Search PubMed⌕ Search

Biomedical subjects

A J Mortimer

Publications and source records attributed to A J Mortimer.

At least 37 records · Page 2Linked to original sources
PubMed1994

Educational projects in Space Life Sciences in Canada.

As part of its mandate the Space Life Sciences Program within the Canadian Space Agency has worked to increase interest in space and develop young scientists. Projects have been undertaken at the public school and high school level, with classroom resource material and science contests; at the university level with summer training programs, and at the post-graduate level with opportunities to complete research projects in a microgravity environment.

Biological Science Disciplines↗
PubMed1993

Severe sepsis following percutaneous or endoscopic procedures for urinary tract stones.

Nine cases of severe sepsis following percutaneous or endoscopic procedures for upper urinary tract stones are reported. The mortality rate was 66%. Despite the fact that approximately 700 procedures were carried out in males and females in roughly equal proportions, a striking but inexplicable feature was that all 9 patients in the study group were female. Severe systemic sepsis has a high mortality rate and any procedure that may put patients at risk of this complication should not be undertaken lightly (and certainly not as an out-patient procedure). Recovery is possible with a high index of suspicion, early intervention and intensive treatment.

Adolescent↗
PubMed1991

Efficiency of an enclosed afferent reservoir breathing system during controlled ventilation.

We describe an enclosed afferent reservoir (EAR) breathing system developed by Ohmeda and designed to operate efficiently in spontaneous and controlled ventilation. The efficiency of the system was evaluated by calculating the fractional utilization of fresh gas in 10 ASA I-III patients during anaesthesia with controlled ventilation. Maximum efficiency occurred when the minute ventilation to fresh gas flow ratio was greater than 1.5. Under these conditions, fractional utilization was relatively constant with a value of 0.73 (95% confidence interval 0.69-0.78). The minimum fresh gas flow for use during controlled ventilation was determined in another eight ASA I-III patients when the minute volume to fresh gas ratio was greater than 1.5. In view of an increased arterial to end-tidal carbon dioxide partial pressure difference in patients in the first part of the study (1.03 kPa), normocapnia was defined as an end-tidal carbon dioxide partial pressure of 4.3 kPa. Normocapnia was achieved with a mean fresh gas flow of 66 ml kg(-1) min(-1), while 70 ml kg(-1) min(-1) produced mild hypocapnia.

Aged↗
PubMed1991

Persistence of supply dependency of oxygen uptake at high levels of delivery in adult respiratory distress syndrome.

OBJECTIVE: To identify any plateau in oxygen consumption (VO2) when oxygen delivery (DO2) is increased in patients with the adult respiratory distress syndrome (ARDS). DESIGN: Clinical prospective study; multiple regression analysis was done to assess the relationship between VO2 and DO2 for pooled data and for each individual patient. SETTING: University hospital ICU. PATIENTS: Twenty consecutive patients aged 18 to 78 yrs (mean 43.5) in whom ARDS was present during their ICU stay. INTERVENTIONS: Multiple measurements were obtained in individual patients (mean number of measurements 40, range 20 to 83) and mathematical models were fitted to both pooled and individual patient data. DO2 ranged from 212 to 1550 mL/min.m2 with a maximum of 758 to 1550 mL/min.m2 (mean 1136). Because of the large variations between patients, it was not justifiable to describe a relationship for the pooled data and each case was analyzed individually. MEASUREMENTS AND MAIN RESULTS: We found the optimal regression model to be linear in 13 patients, cubic in four, and either cubic or linear in one. Two patients demonstrated no significant relationship. The relationship for the group was determined from each patient's data and was best described by linear regression. CONCLUSIONS: In no patient was there evidence of a plateau, despite high levels of DO2 being achieved in all patients.

Adolescent↗
PubMed1989

The significance of membrane changes in the safe and effective use of therapeutic and diagnostic ultrasound.

The cellular changes, such as alterations in motility and the stimulation of synthesis and secretion, induced by relatively low intensities of therapeutic ultrasound (e.g. 500 mW cm-2, SAPA; 100 mW cm-2 SATA) are primarily non-thermal in origin. They appear to be associated with changes in the permeability of the cell (plasma) membrane and in the transport of ions and molecules across it, effects which have been demonstrated in cells irradiated in suspension. In epithelial tissues, both in vitro and in vivo, it has been demonstrated that not only the cellular membrane transport pathways but also the paracellular or intercellular pathways are affected. Although membrane-mediated effects can be of value therapeutically, they could produce adverse effects if they were to occur during development, for the reception and transmission by the membrane of environmental signals are involved in determination of the fate of each cell. Determination is followed by selective gene expression and differentiation, that is, by the progressive increase in structural complexity brought about by the acquisition of specialised characteristics by various cell groups. Most cells of early embryos are ionically coupled via gap junctions which provide an intercellular pathway for electrochemical signalling and the maintenance of the concentration gradients which provide the cells with positional information. Differentiation of the cells varies according to their location with respect to these gradients. Increase in the intracellular concentration of calcium ions, which has been shown to occur after exposure to therapeutic levels of ultrasound, can decrease the permeability of gap junctions and uncouple cells, in the manner which occurs when they differentiate. Ultrasonically induced increases in calcium ion concentration are thus of considerable clinical significance, since they could affect differentiation and consequently histogenesis. Modification of plasma membrane permeability and transport properties, resulting in changes in the availability and activity of second messengers such as free calcium ions, can have profound effects on cell behaviour. Calcium channels appear to be the first channels to develop in the cell membranes of embryos, and internal calcium ion concentration is known to affect the synthesis of fetal proteins. Although generally reversible at intensities of less than 500 mW cm-2, changes in membrane permeability, particularly to calcium ions, could, if prolonged, have undesirable side effects not only on embryogenesis but on late prenatal and postnatal development. It is therefore recommended that the environmental conditions, thresholds, and mechanisms involved in the production of such changes be determined, so that they can be avoided when ultrasound is used diagnostically on sensitive targets such as embryos and fetuses.

Animals↗
PubMed1988

Ultrasound-enhanced diffusion through isolated frog skin.

The effect of ultrasound on the transport of oxygen across excised frog abdominal skin has been studied. Samples were mounted in an exposure chamber in which the Ringer's solution on one side was saturated with oxygen while the other side of the skin had a low initial oxygen concentration. They were treated with ultrasound at 1, 1.5 and 2 W cm-2 SATA c.w., respectively, and increases in the rate of oxygen transport were observed at all intensities. These increases ranged from 38 +/- 4% at 1 W cm-2 to 55 +/- 8% at 2 W cm-2. Variation in the pulse lengths from 25 to 200 ms and a constant average intensity did not affect the rate of transport significantly provided that the temporal intensity was constant. Since the peak acoustic pressure within the pulse increased with decreasing pulse length and increasing acoustic pressure increases the probability of cavitation occurring, the mechanism responsible for this phenomenon is probably not cavitation.

Abdomen↗
PubMed1988

The effect of therapeutic ultrasound on calcium uptake in fibroblasts.

The effect of therapeutic ultrasound on calcium uptake by embryonic chick 3T3 fibroblasts has been studied using calcium-45 radiotracer techniques. Cells were treated while suspended in culture medium at 36 degrees C at intensities from 0.25 W/cm2 SPPA to 1.5 W/cm2 SPPA (1 MHz, pulsed 2 ms on:8 ms off) and for exposure times from 1 min to 20 min. Ultrasound treatment was found to increase calcium uptake for SPPA intensities from 0.5 to 1.0 W/cm2 SPPA, with a maximum increase of 18% after a 5 min exposure. Calcium uptake also increased with increasing exposure time. Measurements performed up to 20 min after treatment showed that the cell was able to reduce this calcium influx, indicating that the membrane did not suffer irreparable damage as a result of the ultrasound exposure.

Animals↗
PubMed1988

A cavitation and free radical dosimeter for ultrasound.

A simple and sensitive method is described for measuring the number of hydroxyl radicals (.OH) produced in aqueous solution by high intensity ultrasound (US). The method is based on the conversion of nonfluorescent terephthalic acid (TA) to highly fluorescent hydroxyterephthalate (HTA). The spectrofluorimeter is calibrated by use of a TA solution which has been exposed to a reference dose of cobalt-60. This allows fluorescence readings produced by ultrasound to be read directly in equivalent centiGrays (cGy). The limit of detection for OH is about 1.3 X 10(-9) M (equivalent to an exposure of about 0.5 cGy of cobalt-60). The threshold for transient cavitation (TC) in an air-saturated aqueous solution was found at 0.7 watts per cm2. Cavitation was consistently produced when TA was exposed in a soft vinyl chamber and only when the chamber was being rotated about an axis which was perpendicular to the US beam. The use of TA as a quantitative indicator of transient cavitation should be of value to the study of ultrasonic biological effects and dosimetry.

Equipment Design↗
PubMed1987

Estimation of arterial PCO2 during high frequency jet ventilation. Studies in the dog.

The arterial to end-tidal PCO2 difference (PaCO2-PE'CO2) was measured in five anaesthetized dogs during controlled ventilation at 0.25 Hz (15 b.p.m.) and during high frequency jet ventilation at 1, 3 and 5 Hz. Because of the slow response of the infra-red carbon dioxide analyser, satisfactory recordings of end-tidal carbon dioxide could not be obtained at frequencies greater than 1 Hz. The interruption of high frequency jet ventilation by conventional ventilation resulted in approximately equal arterial and end-tidal PCO2 values during the first breath, and restoration of the normal arterial to end-tidal PCO2 difference by the third breath. It is concluded that, when high frequency jet ventilation at 1, 3 or 5 Hz is interrupted with normal tidal volumes at low frequencies, the arterial PCO2 can be estimated from recordings of the end-tidal PCO2.

Animals↗
PubMed1986

Carbon dioxide clearance and deadspace during high frequency jet ventilation. Investigations in the dog.

The effects of frequency, tidal volume and added deadspace on carbon dioxide clearance were measured during high frequency jet ventilation at 1, 3 and 5 Hz in dogs. With a short, small volume deadspace, carbon dioxide clearance increased with minute volume at each frequency, but for a given minute volume the clearance decreased with increase in frequency. At 5 Hz, carbon dioxide clearance was less than carbon dioxide production. At 1 Hz, an increase in the volume of added deadspace decreased carbon dioxide clearance, but changes in the length of the deadspace, without change in volume, had no effect. At 5 Hz, an increased volume of added deadspace had little effect on carbon dioxide clearance, but increased length, without change in volume, decreased clearance. Carbon dioxide clearance was increased by placing the jet at the lung end of the tracheostomy tube. It is concluded that at 1 Hz, carbon dioxide elimination is governed by bulk flow, but at 5 Hz other mechanisms are important.

Animals↗
PubMed1986

Carbon dioxide clearance during high frequency jet ventilation. Effect of deadspace in a lung model.

The effects of the volume and length of deadspace on the clearance of carbon dioxide from a lung model have been investigated during high frequency jet ventilation (HFJV) at 1, 3 and 5 Hz. At 1 Hz, increasing the volume of the deadspace without changing the length caused a reduction in the clearance of carbon dioxide. At 5 Hz, an increase in the length of deadspace decreased carbon dioxide clearance, whilst an increase in volume had no effect. Since the delivered tidal volume was less than the volume of the morphological deadspace at this frequency, the elimination of carbon dioxide must have been accomplished by mechanisms which are not considered important at normal tidal volumes and frequencies. Furthermore, the clearance of carbon dioxide at 5 Hz was very inefficient compared with that at 1 Hz. It is concluded that, during HFJV, carbon dioxide is cleared most efficiently when the frequency is low enough for the delivered tidal volume to be greater than the volume of the morphological deadspace.

Carbon Dioxide↗
PubMed1985

Effects of dopamine and dobutamine on the distribution of pulmonary blood flow during lobar ventilation hypoxia and lobar collapse in dogs.

Hypoxic pulmonary vasoconstriction was induced in the left lower lobe of fifteen dogs by ventilating the lobe with 7% O2 or by absorption collapse, and the distribution of flow between the lobe and the remainder of the lung was measured with electromagnetic flow probes. The lobar to total blood flow ratio was reduced by lobar ventilation hypoxia and decreased further during lobar collapse. In seven dogs, an infusion of 20 micrograms kg-1 min-1 of dopamine produced an increase in total blood flow, an increase in pulmonary artery pressure (P less than 0.01), and an increase in lobar to total flow ratio (P less than 0.05) during both hypoxic states. There was a significant fall in arterial PO2 (P less than 0.01) during ventilation hypoxia. Similar changes in total and lobar to total flow ratio (P less than 0.01) were observed in eight dogs given 20 micrograms kg-1 min-1 of dobutamine, but there were no changes in pulmonary artery pressure. The greater increase in total flow (+ 111%) resulted in a marked increase in mixed venous PO2 and no significant changes in arterial PO2 in this group of dogs. It is concluded that both drugs produce an increase in lobar to total blood flow ratio and shunt fraction, but that the mechanisms causing the redistribution of flow may differ.

Animals↗
PubMed1984

Unilateral high frequency jet ventilation. Reduction of leak in bronchopleural fistula.

A young alcoholic presented with severe bilateral bronchopneumonia, which required prolonged treatment with intermittent positive pressure ventilation. High airway pressures were necessary for effective gas exchange. A recurrent tension pneumothorax led to a persistent bronchopleural fistula which resulted in hypercarbia and hypoxaemia despite the use of large minute volumes. Surgical resection was not considered feasible because of extensive local infection. Asynchronous independent lung ventilation was instituted, using a double-lumen endobronchial tube. A considerable leak still occurred through the bronchopleural fistula, and it was only when high frequency jet ventilation was substituted to the fistula-containing lung that the leak was virtually abolished, while improving gas exchange. High frequency jet ventilation in bronchopleural fistula is of potential benefit.

Adult↗