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Biomedical subjects

J Duffin

Publications and source records attributed to J Duffin.

At least 127 records · Page 7Linked to original sources
PubMed1984

Body cooling in human males by cold-water immersion after vigorous exercise.

Five male subjects were immersed to neck level in a whole-body water calorimeter (water temperature 19 degrees C) on two occasions. One immersion was preceded by 30 min of exercise on a treadmill at 80% of the subjects' maximum heart rate, while the other was preceded by no exercise (control). Ventilation, oxygen consumption, hand-grip strength, and heat loss (measured by calorimetry) results showed no significant differences between resting and exercise trials. Minute ventilation and oxygen consumption increased during the immersion but the magnitude of the increase varied among subjects. There was a significant decrease is isometric hand-grip strength after 30 min of immersion. Rectal temperatures fell faster (0.031 degree C +/- 0.004 degree C/min) for exercised subjects than for controls (0.019 degree C +/- 0.005 degree C/min) between 10 and 45 min of immersion (P less than 0.01). It appears that vigorous preimmersion exercise may shorten survival time in cold water due to an increase in cooling rate.

Adult↗
PubMed1981

The regularity and interrelation of respiratory and cardiac rhythms at rest and during exercise.

One of the hypotheses to account for the increase in the drive to ventilation in exercise mediated by the peripheral chemoreceptors is that there is an improved linkage between breathing rate and lung to carotid body circulation time, such that peaks of arterial carbon dioxide arrive during a subsequent inspiration thereby stimulating ventilation. This study was designed to examine the mechanisms which may underlie the improved linkage. Auto- and cross-correlations of breathing and heart rhythms in volunteers at rest and during exercise showed an increased regularity of the rhythms but not entrainment between the rhythms. Although the increased regularity of the cardiac rhythm should promote a decrease in the variability of the lung to carotid body circulation time, the lack of entrainment shows that if there is an improved linkage of breathing and lung to carotid body circulation time, it is not by a coupling of heart rhythm to breathing rhythm.

Female↗
PubMed1981

Critical dependence of respiratory rhythmicity on metabolic CO2 load.

We examined the dependence of respiratory rhythm generation on the rate of CO2 production (VCO2) in six awake sheep using a venous-to-venous extracorporeal perfusion circuit that included two carbon dioxide membrane lungs (CDML) designed to facilitate the removal of CO2 from blood. As progressively greater proportions of the resting VCO2, of the sheep were removed from the venous blood by the CDML, there were proportional reductions in pulmonary CO2 excretion and in minute volume of ventilation (VE); when CO2 was removed by the CDML at a rate equal to its metabolic production by the sheep, VE fell to zero, with normal values of arterial PCO2, pH, and PO2. The results indicate that effective respiratory rhythm generation is critically dependent on stimuli related to VCO2.

Animals↗
PubMed1981

Carotid chemoreceptors in ventilatory responses to changes in venous CO2 load.

We examined the role of the carotid chemoreceptors in the ventilatory response to changes in venous CO2 load in 12 awake sheep using a venovenous extracorporeal perfusion circuit and two carbon dioxide membrane lungs (CDML). Three of the sheep had undergone surgical denervation of the carotid bodies (CBD). In the nine intact sheep, as CO2 was removed from or added to the peripheral venous blood through the CDML under normoxic conditions, there was a linear relationship between the rate of pulmonary CO2 excretion (VCO2) and the resulting rate of ventilation over a VCO2 range of 0--800% of control, so that arterial PCO2 remained close to isocapnic. In contrast, in the three CBD sheep, the ventilatory response to changes in VCO2 was significantly decreased under normoxic conditions, resulting in marked hypercapnia. The results indicate that the carotid chemoreceptors exert a major influence on the ventilatory response to changes in venous CO2 load.

Animals↗
PubMed1981

Preservation of platelets during extracorporeal circulation in sheep. A comparison between aspirin and sulfinpyrazone.

We studied the effect of aspirin and sulfinpyrazone on changes in platelet count, thromboxane B2 production, and pulmonary vascular resistance following the onset of veno-venous membrane oxygenator perfusion in sheep. Perfusion under identical circumstances was performed in three groups of animals, with one group serving as controls, one group receiving pretreatment with 1.5 grams of sulfinpyrazone iv, and one group receiving pretreatment with aspirin 50 mg/kg, iv. Both aspirin and sulfinpyrazone eliminated the rise in thromboxane B2 and the increase in pulmonary vascular resistance seen in control animals. Platelet preservation was improved significantly with sulfinpyrazone pretreatment, but not affected by aspirin. We conclude that sulfinpyrazone and aspirin have different mechanisms of action as far as platelet preservation during extracorporeal perfusion is concerned. The major difference may be sulfinpyrazone's ability to reduce platelet adhesion to the membrane surface. Since both aspirin and sulfinpyrazone eliminated the pulmonary vascular-response, but only sulfinpyrazone preserved platelets, it is apparent that the pulmonary vascular response is more closely related to thromboxane synthesis than to platelet disappearance.

Animals↗
PubMed1981

Role of metabolic CO2 production in ventilatory response to steady-state exercise.

We examined the role of metabolic CO2 production in the hyperpnea of muscular exercise by comparing the response of alveolar ventilation to moderate levels of exercise with the response to venous infusion of CO2 at rest. Studies were performed in four awake sheep that were trained to run on a treadmill. The sheep had been cannulated for veno-venous extracorporeal perfusion so that CO2 could be infused into the peripheral venous blood through membrane lungs in the perfusion circuit. The sheep breathed room air through an endo-tracheal tube inserted through a tracheostomy, and samples of expired gas were collected for measurement of the rates of CO2 production and O2 consumption. All measurements were made in the steady state. In each of the four sheep, the relationship between alveolar ventilation and the rate of CO2 production could be described by a single linear function (r greater than 0.99; P less than 0.001), regardless of whether CO2 production was increased by exercise, venous CO2 infusion, or combinations of both procedures. This relationship applied for values of CO2 production up to 350% of control. In contrast, no unique relationship was found between the rate of alveolar ventilation and either the rate of O2 consumption, cardiac output, or mixed venous blood gas pressures. The findings indicate that the hyperpnea of mild to moderate steady-state exercise can be attributed to the associated increase in the rate of CO2 production. Therefore, there is no need to invoke obligatory nonmetabolic stimuli to account for the ventilatory response to steady-state exercise.

Animals↗
PubMed1980

The ventilatory response to carbon dioxide in hyperoxic exercise.

The sensitivity of the ventilatory response to carbon dioxide in hyperoxia during light (25 W) exercise was compared to that at rest in 14 volunteers. The method used was that of rebreathing. Two factors were found to produce artefactual changes in the slope of the response during exercise. First, breath-by-breath response lines showed that the maximum limit of ventilation was reached in 3 volunteers before the end of rebreathing, despite the low exercise load. The inclusion of such breaths in the calculation of the slope of the response could produce an artefactual decrease in slope. Second, most of the response lines showed an increase in their slope during exercise. However, a model of rebreathing in exercise showed that an increase in sensitivity could be the result of variation in the difference between end-tidal and central chemoreceptor carbon dioxide levels during exercise. A criterion derived from the model, proportional to the variation in this difference, was found to be correlated with the increase in sensitivity from rest to exercise. It was therefore concluded that the sensitivity of the ventilatory response to carbon dioxide during light exercise is unchanged from that at rest.

Adult↗
PubMed1979

The effects of hypercapnia, hypoxia, exercise and anxiety on the pattern of breathing in man.

1. The pattern of breathing, defined as the relations between tidal volume and inspiratory and expiratory times, was measured during the stimulation of breathing by carbon dioxide (hyperoxic rebreathing at rest) in twenty-seven healthy, young volunteers. 2. Most of the patterns (twenty) were divisible into two parts, for low (range 1) and high (range 2) tidal volumes. The relations were curved, inverse proportionalities for both inspiration and expiration in range 2, and for expiration in range 1. The relations for inspiration in range 1 were evenly divided between those with constant inspiratory times (type 1) and those with curved, inverse proportionalities (type 2). 3. In four volunteers, direct proportionalities predominated and the patterns were scattered (type 3). 4. Eight of the volunteers (four type 1, two type 2 and two type 3 patterns) repeated the measurements and one changed from a type 1 to a type 2 pattern. 5. Nine of the volunteers also rebreathed during resting hypoxia. Two altered their patterns, and the others had patterns which were superimposed upon those measured during hyperoxic rebreathing at rest. 6. Eighteen of the volunteers also rebreathed (hyperoxic) during light exercise (25 W). Five entrained their breathing frequency to the exercise rhythm and showed exercise patterns with constant inspiratory and expiratory times. The others had patterns which were extensions of those measured during hyperoxic rebreathing at rest. 7. The pattern of breathing in range 1 was measured by steady-state methods in a further ten volunteers at rest with their eyes closed and open, and during mental arithmetic. The pooled average pattern showed that the stress of mental arithmetic shortened both inspiratory and expiratory times, and changed a type 2 pattern into a type 1 pattern.

Adult↗
PubMed1979

Biocompatibility of standard and silica-free silicone rubber membrane oxygenators.

Spiral coil membrane oxygenators made from either standard silicone rubber or silica-free silicone rubber were compared using three priming techniques. Standard priming, carbon dioxide priming, and denucleation priming were employed with each type of device. Four-hour venovenous membrane oxygenator perfusions were carried out on awake sheep anticoagulated with heparin. Virtually no differences were observed in any parameters measured between standard silicone rubber and filler-free silicone rubber membranes. Significantly greater platelet losses occurred during the first hour of perfusion with standard priming and with carbon dioxide priming than with denucleation priming, using either type of membrane. These experiments demonstrate that denucleation priming reduces platelet losses during extracorporeal membrane oxygenator perfusion, but that the use of filler-free silicone rubber does not improve the biocompatibility of the membrane.

Animals↗
PubMed1978

The effect of ethanol on the ventilatory responses mediated by the peripheral chemoreceptors in man.

The ventilatory responses mediated by the central and peripheral chemoreceptors were separately assessed in eight healthy volunteers before and after the oral ingestion of ethanol in a dose of 0.75 ml/kg. No significant depression of the central response was observed, but a significant depression of the peripheral response was observed at 25 and 95 minutes after the consumption of ethanol. The peripheral chemoreceptor stimulus was the simultaneous increase of hypoxia and hypercapnia and this novel method is described.

Administration, Oral↗
PubMed1978

The recruitment times and firing patterns of the medullary respiratory neurones of the cat.

The brainstem of anaesthetized cats was explored for respiratory neurones with microelectrodes in the regions of the nucleus retroambigualis (ventrolateral region) and the nucleus tractus solitarius (dorsomedial region). These neurones were analysed with respect to their firing patterns and recruitment times, as referenced to the respiratory cycle. All of the respiratory neurones showed a stable and ordered pattern of firing. Four groups of neurones with similar characteristics within each group, but differing from each other, were statistically examined; the inspiratory neurones of the dorsomedial region, the 'late' inspiratory neurones of the ventrolateral region, the 'early' inspiratory neurones of the ventrolateral region and the expiratory neurones of the ventrolateral region.

Action Potentials↗
PubMed1978

Microbubble elimination during priming improves biocompatibility of membrane oxygenators.

We tested the hypothesis that platelet loss following blood contact with foreign materials is partly related to the presence of microbubbles of gas (gas nuclei) trapped in surface defects on the membrane material. Extracorporeal membrane oxygenator perfusions were conducted in two groups of sheep, with use of standard priming techniques for the oxygenator in one group and a new vacuum priming technique in the other group. The vacuum priming technique was developed to eliminate gas nuclei from the oxygenator surface. With denucleation priming, platelet loss during perfusion was markedly reduced, as was thrombus formation on the membrane surface. The platelet particle-size distribution curve showed a shift consistent with platelet aggregation with the standard priming technique but not with the vacuum priming technique. We conclude that the elimination of trapped gas nuclei from the membrane surface during priming reduces the initial interaction between blood elements and the foreign surface.

Animals↗
PubMed1978

Extracorporeal membrane oxygenator support for human lung transplantation.

Extracorporeal membrane oxygenator (ECMO) support was provided for a 19-year-old boy undergoing right lung transplantation. Perfusion was begun several hours prior to transplant, to correct profound hypercapnia. After the operation, ECMO was required because of inadequate gas exchange by the transplanted lung. Perfusion was continued for a total of 96 hours. During this time, the temporary malfunction of the transplanted lung owing to the reimplantation response reversed, and the patient was successfully removed from the oxygenator and subsequently weaned from the ventilator. He died on the eighteenth postoperative day of bronchial dehiscence. ECMO support appears to be a feasible means of supporting patients during lung transplantation and during the period of reversible lung malfunction that may occur in the early postoperative period.

Adult↗