maintain and promote cell function. How this complex balance behaves when subjected to stress is a matter of great importance.
The concept of physiologic reserve often is used to connote the limits of function of a particular physiologic system when a stress is brought to bear upon that system. In such a manner, a tolerance to external stressors that are, in effect, compensated for by the physiologic reserve of the system, is observed. When a stress exceeds the capability of a particular organ system to compensate adequately, physiologic dysfunction ensues. Several factors influence the magnitude of the observed physiological derangement and include: the type of stress, the prior state of the system, and the duration of the stress interval.
Alterations in physiologic function are oftentimes not apparent until a critical level of function is compromised. The generalized, nonlinear deterioration of physiologic performance as related to cell function results in a disparity between the (physiologic) output signal and the (cellular) signal generator (Figure 19-1). Hence, strategies to measure physiologic function (reserve) during stress should be directed at assessing both global organ function and cellular reserve. By this means, information is obtained on the current status of the system and expectations concerning performance potential.
With the ultimate goal of optimization of performance during acute stress, it would be preferable to monitor cellular parameters that were causally, not associatively, related to physiologic outcome. Two advantages are derived from monitoring underlying cell function. As detailed above, early indicators of total cell function will yield information concerning organ function and will serve as an early warning system for impending failure. Additionally, the monitoring of various parameters associated with cell function affords the opportunity to design and test nutritional strategies to treat selective aspects of cell function to optimize performance.