PubMed Health⌕ Search

Biomedical subjects

T McKean

Publications and source records attributed to T McKean.

12 recordsLinked to original sources
PubMed1998

Ischemia and ischemic preconditioning in the buffer-perfused pigeon heart.

Isolated pigeon hearts were perfused with Krebs-Henseleit bicarbonate buffer with 1.25 mM Ca++ at a pressure of 60 cm H2O and paced at 210 beats per min. After an equilibration perfusion of 30 min, hearts were subjected to 10 min global ischemia and then reperfused for 30 min. Left ventricular +dP/dtmax, systolic, and end diastolic pressures differed significantly from baseline values during reperfusion as did the release of lactate dehydrogenase (LDH). When the hearts were preconditioned by interruption of flow for two 2.5-min intervals, followed by 10 min of ischemia and then reperfusion, the short periods of ischemia, followed by reperfusion, protected the hearts against the longer bout of ischemia as evidenced by significant differences between the left ventricular (LV) pressure, +dP/dtmax, LV end diastolic pressure and LDH values obtained from the hearts of control vs. preconditioned hearts. Substitution of 1 microM adenosine for the preconditioning ischemia also resulted in the preconditioning response. Ischemic preconditioning (IP) was not blocked by addition of 100 microM 8-(-p-sulfophenyl) theophylline, an adenosine receptor antagonist. Therefore, isolated, perfused bird hearts can be preconditioned, and the mechanism may involve adenosine receptors, although their activation is not necessary for i.p. to occur. Factors in addition to adenosine are likely involved.

Animals↗
PubMed1997

Hypoxia and ischaemia in buffer-perfused toad hearts.

Previous studies on the effects of ischaemia or hypoxia in ectothermic vertebrate hearts have generally used preparations that were not performing at physiological levels of pressure and flow. The conclusions that ischaemia or hypoxia are not stressful to these organisms were examined in another species, Bufo marinus, in which a buffer-perfused heart was performing physiological levels of work. The in situ preparation demonstrated the Frank-Starling relationship and mechanical characteristics similar to the hearts of intact animals. The hearts recovered from 60 min of ischaemia and reperfusion with no reduction in pressure, flow or heart rate parameters. Hearts exposed to 30 min of hypoxia at physiological filling and diastolic afterload pressures ceased generating a continuous cardiac output during the hypoxia. In most cases, there was a gradual reduction of cardiac output to zero, but in 27% of the hearts studied, intermittent beating was observed. During reoxygenation, the hearts recovered 50-90% of their prehypoxic function and were damaged. Hearts exposed to hypoxia with reduced filling and diastolic afterload continued to develop a cardiac output throughout the hypoxia and demonstrated an overshoot phenomena with the onset of reoxygenation. If demand is in the normal range at the onset of hypoxia, the hearts intrinsically reduce demand either by reducing pressure development or by conversion to intermittent beating. Toad hearts appear not to be damaged by ischaemia, a condition in which demand is low.

Animals↗
PubMed1996

Comparison of the responses to hypoxia, ischaemia and ischaemic preconditioning in wild marmot and laboratory rabbit hearts.

Marmots (Marmota flaviventris) are burrowing mammals that may be subjected to low levels of oxygen and high levels of carbon dioxide in their underground environment. Since marmots successfully deal with this physiological challenge, we hypothesized that the isolated perfused marmot heart would be damaged less and recover better from a bout of induced hypoxia or ischaemia than would the heart of a comparison animal, the New Zealand laboratory rabbit (Oryctolagus cuniculus). Isolated marmot and rabbit hearts were made hypoxic by a 30 min perfusion with an oxygen-deficient buffer. The hearts were then perfused with an oxygen-replete buffer and measurements of heart rate, left ventricular pressure and lactate dehydrogenase (LDH) release (an indicator of cell damage) were made over 5 or 10 min intervals for 30 min of hypoxia and 30 min of recovery. There were no species differences in the responses, except that the heart rate in marmots was about 50% of the rate in rabbits during the hypoxia part of the experiment. There was no evidence that the marmot hearts were damaged less or recovered better from hypoxia and reoxgenation than the rabbit hearts. Marmot and rabbit hearts were also subjected to 30 min of total ischaemia; measurements of heart rate, left ventricular pressure and LDH release were obtained during 30 min of reperfusion and compared with the pre-ischaemia values for these variables. There were no significant species differences. When the 30 min ischaemic period was preceded by a 5 min period of ischaemia and a 10 min reperfusion period (preconditioning), the rabbit hearts were protected by this brief ischaemic insult and recovered better than the hearts that had not been subjected to the preconditioning ischaemia. This was not true in the marmot hearts, however, as the preconditioning ischaemia did not promote a greater recovery over that in its absence. When preconditioned marmots hearts were compared with preconditioned rabbit hearts, there were no statistical differences in the responses. The hypothesis that marmot hearts would be damaged less and recover better from hypoxia and ischaemia was not supported by the experimental data.

Adaptation, Physiological↗
PubMed1982

Cardiovascular adjustments to laboratory diving in beavers and nutria.

Beavers (Castor canadensis) and nutria (Myocastor coypus) were anesthetized with halothane and catheters placed in the left ventricle, aorta and pulmonary artery, right ventricle or right atrium. The animals were strapped to a board and following recovery from anesthesia the following measurements were taken: regional distribution of blood flow, cardiac output, O2 consumption, arterial and venous blood gases, and pH. The animal was then immersed in 15-20 degrees C water for up to 2.75 min (nutria) or 4 min (beaver) and the measurements repeated. Heart rate and cardiac output decreased by 80 and 75%, respectively. Arterial and venous oxygen partial pressure and content fell as did pH whereas CO2 pressures rose during diving. Oxygen consumption at rest was 124 and 102% of that predicted on the basis of body mass for the beaver and nutria, respectively. Rate of decline of O2 stores during diving decreased by 93% in beavers and 89% in nutria compared to the predive value. Regional blood flow decreased to all organs except the adrenals, heart, and lungs. Blood flow to the brain increased during diving.

Adaptation, Physiological↗
PubMed1982

Comparison of the response of muskrat, rabbit, and guinea pig heart muscle to hypoxia.

Papillary muscles were removed from anesthetized muskrats and rabbits and mounted in a muscle chamber maintained at 29 degrees C. Muscles were stimulated at a rate of 12/min and subjected to 30 min of hypoxia followed by 30 min of reoxygenation. Peak tension in muskrats declined less than peak tension in rabbits during oxygen deprivation. During reoxygenation, peak tension in muskrats rapidly returned to control levels and then exceeded control, whereas peak tension in rabbits never recovered. Time to peak tension was largely unaffected in muskrats during hypoxia and decreased in rabbits. During reoxygenation, time to peak tension increased in muskrats and returned to control in rabbits. Hearts from muskrats and guinea pigs were removed under ether anesthesia and perfused retrograde with a physiological saline solution. Developed tension, heart rate, coronary blood flow, and lactate dehydrogenase (LDH) output were monitored. During 30 min of hypoxia, muskrat hearts developed a profound bradycardia compared to guinea pigs. Coronary flow increased in both species but less so in muskrats. Guinea pig hearts developed contracture whereas muskrat hearts relaxed. During reoxygenation heart rate and coronary blood flow returned toward normal but cells released large amounts of LDH, indicating cell damage. It is concluded that the isolated heart of the muskrat, a diving mammal, is better able to deal with hypoxia than the heart of the nondividing guinea pig and rabbit.

Animals↗
PubMed1977

The carotid and orbital retia of the pronghorn, deer and elk.

Selective cooling of the brain during heat stress has been shown by others to be a method of temperature regulation for mammals having carotid retia. This study describes the macroscopic anatomy of the cranial circulation of elk, deer and pronghorn as it might pertain to the functioning of carotid retia and orbital retia as heat exchangers. Emphasis has been placed on describing the source of venous blood bathing these retia, for blood flow from these sources to the ophthalmic plexus and cavernous sinus will establish a temperature difference between arterial and venous blood, and influence the magnitude of this gradient. The pronghorn possesses a carotid rete with greater density and smaller calibre vessels overall and a more highly vascular orbital rete compared to the elk and the deer. These anatomical differences may indicate differences in efficiency of heat exchange in the retia. It is suggested that the orbital rete is anatomically in a position to moderate extremes of temperature by cooling arterial blood flowing to neural tissue of the eye and olfactory bulbs.

Animals↗
PubMed1977

Selected oxygen transport parameters in captive elk.

Five captive elk (cervus canadensis) were immobilized with a mixture of etorphine HC1-acepromazine maleate, and measurements were taken of selected oxygen transport paraments. Heart mass/body mass, hematocrit, hemoglobin, blood volume, mean corpuscular volume and airway resistance were measured and the values compared to other ungulates. It was concluded that the O2 transport system of elk is not as well developed as that in pronghorn but is superior to that found in the goat or ox.

Acepromazine↗
PubMed1977

Oxygen storage in beavers.

Ten wild beavers were anesthetized with pentobarbital and total lung capacity (60.5 +/- 4.8 ml/kg), hemoglobin (12.4 +/- 1.5 g/100 ml), blood volume (6.5 +/- 0.8% body mass), and myoglobin (1.2 +/- 0.3 g/100 mg) were determined. These measured values were used to calculate total oxygen storage capacity. Even though the beaver is a good diver (15-min submersion time), its oxygen stores are not large and are about one-third the stores of a good marine diver, the harbor seal.

Animals↗