An examination of two emergency breathing aids for use during helicopter underwater escape.

BACKGROUND: There is a paucity of published work in which the performance of Emergency Underwater Breathing Aids (EUBA) has been examined in the wide range of scenarios in which helicopter underwater escape may be necessary. In the present investigation two EUBA were examined: the Air Pocket (AP) rebreather and the Short Term Air Supply System (STASS) mini SCUBA set. METHOD: Young, healthy male subjects undertook simple simulated helicopter underwater escapes in water at 15 degrees C and/or 5 degrees C. During the immersions the subjects attempted to remain submerged for 60 s while traversing back and forth along a ladder secured at a depth of 1.25 m. At each temperature the subjects used AP and STASS twice. The subjects were dressed in the Royal Navy winter sea helicopter aircrew equipment assembly and an aircrew helmet. RESULTS: Both AP and STASS significantly extended the underwater survival time of individuals when compared to their maximum breath-hold time (BHT). It is clear from the measurements made of gas concentrations in AP; the volume of air used from STASS; and subjective responses, that the 60-s submersions were achieved more easily with STASS than AP. CONCLUSION: It is concluded that in conditions similar to those of the present experiment STASS will give a longer underwater duration than AP, but this benefit must be offset against the possible risk of pulmonary barotrauma associated with the use of STASS, as well as increased training and maintenance costs. Irrespective of the EUBA which is provided, in-water training, preferably including exposure to cold water, will significantly improve the ability of an individual to use it.

The effect of blood alcohol on the initial responses to cold water immersion in humans.

Many drowning victims have alcohol in their blood, but it is not clear whether there is a causal relationship. This study examined the effect of moderate alcohol consumption on the initial responses to cold water immersion. Sixteen subjects wearing swimming costumes undertook two, 3-min head-out seated immersions in water at 15 degrees C. One hour before immersion, subjects drank either 3.7 ml.kg body water-1 of 40% v:v alcohol as vodka, or an equivalent volume of water (control) mixed with squash. On immersion, the average blood alcohol concentration was 23 mmol.l-1 (105 mg.100 ml-1) after alcohol consumption and zero in the control condition. Respiratory frequency in the first 20 s of immersion was found to be reduced (P < 0.05) by 10% (a total of 2-3 breaths) after alcohol consumption compared to the control immersion. Tidal volume, heart rate, rectal temperature and skin temperatures did not differ significantly between immersions. It is concluded that moderate alcohol consumption does not attenuate the initial "cold shock" responses to a practically significant extent and is thus unlikely to reduce the risk of drowning on immersion in cold water.

Neural involvement in 5-hydroxytryptamine-induced net electrogenic ion secretion in the rat intestine in-vivo.

5-Hydroxytryptamine (5-HT) induces active electrogenic anion secretion by both the small intestine and the colon, responses that can be detected from measurements of transmural electrical activity. This approach was adopted to examine the involvement of neural mechanisms in 5-HT-induced secretion in rat proximal jejunum, distal ileum and proximal colon in-vivo. Under control conditions, 5-HT caused maximum rises in transintestinal potential difference of 4.7 +/- 0.3, 3.8 +/- 0.4 and 7.6 +/- 0.3 mV, respectively, with corresponding ED50 values of 28 +/- 3, 38 +/- 4 and 41 +/- 4 nmol kg-1 (n = 12). In each region examined a neural component in the secretory response to 5-HT was identified. Hexamethonium (22 mumol kg-1) reduced the 5-HT response in each region: in the jejunum and colon, it also attenuated the responses to the 5-HT3 agonist, phenylbiguanide and to 5-methoxytryptamine (5-MeOT), an agonist at all 5-HT receptors except 5-HT3, indicating that in these regions the nicotinic pathway can be activated by more than one 5-HT receptor subtype. Atropine (0.27 and 2.7 mumol kg-1) was found to have regional effects on the intestinal responses to 5-HT receptor agonists. In the jejunum, evidence for a pro-secretory muscarinic pathway which could be activated by more than one 5-HT receptor subtype was found. In the ileum and colon no muscarinic pro-secretory pathway was identified, indeed in the colon, an anti-secretory pathway may be present. This muscarinic anti-secretory pathway was observed with phenylbiguanide and 5-MeOT, but not 5-HT. Substance P release does not appear to be involved in mediating the intestinal secretory response to 5-HT. 5-HT-induced intestinal anion secretion may involve a direct secretory action on the enterocyte which can be modified by neurally-mediated pro-secretory and anti-secretory pathways, the balance between these processes varying down the length of the gut.

Do 5-HT4 receptors mediate the intestinal secretory response to 5-HT in rat in-vivo?

The involvement of the recently characterized 5-HT4 receptor in the actions of 5-hydroxytryptamine (5-HT) on jejunal, ileal and colonic electrogenic ion secretion was investigated in the rat in-vivo. 5-HT and the 5-HT1-, 5-HT2- and 5-HT4-receptor agonist 5-methoxytryptamine (5-MeOT), induced a rise in transintestinal PD in all regions of the gut. However, the 5-HT4-receptor agonists renzapride and cisapride had no effect. Furthermore, the 5-HT4-receptor antagonists SDZ 205-557 (2-diethylaminoethyl-[2-methoxy-4-amino-5-chloro] benzoate), tropisetron and SB 204070 ([1-butyl-4-piperidinylmethyl]-8-amino-7-chloro-1,4- benzodioxan-5-carboxylate hydrochloride) did not affect the secretory response to either 5-HT or 5-MeOT in the jejunum, but did cause a small inhibition in the ileum and colon. It is concluded that 5-HT4 receptors do not make a contribution to the electrically monitored 5-HT intestinal secretory response in the rat jejunum in-vivo, but may play a small role in the ileum and colon.

Is desensitization of intestinal 5-hydroxytryptamine receptors an in-vitro phenomenon?

The responses of proximal jejunum and distal ileum to successive applications of 5-hydroxytryptamine (5-HT) were examined in-vitro and in-vivo by measuring the electrical changes that reflect the stimulation of Cl- secretion. In stripped intestinal sheets the second application of a maximal concentration of 5-HT failed to elicit any response, indicating that complete desensitization had occurred. If submaximal concentrations were used, a second response was observed, although it was smaller than the first, indicating partial desensitization. Replacing the bathing solutions following application of a maximal 5-HT concentration also reduced, but did not abolish, the degree of desensitization observed with a second application of 5-HT. In an in-vivo preparation, however, there was no diminution of the responses to four successive maximal doses of 5-HT. This lack of desensitization was also evident in the cardiovascular responses to 5-HT. It is concluded that desensitization to 5-HT is a phenomenon that is readily observed only in-vitro and which is probably related to the inability of a small amount of isolated tissue to eliminate 5-HT.

Involvement of nitric oxide in the response to 5-hydroxytryptamine in the rat in-vivo.

The involvement of nitric oxide (NO) in the effects of 5-HT on intestinal secretion and cardiovascular function in anaesthetized rats was investigated using NG-nitro-L-arginine methyl ester (L-NAME), a specific NO-synthase antagonist, and its optical isomer D-NAME. L-NAME significantly reduced the prolonged hypotensive response to 5-HT. It also caused a small rightward shift in the colonic 5-HT dose-response curve. This suggests that NO plays a significant role in the prolonged hypotensive response to 5-HT, and may make a small contribution to the secretory response of the colon, but not that of the jejunum, in the rat in-vivo.

Algumas sugestões sobre a conduta delinquente

Os autores, na base de pesquisas experimentais de condicionamento e pela aplicação do sistema de EYSENCK, sugerem que os verdadeiros psicopatas são extrovertidos quanto ao temperamento e tendem a estabelecer reflexos condicionados com relativa dificuldade. Desse ponto de vista, os psicopatas ocupam, sobre o eixo Introversão-Extroversão, uma posição próxima à dos histéricos. (AU)