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Biomedical subjects

L C Chow

Publications and source records attributed to L C Chow.

At least 91 records · Page 5Linked to original sources
PubMed1988

Early changes of right heart geometry after pulmonary thromboendarterectomy.

To determine the changes in right heart hemodynamics and geometry early after surgery for chronic pulmonary hypertension due to large vessel thromboembolic occlusion, 30 patients were evaluated 8 +/- 8 days (mean +/- SD) before and 6 +/- 4 days after pulmonary thromboendarterectomy by two-dimensional echocardiography and right heart catheterization. Surgery resulted in an early significant improvement in hemodynamic variables including mean pulmonary artery pressure (48 +/- 12 to 28 +/- 8 mm Hg, p less than 0.001), right ventricular systolic pressure (76 +/- 20 to 47 +/- 15 mm Hg, p less than 0.001), pulmonary vascular resistance (935 +/- 620 to 278 +/- 252 dynes.s.cm-5, p less than 0.001) and cardiac index (2.0 +/- 0.5 to 2.9 +/- 0.6 liters/min per m2, p less than 0.001). Similarly, echocardiographic variables of right heart structures, which were well outside the normal range preoperatively, improved significantly early after thromboendarterectomy. These included diameters of the pulmonary artery (2.8 +/- 0.3 to 2.4 +/- 0.4 cm, p less than 0.001), inferior vena cava (2.9 +/- 0.6 to 2.2 +/- 0.4 cm, p less than 0.001) and right atrium (6.8 +/- 1.5 to 5.9 +/- 1.5 cm, p less than 0.001) as well as right ventricular short axis (4.5 +/- 0.8 to 3.7 +/- 0.8 cm, p less than 0.001) and long axis (8.7 +/- 0.9 to 8.1 +/- 0.9 cm, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

The determination of extracellular fluid volume in whole dental plaque using potassium- or chloride-selective micro-electrodes.

This paper describes a procedure for the determination of the volume of water available for diffusion in whole plaque samples collected from single sites. In this procedure, known micro volumes of H2O were added to single-site plaque samples with calibrated nanoliter pipettes and the potassium or chloride concentration at each dilution measured with ion-selective micro-electrodes. By plotting the inverse of the concentration versus the volume of H2O added, one can determine the original volume of plaque fluid available for diffusion. Volumes determined in simultaneous measurements performed with chloride and potassium micro-electrodes were statistically indistinguishable. From the observed constancy in the initial potassium concentration in rat and human plaque fluid, a simplified macro method is suggested which allows for estimation of the extracellular fluid volume within 20% error in plaque samples.

Animals↗
PubMed1988

Effects of rinses with an acidic calcium phosphate solution on fluoride uptake, caries, and in situ plaque pH in rats.

The effects of oral rinses on enamel fluoride uptake, caries, and plaque pH in rats were investigated by use of (1) an acidic calcium phosphate solution (CPS) saturated with dicalcium phosphate dihydrate (DCPD) and (2) a 1% fluoride solution. Osborne-Mendel rats, 19 days of age, were randomly assigned to one of four mouth-rinse treatment groups, with the two consecutively administered rinses being: H2O-H2O; H2O-F; CPS-H2O; and CPS-F. The treatments were administered on days 1 through 4, and the animals were provided with a cariogenic challenge throughout the study. The groups treated with F exhibited significantly higher mean levels of enamel-bound F than did the non-F groups. Furthermore, CPS significantly increased uptake of F by enamel when used as an adjunct to the F treatment. The caries scores of the CPS-F and H2O-F groups were not statistically different; however, a strong negative correlation was observed between enamel F content and caries scores, indicating that as more F was incorporated into the teeth, less caries formation occurred. Despite the significant differences in enamel F and caries scores among some of the treatment groups, post mortem in situ plaque pH drop in response to a sucrose rinse showed no differences among these groups.

Animals↗
PubMed1988

Micro-analysis of mineral saturation within enamel during lactic acid demineralization.

In this study, the physicochemical factors responsible for caries-like lesion propagation were investigated by means of a micro-analytical system used to study the fluid within a lesion during a simulation of the decay process. Four 500-microns-thick serial sections prepared from a single human molar were mounted between glass plates with only the natural surface of the tooth exposed. Microwells were then drilled into sound and pre-existing carious regions of the section through one of the plates. These microwells were then filled with fluid under mineral oil, and after a week of equilibration, the natural surface of the section was exposed to a lesion-producing fluid. The concentrations of calcium, phosphate, and hydrogen ions of the fluid in the wells were then followed as a function of time as the lesion advanced. The results of this study, in which lactic acid was used to demineralize enamel, were consistent with those previously reported (Vogel et al., 1987a): The solution within the lesion remained saturated during the acid attack. Differences in initial mobilities of the calcium and phosphate and other ions, a result of the permselectivity of the enamel, increased the concentrations within the lesion and permanently changed the ratio of these ions in the lesion solution. Based on these results, we suggest that the ionic permselectivity of tooth enamel can have a profound effect on the transport of mineral from a caries lesion.

Calcium↗
PubMed1988

Accurate localization of ruptured sinus of Valsalva aneurysm by real-time two-dimensional Doppler flow imaging.

The surgical approach to the repair of a ruptured sinus of Valsalva aneurysm can depend on the cardiac chamber into which rupture occurs. This report details the color flow Doppler images in two patients who developed a right sinus of Valsalva aneurysm to right atrial fistula owing to bacterial endocarditis. In both cases, the color flow Doppler image was superior to contrast aortography in identifying the chamber into which rupture had occurred. The early experience with real-time two-dimensional Doppler flow imaging suggests that this noninvasive technique is valuable in the management of ruptured sinus of Valsalva aneurysms.

Adult↗
PubMed1987

Calcium phosphate phase transformations in serum.

A better knowledge of the pathological calcification mechanisms should provide a rational basis for their control. In the present study, dicalcium phosphate dihydrate (DCPD, CaHPO4 X 2H2O) was used as a source of calcium and phosphate ions to investigate the mechanism of formation of more basic and more insoluble calcium phosphates in ultrafiltered serum (u.f.s.). DCPD crystals were suspended in u.f.s. at 37 degrees C by constant stirring; samples were removed periodically for calcium and phosphate analysis and pH measurement. Occasionally, samples of solids were removed for X-ray diffraction. The experiments were carried out both with and without a 5.5% CO2 atmosphere. After initially becoming saturated with DCPD, the u.f.s. composition changed and became saturated with respect to octacalcium phosphate (OCP, Ca8H2(PO4)6 X 5H2O). At this point OCP crystals were detected in the solid phase by X-ray diffraction. Further stirring changed the composition so that it became undersaturated with both DCPD and OCP and shifted toward, but did not reach, a value so low as to be saturated with hydroxyapatite (OHAp, (Ca5(PO4)3OH). The presence of CO2 in the atmosphere slowed down, but did not prevent, the above sequence of events. The above results strongly suggest that calcifications, beneficial and pathological, that take place in serum may involve OCP as a precursor, which hydrolyzes in situ to a more basic apatitic product. The results also indicate that direct formation of OHAp in u.f.s. is a very slow process and may occur only rarely. The process appears to be similar in whole serum.

Calcium↗
PubMed1987

Calcium phosphate saturation levels in ultrafiltered serum.

Calcifications occurring in arteriosclerotic plaque and other pathological deposits are important health concerns, and the nature of these deposits and their mechanisms of formation warrant investigation. Crystals of the relevant calcium phosphates were equilibrated with the undiluted ultrafiltered human serum (u.f.s.) at 37 degrees C by constant stirring and periodically removing samples for calcium and phosphate analysis and for pH measurement. The solubility measurements were carried out both with and without a 5.5% CO2 atmosphere, the physiological partial pressure of CO2. The apparent ion activity products of well-crystallized dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP), and hydroxyapatite (OHAp) equilibrated in u.f.s. were calculated from the calcium and phosphate concentrations and pH in each case for comparison with their known solubility products. In this way the well-crystallized calcium phosphates serve as fiducial solubility standards, thereby minimizing errors due to complexing of calcium and phosphate ions by u.f.s. constituents. Under 5.5%, CO2 native u.f.s. was found to be substantially undersaturated with respect to DCPD, slightly supersaturated with respect to OCP, and highly supersaturated with respect to OHAp. The ion activity product of DCPD in DCPD-saturated u.f.s. was 2.4 X 10(-7), and the ion activity product of OCP in OCP-saturated u.f.s. was 4 X 10(-49), slightly above their solubility products (Ksp(DCPD) = 2.3 X 10(-7), Ksp(OCP) = 2.5 X 10(-49). The ion activity products of DCPD and OCP in u.f.s. under CO2 indicate that the concentrations of calcium and phosphate complexing agents (except bicarbonate) are quite low. The u.f.s. remained supersaturated with respect to OHAp even after 2 months of equilibration.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1987

Enhanced enamel F uptake by monocalcium phosphate monohydrate gels.

Application of DCPD-forming solutions has been shown to increase substantially the enamel reactivity toward F. The effectiveness of a variation of this treatment procedure, in which the DCPD-forming solution was replaced by a viscous carboxymethylcellulose gel containing monocalcium phosphate monohydrate (MCPM), was evaluated by use of 12 extracted human molars. The MCPM gel was highly effective in enhancing the F uptake by enamel. The mean F uptakes by teeth treated with MCPM gel, followed by exposure to a F solution, were 3972 (+/- 565), 2383 (+/- 312), and 1751 (+/- 313) ppm, respectively, in the outer 5-, 10-, and 15-microns depths in enamel. These uptakes were 2374, 1273, and 852 ppm more than those of the control teeth. Because the F solution was undersaturated with respect to CaF2, the F incorporated into the enamel was believed to be in apatitic form and not as CaF2. The MCPM gel has advantages over the DCPD-forming solution because (1) much longer gel-tooth contact times can be achieved, and (2) the treatment agent can readily be delivered to specific sites where the tooth needs the protection most.

Apatites↗
PubMed1987

Micro-electrode techniques for the analysis of oral fluids.

This paper describes the use of micro-electrodes for the analysis of small fluid volumes recovered from the oral environment. The analysis has several advantages: (1) It directly measures the activity of ions, a quantity more relevant to mineral saturation than the conventionally measured concentration, (2) minimum fluid volume for analysis is usually less than 0.005 microL, small enough to avoid sample pooling in most analyses, (3) numerous ions can be measured simultaneously, (4) the analysis time is very short, and (5) the use of mineral oil to isolate specimens provides a simple method for controlling the CO2 tension and humidity over the specimens.

Calcium↗
PubMed1986

Effects of neutral salts in a bench-scale caries model.

In an earlier paper on bench-scale simulation of the caries process, it was shown that the passage of ions through ion-permselective barriers could have profound effects on the composition of the solution within the "lesion" at steady state. As indicated in earlier papers, these changes are produced by unequal rates of diffusion of Ca and PO4 ions prior to reaching steady state. Comparable effects are attributable to F ions when present. Here, we used the same two-compartment diffusion apparatus and membranes, as described in the earlier paper, to show that a neutral salt, such as NaCl, disproportionates under the influence of membrane potential. Thus, although the Na and Cl concentrations are nearly equal in the "plaque-saliva" compartment, they become very different in the "lesion" solution. An excess of Na over Cl is equivalent to the presence of the component NaOH, and an excess of Cl over Na is equivalent to the presence of HCl. With the highly permselective commercial membranes used in these experiments, the Ca/P ratio in the "lesion" solution changed from an initial value of 1.6 to a value as high as 53 or as low as 0.1 at steady state. These phenomena are relevant to the events taking place in a caries lesion and must be taken into account in devising physicochemical models of the caries process. A valid caries model, in turn, offers the possibility of identifying steps in the caries mechanism which might be blocked to prevent tooth decay.

Calcium↗
PubMed1985

Hydrolysis of dicalcium phosphate dihydrate in the presence or absence of calcium fluoride.

Effects of temperature (25 and 37 degrees C), pH (4.9-10.5), and CaF2 on CaHPO4.2H2O (DCPD) hydrolysis were studied in a pH-stat. Octa-calcium phosphate (OCP) was the product at pH 6.2-6.8 and 25-37 degrees C; thermodynamically stable apatitic compounds were formed at higher pH and/or higher temperature. In the presence of CaF2, apatite was the product, its crystallinity improved, and the fluoride content increased as pH of the reaction decreased. The results demonstrate the remarkable ability of fluoride to promote the hydrolysis of an acidic calcium phosphate, DCPD, to apatite.

Apatites↗
PubMed1985

Enhanced fluoride uptake from mouthrinses.

It has been shown in laboratory and animal studies that tooth enamel becomes considerably more reactive toward low levels of fluoride after receiving pre-treatment which forms dicalcium phosphate dihydrate (DCPD) in the enamel as an intermediate. This in vitro study was undertaken to determine the effect on human enamel fluoride uptake of incorporating DCPD-forming rinses into a conventional fluoride rinsing program. In one group, enamel samples received a one-minute rinse with 0.2% NaF each day for 20 days. Samples in the second group were treated identically, except that they were also given a one-minute DCPD-forming rinse prior to the first, sixth, eleventh, and sixteenth fluoride rinses. At the end of the rinsing program, all samples were washed in 1 M KOH to remove labile fluorides. The enamel biopsy data showed that the fluoride uptake resulting from 0.2% NaF alone was not statistically significant, whereas uptake produced by the DCPD-forming plus NaF rinses was significant. The results suggest that the DCPD-forming rinse may improve the efficacy of fluoride rinse programs.

Apatites↗
PubMed1985

Application of an x-ray image magnifier to the microradiography of dental specimens.

A highly parallel incident x-ray beam combined with x-ray image magnification was used to obtain high-resolution microradiographs of dental specimens. Preliminary results obtained using a rotating anode x-ray generator show that limitations associated with conventional contact microradiography regarding spatial resolution, sample thickness, and sample orientation, relative to the film, were significantly reduced.

Dental Caries↗