The microcirculation as a functional system - PubMed (original) (raw)

Review

. 2005;9 Suppl 4(Suppl 4):S3-8.

doi: 10.1186/cc3751. Epub 2005 Aug 25.

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Review

The microcirculation as a functional system

Christopher G Ellis et al. Crit Care. 2005.

Abstract

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.

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Figures

Figure 1

Figure 1

Oxygen saturation of red blood cells at the venous end of normally perfused capillaries versus the percentage of capillaries with stopped-flow (%CDstop) in extensor digitorum longus muscle in rat. No relationships existed in the sham animals between these parameters. In animals that underwent a 24-hour peritonitis model of sepsis (cecal ligation and perforation [CLP]), there was a decrease in oxygen saturation with increasing %CDstop (linear regression: y = 98.8 - 1.8x; r2 = 0.64; P < 0.05). Reproduced with permission [47].

Figure 2

Figure 2

Functional images of the same capillary bed in the extensor digitorum longus muscle of the rat at 2.5 and 3.5 hours after induction of a peritonitis model of sepsis (cecal ligation and perforation [CLP]). The functional images were generated from captured video sequences (30 seconds) and show those capillaries through which red blood cells were flowing. At 2.5 hours after CLP, most capillaries in the field of view are perfused. One hour later, individual capillary segments from within the capillary network no longer have red blood cell flow, indicating the rapid progression of the remote injury to the microvasculature of this muscle. The procedure used for generating functional (variance) images was described by Japee et al. [70].

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