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Biomedical subjects

R Gray

Publications and source records attributed to R Gray.

At least 181 records · Page 10Linked to original sources
PubMed1996

Drifting vortices of electrical waves underlie ventricular fibrillation in the rabbit heart.

Ventricular fibrillation is the most important cause of cardiac electrical instability leading to sudden death. Fibrillation is believed to be associated with complex three-dimensional (3-D) spatio-temporal patterns of electrical excitation of the myocardium. However, to this date, such patterns have not been directly observed or characterized, and little is known about their dynamics. In this paper, we present results that strongly support the hypothesis that at least some cases of ventricular fibrillation in the structurally normal heart may be the result of a single 3-D electrical scroll wave that moves rapidly throughout the ventricles, giving rise to complex patterns of cardiac muscle excitation.

Animals↗
PubMed1996

Accuracy of reproducing angles: is a right angle special?

The ability to set the angle of a 'V' to a designated value in the following three conditions was compared: (1) verbal designation of V angle; (2) initial 30 s visual demonstration of the designated V angle; (3) verbal designation of V angle plus feedback after every setting. The designated angles were 90 degrees and 45 degrees plus three arbitrary angles (65 degrees, 125 degrees, and 145 degrees). Each run comprised thirty consecutive settings. To ensure that our observers based their settings entirely on V angle it was arranged that line orientation did not provide a reliable cue to V angle. In condition (1), accuracy of setting V angle was significantly worse when the designated angle was other than 90 degrees or 45 degrees. This was not the case in condition (2), indicating that observers maintained a memory of the initial demonstration throughout a run of thirty settings. Setting error was not significant in condition (3) for any of the five angles. However, even in condition (3), setting-to-setting variability was significantly lower for the 90 degrees angle than for the other angles.

Adult↗
PubMed1996

Immunohistochemical and morphological characterization of spontaneously occurring pheochromocytomas in the aging mouse.

Pheochromocytomas in mice are rare tumors, and their expression of functional markers has not previously been assessed. In this study, 29 spontaneously occurring mouse pheochromocytomas were characterized morphologically and immunohistochemically to determine whether there are functional correlates to previously described morphological features and to provide a database for comparison with tumors that arise in genetically engineered animals. The tumors were derived from 28 mice 828-1,489 days old, of three genotypes. Considerable cytological and architectural polymorphism was observed both within and between tumors. Most of the tumor cells were comparable in size to normal chromaffin cells or were larger. Small basophilic cells, which are the predominant cell type in rat pheochromocytomas, were usually in the minority. All of the tumors and most of the cells within individual tumors expressed immunoreactive tyrosine hydroxylase (TH). The tumors were variably positive for phenylethanolamine-N-methyltransferase (PNMT) and chromogranin A (CGA). There did not appear to be a global association of specific cytological features with expression of TH, PNMT, or CGA, although cells of similar appearance often shared similar immunoreactivities within individual tumors. Small basophilic cells could be either PNMT-positive or PNMT-negative. The frequency, morphology, and immunophenotype of mouse pheochromocytomas suggest that the mouse may be more appropriate than the rat as a model for human adrenal medullary pathology. In addition, the expression of immunoreactive PNMT by mouse pheochromocytomas suggests that these tumors are a potential source of epinephrine-producing cell lines, for which adequate models currently do not exist.

Adrenal Gland Neoplasms↗
PubMed1996

Annual hazard rates of recurrence for breast cancer after primary therapy.

PURPOSE: To determine if the long-term increase of recurrence for breast cancer is stable or slowly decreasing, or if it ever reaches zero; and to determine the effect of prognostic factors on the hazard of recurrence. METHODS: All patients entered onto the seven completed and unblinded Eastern Cooperative Oncology Group (ECOG) coordinated studies of postoperative adjuvant therapy for breast cancer were analyzed in terms of annual hazard of recurrence of breast cancer. RESULTS: For the entire group, the peak hazard of recurrence occurred in the interval of 1 to 2 years. The hazard decreased consistently in the interval of 2 to 5 years. Beyond 5 years, the hazard of recurrence decreased very, very slowly through year 12. The average hazard of recurrence between years 5 and 12 for the entire population was 4.3% per year. The pattern of a peak hazard of recurrence during the first 5 years with a slowly decreasing hazard of recurrence beyond 5 years was also observed to varying degrees in most subsets. Higher risk subsets such as patients with more than three nodes positive had a higher hazard of recurrence at all time intervals, while lower risk subsets such as patients with negative nodes had a lower hazard of recurrence in all time periods. CONCLUSION: Patients 5 years postsurgery for breast cancer appear to have a very slowly decreasing hazard of recurrence. The mean hazard of recurrence between years 5 to 12 postsurgery is 4.3% per year. This group of patients may be well suited for trials evaluating cytostatic drugs or differentiating agents.

Breast Neoplasms↗
PubMed1996

Standardization of health relief items needed in the early phase of emergencies.

Concepts, ideas and advocacy for standardization of medical materials have been in existence for over a hundred years and until 1957 were the domain of the Red Cross Movement. Following the Second World War there emerged both national and international organizations concerned with standardization of medical materials. The Gulf War brought deficiencies in emergency relief to the attention of the United Nations System and one of the consequences of this was the decision to standardize all emergency relief items needed in the early phase of emergencies. Standardization of health relief items made up one part of this process.

Disasters↗
PubMed1995

Mitogenic and antimitogenic effects of pituitary adenylate cyclase-activating polypeptide (PACAP) in adult rat chromaffin cell cultures.

The neurotransmitter, pituitary adenylate cyclase-activating polypeptide (PACAP), is present in the rat adrenal medulla and is a potent stimulus for catecholamine secretion. Previous studies have suggested that neurally derived signals stimulate proliferation of chromaffin cells in adult rats. To determine whether PACAP might be involved in mitogenic signalling, its effects on bromodeoxyuridine incorporation were studied in adrenal medullary cell cultures from adult female rats. Both PACAP 27 and PACAP 38 are able to stimulate proliferation of adult rat chromaffin cells in vitro, either alone or in conjunction with PMA, an activator of protein kinase C. BrdU-labelled nuclei are observed in both epinephrine and norepinephrine cells, and proliferation of both cell types is stimulated by the same concentrations of PACAP that elicit secretion of catecholamines. The mitogenic effects of PACAP are potentiated by indolidan, a phosphodiesterase inhibitor known to cause pheochromocytomas in rats, and are inhibited by H-89, an inhibitor of protein kinase A. Mitogenic concentrations of PACAP inhibit mitogenic effects of nerve growth factor. These findings support the hypothesis that neurally derived signals regulate chromaffin cell proliferation in adult rats. Indolidan and a variety of nongenotoxic agents that cause pheochromocytomas in rats may do so indirectly by increasing neurally mediated chromaffin cell turnover. The antagonism between PACAP and NGF suggests that neurotransmitters may supersede growth factors in regulating chromaffin cell proliferation during development by suppressing or co-opting portions of growth factor signaling pathways.

Animals↗
PubMed1995

Corpus cavernosum as an emergency vascular access in dogs.

RATIONALE AND OBJECTIVES: We investigated the feasibility of using the corpus cavernosum as an emergency vascular access in dogs with severe hypovolemia. METHODS: Five male mongrel dogs were brought to hypovolemic shock by withdrawal of blood through an internal jugular venous line. Using the corpus cavernosum as a venous access, normal saline was injected through a 23-gauge needle at the highest possible rate. Cavernosography was performed under fluoroscopy to verify the accurate position of the needle tip. Blood volumes were measured using 125I-labeled human serum albumin. RESULTS: Before the dogs were bled, their mean systolic blood pressure was 121.4 (mean) +/- 5.2 (standard error) mm Hg and their mean blood volume was 1,835.2 +/- 139.7 ml. The mean volume of blood removed from the dogs was 710.0 +/- 67.8 ml. The mean systolic pressure during shock was 40.8 +/- 2.2 mm Hg. After fluid resuscitation, the mean systolic pressure recovered to 114.6 +/- 4.6 mm Hg and their mean blood volume increased to 1,763.2 +/- 112.7 ml. The mean rate of saline infusion into the corpus cavernosum was 50.2 +/- 0.7 ml/min. CONCLUSION: The results of this study demonstrate the feasibility of using the corpus cavernosum as an alternative route for fluid resuscitation in severely hypovolemic dogs.

Animals↗
PubMed1995

Visual processing of the motion of an object in three dimensions for a stationary or a moving observer.

A rate of change of relatively disparity is a sufficient binocular stimulus for the perception of motion in depth. For motion within the meridian that contains the eyes, disparity change associated with approaching motion is processed through four channels, each tuned to a different direction of motion in depth. Directional discrimination is most acute but detection sensitivity falls to a minimum for a trajectory passing approximately midway between the eyes. This can be explained if discrimination depends on the relatively of the four channels. Two binocular retinal-image correlates of the direction of the motion of an object in depth are the ratio between the velocities of the retinal images of the object in the left and right eyes [(d phi/dt)R/(d phi/dt)L], and the ratio between the translational velocity of the binocularly fused images and the rates of change of disparity [(d phi/dt)/(d gamma/dt)]. Directional discrimination is possible by using the second cue alone. An isotropic rate of expansion of the retinal image is a sufficient monocular stimulus for the perception of motion in depth. There is no evidence that expansion is processed through channels tuned to the direction of motion in depth. Two monocular correlates of the direction of the motion of an object in depth are the ratio between the translational velocity and the rate of expansion of the retinal image of the object [(d phi/dt)/(d theta/dt)], and the ratio between the velocities of opposite edges of the retinal image [(d alpha 1/dt)/(d alpha 2/dt)]. Subjects are able monocularly to discriminate the direction of motion in depth with high acuity (better than 0.1 deg threshold) in the vertical, horizontal, or oblique meridians, even when the direction and the speed of translational motion are removed as cues. Visual discrimination of time to contact with an approaching object can be disconfounded from discrimination of its rate of expansion and vice versa with a threshold separation ratio of as much as 100:1.

Cues↗
PubMed1995

Lower urinary tract dysfunction in Parkinson's disease: changes relate to age and not disease.

Lower urinary tract symptoms are frequency report in Parkinson's disease. Whether these are causally related to Parkinson's disease rather than the known effects of age on the urinary tract is unknown. In this study we compared urodynamic data from 1864 women and 357 men with no neurological disease with data from 34 women and 42 men with Parkinson's disease, 96 women and 75 men with cerebrovascular disease and 42 women and 16 men with dementia. We examined isometric and isotonic detrusor contractile function and urethral outflow. Bladder capacity was reduced in both men and women with Parkinson's disease in comparison with patients of similar to that measured in patients without neurological disease and we found no evidence of obstruction in patients with Parkinson's disease. Disease-specific changes were not identified in patients with cerebrovascular disease or dementia. These findings contradict previous reports suggesting specific changes in lower urinary tract function in association with Parkinson's disease.

Aged↗