Search PubMed⌕ Search

Biomedical subjects

M Marcus

Publications and source records attributed to M Marcus.

At least 163 records · Page 9Linked to original sources
PubMed1980

A method for assessing the physiologic significance of coronary obstructions in man at cardiac surgery.

The functional significance of coronary narrowings of intermediate severity is often difficult to assess from preoperative coronary arteriograms. To complement the anatomic data obtained by arteriography, a method for measuring phasic coronary velocity and reactive hyperemia in man at cardiac surgery has been developed. The method uses a single-crystal Doppler probe coupled to surface coronary vessels with a small suction pad. The validity of the measurements has been documented in a series of in vitro and animal experiments. Because physiologically significant coronary narrowings invariably attenuate reactive hyperemic responses, this approach can be used to determine the functional importance of coronary obstruction before placement of coronary bypass grafts. Initial experience in 50 patients indicates that the measurements can be obtained safely and that the functional significance of coronary obstructions can be readily assessed.

Animals↗
PubMed1979

Ascorbic acid and vitamin B12.

Using extraction procedures in which the extracted vitamin B12 was protected by cyanide or metabisulfite, several investigators found no change in vitamin B12 when meals were incubated in the presence of ascorbic acid for 30 minutes at 37 degrees C. A previous report suggested degradation of vitamin B12 under these conditions, but this was apparently caused by incomplete protection of the extracted vitamin B12 in the assay procedure. If incubation at 37 degrees C for 30 minutes is a laboratory mimic of the gastric environment, one must conclude that high doses of ascorbic acid do not affect the stability of vitamin B12 in vivo.

Ascorbic Acid↗
PubMed1979

Condensation of all human chromosomes in phase G2 and early mitosis can be drastically inhibited by 33258-Hoechst treatment.

Condensation of human chromosomes in phase G2 and early mitosis is inhibited by the fluorochrome 33258-Hoechst. This inhibitory effect is most apparent in primary diploid fibroblasts and lymphoblasts and least pronounced in peripheral blood lymphocytes. Condensation of the human Y chromosome, which contains a large heterochromatic region rich in A-T base pairs, is drastically inhibited by 33258-Hoechst treatment of fibroblasts and lymphoblasts. The difference in sensitivity of human chromosomes in different cell types to 33258-Hoechst probably reflects differences in the cell-membrane permeabilities to 33258-Hoechst.

Animals↗
PubMed1979

Inhibition of condensation of human Y chromosome by the fluorochrome Hoechst 33258 in a mouse-human cell hybrid.

The fluorochrome Hoechst 33258 which binds preferentially to A-T base pairs, drastically inhibits the condensation of A-T-rich centromeric heterochromatin regions in mouse cell lines. The condensation of all other regions of these chromosomes is also inhibited to some extent. The human Y chromosome contains a large heterochromatic region, which is also rich in A-T base pairs. This chromosome is not affected by Hoechst 33258 in human leukocyte cell cultures. On the other hand, condensation of the multiple copies of human Y chromosome in the mouse-human cell hybrid RH-28Y-23 is inhibited and the chromosomes appear distorted in Hoechst 33258-treated cells.

Animals↗
PubMed1979

A Markovian model for evaluating dental care programs.

A Markov model is suggested as a means of evaluating dental care programs. Four mutually exclusive states of dental care are defined as Markovian states. These are episodic, initial, maintenance and nonuse. Records for all patients entering a university teaching clinic (n = 578) over a 12-month period were examined and classified in one of the states of care at entry into the clinic and at 1-year intervals from the date of entry for 3 years. An analysis of the findings indicated that the Markov model did fit reasonably well and provided a good approximation of the empirical data.

Dental Care↗
PubMed1978

Effects of the volume conductor on the apparent orientation of a known cardiac dipole.

The surface electrocardiogram (EKG) is dependent on two major factors: the cardiac generator and the volume conductor. This investigation assessed the effects of the volume conductor in man on the apparent orientation of a simulated cardiac dipole. The apparent orientation of the dipole was calculated from measured surface potentials from about 60 locations on the body of five patients with implanted cardiac pacemakers. The real orientation of the dipole (an implanted pacemaker) was determined radiographically. The effects of both inhomogeneity and boundary characteristics of the volume conductor on the apparent orientation of the dipole were assessed using a new inverse algorithm. The difference between the orientation of the real and the calculated dipoles averaged 30 degrees (range 15 degrees--40 degrees) when the torso was assumed to be an infinite-homogeneous volume conductor. When the configuration of the torso was accounted for, however, the difference between the orientation of the real and calculated dipoles was reduced to 9 degrees (range 5 degrees--13 degrees). Thus, by taking into account the geometry of the torso and neglecting the inhomogeneities in the volume conductor, it is possible to calculate the orientation of a dipole in the cardiac region with an accuracy of about 9 degrees. It is reasonable to assume that the orientation of real activation wave fronts from localized areas of the heart could be calculated with a similar degree of accuracy.

Aged↗
PubMed1977

DID: a direct measure of delegation.

The DID measures the degree of delegation existing in a dental practice at a given time. Its four elements are: 1) the delegable tasks, 2) the personnel involved, 3) the task frequency, and 4) the task time. The formula yields the ratio of the Maximum State of Delegation to the Actual State of Delegation or, in other words, the theoretical potential for delegation divided by the observed state of actual delegation. Both are expressed in cost-related terms based upon the relative costs of the personnel in the practice. The DID has merit as a diagnostic tool to aid the practitioner in assessing his/her staff use. For example, a low DID might indicate an overqualified staff for his/her patient load, or underutilization of auxiliaries. The DID can also be used to compare levels of delegation between several practices at a given point in time. Such an application was made for 17 Washington private practices. In using the DID, it was found that delegation levels varied among the 17 practices; however, on the average the degree of delegation approached only one third of the maximum allowed under law. The DID, in its direct approach to task delegation, is a concept that can be applied to dental practices and, with appropriate adaptation, to other health care settings as well. All the influences on the DID and delegation, however are not fully understood and further study is warranted.

Adult↗
PubMed1977

Differences in social perceptions between male and female first-year dental students.

Male and female first-year dental students generally possess the same attitudes and the same perceptions about themselves, dentists they observe, and about their ideals for dentists and patients. The null-hypothesis, that is, assuming no difference between the two groups on the basis of these data, is accepted. In general, one must assume that those women who choose dentistry as a career are not significantly different from their men counterparts, although indirect evidence shows a possible exception of a more compassionate identification with the patient by female students. The findings suggest that it would not be appropriate or accurate to either admit or exclude male or female students based on what may well be "sexist" assumptions regarding women's perceptions of themselves as dentists or their perception of their relationships to patients. The findings should be generalized very cautiously beyond the UCLA School of Dentistry. However, at the time this study was conducted, this dental school had both the largest number of female students and the highest percentage of female students in the United States. The study is limited to perceptual differences of freshmen and does not attempt to deal with issues such as productivity or longevity of professional involvement. These issues may have some bearing on the formation of attitudes toward women entering the profession, but additional longitudinal studies following the careers of the current cohort of female dental students will be necessary to allay criticisms of women in dentistry.

Attitude↗
PubMed1977

Changes in role perceptions by first-year dental students.

Dental education combines the learning of technical skills with the professional role of health care provider. The investigation compared first-year dental students perception of themselves, dental practitioners, dental school upper-class students, and patients. The study indicated that first-year students are more likely to identify with upper-class students than with dental practitioners. They also tended to see themselves as clearly different from dental patients. It is suggested that dental educators should recognize this fact in order to avoid the depersonalization of dental care delivery.

California↗