422 



PHYSIOLOGY OF STRESS 



competent lookouts and watches. The same 

 is true of effects on sensory-motor (reaction 

 time) changes. Although many of these 

 data have been obtained relative to flight 

 problems where lower O2 and CO2 values pre- 

 vail than in submarines, they are mentioned 

 here because they constitute basic research 

 some of which is apphcable to the submarine. 

 (See Section V, 1.) 



Vision. There is evidence that O2 lack 

 and CO2 excess exert their effects somewhere 

 central of the photoreceptor systems (3). 

 While the course and shape of the dark 

 adaptation curve shows little change, anoxia 

 decreases visual sensitivity by more than 

 one-half at 13% O2 (51, 52, 85). Hyper- 

 ventilation and the blowing off of CO2 add 

 to this effect, further decreasing visual sen- 

 sitivity. Hypoglycemia hkewise increases 

 the visual threshold. The latency of nega- 

 tive after images is also increased by anoxia 

 (52). 



That impairment of visual function may 

 be cumulative and result from even mild 

 degrees of anoxia is sho%vn by recent Uni- 

 versity of Chicago studies (16) using the 

 critical fusion frequency (cff) and the dy- 

 namic visual field (dvf) test as measures of 

 performance (58). The dvf test is a con- 

 trast discrimination involving both central 

 and peripheral fields. Of 20 men passing 

 Air Corps standards exposed to low O2 (pres- 

 sure chamber) for five to six hours per day, 

 six days per week for four to six weeks, 13 

 (65%) showed visual impairment even at 

 10,000 feet (14% O2). It is of interest that 

 this impairment took several weeks to de- 

 velop, that it could be prevented by breath- 

 ing pure O2 for one hour daily, and that the 

 individuals were completely unaware of their 

 impairment. Recoveiy was delayed for sev- 

 eral weeks and subsequent re-exposure re- 

 sulted in more rapid deterioration. Tests of 

 cff for intermittent light also showed a clear 

 impairment at 10,000 feet. 



It should be emphasized that the per- 

 formance decrement on these tests was found 

 «it oxygen levels where intelhgence, deter- 



mined by the usual psychometric tests, was 

 unaffected. The insidious onset of this rel- 

 ative bhndness with the accompanying 

 minor complaints of headache, blurred vision, 

 drowsiness and lassitude, depression, rest- 

 lessness, and even euphoria could easily re- 

 sult in undetected and potentially dangerous 

 degree of incompetence. This would be 

 particularly hkely to occur when men "stuck 

 it out" without complaining. 



Consciously resolving not to "give up" and 

 ask for reUef introduces subtle changes in 

 the inter-relationship between the individual 

 and his job. He may become irritable and 

 susceptible to emotional upsets over his 

 errors (with perhaps a tendency to "cover 

 up" — although normally he would reahze 

 the possible fatal consequences of so doing). 

 Further changes correlated with his increased 

 effort could lead to inappropriate psycho- 

 physiological effects, along with a severe 

 conflict and frustration. How far such a 

 sequence might progress would be a function 

 of numerous variables including the stabihty 

 and resources of the individual; his degree of 

 fatigue and impairment; his confidence in 

 the boat, its skipper, and his mates; and his 

 evaluation of the factor of potential rehef or 

 removal. 



Hearing. The effect of anoxia on auditory 

 thresholds is similar to the effect on vision. 

 The degree of loss is a function of both dura- 

 tion of exposure and degree of anoxia (Gell- 

 hom, 46); 10% O2 for 15 to 30 minutes 

 sometimes results in a hearing deficit for 

 several hours. Similarly to its effect on 

 vision, alkalosis induced by hyperventila- 

 tion in room air also decreased auditory 

 activity. Any impairment resulting from 

 the chronic moderate-to-loud noise level of 

 submarine operation would presumably be 

 aggravated by low O2. 



Further complication, because of the inter- 

 relationship with both visual and auditory 

 functions, may well come from chronic sub- 

 acute vestibular stimulation. It is probable 

 that the "noise" or wave motion spectrum on 

 a submarine extends over a very wide range; 



