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Biomedical subjects

M A Gordon

Publications and source records attributed to M A Gordon.

At least 55 records · Page 3Linked to original sources
PubMed1993

The pressure rate quotient is not an indicator of myocardial ischemia in humans. An echocardiographic evaluation.

BACKGROUND: The pressure rate quotient (PRQ; mean arterial pressure/heart rate [MAP/HR]) less than one (PRQ < 1) has been proposed as a simple, clinically available hemodynamic index of myocardial ischemia. Recent investigations using electrocardiography (ECG) detection of myocardial ischemia have not found this index reliable. We prospectively compared PRQ < 1 to detection of myocardial ischemia via transesophageal echocardiography (TEE) and ECG in patients undergoing elective coronary artery bypass graft. METHODS: Forty-six of 50 patients admitted into the study had acceptable data acquisition. Calibrated ECG leads II and V5 were recorded with a computerized ST-segment analyzer. Hemodynamic data were stored at 2-min intervals. After tracheal intubation, a 5.0-MHz TEE probe was inserted. Electrocardiography-detected ischemia was defined as new onset ST-segment deviation (> or = 1 mm) lasting for > 1 min. Transesophageal echocardiography determination of ischemia was worsening of wall motion > or = 1 grade and lasting > 1 min. PRQ < 1 was compared to ECG and/or TEE as a predictor or indicator of myocardial ischemia. RESULTS: Electrocardiography ischemia occurred during 230 intervals in 10 patients, and in only 41 of 230 (18%) was PRQ < 1. Transesophageal echocardiography-defined ischemia occurred during 592 intervals in 9 patients, and in 119 of 592 (20%) PRQ < 1. Compared to ECG and TEE, PRQ < 1 had a low sensitivity (21%) and poor positive predictive value (25%). CONCLUSIONS: Pressure rate quotient < 1 is an unreliable indicator and predictor of myocardial ischemia when evaluated by ECG, TEE, and the combination of these modalities in patients undergoing coronary artery bypass graft surgery.

Adult↗
PubMed1993

A comparison of growth rates of acoustic neuromas: nonsurgical patients vs. subtotal resection.

A conservative approach to the management of acoustic neuromas in elderly patients has been used since 1971. Elderly patients without symptoms of brain stem compression are initially treated by observation and yearly radiographic imaging. A translabyrinthine radical-subtotal resection is performed if brain stem compression is present or if tumor is growing rapidly. Twenty-three patients, ages 65 to 86 years, had initial nonsurgical management of their tumors. Growth rates could be determined for 16 patients. Thirteen patients not requiring surgery had an average tumor growth rate of 0.6 mm/yr. Three patients with an average growth rate of 6.8 mm/yr eventually required surgery. No patient whose tumor was < 15 mm at initial evaluation has experienced brain stem symptoms or demonstrated rapid tumor growth. Twenty-four patients ages 65 to 86 years underwent planned subtotal tumor excision. Eighteen patients followed postoperatively for more than 1 year demonstrated an average rate of regrowth of tumor of 0.7 mm/yr.

Aged↗
PubMed1993

Intraoperative hemodynamic changes are not good indicators of myocardial ischemia.

Intraoperative myocardial ischemia is associated with an increased risk of a perioperative myocardial infarction (PMI) in patients undergoing coronary artery bypass graft surgery. If reversible physiologic variables could be identified that are indicators of myocardial ischemia, treatment might be instituted early to prevent cardiac morbidity. In patients undergoing elective coronary artery bypass graft surgery, we evaluated the relationship between several premorbid patient characteristics, selected hemodynamic variables, intraoperative myocardial ischemia, and a PMI. In addition we evaluated these selected hemodynamic variables as intraoperative indicators of myocardial ischemia. The following variables were evaluated: heart rate, > 80 beats/min; systolic arterial blood pressure, > 160 mm Hg; systolic arterial blood pressure, < 80 mm Hg; mean arterial blood pressure, < 60 mm Hg; pulmonary artery diastolic pressure, > 18 mm Hg; a 5 mm Hg increase in pulmonary artery diastolic pressure; rate pressure product, > 12,000 beats/min.mm Hg; and a pressure rate quotient, < 1.0 mm Hg/beats/min. The premorbid patient characteristics selected were previous myocardial infarction, recent myocardial infarction (within 1 wk of surgery), type and number of coronary lesions, beta-blocker therapy, and calcium blocker therapy. One hundred consecutive (n = 100) patients for elective coronary artery bypass graft surgery were studied prospectively before the initiation of cardiopulmonary bypass (CPB). Patients were monitored with a Hewlett Packard computer ST segment analyzer using leads II and V5. Ischemia was defined as the new onset of ST segment deviation of > or = 1 mm from the baseline electrocardiogram (ECG) (preinduction) for at least 2 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Aberration of the tissue collagenase system in association with otosclerosis.

Studies of aural and other body tissues suggest that otosclerosis represents the local manifestation of a general disorder of connective tissue. In particular, collagen abnormalities have been described. We have undertaken a pilot study of the in vivo messenger RNA (mRNA) transcription for procollagenase (precursor of collagenase), as well as for stromelysin and tissue inhibitor of metalloprotease (TIMP), an activator and a specific inhibitor of tissue collagenase activity, respectively. Human skin from individuals with surgically confirmed otosclerosis was compared to skin from their family members (clinically positive and clinically negative) and from unrelated normal controls. Preliminary data indicate that on average there are significantly lower levels of mRNA production for stromelysin among individuals with otosclerosis as compared to all others tested. Similar trends were demonstrated for TIMP and procollagenase, although these did not achieve statistical significance. In addition to suggesting a pathogenetic mechanism for the development of the disease, these data could serve as the basis of possible confirmatory tests for early diagnosis of otosclerosis and as a method for evaluating the genotype of offspring of affected individuals prior to their age of clinical manifestation. This could translate into the application of prophylactic treatment regimens in the future. The proposed abnormalities also suggest candidate genes for otosclerosis.

Audiometry↗
PubMed1991

A preliminary investigation of prediction of mean arterial pressure after self-regulatory treatments.

This study investigated the ability of pretreatment variables from three different domains (social-demographic, psychological, and psychophysiological) to predict posttreatment mean arterial pressure (MAP) for 59 unmedicated males with mild hypertension who were participating in a cross-cultural (USA-USSR) comparison of autogenic training and thermal biofeedback to a self-relaxation control. The overall multiple regression equation consisted of two variables and indicated that higher diastolic blood pressures during a cold pressor task were predictive of greater MAP reductions while higher scores on the Irritability subscale of the Buss-Durkee Hostility Scale were predictive of less MAP reductions. Suggestions for future research in this area are provided.

Adult↗
PubMed1991

Is the pressure rate quotient a predictor or indicator of myocardial ischemia as measured by ST-segment changes in patients undergoing coronary artery bypass surgery?

Perioperative myocardial ischemia is associated with an increased risk of perioperative myocardial infarction (PMI). Several attempts have been made to define intraoperative hemodynamic predictors of myocardial ischemia. In a canine preparation with coronary stenosis, a pressure rate quotient (PRQ = mean arterial pressure/heart rate) less than one (PRQ less than 1) indicated subendocardial myocardial ischemia. The authors tested this hypothesis in patients undergoing elective coronary artery bypass graft operation (CABG), using electrocardiogram (ECG) ST-segment changes (leads II/V5) to diagnose myocardial ischemia. Sixty (n = 60) patients having CABG surgery were prospectively studied before initiation of cardiopulmonary bypass. Calibrated ECG leads II and V5 (diagnostic mode) were monitored continuously and recorded with the use of a Hewlett-Packard computer ST-segment analyzer. In addition, arterial and pulmonary artery pressures were monitored. Ischemia was defined as new-onset ST deviation (greater than or equal to 1 mm from the baseline ECG). ECG and hemodynamic data were stored at 2-min intervals for subsequent computer analysis. Serial creatinine phosphokinase (CPK) X MB (%) determinations and 12-lead ECGs were collected for the initial 3 postoperative days. Of the 3,463 intervals (2 min) available for study, 3,322 (96%) were satisfactorily recorded for 60 patients. Ischemia occurred during 65 intervals in 9 patients (9 of 60), of which only 34% (22 of 65) were associated with a PRQ less than 1 (P less than 0.01). In contrast, there were 466 intervals during which PRQ was less than 1, but without ECG evidence of ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

The genetics of otosclerosis: a review.

Otosclerosis is a heritable disease affecting the otic capsule. Its genetics have been studied, but remain incompletely elucidated. Presented is a detailed analysis of the literature pertaining to the mode of inheritance and epidemiology of clinical and histologic otosclerosis. Consideration is given to connective tissue abnormalities found in association with the disease. The hypothesis that otosclerosis is an isolated manifestation of a generalized connective tissue disorder is discussed. The author also suggests that otosclerosis, rather than being a discrete entity, may represent a heterogeneous group of diseases.

Adolescent↗
PubMed1988

Interactions of pyrethroids with gramicidin-containing liposomal membranes.

Fluorescence steady-state anisotropy and phase-modulation lifetime techniques have been utilized to study the interactions of pyrethroid compounds with fluid-phase phosphatidylcholine membranes containing the polypeptide gramicidin. This polypeptide is considered to be a model of hydrophobic regions of cellular integral membrane proteins. The pyrethroids disorder lipid packing in cellular membranes and gel-phase liposomes but do not disorder lipid packing in fluid-phase lipid (Stelzer, K.J. and Gordon, M.A. (1984) J. Immunopharmacol. 6, 381-410; (1985) Biochim. Biophys. Acta 812, 361-368) Irrespective of liposomal size, gramicidin incorporation resulted in a substantial increase in anisotropy of the fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene (DPH), in fluid phase lipid. In the absence of gramicidin, permethrin and three other pyrethroids, allethrin, cypermethrin and fenpropathrin, increased DPH anisotropy. In these fluid phase systems, as the protein:lipid ratio was increased, the extent of the pyrethroid-mediated increase in fluorescence anisotropy diminished. Also, the pyrethroids shortened DPH fluorescence lifetimes. At high gramicidin:lipid ratios, permethrin substantially lowered anisotropy in the fluid phase lipid, relative to controls. The data suggest that pyrethroids disturb fluid-phase lipids which have been promoted to a relative state of order by proximity to an integral membrane protein. This type of order is one which is represented by DPH fluorescence anisotropy. A model based on these results is proposed to explain the effects of pyrethroids on lipid packing order in cellular membranes, as determined by DPH fluorescence anisotropy.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1988

Dermatophilus congolensis and "hairy" leukoplakia.

The authors report the first human case (to our knowledge) of infection of the oral mucosa by Dermatophilus congolensis. Septate branching filaments morphologically identical to those of D. congolensis were identified in the lingual epithelium of a male homosexual employed as an animal handler. This actinomycete is the cause of dermatophilosis, a proliferative exudative dermatitis affecting many animal species. Clinical features suggested "hairy" leukoplakia (HL), a hyperkeratotic tongue lesion for which human papillomavirus (HPV) and Epstein-Barr virus (EBV) have been implicated as etiologic agents. Immunoperoxidase staining for HPV capsid antigen was negative. Direct immunofluorescent staining with a conjugate specific for D. congolensis identified the bacterial structures as those of this species while excluding morphologically similar organisms.

Actinomycetales↗
PubMed1988

Improved method for azole antifungal susceptibility testing.

A reproducible method is described for the determination of the MICs of ketoconazole, miconazole, fluconazole, and itraconazole with sharp endpoints when employed with either yeasts or molds. A semisolid medium is used with controlled pH and standardized inoculum. The time of reading results is a critical factor in the conduct of this test. The medium is simple to prepare and has a relatively long refrigerator shelf life in a user-ready state, requiring only the addition of a freshly prepared inoculum after restoration to room temperature.

Antifungal Agents↗
PubMed1987

Comparison of relative susceptibilities of Candida species to three antifungal agents as determined by unstandardized methods.

Three groups of isolates, each comprising four isolates of Candida species, were selected for their diversity of susceptibilities to amphotericin B, flucytosine, or ketoconazole. The isolates were distributed in duplicate and in blinded fashion to three laboratories where a total of eight procedures were performed for each drug. From the decoded results, intralaboratory variability among replicate determinations was found usually to fall within a fourfold range. Interlaboratory variation, however, was 16-fold or greater for all isolates, ranging to 50,000-fold differences for some isolates. Relative susceptibilities of isolates within each method could be determined in 11 of the 24 drug-method combinations and agreed with the reference rank order in all but one instance. Our findings underscore the lack of agreement among laboratories for the susceptibility testing of yeasts but indicate that such differences could likely be resolved by standardization without loss of clinical value.

Agar↗
PubMed1986

Application of constrained regularization analysis to low-angle quasi-elastic light scattering.

A constrained regularization procedure has been applied to a low-angle quasi-elastic light scattering system in order to determine particle size distributions. The conditions under which this procedure may be successfully applied to low-angle photon correlation spectroscopy have been characterized. Acquisition of photon count data over a short time period, relative to the long exponential decay constants of correlation functions obtained at low forward angles, resulted in particle size distributions which were stable with regard to peak width and weighted mean particle radius. Irrespective of the number of photon counts obtained, peak resolution and position on the particle size scale were not optimized unless anomalies in the correlation function due to transient increases in the mean photon counting rate were removed from the photon count data prior to autocorrelation. When such measures were taken, reasonable size distributions were obtained for well characterized protein standards and for liposomal suspensions.

Light↗
PubMed1986

Effect of alterations in lipid packing order by hydrophobic solutes on the association state of protein assemblies in model membranes.

The effects of two hydrophobic solutes which perturb lipid packing order, permethrin and allethrin, on the aggregated state of a lipid membrane-incorporated protein, bacteriorhodopsin (BR), have been determined by resonance energy transfer measurements. As temperature is increased from well below the main gel-fluid phase transition temperature (Tc) of the lipid, patches of aggregated BR dissociate into monomers, a few degrees below the Tc (M.P. Heyn, A. Blume, M. Rehorek and N.A. Dencher, Biochemistry 20 (1981) 7109; M.P. Heyn, R.J. Cherry and N.A. Dencher, Biochemistry 20 (1981) 840). Permethrin and allethrin were found to cause a decrease in the temperature of BR disaggregation which was associated with a decrease in the Tc of the lipid. In gel phase dipalmitoylphosphatidylcholine at 25 degrees C, the pertubing effects of permethrin on lipid packing order were associated with a decrease in the average patch radius from 123 to 33 A. It is concluded that perturbation of lipid packing order by small hydrophobic molecules may alter the stability of protein assemblies in membranes.

Bacteriorhodopsins↗
PubMed1985

Interactions of pyrethroids with phosphatidylcholine liposomal membranes.

Interactions of several pyrethroids with membrane lipids in the form of dipalmitoylphosphatidylcholine (DPPC) liposomes have been studied using fluorescent membrane probes. Fluorescence anisotropy values and lifetimes (determined by phase-shift and demodulation techniques) of the fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene, were decreased in gel phase liposomes by pyrethroids at concentrations on the order of 10 microM. The pyrethroids containing a cyano substituent were also observed to cause collisional quenching of diphenylhexatriene fluorescence. Pyrethroids differed in their effectiveness at lowering the phase transition temperature of DPPC, and in their ability to broaden the temperature range of this transition. The fluorescence intensity of DPPC-incorporated chlorophyll a was used to monitor the pretransition of DPPC and the lateral diffusion of a membrane component located in the polar headgroup region. Permethrin did not affect chlorophyll a fluorescence intensity at any temperature. It may be concluded from these results that pyrethroids are preferentially located in the interior hydrophobic regions of the lipid bilayer, and that these compounds can disorder hydrocarbon packing in the bilayer core. However, polar headgroups were not disordered, and diffusion of membrane components in the polar headgroup region was not altered.

Allethrins↗