Effects of sevoflurane on autonomic nerve activities controlling cardiovascular functions in rats

Effects of different inspiratory concentrations of sevoflurane (fluorometyl-1,1,1,3,3,3,-hexafluoro-2-propylether) on blood pressure, heart rate and efferent activities of cardiac sympathetic, cardiac parasympathetic and renal sympathetic nerves were examined using rats either under the resting condition or during noxious mechanical stimulation of a hindpaw. Under the resting condition, an increase in the inspiratory concentration of sevoflurane from 2.1% to 4.2% gradually caused a decrease in blood pressure and heart rate. With the increase in the sevoflurane concentration, cardiac sympathetic nerve activity decreased, whereas renal sympathetic nerve and cardiac parasympathetic nerve activities did not change significantly. When noxious mechanical stimulation was applied to a hind-paw by pinching, blood pressure and heart rate, renal sympathetic and cardiac sympathetic nerve activities all increased at the 2.1% concentration of sevoflurane. The responses of these parameters were attenuated at the 3.1% concentration of sevoflurane and almost disappeared at the 4.2% concentration. Cardiac parasympathetic nerve activity did not change significantly during the pinching stimulation throughout the 2.1–4.2% concentration increase.(Kurosawa M, Meguro K, Nagayama T et al.: Effects of sevoflurane on autonomic nerve activities controlling cardiovascular functions in rats. J Anesth 3: 109–117, 1989)     

A new closed-system using partially frozen injectate for thermodilution cardiac output determinations

The FI (partially frozen injectate) system, a new closed-system devised by the authors for thermodilution cardiac output determinations, has two major features: 1) it needs no ice-filled receptacle to keep injectate cold because it uses partially frozen injectate, and 2) it can go without monitoring the injectate temperatures during the whole process of cardiac output determinations. The author evaluated the accuracy and reproducibility of cardiac output determinations with the FI system in 10 critically ill patients, as compared with another closed-system (which is commercially available) and the standard open method. The injectate temperatures in the FI system were also measured in vitro. The mean injectate temperature in the FI system was 0.71 ± 0.26°C and 80% of the injectate temperatures were lower than 1.0°C. Even when no monitoring of injectate temperatures was made, the predicated error in the calculated cardiac output resulted as low as 2% with the FI system. The mean cardiac output values were not statistically different between the FI system and the other two systems.(Maruta H, Usuda Y, Okutsu Y et al.: A new closed-system using partially frozen injectate for thermodilution cardiac output determinations. J Anesth 3: 35–39, 1989)     

Autoregulation of contractility in the myocardial cell

Summary An investigation was carried out on isolated cat's papillary muscle in order to study displacement effects upon the intensity and the time course of the contractile activity. Displacements occurring before or very early during a contractile cycle produce effects which can be entirely explained on the basis of the cardiac active length-tension relation. Displacements occurring later exhibit additional effects in so far as either stretches or releases induce a drop of contractile activation such that the course of the subsequent tension development is markedly below that of the same displacement applied earlier. In order to separate these effects from those based on the active length-tension correlation experiments were performed in which very short release-stretch or stretch-release operations were applied so that the muscle length was virtually the same at the beginning and at the end of the operation. The results obtained under these conditions can be summarized as follows.The extend to which contractile tension drops after a stretch-release or a release-stretch cycle has been applied depends upon (1) the stimulus intervention interval (2) the length change performed (3) the velocity of displacement during the intervention. It is not dependent on the initial muscle length. Increasing the extracellular Ca-concentration considerably reduces the displacement effects. The results are tentatively explained by assuming an internal feedback loop between a variable of the contractile machinary and the preceding mechanism of activation.This investigation was supported by the Deutsche Forschungsgemeinschaft (grant Ka 287, 1+3).     

CARDIAC RATE RESPONSES TO CIGARETTE SMOKING: A STUDY UTILIZING RADIOTELEMETRY

Radiotelemetry of the human EKG was obtained to observe for rate alterations during spontaneous cigarette smoking. Ten subjects were observed for a total of 26 hours during which time 50 cigarettes were smoked. The utilization of telemetry allowed the subjects to continue their usual afternoon behavior. There were no rate changes before, during, or after smoking which could be attributed to the cigarette. These results differ from most previous reports. Telemetry allows for two departures from past designs; subjects were ambulant and smoking behavior was spontaneous (both in initiation and rate). It is suggested that these departures are related to the results of the present study.     

Irregular connexin43 expressed in a rare cardiac hamartoma containing adipose tissue in the crista terminalis

Cardiac hamartomas are very rare and are demarcated masses of enlarged, hypertrophied, mature myocytes and collagen tissue. Cardiac hamartomas are generally circumscribed in the right ventricle or atrium, but not reported in the crista terminalis (CRT). The CRT is crucial in electrophysiology, is related to arrhythmogenesis, and is targeted by radiofrequency catheter procedures. Previous works only described the benign natures of prominent CRT using non-invasive methods. This study describes an unusual cardiac hamartoma originating from the CRT and extending toward the tricuspid valve. Microscopically, this hamartoma comprised dense collagen and adipose tissue, mixed with hypertrophy, but with disarrayed cardiomyocytes. An irregular gap junction, connexin43, was demonstrated in this cardiac hamartoma.     

Effects of arousal and natural baroreceptor activation on the human muscle stretch reflex

The nociceptive flexion reflex is inhibited during systole; this inhibition may be due to increased baroreceptor stimulation. It is yet to be determined whether other spinal reflexes are similarly modulated across the cardiac cycle. There is also evidence that stretch and tendon reflexes are facilitated by increased arousal. This study investigated the effects of phase of the cardiac cycle and arousal on the muscle stretch reflex components M1, M2, and M3. Stretch reflexes were elicited in leg muscles at six intervals across the cardiac cycle during rest, number repetition, and mental arithmetic. Mental arithmetic provoked increased cardiovascular arousal and facilitated both M1 and M2 compared to rest and number repetition. The stretch reflex did not vary with the phase of the cardiac cycle. While the stretch reflex is susceptible to arousal, natural baroreceptor-mediated modulation across the cardiac cycle may be specific to nociception.     

Kubicek每搏心输出量计算公式的三维有限元仿真研究

我们从 Kubicek模型三维有限元仿真的角度对 Kubicek每搏心输出量计算公式的临床应用价值进行了研究。在计算机仿真研究中 ,我们对比了模型仿真结果、具体采用 Kubicek每搏心输出量计算公式所得结果以及所设模型的理论计算结果。仿真结果表明 :模型中阻抗改变与主动脉中血液容积改变之间存在着近似的线性关系 ,证明了 Kubicek每搏心输出量计算公式具有一定的临床应用价值 ,同时也为心阻抗血流图基础理论提供了新的研究途径。     

Changes in the blood supply of the gastrointestinal tract in rats with age

Summary Regional blood flow of the gastrointestinal (GI) tract and cardiac output have been determined in male Sprague-Dawley rats weighing from 30–726 g. The cardiac output (ml/min per kg) was highest in rats weighing 80–100 g. In heavier rats the cardiac output decreased proportionally with the body weight. The gradient of blood flow to the different parts of the GI tract develops step by step. In the weaning period the blood flow (ml/min per g tissue) through the stomach was less than that through the distal parts of the GI tract. However, the blood flow through the small intestine, cecum and large intestine was uniform at this age. In rats weighing 80–100 g the blood flow through both the cecum and large intestine was less than that through the small intestine. The gradient in blood flow through the various segments of small intestine developed last.     

Quantitative Characterization of Epicardial Wave Fronts During Regional Ischemia and Elevated Extracellular Potassium Ion Concentration

This study applied zero-delay wave number spectral estimation as a means of quantifying the changes in activation and recovery sequences of propagating plane waves on the epicardial surface of in situ porcine hearts during regional hyperkalemia and ischemia. Unipolar electrograms (104) were recorded from the left ventricular surface of nine hearts using a plaque electrode array with 1 mm spatial sampling intervals. The objectives were (1) to define a set of parameters capable of quantifying the spatial and temporal changes in measured extracellular potentials associated with localized ischemia prior to the onset of conduction block; (2) to elevate regional levels of extracellular potassium ion concentration and quantify potential changes due to this known physiologic manipulation; and (3) to use quantitative parameters to make statistical comparisons in order to distinguish wave fronts during normal, ischemic and hyperkalemic conditions. Results showed that the parameters of wave number and average temporal frequency and the associated power, as determined from the wave number spectrum, provided statistically significant (p < 0.05) quantification of changes in wave front features during normal and ischemic or hyperkalemic conditions. The results were consistent with results obtained from conventional time–space domain methods like isochronal mapping and electrograms, with the advantage of a quantitative result enabling simple comparisons and trend analysis for large numbers of heart beats. © 1998 Biomedical Engineering Society. PAC98: 8759Wc, 8722Fy, 8780+s     

The sustained inward current in sino-atrial node cells of guinea-pig heart

 Single myocytes were dissociated from the sino-atrial (SA) node of guinea-pig hearts. Only a quite small fraction of the cell population showed spontaneous action potentials and these cells were characterized by the presence of the hyperpolarization-activated cation current I _f , the delayed rectifier K⁺ current I _K and the L-type Ca²⁺ current I _Ca,L as well as by the absence of both the transient outward current I _to and the inward rectifier K⁺ current I _K,1. After blocking I _f and I _K, depolarizing pulses from –80 mV revealed a large nicardipine-sensitive late current (NSLC). The NSLC was scarcely affected by decreasing extracellular [Ca²⁺] ([Ca²⁺]_o) from 1.8 to 0.1 mM, while it was decreased significantly by depleting [Na⁺]_o, differently from I _Ca,L. NSLC was blocked by nicardipine and was increased by Bay K 8644. NSLC was increased by isoprenaline and the additional application of acetylcholine reversed the increase of this current. We conclude that NSLC is largely composed of I _st described in the rabbit SA node pacemaker cells, and that I _st is unique for the pacemaker cells in mammalian SA node cells. Most of the quiescent cells showed neither I _f nor I _st. Received: 22 July 1996 / Received after revision: 30 September 1996 / Accepted: 9 October 1996