Short and long term effects of exercise training on the tonic autonomic modulation of heart rate variability after myocardial infarction

We studied the effects of cardiac rehabilitation on the sympathovagalcontrol of heart rate variability in 30 patients after a first,uncomplicated myocardial infarction. Twenty-two patients completed8 weeks of endurance training (trained), while eight decidednot to engage in the rehabilitation programme for logisticalreasons, and were taken as untrained controls. Age, site ofinfarction, ejection fraction, ventricular diameter and stresstest duration were similar in the two groups at baseline. Heartrate variability was evaluated 4 weeks after infarction beforestarting rehabilitation, and repeated 8 weeks and one year laterin both trained and untrained patients. Measures of heart ratevariability, obtained from both time- and frequency- domainanalysis of a 15 min ECG recording in resting conditions, wereas follows: mean RR interval and its standard deviation (RRSD),the mean square successive differences (MSSD), the percent ofRR intervals differing >50 ms from the preceding RR (pNTN50),the low and high frequency components of the autoregressivepower spectrum of the RR intervals and their ratio (LF/HF).At baseline, heart rate variability was similar in trained anduntrained patients. In the short term (8 weeks after infarction),training increased RRSD by 25% (P<0·01), MSSD by 69%(P<0·01), pNN50 by 120% (P<0·01), and reducedLF/HF ratio by 30% (P<0·01). The effects persistedafter one year in trained patients. In untrained patients, theautonomic control of heart rate variability did not change 8weeks after myocardial infarction and was only slightly modifiedby time. Thus, exercise training, performed for 8 weeks aftera myocardial infarction, modifies the sympathovagal controlof heart rate variability toward a persistent increase in parasympathetictone, known to be associated with a better prognosis. This maypartly account for the favourable outcome of patients who undergorehabilitation.     

运动负荷对高原地区青少年心缩间期的影响

采用逐级负荷踏车实验和阻抗心动图的方法,测定居住3417m高原13～16岁藏汉族青少年静息状态下,运动后即刻及恢复期心率和左心收缩间期,结果显示,静息状态下两组STI各数值无差异,藏族运动后即刻的PEP短于汉族,LVET长于汉族,P/L有明显差异(P<0.01),经心率矫正后藏族运动后即刻LVETI及QS_2I均长于汉族,恢复期短于汉族,形成交叉曲线,说明居住高原的汉藏族人群的心功能差别在青少年时已经出现。提示:藏族在运动状态下有良好的心力储备及对运动负荷的适应能力,其原因可能与生长发育的环境及种群遗传有关。     

Myocardial blood flow in awake dogs with chronic tricuspid regurgitation

The primary purpose of this study was to define regional blood flow in dogs with chronic tricuspid regurgitation (TR) in order to determine if the marked hypertrophy of the right atria resulted in compromised myocardial perfusion. Myocardial blood flow (ml/min/gm) was measured with radiolabeled microspheres in eight dogs with TR during rest, moderate exercise (5 dogs), and infusion of adenosine (1 mg/kg/min), an index of minimal vascular resistance. Similar measurements were obtained in eight normal dogs. In TR, the ratio of right atrium (RA) and right ventricle (RV) to body weight was greater than in normal dogs, 77 % and 30 %, respectively. During rest, flow in RA appendage was less than in nonappendage region in the normal dogs; no differences were noted in TR dogs, indicating an augmented hemodynamic role of the appendage in TR. Both RA and RV blood flow was greater in TR during rest but no other differences in flow were found between the two groups. Minimum vascular resistance in RV but not RA was slightly increased in TR versus normal. During marked myocyte hypertrophy, the vasculature of RA develops sufficiently to provide the same flow capacity as in the normal heart. Received: 11 June 1997, Returned for revision: 15 July 1997, Revision received: 11 August 1997, Accepted: 7 September 1997     

Muscular performance after a 3 month progressive physical exercise program and 9 month follow-up in subjects with low back pain. A controlled study

The purpose of this study was to assess, in subjects with low back pain, the changes and their permanence in muscular performance after a 3 month progressive physical exercise program. Ninety subjects with chronic low back pain participated in the study. The study design was controlled and it was carried out in three groups: intensive training, home exercise, and control group. Isometric and dynamic muscle strength of the trunk and lower limb were measured, at the beginning of the study and after the 3 months exercise program, and then during each of the follow-up sessions. The Oswestry Index and back pain intensity were also determined. Both exercise groups received benefit from the progressive exercise program. Their muscular performance improved and their back pain intensity decreased significantly. Among the home exercise group, the Oswestry Index also changed positively. The results demonstrate that the home exercise program could be as effective as the intensive training program in increasing muscle strength, as well as decreasing back pain and functional disability among low back pain patients with mild functional limitations.     

Proteoglycan fragments in knee joint fluid after exercise

The concentration of cartilage proteoglycan fragments in knee joint fluid was measured before and after one event of physical exercise in 33 healthy athletes. Nine athletes ran on a treadmill for 60 min, 16 ran on road for 80 min and 8 played one soccer game (90 min). Before exercise, the levels of proteoglycan fragments in the athlete joint fluid were lower than in a previously analyzed reference group. After exercise, the concentration of proteoglycan fragments increased in all of the 7 athletes that could be directly compared before and after exercise. This increased concentration of proteoglycan fragments in the joint fluid could be an effect of mechanical loading of the cartilage in combination with a possible high turn-over rate of the cartilage matrix in the athletes.     

A neural network confirms that physical exercise reverses EEG changes in depressed rats

The use of an artificial neural network (ANN) system to differentiate the EEG power density spectra in depressed from normal rats was tried. The beneficial effects of chronic physical exercise in reducing the effects of stress and therefore depression was also to be tested in animals by the same method. In this study, rats were divided into 4 groups, subjected to (i) chronic stress (D group); (ii) chronic exercise by treadmill running (EO group); (iii) exercise with stress (ES group) and (iv) handling (C group). The prefrontal cortical EEG, EMG and EOG were recorded simultaneously on paper and the digitized EEG signals were also stored in the hard-disk of a PC-AT through an ADC. After filtering the digitize signals, the EEG power spectra were calculated by an FFT routine. Three successive 4 s artefact-free epochs were averaged. The REM and NREM sleep periods as well as the awake period signals were analyzed separately. The FFT values from each of the 3 states, in the 4 groups of animals were tested by an ANN with 30 first layer neurons and a 2nd layer of a majority-vote-taker. The ANN could distinguish the depressed from the normal rats' EEG very well in REM (99%) sleep, NREM (95%) sleep and awake (81%) states. In most of the cases it identified the exercised rats' EEG as normal.     

不同强度运动对女子游泳运动员性激素水平的影响及特点

本研究以放兔分析法观察不同强度运动前后19名女子游泳运动员血清促卵泡激素(FSH)、黄体生成素(LH)、雌二醇(E_2)、孕酮(P)、睾酮(T)及胰岛素(Ins)的变化。受试者在卵泡及黄体两期分别进行短时间高强度间歇运动——6×50m全速力竭性游泳和长时间持续运动——1000m全速力竭性游泳。在运动前5分钟及运动后即刻分别采集静脉血测定各种激素含量。主要结果如下:受试者从事6×50m最大速度间歇游泳后,卵泡期各种激素浓度的变化均显著高于运动前安静状态,黄体期变化不一,FSH、LH降低,E_2、P、T及Ins升高。从事1000m全速游泳后,激素变化表现为卵泡期FSH、LH、E_2、P均升高,T及Ins降低;黄体期E_2、P、T升高,Ins降低,FSH、LH无显著变化,两期相比黄体期运动成绩优于卵泡期。上述结果提示:①受试者月经周期的黄体期机体有氧能力强于卵泡期,运动能力的增强与黄体期E_2、P、T水平升高有关。②FSH、LH与E_2、P分泌变化并非同步一致,说明运动中E_2升高并非受制于促性腺激素,而主要是卵巢分泌量升高所致。③运动中E_2、P、T具有协同效应,可抵抗疲劳,提高人体运动能力。     

Self-efficacy and the maintenance of exercise participation in older adults

The role played by exercise self-efficacy in the maintenance of exercise participation of previously sedentary middle-aged adults 4 months after the termination of a formal exercise program is reported. Correlational and multiple regression analyses examined the influence of self-efficacy, physiological (aerobic capacity, sex, body composition), and behavioral (past exercise frequency and intensity) parameters in the maintenance of exercise participation. Self-efficacy significantly predicted exercise behavior at follow-up when controlling for biological and behavioral influences. Aerobic capacity, exercise efficacy, and exercise behavior in combination were significantly related to current energy expenditure in aerobic physical activity. The discussion focuses on the need to examine the impact of different correlates of exercise behavior at different stages of the exercise process.This project was funded by Grant AG07907 from the National Institute on Aging.     

Rate-responsive pacing with a pacemaker that detects respiratory rate (Biorate): clinical advantages and complications

The respiratory-dependent pacemaker (RDP3 or MB-1, Biorate, Biotec International, S.p.A., Bologna, Italy) detects the respiratory rate by measuring thoracic impedance using a subcutaneous auxiliary lead. The sensed respiratory rate is used to determine the pacing rate response. This pacemaker had been implanted in 9 patients with a mean age of 58 (range 42-69) years. During symptom-limited treadmill exercise, rate-modulated pacing resulted in a significant increase in pacing rate (mean +/- SD, 124 +/- 10 vs. 71 +/- 3 beats/min p less than 0.001) and exercise capacity (343 +/- 147 vs. 463 +/- 120 s, p less than 0.05) compared to those achieved with constant rate ventricular pacing. Brief treadmill exercise tests showed appropriate rate response to increased walking speed and gradient. However, rate response was modified by arm swinging-induced motion artefact which affected the measured "impedance." Complications observed on follow-up included perforation of the auxiliary lead in 2 patients and symptomatic myopotential interference in 3 patients with the RDP3 pacemaker, all of whom required unit replacement. It is concluded that although the respiratory-dependent pacemaker can confer physiological benefit in patients with bradycardia, myopotential interference (largely overcome by the new version MB-1 with programmable sensitivity) and the auxiliary lead can be problematic in some patients.     

Determination of left ventricular wall thickness and muscle mass by intravenous digital subtractionangiocardiography: validation of the method

Left ventricular (LV) wall thickness and muscle mass are importantmeasures of LV hypertrophy. In 24 patients LV end-diastolicwall thickness and muscle mass were determined (two observers)by digital subtraction angiocardiography (DSA) and conventionalLV angiocardiography (LVA). Wall thickness was determined overthe anterolateral wall of the left ventricle according to thetechnique of Rackley (method 1) or by planimetry (method 2).Seventeen patients were studied at rest and seven during dynamicexercise. Wall thickness correlated well between LVA and DSA;the best correlations were obtained by a combined subtractionmode using either method 1 or 2 (method 1, r0–80; method2,r0. 75). The standard error of estimate of the mean (SEE) wasslightly lower for method 2 ( 10%) than for method 1 ( 13%).DSA significantly overestimated wall thickness by 5–7%with method 1 and underestimated by 12–14% with method2. Muscle mass correlated well between LVA and DSA; the SEEwas 15% for method 1 and 12% for method 2. Overestimation ofmuscle mass by DSA was 7–11% with method 1 and underestimationwas 13–15% with method 2.It is concluded that LV wallthickness can be determined accurately by DSA with an SEE rangingbetween 10 and 13%. Determination of LV muscle mass is slightlyless accurate and the SEE is slightly larger ranging between13 to 17%. With method 1, wall thickness and muscle mass wereover estimated and with method 2 underestimated.