Organized neurologic responses to acute cold stress

sponses were examined in pre-immersion and immers ion states in untreated ducks, and in the same ducks following acute treat- ment wi th a beta-adrenergic b locking agent (propranolol) and subsequent ly wi th atropine. These exper iments were repeated after deple t ion of the o r thosympa the t i c ca techo lamines wi th guanethidine. The experiments yielded the following primary ob- servations: (1) diving bradycardia does not resul t f rom a bar- oreceptor media ted mechan i sm, a l though baroreceptor reflexes are active during recovery from diving; (2) vasodilation observed during the dive is due to loss in alpha adrenergic-induced vaso- cons t r i c t ion and /or non-cho l inerg ic , non-ad rene rg ic - induced vasodilation; and (3) heart rate increases during immers ion fol- lowing sympathet ic and parasympathet ic blockade, suggesting a third neuronal system controll ing heart rate.

7 Organized Neurologic Responses to Acute Cold Stress

Robert S Pozos, PhD; D Israel; Larry Wittmers, MD, PhD; R Hoffman; arid William Mills / Associate Professor of Physiology; Director, Department of Physiology, University of Minnesota - - Duluth

Shiver is an over~ coordinated response of the central nervous system to cold stress. There is controversy as to whether or not this oscillation is programmed by a "central oscillator" or is sen- sitive to peripheral signals which would suggest tha t shiver is a segmental oscillator. Shiver can be recorded over all muscles and waxes and wanes in terms of its amplitude. This latter frequency is thought to be related to ei ther inspiration or expiratio n. Stud- ies were conducted on h u m a n subjects in which rectal and pe- r ipheral t empera tures Were moni to red along w i th surface elec- t r omyograms f rom the fo l lowing musc les : t rapezius , biceps, extensors and flexors of the wrists, rectus femoris, rectus abdom- inis, soleus and tibialis. Subjects were placed in an environmen- tal chamber in a supine posit ion in which the temperature was set at 20 ° E Shivering was found to have a number of frequencies. The frequencies of the electromyogram were 10-12 hz. There were few cionic-like oscillations Over any of the muscles studied. The waxing and waning had a frequency of 6-8 cycles per minu te syn- chronized over the body, wi th no consis tent correlation to ven- tilation. During these experiments, the rectal temperature would rise 0.2°-3 ° C per 20 minutes and the oscillation would cont inue for prolonged periods of time. The shiver could be st6pped or re- duced by the subject "relaxing" or after intense overall body con- traction, which suggests that shiver has a central component. A change in blood flow to the periphery is associated wi th cold stress, so tha t there are periodic bursts of vasoconstr ict ion fol- lowed by vasodilation, known as the cold-induced vasodilation ICIVD) reflex. Changes in finger t empera ture were moni to red while the subject had his hand in cold (1-3 ° C) water. In 15 sub- jects the cycles of CIVD were synchronized in the index and litt le finger for 60-80 minutes , after which there seemed to be some loss of synchronization. Since these fingers have different inner- vation, the data suggests tha t the autonomic nervous system con- trols the phases of vasoconstr ict ion and vasodilation during the init ial stages of cold stress. The frequency of this oscillation does not appear to be related to the onset of shiver ing or the Waxing and waning of shiver. Shivering and CIVD seem to have both pe- ripheral and central components of control. Both responses will be discussed as coordinated input and output CNS models.

8 Multicenter Hypothermia Survey

Daniel F Danzl, MD; and Robert S Pozos, PhD / Investigators: PS Auerbach, S Glazer, W Goetz, J Jui, P Lilja, J Marx, J Miller, W Mills, R Nowak, R Shields, S Vicario, and M Wayne /

Clinical experiments investigating the t rea tment of hypother- mia are generally l imited tO heal thy subjects whose cooling is terminated at 35 ° C (95 ° F), prior to development of the most sig-

n i f icant hypo the rmic pathophysiology. No ideal an imal model exists. Therefore. c l inical Observat ions and cont ro l led phys- iological exper iments are essential . A mul t i cen te r pi lot survey evaluated the clinical presentation, t rea tment and outcome of ci- vil ian accidental hypothermia. Data was collected from 14 emer- gency departments. 428 cases presented during a two year study period. Data was additionally analyzed after inclusion of 27 cases from Alaskan sites. Patient temperatures ranged from 95 ° F to 60 ° E wi th 272 cases < 90 ° F (63.6%1. Male rectal temperatures aver- aged 86.50 ~ 6.20 ° F and females 87.9 ° = 6.50 * E There were no signif icant differences in male versus female profiles regarding physiological data, laboratory results, rewarmlng or mor ta l i ty rares. There were 77 fatalities. Ninety-eight of the 169 patients who were located indoors were Severely hypothermic (~ 90 ° FI, as were 25 Of the 37 immersions ,10 fatalitiesl. Fifty-four of the 82 patients ,15 fatalitiesl wi th associated t rauma were ~ 90 ° E A "significant" medical illness was identified in 188 cases, wi th 30 fatalities. There were 33 cases of frostbite, 27 drug overdoses, and 78 coexistent infections diagnosed in the emergency department. In 174 cases, ethanol was a factor. The populat ion wi th high eth- anol levels 315 - 800 rag%) did not differ in rewarming or mor- tality rates from that wi th low levels. The first hour rewarmlng rate was significantly faster in those ~ 59 years of age L1.95 + 2.50 ° F/hr~ than in those /> 60 years 11.35 -~ 2.09 ° F/hrL There were no significant differences by age in presenting temperature. rewarming strategies or mortality. A total of 41 pat ients received pre-hoSpital (N = 27 ' or emergency department (N = 141 cardio- pulmonary resuscitation, wi th 15 survivors (37% J. The profile of the CPR versus non-CPR population differed significantly in: lo- cat ion (outdoors), in i t ia l rectal t empera ture W6.70 z 6.80 vs. 87.70 _~ 5.62 ° F]. third hour rewarming rate 14.11 z 2.75 vs. 2.10 -~ 2.13 ° F/hr}, and numerous laboratory parameters. Emergency depar tment acuve core rewarming was applied in 85.2% (N = 1551 of patients. Mortal i ty profiles and rewarming rates based on passive versus various active rewarming strategms at each level of hypothermia will be discussed.

9 Clinical and Experimental Observations on Frostbite

John P Heggers, PhD; Martin C Robson, MD', K Malqavalan, MD; Mark D Weingarten; John M Carethers; Jane A Boertman; and Robert J Sachs, MS / Professor of Surgery, Director of Research, Division of Plastic and Reconstructive Surgery, Wayne State University School of Medicine, Detroit

Experimental ischemia by t h e classic rabbit ear model of frost- bite injury clearly defined the role of thr0mboxane as a mediator of progressive dermal ischemia in frostbite injuries. After demon- strating that h u m a n frostbite blister fluid was high in thrombox- ane, we established a therapeutic protocol which included a top- ical an t i - th r0mboxane agent in combina t ion w i th a sys temic anti-prostanoid. Of 154 patients treated for frostbite from 1982 to 1985, 56 were treated wi th the frostbite protocol; the remaining 98 were treated wi th a wide variety of therapeutic modalities. In the group of patients tha t were treated outside of our service, the average pat ient age was 48.5 years (range: 18-82 years). On admis: sion, there were 11 patients wi th 1st degree frostbite, 51 patients wi th 2nd degree frostbite and 365 patients wi th 3rd degree frost- bite: Of these, 14 patients were chronic (one or more previous episodes of frostbite), 56 were acute admissions (< 24 hours after injury), a n d 28 were subaeute admissions (> 24 hours after inju- ry). The mean length of hospital stay for the three groups was 17.5 days, i9.0 days, and 22:6 days. Of these 32.7% healed with- out tissue loss (all degrees of frostbite), 34.6% healed wi th tissue loss and 32.7% required amputat ion. The average age for those pa t ien ts on the f rostbi te protocol was 43.5 years (range: 17-82 years). On admission, there were 18 patients wi th 1st degree frost- bite, 25 patients wi th 2nd degree frostbite, and i3 pat ients wi th 3rd degree frostbite. Of these, five were chronic admissions, 32 were acute admiss ions and 19 were subacute admissions. The mean length of hospital stay for each group was 18.5 days, 8.5

16:1 January 1987 Annals of Emergency Medicine 126/171