吸烟对心脏自主神经功能的影响

探讨吸烟对心脏自主神经功能的影响。方法应用时域法和频域法２０例正常人进行吸烟前后心率变异性分析。结论吸烟后交感神经活性明显增强,副交感神经活性明显降低,心率变异程度减低。吸 心脏自主神经的影响。特别是对副交感神经的抑制作用的不容忽视。其机制可能与烟碱型胆碱能受体参与副交感神经节的传递有关。     

The influence of heart rate on echocardiographic assessment of aerobic training

The purpose of this investigation was to determine if echocardiographic measures of ventricular structure and function ascribed to aerobic training might be an artifact of heart rate (HR) differences between trained and untrained subjects. Comparisons were made at rest, of 10 young, male, aerobically well-trained athletes [((VO₂)_max 65>ml/kg/min] and 10 young, healthy controls [((VO₂)_max<56ml/kg/min]. Additionally, the echocardiographic responses to low (HR=80 beats/min) and moderate intensity (HR=120 beats/min) supine cycling exercise were analyzed. Echocardiographic measures were made as described by Sahnet al. (1978). Results of echocardiographic comparisons between groups, both during supine rest and at a constant heart rate of 80 beats/min during supine cycling confirmed that athletes had significantly greater left ventricular mass (LV mass) and end-diastolic size per square meter of body surface area (p<0.05). When supine cycling loads were increased to elevate HR to 120 beats/min in groups of 7 athletes and 5 controls, athletes exhibited a progressive and significant (p<0.05) enlargement of left ventricular end-diastolic size (LVEDS), while left ventricular end-systolic size (LVESS) showed negligible change. The control group showed little change in LVEDS, but decreased LVESS significantly (p<0.05). Contractility measures, i.e., estimated ejection fraction (EF) and velocity of circumferential shortening ( (V_cf) increased in both groups in a similar manner. It was concluded that echocardiographic differences in ventricular structure and function observed between aerobically trained and untrained subjects are not an artifact of heart rate differences. Clearly, aerobic training results in increased LV mass and diastolic size which allows for further dilitation with supine exercise. Aerobic training does not appear to alter indices of myocardial contractility.     

The influence of fetal and postnatal growth on heart rate variability in young infants.

Heart rate variability (HRV), a measure of cardiac autonomic control, was analyzed in infants to assess the hypothesis that early undernutrition may induce autonomic dysfunction that could play a role in the programming of later cardiovascular disease. HRV data were collected during a night session in 546 healthy infants at 5-12 weeks of adjusted age, and statistical associations with fetal and postnatal growth indices were established. A significant positive correlation between birth weight, the ratio of neonatal weight to head circumference and postnatal weight gain, and HRV indices mostly influenced by sympathetic activity was demonstrated in 11- and 12-week-old infants. A slight correlation (p > 0.05) was also found in younger infants. These data suggest the influence of fetal and postnatal growth on the programming of the autonomic nervous system beyond the neonatal period. This influence may be one of the important mechanisms that link impaired growth in fetal and infant life to high blood pressure and other cardiovascular disease during childhood and adulthood (the Barker hypothesis).     

Quantitation in gated perfusion SPECT imaging: the Cedars-Sinai approach.

Cedars-Sinai's approach to the automation of gated perfusion single photon emission computed tomography (SPECT) imaging is based on the identification of key procedural steps (processing, quantitation, reporting), each of which is then implemented, in completely automated fashion, by use of mathematic algorithms and logical rules combined into expert systems. Our current suite of software applications has been designed to be platform- and operating system-independent, and every algorithm is based on the same 3-dimensional sampling scheme for the myocardium. The widespread acceptance of quantitative software by the nuclear cardiology community (QGS alone is used at over 20,000 locations) has provided the opportunity for extensive validation of quantitative measurements of myocardial perfusion and function, in our opinion, helping to make nuclear cardiology the most accurate and reproducible modality available for the assessment of the human heart.     

Overestimation of postischemic myocardial stunning on gated SPECT imaging: correlation with echocardiography.

BACKGROUND: Postischemic global and regional left ventricular (LV) dysfunction on stress-gated single photon emission computed tomography (SPECT) imaging is attributed widely to myocardial stunning. We sought to determine the specificity of gated SPECT for the detection of myocardial stunning after ischemic stress. METHODS AND RESULTS: Twenty-seven patients with an ischemic response to stress on dual-isotope exercise SPECT were enrolled prospectively. Transthoracic echocardiography was performed just before stress gated SPECT for assessment of regional wall motion and quantitative LV ejection fraction (LVEF). The 17 myocardial segments for each patient were scored for myocardial perfusion by stress gated SPECT, and regional wall motion by stress gated SPECT and echo. Of the 459 myocardial segments, 41% had perfusion defects, 15% had stress gated SPECT regional wall motion abnormality, 4.8% had poststress echo regional wall motion abnormality, and 3.9% had baseline regional wall motion abnormality. Overall, a stress gated SPECT regional wall motion abnormality had a sensitivity of 100% and a specificity of 89%. Among reversible perfusion defects of moderate severity or more, a stress gated SPECT regional wall motion abnormality had a specificity of 41% and a positive predictive value of 8%. Stress gated SPECT LVEF was similar to poststress echo LVEF for all patients, but significantly lower in patients with reversible perfusion defects of moderate severity or more. CONCLUSION: Post-stress gated SPECT imaging overestimates global and regional myocardial stunning. Caution should be exercised in interpreting poststress global or regional LV function on stress gated SPECT in scans with reversible ischemia.     

Prognostic value of gated SPECT in patients with left bundle branch block.

BACKGROUND: The aim of this study was to assess the prognostic value of quantitative gated technetium 99m tetrofosmin single photon emission computed tomography (SPECT) imaging in patients with left bundle branch block (LBBB). METHODS AND RESULTS: We followed up 101 consecutive patients with LBBB using Tc-99m tetrofosmin gated SPECT imaging. The mean follow-up was 1.24 years (maximum, 2.48 years). Hard endpoints were all-cause death and acute myocardial infarction. Event-free survival curves were obtained. Optimal cutoff points for left ventricular (LV) volumes and LV ejection fraction (EF) to predict outcome were determined by receiver operating characteristic curve analysis. Of the patients, 94 had an abnormal study. Fifteen hard events occurred (thirteen deaths). Perfusion abnormalities were similar for patients with or without events. For LV function parameters, the survival curves were maximally separated when we used cutoff values of 160 mL or greater for end-diastolic volume (P = .019 and hazard ratio [HR] of 1.04 for hard events, P = .024 and HR of 1.04 for all-cause death), 100 mL or greater for end-systolic volume (P = .043 and HR of 1.04 for hard events, P = .062 and HR of 1.04 for all-cause death), and lower than 35% for LVEF (P = .013 and HR of 0.81 for hard events, P = .047 and HR of 0.81 for all-cause death). CONCLUSION: By use of quantitative gated SPECT imaging, LBBB patients with an end-diastolic volume of 160 mL or greater, end-systolic volume of 100 mL or greater, or LVEF lower than 35% are at increased risk for subsequent cardiac events.     

阻塞性睡眠呼吸暂停综合征心率变异性的变化及其意义

目的 :研究阻塞性睡眠呼吸暂停综合征 （OSAS）患者心率变异性 （HRV ）的变化。方法 :经夜间多导睡眠图（PSG） 7h监测及动态心电图检查 ,选取重度 OSAS患者及正常受试者各 2 0例 ,采用时域法和频域法分析 HRV。结果 :OSAS组与对照组比较时域指标 SDANN ,SDNN ,r MSSD显著增高 ,SDNN- index则显著降低 ,频域指标VL F,L F,HF,L Fnrom,HFnorm及 L F/HF均较对照组显著增高。结论 :OSAS患者交感神经及副交感神经活动均增强 ,交感神经活动增强占优势     

门控心肌灌注断层显像测得心功能参数对老年冠心病预后的评价

目的　评价 99m Tc- MIBI门控心肌灌注断层显像中测得的心功能参数对老年冠心病 (CHD)预后的评定。方法　对老年人冠心病非心肌梗死组 (CHD- NMI) 33例 ,陈旧心肌梗死组 1 3例 (CHD- OMI)及 1 2例正常对照组进行 99m Tc- MIBI门控心肌灌注断层显像 ,利用计数法测得左室舒张末期容积 (EDV)、左室收缩末期容积 (ESV)和左室射血分数 (LVEF)。测得心功能参数对照组与 CHD- NMI组比较有差异 (P<0 .0 5) ,CHD-NMI与 CHD- OMI组比较有显著差异 (P<0 .0 1 )。结论　 EDV、ESV、LVEF是评价左室功能的重要指标 ,对 CHD的功能评价 ,疗效观察及预后的判定均有重要意义。     

Age-dependent influence of heart rate on Doppler indexes of left ventricular filling

Abstract. Background and objective . The Doppler indexes of left ventricular filling are related to age and heart rate. The aim of this study was to assess whether the influences of heart rate and age interactions (that is, whether the effect of heart rate on the Doppler indexes) is modified by age. Subjects and methods . The effects of atropine-induced heart rate increases on the transmitral velocities were compared in 10 younger healthy subjects aged 26–38 years and 12 older healthy subjects aged 50–67 years. Results . With a comparable total rise in heart rate (on average 20 beats min^-1), the peak early diastolic velocity decreased likewise in both groups (from 66±9 to 57±9 cm s^-1 in the younger age group and from 58 ± 15 to 47±13 cm s^-1 in the older age group). The peak atrial velocity remained unaltered in the older group (53 ± 16 vs. 52 ± 14 cm s^-1) but rose from 33 ± 6 to 44 ± 12 cm s^-1 in the younger (P = 0.02). The early-to-atrial peak velocity ratio decreased from 1.2 ± 0.6 to 1.0 ± 0.4 cm s^-1 in the older subjects and from 2.0 ± 0.5 to 1.4 ± 0.5 cm s^-1 in the younger subjects (P = 0.01). Changes in the other Doppler indexes were similar in both groups. Conclusions . The effect of heart rate on certain Doppler indexes of left ventricular filling is age-dependent. The peak velocity ratio cannot be interpreted without adjusting for heart rate in younger subjects, whilst in older people heart rate variation is of less importance.     

The effect of exercise and heart rate on fibrinolytic activity.

The effect of heart rate on plasma fibrinolytic activity was investigated in nine patients with dual chamber cardiac pacemakers before and after 10 min of stimulated tachycardia to 123 beats/min. The results were compared to seven volunteers who performed submaximal exercise to 90% target heart rate and to five of the seven who underwent a second period of exercise to a heart rate of 120 beats/min. During submaximal exercise (mean heart rate 152 beats/min) the median ECLT fell from 248 min (interquartile range 147.5-305) to 90 (55-202) P less than 0.01 and t-PA:Ag increased from 6.1 ng/ml (3.92-7.95) to 9.3 (8.45-12.7), P less than 0.025. PAI and PAI-1:Ag fell from 12.0 IU/ml (5.85-15.5) to 4.1 (1.85-11.67), P less than 0.01, and 9.7 ng/ml (2.8-10.6) to 6.7 (2.1-9.9), P less than 0.01 respectively. A lower level of exercise to 120 beats/min resulted in a reduction in ECLT from 215 min (167.5-228.5) to 135 (116-154), P = 0.05 and an increase in t-PA:Ag from 4 ng/ml (3.07-4.45) to 5.0 (3.3-5.22) P less than 0.05. PAI and PAI-1:Ag fell from 7.6 IU/ml (3.27-8.5) to 7.1 (2.77-7.4) and from 7.7 ng/ml (6.0-7.92) to 6.4 (4.8-7.3) respectively but these changes were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of heart rate on the refractory period of the atrium and A-V conducting system

The refractory periods of the atrium and A-V transmission system were studied in the cat and man using the interpolated extrasystole technique. Increasing heart rate by atrial pacing shortened the atrial refractory period, and the A-V functional refractory period. However, the A-V effective refractory period was prolonged by increased frequency of pacing. In the cat, bilateral section of the vagus nerve usually made the A-V effective refractory period impossible to measure.     

The influence of thyroid function on the circadian rhythm of heart rate in elderly euthyroid subjects

The influence of thyroid function on the circadian rhythm of heart rate was assessed using 24 hour electrocardiographic recordings in 196 elderly euthyroid subjects (78.4 +/- 8.1 years; male 60, 76.1 +/- 9.1 years; female 136, 79.4 +/- 7.4 years). Serum free T3, free T4 and TSH levels were measured by radioimmunoassay. To determine if heart rate fluctuates rhythmically with a circadian period, mean hourly heart rates in 24 hour electrocardiographic recordings were used to fit cosine curves by the statistical technique of least squares, and the parameters of the rhythm--the mesor, amplitude, acrophase, maximal and minimal hourly heart rates--were estimated. To investigate the factors influencing the diurnal variation of heart rate, we applied multiple regression analysis. The cosine curves were fitted with a P value of 0.01 or less in all subjects. The mesor, maximal and minimal hourly heart rates were inversely proportional to serum TSH concentrations in males. Neither amplitude nor acrophase had relation to the thyroid function in males. The mesor, maximal and minimal hourly heart rates were directly proportional to serum-free T4 concentrations and inversely proportional to serum TSH concentrations in females. The increase in the acrophase correlated with the increase in serum-free T4 levels, and the acrophase increased in proportion to serum-free T3 levels in females.     

Circadian rhythm of heart rate variability after acute myocardial infarction and its influence on the prognostic value of heart rate variability

This study examined heart rate (HR) variability in patients surviving acute myocardial infarction (AMI) to find the optimum time and duration of recording of the ambulatory electrocardiogram for the prediction of the risk of sudden cardiac death, or serious arrhythmic events, or both. Twenty patients (group I) who initially survived an AMI but later experienced serious events (death or symptomatic sustained ventricular tachycardia) during a 6-month follow-up were compared with 20 patients (group II) who remained free of complications for greater than 6 months after discharge. Groups I and II were matched with regard to age, gender, infarct site, ejection fraction, and beta-blocker treatment. HR variability was assessed in the 24-hour electrocardiograms recorded during the first 2 weeks after an AMI and in various portions of the complete 24-hour recording, with both the beginning and the length of the analyzed portion varied by 20 minutes (a total of 5,113 possibilities). The maximum reduction of HR variability in group I patients was systematically found when assessing HR variability in recordings starting approximately at 6 A.M. and lasting for approximately 8 hours. In the low-risk patient, the diurnal rhythm of HR variability is more marked than in the high-risk patient and the long-term components of HR variability due to the diurnal variation must be included in the measurement of HR variability when using it as a long-term predictor of risk from arrhythmic events after an AMI.