Normothermic Levels Research Articles

Comparative thermoregulation of four breeds of fowls ( Callus domesticus), exposed to a gradual increase of ambient temperatures

1. I. Fowls of four breeds, Sinai, Leghorn, Sinai × Leghorn and Leghorn × Sinai, were gradually exposed to increasing ambient temperatures. 2. 2. Body temperature ( T b ) increased at the rate of 0.121 C for every 1 C increase of ambient temperature ( T a ) in the range of 25–45 C T a . 3. 3. Heart rate (HR) was regulated at a stable, lower than normothermic level. 4. 4. Respiration rates (ƒ) increased 17 fold over the normal rates, contributing to a 6.64 fold increase in evaporative water loss (EWL), and this dissipated 170% of the metabolic heat production at 45 C T a . 5. 5. The fowls maintained a stable oxygen consumption up to 42 C and at 45 C it increased by only 15% over the normothermic level. 6. 6. All breeds efficiently regulated their body temperature below ambient temperature at 45 C. However, the desert Sinai breed was characterized by 10% lower than predicted SMR and by a shallow high frequency panting compared to the Leghorn.

Blood coagulation studies in normothermic, hibernating, and aroused Spermophilus franklini

The blood coagulation system of Spermophilus franklini was evaluated from normothermic, hibernating, and aroused individuals. Clotting time, thrombin time, prothrombin time, and partial thromboplastin time were measured to test the state of coagulability. The concentrations of the formed elements and the titers of five plasma factors were also determined. During hibernation, clotting time significantly increased above normothermic levels. Arousal resulted in clotting time returning toward normothermic values. Both thrombin time and partial thromboplastin time significantly increased above normothermic levels in blood from hibernators. The two tests exhibited normothermic levels in arousing individuals. Prothrombin time did not increase in blood from hibernating animals. Erythrocytes, leukocytes, and platelets were found to be significantly reduced in number in hibernating animals. Leukocyte and platelet numbers returned to normothermic levels during arousal. Factor VII, Factor X, prothrombin, and heparin concentrations did not significantly change from normothermic levels in hibernating individuals. Factor V, however, displayed a 45% decrease in concentration in hibernating individuals, with arousal resulting in near-normothermic levels. Aroused individuals displayed a doubling of prothrombin concentrations relative to normothermic individuals.

Myocardial norepinephrine turnover during induced hypothermia and rewarming.

Norepinephrine (NE) turnover in myocardial tissue was measured in male golden hamsters (Mesocricetus auratus) during 1) continuous hypothermia, 2) rewarming from hypothermia initiated by exposure to 22 degrees C ambient, and 3) normothermic control state. Hypothermia was induced by exposure to 80% He-20% O2 atmosphere at 0 to -10 degrees C. At sequential periods after tritiated norepinephrine ([3H]NE) infusion, hamsters were killed by cervical transection and hearts were removed and analyzed for NE and [3H]NE content. Rate constants, turnover times, and turnover rates were determined from regression analysis of [3H]NE/micrograms NE tissue decay. Myocardial concentrations of NE were constant during NE-turnover measurements in each group. However, myocardial NE levels were reduced by 37% in both continuous hypothermia and rewarming from hypothermia compared with normothermic controls. NE turnover was highest during rewarming from hypothermia (0.34 micrograms.g-1.h-1), but no decay in myocardial [3H]NE was detectable during continuous hypothermia. Control animals had turnover values of 0.15 micrograms.g-1.h-1. Turnover data indicate severe depression in myocardial sympathetic nerve activity during hypothermia but a significant increase above normothermic control levels during rewarming from hypothermia.

The effect of blood oxygen content and the no-reflow phenomenon on the subendocardial ultrastructural reversibility following anoxic arrest using hemodilution variables in the experimental model.

Hemodilution is an accepted modality for the conduct of cardiopulmonary bypass. The degree of hemodilution clinically employed has been in the range of 20 per cent of the initial hematocrit levels. This study was designed to evaluate the effects of hemoglobin levels and oxygen content on the reversibility of the damaged or altered ultrastructure of the endocardial layer of the ventricle and the possible role of the no-reflow phenomenon. Two series of mongrel dogs were subjected to cardiopulmonary bypass at normothermic levels and a standard period of ischemic arrest. One series was with hemoglobin levels between 5 and 10 grams (mean 7.25 grams) designated as moderate hemodilution (MH). The second series was of hemodilution with less than 5 grams of hemoglobin (mean 4.8 grams) designated as severe hemodilution (SH). The ultrastructural alteration gradient (UAG) between the epicardium and endocardium was studied with its relationship to reversibility of myocardial function and animal survival. The study demonstrated a definitive relationship between oxygen content and the reversibility of myocardial damage under normothermic conditions and anoxic arrest. The poor survival results in the SH group; two of 12 are attributed to the low oxygen availability possibly triggering the no-reflow phenomenon which prevents reversibility of the myocardial ultrastructural damage and ultimately the functional integrity of the ventricle.

Effects of artificial rewarming upon hypothermia-induced retrograde amnesia

Three experiments were conducted to examine the relationship between recovery rate from deep body cooling and later memory loss. In each of these three investigations, a passive avoidance trial was followed immediately by hypothermia and recovery was manipulated by exposing rats to warm water. In Experiment I, rats returned to near normothermic levels by immersion in 36.4°C water for 20 min following the training-hypothermia treatment showed good retention, while rats allowed to recover under room temperature conditions showed the typical RA. Results from Experiment II indicated that extent of amnesia was inversely related to the duration of immersion in warm water following training-hypothermia treatment. In Experiment III. the prevention of RA by rewarming was shown to follow a time-dependent course. Initiation of rewarming 0, 5, or 10 min after hypothermia treatment eliminated RA, but the same rewarming given 30 min after treatment had no protective effect. The implications of these findings for consolidation and retrieval models of RA were considered.

A gradient calorimeter study of normothermic and hibernating eastern chipmunks, Tamias striatus

Abstract o 1. The construction of a gradient calorimeter composed of flux plates is described. 2. The heat loss of normothermic Tamias striatus over the temperature range of 4–14°C can be described by the equation cal/g min = 0·35–0·014Ta. 3. The heat loss of chipmunks hibernating at 9 and 11°C was approx 2·12% of normothermic levels.

The "stone heart" syndrome.

Two types of myocardial failure have been encountered in patients undergoing open-heart surgery with ischemic cardiac arrest and nonblood prime while maintaining the patient at normothermic levels: [ 1) in which the left ventricle is flaccid and nonresponsive to inotropic drugs and (2) a tetanic contracture or myocardial rigidity which we have called “stone heart.” From July, 1966, through June, 1971,4,732 patients underwent total cardiopulmonary bypass with the use of this technique at the Texas Heart Institute, and 51 died in the operating room from acute myocardial insufficiency. Among these, 13 patients developed stone heart during or immediately after bypass. Exhaustive attempts to resuscitate these hearts by using pharmacological and physical means were uniformly unsuccessful. Before operation all patients had evidence of advanced left ventricular hypertrophy and myocardial conduction disturbance. Patients with concentric hypertrophy and high pressure gradients across a stenotic aortic valve were most prone to develop this complication. Microscopic study of the myocardium revealed only hypertrophy and usually diffuse fibrosis. Since September, 1971, all patients having left ventricular hypertrophy caused by aortic and/or mitral valve disease have been cooled to 30” C. before the ascending aorta was cross-clamped. lschemic arrest was used, and while the aorta was cross-clamped, body temperature was raised to 34” C. No instance of stone heart has occurred when hypothermia was utilized in a consecutive series of 266 patients undergoing aortic valve replacement in whom an incidence of 0,8 percent would have been expected if normothermic anoxic arrest had been used. We believe that the mechanism causing this myocardial complication is prevented by the hypothermic technique.

Unit activity during focal cortical hypothermia in the normal cortex

Changes in neuronal firing were measured by intracellular and extracellular microelectrode recording during focal cooling of cat sensory motor cortex using a Peltier cooling device. Analysis was confined to neurons followed through cooling and rewarming back to normothermic levels. Rapidly cooling the cortex to temperature levels (19–21 C) were no unit activity could be recorded was associated with a steady decrease in firing frequency until silence, and a steady widening and lowering of amplitude of the action potential. Rapidly cooling the cortex to, and maintaining it at moderate temperature levels (27–29 C) was associated after 8–10 min with a brief period of high frequency repetitive firing (seizure) followed by silence until rewarming began. Burst activity was sometimes seen during rewarming. These findings were interpreted as suggesting that cooling to moderate temperature levels impeded the pump mechanisms exchanging Na and K across the neuron membrane. Further cooling to lower temperatures blocked the passive exchange of Na and K across membrane pores. These differential effects of cooling explain some of the variability in reports in the literature on the association between hypothermia and seizures.

Spinal cord hypothermia by localized perfusion cooling.

A NEW technique has been developed which will rapidly and selectively cool the mammalian spinal cord while the temperature of the body core remains near normothermic levels. This becomes specially relevant in the light of the utilization of profound hypothermic levels1 and isolated cerebral perfusion techniques in neurovascular surgery2,3. With this method both acute and chronic preparations can be used to investigate the neurophysiological and cardiovascular events associated with spinal cord cooling as well as to evaluate the efficacy of hypothermia in clinical situations associated with spinal cord trauma and disease.