6 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



respect to rate and temperature warrants the further investigation of their poten- 

 tiahty in hypothermia. 



A very important reason for considering the treppe state is that recent studies 

 have shown that it depends upon events occiu'ring coincident with the brief period 

 of activation of the heart. 



The treppe studies of Twente were based on observations (Brow-n, unpubHshed) 

 on the manner in which high pressure increases the isometric tension of the auricu- 

 lar muscle of the turtle. Here it was shown that the greater tension developed under 

 pressure was produced only if the muscle was under compression during the latent 

 period and the initial one-tenth of the contraction phase. Pressure applied at the end 

 of this period and sustained throughout the contraction did not increase the tension. 

 Since the pressure-efifective period coincides approximately with the QRS com- 

 plex of the action potential, it seems clear that some process restricted to this period 

 is augmented by pressure. 



Recently Twente demonstrated that at 20° C. pressure increased twitch tension 

 to the greatest extent (100%) in a non-beating auricular strip capable of treppe. 

 If the maximum treppe tension is allowed to develop by stimulation at the optimum 

 rate, pressure has only a slight effect (10%). When the treppe condition is elimi- 

 nated by treatment with /i strophanthin the tension is not altered by pressures up 

 to 10,000 psi. 



The conclusion to be drawn from the foregoing is that pressure increases the ten- 

 sion by eliminating the treppe condition. Since the pressure-effective period coincides 

 with the QRS complex of the action potential, it follows that treppe also depends 

 on events restricted to this period. Further, since /5 strophanthin eliminates both 

 treppe and the action of pressure, it may be concluded that the action of this agent 

 is also on events restricted to this period in the cycle. 



On the basis of the pressvire data on tension in striated muscle it was proposed 

 earlier (1941) that stimulation induces an alpha process which reaches a maximum 

 within the first one-tenth of the contraction cycle and then diminishes. The change 

 in state set up by the alpha process then causes activation of the actomyosin and the 

 development of the active state. It was considered that under pressure the alpha 

 process was increased and therefore a larger tension developed. 



On the basis of the heart studies it may be concluded that the above explanation 

 is applicable to this tissue and that the alpha process reaches a maximum within the 

 QRS interval of the action potential. In terms of the preceding, it would be con- 

 cluded that pressure and /i strophanthin acted on the alpha process, increasing its 

 magnitude, while the treppe condition would depend on a decrease in this process. 



According to the proposal of Hill (1949), the tension developed in the isometric 

 twitch is determined by the duration of the "active state." Clearly pressure does not 

 directly affect the rate of de-activation since compression applied at the end of the 

 alpha process and maintained throughout the remainder of the contraction cycle fails 

 to increase the tension. From this it may be concluded that the magnitude of the 

 alpha process determines the duration of the active state and that pressure, treppe 

 and /5 strophanthin, by modifying this process, influence the development of tension. 



The coincidence of the alpha process and depolarization of the muscle suggest that 

 an increase in the alpha process may represent a longer persistence of the state of 



