CONDITIONS OF STRESS IN UNDERSEA WARFARE 



423 



perhaps from a slow 20 second roll of the 

 boat through the intermediate range of vi- 

 bration and well up into auditory frequen- 

 cies. It has been long reahzed that noise can 

 be a potent distracting and interfering factor 

 in many kinds of activities. While these 

 subjects are treated separately in other chap- 

 ters, we wish to emphasize the possible cumu- 

 lative effects of these manifold and com- 

 pletely unavoidable stimuli, and to suggest 

 that their effects may be something other 

 than purely additive on a severely stressed 

 organism. 



A possible further corollary here may be 

 body temperature, which tends to drop dur- 

 ing anoxia, thus reducing metabolic demand 

 and compensating somewhat for the di- 

 minished O2 supply (49, 74). 



3. Temperature and Humidity 



Temperature control is, of course, only 

 one facet of the regulation of energy ex- 

 change between the body and its environ- 

 ment. The submariner is homeothermic to 

 a remarkable degree, even if his air-condi- 

 tioned submarine is not. The close control 

 of body temperature is a prerequisite for 

 adequate functioning of other homeostatic 

 systems, for without it, basic biochemical 

 and metaboHc reactions could nof, be main- 

 tained. The critical problem in submarines 

 is usually one of heat dissipation; this may 

 occur through radiation, conduction, and 

 water vaporization. The latter is the most 

 effective but is most critically affected by 

 humidity. 



The autonomic homeostatic mechanisms 

 that maintain temperature control have been 

 widely studied (45, 64). Experimentally 

 placed lesions in the hypothalamic thenno- 

 stat have revealed that there are separate 

 but anatomically close regions that are sen- 

 sitive to the temperature of the circulating 

 blood. The more caudal hypothalamic re- 

 gion is activated by relative cold, and gives 

 rise to shivering and muscle tension, vaso- 

 constriction, piloerection, and adrenaline se- 

 cretion — sympathetic reactions. The more 



rostral region responds to warmer blood with 

 consequent vasodilatation and sweating. 

 The range of change in blood flow in pe- 

 ripheral tissues is high — of the order of 100: 1. 



That both sympathico-adrenal and vago- 

 insuUn mechanisms are activated by ex- 

 posure to both heat and cold and that it is 

 only the relative dominance of one over the 

 other that provides regulation appear well 

 supported by Gellhorn (52). The predom- 

 inating effect of excessive heat and humidity 

 apparently involves both a mobihzation of 

 the vago-insulin or parasympathetic system 

 and an inliibition of the sympathico-adrenal 

 system. Vaso-dilatation, sweating, and in- 

 creased respiration are the chief mechanisms 

 of heat elimination. The result of dilata- 

 tion and of hyperpnea may be a loss of 

 venous pressure, and, presumably, by way of 

 pressure receptors and inhibition of para- 

 sympathetic activity, a marked increased in 

 heart rate. Increased rectal temperature, 

 lowered blood pressure, tachycardia, and re- 

 duction of CO2 by hyperpnea are condi- 

 tions which have been found indicative of 

 failing abihty to adjust to high temperature 

 (1, 5, 7, 36, 71, 74, 99). EEG studies 

 have shoAvn that these conditions may be 

 associated with impairment of cerebral func- 

 tion. 



The sldn and lungs are the main hnes of 

 defense in temperature control. In the sub- 

 marine, as in other environments, protection 

 by clothing exerts an important influence on 

 heat exchange. Except in extreme heat, 

 nude men can work in higher temperature 

 and higher humidity; e.g., at 90 degrees F. 

 some evaporative coohng occurs even at 99% • 

 humidity, while with clothed men this hmit 

 is 89% (99). With elevated dry and wet 

 bulb temperature extreme discomfort and 

 sharply decreased working efficiency will re- 

 sult. Since muscular Avork greatly increases 

 heat production in the body, the job of the 

 planesman, for example, in silent operation 

 with air conditioning and power controls 

 off is a severely taxing one. FaciHties to 

 increase air movement would be helpful. 



