Search PubMed⌕ Search

Biomedical subjects

C D White

Publications and source records attributed to C D White.

At least 37 records · Page 2Linked to original sources
PubMed1996

Sutural effects of fronto-occipital cranial modification.

Maya adult crania from the site of Lamanai, Belize provide a retrospective means of examining growth processes in the cranial vault. The Lamanai population practiced fronto-occipital deformation which is found to be significantly associated with premature sagittal synostosis and wormian bones of the lambdoidal suture. The undeformed members of the population also exhibit an abnormally high frequency of sagittal synostosis, but a significantly lower frequency than the deformed sample. It is suggested that the deforming apparatus creates tensile forces on the sagittal suture during the peak period of growth of the parietals, and that these forces might induce an adaptive response important in producing premature sagittal synostosis. The undeformed sample may have an increased congenital risk of sagittal synostosis created by their natural brachycephalic morphology in utero. The frequency patterning of wormian bones suggests a mixture of genetic and environmental causes in which tensile forces may also play a role.

Adult↗
PubMed1996

Differences between syncope resulting from rapid onset acceleration and orthostatic stress.

BACKGROUND AND HYPOTHESIS: Orthostatically-induced syncope is accompanied by venous pooling and vasodilatation. Loss of consciousness during head-to-foot acceleration (G-LOC) in aviators may be caused by a different mechanism, as venous pooling should be prevented through the use of an anti-G suit. This research was conducted to test the hypothesis that in individuals wearing a well-fitted anti-G garment, no important changes occur in the volume of dependent regions during loss of consciousness resulting from rapid onset acceleration stress. Further, this work compares venous pooling patterns in G-LOC subjects to patterns seen during syncope in volunteers and patients subjected to orthostatic stress. We conducted the tilt/LBNP tests to establish what level of venous pooling was required to induce syncope in the absence of a hydrostatic component (other than 1 G) and to confirm that our equipment was sensitive enough to detect volume changes large enough to cause syncope. METHODS: Shifts in blood volume to the calf, thigh and abdominal segments were compared in subjects with G-LOC to those in subjects taken to presyncope with orthostatic stress created by upright tilt and lower body negative pressure (LBNP). Centrifuge subjects were exposed to a 15 s rapid onset (6 G.s-1) + 5 Gz exposure on the centrifuge while remaining relaxed and wearing a well-fitting anti-G suit, but with the anti-G suit pressure inactivated. RESULTS: Blood volume decreased an average of 14.9 +/- 22.1 ml in the calf segment; increased an average of 64.1 +/- 7.9 ml in the thigh segment, and decreased an average of 80.1 +/- 29.7 ml in the abdominal segment. The mean net change in volume of the three combined regions was not significantly different from zero. Presyncope was induced in subjects by a progressive exposure to upright tilt, and then addition of LBNP at -20 mm Hg and -40 mm Hg. In the tilt/LBNP group, there was a net increase of 1022 +/- 269.8 ml for the combined segments. Changes in all three segments were significantly different than the mean segmental volume changes seen in centrifuge subjects at G-LOC endpoints. Significant changes from baseline mean arterial pressure, but not heart rate were also seen within, but not between the 2 groups, with mean eye level blood pressures (ELBP) falling an average of 45.6 +/- 7.7 mm Hg in the tilt/LBNP group at syncope and 105.1 +/- 15.5 mm Hg in the centrifuge subjects at G-LOC. CONCLUSIONS: These differences suggest that G-LOC may be due entirely to hydrostatic effects, with venous pooling being prevented by the wearing of an ant-G garment, even when it remains uninflated.

Acceleration↗
PubMed1995

Adrenergic desensitization in left ventricle from streptozotocin diabetic swine.

Patients with diabetes mellitus that exhibit cardiac pump failure display compromised stroke volume, ejection fraction, and slower rates of rise and fall of left ventricular (LV) dP/dt in the absence of ischemic injury. We hypothesized that diabetic cardiomyopathy may involve decrements in adrenergic sensitivity, with specific molecular alterations in the beta-adrenergic receptor (beta AR)- G protein- adenylyl cyclase (AC) signal transduction system. We assessed the effects of 3 months of streptozotocin-induced diabetes (125 mg/kg i.v.; DIAB, n = 10) on myocardial signal transduction in mini-pigs. DIAB were hyperglycemic compared to controls (CON, n = 10; 20.92 +/- 2.64 v 5.24 +/- 0.35 mM glucose), and had lower fasting insulin levels (6.46 +/- 0.97 v 13.68 +/- 3.91 microU/ml). Transmural LV free wall homogenates from DIAB exhibited similar beta AR density as CON, but decreased cAMP production (pmol cAMP/mg prot.min) using these pharmacological stimulators: 10 microM Isoproterenol plus 100 microM GTP (74 +/- 5 v 97 +/- 11); 100 microM Gpp(NH)p (116 +/- 7 v 161 +/- 17); 10 mM fluoride ion (266 +/- 16 v 324 +/- 25). No differences between DIAB and CON were observed when stimulated by 100 microM forskolin (440 +/- 20 v 429 +/- 33), suggesting no alterations in the catalytic subunit of AC. In DIAB, quantitative immunoblotting indicated slightly depressed levels of Gs (552 +/- 44 v 630 +/- 59 pmol/g ww; NS), but a significant redistribution of alpha s from the sarcolemma to the cytosol (32.7 +/- 0.82% v 25.9 +/- 1.7%). Significantly elevated levels of cardiac Gi were seen in DIAB homogenates compared to CON ventricles (2326 +/- 145 v 1522 +/- 181 pmol/g ww), with no alpha i subunit redistribution. We conclude that despite maintained beta AR density, receptor-dependent and G protein-dependent stimulation of AC is depressed so that streptozotocin-induced diabetic LV is affected by increased cardiac Gi, redistribution of Gs alpha to the cytosol, and an increase in the Gi/Gs ratio. These results help explain depressed catecholamine responsiveness and cardiac performance exhibited by diabetic patients.

Adenylyl Cyclases↗
PubMed1994

Temporal trends in stable isotopes for Nubian mummy tissues.

From Meroitic to Christian times (350 B.C.-A.D. 1400), Sudanese Nubia experienced political, economic, cultural, and environmental upheaval. Change in any one of these aspects of ancient lifeways can affect subsistence. Dietary patterns from this period are reconstructed by measuring stable carbon and nitrogen isotope ratios in tissue samples from 146 mummies excavated from five sites in the Wadi Halfa area. On average, delta 13C values of bone collagen, muscle, and skin indicate high consumption levels of C3 plants (presumably wheat or barley staples, mixed vegetables, and fruits) throughout the sequence. However, during the X-Group period (A.D. 350-550), there is a statistically significant increase in consumption of C4 plants (millet or sorghum), which are predominant in both the archeological record and in modern crop production for most of the Northern Sudan. The X-Group period was also associated with a low Nile and political and economic restructuring. Increased use of C4 plants on a seasonal basis is also indicated by shifting delta 13C values along hair shafts for both X-Group and Christian periods. delta 15N values suggest that the major source of protein for all time periods came from herbivorous animals. A small, but significant increase in 15N over the 1,000-year sequence could be the result of fertilization.

Adult↗
PubMed1993

Effect of upright tilt on ventricular/vascular coupling in chronically instrumented primates.

Studies of the hydraulic loading conditions on the heart in humans, especially pulsatile load, have primarily been limited to the supine state. Therefore, we have chosen a nonhuman primate model, the baboon, to assess left ventricular/vascular coupling in both supine and upright positions. Primate subjects were studied by catheterization under sedation and then after surgical implantation of transducers. This allowed the evaluation of postural stress in the chronically instrumented conscious baboon and then after light dissociative doses of ketamine. Basic hemodynamic variables were evaluated for baboons in supine and upright positions. Fourier analysis was applied to aortic pressure and flow to obtain input and characteristic impedance and the ratio of pulsatile (Wp) to total (Wt) left ventricular power (Wp/Wt). The aortic reflected, or backward, pressure was also calculated. Peripheral resistance increased (P = 0.01) and reflected pressure decreased (17.74 +/- 1.50 vs. 15.21 +/- 2 mmHg; P < 0.01) in upright subjects. Characteristic impedance and Wp/Wt were unchanged. Postoperatively, peripheral resistance increased (2,651 +/- 311 vs. 3,667 +/- 276; P < 0.05) and mean power and Wt decreased (P < 0.01) without changes in reflected pressure. All variables were unchanged after light dissociative doses of ketamine. Thus there is no significant change in efficiency of left ventricular/vascular coupling formulated in terms of Wp/Wt or input impedance with postural stress.

Animals↗
PubMed1993

Circulatory filling pressures during transient microgravity induced by parabolic flight.

Theoretical concepts hold that blood in the gravity-dependent portion of the body would relocate to more cephalad compartments under microgravity conditions. The result is an increase in blood volume in the thoracic and cardiac chambers. This increase in central volume shift should result in an increase in central atrial filling pressures. However, experimental data has been somewhat contradictory and nonconclusive to date. Early investigations of peripheral venous pressure and estimates of central venous pressure (CVP) from these data did not show an increase in CVP in the microgravity condition. However, CVP recorded in human volunteers during the parabolic flight by Norsk revealed an increase in CVP during the microgravity state. On the June 1991 STS 40 shuttle mission, a payload specialist wore a fluid line that recorded CVP during the first few hours of orbital insertion. These data revealed decreased CVP. When this CVP catheter was tested during parabolic flight in four subjects, two subjects had increased CVP recordings and two other subjects had decreased CVP measurements. In April 1991, our laboratory performed parabolic flight studies in several chronic-instrumented baboon subjects. It was again noted that centrally recorded right atrial pressure varied with exposure to microgravity, some animals having an increase and others having a decrease. Thus, data presently available has demonstrated a variable response in the mechanism not clearly defined. In April 1992, we determined a test hypothesis relating the possible mechanism of these variable pressure responses to venous pressure-volume relationships.

Animals↗
PubMed1993

The gynecologist and treatment of carcinoma of the breast.

The treatment of breast carcinoma has traditionally been relegated to the general surgeon. The gynecologist, in his/her role of treating women's diseases, will likely become more involved in the future. This article describes the experience of one gynecologist in the treatment of carcinoma of the breast involving 234 biopsies which were performed from January 1985 to December 1992. Invasive carcinoma was found in 81 of the cases, and five showed in situ carcinoma.

Adult↗
PubMed1993

Management of residual squamous intraepithelial lesions of the cervix after conization.

From January 1985 to October 1992, 158 conizations of the cervix were performed for squamous intraepithelial lesions (SIL) of the cervix. Thirty-one (20.4%) of these cases had disease extending to the margins of resection. The majority (60.7%) had spontaneous resolution of disease. Conservative follow-up aided by the body's own immune system may allow an even greater percentage to resolve spontaneously. Smoking presents an added factor for persistent as well as recurrent disease.

Adolescent↗
PubMed1993

Real-time identification of parameters of the ARMA model of the human EEG waveforms.

Electroencephalogram (EEG) can provide important information about the functioning of the human brain. In particular, the EEG waveforms manifest certain changes due to application of drugs, such as general anesthetics. Measurement of the changes in the EEG waveforms in real time, may therefore be used to determine the global effects of the administered drug. Among numerous mathematical techniques used in the analysis of the EEG waveforms, perhaps, the fast Fourier transform (FFT) is the most widely used. Recently some researchers have suggested the use of the autoregressive moving average (ARMA) model for the EEG analysis. In this method the coefficients of the ARMA model are identified and used to describe the waveform. We consider a first order ARMA model, and use the Extended Least Squares (ELS) and its recursive version (RELS) for parameter estimation. The identified parameters are then used to describe the time-domain or the frequency-domain properties of the EEG waveforms. Since the parameters of the model may change with time, a forgetting factor is incorporated in the RELS algorithm to allow for tracking of time varying parameters. The advantage of recursive estimation of the coefficients of the ARMA model over the non-recursive estimation and the FFT method, is substantial reduction in computation as well as its capability to track the time varying process.

Algorithms↗
PubMed1993

Papillary intraperitoneal neoplasia resembling ovarian carcinoma after removal of benign ovaries.

Ovarian cancer continues to be a major cause of death in women since there are no reliable screening methods and because symptoms usually do not appear until the disease has progressed to Stage III or IV, when the chances of cure are very poor. Prophylactic oophorectomy is being considered by some physicians for any woman undergoing hysterectomy after age 40-45. Even with the removal of benign ovaries, intraperitoneal carcinomatosis histologically resembling ovarian cancer can occur. This article describes a case of primary papillary intraperitoneal neoplasia resembling serous adenocarcinoma of the ovary which presented two years after removal of benign ovaries.

Carcinoma, Papillary↗
PubMed1992

Inflammatory cell infiltrate in the cervix as a predictor of residual cervical intraepithelial neoplasia after conization.

From January 1985 to January 1991, 112 patients underwent conization of the cervix for dysplasia. Twenty-one had incomplete resection, with cervical intraepithelial neoplasia (CIN) extending to the endocervical margins of resection. Only 10 had persistent CIN in follow-up. A decrease in the inflammatory cell infiltrate in the cervical stroma of the conization specimen was associated with persistent disease. A simple technique for quantitating this inflammatory cell infiltrate was used. Smoking was associated with a suppression of this local immune response in the cervix.

Adult↗
PubMed1991

Varying presentations of methemoglobinemia: two cases.

The cases of two patients with methemoglobin levels approaching 30% are presented. No history of exposure to an oxidant was ever determined for the first case; the second patient had taken amyl nitrate orally along with alcohol as well as a self-injected narcotic and antihistamine. Due to their symptomatology, both patients were treated with methylene blue with good results; however, the patient described in case one had a brief episode of symptoms and pulse oximetry changes, not previously emphasized, consistent with the administration of methylene blue. The pathophysiology of methemoglobinemia, the utility of bedside diagnostic techniques, and the use of pulse oximetry are discussed.

Adult↗
PubMed1991

Cervical intraepithelial neoplasia extending to the margins of resection in conization of the cervix.

Conization of the cervix is still widely utilized under certain conditions for the diagnosis and treatment of cervical intraepithelial neoplasia (CIN). Little has been written about the management of disease extending to the margins of resection. Ninety-four patients underwent conization of the cervix for cervical intraepithelial neoplasia (CIN). Nineteen (20%) had positive margins of resection; 10 (56%) of them had no evidence of disease in follow-up of one to four years. The inflammatory response of healing may play a role in a cure. Positive margins of resection and persistent disease, noted in 44%, were positively associated with higher grades of CIN and smoking. Smoking was also a risk factor for recurrent disease in those with negative margins of resection.

Adolescent↗
PubMed1991

Parovarian cystadenocarcinoma of low malignant potential.

Malignant parovarian tumors are rare, with only 20 cases previously reported. Only eight of these were cystadenocarcinomas of low malignant potential and only two had both mucinous and serous components. In this article, we report the third case of a parovarian cystadenocarcinoma with both serous and mucinous components--A 26-year-old female who was treated by conservative surgery and later carried a pregnancy to term. Prognosis and management of these lesions are discussed.

Adult↗