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Biomedical subjects

G M Hughes

Publications and source records attributed to G M Hughes.

At least 19 recordsLinked to original sources
PubMed1989

Research collaboration.

The complexity and cost of cardiovascular medical care dictate research to deliver high quality and cost-conscious cardiovascular care. This goal is aided by modeling medical decision making. To be useful, the modeling must be based on real data so that the results can serve as a guide to actual practice. It is suggested that a registry of randomized clinical trials and larger data bases in cardiovascular disease and health care delivery be established. The registry would be a resource for those desiring to model decision making. The registry would contain key words allowing retrieval by modelers accessing the registry and would contain contact information for consideration of possible collaborative work. The initiation of such a registry should contain plans for its evaluation to determine whether the registry itself is a cost-effective tool to encourage the needed research.

Clinical Trials as Topic↗
PubMed1988

Relationships between swimming speed, oxygen consumption, plasma catecholamines and heart performance in rainbow trout (S. gairdneri R.).

Rainbow trout swimming at controlled speeds in a tunnel respirometer have been used to measure oxygen consumption and plasma catecholamine levels, and systolic pressure/frequency relationships. Catecholamine (CA) levels evaluated in trout plasma at low swimming speed [0.5 bodylengths/second (bl/s)] were: adrenaline (A) 1.77 +/- 0.22 nM; noradrenaline (NA) 3.94 +/- 0.83 nM; dopamine (DA) 2.40 +/- 0.36 nM. No significant increase was observed during moderate exercise (1.5 bl/s): A 1.60 +/- 0.20 nM; NA 5.76 +/- 1.07 nM; DA 2.31 +/- 0.80 nM, or stronger exercise (2.0 and 2.5 bl/s-1): A 2.10 +/- 0.21 nM; NA 5.90 +/- 0.90 nM; DA 2.21 +/- 0.40 nM. A correlation was found between heart rate at these swimming speeds, and its position on the systolic pressure frequency curve of isolated hearts, which suggests that the heart functions at maximum systolic pressure at low (0.5 bl/s-1) swimming speeds and that this pressure decreases during exercise as cardiac frequency rises.

Animals↗
PubMed1986

Comparison of the osmotic fragility of red blood cells in samples from anaesthetised and unanaesthetised trout and eel and the effect of varying oxygen levels.

The osmotic fragility of trout and eel red blood cells has been tested in fresh blood samples and following equilibration at low PO2 (7.5-25 mmHg). Percentage haemolysis curves obtained were similar to those in other vertebrates. Blood sampled shortly after cannulation (OP) shows higher % haemolysis at a given saline concentration than in samples taken 24 h after recovery from anaesthesia. Following exposure to low PO2's greater haemolysis is present and is reduced by raising the oxygen level.

Aminobenzoates↗
PubMed1985

Effects of temperature and transfer from seawater to freshwater on blood microrheology in Pacific salmon.

Blood of Pacific salmon was studied with particular interest in red blood cell (RBC) deformability in relation to migration. Blood samples were taken via cardiac puncture or chronic cannula placed in the dorsal aorta and heparinized. As an index of RBC deformability the mean passage time of single RBCs through micropores of 8 micron in diameter and 10 micron in length was determined under a pressure difference of 10 cmH2O. Despite about 100 mOsmol/l difference in plasma osmolality, there was no marked difference in RBC passage time between fish in seawater and those well acclimatized to freshwater. However, it seemed probable that a transient decrease in RBC passage time, i.e., an increase in RBC deformability, occurred immediately following transfer from seawater to freshwater. Plasma osmolality decreased to about 300 mOsmol/l within 1 hr after the transfer and showed no fluctuations thereafter. The temperature dependence of RBC deformability was much smaller in comparison with those previously observed in yellowtail and carp; salmon RBCs were still highly deformable even at 5 degrees C, a possible temperature of cold river water.

Animals↗
PubMed1985

Recovery of cardiac and ventilatory frequencies after sub-acute pesticide (ABOL-X) treatment in rainbow trout, Salmo gairdneri Richardson.

Short term, sublethal changes in coughing rate, cardiac and ventilatory frequencies in hatchery-reared rainbow trout (27-34 cm) exposed to menazon and gamma BHC containing pesticide were monitored at 15 +/- 1 degree C during recovery period to investigate the effects of this chemical on fish respiratory and cardiovascular systems. Laboratory conditions simulated a rapid environmental pollution often occurring in running waters. The coughing response was particularly sensitive to water pollutants. Average rate of ventilation was lower in treated fish than in control specimens and decreased parallel with the time of recovery. Average heart rate was higher in treated trout as compared to the controls. These changes were characteristic for hypoxic conditions and provide useful sublethal physiological indications for a rapid environmental stress. Percentage coupling and phase angle of ECGs within the ventilatory cycle were also studied during recovery when significant differences were observed between treated and untreated groups of fish.

Animals↗
PubMed1979

Histochemistry of some trout respiratory muscles.

A histochemical study has been made of the main cranial muscles which produce ventilation movements of the rainbow trout. It is shown that a greater proportion of red(aerobic) fibres is present in those muscles known to be active during shallow ventilation than those which become active at greater ventilation volumes. An ordered recruitment of red, pink and white fibres within these muscles is also likely.

Animals↗
PubMed1978

Scanning electron microscopy of the respiratory surfaces of Saccobranchus (= Heteropneustes) fossilis (Bloch).

The gill secondary lamellae are generally covered with epithelial cells whose outer surfaces form numerous microvilli. The surface of the primary lamellae is characterised by microridges. A particular type of surface sculpturing seems to be associated with given cell boundaries. Further evidence for the derivation of the air tube and fans which guard its entrance by modification of the basic gill structure has been obtained from both the gross surface architecture and microstructure of the individual cell surfaces. Secondary lamellae are represented by stubby projections which generally have a biserial arrangement. The outer surfaces of the epithelia overlying the capillaries of these respiratory islets are coated with microvilli as in the secondary lamellae. On the other hand, the relatively smooth-surfaced 'lanes' between groups of respiratory islets have a microridged surface similar to that of the primary gill lamellae. It is suggested that previous estimates of surface area, and consequently diffusing capacities of the air-breathing organ, have been low in view of the increased surface, due to both their gross and microstructure. Estimates for gill surface area may need very little correction as the spaces between the microvilli and microridges are probably filled with mucus under normal conditions.

Animals↗
PubMed1978

Visualization of layers lining the lung of the South American lungfish (Lepidosiren paradoxa) and a comparison with the frog and rat.

Comarisons have been made of the structure of layers lining the lungs of lungfish, frog and rat using material fixed by perfusion of the pulmonary circulation of physiological pressures and at normal air pressures within the lung. The lining consists of a thin densely osmiophilic surface layer which covers a much thicker hypophase of generally floccular appearance. Tubular myelin, present in the frog and rat lung lining, was not observed in the layers lining the lung of Lepidosiren.

Animals↗
PubMed1978

Some responses of the electric ray (Torpedo marmorata) to low ambient oxygen tensions.

I. Blood samples were taken during prolonged hypoxia experiments in which the inspired water oxygen tension was less than 10 mmHg. The oxygen tension of the post-branchial blood was about 5 mmHg and its pH shows a significant lowering from normoxic levels. 2. The decrease in blood pH is correlated with increases in levels of lactate and pyruvate. The lactate/pyruvate ratio increases during hypoxia. 3. An increase in blood succinate was also found, and strongly suggests the accumulation of multiple anaerobic end-products within the tissues. 4. Recovery of normoxic levels of succinate takes place almost immediately following the restart of ventilation whereas the decrease in lactate concentration is slower. 5. It is concluded that these adaptations may be related to the habitat of the fish at low tide in pools where the Po2 may fall very markedly.

Animals↗
PubMed1978

On the respiration of Torpedo marmorata.

1. The oxygen consumption of resting Torpedo marmorata was measured using three different methods. The results indicate that this species has a much lower oxygen consumption than other elasmobranchs of comparable size. 2. The gills are ventilated by a mechanism similar to that of other rays, but a relatively small spiracular opening seems to be associated with a more important role of the oro-branchial pump. During hypoxia there is a marked increase in both frequency and amplitude of the ventilatory movements. 3. The frequency of the heart beat is low and shows little change during hypoxia, except under extreme conditions when bradycardia occurs. 4. In some individuals, coupling between cardiac and ventilatory pumps is relatively low but seems to increase at lower ventilatory frequencies and when the ratio between the ventilatory and cardiac frequencies is a whole number. 5. Extreme hypoxia can be withstood for many hours but eventually the ventilatory rhythm ceases; it does not recommence immediately following a rise in ambient oxygen tension. 6. The blood has a low oxygen-carrying capacity and a high affinity. 7. The surface area of the gills is smaller than that of other species that have been investigated, but the quantity of oxygen transferred/unit surface area is similar to that known for other species. 8. It is concluded that Torpedo is a sluggish fish adapted to conditions of low oxygen, but the conditions under which this occurs remain to be determined.

Animals↗
PubMed1978

Static pressure-volume curves for the lung of the frog (Rana pipiens).

1. Static pressure/volume curves have been determined for isolated frog lungs inflated with either air or saline. In both cases a hysteresis was present: the pressure required to produce unit change of volume being greater during inflation than deflation 2. The pressure necessary for a given volume change was less for the saline-filled than the air-filled lungs. The difference between these curves is due to the surface tension at the air/lung interface. 3. Pressure/volume curves for air-filled lungs in situ were similar to curves for isolated lungs. However, a greater pressure was required for the same volume change during both inflation and deflation. 4. Compliance was calculated from different parts of air pressure/volume curves and gave values greater than those obtained using similar calculations for higher vertebrates. 5. These observations support other evidence for the presence of a surfactant in the lung lining of frogs in spite of the relatively large diameter of their 'alveoli.' The precise role of such a lining is uncertain and it is concluded that similar forces may be involved during the inflation and deflation of lungs of frogs and higher vertebrates in spite of differences in gross morphology.

Animals↗
PubMed1976

An electrolytic method for determining oxygen dissociation curves using small blood samples: the effect of temperature on trout and human blood.

1. A detailed account is given of an electrolytic method for determining the oxygen dissociation curve of fish blood using a single sample of 50-100 mul for the whole curve. The accuracy and some of the problems arising from its uses are discussed. 2. Oxygen dissociation curves have been determined for trout blood and human blood at temperatures of 15 and 37 degrees C. The relationship between P50 and temperature is similar to that obtained using other methods. Absolute values of P50 are generally lower than those obtained by other methods, especially in the case of fish blood. 3. The effect of PCO2 and pH on the oxygen dissociation curve of trout blood is tested and it is shown that PCO2 has a more marked effect than pH when the other factor is maintained at a constant level. The Bohr factor (delta log P50/delta pH) appears to be approximately the same and independent of the PCO2. 4. The P50 of ray blood determined from fish during and after an operation showed an increased Bohr factor.

Animals↗