Justin Jagger | PubMed Health

PubMed2005

The microcirculation as a functional system.

This review examines experimental evidence that the microvascular dysfunction that occurs early in sepsis is the critical first stage in tissue hypoxia and organ failure. A functional microvasculature maintains tissue oxygenation despite limitations on oxygen delivery from blood to tissue imposed by diffusion; the density of perfused (functional) capillaries is high enough to ensure appropriate diffusion distances, and arterioles regulate the distribution of oxygen within the organ precisely to where it is needed. Key components of this regulatory system are the endothelium, which communicates and integrates signals along the microvascular network, and the erythrocytes, which directly monitor and regulate oxygen delivery. During hypovolemic shock, a functional microvasculature responds to diminish the impact of a decrease in oxygen supply on tissue perfusion. However, within hours of the onset of sepsis, a dysfunctional microcirculation is, due to a loss of functional capillary density and impaired regulation of oxygen delivery, unable to maintain capillary oxygen saturation levels and prevent the rapid onset of tissue hypoxia despite adequate oxygen supply to the organ. The mechanism(s) responsible for this dysfunctional microvasculature must be understood in order to develop appropriate management strategies for sepsis.

Animals↗

PubMed2002

Flow field measurements in the cell culture unit.

The cell culture unit (CCU) is being designed to support cell growth for long-duration life science experiments on the International Space Station (ISS). The CCU is a perfused loop system that provides a fluid environment for controlled cell growth experiments within cell specimen chambers (CSCs), and is intended to accommodate diverse cell specimen types. Many of the functional requirements depend on the fluid flow field within the CSC (e.g., feeding and gas management). A design goal of the CCU is to match, within experimental limits, all environmental conditions, other than the effects of gravity on the cells, whether the hardware is in microgravity ( micro g), normal Earth gravity, or up to 2g on the ISS centrifuge. In order to achieve this goal, two steps are being taken. The first step is to characterize the environmental conditions of current 1g cell biology experiments being performed in laboratories using ground-based hardware. The second step is to ensure that the design of the CCU allows the fluid flow conditions found in 1g to be replicated from microgravity up to 2g. The techniques that are being used to take these steps include flow visualization, particle image velocimetry (PIV), and computational fluid dynamics (CFD). Flow visualization using the injection of dye has been used to gain a global perspective of the characteristics of the CSC flow field. To characterize laboratory cell culture conditions, PIV is being used to determine the flow field parameters of cell suspension cultures grown in Erlenmeyer flasks on orbital shakers. These measured parameters will be compared to PIV measurements in the CSCs to ensure that the flow field that cells encounter in CSCs is within the bounds determined for typical laboratory experiments. Using CFD, a detailed simulation is being developed to predict the flow field within the CSC for a wide variety of flow conditions, including microgravity environments. Results from all these measurements and analyses of the CSC flow environment are presented and discussed. The final configuration of the CSC employs magnetic stir bars with angled paddles to achieve the necessary flow requirements within the CSC.

Bioreactors↗