430 



PHYSIOLOGY OF STRESS 



the taking of food. It is preparatory for and 

 facilitative of better grip on objects, and is 

 more automatic, dependable, and sanitary 

 than the famihar practice of spitting on the 

 hands. The reaction is neurologically con- 

 trolled via the symipathetic system from pre- 

 motor areas of the cortex and mediated 

 peripherally at the sweat glands by acetyl- 

 choline. These observations may help ac- 

 count for the fact that the GSR is probably 

 our best expressive indicator for alertness 

 and changes in "attention" (21). This meas- 

 ure has provided particularily valuable in- 

 formation bearing on individual differences 

 in stability and the relative excitation level 

 and the rate at which a person will recover 

 following stress (22, 43, 44). 



3. Blood pressure is another frequently re- 

 corded preparatory and facilitative activity 

 (21), but it appears less closely related than 

 the GSR to higher level processes of atten- 

 tion etc., and more closely hnked with more 

 primitive activities of defense and self pres- 

 ervation. This may explain its value as an 

 index of disturbed emotion. It may account 

 for the fact that it has proved the most use- 

 ful physiological index in so called "he de- 

 tectors" in situations where an individual's 

 hfe, hberty, reputation and so forth are being 

 defended. 



4. Respiration is also easily recorded, but 

 has both the advantage and disadvantage 

 that it is partially under voluntary control. 

 It is primarily an index of the need of the 

 body, real or imagined, for increase of oxygen 

 or elimination of carbon dioxide. The in- 

 hibition of respiration or its voluntary regu- 

 lation following critical emotional stimuH, 

 and the deep sighing inspiration, indicative 

 of respiratory debt when the crucial point 

 has passed, may betray unwary subjects of 

 such tests. 



5. Oxygenation of the blood recorded photo- 

 electrically from the ear by an "oximeter" 

 has proved of value in the study of stress, 

 particularly of the kind encountered under 

 conditions of flight (102). 



6. Vasomotor changes recorded in the ex- 

 tremities or elsewhere by volumetric (ple- 

 thysmographic), photoelectric (62), or ther- 

 moelectric methods provide information 

 regarding control of the peripheral vascular 

 bed, metabohc and autonomic (sympathetic) 

 reaction to stimulation. 



7. Heart rate, particularly when combined 

 with a record of blood pressure, may provide 

 valuable clues as to shifts in activity of the 

 autonomic system. Sympathetic excitation 

 will tend to increase it, often in association 

 with a rise in blood pressure. A rise in blood 

 pressure, via effects on carotid sinus and 

 aortic pressure receptors, on the other hand, 

 tends to slow it. Accordingly changes in 

 heart rate, taken by themselves, may be mis- 

 leading (23). Sinus arhythmia (101) at- 

 tributable to inhibition of vagal impulses to 

 the heart during inspiration may provide 

 some indication of the amount of the unin- 

 hibited parasympathetic tone. 



8. Blood sugar, as pointed out by Cannon 

 (12) may provide valuable information re- 

 garding mobilization of the sympathico- 

 adrenal system. More recently Gellhom 

 and collaborators (52) have demonstrated 

 that the vago-insuhn system also participates 

 in response to excitation, its activity being 

 overshadowed by the sympathetic in strong 

 excitation, but its effects being experimen- 

 tally demonstrable. Its effects often persist 

 following the recession of the sympathetic 

 phase. The latter observation may help ex- 

 plain many exaggerations of parasympathetic 

 activity, effects on the gastro-intestinal sys- 

 tem, etc., which tend to follow emotional 

 reactions, which, in their initial phase, ob- 

 viously involve sympathico-adrenal mech- 

 anisms. 



9. Metabolism, either basal or relative, 

 may be measured by respiratory methods 

 recording gaseous exchange (6, 31). It may 

 be measured in the brain by arteriovenous 

 differences in composition of the blood (63). 

 It may be indicated less exactly by one of its 

 peripheral manifestations, the total insensible 



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