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Biomedical subjects

D G Davies

Publications and source records attributed to D G Davies.

18 recordsLinked to original sources
PubMed1991

Chemical regulation of cerebral blood flow in turtles.

This study was performed to test the effect of the chemical composition of the blood on cerebral blood flow (CBF) regulation in turtles. The CBF response to increases in arterial PCO2 (PaCO2) (hypercapnia) was measured during normoxia and anoxia in anesthetized freshwater turtles Pseudemys scripta. The radioactive-microsphere technique was used to measure CBF. CBF increased with increases in PaCO2. The sensitivity of the CBF response to hypercapnia (delta CBF/delta PaCO2) was 0.68 ml.min-1.100 g-1. Torr-1 during normoxia. delta CBF/delta PaCO2 increased to 3.44 ml.min-1.100 g-1. Torr-1 during anoxia. The increases in CBF occurred at constant mean arterial blood pressure, which indicates that cerebral vascular resistance decreased. The increased CBF response during asphyxia (hypercapnia-anoxia) could be beneficial for survival during prolonged dives by increasing glucose delivery for brain anaerobic metabolism. In addition, increased CBF could aid in regulating brain acid-base composition by controlling extracellular fluid PCO2.

Animals↗
PubMed1991

Massive haemorrhage in pancreatitis.

Massive haemorrhage in pancreatitis is a very rare complication of pancreatitis but it is the most rapidly lethal, haemorrhage being the major cause of death in more than half of the fatal cases. We present three patients who illustrate this rare complication in its diversity of presentation, and advise that doctors should have a keen clinical awareness of this condition if there is to be an effective and expeditious management. An understanding of the condition, coupled with immediate treatment, using embolisation or laparotomy with direct ligation of the bleeding vessel, can be lifesaving.

Adult↗
PubMed1989

Arterial blood gas status in rats exposed to chronic CO at low and high altitude.

Arterial blood gases were measured in 52 unanesthetized Sprague-Dawley rats following six weeks exposure to either room air at ambient altitude (950 m), room air containing 100 ppm CO at ambient altitude, room air at 4575 m simulated high altitude, or room air containing 100 ppm CO at 4575 m simulated high altitude. PaCO2 was significantly higher in animals exposed to CO both at ambient altitude (38.2 vs 34.5 Torr) and simulated high altitude (28.3 vs 23.6 Torr). The data show that chronic exposure to low concentrations of CO depresses ventilatory drive at both ambient and simulated high altitude. This depression could be related to changes in brain blood flow and the acidity of the central medullary chemosensitive area or to changes in peripheral chemoreceptor activity.

Altitude↗
PubMed1989

Distribution of systemic blood flow during anoxia in the turtle, Chrysemys scripta.

Hypoxia causes a reflex redistribution of regional blood flow in mammals that maintains delivery of oxygen to vital organs such as the brain during periods of decreased oxygen availability. The present study was performed to test if this response is developed in lower vertebrates. Regional organ blood flow and arterial blood gases were measured during normoxia (room air) and anoxia (nitrogen breathing) in anesthetized turtles, Chrysemys scripta. Organ blood flow was measured by the distribution of radioactive microspheres injected into the left atrium. The concentration of the microspheres in the organ is directly related to the blood flow rate. By knowing the reference blood flow rate, the reference microsphere concentration, and the total counts in the tissue, the tissue blood flow rate can be calculated. Anoxia caused a redistribution of blood flow away from the kidneys and splanchnic bed to the brain. Coronary blood flow and skeletal muscle blood flow remained constant. Brain blood flow increased approximately 260%. Blood flow to the kidneys and stomach was reduced approximately 50%. Blood flow to the pancreas, small intestine, and liver decreased almost to zero. The observation of anoxia-induced reflex redistribution of organ blood flow in a lower vertebrate suggests that this mechanism could be characteristic of vertebrates in general.

Animals↗
PubMed1989

Ventilatory responses of the ground squirrel, Spermophilus tridecemlineatus, to various levels of hypoxia.

1. Minute ventilation (VE) in the semifossorial ground squirrel (Spermophilus tridecemlineatus) increased with increased levels of hypoxia. 2. The increase in VE was brought about primarily by an increase in breathing frequency (f). There was no significant change in tidal volume (VT). 3. The PiO2 threshold for the ventilatory response to hypoxia and position of the ventilatory response curve in the ground squirrel were closer to the semifossorial echidna (Tachyglossus aculeatus) than the completely fossorial mole rate (Spalax ehrenbergi); both the ground squirrel and echidna had a higher PiO2 threshold than the mole rat. 4. The ventilatory response curve was shifted to the left in the mole rat. 5. These observations indicate that the mole rat is the least responsive to hypoxia of the three species.

Animals↗
PubMed1979

Effect of cerebral extracellular fluid acidity on total and regional cerebral blood flow.

Total and regional cerebral blood flow (CBF), and cerebrospinal fluid (CSF), and arterial blood acid-base status were measured in 26 chloralose-urethan-anesthetized dogs before and after 30 and 60 min of ventriculocisternal perfusion with artificial CSF equilibrated with 7% CO2 and containing either low (8.7 or 9.1 meq/l), normal (19.6 meq/l), or high (34.7 meq/l) bicarbonate ion concentration ([HCO3-]). An inverse linear relationship was observed between the CSF pH and total CBF. Regional blood flow changes were greater in structures that were closest to the ventricular system. In addition, regional blood flow changes were greater in all tissues studied after 60 min of perfusion than after 30. Perfusion with the control [HCO3-] caused no significant changes in either acid-base status or CBF. We believe that the regional cerebral blood flow changes are the result of changes in the H+ concentration gradient across the cerebral extracellular fluid (ECF) space due to the diffusional exchange of HCO3- between CSF and ECF. It is concluded that cerebral ECF acidity is important in the local regulation of cerebral blood flow.

Acid-Base Imbalance↗
PubMed1978

Cutaneous blood flow during heating and cooling in the American alligator.

Nine alligators, Alligator mississippiensis, were injected with 133Xe and the clearance half times measured in response to heating and cooling. Mean half times for thermostable, heating, and cooling conditions were 12.2, 8.6, and 28.3 min, respectively, indicating cutaneous vasodilation in response to local heating and reduced blood flow during cooling. Alterations of cutaneous blood flow occurred before changes in body temperature or heart rate. Warming portions of the animal while shading the injection site resulted in reduced blood flow when heat loss occurred. Skin thickness (S in cm) was related to body mass (M in kg) as S = 0.08 M0.38. Cutaneous blood flow per unit area was found to increase with increasing body mass from approximately 0.0025 to 0.025 ml blood-cm-2 of skin-min-1 during warming and from 0.0018 to 0.0045 during cooling for the 0.18--8.6 kg animals, respectively.

Alligators and Crocodiles↗
PubMed1978

Temperature-induced changes in blood acid-base status in the alligator, Alligator mississipiensis.

Gas exchange and arterial blood acid-base status were measured in 13 conscious alligators, Alligator mississipiensis, at 15, 25, and 35 degrees C. Arterial pH decreased by 0.250 units (from 7.635 to 7.385) and arterial carbon dioxide partial pressure increased by 11.4 Torr (from 11.8 to 23.2) as body temperature increased from 15 to 35 degrees C. No statistically significant changes occurred in arterial bicarbonate concentration. When OH-/H+ and alpha-imidazole were compared at each temperature, more variability was observed in OH-/H+, which increased from 8.7 to 12.0 as temperature increased from 15 to 35 degrees C. alpha-Imidazole remained essentially constant (0.76 at 15 degrees C and 0.80 at 35 degrees C). Body temperature increase caused marked increases in minute ventilation (VE), oxygen consumption (VO2), and carbon dioxide production (VCO2). The relative changes in these parameters resulted in a decrease in both VE/VO2 and VE/VCO2. The data of the present study are consistent with the concept that poikilotherms regulate their alveolar ventilation with changes in body temperature in order to keep OH-/H+ or alpha-imidazole constant.

Acid-Base Equilibrium↗
PubMed1977

An interactive program on the PDP-11 for computing organ blood flow from data obtained using the radioactive microsphere technique.

An interactive, BASIC-PLUS language program is described for computation of various parameters of blood flow in research animals from data obtained using the radioactive microsphere technique. This program used in conjunction with the PDP-11 computer gives the following output for a variable number of organs studied simultaneously: (1) descriptive statistics on counts per minute; (2) total blood flow to an organ; (3) blood flow to an organ per unit weight; (4) resistance to flow in that organ; (5) total systemic arterial resistance; (6) cardiac output; and (7) percent of cardiac output distributed to each organ. Further, separate outputs can be generated when a series of different isotopes are used in the same animal to study different experimental conditions.

Animals↗
PubMed1977

The Wien effect in compensated metabolic acidosis.

CSF and blood acid-base values were measured in compensated metabolic acidosis, induced in anesthetized dogs by infusion of dilute HCl during hyperventilation. We observed cerebral blood flow-related steady-state differences in PCO2 between CSF and arterial venous blood from the brain. The steady-state values of CSF-blood PCO2 differences and blood H+ activity were intermediate to those observed by us previously during uncompensated acidosis and alkalosis (J. Appl. Physiol. 34: 249-254, 1973). These results are consistent with predictions of the "charged membrane hypothesis" proposed by us to explain CSF and blood acid-base relationship during uncompensated acid-base derangements (J. Appl. Physiol. 34: 243-248, 1973).

Acidosis↗
PubMed1976

The skin flora of the hemiplegic hand.

More organisms were found on the paralysed hands of hemiplegic patients than on their unaffected ones. However, both showed considerably higher bacterial counts than did geriatric patients without paralysis. An infection rate for Cl. welchi of 15% was found in the paralysed hands.

Aged↗
PubMed1976

Cerebrospinal fluid sampling technique and Astrup pH and PCO2 values.

The pH and PCO2 values measured by the Astrup technique were compared in cerebrospinal fluid (CSF) obtained using two different sampling techniques: 1) a direct or in vivo technique and 2) the widely accepted syringe sampling technique. In 65 pairs of measurements in 9 dogs it was found that the pH was always overestimated and the PCO2 always underestimated in the syringe sample when compared to the in vivo sample. The equations describing the relationships are as follows: 1) pH (syringe = 0.995 pH (in vivo) + 0.084 and 2) PCO2 (syringe) = 0.873 PCO2 (in vivo) + 0.2. The amount by which the syringe sample underestimated the true PCO2 value increased with the absolute PCO2 value, consistent with the possibility of there being a diffusional loss of CO2 during the transfer of CSF from the syringe to the pH electrode (PCO2 (in vivo)- PCO2 (syringe) = 2.4, 4.9, 7.5, and 10.0 mmHg at in vivo PCO2's of 20, 40, 60, and 80 mmHg). This study indicates that the technique used for sampling CSF is crucial to the expected accuracy of the results and that the number of transfers of CSF during the sampling and measurement procedures should be minimized in order to obtain reliable results.

Animals↗
PubMed1975

Letter: Wien effect.

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Acid-Base Equilibrium↗
PubMed1975

Gas-blood PCO2 gradients during avian gas exchange.

The avian respiratory system is a crosscurrent gas exchange system. One of the aspects of this type of gas exchange system is that end-expired PCO2 is greater than arterial PCO2, the highest possible value being equal to mixed venous PCO2. We made steady-state measurements of arterial, mixed venous, and end-expired PCO2 in anesthetized, spontaneously breathing chickens during inhalation of room air or 4-8% CO2. We found end-expired PCO2 to be higher than both arterial and mixed venous PCO2, the sign of the differences being such as to oppose passive diffusion. The observation that end-expired PCO2 was higher than arterial PCO2 can be explained on the basis of crosscurrent gas exchange. However, the observation that end-expired PCO2 exceeded mixed venous PCO2 must be accounted for by some other mechanism. The positive end-expired to mixed venous PCO2 gradients can be explained if it is postulated that the charged membrane mechanism suggested by Gurtner et al. (Respiration Physiol. 7: 173-187, 1969) is present in the avian lung.

Acetazolamide↗