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Biomedical subjects

A G Shapiro

Publications and source records attributed to A G Shapiro.

At least 19 recordsLinked to original sources
PubMed1998

Equivalence between temporal frequency and modulation depth for flicker response suppression: analysis of a three-process model of visual adaptation.

We analyze adaptation processes responsible for eliciting and alleviating flicker response suppression, which is a class of phenomena characterized by the selective reduction of visual response to the ac component of a flickering light. Stimulus conditions were chosen that would allow characteristic features of flicker response suppression to be defined and manipulated systematically. Data are presented to show that reducing the sinusoidal modulation depth of an 11-Hz stimulus can correspond precisely to raising the temporal frequency of a fully modulated stimulus. In each case there is a nonmonotonic relation between flicker response and dc test illuminance. The nonmonotonic relation cannot be explained by adaptation models that postulate multiplicative and subtractive adaptation processes followed by a single static saturating nonlinearity, even when temporal frequency filters are incorporated into such models. A satisfactory explanation requires an additional contrast gain-control process. This process enhances flicker response at progressively lower temporal response contrasts as the illuminance of a surrounding field increases.

Adaptation, Physiological↗
PubMed1996

Cone-rod receptor spaces with illustrations that use CRT phosphor and light-emitting-diode spectra.

The purpose of the study is to characterize the excitation of the three cone types and the rods in a colorimetric system. Two representations of photoreceptor activity are developed. In the first, rod activity is characterized within a cone colorimetric system that is based on three known physical primaries. Examples are given that use color CRT phosphor spectra. We illustrate how this representation can be used to evaluate the range of chromaticities over which rod signals may intrude into color-monitor-based investigations of cone function. In the second representation, mixtures of four physical primary lights are used to manipulate the four receptor excitations independently. This method allows specification of sets of lights that isolate or silence up to three receptor classes or any combination of receptor classes. Examples are given that use spectra from four light-emitting diodes. This approach opens a field of research in which rod input to various retinal pathways can be evaluated.

Color Perception↗
PubMed1993

Adaptive orthogonalization of opponent-color signals.

This paper concerns the processing of the outputs of the two opponent-color mechanisms in the human visual system. We present experimental evidence that opponent-color signals interact after joint modulation even though they are essentially independent under neutral steady adaptation and after exclusive modulation of each mechanism. In addition, prolonged modulation linearizes the response function of each mechanism. The changes in interaction serve to orthogonalize opponent signals with respect to the adapting modulation, and the changes in response functions serve to equalize the relative frequencies of different levels of response to the adapting modulation. Adaptive orthogonalization reduces sensitivity to the adapting color direction, improves sensitivity to the orthogonal direction, and predicts shifts in color appearance. Response equalization enhances effective contrast and explains the difference between the effects of adaptation to uniform versus temporally or spatially modulated stimuli.

Adaptation, Ocular↗
PubMed1992

The effects of prolonged temporal modulation on the differential response of color mechanisms.

The identification of three independent cardinal directions in color space suggests the existence of three independent post-receptoral mechanisms that can be desensitized by habituation to a temporally modulated light. In this paper, the differential response of each cardinal mechanism is estimated over a range of inputs before and after habituation. Simple mathematical considerations show that the threshold elevations following temporal modulation are not consistent with multiplicative gain changes; rather, these elevations require a change in the shape of each cardinal mechanism's response function. With this method, the effects of habituation can also be differentiated from the effects of a change in the steady adapting light.

Adaptation, Ocular↗
PubMed1989

Endovaginal and transabdominal sonography of ovarian follicles.

Endovaginal and transabdominal sonography (EVS and TAS, respectively) are effective methods for monitoring ovarian follicular development. Our study evaluates both modalities by subjective comparisons and objective correlations with serum estradiol levels. In 21 of 41 studies, TVS showed more follicles over 1 cm than did TAS. The same number was seen by both in 17 studies and more by TAS in only 3 studies. Margins of the follicles were sharply defined in 37 of 41 EVS studies (90%) but only in 18 of 41 TAS studies (41%). In each of the 4 cases in which follicles were not sharply defined by EVS the ovaries were located high in the pelvis. In 29 sonographic studies, there were corresponding estradiol levels. The number and size of dominant follicles correlated well with estradiol levels (r = .9074) for EVS but less so (r = .3816) for TAS. EVS has several advantages when monitoring follicular development.

Abdomen↗
PubMed1987

Conventional reanastomosis versus laser welding of rat uterine horns.

In this study we compared conventional surgical techniques with those of low-power CO2 lasers (output 140 mW; spot size 0.4 mm) used to weld transected rat uterine horns. On one side a microanastomosis was made by standard surgical technique of 8-0 nylon; the other side was "welded" either after doing the anastomosis with 8-0 sutures or without any anastomotic sutures. Histologic sections obtained from rats' uteri treated with conventional and laser surgery showed that on the laser-treated sutured side there was less necrosis and inflammatory and giant cells. The animals that underwent laser welding without suturing had no necrosis, suppuration, or granulation; giant cells were not present. We conclude that in the tissue from the laser-treated animals, when compared with conventional and laser-with-suture surgery, histologic features indicate healing process by primary intention via an aseptic noninflammatory reaction.

Animals↗
PubMed1987

Emergency treatment of menstrual disorders in a nonpregnant woman.

Women who present to the Emergency room with menstrual-related problems are a common occurrence. In this article, we will concern ourselves with common problems that the nonpregnant woman in the reproductive years may present to the emergency room, including symptoms such as vaginal bleeding, painful menses, or premenstrual syndrome. Although the treatment within the emergency room is temporizing in nature, to better understand these problems and their appropriate management, these areas will be discussed as to their etiology, treatment, and prognosis.

Amenorrhea↗
PubMed1985

Intrauterine and ectopic pregnancies after a tubal ligation with documented tubal occlusion.

The patient described had both an intrauterine and an extrauterine pregnancy after a previous vaginal tubal ligation using a Pomeroy technique. A hysterosalpingogram showed midtubal occlusion. Although pregnancy after tubal ligation is not unusual, this case does show that a hysterosalpingogram may also be inconclusive in ruling out the possibility of future pregnancy.

Adult↗
PubMed1984

Efficacy of bromocriptine versus breast binders as inhibitors of postpartum lactation.

Fifty postpartum patients were randomly given either bromocriptine (2.5 mg by mouth b.i.d. X 30 doses) or breast binders for inhibiting lactation. The breast binder group had a high incidence of symptoms (breast pain, engorgement, secretion) for the first week postpartum; these symptoms rapidly decreased by the second week. Bromocriptine successfully suppressed the breast problems in virtually all of the patients who took the drug correctly. Because of the high rate of side effects and a significant incidence of "rebound," the dosage of bromocriptine should probably be changed, and we recommend a revised dosage.

Adolescent↗
PubMed1977

Management of hyperstimulation syndrome.

A case of hyperstimulation syndrome secondary to Pergonal therapy is presented. Successful management was based principally on severe sodium and fluid restriction without the use of volume expanders. The rationale for this therapeutic approach is presented and discussed. Although this iatrogenic disease should be virtually eliminated with the monitoring of daily urinary estrogens, severe hyperstimulation may still occur as a result of laboratory error.

Adult↗
PubMed1977

Pituitary response to luteinizing hormone-releasing hormone after induced abortion in the first and second trimesters.

Luteinizing hormone-releasing hormone (LHRH) (100 microng) was administered subcutaneously to healthy female volunteers 2 and 4 weeks after induced abortion in the first trimester (group A) and the midtrimester (group B). Four patients were studied in each group. The response to LHRH was determined in terms of plasma LH and follicle-stimulating hormone levels. Adequate pituitary response occurred in subjects of group A at both 2 and 4 weeks. In group B pituitary unresponsiveness was found at 2 weeks which persisted to some extent at 4 weeks. These data are in accord with the pituitary unresponsiveness observed after termination of pregnancy at term and suggest that the duration of pregnancy has an influence on the development of this unresponsiveness.

Abortion, Induced↗
PubMed1977

Use of brom-ergocryptine in treating amenorrhea/galactorrhea.

Seven women with amenorrhea and galactorrhea, and no evidence of pituitary adenoma, were treated with brom-ergocryptine for two to 24 weeks. All seven patients had the resumption of regular menses within eight weeks, but six patients required 24 weeks of therapy to completely cease lacting. Two of the five women attempting to conceive became pregnant. Four of the five nonpregnant patients had a total recurrence of their symptoms after discontinuing the drug. Brom-ergocryptine appears to be very effective in inhibiting prolactin secretion and thus reestablishing normal ovulatory menstrual cycles and fertility.

Adult↗
PubMed1977

Management of the lost intrauterine contraceptive device.

In order to establish that a lost IUD is within the uterine cavity, a special hook-type instrument was designed to enable removal of the device when it was located within the uterine cavity. This instrument was 100% successful in removing 17 IUDs with no visivle tails and which were within the uterine cavity. Failure to remove a lost IUD by this method in 4 other patients indicated the device's absence from the uterine cavity. The technic is simple and has not been associated with any patient discomfort or complications. X-ray procedures or operative manipulations may thereby be avoided. Therefore, when the tail of an IUD is no longer visible, immediate removal can be attempted in order to establish the intrauterine location of the device. If the patient wishes to continue using this form of contraception, a new device should be inserted.

Female↗