Highly effective adsorption of heavy metal ions by a thiol-functionalized magnesium phyllosilicate clay.

A thiol-functionalized layered magnesium phyllosilicate material (called Mg-MTMS), prepared by a direct and cost-effective co-condensation synthesis, has been investigated as a high-capacity adsorbent for heavy metal ions. Structural characterization by powder X-ray diffraction, infrared spectroscopy, solid-state 13C and 29Si NMR spectroscopies, and elemental analyses confirms the smectite-type structure and the high organic moiety content of this material. Mg-MTMS was found to be highly effective for the adsorption of Hg(II), Pb(II), and Cd(II) ions, exhibiting unprecedented metal ion uptake capacities of 603, 365, and 210 mg of metal/g of adsorbent, respectively. Mg-MTMS shows an equivalent affinity for the three metal ions, removing them from mixed metal solutions with an equal ion uptake capacity (approximately 400 mg of metal/g of adsorbent). Metal-loaded Mg-MTMS can be regenerated by acid treatment without altering the adsorbent properties. The high effectiveness of Mg-MTMS for the capture of metal ions is attributed to both the high concentration of complexing thiol groups (6.4 mmol of SH/g of Mg-MTMS) and the expansion capability of the framework, which facilitates the accessibility of the binding sites.

New nonradioactive microspheres and more sensitive X-ray fluorescence to measure regional blood flow.

We developed new nonradioactive microspheres and used more sensitive X-ray fluorescence spectrometers than used previously to measure regional blood flow in the heart and other organs. We demonstrated the chemical stability of eight kinds of heavy element-loaded microspheres and validated their use for regional blood flow measurement by comparing duplicate flows measured with radioactive and/or nonradioactive microspheres in both acute and chronic dog experiments. The wavelength-dispersive spectrometer (Philips PW 1480) has a higher sensitivity than the previously described X-ray fluorescent system and reduced the number of microspheres required for accurate measurement. The fine energy resolution of this system makes it possible to increase the numbers of different kinds of microspheres to be quantitated, but at present only eight kinds are available. We also used a synchrotron radiation-excited energy dispersive spectrometer. The monochromatic synchrotron radiation allowed us to obtain much higher signal-to-background ratios of X-ray fluorescence spectra than with the wavelength-dispersive system (50 dB more for Zr-loaded microspheres) and will enable analysis of fluorescent activity in smaller regions (< 20 mg) than the radioactive method does.

In utero ventilation augments the left ventricular response to isoproterenol and volume loading in fetal sheep.

In its normal circulatory environment, the fetal left ventricle can maximally increase output less than 2-fold, in contrast to the nearly 3-fold increase that occurs at birth. Several studies have attributed this finding to fetal myocardial "immaturity," and speculated that there is a rapid maturation of the myocardium in the perinatal period. We investigated the importance of the circulatory environment itself, rather than myocardial immaturity, by measuring left ventricular output (LVO) during in utero oxygen ventilation and isoproterenol infusion. We studied seven near-term fetal sheep greater than or equal to 2 d after placement of intravascular catheters, an endotracheal tube, and an electromagnetic flow transducer around the ascending aorta. We measured hemodynamic variables in the presence and absence of all combinations of oxygen ventilation, isoproterenol infusion, and volume infusion. Baseline LVO was normal (133 +/- 27 mL.kg-1.min-1). Individually, oxygen ventilation (136 +/- 11 mL.kg-1.min-1, p less than 0.001) and isoproterenol (48 +/- 11 mL.kg-1.min-1, p less than 0.05) increased LVO significantly; volume infusion did not. Their cumulative effect increased LVO nearly 3-fold (to 387 +/- 98 mL.kg-1.min-1), similar to levels seen in the newborn lamb. Mean left atrial pressure increased above right during oxygen ventilation (from 0.05 +/- 0.54 kPa to 0.82 +/- 0.39 kPa, p less than or equal to 0.0001). We conclude that the previously observed limitation in maximal LVO in the near-term fetus is primarily caused by its circulatory environment rather than relative myocardial immaturity, and speculate that a prominent Starling response is uncovered by decreases in left ventricular afterload and right ventricular constraint.

Local blood flow measured by fluorescence excitation of nonradioactive microspheres.

An X-ray fluorescence system with low Compton background and high counting efficiency was developed to measure regional blood flow with nonradioactive microspheres. The performance of the system was tested in vitro by counting mixed aqueous solutions of either Mo, Ag, and I; Nb, Ag, and Ba; or Zr, Mo, Rh, Ag, Sn, I, and Ba, as well as a mixture of Ag and Ba nonradioactive microspheres. Mixtures containing 2-20 ppm of each element were counted for 10 min by the fluorescence system, and the individual elements in mixtures of three to seven nonradioactive elements were measured with high accuracy. The best counting statistics were obtained for Ag. For 10-min counts, the system measures as few as 120 Ag microspheres with 30% standard deviation but measures 800 Ag microspheres per sample with 3.6% standard deviation. We compared regional myocardial blood flows determined simultaneously by fluorescence and radioactive microsphere methods; the latter samples were counted by a 3-in. NaI (Tl) well detector and pulse-height analyzer. The radioactive and nonradioactive measurements showed good correlations.

Red blood cell volume of the pig fetus.

A non-radioactive fluorescent excitation analysis technique was used to measure total red blood cell volume in 31 unanaesthetised pig fetuses in utero. Red blood cell volume (y in ml) was closely related (r = 0.94) to fetal bodyweight (x in g): where y = 2.92 + 0.0291x. Average red blood cell volume was 34 +/- 1 ml kg-1 fetal bodyweight. Average estimated (total) blood volume was 117 +/- 3 ml kg-1 fetal bodyweight. It was concluded that this non-radioactive indicator dilution measurement of red blood cell volume is a significant advance over the established 51Cr method, and that measurement of red blood cell volume may be used to estimate fetal bodyweight in utero.

Increased number of myocardial blood flow measurements with radionuclide-labeled microspheres.

We evaluated the use of a least-squares radionuclide separation technique to allow an increased number of myocardial blood flow measurements with radionuclide-labeled microspheres in dogs. Two sets of labeled microspheres were studied: a set of eight labeled with 125I, 153Gd, 57Co, 51Cr, 113Sn, 85Sr, 95Nb, and 46Sc; and a set of nine in which 125I and 46Sc were replaced with 114In, 54Mn, and 65Zn. For each microsphere label the nuclide activities determined by least-squares separation compared favorably with those actually added to in vitro samples containing a fixed amount of the other nuclides in the set. For the set of eight radionuclide-labeled microspheres, myocardial flow measurements made with the least-squares separation technique and the reference sample method were usually within 15% and almost all within 20% of direct measurements of coronary venous outflow in a right heart bypass preparation. Serial left atrial injections of 15-micron microspheres totaling 48 X 10(6) caused no significant changes in systemic hemodynamics, regional myocardial flows, or coronary pressure-flow relations, whether the coronary bed was autorelating or vasodilated with chromonar. We conclude that at least nine myocardial blood flow measurements can be made in dogs with acceptable accuracy and without evidence of dysfunction due to embolization of the coronary vascular bed. With appropriate validation, this method should be applicable to other organs and animal models as well.

Acute and chronic microsphere loss from canine left ventricular myocardium.

We determined the effects of time, type of anesthesia, and myocardial infarction on loss of radioactive microspheres averaging 9 or 15 micrometers diameter from left ventricular myocardium. The principle used to compute losses was comparison of the number of microspheres injected directly into coronary arteries to the numbers remaining in myocardium, appearing within 2-4 min in the coronary sinus, or trapped in the lungs. Losses of 9-micrometers microspheres within 2 min of injection were significantly greater for halothane (mean 6.3%) than nitrous oxide anesthesia (mean 3.3%), and in the next 2 h increased to 11.7 and 7.9%, respectively. Over 5 wk in conscious dogs losses were as high as 40 and 11% for 9 and 15 micrometers microspheres, respectively. Losses were not greater for infarcted than normal muscle, and negligible radioactivity appeared in paracardiac lymph nodes. Microspheres leaving the heart were almost all below 10.3 micrometers diameter, so that microspheres with diameters 10-14 (mean 12) micrometers might be the best size to use for myocardial studies.

Blood flow measurements with radionuclide-labeled particles.

When appropriately and correctly applied, the microsphere technique is relatively simple and extremely accurate. Distribution patterns, both of total systemic arterial blood flow or venous return as well as within specific organs, can be measured. Several techniques have been applied to quantitate flow using microspheres; the reference sample method is extremely simple and by far the most accurate of all. Collection of venous effluent is perhaps more accurate but requires extensive surgery and is almost certainly the least physiologic. Other methods used for quantitation, such as bolus injections of indocyanine green dye or in fusions of diffusable indicators, are considerably less accurate and therefore significantly reduce the reliability of the microsphere technique. Selection of the appropriate size microspheres allows for definition of arteriovenous anastomoses as well as the measurement of organ blood flows and distribution of blood flow within those organs. In most instances, smaller microspheres (15mu diameter or 8-10mu diameter) have significant advantages over larger ones. They are distributed more like red cells, obstruct less of the vascular bed, are less variable in size, and can be given in significantly greater numbers. This latter point is important, since the statistical criteria need to be satisfied and the use of small spheres allows for the more reliable measurement of blood flow to small organs or to small regions of organs.