Cognitive performance of military men and women during prolonged load carriage.

BACKGROUND: This study evaluated cognitive workload in soldiers undertaking a long duration march wearing different loads. METHODS: Military participants (n=12 men and n=10 women) performed four 3-hour loaded marches (12.25 km at 4.9 km/hour) wearing either 21 kg, 26 kg, 33 kg or 43 kg. During the march, accuracy and response time were measured using the verbal working memory n-back test (0, 1, 2 and 3) and two bespoke Go/No Go tests (visual/auditory) to assess inhibition of a pre-potent response. RESULTS: The physical demands of the march increased with load and march duration but remained at moderate intensity. N-back test accuracy ranged from 74% to 98% in men and 62% to 98% in women. Reduced accuracy was observed as load and time increased. Accuracy during the visual Go/No Go test also reduced with load, accuracy ranged from 69% to 89% in men and 65% to 90% in women. No differences due to load or time were observed during completion of the auditory Go/No Go task; accuracy ranged from 93% to 97% in men and 77% to 95% in women. A number of participants were unable to complete the march due to discomfort. Reports of discomfort were more frequent in women, which may have contributed to the greater reductions in accuracy observed. CONCLUSION: These data provide further evidence that cognitive performance of military personnel can be affected during long duration loaded marching. Women reported discomfort from equipment more frequently than men, which may make them more susceptible to declines in cognitive performance. These findings highlight important considerations for equipment procurement.

The influence of a menthol and ethanol soaked garment on human temperature regulation and perception during exercise and rest in warm, humid conditions.

UNLABELLED: This study assessed whether donning a garment saturated with menthol and ethanol (M/E) can improve evaporative cooling and thermal perceptions versus water (W) or nothing (CON) during low intensity exercise and rest in warm, humid conditions often encountered in recreational/occupational settings. It was hypothesised there would be no difference in rectal (Tre) and skin (Tsk) temperature, infra-red thermal imagery of the chest/back, thermal comfort (TC) and rating of perceived exertion (RPE) between M/E, W and CON, but participants would feel cooler in M/E versus W or CON. METHODS: Six volunteers (mean [SD] 22 [4] years, 72.4 [7.4] kg and 173.6 [3.7] cm) completed (separate days) three, 60-min tests in 30°C, 70%rh, in a balanced order. After 15-min of seated rest participants donned a dry (CON) or 80mL soaked (M/E, W) long sleeve shirt appropriate to their intervention. They then undertook 30-min of low intensity stepping at a rate of 12steps/min on a 22.5cm box, followed by 15-min of seated rest. Measurements included heart rate (HR), Tre, Tsk (chest/back/forearm), thermal imaging (back/chest), thermal sensation (TS), TC and RPE. Data were reported every fifth minute as they changed from baseline and the area under the curves were compared by condition using one-way repeated measures ANOVA, with an alpha level of 0.05. RESULTS: Tre differed by condition, with the largest heat storage response observed in M/E (p<0.05). Skin temperature at the chest/back/forearm, and thermal imaging of the chest all differed by condition, with the greatest rate of heat loss observed in W and M/E respectively (p<0.01). Thermal sensation differed by condition, with the coolest sensations observed in M/E (p<0.001). No other differences were observed. CONCLUSIONS: Both M/E and W enhanced evaporative cooling compared CON, but M/E causes cooler sensations and a heat storage response, both of which are likely mediated by menthol.

The determinants of thermal comfort in cool water.

Water-based activities may result in the loss of thermal comfort (TC). We hypothesized that in cooling water, the hands and feet would be responsible. Supine immersions were conducted in up to five clothing conditions (exposing various regions), as well as investigations to determine if a "reference" skin temperature (Tsk) distribution in thermoneutral air would help interpret our findings. After 10 min in 34.5 °C water, the temperature was decreased to 19.5 °C over 20 min; eight resting or exercising volunteers reported when they no longer felt comfortable and which region was responsible. TC, rectal temperature, and Tsk were measured. Rather than the extremities, the lower back and chest caused the loss of overall TC. At this point, mean (SD) chest Tsk was 3.3 (1.7) °C lower than the reference temperature (P = 0.005), and 3.8 (1.5) °C lower for the back (P = 0.002). Finger Tsk was 3.1 (2.7) °C higher than the reference temperature (P = 0.037). In cool and cooling water, hands and feet, already adapted to colder air temperatures, will not cause discomfort. Contrarily, more discomfort may arise from the chest and lower back, as these regions cool by more than normal. Thus, Tsk distribution in thermoneutral air may help understand variations in TC responses across the body.

Modelling the effectiveness of techniques for reducing heat strain in Royal Navy nuclear, biological and chemical cleansing stations' teams.

High temperatures, combined with wearing nuclear biological chemical (NBC) individual protective equipment (IPE), produce significant heat strain in personnel working in ships' NBC cleansing stations (CS) and limit the ability of ships to operate in a contaminated environment. This report reviews the potential solutions to this problem and concludes that only a method of actively cooling personnel will reduce heat strain and increase the number of people that can be processed through ships' NBC CS. Amongst the wide range of cooling equipment that might offer a benefit, only hand immersion in cold water and ice-vests are practically useful for use in NBC CS. To assess how effective these techniques are likely to be INM has modelled the thermal effects under environmental conditions expected in the CS when operating in a hot climate. The model predicted that hand immersion in cold water (10 degrees C) would be the most effective cooling method, providing that personnel were able to take regular rest periods to immerse the hands. If it is preferred that personnel in the CS be able to work continuously, then ice-vests would be effective. The safe total work time that can be achieved in a three hour period without a cooling intervention is approximately 72 minutes, regular rest periods must be taken throughout the three hour work period, to total of 108 minutes. Safe work times can be increased to 99 minutes by using an ice-vest and 117 minutes by using hand immersion in 10 degrees C water, with required rest times reduced accordingly, thereby increasing capacity of CS teams to decontaminate personnel.

Testing the effectiveness of techniques for reducing heat strain in Royal Navy nuclear, biological and chemical cleansing stations' teams.

Nine personnel simulating the work of an NBC cleansing station (CS) in conditions expected in Middle Eastern waters had a limited work duration due to incapacitating heat strain. When the subjects were allowed five minutes rest periods after every 10 minutes of work, the endurance of seven of the subjects was limited to between 75-105 minutes due to heat strain and heat illness. By the point of withdrawal mean (SD) rectal temperature (Tre) had risen by 1.8 degrees C (0.4 degree C). The other two subjects were withdrawn earlier because they reached cardiac safety limits. When the hands were immersed (HI) in 10 degrees C water during the five minute rest periods heat strain was significantly lower (P < 0.01) and work endurance times were increased. One subject was withdrawn early on reaching cardiac safety limits, two on reaching Tre limits (39 degrees C) at 105 minutes, and six subjects completed the 180 minute exposure with a final Tre of 38.4 degrees C (0.3 degree C). Using 'iced' (0 degree C) rather than 10 degrees C water for HI further reduced heat strain (P < 0.01) and increased endurance times. Three subjects were withdrawn early on reaching cardiac safety limits, the remaining six completing the 180 minute exposure, with a final Tre of 38.3 degrees C (0.5 degree C). Using an ice-vest (IV) in conjunction with HI further reduced heat strain (P < 0.01) and increased endurance times. Two subjects were withdrawn early on reaching cardiac safety limits, the remaining seven completing the 180 minute exposure, with a final Tre of 38.2 degrees C (0.8 degree C) when 10 degrees C HI water was used, and Tre 38.0 degrees C (0.4 degree C) when 0 degree C HI water was used. There were no reports of finger numbness or loss of dexterity due to HI, and all personnel were able to remove their own individual Protective Equipment (IPE) without difficulty. It is expected that using HI will not reduce the ability to decontaminate or undress others. The HI technique and IV equipment should be introduced into the Fleet. 'Iced' water should be used in preference to 10 degrees C, although any water colder than 25 degrees C will provide some benefit. The IVs increased torso girth and personnel should try them on (with frozen ice packs inserted) prior to their use and ensure that their protective clothing still fits, or obtain a larger size.

Heated socks maintain toe temperature but not always skin blood flow as mean skin temperature falls.

INTRODUCTION: This study was conducted to examine whether toe skin blood flow (Q(toe)) could be maintained in subjects exposed to cold air by warming the foot using a heated sock. METHODS: Four male subjects were exposed to air at 4 degrees C. They wore aramid shirt and trousers, a coverall made from metalized spun bonded polyethylene ("space blanket" fabric), arctic mittens, a 4-ply aramid balaclava, and loose fitting padded boot liners. The subjects rested recumbent on a couch with a pair of heated socks turned on for 120 min and with socks turned off for a further 60 min. Q(toe) was measured using laser Doppler flowmetry. RSULTS: Although the heated socks maintained the skin temperature of the feet above 37 degrees C, Q(toe) was not maintained in two of the four male subjects for the 120 min that the socks were turned on. DISCUSSION: Heated socks cannot be relied on to maintain Q(toe) or to prevent non-freezing cold injuries during prolonged exposure to cold conditions.

Findings from a simulated disabled submarine survival trial.

Eleven volunteer submariners were exposed to simulated disabled submarine conditions for a maximum of 7 days to determine if the limited clothing and rations provided in escape compartments would compromise survival prospects. Daily rations were 0.568 liters of water (none on Day 1) and 100 g of barley sugar. The subjects wore working rig and the liner from the Mark 10 submarine escape and immersion equipment throughout, and slept in the outer dry suit. Air temperature fell from 22 degrees to 4.4 degrees C over 2 days and then remained at 4.4 degrees C. Although the subjects felt cold they were able to maintain their deep body temperature. The greatest threat to survival in this situation would be dehydration, one subject was withdrawn on Day 4 as his urine production over the previous 24 h was 130 ml and if not withdrawn and rehydrated this may have led to renal failure. Other medical problems suffered by the subjects during the 7 days included diarrhea, vomiting, hypoglycemia, headaches, and back pains, and, following the trial, non-freezing cold injuries to their feet. It is concluded that the rations are not adequate and could compromise the submariners ability to survive for 7 days in these conditions and during a subsequent escape procedure.

Heat strain in Royal Navy helicopter aircrew.

A review of the literature on heat strain and aircrew and a questionnaire survey of Royal Navy aircrew have been completed. Aircrew appreciate, some 50% from first hand experience, that heat strain can reduce their operational endurance and performance. They are at greatest risk of developing it in the pre-flight period, especially when wearing Nuclear, Biological, or Chemical (NBC) protective equipment. Several techniques they use to reduce this risk are described. Some may be of particular assistance in the field should air conditioned facilities be unavailable. However, opportunities to improve the thermal environment within the aircraft on the ground and in flight are limited as the heat generated within it and high levels of solar radiation impinging on it severely challenge air conditioning units, themselves constrained by weight and size. Other demands placed on protective clothing offer little potential to increase the rate at which aircrew can lose accumulated heat. It is concluded that an appropriate micro-climate cooling system worn next to the skin may be required to achieve truly significant reductions in heat strain. Research at the Institute of Naval Medicine has identified liquid cooling techniques which may be suitable for aircrew in all but the smallest helicopters. Any views expressed are those of the author and do not necessarily represent those of the Department.

Preoperative electroneuronography and facial nerve outcome in acoustic neuroma surgery.

OBJECTIVE: To determine whether preoperative electroneuronography (ENoG) predicts facial nerve outcome in patients undergoing acoustic neuroma surgery. STUDY DESIGN: Prospective, consecutive patients undergoing surgery for acoustic neuroma. SETTING: A private tertiary otology and neurotology practice. PATIENTS: One hundred consecutive patients presented for surgical removal of an acoustic neuroma between May 1992 and September 1993. The mean patient age was 49 years (range 17-77). Forty-three percent were male and 57% were female. The mean tumor size was 1.77 cm (range 3 mm to 5 cm). The tumors were removed by a translabyrinthine approach in 59% of patients, via the middle fossa in 40%, and retrosigmoid in 1%. The facial nerve was anatomically intact at the conclusion of the operation in all but one patient. INTERVENTION: Preoperative ENoG in all patients undergoing surgical removal of their acoustic neuromas. MAIN OUTCOME MEASURES: Facial nerve outcome was measured using the House-Brackmann scale immediately after the operation. 5-7 days after surgery, and > 1 year after surgical resection. RESULTS: Preoperative ENoG had no predictive value in determining immediate or eventual facial nerve outcome. CONCLUSIONS: ENoG has no value in predicting the facial nerve outcome in acoustic neuroma patients. The results of this study are similar to reports with smaller series in the literature. Preoperative ENoG has proven useful, in another study from this institution, in predicting the possible presence of a facial nerve neuroma. This test may be helpful in determining the possible etiology of an intracanalicular mass.

Prevention of heat strain by immersing the hands and forearms in water.

The effectiveness of hand immersion in water at 10 degrees C, 20 degrees C and 30 degrees C as a technique for reducing heat strain in Royal Navy (RN) personnel has been investigated at the Institute of Naval Medicine (INM). Four subjects exercised at a moderate work rate, whilst wearing fire fighting clothing in an environmental chamber at 40 degrees C. The subjects reached heat strain safety limits within 45 minutes of commencing work at which point they rested in the heat for 30 minutes whilst they underwent one of four experimental conditions: without intervention (control); or with their hands immersed in water at 10 degrees C, 20 degrees C or 30 degrees C. The experiment was repeated on a further three days so that the subjects undertook each experimental condition in a balanced randomised order. During the control condition without hand immersion the subjects were unable to cool. Immersion of the hands in water (at 10 degrees C, 20 degrees C or 30 degrees C) significantly (P < 0.05) lowered body core (auditory canal) temperature within ten minutes. Assessing the effectiveness of this technique by the initial rates of core temperature reduction, revealed that immersion of the hands was more effective the colder the water. Following 20 minutes of hand immersion mean core temperature had dropped from 38.5C to: 36.9(standard deviation 0.19) degrees C, 37.3(0.18) degrees C, and 37.8(0.10) degrees C, in 10 degrees C, 20 degrees C and 30 degrees C water respectively. Cooling powers estimated from changes in mean body temperature were 334, 307 and 113 watts using 10 degrees C, 20 degrees C and 30 degrees C water respectively. These results indicate that hand immersion in water at a temperature of between 10 degrees C and 30 degrees C is an efficient means of cooling heat stressed personnel who have been exercising. This simple and effective technique may be applied to many industrial and military tasks to reduce heat strain, lower the risk of heat injury, and increase safe total work times in the heat. For the RN, hand immersion could be used in fire fighting, damage control and NBC operations where personnel alternately work and rest.

A simple technique for introducing anterograde and retrograde tracers into the vestibular and cochlear sensory organs.

The standard method for labeling the afferent and efferent innervation of the cochlear and vestibular sensory organs is by microinjection of tracer substances into the labyrinth. Injection of small amounts of tracer often result in incomplete and inconsistent labeling, but large injections can cause spurious labeling of brainstem structures due to diffusion from perilymph to cerebrospinal fluid. Effective labeling with minimal artifact can, however, be achieved by a relatively simple method involving placement of a tracer-saturated pledglet of gelatin sponge in the round window after rupture of its membrane. The gelatin sponge simultaneously acts as a continuous-release vehicle for the tracer and prevents reflux of perilymph and tracer into the middle ear cavity. Use of this technique produces labeling with a degree of intensity and anatomic detail that rivals that seen with more complicated methods of tracer placement.

Technical modifications to the middle fossa craniotomy approach in removal of acoustic neuromas.

With the increased use of gadolinium-enhanced magnetic resonance imaging studies to detect acoustic neuromas, smaller tumors are discovered more frequently. The middle fossa craniotomy approach for removal of small tumors is ideal for hearing preservation. The authors report hearing preserved at or near the preoperative levels in 71 percent of a series of 24 consecutive patients in whom the middle fossa craniotomy approach was employed. Several technical modifications, including more extensive bony exposure medially, tumor dissection in a medial-to-lateral direction, and topical application of papaverine to the cochlear nerve at the modiolus, have enhanced the ability to preserve hearing.

Routine pre-oxygenation using a Hudson mask. A comparison with a conventional pre-oxygenation technique.

Two techniques of pre-oxygenation were studied by continuous analysis of respired gases using a mass spectrometer in 10 healthy volunteers. The first was a conventional technique as commonly used in anaesthesia with a Bain system and tightly-fitting anaesthetic face-mask and an oxygen flow of 8 l.min-1. The second technique also used a Bain system with an oxygen flow of 8 l.min-1, but with a Hudson mask attached. The mean fractional end-tidal oxygen concentrations after 3 min were 0.812 and 0.46 respectively for each of the pre-oxygenation techniques against 0.16 for subjects breathing air. This represents a considerable increase in pulmonary oxygen reserve for both techniques. The second technique is not an alternative to conventional pre-oxygenation for emergency anaesthesia, but is a useful and simple method that is acceptable to both patient and anaesthetist in routine cases.

Facial nerve injury in cochlear implantation.

We present eight cases of FN dysfunction after cochlear implantation. Four mechanisms of injury are proposed. The most common injury occurs from the heat of a bur shaft rotating over the FN in the facial recess. Several suggestions are made to help prevent the type of injuries we have seen. Preoperative imaging and intraoperative FN monitoring may be of general assistance in avoiding injuries to the FN, especially in cases of revision surgery and congenital malformations.

Hand immersion as a method of cooling and rewarming: a short review.

Many cooling and warming procedures have been proposed for the treatment of hyperthermic or hypothermic individuals. One of the most recent of these is the use of hand immersion as a simple method to gain or lose heat. In the present paper the principles underlying this approach, and the evidence for and against hand rewarming/cooling, are briefly reviewed. It is concluded that hand immersion is likely to be more effective for cooling than rewarming individuals.

Isolated Castleman's disease in the neck.

It can be difficult for the clinician to diagnose Castleman's disease when cervical lymphadenopathy is its only manifestation. The diagnostic challenge may be compounded by the presence of a profound fibrotic reaction secondary to multiple biopsy attempts that are frequently required to establish a diagnosis. Castleman's disease is a benign lymphoproliferative disorder and it most frequently involves the mediastinal lymph nodes. The recognition of an occasional variant of this disorder with a potential malignant course and its association with AIDS calls for a greater awareness of this disease among all clinicians.