Robert S. Pozos

Hypothermia outcome score: development and implications

Multiple rewarming methods have been recommended for the treatment of hypothermia in the ED. Because the hypothermic patient population is heterogenous, a method for stratifying mortality risk when comparing therapies is desired. We used univariable and multivariable statistical analyses to identify variables which discriminated between patient death or survival in the 24 h after arrival in the ED. Prehospital cardiac arrest, a low or absent presenting BP, elevated BUN, and the need for either tracheal intubation or NG tube placement in the ED were found to be significant predictors of patient demise in a large database (n = 428). The likelihood ratio was used to develop and validate an empiric hypothermia outcome score that can be used in future hypothermia treatment studies to account for differences of patient presentation.

Electrophysiologic effects of acute ethanol exposure. II. Alterations in the calcium component of action potentials from sensory neurons in dissociated culture

Dissociated dorsal root ganglion neurons were exposed to 0.05-0.50 g% ethanol. The recording medium was altered in order to produce an action potential with an increased duration which was Ca2+-dependent. Ethanol was observed to decrease the duration of sensory neuron action potentials indicating a decreased inward Ca2+ current. The ethanol induced decrease in duration was reversible and dose-dependent. No alterations in resting membrane potential, spike amplitude, or maximum rate of rise were observed during ethanol exposure. An increased threshold was also observed with application of ethanol. These findings are discussed in regard to the possible effects of ethanol on Ca2+ movement at the presynaptic terminal.

Electrophysiologic effects of acute ethanol exposure. I. Alterations in the action potentials of dorsal root ganglia neurons in dissociated culture

Dissociated dorsal root ganglion neurons from embryonic rats were exposed to 0.05, 0.15 and 0.30 g% ethanol for 1 h. Action potentials were recorded and statistically compared for differences from the control values. Exposure to ethanol produced no significant alterations in the resting membrane potential, spike amplitude, or maximum rate of rise in any of the experimental conditions. Significant differences were noted in parameters associated with the repolarization phase including decreases in the maximum rate of fall and one-half time to convergence and increases in the full width of half maximum and full width of base parameters. These alterations were reversed within 30 min after ethanol removal. In order to determine the specific ionic conductances affected by ethanol, action potentials were recorded from neurons exposed to specific Na+, Ca2+, and K+ current blockers. Analysis of the data indicates that K+ conductance is decreased as a result of a decreased Ca2+ current. Further, maximum Na+ conductance is not significantly affected by physiologic concentrations of ethanol.

Electrophysiological Changes of HSV-1-Infected Dorsal Root Ganglia Neurons in Culture

Dissociated rat dorsal root ganglion cultures were infected with herpes simplex virus type 1 and studied electrophysiologically throughout the course of infection. Alterations in the electrical parameters of the action potentials of these neurons occurred as early as 4 hours post infection. The maximum rate of rise, spike amplitude, and overshoot were decreased, and the full width at half maximum and resting membrane potential were increased. At 6 hours post infection there is a movement back to normal values for these parameters. This reversal is transient, however, and the types of alterations seen at 4 hours post infection are more pronounced at 12 hours post infection. The first morphological alterations occur at 16 hours post infection, at which time less than 50% of the neurons impaled produced action potentials. Application of cyclohexamide to inhibit protein synthesis 1 hour post infection prevented electrophysiological changes normally seen at 4 hours and 6 hours post infection. It is concluded that the sodium conductance is specially reduced by acute HSV infection, and that this reduction is attributed to viral specific or modified host cell protein synthesis.

Human Studies Concerning Thermal-Induced Shivering, Postoperative "Shivering," and Cold-Induced Vasodilation

Human reaction to cold stress and hypothermia involves shivering. Another form of overt shaking, postoperative shivering, has been attributed as a thermoregulatory response to postoperative hypothermia. Analysis of the normal human shivering pattern showed a synchronized, slow amplitude modulation (six to eight cycles/min) over all muscles sampled. In addition, there was a frequency of 8 to 10 Hz associated with each low-frequency amplitude modulation. EMG signals from postoperative patients revealed none of the major patterns seen in thermal-induced shivering. Cold-induced vasodilation also was studied and found to occur simultaneously in all cold-stressed fingers regardless of size or innervation. Thermal shivering and cold-induced vasodilation are considered to be manifestations of central neural oscillators.

Co-culture of rat trigeminal ganglion neurons and corneal epithelium

Corneal epithelium and the trigeminal ganglion neurons which normally innervate the epithelium have been grown in adjacent chambers of a 35 mm tissue culture plate. Dissociated nerve cells from late embryonic rats were plated inside an 8 mm cloning cylinder attached to the center of the culture plate by silicone grease. In 7-10 days neurites extended out of this inner chamber by growing through the grease seal and along parallel scratches in the collagen coating of the tissue culture plate. Once this occurred, pure corneal epithelial explants were isolated from young adult rats and plated in the area surrounding the cloning cylinder, i.e. in the outer chamber. Cultures were monitored regularly with phase microscopy and, at various times, were fixed for ultrastructural examination. Within 24-48 hours of the epithelial plating, there were both individual neurites and bundles of neurites in contact with the epithelium. This interaction increased substantially over the next few days. Growth cones of the neurites could be seen to approach the microvilli-covered surface of the epithelium, travel over the surface and penetrate between the epithelial cells. This tissue culture model of the innervated ocular surface may prove valuable in the study of a variety of ocular conditions or diseases, as well as provide a means to study functional relationships and mechanisms of cellular interaction between neurons and their target cells.

Core temperature response to immersed bicycle ergometer exercise at water temperatures of 21 degrees, 25 degrees, and 29 degrees C.

A bicycle ergometer modified for aquatic exercise was used to determine the effects of immersion on core temperature during submaximal exercise at different water temperatures. An exercise intensity (60% of maximal oxygen consumption) and duration (30 minutes) considered appropriate for cardiovascular conditioning were used. These data will be useful in cardiovascular and leg-strengthening hydrotherapy programs. Rectal temperature, skin temperature, and a rating of thermal comfort were studied in five normal men (14.8% +/- 5.6% fat) during headout immersion at water temperatures of 21.1 degrees, 25.3 degrees, and 29.4 degrees C and exercise in air of 21.1 degrees C. Subjects were immersed for 30 minutes during static and exercise (63% +/- 0.6% maximal oxygen consumption) conditions. Data were collected every 5 minutes and analyzed by repeated measured analysis of variance. At water temperatures, rectal temperature fell from control during static immersion (p less than or equal to 0.05) and was lower than control at the end of the 30-minute recovery period (p less than or equal to 0.05). During exercise there was no change in rectal temperature at water temperatures of 21.1 degrees and 25.3 degrees C; however, rectal temperature rose at water temperatures of 29.4 degrees (p less than or equal to 0.05) and air 21.1 degrees C (p less than or equal to 0.05). At the end of recovery rectal temperature was lower than control at water temperatures 21.1 degrees C (p less than or equal to 0.05) and greater than control at water temperatures 29.4 degrees C (p less than or equal to 0.05). There was no change from control in rectal temperatures at water temperatures 25.3 degrees C and air at 21.1 degrees C. These results indicate that immersion in 25.3 degrees and 21.1 degrees C water effectively attenuates the rise in rectal temperature during exercise at 63% of maximal oxygen consumption, whereas immersion in 29.4 degrees C water does not. In addition, both skin and rectal temperatures affect perception of thermal state but do not give the subjects an accurate estimation of thermal balance.

Cardiovascular responses to face immersion (the diving reflex) in human beings after alcohol consumption.

The diving reflex is a complex cardiovascular-respiratory response to immersion. This multireflex response in animals consists of apnea; bradycardia (the experimental parameter most often measured); peripheral vasoconstriction (resulting in preferential perfusion of the brain and heart); decreased cardiac output (with a maintained or increased stroke volume); and an increase in mean arterial blood pressure. These cardiovascular alterations act in a manner that conserves oxygen for the heart and brain. Because alcohol is often involved in water accidents with associated submersions, these initial experiments dealt with human volunteers who consumed alcohol to a blood level of 0.1 g% (legal level of intoxication). The diving reflex was elicited before and after alcohol consumption. Heart rate, blood pressure, and cardiac output were measured before, during, and after face immersion in 4 C water. In the sober state, immersion decreased heart rate, increased stroke volume, increased blood pressure, and increased total peripheral resistance. In comparison to the sober state, alcohol consumption increased pre-immersion heart rate, but did not significantly alter pre-immersion blood pressure or stroke volume. Following alcohol consumption, facial immersion decreased heart rate, but not to the same low rate as in the sober state. Alcohol consumption also evoked a lesser increase in blood pressure and failed to increase stroke volume significantly.

Ultrastructural Effects of Herpes Simplex Virus Type 2 Infection of Rat Dorsal Root Ganglia in Culture

The ultrastructural consequences of herpes simplex virus type 2 (strain R-2) infection of organotypic cultures of embryonic rat dorsal root ganglia were studied. The initial consequences (dilation of endoplasmic reticulum and/or Golgi apparatus and distortion of mitochondrial structure) occurred in the cytoplasm. These effects were followed by several nuclear changes including loss of nucleoplasm, and margination of chromatin. Extensive nuclear membrane proliferation was accompanied by the viral maturation process. Two previously unreported observations were made. First, productive virus replications occurred in glial cells, as well as in neurons. Mature, enveloped virus was produced by nuclear budding and envelopment in the cytoplasm in both cell types. Second, neurons were observed to participate in polykaryocyte formation with other neurons and with glial cells. These polykaryocytes were usually composed of only three or four cells. Neuronal-glial polykaryocytes were more prevalent than neuronal-neuronal polykaryocytes. In general, however, the ultrastructural changes in neurons and glial cells in culture were consistent with previously reported changes occurring in nervous tissue of experimental animals suffering from acute herpes simplex virus infections. Therefore, the utilization of this in vitro system to further study the pathogenesis of acute herpetic infections of sensory ganglia appears to be reasonable.

Characterization of rat corneal epithelium maintained in tissue culture

Using Dispase-treated rat corneas, primary cultures of corneal epithelium have been established which are free of contaminating cell types. Cultures were maintained for periods up to 36 days and were monitored with morphological and electrophysiological methods. Phase and scanning electron microscopy revealed a mosaic of polygonal epithelial cells which migrated over the culture plate. Actively migrating cells at the periphery of the culture presented a complex border of ruffles and filopodia. Surface specializations of the epithelial cells, i.e. microvilli, reflected those seen in vivo. Transmission electron microscopy revealed many cytological features common to the intact cornea: bundles of tonofilaments, desmosomes between adjacent cells and glycocalyx-covered microvilli on all free surfaces. These features developed over time in culture. Membrane potentials of the cultured epithelial cells could be recorded intracellularly. Therefore, it appears that pure cultures of rat corneal epithelium which maintain the morphological characteristics of their in vivo counterparts can be grown for considerable periods of time and that their electrophysiological properties can be monitored. This system offers the possibility of studying, under the controlled conditions of tissue culture, a wide variety of factors which might influence the integrity of the corneal epithelium or alter its susceptibility to disease.