Respiration-dependent ventricular pacing compared with fixed ventricular and atrial-ventricular synchronous pacing: aerobic and hemodynamic variables

A pacemaker that adapts heart rate in response to the patient's metabolic requirements has been developed. The pacemaker uses breathing frequency and tidal volume as the indicators of physiologic demand. Maximal physical work capacity, anaerobic threshold, oxygen uptake (16 patients) and hemodynamic variables (9 patients) were assessed with fixed rate (VVI), atrial synchronous (VDT/I) and respiration-dependent ventricular (VVI-RD) pacing. All subjects attained their anaerobic threshold in stress tests with VVI pacing. The maximal physical capacity (p less than 0.001), work time to attain the anaerobic threshold (p less than 0.01) and oxygen uptake (p less than 0.001) were significantly greater with VVI-RD than with VVI pacing. The transition from the supine to the standing position was characterized by a significant increase of cardiac index at rest with both VDT/I and VVI-RD pacing as compared with VVI pacing. Progressive increments in the cardiac index and average left ventricular stroke work index were significantly different at submaximal and maximal exercise when VVI and VVI-RD were compared. At maximal exercise, mean cardiac output was also significantly different: 10.21 +/- 2.5 (SD) liters/min with VVI, 11.2 +/- 0.8 liters/min with VDT/I (p less than 0.05) and 12.65 +/- 3.1 liters/min with VVI-RD (p less than 0.05) pacing. Maximal oxygen extraction values were greater with VVI and VVI-RD pacing than with VDT/I pacing. Pulmonary artery end-diastolic pressures at maximal exercise were within the normal range with the three different modes of pacing. In conclusion, there is a significant (25%) improvement in exercise performance with VVI-RD pacing as compared with VVI pacing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Direct determination of distribution volume and disappearance rate of native creatine kinase in humans

Distribution volume (DV) and disappearance rate (K_d) of native creatine kinase (CK), parameters needed for enzymatic estimation of infarct size, have not been characterized in humans. Values for these parameters have been determined in experimental models and extrapolated for use in humans. During hemodynamic monitoring, 100 to 150 ml of enzyme-rich plasma was collected from 10 patients with acute myocardial infarction, stored at ?30° C for a maximum of 6 days, and then rapidly reinfused back to the same patient after return of CK serum activity to baseline levels. After reinfusion, blood samples were obtained at 5- to 15-minute intervals for 2 hours and at 30- to 60-minute intervals for an additional 10 hours. In each specimen, total CK activity and MM-CK and MB-CK concentrations were determined by spectrophotometry and radioimmunoassay. Data were analyzed by either nonlinear least-squares approximation or the noncompartmental approach after baseline subtraction. Concentration of immunologically active molecules appeared to decline in parallel to enzymatic activity. In three patients a double exponential decay was demonstrated. All others exhibited single exponential decay, with a K_d of 0.0023 ± 0.00057 (SD) min^?1. DV averaged 3284 ± 693 (SD) ml, 5% of body weight. There was no correlation between K_d estimated from terminal portions of CK time-activity curves following infarction and K_d calculated after reinfused plasma. It was concluded that a one-compartment model using values for K_d and a DV compatible with plasma volume is suitable for clinical application, and that true K_d cannot be determined from the terminal portion of CK time-activity curves after acute infarction.     

生物安全实验室(BSL-3;ABSL-3)安全性稳定性试验效应的探讨

目的高等级生物安全实验室建设是一个系统工程。从工艺平面布局、人流物流气流组织、空调系统设置、自动控制方案、软件管理以至材料选用都直接关系到生物安全实验室的建设质量，本文介绍了BSL-3；ABSL-3实验室在设计和系统调试过程中的一些经验和体会。     

学龄前住院患儿心理护理体会

针对现代护理对医疗技术和理念的新要求,通过对儿科心理护理工作实践的归纳总结,探讨儿科护理中心理护理的理念及措施,提高患儿及家属对儿科护理的满意度。     

Predictive value of changes in R-wave amplitude after exercise in coronary heart disease

To assess the predictive value of coronary events reflected by changes in R-wave amplitude after exercise, 146 patients with angiographically documented coronary heart disease were studied. All patients were followed up for 6 years, during which time myocardial infarction and death of cardiovascular origin were considered endpoints. The incidence of events in patients in whom R-wave amplitude decreased (normal response) and in those in whom R-wave amplitude did not change or increase (abnormal response) were compared. The incidence of coronary events in patients with a normal response was 23% and in those with an abnormal response, 45.8% (p less than 0.01). Correlating the results with several noninvasive and angiographic variables, an abnormal R-wave response showed a significantly higher rate of events in the subsets of patients with prior myocardial infarction, absence of cardiomegaly, maximal functional capacity lower than 4 METs, maximal heart rate higher than 140 beats/min and abnormal left ventricular function. Thus, the changes in R-wave amplitude after exercise is a variable that should be taken into account when assessing the risk of future events in patients with coronary heart disease.     

Ventricular septal rupture after myocardial infarction: Diagnosis by two-dimensional and pulsed doppler echocardiography

Rupture of the ventricular septum in the acute phase of myocardial infarction (MI) requires prompt recognition for correct management. The 2-dimensional and pulsed Doppler echocardiographic findings are reported from 11 patients with ventricular septal (VS) rupture. VS rupture was confirmed by cardiac catheterization in 9 patients, surgery in 4 patients and necropsy examination in 3 patients. Two-dimensional echocardiography (echo) directly visualized the rupture in 7 patients and assessed the size and location of an associated aneurysm in 10. In all patients, M-mode pulsed Doppler echo allowed detection of the left-to-right shunting due to VS rupture, but failed to indicate the rupture site. M-mode pulsed Doppler echo was reliable for detecting VS rupture after MI. Conversely, 2-dimensional echo was less effective in the direct visualization of the rupture, but provided anatomic and functional information that was useful in medical and surgical management. Thus, the techniques are complementary and should be used in combination for the assessment of VS rupture in acute MI.