In 1987, Fitzpatrick expressed concern that gerontologica! nurses had engaged in "theory shopping" (p. 8) by explaining older adults' behavior in terms of theories from disciplines other than nursing. Instead, Fitzpatrick (1987) suggested that "nursing models should be used to develop a practice approach" (p. 9) for gerontological nursing.
There are reasons to reconsider Fitzpatrick's (1987) assertion. Nursing conceptual models are not purely "nursing" in origin; nursing theorists have borrowed ideas from other disciplines. Therefore, it cannot be claimed that such models are the only appropriate frameworks for practice. It is vital that practitioners use a variety of theories to undergird practice (Koziol-McLain & Maeve, 1993; Visintainer, 1986). Therefore, gerontological nurses may gain valuable insight from general theories that are applicable to aging.
Non-equilibrium systems theory (NEST) is a general theory that is very relevant to aging. However, it has received little attention in the gerontological nursing literature. In this article, NEST is described and compared to life-span developmental theory. The use of NEST by several nursing theorists is explored briefly. Three concepts of aging related to NEST are explained and used to undergird implications for gerontological nursing practice.
NON-EQUIUBRIUM SYSTEMS THEORY: AN OVERVIEW
The theory of non-equilibrium systems was Prigogine's (1980) solution to the paradox of two opposing tendencies of living open systems (LOS): (a) increasing chaos or disorder and (b) increasing organization or order. According to the second law of thermodynamics, closed systems evolve toward a state of equilibrium in which there is maximum disorder, or entropy. Prigogine (1967; 1980) and his colleagues determined that the equilibrium thermodynamics of closed systems could not be applied completely to LOS. Unlike a closed system, which hovers near equilibrium, the LOS exchanges matter and energy with the environment. While certain chemical reactions within the LOS are "close to equilibrium" (Prigogine & Stengers, 1984, p. 156), the LOS itself is viewed as existing far-from-equilibrium (Nicolis & Prigogine, 1989; Prigogine & Stengers, 1984; Prigogine, 1980).
A dosed system evolves toward disorder. However, the LOS evolves toward increasingly complex behavior (Nicolis & Prigogine, 1989) through irreversible processes (those that depend upon Ine direction of time). It is only through these irreversible processes that entropy (disorder) can be produced; entropy also is exchanged between the system and the environment. Over time, there is a greater tendency toward disorder in living open systems (Schroots, 1988; Yates, 1988). The eventual occurrence is not a steady state but a "stationary state [that] may be equivalent to senile death" (Hershey & Wang, 1980, p. 61).
According to NEST, randomness and instability are implied in the irreversible evolution of the LOS (Prigogine & Stengers, 1984). The organization of the LOS may be shattered by energy fluctuations during systemenvironment interaction. At this bifurcation point (Prigogine, 1980), the nature of the fluctuation "playfs] an essential role and determinefs] the branch' that the system will follow" (Prigogine, 1980, p. 106), and the system moves either toward chaos or toward greater complexity (Schroots, 1988).
It is through self-organization processes that the system moves toward greater complexity. Through selforganization processes, "new types of structures originate spontaneously" (Prigogine & Stengers, 1984, p. 12). On a macroscopic scale, selforganization phenomena appear as "spatial patterns or temporal rhythms" (Nicolis & Prigogine, 1989, p. 8). The new structure, pattern, or form (termed a dissipative structure) is more differentiated and complex (Schroots, 1988) than the system's previous regime (Hershey & Wang, 1980). The more complex the dissipative structure, the more energy the system must dissipate in order to maintain its complexity. Through selforganization processes, order can emerge spontaneously from disorder (Prigogine & Stengers, 1984).
NEST is a general theory that scholars have used to understand aging (cf. Yates, 1988). For instance, Schroots (1988) used a branching tree to diagram the formative change of a human being from conception to death; the tree metaphor was based upon Prigogine's (1980) concept of bifurcation point. From this perspective, Schroots (1988) defined aging as a process of formative change or a series of transformations toward increasing disorder and order in form, pattern, or structure; this definition is used throughout this work.
NEST AND DEVELOPMENIAL THEORIES: A COMtWRlSON
It is useful to contrast NEST with theories of human development. A major tenet of life-span developmental theory is that personal and biocultural change are linked within a contextual, interactive framework (Baltes, 1982). Persons are considered products of their contexts, who also affect their own development by altering their contexts (Lerner, 1986). The adult is understood as possessing an "increasing ability to purposefully transform the current context with all of its problems and contradictions into energy for development" (Reed, 1983, p. 19).
There are several basic differences between life-span developmental theory and NEST. Life-span theory is based upon the notion that there is limitless energy available for development (Lerner, 1986). Developmental theories "do not take into account biological decline ... in the OJd old'" (Archbold, 1981, p. 411). With its focus on phases of the organism's development (Reed, 1983; 1991), lifespan developmental theory is not a meaningful explanation for death. In contrast, NEST theorists focus upon the production of entropy through the system's internal processes and the entropy flux due to exchange of matter and energy with the environment (Nicolis & Prigogine, 1989). Based on this perspective, Schroots (1988) proposed that there are a finite number of energy transformations in concert with a finite lifespan; the energy available for selforganization is eventually exhausted.
In life-span developmental theory, development is viewed as the trading away of less-developed patterns for more highly developed patterns (Reed, 1983; 1991). No qualitative inference is to be drawn from the higherlower designation (Reed, 1983; 1991). However, when there is "a failure to trade away outdated patterns for new" developmental progress may be compromised (Reed, 1991, p. 69). Thus, one inference of life-span developmental theory is that of life-long developmental progress.
The notion of developmental progress is not consistent with NEST. Rather than viewing aging as a process of continued order, NEST theorists have understood it as a process in which order emerges from disorder. Schroots (1988) noted that NEST is the only theory that can be an explanation for both "disorderly formative change over the individual's Ufespan [and] orderly change" (p. 318). So, in contrast to developmental theory, NEST is a springboard for dialogue about death as well as life and decrement as well as development.
NURSING THEORISTS' USE OF CONCEPTS RELEVANT TO NEST
Several conceptual models of nursing are linked closely to NEST. Newman (1986; 1987) used NEST as one basis for her theories about aging; specifically, she emphasized the selforganizing tendency of living systems as they move toward increasing complexity (1987). Rogers' (1970) emphasis on the "increasing order, complexity, and heterogeneity" (p. 51) of living systems is particularly consistent with NEST.
However, it is not clear that Newman and Rogers addressed the inconsistencies between NEST and developmental theory. In addition to NEST, Newman (1987) employed Bentov's (1977) idea that life evolves toward higher consciousness levels; this has been considered a developmental theory (Reed, 1983). Rogers (1985) also used developmental ideas. While the aging of a closed system was "a running down" (Rogers, 1985, p. 21), aging was understood according to the science of unitary human beings as "a developmental process [that is] continuous from conception through the dying process" (p. 21).
Further study is needed of the similarities and distinctions between NEST and developmental models; Fitzpatrick (1987) noted that gerontological nurses must evaluate theories from other disciplines for "logical inconsistencies" (p. 8). Fawcett (1989) noted that when "borrowed theories are linked with conceptual models, care must be taken to ensure logical congruence" (p. 28). Therefore, theorists and practitioners must consider the implications of using both NEST and developmental theories in one conceptual model or in one middlerange theory.
CONCEPTS OF AGING THAT ARE CONSISTENT WITH NEST
Several scholars have proposed that the concepts of self -organization (or self-regulation, cf. Schroots, 1988), individuation, and aged heterogeneity are particularly relevant to aging; these concepts are consistent with NEST (Dannefer, 1988; Reker & Wong, 1988; Schroots, 1988; Yates, 1988). Because NEST is grounded in physics and biology, the three concepts are explained by demonstrating how older adults use central cognitive and neural capacities to regulate perceived deterioration in motor performance. In these explanations, motor performance research is integrated with results of a phenomenological investigation of older widows' experience of living alone at home (Porter, 1994).
Schroots (1988) described selforganization (or self-regulation) as the most fundamental concept of aging; it is the basic concept of NEST. Although there may be increasing disorganization of the system with aging, self-organization processes, or attempts to bring about order, occur in the presence of this disorganization (Schroots, 1988).
A basic feature of motor performance in old age is slow and hesitant movement (Welford, 1977), which is due in part to a lowered signal-tonoise ratio in the central nervous system. Neural signals tend to decrease with aging, and they have to compete with a "background of random neural activity" (Welford, 1982, p. 163) that tends to increase over time. "The clarity and effectiveness of signals depends on the ratio between the signaling impulses and the random activity" (Welford, 1982, p. 163).
Although inaccurate motor performance can be an outcome of a lowered signal-to-noise ratio, older persons can trade speed for accuracy (Pew, 1969). As well as learning "to monitor and select their own speedaccuracy trade-offs" (Rabbitt, 1981, p. 174), older persons can change their motor performance through organizational maneuvers of the neuromuscular system. In effect, older persons can make an action simpler or more "neuroeconomically efficient" (Stelmach & Hughes, 1983, p. 86).
Thus, through self-organization processes, older persons can compensate for inaccurate motor performance. Self-organization processes involve cognitive and neuromuscular attention to the efficient performance of automatic behaviors. Those behaviors resulting from such self-organization processes can be understood as dissipative structures that are reflective of the older person's increasing complexity. Maintaining these behaviors over time would require a considerable expenditure of energy.
Individuation is the increasingly unique behavioral pattern resulting from a finite series of behavioral transformations (Schroots, 1988). At countless bifurcation points, new dissipative structures are generated; the unique configuration of the branching leads to increasing complexity of individual behavior.
Individuation can be understood in relation to motor performance. The complexity of a particular motor response is a factor affecting the degree to which that motor response is slowed (Welford, 1977). Any decline in central capacities with aging first affects performance of complex tasks, which involve "choices between potentially confusing alternatives . . . [and] make greater demands on central capacities" (Welford, 1985, p. 353). The history of one's experience with a task may be a key factor in the perception of task complexity. In fact, one's experience with a given task may be as critical as its actual demands in determining its difficulty (Kinsbourne, 1981). Thus, the perception of task complexity is a uniquely personal matter that may depend, in part, on one's experience with a certain task.
Individuation is exemplified in each older person's claim to expertise in a unique set of tasks requiring motor skills. Through a phenomenological study of older widows' experience of living alone at home (Porter, 1994), it was found that the seven participants were experts in very different tasks. While climbing a tall ladder to wash windows was "no problem" for one woman, baking elaborate pastries was "a snap" for another woman. Both women had spent years honing their respective skills. Neither woman claimed skill in the other's forte; nor did she indicate a desire to begin cultivating such skill.
By experiencing unique behavioral transformations, a person becomes less like other persons; as persons grow older, these inter-individual differences become more apparent (Dannefer, 1988). Maddox and Douglas (1974) found that when inter-individual differences in physical, social, and psychological characteristics were compared, older persons were more diverse than persons of other age groups.
Aged heterogeneity had been considered a simple expression of individuality (Maddox & Douglas, 1974), but Dannefer (1988) found that the social environment precipitated variation among persons as they aged. Because a person's actions can be viewed as "realizations of what the environment affords the [person]" (Reed, 1982, p. 101), variability in environments may be a factor contributing to the heterogeneity of aged persons on physiologic as well as social parameters. This conclusion is supported by the following review of research pertaining to aging adults' stability and postural control.
Recovery of stability is hampered in older adults by an age-attendant loss of equilibrium (known as presbystasis) (Krmpotic-Nemanic, 1969) and by various changes in the nervous and sensory systems (Ochs, Newberry, Lenhardt, & Harkins, 1985). To determine whether the stability and postural control of older women could be improved through exercise, a random sample of 50 older women was selected from persons residing in two apartment buildings; one building was the control site and the other was the exercise site (Lichtenstein, Shields, Shiavi, & Burger, 1989).
While there were no differences between the groups on pre-test measures of stability, there were significant post-test differences; the exercise group improved on several measures of stability. Also, persons identified as "high compilers" improved more than those identified as "low compilers" (Lichtenstein et al., 1989, p. 142).
The post-test diversity between control and experimental subjects and among experimental subjects of various compliance levels is illustrative of the concept of aged heterogeneity. The circumstances afforded by older persons' unique environments are factors that influence the heterogeneity of older persons.
Linkages Among the Three Concepts of Aging
It is proposed that the concepts of self-organization, individuation, and aged heterogeneity are linked sequentially. Self-organization is the umbrella concept upon which individuation is based; in turn, the concept of aged heterogeneity is grounded in individuation. Self-organization processes result in increasingly singular perceptions and behavior patterns. As an older person becomes more unique or individuated, she or he becomes increasingly different from other older persons.
Non-equilibrium systems theory has been proposed as one possible template for understanding the selforganization processes of older persons. If NEST is used as a framework for gerontological nursing practice, then self-organization processes are appropriate foci for practice.
In nursing practice based on NEST, one critical goal is that of trying to understand older persons' behaviors as outcomes of self-organization processes (as attempts to bring order out of disorder). To recognize a selforganization process, the nurse must be able to differentiate order from disorder in the context of an older adult's very unique situation. Making this distinction may be problematic because order and disorder are ambiguous concepts that flow into each other Prigogine & Stengers, 1984).
To achieve an understanding of an older person's self-organization processes, gerontological nurses may use strategies from a phenomenological research method based upon Husserl's (1913/1962) philosophy (cf. Porter, 1994). The central focus is the older adult's lived experience. An attempt is made to understand the person's intention or what the person "seeks to do with his world" (Kohak, 1978, p. 110). If older persons are experiencing disorder and trying to bring order out of disorder, they will reveal this to the nurse through their words and actions.
During a phenomenological study (Porter, 1994), seven widows, who ranged from 75 to 83 years of age and lived alone in their own homes, described the changes that they had perceived in their balance, strength, stamina, and memory. They had noticed these changes especially during the preceding 10 years. Over time, they had been "detecting deterioration." It is conjectured that other older persons have similar experiences.
It is important for nurses to explore older persons' perceptions of deterioration and its influences upon their actions. Due to perceived deterioration, the seven older widows (Porter, 1994) had implemented various behavioral changes that can be understood as self -organization processes. They planned new ways to carry out household, self-care, and home maintenance tasks. For instance, when one woman found it "too hard" to push a conventional lawn-mower, she bought a selfpropelled mower. When another woman believed that she "was not with it enough" during the night to walk safely downstairs to the bathroom, she brought a "slop jar" to her upstairs bedroom. Another woman, who moved about with her four-legged cane, contrived a careful scheme to avoid tripping over an extension cord that was taped to her carpet. Thus, against a background of perceived disorder, the women had implemented self-organization processes; they sought to bring order out of disorder.
As aging continues, each older person becomes increasingly individuated. Because the most important influence upon an older person's behavior is the person's own past (Birren, 1960; Schroots, 1988; Waddington, 1966), the personal history may be a critical influence upon a specific self-organization process through which a dissipative structure emerges. This new behavior is linked to the person's previous behaviors through an increasingly individuated pattern of bifurcations. Thus, the woman who began using a "slop jar" explained this choice by relating that "we grew up with the same thing. At night, we'd have a potty under the bed. I grew up with that. So, it doesn't bother me a bit." This woman had a uniquely personal and historical point of reference around which she developed a new self-organization process.
As they engaged in self-organization processes, the seven older widows learned much from their successes and difficulties. They shared this information readily (Porter, 1994). It is recommended that nurses access the practical knowledge that older persons possess about such matters. By talking with older persons about their perceptions of disorder and the actions they take to bring order out of disorder, nurses can reinforce older persons' efforts to create unique behaviors that "work" in their own singular environments. Nurses can also use this practical knowledge to support the selforganization activities of other older clients.
Older persons may struggle with a crisis that has precipitated the need to initiate new self-organization processes. In such situations, there are two critical parameters of quality care. The nurse must be able: (a) to identify these situations as crucial bifurcation points in which the older person can move toward, chaos or toward greater complexity and (b) to act in support of self-organization processes that will enable movement toward greater complexity.
Although these parameters were derived from principles of NEST, their importance is underscored in a story that was shared by an older widow.
Several weeks earlier, she had climbed a ladder to clean the eaves. Having finished the job, she was coming down the ladder when she missed the last step and sprained her ankle. When she went to the emergency room, she was outraged when the "head nurse" told her never to climb a ladder again. The nurse did not ask the woman why she had climbed the ladder; so, she intervened without knowledge that was central to the woman's very existence.
The woman had "a deal" with her children that she could continue living alone at home as long as she "could take care of it." She believed that her caretaking tasks included cleaning the eaves; cleaning the eaves meant climbing a ladder. She climbed the ladder so that she could live in her own home. Although she planned to continue climbing the ladder, she intended to initiate new selforganization processes. She planned to think more about her movements while on the ladder, to "stop pushing," and to "take my time" (Porter, 1991/1992).
As older persons try to bring order from disorder, they do so in ways that are uniquely their own. Before nurses give advice based on their own experiences or ideas, they must ask older adults to describe their specific situations, their perceptions of disorder, and their plans for bringing order out of disorder. Counseling and suggestions can be designed in accord with the older person's intentions toward self-organization and in keeping with the concepts of individuation and aged heterogeneity. For instance, educational sessions for a group of older persons on the topic of home safety can be supplemented with individualized assessments and interventions.
The practice implications described here are focused upon older adults who are able to intentionally undertake self-organization processes. While NEST is applicable to older persons with more serious deficits in central cognitive, sensory, and neural capacities, discussion of these applications is beyond the scope of this article.
In conclusion, it is suggested that gerontological nurses consider encounters with older adults as opportunities to recognize and to support their self-organization processes. Gerontological nurses are encouraged to investigate the unique ways in which older persons bring order out of disorder, to describe these processes in terms of each person's uniqueness, and to use this knowledge in providing creative nursing care.
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