Observations suggesting a high incidence of exercise-induced severe mitral regurgitation in patients with mild rheumatic mitral valve disease at rest

OBJECTIVES

The aim of this study was to determine the hemodynamic effects of upright bicycle ergometry in symptomatic patients with mild, mixed mitral stenosis and regurgitation.

BACKGROUND

Patients with seemingly mild rheumatic mitral valve disease often complain of exertional dyspnea or fatigue. These symptoms are usually ascribed to flow-dependent increases in the gradient across the stenotic mitral valve. Although catheterization studies in these patients may demonstrate an increase in mitral valve gradient proportional to an increase in cardiac output, this approach does not specifically address the underlying mechanism of any observed increases in mitral gradient or left atrial (i.e., pulmonary capillary wedge) pressure. Exercise echocardiography is uniquely suited to the dynamic assessment of exercise-induced hemodynamic changes.

METHODS

Fourteen symptomatic patients with exertional dyspnea and mild mitral stenosis and regurgitation at rest performed symptom-limited upright bicycle ergometry with quantitative two-dimensional, Doppler and color Doppler echocardiographic analysis.

RESULTS

Average pulmonary artery systolic pressure in the 13 patients with adequate spectral signals of tricuspid regurgitation increased from 36 +/- 5 mm Hg (mean +/- SD) at rest to 63 +/- 14 mm Hg at peak exercise (p < 0.001). The mean transmitral pressure gradient in all patients increased from 4.5 +/- 1.4 mm Hg at rest to 12.7 +/- 2.7 mm Hg at peak exercise (p < 0.001). Five patients developed severe mitral regurgitation during exercise.

CONCLUSIONS

Patients with exertional dyspnea and mild mitral stenosis and regurgitation at rest demonstrate a marked increase in pulmonary artery systolic pressure and mean transmitral pressure gradient during dynamic exercise. In a subset of these patients, marked worsening of mitral regurgitation appears to be the underlying mechanism of this hemodynamic deterioration. Because of the small sample size, this novel observation must be considered preliminary with respect to the true prevalence of exercise-related development of severe mitral regurgitation. If additional studies confirm the importance of this phenomenon, it has important implications for the management of patients with rheumatic mitral valve disease.

Lung uptake of technetium 99m sestamibi: relation to clinical, exercise, hemodynamic, and left ventricular function variables

BACKGROUND

Technetium 99m sestamibi (2-methoxyisobutyl isonitrile [MIBI]) is a relatively new radiopharmaceutical with improved imaging characteristics for exercise myocardial perfusion studies compared with thallium 201. Although increased lung uptake of 201Tl has been shown to have important clinical significance, reflecting severity of coronary artery disease and left ventricular function, the factors affecting MIBI lung uptake are unknown. Therefore we examined the potential clinical, exercise, hemodynamic, myocardial perfusion, and ventricular function determinants of lung uptake of MIBI on exercise myocardial perfusion studies.

METHODS AND RESULTS

The study cohort consisted of 103 patients referred for evaluation of coronary artery disease with exercise MIBI myocardial perfusion imaging. All patients underwent both a standard 1-day rest-stress MIBI planar imaging protocol and rest echocardiography. With the anterior-view stress images obtained 1 hour after MIBI injection, regions of interest were drawn over peak lung and myocardial activities and a lung/heart ratio was calculated. Multivariate regression analysis was used to relate the lung/heart ratio to clinical, exercise and hemodynamic, myocardial perfusion, and echocardiographic left ventricular function scores. We found no significant relation between lung/heart ratio and any patient variable.

CONCLUSIONS

Unlike 201Tl, lung uptake of MIBI is not related to indexes of exercise, left ventricular dysfunction, or perfusion abnormalities. Thus MIBI lung uptake does not appear to have the same clinical significance as 201Tl lung uptake.

Chemical transformation/derivatization of O6-methyl- and O6-(hydroxyethyl)guanine for detection by GC-EC/MS

In this project we set out to make an important class of DNA adducts, comprising O6-alkyl and O6-(hydroxyalkyl)guanines, susceptible to sensitive detection by GC-EC/MS. While existing literature indicated that pentafluorobenzylation would be useful for the ring NH site on these compounds, how to best overcome the polarity of the exocyclic NH2 and OH groups, without losing the O6-alkyl moiety, was less clear. Working with O6-methylguanine and O6-(2'-hydroxyethyl)guanine as representative analytes, we found that the NH2 group could be converted into fluoro without loss of the O6 substituent. For the OH group, a comparison of several derivatives (OR') led to R' = tert-butyl as the best choice at this stage. The latter work, especially via NMR, also allowed exact structural assignments to be made for the N7 and N9 pentafluorobenzyl isomeric derivatives that formed. Of these R' derivatives, the N7 isomers migrated slower on silica-TLC, had higher GC retention times, had lower responses by GC-EC/MS, and were preferentially destroyed as the GC column aged. However, the N9 isomer was slower on TLC when the OH was not derivatized. This behavior was rationalized using a concept of "polar footprint" for the derivatives. The concept also seemed to explain the puzzling GC-EC/MS behavior of some related compounds in our laboratory. Apparently the polar footprint should be minimized in designing derivatives for trace detection by GC-EC/MS.

The impact of cardiac index on cerebral hemodynamics

BACKGROUND AND PURPOSE

Current noninvasive testing allows accurate assessment of cerebrovascular hemodynamics. The cardiovascular influence on the noninvasive assessment of cerebrovascular studies has not been defined. This study was designed to determine the effect of cardiac index (CI) on cerebral blood flow velocities, ocular pulse amplitude, ophthalmic systolic pressure, and ocular blood flow (OBF) as currently estimated by noninvasive laboratories.

METHODS

Based on a retrospective study of 181 patients, we prospectively evaluated 45 patients undergoing right heart catheterization for hemodynamic monitoring to correlate the relation between CI, transcranial Doppler sonography, and ocular pneumoplethysmography. Patients with hemodynamic instability, severe carotid stenoses, massive cerebral infarct, or sepsis were ineligible for the study. Simultaneous recordings of systemic blood pressure, ophthalmic systolic pressure, heart rate, ocular pulse amplitude, middle cerebral artery blood flow velocities, and cardiac output were obtained on all patients. OBF was calculated from the heart rate and ocular pulse amplitude.

RESULTS

The relation between OBF and CI is expressed by the equation CI = 2.36 + 0.61 x OBF (r = .47, P = .0010). The middle cerebral artery peak systolic velocities and CI had a correlation of .36 (P = .0181). The equation, derived from the linear relation between OBF and CI, was then validated on a sample of 15 patients. With the apparent linear relation between OBF and CI, we used the derived equation to predict CI from OBF. The OBF determination predicted CI within 30% in all patients and within 20% in 53.3% of the patients.

CONCLUSIONS

We demonstrated that OBF and middle cerebral artery systolic velocity decrease with diminishing CI. Our findings suggest that CI may be potentially estimated in selected patients by noninvasive assessment of OBF using ocular pneumoplethysmography.

4-(Trifluoromethyl)-2,3,5,6-tetrafluorobenzyl bromide as a new electrophoric derivatizing reagent

4-(Trifluoromethyl)-2,3,5,6-tetrafluorobenzyl bromide (TTBB) was synthesized in a single step from alpha,alpha,alpha,2,3,5,6-heptafluoro-p-xylene. The purpose of TTBB is to function as an analogue of pentafluorobenzyl bromide (PFBB) in electrophoric derivatization reactions prior to detection by gas chromatography-electron-capture negative ion mass spectrometry (GC-ECNI-MS). In more detail, it was anticipated that TTBB could be used along with, or as a substitute for, PFBB to help control some interferences and confirm results. This is because a TTBB-product (of an analyte) would have different retention and sometimes m/z characteristics than a corresponding PFBB product in GC-ECNI-MS, while the two products should be similar in their ease of formation and yields. Results demonstrating these expectations were achieved by derivatizing and detecting two analytes with these reagents: N7-(2-hydroxyethyl)xanthine, and 2,3-pyrenedicarboxylic acid.

Interphotoreceptor retinoid-binding protein (IRBP), a major 124 kDa glycoprotein in the interphotoreceptor matrix of Xenopus laevis. Characterization, molecular cloning and biosynthesis

We have demonstrated that the neural retina of Xenopus laevis secretes into the extracellular matrix surrounding the inner and outer segments of its photoreceptors a glycoprotein containing hydrophobic domains conserved in mammalian interphotoreceptor retinoid-binding proteins (IRBPs). The soluble extract of the interphotoreceptor matrix contains a 124 kDa protein that cross-reacts with anti-bovine IRBP immunoglobulins. In vitro [3H]fucose incorporation studies combined with in vivo light and electron microscopic autoradiographic analysis, showed that the IRBP-like glycoprotein is synthesized by the neural retina and secreted into the interphotoreceptor matrix. A 1.2 kb Xenopus IRBP cDNA was isolated by screening a stage 42 (swimming tadpole) lambda Zap II library with a human IRBP cDNA under low-stringency conditions. The cDNA hybridizes with a 4.2 kb mRNA in adult Xenopus neural retina, tadpole heads as well as a less-abundant mRNA of the same size in brain. During development, IRBP and opsin mRNA expression correlates with photoreceptor differentiation. The translated amino acid sequence of the Xenopus IRBP clone has an overall 70% identity with the fourth repeat of the human protein. Sequence alignment with the four repeats of human IRBP showed three highly conserved regions, rich in hydrophobic residues. This focal conservation predicts domains important to the protein's function, which presumably is to facilitate the exchange of 11-cis retinal and all-trans retinol between the pigment epithelium and photoreceptors, and to the transport of fatty acids through the hydrophilic interphotoreceptor matrix.

Footwear dermatitis

We conducted a study to determine the prevalence and clinical patterns of footwear dermatitis, patch testing 50 patients with suspected footwear dermatitis and 30 controls with 22 allergens of a shoe series (Chemotechnique Diagnostics AB, Malmö, Sweden). The overall prevalence among contact dermatitis cases was 11.7%. The dorsa of the feet and toes were the commonest sites involved. 70% of patients showed sensitivity to footwear allergen(s), as opposed to 6.67% of controls. Potassium dichromate and colophony were the commonest sensitizers. Other sensitizers were the rubber accelerators 2-mercaptobenzothiazole (MBT) and diphenylguanidine (DPG) and a dye p-aminoazobenzene. Of the 23 patients patch tested with pieces or scrapings of footwear, only 3 showed positive reactions. We recommend that there should be primary and secondary footwear screening series to detect the responsible allergens, with the ultimate objective of providing correct nonallergenic footwear for our patients, with the help of manufacturers and research institutes.

Primary contribution of the injector to carryover of a trace analyte in high-performance liquid chromatography

When a low-nanogram amount of N1,N3-bis-(pentafluorobenzyl)-N7-(2- [pentafluorobenzyloxy]ethyl)xanthine was subjected to HPLC, low-picogram amounts of the compound could be detected subsequently (off-line by gas chromatography-electron-capture negative-ion mass spectrometry) after injection of pure mobile phase. This was in spite of significant, intermediate washing of the injector and column. It was determined that essentially 99.9% of this analyte contamination came from the injector. Use of two injectors is a practical remedy for this problem.

High-performance liquid chromatography versus solid-phase extraction for post-derivatization cleanup prior to gas chromatography-electron-capture negative-ion mass spectrometry of N1,N3-bis-(pentafluorobenzyl)-N7- (2-[pentafluorobenzyloxy]ethyl)xanthine, a product derived from an ethylene oxide DNA adduct

N7-(2-Hydroxyethyl)xanthine (N7-HEX), as a standard, has been measured at the low picomole level by the following sequence of steps: (1) derivatization with pentafluorobenzyl bromide; (2) post-derivatization sample cleanup by reversed-phase high-performance liquid chromatography (HPLC) or silica solid-phase extraction; and (3) separation/detection by gas chromatography electron-capture negative-ion mass spectrometry (GC-ECNI-MS). The average yield of product from the two sample cleanup procedures applied to 95 pg (0.48 pmol) of N7-HEX was comparable: 60% for HPLC; 56% for solid-phase extraction. The reaction blanks (0 pg N7-HEX) showed an interfering GC-ECNI-MS peak after HPLC cleanup. This problem was not encountered with solid-phase extraction, which, along with its greater convenience, made it the preferred technique for post-derivatization sample cleanup.

Studies on phospholipids of different mutants of Salmonella minnesota

Lipid composition of the cells of smooth (S form) and core-defective rough mutants (Ra, Rb & Re) of Salmonella minnesota has been studied. The readily-extractable lipids (RELs), acid-extractable lipids, and polar and nonpolar phospholipids have been analysed. Fatty acid composition of the different fractions containing phospholipids and other neutral lipids have been determined by GLC and GC-MS techniques. Phosphatidyl glycerol (PG), phosphatidylethanolamine (PE) and diphosphatidyl glycerol (DPG) were the major phospholipids present in all the strains. The major saturated fatty acid found was C16:0, and unsaturated fatty acids were, C16:1 and C18:1. Cyclopropane fatty acids, C17cy and C19cy, were also present in small amounts. Increased amounts of REL and unsaturated fatty acids were found in the mutants compared with the smooth strain. The amount of PG and PE decreased and DPG increased in the mutant strains.

Preparation of electrophoric derivatives of N7-(2-hydroxyethyl)guanine, an ethylene oxide DNA adduct

Ethylene oxide, a potential human carcinogen, mainly damages DNA by reacting at guanine sites to form N7-(2-hydroxyethyl)guanine. In order to determine this DNA adduct with high sensitivity by gas chromatography, we have prepared, for comparison purposes, four electrophoric derivatives. The two that are most promising to date are bis- and tris-pentafluorobenzyl products prepared by first chemically transforming the N7-(2-hydroxyethyl)guanine to a corresponding xanthine, and then reacting the latter with pentafluorobenzyl bromide. These two derivatives are obtained in good yields and give molar responses of 0.6 and 0.5, respectively, relative to that of lindane by gas chromatography with electron-capture detection.

Preparation and mass spectral characterization of pentafluorobenzyl derivatives of alkyl and hydroxyalkyl-nucleobase DNA adducts

Pentafluorobenzyl (PFBz) derivatives of the following nucleobases were prepared: cytosine, 5-methylcytosine, O2-methylcytosine, O2-ethylthymine, O4-ethylthymine, 5-hydroxymethyluracil, N6-methyladenine, O6-methylguanine, O6-hydroxyethylguanine and O6-hydroxyethylpurine. 13C nuclear magnetic resonance was diagnostic for O- versus N-attachment of the PFBz moiety: the resonance of the methylene carbon appeared in the range 29.15-42.13 ppm for NCH2C6F5, and 58.45-69.01 for OCH2C6F5. Considerable structural information was provided by mass spectrometry with ionization by electron impact. All of the derivatives were detected with high sensitivity and specificity by gas chromatography with detection by electron capture negative ion mass spectrometry, reflecting not only their chemical and physical stability, but also their strong tendency to form a structurally diagnostic anion, [M - PFBz]-, in high yield under these ionization conditions. PFBz derivatives are therefore attractive forms of alkyl-substituted nucleobases for analysis by mass spectrometry.

Ester and related derivatives of ring N-pentafluorobenzylated 5-hydroxymethyluracil. Hydrolytic stability, mass spectral properties, and trace detection by gas chromatography-electron-capture detection, gas chromatography-electron-capture negative ion mass spectrometry, and moving-belt liquid chromatography-electron-capture negative ion mass spectrometry

One consequence of radiation damage to DNA is the conversion of thymine to 5-hydroxymethyluracil (HMU). In order to sensitively detect this DNA adduct by gas chromatography (GC) or high-performance liquid chromatography (HPLC) with electron-capture detection techniques, it is necessary to derivatize it. This study was designed to select an optimum ester derivative of the aliphatic hydroxyl group on HMU. N1, N3-Bis(pentafluorobenzyl)-HMU was formed as a parent derivative, and from this a series of esters. Also O-pentafluorobenzyl and O-tetrafluorobenzyl ether derivatives were prepared. Of the esters the pivalyl derivative was the best choice because it formed easily, was relatively stable to aqueous hydrolysis (t 1/2 = 9.8 days at pH 11.5, 24 degrees C) and gave a response at fmol levels by GC and LC comparable to that of the ethers. Unanticipated was a good response as well for the parent derivative, a free hydroxyl compound, by GC and LC at this level. The work also demonstrates a high performance by LC-electron-capture negative ion mass spectrometry with a belt interface for the trace detection of derivatives of this type.