Electron temperature and density probe for small aeronomy satellites.

A compact and low power consumption instrument for measuring the electron density and temperature in the ionosphere has been developed by modifying the previously developed Electron Temperature Probe (ETP). A circuit block which controls frequency of the sinusoidal signal is added to the ETP so that the instrument can measure both T(e) in low frequency mode and N(e) in high frequency mode from the floating potential shift of the electrode. The floating potential shift shows a minimum at the upper hybrid resonance frequency (f(UHR)). The instrument which is named "TeNeP" can be used for tiny satellites which do not have enough conductive surface area for conventional DC Langmuir probe measurements. The instrument also eliminates the serious problems associated with the contamination of satellite surface as well as the sensor electrode.

Electrode contamination effects of retarding potential analyzer.

The electrode contamination in electrostatic analyzers such as Langmuir probes and retarding potential analyzers (RPA) is a serious problem for space measurements. The contamination layer acts as extra capacitance and resistance and leads to distortion in the measured I-V curve, which leads to erroneous measurement results. There are two main effects of the contamination layer: one is the impedance effect and the other is the charge attachment and accumulation due to the capacitance. The impedance effect can be reduced or eliminated by choosing the proper sweeping frequency. However, for RPA the charge accumulation effect becomes serious because the capacitance of the contamination layer is much larger than that of the Langmuir probe of similar dimension. The charge accumulation on the retarding potential grid causes the effective potential, that ions experience, to be changed from the applied voltage. Then, the number of ions that can pass through the retarding potential grid to reach the collector and, thus, the measured ion current are changed. This effect causes the measured ion drift velocity and ion temperature to be changed from the actual values. The error caused by the RPA electrode contamination is expected to be significant for sounding rocket measurements with low rocket velocity (1-2 km/s) and low ion temperature of 200-300 K in the height range of 100-300 km. In this paper we discuss the effects associated with the RPA contaminated electrodes based on theoretical analysis and experiments performed in a space plasma operation chamber. Finally, the development of a contamination-free RPA for sounding rocket missions is presented.

Means to remove electrode contamination effect of Langmuir probe measurement in space.

Precaution to remove the serious effect of electrode contamination in Langmuir probe experiments has not been taken in many space measurements because the effect is either not understood or ignored. We stress here that one should pay extra attention to the electrode contamination effect to get accurate and reliable plasma measurements so that the long time effort for sounding rocket/satellite missions does not end in vain or becomes less fruitful. In this paper, we describe two main features of voltage-current characteristic curves associated with the contaminated Langmuir probe, which are predicted from the equivalent circuit model, which we proposed in 1970's. We then show that fast sweeping dc Langmuir probes can give reliable results in the steady state regime. The fast sweeping probe can also give reliable results in transient situations such as satellite moves through plasma bubble in the ionosphere where the electron density drastically changes. This fact was first confirmed in our laboratory experiment.

Cardiac contractile function during coronary stenosis in dogs: association of adenosine in glycolytic dependence.

We tested the hypothesis that during critical coronary stenosis, endogenous adenosine alters myocardial glucose utilization to support myocardial contractile function (MCF). Anesthetized mongrel dogs were instrumented to measure hemodynamic variables, regional MCF (sonomicrometry), and substrate uptakes. Critical coronary artery stenosis was established with a screw clamp on the left circumflex coronary artery (LCX). Either 8-phenyltheophylline (3 x 10(-7) mol/min; adenosine-receptor blockade), iodoacetate (1 x 10(-5) mol/min; glycolysis blockade), or vehicle was infused into the LCX and the left anterior descending coronary artery (LAD). Critical coronary stenosis caused small decreases in arterial blood pressure and LCX blood flow, but no significant changes in MCF or other hemodynamics. There was a significant decrease in the O2 supply-to-consumption ratio in the stenotic region and an increased glucose uptake. Infusion of either 8-phenyltheophylline or iodoacetate caused a decrease in MCF in the stenotic LCX region concomitant with a decreased glucose uptake and without further changes in blood flow. This was not seen in the nonstenotic (LAD) region. These data support the hypothesis, indicating that glycolysis is vital for maintaining regional MCF during a decrease in the myocardial O2 supply-to-consumption ratio and that adenosine is important in this regard, independent of its vasoactive properties.

Iced temperature injectate for thermodilution cardiac output determination causes minimal effects on cardiodynamics.

OBJECTIVES: Controversy exists regarding the ideal injectate temperature for measuring cardiac output. Iced temperature injectate gives a higher signal/noise ratio and less variability in the measured cardiac output. Thus, less volume and fewer measurements are required. Advocates of room temperature injectate have suggested that iced temperature injectate may perturb cardiodynamics. This concern has remained largely untested. To help resolve this controversy, we examined the effects of 5 mL iced injectate (0 degrees to 4 degrees) infusions on cardiodynamics. DESIGN: Prospective, randomized, controlled study. SETTING: A critical care research laboratory. SUBJECTS: Five domestic pigs, weighing between 20 to 25 kg. INTERVENTIONS: Under barbiturate anesthesia, pigs underwent placement of a) a thermodilution catheter in the right internal jugular vein; b) a right carotid artery catheter for mean arterial pressure; and c) sonomicrometry crystals for dynamic measurements of left ventricular dimensions. Calculations were made of end-systolic and end-diastolic left ventricular volume and ejection fraction. Six cardiac output measurements were performed in each pig. Data were obtained at baseline (just before iced temperature injectate infusion) and every 3 sec for 9 secs. MEASUREMENTS AND MAIN RESULTS: The only significant effect seen with iced temperature injectate infusion was a small, transient decrease in heart rate (-5.9 +/- 1.1 beats/min from a baseline heart rate of 144.8 +/- 20.6 beats/min). Indices of preload, contractile function, and dynamic cardiac geometry were unaffected. CONCLUSIONS: Iced temperature injectate used in clinically relevant volumes causes transient negative chronotropic effects, but reservations regarding other perturbations of cardiodynamics are unfounded. Thus, the use of iced temperature injectate for cardiac output determination is still a viable alternative to room temperature injectate use, especially when a larger signal/noise ratio is required.

Pulmonary capillary wedge pressure estimates of left ventricular preload are inaccurate in endotoxin shock: contribution of Starling resistor forces to septic pulmonary hypertension.

We tested the hypothesis that Starling resistor forces play a significant role in the increase in pulmonary vascular resistance during endotoxin shock. Anesthetized pigs (n = 9) were given Escherichia coli endotoxin (ETX; .5 mg/kg intravenously over 30 min). Mean pulmonary arterial pressure (MPAP) and pulmonary capillary wedge pressure (PCWP) were recorded through a Swan-Ganz catheter. Pulmonary capillary pressure (Pc) was obtained from the analysis of the transient pulmonary artery pressure decay curve upon balloon inflation. Both proximal (Ra) and distal (Rv) pulmonary vascular resistance were calculated from cardiac output (CO), MPAP, Pc, and PCWP. Left atrial pressure (LAP) was measured directly via a left atrial catheter. Left ventricular end-diastolic wall thickness (LV-EDWT) was monitored by sonomicrometry, and used as an index of left ventricular preload. The results at baseline (t = 0) and t = 60 (30 min after the cessation of endotoxin infusion) were compared with saline control animals (n = 6). Data were analyzed with a two-way ANOVA followed by contrast of residuals (p < or = .05). After endotoxin, arterial blood pressure and CO fell significantly, an effect not seen in control pigs. In the control group neither LAP nor PCWP changed significantly over time, and remained equivalent to each other. In the septic shock group there was no difference between LAP and PCWP at t = 0. However, by t = 60 LAP dropped and PCWP rose significantly. This fall in LAP and increase in PCWP were significantly different from the time-matched control values, and from each other.(ABSTRACT TRUNCATED AT 250 WORDS)