Myopericarditis and sudden cardiac death due to physical exercise in male athletes

In the period 1998-, we registered four sudden and unexpected cardiac deaths in male athletes due to myopericarditis during or after physical exercise. Three of them were professional soccer players and the fourth was engaged in swimming. One aged 29, had symptoms of tiredness, heart enlargement and left ventricular premature beats during training. Three of them, aged 17-18-18, were without symptoms. Three died during training and the fourth died in the hospital after head trauma at training. In the first one, aged 29, forensic autopsy showed chronic myopericarditis, thickening of the left ventricular wall of 15 mm and enlargement of the whole heart. The second one, aged 17, had subacute diffuse myopericarditis, suppurative tonsillitis and narrowed ascending aorta. The third, aged 18, had chronic myopericarditis and cardiac aneurysm of the left ventricle. The fourth, aged 18, had fibrinous pericarditis, thickening of the left ventricle 20 mm, hypoplastic ascending aorta, bilateral bronchopneumonia and cerebral contusion with edema. In Croatia, death rate among athletes, including all its causes, reached 0.15/100,000, in athletes suffering from myopericarditis it was 0.34/100,000, in others who practice exercise recreatively it amounted to 0.57/100,000 (p=0.0068), and in all males who practice exercise it measured 0.75/100,000 (p=0.0014). Physical exercise has to be contraindicated in cases of myopericarditis for at least six months from the onset of the illness.     

Effect of endurance exercise training on heart rate onset and heart rate recovery responses to submaximal exercise in animals susceptible to ventricular fibrillation.

Both a large heart rate (HR) increase at exercise onset and a slow heart rate (HR) recovery following the termination of exercise have been linked to an increased risk for ventricular fibrillation (VF) in patients with coronary artery disease. Endurance exercise training can alter cardiac autonomic regulation. Therefore, it is possible that this intervention could restore a more normal HR regulation in high-risk individuals. To test this hypothesis, HR and HR variability (HRV, 0.24- to 1.04-Hz frequency component; an index of cardiac vagal activity) responses to submaximal exercise were measured 30, 60, and 120 s after exercise onset and 30, 60, and 120 s following the termination of exercise in dogs with healed myocardial infarctions known to be susceptible (n = 19) to VF (induced by a 2-min coronary occlusion during the last minute of a submaximal exercise test). These studies were then repeated after either a 10-wk exercise program (treadmill running, n = 10) or an equivalent sedentary period (n = 9). After 10 wk, the response to exercise was not altered in the sedentary animals. In contrast, endurance exercise increased indexes of cardiac vagal activity such that HR at exercise onset was reduced (30 s after exercise onset: HR pretraining 179 +/- 8.4 vs. posttraining 151.4 +/- 6.6 beats/min; HRV pretraining 4.0 +/- 0.4 vs. posttraining 5.8 +/- 0.4 ln ms(2)), whereas HR recovery 30 s after the termination of exercise increased (HR pretraining 186 +/- 7.8 vs. posttraining 159.4 +/- 7.7 beats/min; HRV pretraining 2.4 +/- 0.3 vs. posttraining 4.0 +/- 0.6 ln ms(2)). Thus endurance exercise training restored a more normal HR regulation in dogs susceptible to VF.     

Suppurative tonsillitis and sudden cardiac death due to physical training in a young soccer player

A teenager aged 17 was a professional soccer player, and was without symptoms. He died suddenly during physical exercise at the field. All reanimation efforts were unsuccessfull. At the forensic autopsy he had suppurative bacterial tonsillitis, subacute diffuse myopericarditis and narrowing of the ascending aorta of 10 mm. In Croatia the death rate among athletes reached 0.15/100,000, in athletes suffered of acute respiratory tract infections 0.34/100,000, in males who practice exercise recreatively 0.75/100,000 (p = 0.0014), in school children 1.0/100,000 (p = 0.0010). Physical exercise is contraindicated in acute respiratory tract infections. Every such case has to be treated by physician. When to start with physical training after suppurative-bacterial tonsillitis depends on disappearing of clinical signs, normalization of erythrocite sedimentation rate; of white cell count and serum level of C-reactive protein. Physical exercise is contraindicated in patients suffering of myopericarditis for at least 6 months. When to start exercise depends on disappearing of subjective symptoms and normalization of clinical and laboratory findings.     

电刺激迷走神经对蟾蜍心率和心率变异的影响

目的:观察不同频率迷走神经刺激对蟾蜍离体心脏的心率及心率变异的影响。方法:将蟾蜍心脏和右侧迷走交感干离体后,以不同频率电刺激神经,记录心电图曲线并作心率变异性(HRV)分析。结果:交感神经阻断后,电刺激迷走交感干,心率(HR)显著下降(P0.01),全部正常心动周期的标准差(SDNN)和相邻正常心动周期差值的均方根(RMSSD)显著升高(P0.01),不同频率刺激组之间没有明显差异;与对照组相比,各指标变化较大;给药组0.2Hz时高频(HF)显著升高(P0.01),低频/高频比值(LF/HF)明显降低(P0.05),0.8Hz时HF和LF/HF接近刺激前水平。结论:一定范围内增加刺激频率,迷走神经降低心率的作用增强;没有交感神经调节条件下的迷走神经对心率和心率变异的调节可能存在不同的机制。     

Hypertrophic cardiomyopathy and sudden cardiac death due to physical exercise in Croatia in a 27-year period

The paper deals with the sudden cardiac death during physical exercise in males in Croatia. The data are a part of a retrospective study dealing with 69 sudden death due to physical activity in men in Croatia during 27 years: from January 1, 1984 to December 31, 2010. Three of them suddenly died during training and two of them died during recreational physical exercise, probably because of malignant ventricular arrhythmia due to hyperthrophic cardiomyopathy. One had an obstructive form of hypertrophic cardiomyopathy with i.v. septum of 40 mm and four had a non-obstructive forms of hyperthrophic cardiomyopathy with left ventricular wall of 18-20-22-25 mm. First athlete was a short trails runner, aged 24, with no any previous physical discomforts, who suddenly collapsed and died during training. The second athlete was a soccer player aged 18, with no any previous physical discomfort, who suddenly collapsed and died during training. The third aged 15, was a school boy, basketball player, with no any previous physical discomfort, who collapsed and died during training. Two aged 25 and 34, were with no physical discomfort during exercise and died suddenly during recreational soccer games. A sudden cardiac death due to physical exercise in young athletes in Croatia suffered of hyperthropic cardiomyopathy reached 0.06/100 000 yearly (p = 0.00000) in 27 years, in teenagers 0.26/100 000 (p = 0.00226), in teenagers suffered of hypertrophic cardiomyopathy reached 0.10/100 000 (p = 0.00000), in all young athletes suffered of other heart diseases reached 0.19/100 000 (p = 0.00005), and in the total male population aged 15 or more, engaged in sports and recreational physical exercise: 0.71/100.0000 (p = 0.00001).     

Intraindividual validation of heart rate variability indexes to measure vagal effects on hearts

Heart rate variability (HRV) has been widely used as a measure of vagal activation in physiological, psychological, and clinical examinations. We studied the within-subject quantitative relationship between HRV and vagal effects on the heart in different body postures during a gradually decreasing vagal blockade. Electrocardiogram and respiratory frequency were measured in subjects (8 endurance athletes and 10 participants of nonendurance sports) in supine, sitting, and standing postures before the blockade, under vagal blockade (atropine sulfate, 0.04 mg/kg), and four times during a 150-min recovery from the blockade. Fast Fourier transform was used to calculate low-frequency power (LFP, 0.04-0.15 Hz), high-frequency power (HFP, 0.15-0.40 Hz), and total power (TP, 0.04-0.40 Hz). A within-subject linear regression analysis of recovery time on each HRV index was conducted. Complete vagal blockade decreased all HRV significantly, particularly HFP (P < 0.001). A linear fit explained a large portion of the within-subject variance between recovery time and natural log-transformed (ln) HRV indexes in every posture, with coefficients of determination (R2) in the supine posture [means (SD)]: 98 (SD 2)% for mean R-R interval, 87 (SD 10)% for lnLFP, 87 (SD 13)% for lnHFP, and 91 (SD 10)% for lnTP. Neither body posture nor endurance-training background had an impact on R2 values. There was marked between-subject variation in the R2 values, slopes, and intercepts. In conclusion, all HRV, particularly HFP, is predominantly under vagal control. Within subjects, lnLFP, lnHFP, and lnTP increased linearly with the gradually decreasing vagal blockade in all postures.     

Effects of endurance training and acute exhaustive exercise on antioxidant defense mechanisms in rat heart

We investigated whether 8-week treadmill training strengthens antioxidant enzymes and decreases lipid peroxidation in rat heart. The effects of acute exhaustive exercise were also investigated. Male rats (Rattus norvegicus, Sprague-Dawley strain) were divided into trained and untrained groups. Both groups were further divided equally into two groups where the rats were studied at rest and immediately after exhaustive exercise. Endurance training consisted of treadmill running 1.5 h day(-1), 5 days week(-1) for 8 weeks. For acute exhaustive exercise, graded treadmill running was conducted. Malondialdehyde level in heart tissue was not affected by acute exhaustive exercise in untrained and trained rats. The activities of glutathione peroxidase and glutathione reductase enzymes decreased by both acute exercise and training. Glutathione S-transferase and catalase activities were not affected. Total and non-enzymatic superoxide scavenger activities were not affected either. Superoxide dismutase activity decreased by acute exercise in untrained rats; however, this decrease was not observed in trained rats. Our results suggested that rat heart has sufficient antioxidant enzyme capacity to cope with exercise-induced oxidative stress, and adaptive changes in antioxidant enzymes due to endurance training are limited.     

Go but not Gi2 or Gi3 is required for muscarinic regulation of heart rate and heart rate variability in mice

Muscarinic receptor-mediated cardiac parasympathetic activity is essential for regulating heart rate and heart rate variability (HRV). It has not been clear which G(i)/G(o) protein is responsible for these effects. We addressed this question using knockout mice that lack G protein alpha(i2), alpha(i3), or alpha(o) specifically. Unlike previously reported, our alpha(o)-null mice had significantly more survivors with normal life span. Isolated hearts from alpha(o)-null mice demonstrated much less sensitivity to the negative chronotropic effects of the muscarinic agonist carbachol to lower heart rate at baseline and a more profound effect under the stimulation of the beta-adrenergic agonist isoproterenol. In the presence of parasympathetic activation indirectly produced by methoxamine, an alpha(1)-adrenergic agonist, alpha(o)-null mice showed markedly decreased HRV compared with wild-type control mice. These differences in heart rate and HRV were not observed in alpha(i2)-null or alpha(i3)-null mice. Our findings establish an essential role for alpha(o) G protein in the anti-adrenergic effect of carbachol on heart rate regulation.     

Heritability of submaximal exercise heart rate response to exercise training is accounted for by nine SNPs

Endurance training-induced changes in hemodynamic traits are heritable. However, few genes associated with heart rate training responses have been identified. The purpose of our study was to perform a genome-wide association study to uncover DNA sequence variants associated with submaximal exercise heart rate training responses in the HERITAGE Family Study. Heart rate was measured during steady-state exercise at 50 W (HR50) on 2 separate days before and after a 20-wk endurance training program in 483 white subjects from 99 families. Illumina HumanCNV370-Quad v3.0 BeadChips were genotyped using the Illumina BeadStation 500GX platform. After quality control procedures, 320,000 single-nucleotide polymorphisms (SNPs) were available for the genome-wide association study analyses, which were performed using the MERLIN software package (single-SNP analyses and conditional heritability tests) and standard regression models (multivariate analyses). The strongest associations for HR50 training response adjusted for age, sex, body mass index, and baseline HR50 were detected with SNPs at the YWHAQ locus on chromosome 2p25 (P = 8.1 × 10(-7)), the RBPMS locus on chromosome 8p12 (P = 3.8 × 10(-6)), and the CREB1 locus on chromosome 2q34 (P = 1.6 × 10(-5)). In addition, 37 other SNPs showed P values <9.9 × 10(-5). After removal of redundant SNPs, the 10 most significant SNPs explained 35.9% of the ΔHR50 variance in a multivariate regression model. Conditional heritability tests showed that nine of these SNPs (all intragenic) accounted for 100% of the ΔHR50 heritability. Our results indicate that SNPs in nine genes related to cardiomyocyte and neuronal functions, as well as cardiac memory formation, fully account for the heritability of the submaximal heart rate training response.     

Effects of endurance exercise training on muscle glycogen accumulation in humans.

The purpose of this investigation was to determine whether endurance exercise training increases the ability of human skeletal muscle to accumulate glycogen after exercise. Subjects (4 women and 2 men, 31 +/- 8 yr old) performed high-intensity stationary cycling 3 days/wk and continuous running 3 days/wk for 10 wk. Muscle glycogen concentration was measured after a glycogen-depleting exercise bout before and after endurance training. Muscle glycogen accumulation rate from 15 min to 6 h after exercise was twofold higher (P < 0.05) in the trained than in the untrained state: 10.5 +/- 0.2 and 4.5 +/- 1.3 mmol. kg wet wt(-1). h(-1), respectively. Muscle glycogen concentration was higher (P < 0.05) in the trained than in the untrained state at 15 min, 6 h, and 48 h after exercise. Muscle GLUT-4 content after exercise was twofold higher (P < 0.05) in the trained than in the untrained state (10.7 +/- 1.2 and 4.7 +/- 0.7 optical density units, respectively) and was correlated with muscle glycogen concentration 6 h after exercise (r = 0.64, P < 0.05). Total glycogen synthase activity and the percentage of glycogen synthase I were not significantly different before and after training at 15 min, 6 h, and 48 h after exercise. We conclude that endurance exercise training enhances the capacity of human skeletal muscle to accumulate glycogen after glycogen-depleting exercise.     

Endurance exercise training attenuates cardiac beta2-adrenoceptor responsiveness and prevents ventricular fibrillation in animals susceptible to sudden death

Enhanced cardiac beta(2)-adrenoceptor (beta(2)-AR) responsiveness can increase susceptibility to ventricular fibrillation (VF). Exercise training can decrease cardiac sympathetic activity and could, thereby, reduce beta(2)-AR responsiveness and decrease the risk for VF. Therefore, dogs with healed myocardial infarctions were subjected to 2 min of coronary occlusion during the last minute of a submaximal exercise test; VF was observed in 20 susceptible, but not in 13 resistant, dogs. The dogs were then subjected to a 10-wk exercise-training program (n = 9 susceptible and 8 resistant) or an equivalent sedentary period (n = 11 susceptible and 5 resistant). Before training, the beta(2)-AR antagonist ICI-118551 (0.2 mg/kg) significantly reduced the peak contractile (by echocardiography) response to isoproterenol more in the susceptible than in the resistant dogs: -45.5 +/- 6.5 vs. -19.2 +/- 6.3%. After training, the susceptible and resistant dogs exhibited similar responses to the beta(2)-AR antagonist: -12.1 +/- 5.7 and -16.2 +/- 6.4%, respectively. In contrast, ICI-118551 provoked even greater reductions in the isoproterenol response in the sedentary susceptible dogs: -62.3 +/- 4.6%. The beta(2)-AR agonist zinterol (1 microM) elicited significantly smaller increases in isotonic shortening in ventricular myocytes from susceptible dogs after training (n = 8, +7.2 +/- 4.8%) than in those from sedentary dogs (n = 7, +42.8 +/- 5.8%), a response similar to that of the resistant dogs: +3.0 +/- 1.4% (n = 6) and +3.2 +/- 1.8% (n = 5) for trained and sedentary, respectively. After training, VF could no longer be induced in the susceptible dogs, whereas four sedentary susceptible dogs died during the 10-wk control period and VF could still be induced in the remaining seven animals. Thus exercise training can restore cardiac beta-AR balance (by reducing beta(2)-AR responsiveness) and could, thereby, prevent VF.     

Effect of energy drink dose on exercise capacity,heart rate recovery and heart rate variability after high-intensity exercise

[Purpose]

The purpose of this research was to investigate the effects of exercise capacity, heart rate recovery and heart rate variability after high-intensity exercise on caffeine concentration of energy drink.

[Methods]

The volunteers for this study were 15 male university student. 15 subjects were taken basic physical examinations such as height, weight and BMI before the experiment. Primary tests were examined of VO₂max per weight of each subjects by graded exercise test using Bruce protocol. Each of five subject was divided 3 groups (CON, ECGⅠ, ECGⅡ) by matched method based on weight and VO₂max per weight what gained of primary test for minimize the differences of exercise capacity and ingestion of each groups. For the secondary tests, the groups of subjects were taken their materials before and after exercise as a blind test. After the ingestion, subjects were experimented on exercise test of VO₂max 80% by treadmill until the all-out. Heart rate was measured by 1minute interval, and respiratory variables were analyzed VO2, VE, VT, RR and so on by automatic respiratory analyzer. And exercise exhaustion time was determined by stopwatch. Moreover, HRV was measured after exercise and recovery 3 min.

[Results]

Among the intake groups, ECGⅡ was showed the longest of exercise exhaustion time more than CON group (p = .05). Result of heart rate during exercise according to intake groups, there was significant differences of each time (p < .001), however, not significant differences of each groups and group verse time (p > .05). Result of RPE during exercise according to intake groups, there was significant differences of each time (p < .001), however, not significant differences of each groups and group verse time (p > .05).

[Conclusion]

In conclusion, EDGⅡ showed the significant increase of exercise exhaustion time more than CON group (p=.05) and not significant differences in HR, RPE, RER, HRV, HRR, blood pressure (p > .05). Therefore, 2.5 mg/kg^-1 ingestion of energy drink might be positive effect to increase exercise performance capacity without side-effect in cardiovascular disease.     

Effects of residential exercise training on heart rate recovery in coronary artery patients

The aims of the present study are twofold: 1) to investigate whether heart rate recovery (HRR) after a cycle ergometry test is affected by exercise training and 2) to test the ability of HRR to replicate the baroreflex sensitivity (BRS) changes that occur in response to an exercise training program in coronary artery patients. We randomized 82 coronary artery patients undergoing a residential cardiac rehabilitation program to an exercise training group (TR; n = 43) and an untrained group (UTR; n = 39). All of the patients underwent an exercise test before and after the rehabilitation program. HRR was recorded at the end of the 1st and 2nd min after exercise. BRS was determined at rest before and after treatment. HRR after the 2nd min was significantly improved in TR patients (-21.4 +/- 0.9 beats/min) compared with UTR patients (-17.8 +/- 1.2 beats/min) at the end of the training program. Improvement in HRR paralleled that in BRS in TR patients (from 3.2 +/- 0.3 to 5.3 +/- 0.8 ms/mmHg; P < 0.001), whereas no significant change was evident in UTR patients (from 3.5 +/- 0 to 4.0 +/- 0.4 ms/mmHg; P = 0.230). Our data show that HRR in the 2nd min after the cessation of a cycle ergometer exercise test increased in coronary artery patients after an exercise training period. This result confirms the positive effect induced by exercise training on HRR and extends the conclusions of previous studies to different modalities of exercise (i.e., cycle ergometer). HRR might provide an additional simple marker of the effectiveness of physical training programs in cardiac patients.     

Effects of endurance exercise training on markers of cholesterol absorption and synthesis

Abnormal cholesterol metabolism, including low intestinal cholesterol absorption and elevated synthesis, is prevalent in diabetes, obesity, hyperlipidemia, and the metabolic syndrome. Diet-induced weight loss improves cholesterol absorption in these populations, but it is not known if endurance exercise training also improves cholesterol homeostasis. To examine this, we measured circulating levels of campesterol, sitosterol, and lathosterol in 65 sedentary subjects (average age 59 years; with at least one metabolic syndrome risk factor) before and after 6 months of endurance exercise training. Campesterol and sitosterol are plant sterols that correlate with intestinal cholesterol absorption, while lathosterol is a marker of whole body cholesterol synthesis. Following the intervention, plant sterol levels were increased by 10% (p<0.05), but there was no change in plasma lathosterol. In addition, total and LDL-cholesterol were reduced by 0.16 mmol and 0.10 mmol, respectively (p<0.05), while HDL-C levels increased by 0.09 mmol (p<0.05). Furthermore, the change in plant sterols was positively correlated with the change in VO2max (r=0.310, p=0.004), independent of other metabolic syndrome risk factors. These data indicate that exercise training reduces plasma cholesterol despite increasing cholesterol absorption in subjects with metabolic syndrome risk factors.     

Effects of body weight-supported treadmill training on heart rate variability and blood pressure variability in individuals with spinal cord injury.

Individuals with spinal cord injury are prone to cardiovascular dysfunction and an increased risk of cardiovascular disease. Body weight-supported treadmill training (BWSTT) may enhance ambulation in individuals with incomplete spinal cord injury; however, its effects on cardiovascular regulation have not been investigated. The purpose of this study was to examine the effects of 6-mo of BWSTT on the autonomic regulation of heart rate (HR) and blood pressure (BP) in individuals with incomplete tetraplegia. Eight individuals [age 27.6 yr (SD 5.2)] with spinal cord injury [C4-C5; American Spinal Injury Association B-C; 9.6 yr (SD 7.5) postinjury] participated. Ten-minute HR and finger arterial pressure (Finapres) recordings were collected during 1) supine rest and 2) an orthostatic stress (60 degrees head-up tilt) before and after 6 mo of BWSTT. Frequency domain measures of HR variability [low-frequency (LF) power, high-frequency (HF) power, and LF-to-HF ratio] and BP variability (systolic and diastolic LF power) were used as clinically valuable indexes of neurocardiac and neurovascular control, respectively. There was a significant reduction in HR [61.9 (SD 6.9) vs. 55.7 beats/min (SD 7.7); P=0.05] and LF-to-HF ratio [1.23 (SD 0.47) vs. 0.99 (SD 0.40); P < 0.05] after BWSTT. There was a significant reduction in LF systolic BP [183.1 (SD 46.8) vs. 158.4 mmHg2 (SD 45.2); P < 0.01] but no change in BP. There were no significant effects of training on HR variability or BP variability during 60 degrees head-up tilt. In conclusion, individuals with incomplete tetraplegia retain the ability to make positive changes in cardiovascular autonomic regulation with BWSTT without worsening orthostatic intolerance.     

共振呼吸反馈训练对运动员心率变异性和选择反应时的影响

目的:探讨共振呼吸调节对运动员认知任务表现的提升作用。方法:将30名射击运动员随机分为试验组(n=15)和对照组(n=15)。试验组运动员进行每次30～40 min、每周5 d,共计4周的心率变异性生物反馈训练(HRV训练),掌握共振呼吸调节方法,以相同频次进行呼吸调节(每分钟6次);试验采用试验组、对照组前后测的设计,利用第三版神经行为测试评价系统(NES-C3)、生理相干和自主平衡系统SPCS采集运动员的选择反应时和心率变异性(HRV)数据;正式检测,首先让所有运动员经历安静阶段并进行选择反应时测试,随后试验组运动员进行共振呼吸调节,而对照组运动员休息,最后所有运动员再次进行选择反应时测试,测量运动员的心率变异性。结果:与安静阶段相比,试验组运动员心率(HR)显著下降(P<0.05),心脏总功率(TP)和低频功率(LF)与安静阶段相比显著增加(P<0.01),低频/高频功率(LF/HF)也显著增加(P<0.05),自我调节后的选择反应时显著降低(P<0.05);而对照组无显著变化(P>0.05)。结论:共振呼吸调节法可以显著增强运动员的心率变异性水平,...     

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

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.     

Respiratory and heart rate patterns in infants destined to be victims of sudden infant death syndrome: average rates and their variability measured over 24 hours.

From a prospective study in which 24 hour recordings of the electrocardiogram and respiratory activity (abdominal wall movement) were made on a population of full term infants, 22 recordings were obtained from 16 infants who later were victims of the sudden infant death syndrome. The average heart rate, average heart rate variability, average breath to breath interval, and average breath to breath interval variability over the whole of each recording for the 22 recordings were compared with those from a control group of 324 infants selected at random from the rest of the population. No significance was found in the number of recordings from those infants who suffered the sudden infant death syndrome which lay outside the 5th-95th percentile range of the control group for the four variables studied. In a group comparison no difference was found between the sudden infant death syndrome group and the controls either in terms of the respiratory variables studied or in terms of the average heart rate variability. The results did, however, suggest that there may be a group difference in terms of the average instantaneous heart rate.