Search Results - (Author, Cooperation:A. A. Fawcett)

2015-11-28

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1440-1681

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

1. Although heat stroke is a frequent cause of death in both humans and animals as a result of climatic or exercise-imposed stress, underlying mechanisms are understood poorly. In order to develop more effective strategies for prevention and treatment of this cause of death and suffering, controlled experiments were conducted on a small number of sheep to examine cardiovascular involvement in the thermoregulatory failure of heat stroke.2. Sheep were studied in a hot environment at rest and then during exercise until collapse.3. With exercise, mean arterial pressure (MAP) increased slightly, cardiac output (CO) increased markedly and total peripheral resistance (TPR) decreased slightly. As collapse was imminent, MAP increased but CO and TPR did not change significantly. On collapse, MAP and TPR increased markedly and CO decreased markedly.4. Radioactive microsphere measurements demonstrated during exercise a redistribution of blood flow (BF) away from abdominal viscera and torso skin, to muscles involved in exercise, respiratory muscles, myocardium, fat, limb skin and nasobuccal tissues. With progressively increasing heat stress and exercise, BF increased in exercise muscles and decreased in limb skin and fat. As collapse was imminent, there were sharp increases in BF in exercise muscles, brain and spinal cord. On collapse, BF decreased markedly in exercise and respiratory muscles and fat.5. It is concluded that collapse and ultimately heat stroke are not due primarily to cardiovascular ‘failure’ but, rather, to consequences of high body temperatures resulting from thermoregulatory failure attributable to demands for blood pressure regulation dominating requirements for body temperature regulation.

Electronic Resource

1440-1681

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

1. A ‘tissue perfusion monitor’ (TPM) to non-invasively provide an index of skin blood flow (SkBF) has been developed; it employs photoelectric plethysmographic principles to measure changes in the nett flux of red blood cells in superficial microvasculature.2. The ‘tissue perfusion index’ (TPI) varies in proportion to SkBF, provided local haemoglobin concentration does not change significantly. TPI of humans and experimental animals has been shown to indicate reliably, well established phenomena such as decreased SkBF in response to mechanical restriction, cold or Valsalva's manoeuvre, or increased SkBF in response to heat, acetylcholine, sodium nitrite or local nerve blockade.3. SkBF in sheep was varied between 1 and 156 mL/100g per min as measured with radioactive microspheres. Simultaneous measurements were made using the TPM and four laser-Doppler instruments. The TPI yielded a correlation coefficient of 0.938, and when data were expressed as percentage change, the regression line did not differ significantly from the line of identity and the root-mean-square-error was 6.2%. Data for the laser-Doppler indices of SkBF were, respectively, 0.549–0.786, highly significant deviations in slopes, and 13.6–16.7%.4. Thus, the TPI is a reliable index of changes in SkBF. Compared with some other available instruments, the TPM is more precise; it is also less sensitive to movement artefact, can be completely portable by battery operation, probes can be multiplexed to a single meter and it is likely to be much less expensive than current lasers.5. Applications include, for example, experimental investigations of SkBF in man and animals, clinical uses such as evaluation of the efficacy of regional nerve blockade or of circulatory restitution after reconstructive surgery, and clinical tests of neuro vascular function.

Electronic Resource

1420-9071

Springer Online Journal Archives 1860-2000

Biology

Medicine

Summary Blood flow has been measured in bovine skin following the injection of tick antigens and a number of pharmacological mediators; including histamine, prostaglandins and slow reacting substance of anaphylaxis. The greates increase in blood flow (20 times normal) was recorded with tick antigens and with prostaglandin F2. This mediator may therefore influence blood flow during immune reactions to ticks and during the rapid ingestion of blood by the ticks.

Electronic Resource

1432-2013

Thermoregulation ; Microspheres ; Arteriovenous anastomoses ; Adrenoceptor agonists/antagonists ; Blood flow partition ; Skin ; Bone

Springer Online Journal Archives 1860-2000

Medicine

Abstract The possible role of adrenergic mechanisms in thermoregulatory changes in the partition of femoral blood flow between nutrient (capillary) and non-nutrient (arteriovenous anastomoses, AVA) circuits in the hind limb of conscious sheep has been investigated employing radioactive microsphere and electromagnetic blood flow measurement techniques. Constriction of AVAs, normally induced by spinal cooling, could be inhibited by phentolamine, whereas dilatation of AVAs, noramally induced by spinal heating, could be inhibited by noradrenaline or methoxamine. AVA constriction could be induced by noradrenaline or methoxamine, or dialation by phentolamine. Isoprenaline had a small dilator and propranolol a small constrictor effect on AVAs. It is concluded that adrenergic pathways involving predominantly α-receptors play a role in thermoregulatory changes in skin blood flow (through AVAs) elicited by manipulation of CNS temperature; under these conditions, β-receptors do not play any role, although manipulation of their activity will influence AVAs under non-thermoregulatory conditions. Capillary blood flows in skin, bone and fat were sensitive, at different ambient temperatures and to varying degrees, to some α-and β-adrenergic agents.

Electronic Resource

1432-2013

Skin blood flow ; Arteriovenous anastomoses ; Thermoregulation ; Heat stress ; Cold stress ; Microspheres

Springer Online Journal Archives 1860-2000

Medicine

Abstract Using radioactive microsphere and electromagnetic techniques, hindleg vascular responses were studied in 38 conscious, chronically prepared sheep subjected to either exposure to a warm environment, and/or local warming of the hypothalamus, spinal cord, forelegs or hindlegs. The total proportion of cardiac output passing through AVA's was increased by all treatments. AVA flow in hindleg skin was increased but capillary flow was unchanged by warming the hypothalamus, spinal cord or forelegs. AVA flow was unchanged but capillary flow was increased by warming the ambient air or the hindlegs alone. Equivalent cooling treatments resulted in AVA and capillary flow changes converse to warming. It is concluded that, in sheep, blood flow through cutaneous AVA's is controlled by specific thermoregulatory reflexes, whereas capillary flow is the target of local temperature effects. A significant role for the direction of the thermal gradient across the skin is implicated.

Electronic Resource

1432-2013

Blood flow ; Cardiac output distribution ; Cold stress ; Microspheres ; Thermoregulation ; Sheep circulation

Springer Online Journal Archives 1860-2000

Medicine

Summary Conscious adult Merino sheep were studied in a thermoneutral environment and then during cold exposure. Microspheres labelled with141Ce,51Cr,85Sr, and46Sc were used to measure blood flow ( $$\dot Q$$ ) in most tissues of the body. (Microspheres labelled with125I were found to be unsatisfactory.) Cold exposure which caused a marked decrease in skin surface temperature and mild, continuous shivering but no change in deep body temperature, was associated with mean increases in oxygen consumption, heart rate, and cardiac output (C.O.) of 100%, 62%, and 48%, respectively; blood pressure and total peripheral resistance were unchanged. There was approximately a 6-fold increase in $$\dot Q$$ in perirenal white adipose tissue, and a 3- to 4-fold increase in muscles of the upper foreleg and hindleg, and the intercostals; myocardial $$\dot Q$$ also increased significantly. There was a marked decrease in $$\dot Q$$ in skin of the legs and ears, in the maxillo turbinals and in the nasal mucosa, and a decrease in the total proportion of C.O. passing through arteriovenous anastomoses. Thus, not only did C.O. increase, but there was a redistribution appropriate to meet the challenge with which the animal was confronted.

Electronic Resource

1432-2013

Microspheres ; Blood Flow

Springer Online Journal Archives 1860-2000

Medicine

Summary “NEN-TRAC” brand of radioactive microspheres, 15 μm in diameter, have recently become available and therefore organ blood flow (Q) values obtained using these have been compared with values simultaneously obtained with the well-established “TRACER” brand of microspheres. For all major tissues of the body of two conscious sheep, there was excellent agreement between Q values obtained using NEN-TRAC Ce-141 and TRACER Sr-85 in one sheep, and between Q values obtained using NEN-TRAC Ce-141 and Sn-113 and TRACER Cr-51, Sr-85 and Nb-95 in a second sheep. It is concluded that NEN-TRAC microspheres satisfy the major validation tests to which TRACER microspheres have been previously subjected, and therefore it is valid to proceed with use of the new product.

Electronic Resource

1432-2013

Skin blood flow ; Arteriovenous anastomoses ; Microspheres

Springer Online Journal Archives 1860-2000

Medicine

Abstract Using radioactive plastic microspheres in conscious sheep, cardiac output is measured by dose injection into a vein, and sampling from the pulmonary artery. Partition of organ blood flow between capillaries and arteriovenous anastomoses is derived from cardiac output and the radioactivity in pulmonary artery blood sampled after dose injection into the artery supplying the organ. Validation tests are presented. The hindlimb is shown to be a suitable model for studying thermal influences on skin blood flow. In contrast to other techniques or previous applications of microspheres: (a) conscious, chronically prepared animals are used, (b) there is no need to kill the animal to obtain results, (c) only small doses are necessary, (d) the one nuclide label can be used repeatedly, and (e) there is no need for precisely matched doses.

Electronic Resource

1432-2013

Blood flow ; Cardiac output distribution ; Hypothalamic control of blood flow ; Thermoregulation ; Microspheres

Springer Online Journal Archives 1860-2000

Medicine

Summary Radioactive microspheres were used to assess the influence of hypothalamic temperature on tissue blood flow and the regional distribution of cardiac output in conscious sheep chronically prepared with hypothalamic thermodes. Hypothalamic heating elicited panting in 6 animals, and in these, blood flow rate increased in respiratory muscles and decreased in the thyroids, kidneys, spleen and gut; cardiac output did not change, but was redistributed in a pattern similar to that seen during spinal cord heating, which differs from that which occurs during exposure to a warm environment. Four other animals did not pant in response to hypothalamic heating, but showed small but definite increases in capillary blood flow in skin of extremities. Reasons for the two different types of response to heating are discussed. The failure to detect increases in microsphere-measured extremity skin blood flow in the first group and only small changes in the second group above, despite the increased skin temperature always seen with hypothalamic heating, is attributed to specific influences of CNS stimulation on arteriovenous anastomoses. In 6 animals, hypothalamic cooling elicited visible shivering associated with increased oxygen consumption; blood flow rate decreased in skin and increased in respiratory and non-respiratory muscles, fat and the myocardium; cardiac output showed an increase and a redistribution similar to that which occurs during exposure to a cold environment. Arterial blood pressure was steady, but there were changes in regional vascular resistance. Therefore, and in view of other studies, the blood flow responses observed are attributed to regional differentiation of sympathetic activity.

Electronic Resource

1432-2013

Prostaglandins ; Thermoregulation ; Hypothalamic Neurotransmitters ; Brain Prostaglandins

Springer Online Journal Archives 1860-2000

Medicine

Summary ProstaglandinsE 1,E 2,F 1α andF 2α injected into a lateral cerebral ventricle of the conscious sheep during exposure to various environmental conditions caused deep body temperature to rise. In a cool environment, faint shivering which was normally present became intensified and peripheral vasoconstriction became maximal. In a thermoneutral environment, shivering and vasoconstriction were elicited. In a warm environment, panting was markedly reduced and there was sometimes slight vasoconstriction. ProstaglandinsE 1 andE 2 were most effective,F 2α was slightly less, andF 1α considerably less effective. It was concluded that prostaglandins may be involved in transmission along brain neuronal pathways involved in the stimulation of heat production and increased peripheral vasomotor tone, and in the inhibition of heat loss mechanisms.

Electronic Resource

1432-2013

Arteriovenous Anastomoses ; Cutaneous Blood Flow ; Thermoregulation ; Microspheres

Springer Online Journal Archives 1860-2000

Medicine

Summary Radioactive microsphere measurements of blood flow in the hindlimb of the conscious sheep indicate that CNS temperatures have a potent influence on blood flow through cutaneous AVA's but not capillaries, and vice versa for superficial body temperatures.

Electronic Resource

1432-2013

Blood flow ; Microspheres ; Skin ; Thermoregulation

Springer Online Journal Archives 1860-2000

Medicine

Abstract In conscious sheep, total femoral blood flow and flow through arteriovenous anastomoses (AVAs) and capillaries (CAP) in skin of the hindleg were measured employing electromagnetic and radioactive microsphere techniques. Core temperature (T c) was manipulated using intravascular heat exchangers and hindleg skin temperature (T sk) was manipulated by immersion in temperature controlled water. WithT c set 1°C above normal, AVA flow was highest at the lowestT sk tested (34°C); AVAs progressively constricted asT sk was increased from 34 to 40–41°C, then dilated again asT sk reached the highest levels tested (42–44°C). Skin CAP flow was not altered byT sk of 34 to 42°C but was increased at aT sk of 44°C. Therefore total skin blood flow followed essentially the same pattern as AVA flow; total femoral flow also followed this pattern. WhenT c was set 0.5°C below normal, AVA flow was low at all levels ofT sk. It is concluded thatT c plays a dominant role in control of skin blood flow, however, onceT c is at a level requiring increased heat loss,T sk exerts an extremely potent influence on the nature and magnitude of changes in skin blood flow. The pattern of flow changes appears to reflect principally a negative feedback mechanism aimed at maintainingT sk at approximately 40°C; this may contrast with mechanisms associated with sweating and/or active vasodilation in other species.

Electronic Resource