Cardiac vagal modulation of heart rate during prolonged submaximal exercise in animals with healed myocardial infarctions: Effects of training

Dept. of Physiology, The Ohio State University, Columbus, OH 43210-1218, USA.
AJP Heart and Circulatory Physiology (Impact Factor: 3.84). 05/2006; 290(4):H1680-5. DOI: 10.1152/ajpheart.01034.2005
Source: PubMed


The present study investigated the effects of long-duration exercise on heart rate variability [as a marker of cardiac vagal tone (VT)]. Heart rate variability (time series analysis) was measured in mongrel dogs (n = 24) with healed myocardial infarctions during 1 h of submaximal exercise (treadmill running at 6.4 km/h at 10% grade). Long-duration exercise provoked a significant (ANOVA, all P < 0.01, means +/- SD) increase in heart rate (1st min, 165.3 +/- 15.6 vs. last min, 197.5 +/- 21.5 beats/min) and significant reductions in high frequency (0.24 to 1.04 Hz) power (VT: 1st min, 3.7 +/- 1.5 vs. last min, 1.0 +/- 0.9 ln ms(2)), R-R interval range (1st min, 107.9 +/- 38.3 vs. last min, 28.8 +/- 13.2 ms), and R-R interval SD (1st min, 24.3 +/- 7.7 vs. last min 6.3 +/- 1.7 ms). Because endurance exercise training can increase cardiac vagal regulation, the studies were repeated after either a 10-wk exercise training (n = 9) or a 10-wk sedentary period (n = 7). After training was completed, long-duration exercise elicited smaller increases in heart rate (pretraining: 1st min, 156.0 +/- 13.8 vs. last min, 189.6 +/- 21.9 beats/min; and posttraining: 1st min, 149.8 +/- 14.6 vs. last min, 172.7 +/- 8.8 beats/min) and smaller reductions in heart rate variability (e.g., VT, pretraining: 1st min, 4.2 +/- 1.7 vs. last min, 0.9 +/- 1.1 ln ms(2); and posttraining: 1st min, 4.8 +/- 1.1 vs. last min, 2.0 +/- 0.6 ln ms(2)). The response to long-duration exercise did not change in the sedentary animals. Thus the heart rate increase that accompanies long-duration exercise results, at least in part, from reductions in cardiac vagal regulation. Furthermore, exercise training attenuated these exercise-induced reductions in heart rate variability, suggesting maintenance of a higher cardiac vagal activity during exercise in the trained state.

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Available from: George Billman, Oct 27, 2014
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    • "As previously reported (Billman et al., 1984, 2006; Billman, 2006; Billman and Kukielka, 2006, 2007; Kukielka et al., 2006; Holycross et al., 2007), exercise training completely suppressed VF induced by the exercise plus ischemia test (all nine dogs were protected from VF). In contrast, VF was still induced in the all of the sedentary susceptible animals (n = 7) that were tested at the end of the 10-week sedentary period; three animals could not be tested due to failure of the hydraulic occluder. "
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    ABSTRACT: Aim: Increased sodium/calcium exchanger activity (NCX1, an important regulator of cardiomyocyte cystolic calcium) may provoke arrhythmias. Exercise training can decrease NCX1 expression in animals with heart failure improving cytosolic calcium regulation, and could thereby reduce the risk for ventricular fibrillation (VF). Methods: To test this hypothesis, a 2-min coronary occlusion was made during the last minute of exercise in dogs with healed myocardial infarctions; 23 had VF (S, susceptible) and 13 did not (R, resistant). The animals were randomly assigned to either 10-week exercise training (progressively increasing treadmill running; S n = 9; R n = 8) or 10-week sedentary (S n = 14; R n = 5) groups. At the end of the 10-week period, the exercise + ischemia test provoked VF in sedentary but not trained susceptible dogs. On a subsequent day, cardiac tissue was harvested and NCX1 protein expression was determined by Western blot. RESULTS: In the sedentary group, NCX1 expression was significantly (ANOVA, P < 0.05) higher in susceptible compared to resistant dogs. In contrast, NCX1 levels were similar in the exercise trained resistant and susceptible animals. Conclusion: These data suggest that exercise training can restore a more normal NCX1 level in dogs susceptible to VF, improving cystolic calcium regulation and could thereby reduce the risk for sudden death following myocardial infarction.
    Frontiers in Physiology 02/2011; 2(2):3. DOI:10.3389/fphys.2011.00003 · 3.53 Impact Factor
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    • "From experiments with dogs, Billmann et al. (11) considered the possibility that even independently from physical training, increased baroreflex sensitivity would be associated with a reduced risk for cardiac mortality after myocardial infarction. Also in experiments with dogs after healed myocardial infarction, Kukielka et al. (12) reported that submaximal long-duration exercise reduced cardial vagal regulation initially, but further exercise training attenuated the initially exercise-induced reductions in heart rate variability, suggesting a maintained higher cardiac vagal activity during exercise in the trained state. On the other hand, Duru et al. (13) found no significant effect of high-intensity exercise training on HRV indexes among patients with new-onset left ventricular dysfunction after myocardial infarction after 1, 2 and 12 months of training in a rehabilitation center, despite beneficial effects on clinical variables. "
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    ABSTRACT: Relaxation techniques are established in managing of cardiac patients during rehabilitation aiming to reduce future adverse cardiac events. It has been hypothesized that relaxation-training programs may significantly improve cardiac autonomic nervous tone. However, this has not been proven for all available relaxation techniques. We tested this assumption by investigating cardiac vagal modulation during yoga.We examined 11 healthy yoga practitioners (7 women and 4 men, mean age: 43 +/- 11; range: 26-58 years). Each individual was subjected to training units of 90 min once a week over five successive weeks. During two sessions, they practiced a yoga program developed for cardiac patients by B.K.S. Iyengar. On three sessions, they practiced a placebo program of relaxation. On each training day they underwent ambulatory 24 h Holter monitoring. The group of yoga practitioners was compared to a matched group of healthy individuals not practicing any relaxation techniques. Parameters of heart rate variability (HRV) were determined hourly by a blinded observer. Mean RR interval (interval between two R-waves of the ECG) was significantly higher during the time of yoga intervention compared to placebo and to control (P < 0.001 for both). The increase in HRV parameters was significantly higher during yoga exercise than during placebo and control especially for the parameters associated with vagal tone, i.e. mean standard deviation of NN (Normal Beat to Normal Beat of the ECG) intervals for all 5-min intervals (SDNNi, P < 0.001 for both) and root mean square successive difference (rMSSD, P < 0.01 for both). In conclusion, relaxation by yoga training is associated with a significant increase of cardiac vagal modulation. Since this method is easy to apply with no side effects, it could be a suitable intervention in cardiac rehabilitation programs.
    Evidence-based Complementary and Alternative Medicine 01/2008; 4(4):511-7. DOI:10.1093/ecam/nem087 · 1.88 Impact Factor
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    ABSTRACT: Les chiens de la gendarmerie sont amenés à produire des efforts tels que des exercices de mordant ou de pistage. Il arrive que certains d'entre eux deviennent insuffisants à l'effort. Ils doivent alors être réformés. Après un état des lieux relatifs aux connaissances concernant la physiologie de l'effort et les pathologies pouvant apparaître suite à l'entraînement, ce travail se penche sur l'entraînement dispensé au Centre National d'Instruction Cynophile de la Gendarmerie. Un groupe de 17 chiens a été suivi lors des 3 mois de stage. Un examen clinique a été effectué à deux reprises au début et à la fin du stage dans le but de trouver un paramètre clinique pouvant permettre d'évaluer le devenir du chien vis-à-vis de l'effort. Cet examen comprenait la prise de la fréquence cardiaque, de la fréquence respiratoire, de la température rectale et du poids ainsi qu'un tracé électrocardiographique. Aucun chien du groupe n'ayant présenté d'insuffisance à l'effort, cette étude a permis de trouver certains paramètres pouvant servir au suivi de l'entraînement des chiens. La fréquence respiratoire semble peu exploitable dans le contexte de la gendarmerie étant donné le port de la muselière lors de l'examen clinique. La température rectale peut, quand à elle, être suivie avec attention notamment lors d'efforts produits lors de fortes chaleurs. L'évolution de la fréquence cardiaque lors d'un effort est modifiée suite à l'entraînement. Il semble que les intervalles ébauchés dans cette étude peuvent être affinés afin de suivre et d'adapter l'entraînement des chiens.
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