Tribunal Calificador de la Tesis: Francisco Javier Moreno Hernández (presid.), Vicente E. Climent Payá (secret.), Alberto Jorge Carvalho Alves (voc.)
- Programa de doctorado: Programa de Doctorado en Deporte y Salud por la Universidad Miguel Hernández de Elche
- Materias:
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- Resumen
Background: Parasympathetic nervous system (PNS) activity can be indirectly assessed by heart rate (HR)-based indices (i.e., resting HR, resting vagal-related HR variability [HRV] indices, and post-exercise HR recovery 1 min [HRR 1 min]). Decreased PNS activity is considered an independent mortality predictor. In the same vein, cardiorespiratory fitness (CRF), assessed by peak oxygen uptake (V̇O2 peak), is also considered an independent mortality predictor. There is evidence showing the positive effect of exercise-based cardiac rehabilitation (CR) on mortality rates in patients with coronary artery disease (CAD). However, the results of previous studies of the effects of exercise-based CR on mortality predictors (i.e., HR-based indices and V̇O2 peak) are controversial. The sparse findings could be due to the influence of methodological factors (e.g., breathing pattern, use of averaged or isolated values, and assessment position) on the sensitivity of HR-based indices to detect PNS hyperactivity, which has mainly been investigated in endurance-trained athletes with functional overreaching (F OR) symptoms. Moreover, controversial findings about the effects of exercise-based CR on mortality predictors could be explained by the influence of potential moderator variables (e.g., aerobic training method) on the training-induced effect. In this regard, previous systematic reviews with meta-analyses showed that high-intensity interval training (HIIT) enhances V̇O2 peak to a higher extent than moderate continuous training (MCT) in patients with CAD. Nonetheless, there is less evidence of the influence of other variables (e.g., training frequency) on the effect of exercise-based CR on CRF and PNS activity. Finally, high heterogeneity in the individual response to the same predefined training programme has also been previously reported. Therefore, the effects of individualised training programmes based on daily HRV measurements (i.e., HRV-guided training) have been tested in healthy people (i.e., sedentary or physically active people and endurance-trained athletes) and in patients with chronic heart failure, showing optimistic findings for improving CRF. However, the effects of HRV-guided training on HR-based indices have been less studied, and it has not been tested in patients with CAD.
Therefore, the main objectives of this doctoral thesis were: a) to study the influence of methodological factors on the sensitivity of HR-based indices for inferring increased PNS activity; and b) to know the effect of exercise-based CR (i.e., predefined training and HRV-guided training) on mortality predictors (i.e., HR-based indices and V̇O2 peak) in patients with CAD.
Methods: Systematic reviews with meta-analyses and experimental methods were used to address the aims of this doctoral thesis. Regarding the systematic reviews with meta-analyses, electronic searches were conducted in at least two databases. Selected terms were established based on the PICOS (participants, intervention, comparison, outcomes, and study design) guideline. Random-effects models of standardised mean difference or mean difference were estimated. On the other hand, in the experimental study, male and female adult patients diagnosed with CAD were randomly allocated to the HRV-guided training group (HRV G = 11) or the predefined training group (PRED G = 12). All the participants measured their HRV daily at home after waking up and trained three times a week for six weeks. Patients allocated to the HRV G performed HIIT sessions based on their daily HRV measurements, while those patients allocated to the PRED G followed a predefined training programme. HR-based indices and V̇O2 peak were assessed before and after the exercise-based CR programme. Regarding vagal-related HRV indices, isolated values were obtained in the time-domain (the root-mean-square difference of successive normal R R intervals [RMSSD]) and frequency-domain (high frequency [HF]), as well as by using the Poincaré plot method (the standard deviation of the instantaneous beat to beat R R interval variability [SD1]). In addition, daily RMSSD values measured at home across one week were pooled to obtain weekly averaged RMSSD before and after the intervention. Comparisons between the two groups were reported as difference in mean or median changes with 95% confidence interval. Moreover, the effect of exercise-based CR, regardless of the training group, on mortality predictors was also estimated if there was no difference between the two training prescription methods.
Results: The first systematic review with meta-analysis showed an increase in averaged vagal-related HRV values (i.e., weekly averaged RMSSD) in F OR athletes, while no changes in isolated vagal-related HRV indices were noticed. In addition, the results showed increased HRR 1 min in F OR athletes. The second and third systematic review with meta-analysis showed that exercise-based CR enhances HRR 1 min and V̇O2 peak, respectively, in patients with CAD. The findings also confirmed that HIIT is more effective than MCT for improving V̇O2 peak. Regarding heterogeneity analyses, the training-induced effect on HRR 1 min was higher in studies which included younger patients. The improvement in V̇O2 peak after MCT was larger in studies which performed training sessions on a bicycle, as well as in studies which included patients with worse prognosis (e.g., increased risk of a new event) or lower CRF at baseline. In contrast, the results of the included studies of the effect of exercise-based CR programmes on vagal-related HRV indices (i.e., RMSSD or HF) were controversial. The findings showed an increase in RMSSD after an exercise-based CR programme. Nonetheless, there were no changes in HF, and the results of the included studies were sparse (i.e., high heterogeneity). In addition, no influence of potential moderator variables on the training-induced effect on HF was found. The fourth systematic review with meta-analysis showed that, accounting for methodological factors, HRV-guided training is more effective than predefined training for improving vagal-related HRV indices (i.e., RMSSD and SD1) in healthy people (i.e., sedentary or physically active people and endurance-trained athletes). Nonetheless, no differences were found between HRV-guided training and predefined training for improving CRF. In the same line, the fifth study showed that, taking methodological factors into account, HRV-guided training increases vagal-related HRV indices (i.e., weekly averaged RMSSD) to a greater extent than predefined training in patients with CAD. Regardless of the training prescription method used, the results showed that exercise-based CR enhances resting HR and V̇O2 peak, but not HRR 1 min, in patients with CAD.
Conclusions: PNS hyperactivity found in F OR athletes can be identified by means of HRR 1 min and weekly averaged RMSSD. On the other hand, exercise-based CR is effective for improving PNS tone (i.e., HRR 1 min) and CRF in patients with CAD. Nonetheless, the training-induced effect on PNS modulation is more controversial. Finally, accounting for methodological factors, HRV-guided training seems to be more effective than predefined training for enhancing PNS modulation (e.g., weekly averaged RMSSD) in patients with CAD, as well as in healthy people. The results of this doctoral thesis show the importance of considering methodological factors in measuring vagal-related HRV indices to detect increased PNS modulation, as well as the beneficial effect of exercise-based CR programmes on mortality predictors in patients with CAD.
