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Biomedical subjects

S Hemmings

Publications and source records attributed to S Hemmings.

6 recordsLinked to original sources
PubMed1996

Characteristics of a blood pump combining the centrifugal and axial pumping principles: the spiral pump.

Two well-known centrifugal and axial pumping principles are used simultaneously in a new blood pump design. Inside the pump housing is a spiral impeller, a conically shaped structure with threads on the surface. The worm gears provide an axial motion of the blood column through the threads of the central cone. The rotational motion of the conical shape generates the centrifugal pumping effect and improves the efficiency of the pump without increasing hemolysis. The hydrodynamic performance of the pump was examined with a 40% glycerin-water solution at several rotation speeds. The gap between the housing and the top of the thread is a very important factor: when the gap increases, the hydrodynamic performance decreases. To determine the optimum gap, several in vitro hemolysis tests were performed with different gaps using bovine blood in a closed circuit loop under two conditions. The first simulated condition was a left ventricular assist device (LVAD) with a flow rate of 5 L/min against a pressure head of 100 mm Hg, and the second was a cardiopulmonary bypass (CPB) simulation with a flow rate of 5 L/min against 350 mm Hg of pressure. The best hemolysis results were seen at a gap of 1.5 mm with the normalized index of hemolysis (NIH) of 0.0063 +/- 0.0020 g/100 L and 0.0251 +/- 0.0124 g/100 L (mean +/- SD; n = 4) for LVAD and CPB conditions, respectively.

Animals↗
PubMed1994

Hypothyroidism protects the brain during transient forebrain ischemia in gerbils.

The mechanisms by which brain cells die after brief episodes of cerebral ischemia are not fully understood. In certain brain regions this damage may not be apparent for days. Hypothyroidism is known to decrease cerebral metabolism. We postulated that this slowing in cerebral metabolism may be neuroprotective after transient cerebral ischemia. To test this hypothesis, a total of 10 gerbils had thyroidectomies performed 2 weeks prior to ischemia. Six gerbils served as euthyroid controls. All animals were exposed to 5 min of transient ischemia and sacrificed 7 days after the insult. Silver degeneration staining was used for histological evaluation. Hippocampal damage [subiculum (P < 0.001), CA1 (P = 0. < .001), CA3 (P < 0.05), and CA4 (P < 0.001)] was significantly less in the hypothyroid animals. There was also significantly less damage in the cerebral cortex (P < 0.05) and thalamus (P < 0.05) in the hypothyroid animals. The exact mechanism of this protection is not fully understood but could be secondary to a decrease in the metabolic activity, or a reduced generation of free radicals (as is seen with protection from ischemia in kidney and liver under hypothyroid conditions). Further studies are required in order to gain a better understanding of the protective effects of hypothyroidism on cerebral ischemia.

Animals↗
PubMed1994

Decreased glutamate release during hypothyroidism may contribute to protection in cerebral ischemia.

Hypothyroidism protects the brain from the effects of transient forebrain ischemia in gerbils. The mechanism for this protection is not fully understood. In this study we looked at the release of glutamate during ischemia in gerbils exposed to surgical hypothyroidism (n = 7), chemical hypothyroidism (n = 8), and surgical hypothyroidism thyroxine-treated (n = 3) and compared them to control euthyroid animals (n = 8). The duration of ischemia was 10 min. Glutamate release was measured with in vivo microdialysis. Microdialysis analysis began 2 h after the placement of the probes (to stabilize the baseline) and collections were obtained in 10-min samples. During ischemia, there was an increase in the release of glutamate that returned to the baseline within 20 min following the insult. In animals made hypothyroid surgically and chemically, the extent of glutamate release was significantly lower than that in the controls. The release of glutamate in the surgically hypothyroid thyroxine-treated animals was similar to that in controls. The attenuated glutamate release could be a mechanism of protection during ischemia in hypothyroid gerbils.

Animals↗
PubMed1993

Tendency toward controlling behavior in adult children of problem drinkers: an experimental study.

Several clinicians have remarked on an obsessive need to control among adult children of alcoholics. In an experimental test of this hypothesis 30 adult children of problem drinkers and 31 control subjects performed a computer-simulated coin-tossing task. On half of the trials the outcome of the coin toss was open to control; the outcome was random on the remainder of the trials. The children of problem drinkers and the control group did not differ in their success on the task, but in comparison to control subjects the children of problem drinkers tended to perceive a greater difference between controllable and random trials in the coin-tossing task's openness to control. Of the two groups, the control subjects proved to be more realistic in their assessment of the control they had exercised during the task. These findings are discussed in terms of the theme of control in the lives of the adult children of alcoholics.

Adult↗