Cutaneous vascular and sudomotor responses in human skin grafts

Abstract

Each year millions of individuals sustain burns. Within the US 40,000-70,000 individuals are hospitalized for burn-related injuries, some of which are quite severe, requiring skin grafting. The grafting procedure disrupts neural and vascular connections between the host site and the graft, both of which are necessary for that region of skin to contribute to temperature regulation. With the use of relatively modern techniques such as laser-Doppler flowmetry and intradermal microdialysis, a wealth of information has become available regarding the consequences of skin grafting on heat dissipation and heat conservation mechanisms. The prevailing data suggest that cutaneous vasodilator capacity to an indirect heat stress (i.e., heating the individual but not the evaluated graft area) and a local heating stimulus (i.e., directly heating the graft area) is impaired in grafted skin. These impairments persist for ≥4 yr following the grafting procedures and are perhaps permanent. The capacity for grafted skin to vasodilate to an endothelial-dependent vasodilator is likewise impaired, whereas its capacity to vasodilate to an endothelial-independent vasodilator is generally preserved. Sweating responsiveness is minimal to nonexistent in grafted skin to both a whole body heat stress and local administration of the primary neurotransmitter responsible for stimulating sweat glands (i.e., acetylcholine). Likewise, there is no evidence that this absence of sweat gland responsiveness improves as the graft matures. In contrast to the heating stimuli, cutaneous vasoconstrictor responses to both indirect whole body cooling (i.e., exposing the individual to a cold stress but not at the evaluated graft area) and direct local cooling (i.e., directly cooling the graft area) are preserved in grafted skin as early as 5-9 mo postgrafting. If uninjured skin does not compensate for impaired heat dissipation of grafted skin, individuals having skin grafts encompassing significant fractions of their body surface area will be at a greater risk for a hyperthermic-related injury. Conversely, the prevailing data suggest that such individuals will not be at a greater risk of hypothermia upon exposure to cold environmental conditions.

Fig. 1.

Laser-Doppler scanner images (left: photo image; right: flow images) from a representative subject during normothermia and indirect whole body heating at a grafted and adjacent control site. The black line in the middle of the photo image is the border between uninjured and grafted skin. Progressively higher skin blood flows were observed at the uninjured site during the heat stress (expressed in green, yellow, and red) compared with much lower skin blood flows in grafted skin (depicted in shades of blue). Figure modified, with permission, from Davis et al. (16).

Fig. 2.

Increases in cutaneous vascular conductance (ΔCVC) from normothermic baseline during indirect whole body heating in grafted (graft) and adjacent noninjured (control) skin in the indicated groups. Values are expressed as means ± SE. Significant main effect for skin site demonstrates attenuated vasodilator responses to indirect whole body heating at the grafted sites regardless of the duration postsurgery (P < 0.001). Figure reprinted from Davis et al. (17) with permission.

Fig. 3.

Decreases in ΔCVC from normothermic baseline during whole body cooling from grafted (graft) and adjacent noninjured (control) skin in the indicated groups. Values are expressed as means ± SE. Figure reprinted from Davis et al. (17) with permission.

Fig. 4.

Increases in CVC during local heating in grafted (graft) and adjacent noninjured (control) skin in the indicated groups. Values are expressed as means ± SE. Significant main effect for skin site demonstrates attenuated vasodilator responses to local heating at the grafted sites regardless of the duration postsurgery (P < 0.001). Figure reprinted from Davis et al. (17) with permission.

Fig. 5.

Top: illustration of the placement of the microdialysis probes in uninjured and grafted skin as well as a schematic of the principle of intradermal microdialysis. Substances in the perfusate diffuse through the semipermeable portion of the probe and exert an effect in the surrounding tissue. Bottom: cutaneous vascular responses, expressed as CVC, to the indicated doses of acetylcholine (Ach) administered via intradermal microdialysis in the 5- to 9-mo postgraft group. Values are expressed as means ± SE. From these data the effective concentration causing 50% of the maximal response and the maximal responses are calculated. Bottom part of figure reprinted from Davis et al. (16) with permission.

Fig. 6.

Changes in sweat rate (ΔSR) from normothermic baseline during whole body heating from grafted (graft) and adjacent noninjured (control) skin in the indicated groups. Values are expressed as means ± SE. Significant main effect for skin site demonstrates attenuated sweating responses to whole body heating at the grafted sites regardless of the duration postsurgery (P < 0.001). Figure reprinted from Davis et al. (17) with permission.