Estimation of intravascular volume status by clinical examination and static measurements such as central venous pressure and pulmonary capillary wedge pressure do not predict fluid responsiveness. Current evidence indicates that dynamic monitoring of arterial pressure and derived indices are the most sensitive and specific means of determining fluid responsiveness, especially in mechanically ventilated patients. Several monitors that automate and embellish this approach, a few of which are noninvasive, are now commercially available and they are gradually being incorporated into intensive and perioperative care practice. This chapter reviews the physiologic underpinnings of how and why the arterial pressure waveform can be used to determine fluid responsiveness and gives an overview of the devices incorporating these principles.

Introduction

The lens consists of two morphologically distinct cell types, an unremarkable cuboidal epithelium that covers the anterior surface and concentric layers of fiber cells that account for the remainder, and vast majority, of the tissue volume (Fig. 9.1). The fiber cells are unique in the body. They have an enormous aspect ratio, being no more than a few micrometers wide but often exceeding a thousand micrometers in length. In cross-sectional profile, they appear as flattened hexagons, and their sharply angled membranes enclose a transparent cytoplasm that lacks the organelles found in typical cells. It is striking that these cells of remarkable shape and composition are derived from the more typical cells of the overlying epithelium.

In this chapter, we examine what is known (and, more often, what is not) about the process of terminal differentiation in the lens. We propose a staging system that allows one to discriminate critical periods in the maturation of a lens fiber cell. Using this system, we follow a hypothetical fiber cell through the differentiation program, from the time when it is an unspecialized epithelial cell near the lens equator to the cessation of protein synthesis that occurs when it is a mature fiber cell buried in the lens core. We include speculations on how the differentiation program might act to influence the shape and thus the optical properties of the lens as a whole. Finally, it seems evident that in some cataracts at least, the differentiation program has been interrupted or corrupted.

This chapter addresses the issue of how specific educational events are remembered, and how they influence the lives of college students and alumni. Mainstream psychological and educational researchers have rarely looked at the impact of specific college events on students. Rather, research has focused on learning and retention of course content, as assessed by exams, written assignments, standardized tests, and graduation rates. Acquiring general knowledge is seen as paramount, not remembering the specifics of how or when the knowledge was acquired. Endel Tulving (1983, p. 51), perhaps the world's leading authority on episodic memory, stated that “children and people of all ages go to school in order to learn skills and knowledges that they need for life. They do not go to school in order to acquire a storehouse of temporally dated personal memories.”

Educational psychologists are not alone in their neglect of the specific. The primary focus in educational research on general rather than episodic learning is consistent with dominant research strategies in cognitive psychology. Tulving (1983) commented that episodic memory “has received little direct attention from psychologists or other scientists” (p. 1), and that “experiments done in the past can be interpreted as episodic- rather than semantic-memory experiments … but they were not designed as part of a grand plan to understand how people remember personal experiences” (p. 129). This situation is changing. Once one accepts the idea that people's subjective experience of memory, and the belief systems associated with memory, are topics worthy of study in their own right, then research can address areas of personal experience for which controlled experimentation is not possible.