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Biomedical subjects

R Stephenson

Publications and source records attributed to R Stephenson.

At least 37 records · Page 2Linked to original sources
PubMed1997

Day-night differences in the respiratory response to hypercapnia in awake adult rats.

We investigated whether resting ventilation and the hypercapnic ventilatory response vary with time of day in awake adult rats. Respiratory frequency (fR), tidal volume (VT), inspired ventilation (VI), inspiratory interval (tI), carbon dioxide production (VCO2) and abdominal temperature (Tb) were measured before and during a hypercapnic stimulus (3.5% CO2 in air) at 10:00 and 22:00 h. VCO2, Tb and mean inspiratory air flow (VT/tI) were significantly higher at 22:00 h in air. VI/VCO2 was similar at 10:00 and 22:00 h. VI was significantly elevated by hypercapnia and the response at 22:00 h was 2.3 times greater than that at 10:00 h. VT/tI was unchanged at 10:00 h but significantly increased by hypercapnia at 22:00 h. VCO2 was significantly depressed at 10:00 h but not at 22:00 h. Tb was unaffected by hypercapnia. We conclude that the metabolic and ventilatory responses to hypercapnia are dependent on the time of day.

Animals↗
PubMed1997

Disasters and the information technology revolution.

This paper, the second in a series of state-of-the art reviews, examines the evolution and possible medium-term future of information technology (IT) in disaster management. Until the end of the 1970s, civilian application of IT to disaster management was confined to a few specialised departments of universities, large companies and government. Between the late 1970s and mid-1980s, microprocessor-based devices brought limited, though rapidly improving, computing capacity to a wider range of organisations and individuals. Operational applications included real-time emergency information, management decision support and programme and project planning. Extensive innovation occurred, though operational implementation was often long delayed or limited in scope. During the late 1980s, desktop systems became more powerful, more networked, more portable and generally more mature, with a range of practical emergency-related tools emerging. Computer communications emerged as a practical technology for linking emergency professionals on a global basis. From the early 1990s onwards, powerful and inter-connectable computer equipment has evolved to become an indispensable component of disaster operations worldwide. There are presently major changes under way in emergency-related global information access and networking--the implications of which have yet to be played out. The last part of the paper highlights a set of key technologies which seems likely to shape disaster planning, management and research over the next 10 years, and draws out some operational and organisational implications.

Computer Communication Networks↗
PubMed1996

Introducing alexithymia: a concept within the psychosomatic process.

Alexithymia (Greek, a = lack, lexis = word, thymos = emotion) is a new concept which, whilst being based upon longstanding clinical observation, remains unproven clinically. The lack of definite criteria for inclusion, and the absence of reliable and valid assessment tools, ensures that past data collection has been flawed and that no real inter-study comparisons can be made. However, the theoretical concept employed at clinical level provides a personality trait that is of great interest to the therapist. Alexithymic individuals lack the ability to transfer the emotional (biological) arousal of experience into feelings and fantasy that symbolize and express the emotion. Literally, they have no words for feeling, and express their arousal in physical (somatic) ways. This paper reviews the clinical components of this trait and the somatic symptomatology associated with it. It also reviews the present 'tools' for 'measuring' alexithymia, and relates these to suggested aetiology. It recommends that all rehabilitation personnel should be aware of this phenomenon, as the somatized symptom may be the presenting complaint of a client. It also encourages therapists to begin screening for alexithymia so that more comprehensive epidemiology information can be gathered, particularly relating to the influences on treatment and physical manifestation.

Adult↗
PubMed1996

[Behavioral and cognitive models of post-traumatic stress disorder].

The necessity of developing efficient treatment for the numerous victims of violence and catastrophes render essential the understanding of the mechanisms of development, maintainance and resorption of the Posttraumatic Stress Disorder (PTSD). Consequently, this article presents the most influential behavior and cognitive models followed by a brief critical analysis. The etiological models chosen are those of Mowrer (1960), Foa and al. (1989), Jones and Barlow (1990), Chemtob and al. (1988) and Janoff-Bulman (1985). Finally these models are compared and discussed.

Behavior Therapy↗
PubMed1995

Correlation of serum concentrations of PSA-ACT complex with total PSA in random and serial specimens from patients with BPH and prostate cancer.

The current assays for serum prostate specific antigen (PSA) have failed to produce the same PSA values on the same specimens because of problems with antibody specificity and calibrator preparation. To eliminate these problems, we proposed to replace the current serum PSA assay with an assay specific for the PSA-ACT (PSA-alpha 1-antichymotrypsin) complex in the serum. An assay specific for the PSA-ACT complex was established using the anti-PSA antibody to coat the microplate for capturing the PSA complex and anti-ACT polyclonal antibodies for quantification. There was an excellent correlation between serum concentrations of PSA-ACT and total PSA, using either the Hybritech calibrator (gamma = 0.996) or a serum calibrator prepared in house (gamma = 0.993), in random as well as in serial specimens from 14 individual patients. Even though we did not find a gradual increase in the percentage of PSA-ACT with the increase of total PSA in cancer patients, a slightly higher percentage of free PSA was measured in pooled normal sera (18%) and in pooled sera containing only 12 ng/ml of total PSA (12%), compared to serum pools containing elevated PSA (> 100 ng/ml) level, in which most PSA was in the complex form (95%). Therefore, using an assay that specifically measures the PSA-ACT complex in the serum not only simplifies the preparation of calibrator but eliminates the difficulty of antibody selection, it also allows various assay kits to produce identical PSA values and also improve the test specificity for prostate cancer.

Humans↗
PubMed1995

PSA immunoreactivity detected in LNCaP cell medium, breast tumor cytosol, and female serum.

We made an effort to identify a reliable source for obtaining large quantities of both free (PSA) and PSA-ACT complex for the preparation of the calibrator for the PSA assay. Using size exclusion chromatography, we found both free PSA and PSA-ACT complex in the conditioned cell medium of the LNCaP cell line, which was derived from a human metastatic adenocarcinoma of the prostate. An assay specific for PSA-ACT reacted only with the PSA-ACT complex from cells grown in serum-free medium, and not with the complex from the cell medium grown in 10% calf serum. We also found both free PSA and PSA-ACT complex in 15% of cytosols prepared from breast tumor tissues; the cytosol PSA concentrations ranged from 0.1 to 110 ng/ml. No correlation was found between cytosol PSA and concentrations of estrogen receptor, progestin receptor, epidermal growth factor receptor, cathepsin D, or the ectodomain of c-erbB-2 protein. Based on chromatographic characterizations and the slope of their dose-response curves, it appears that both free PSA and PSA-ACT complex found in the cytosols are similar to PSA complex from the cell medium and the serum of prostate cancer patients. Ectopic PSA was also detected in pooled sera from patients with breast, ovarian, pancreatic, and colon carcinoma. The PSA concentrations in these serum pools increased with the level of their dominant tumor marker. In any event, the LNCaP cell medium appears to be a reliable source for obtaining both free and ACT-complexed PSA of human tumor origin for the preparation of PSA assay calibrators.

Breast Neoplasms↗
PubMed1995

Respiratory and plumage gas volumes in unrestrained diving ducks (Aythya affinis).

Closed-circuit plethysmography and inert gas equilibration analysis were used to measure the volumes of gas in the respiratory system and plumage at the end of voluntary dives in unrestrained lesser scaup (Aythya affinis). Total (respiratory plus plumage) gas volumes were measured by helium dilution and estimated from body mass, body tissue density and buoyant force. These two techniques yielded results that differed by only 2.1 +/- 1.5%. Buoyancy decreased from a maximum of 3.46 +/- 0.16 N at immersion to a minimum of 2.65 +/- 0.16 N at 1.5 m depth at the end of the feeding phase of voluntary dives. At 0.193 +/- 0.013 L BTPS, the respiratory system contributed 52% of the initial buoyancy and 65% of the minimum value. The increasing relative influence of the respiratory system on buoyancy was due to the loss of 47 +/- 5% of the air in the plumage layer during the dive. These data differ significantly from estimates based on restrained ducks, and this has implications for modelling of mechanical costs of diving, oxygen storage capacity and thermal insulation in foraging ducks.

Air↗
PubMed1994

Regional cerebral blood flow during submergence asphyxia in Pekin duck.

The cerebrovascular response to submergence asphyxia was studied in the Pekin duck (Anas platyrhynchos var.) by use of the cerebral blood flow (CBF) tracer [14C]isopropyliodoamphetamine and quantitative autoradiography. Blood flow of the whole brain was 158 +/- 14 (SE) ml.min-1 x 100 g-1 (n = 7) in control animals. There was a doubling of flow to 320 +/- 61 ml.min-1 x 100 g-1 (n = 6) during submergence asphyxia. The hypothesis that CBF is redistributed within the brain during asphyxia was not supported. There were no regional reductions in CBF during submergence asphyxia. Mean arterial blood pressure was similar (approximately 140 mmHg), but heart rate, arterial blood gas tensions, and arterial pH were significantly different in control and submerged ducks at the time CBF was measured. The differences in CBF among submerged animals correlated strongly with arterial PCO2 and mean arterial blood pressure. The smallest proportional difference in regional CBF between control and submerged ducks occurred in the ectostriatum (+141%) and the largest in the locus ceruleus (+241%). The largest absolute difference in regional CBF was in the nucleus ruber (+322 ml.min-1 x 100 g-1). These are the first measurements of blood flow in discrete nuclei and regions of the avian brain.

Amphetamines↗
PubMed1994

DIVING ENERGETICS IN LESSER SCAUP (AYTHYTA AFFINIS, EYTON)

Mechanical and aerobic energy costs of diving were measured simultaneously by closed-circuit respirometry in six lesser scaup Aythya affinis Eyton (body mass=591±30 g) during bouts of voluntary feeding dives. Durations of dives (td=13.5±1.4 s) and surface intervals (ti=16.3±2.2 s) were within the normal range for ducks diving to 1.5 m depth. Mechanical power output (3.69±0.24 W kg-1) and aerobic power input (29.32±2.47 W kg-1) were both higher than previous estimates. Buoyancy was found to be the dominant factor determining dive costs, contributing 62 % of the mechanical cost of descent and 87 % of the cost of staying at the bottom while feeding. Drag forces, including the contribution from the forward-moving hindlimbs during the recovery stroke of the leg-beat cycle, contributed 27 % and 13 % of the mechanical costs of descent and feeding, respectively. Inertial forces created by net acceleration during descent contributed approximately 11 % during descent but not at all during the feeding phase. Buoyant force at the start of voluntary dives (6.2±0.35 N kg-1) was significantly greater than that measured in restrained ducks (4.9±0.2 N kg-1). Loss of air from the plumage layer and compression due to hydrostatic pressure decreased buoyancy by 32 %. Mechanical work and power output were 1.9 and 2.4 times greater during descent than during the feeding phase. Therefore, energetic costs are strongly affected by dive-phase durations. Estimates by unsteady and steady biomechanical models differ significantly during descent but not during the feeding phase.

Journal Article↗
PubMed1992

Metabolic responses to forced dives in Pekin duck measured by indirect calorimetry and 31P-MRS.

We tested the hypothesis that forced-dived ducks experience a reduction in metabolic rate during prolonged submergence. Unidirectionally ventilated conscious ducks were subjected to forced dives by temporarily stopping the airflow in the ventilation system and simultaneously filling a face mask with cold water. A typical cardiovascular response to submergence was observed: bradycardia and maintained arterial blood pressure. Phosphorylated metabolite concentrations in the pectoral muscle were measured noninvasively by phosphorus magnetic resonance spectroscopy (31P-MRS). ATP content was constant, and phosphocreatine was depleted via the creatine kinase reaction at a rate similar to the resting rate of ATP turnover, which was estimated to be 0.9 mumol.min-1 x g-1 in resting perfused pectoral muscle of pentobarbital-anesthetized ducks. Oxygen from myoglobin supplied at most 12% of the ATP required by the resting muscle during dives. Whole animal postdive excess oxygen consumption and blood lactic acid accumulation suggested that the shortfall in aerobic metabolism during forced dives was compensated by an increase in anaerobic metabolism.

Adenosine Triphosphate↗
PubMed1992

Blood flow distribution in submerged and surface-swimming ducks.

Observations that the response of the avian heart rate to submergence varies under different circumstances have led to speculation about variability of blood flow distribution during voluntary dives. We used a radiological imaging technique to examine the patterns of circulating blood flow in captive redhead ducks (Aythya americana) during rest, swimming, escape dives, forced dives and trapped escape dives and have shown that blood flow distribution in escape dives was the same as that in ducks swimming at the water surface. The response during trapped escape dives, however, was highly variable. Blood pressure was unchanged from the resting value during all activities. Predictions made about blood flow distribution during unrestrained dives on the basis of heart rate and other indirect data were confirmed in this study. However, the trapped escape dive responses indicated that heart rate alone is not always a reliable indicator of tissue blood flow in exercising ducks.

Animals↗
PubMed1989

Rickettsia in the regiment.

A case of Rocky Mountain Spotted Fever (RMSF) is described, together with other cases of pyrexia whose occurrence originally gave the impression of a significant outbreak of the disease in a TA regiment after annual training in the USA. The role of the RMO is considered in such circumstances.

Adult↗
PubMed1988

Chemoreceptor control of heart rate and behaviour during diving in the tufted duck (Aythya fuligula).

1. The role of chemoreceptors in the control of heart rate and behaviour during diving activity in the tufted duck was investigated in two ways. In a closed-loop experiment, ducks were exposed to ambient gas mixtures of varied composition during diving activity in an indoor tank. Characteristics of diving behaviour, heart rate and deep body temperature were monitored under hypoxic, hyperoxic and hypercapnic conditions and compared with those in air. Secondly, in an open-loop experiment the role of the carotid body (CB) chemoreceptors in the control of the responses to altered inspired gas composition and in the cardiac responses to extended and enclosed dives (Stephenson, Butler & Woakes, 1986) was investigated by chronic bilateral denervation of these receptors. 2. Heart rate during submersion was unaffected by inspired gas composition in control (data from intact and sham-operated ducks combined) and CB-denervated ducks, though diving behaviour was significantly modified in both groups of animals in response to altered inspired gas composition. Hypoxia and hypercapnia resulted in an increase in the proportion of total diving time spent breathing at the surface. The main effect of hypoxia (9-10% O2) was to reduce dive duration in control ducks and this effect was almost completely abolished after CB denervation. Hypercapnia (5-6% CO2) reduced dive duration less markedly than hypoxia but it greatly increased the duration of the inter-dive interval, effects which were not significantly influenced by CB denervation. Hyperoxia (40-45% O2) had very little effect on either behaviour or heart rate during diving, although deep body temperature was significantly elevated in this gas mixture during diving activity. There was also a less marked, but nevertheless significant, apparent hyperthermia during diving activity in air on an indoor tank but not on an outdoor pond. Conversely, there was a significant apparent hypothermia during diving activity under hypoxic conditions. 3. The CB chemoreceptors were shown to play a role in cardiac control during diving under certain circumstances. The duration of pre-dive tachycardia was significantly increased in hypoxia and this increase was abolished after CB denervation. The rate of development of bradycardia during extended and enclosed dives was slowed following CB denervation, though the initiation of the responses in extended and enclosed dives and the eventual attainment of sub-resting heart rates in enclosed dives were not prevented, indicating that other, as yet unidentified, sensory inputs are involved in cardiac control under these conditions.

Animals↗