The Effect of Shear Force on Skin Viability in Patients with Type 2 Diabetes

Abstract

Background: Shear is a major risk factor in the development of diabetic foot ulcers, but its effect on the skin of patients with type 2 diabetes mellitus (DM) remains to be elucidated. The aim was to determine skin responses to shear in DM patients with and without diabetic polyneuropathy (DNP).

Methods: The forearm skin was loaded with 14.5 N shear (+2.4 kPa pressure) and with 3.5 kPa pressure for 30 minutes in 10 type 2 DM patients without DNP, 10 type 2 DM patients with DNP, and 10 healthy participants. A Sebutape collected IL-1α (measure of tissue damage). A laser Doppler flowmeter measured cutaneous blood cell flux (CBF) as a measure of the reactive hyperaemic skin response.

Findings: Reactive hyperaemia and IL-1α release was significantly increased after shear loading in all three groups and was higher compared to the responses to pressure loading. The reactive hyperaemic response after shear loading was impaired in patients with type 2 DM compared to healthy participants but did not differ between patients with and without DNP. The reactive hyperaemic response was negatively correlated with the blood glucose level but did not correlate with the DNP severity score.

Interpretation: Shear is important in the development of tissue damage, but the reparative responses to shear are impaired in patients with type 2 DM. DNP was not associated with altered skin responses, suggesting that the loss of protective sensation to sense shear to skin remains a key factor in the development of diabetic foot ulcers in patients with DNP.

Figure 1

Cutaneous blood cell flux in arbitrary units (AU) presented as mean ± SD. BM indicates baseline measurement before loading. 0, 5, 10, 15, 20, and 60 indicate the time points after loading of the skin (in minutes). (a) Cutaneous blood cell flux measurements after the application of pressure and shear. ^∗DM PNP+ vs. control (P < 0.05) at this time point. ^∗∗DM PNP- vs. control (P < 0.05) and DM PNP+ vs. control (P < 0.01). ^#Statistical significant value of P < 0.0001 in the control group, P < 0.001 in the DM PNP- group, and P < 0.01 compared to their own baseline measurements. (b) Cutaneous blood cell flux measurements after the application of pressure alone. ^∗Statistical significant value of P < 0.05 at this time point of the DM PNP+ group or the control group compared with their own baseline measurement. No statistically significant differences were measured between the groups.

Figure 2

IL-1α concentration (pg/ml) presented as median and IQR. BM indicates baseline measurement before loading. 0, 5, 10, 15, and 60 indicate the time points after loading of the skin (in minutes). (a) IL-1α concentration measurements after the application of pressure and shear. ^∗Statistical significant value of P < 0.01 in all three groups compared with their own baseline measurement. No statistically significant differences were measured between the groups. (b) IL-1α concentration measurements after the application of pressure and shear. ^∗Statistical significant value of P < 0.01 in all three groups compared with their own baseline measurement.

Figure 3

(a) IL-1α concentration directly after pressure and shear loading (time point 0). The bar indicates the median, while a dot represents the IL-1α concentration in one participant. No statistically significant differences were measured between the groups. (b) IL-1α concentration directly after pressure alone (time point 0). The bar indicates the median, while a dot represents the IL-1α concentration in one participant. No statistically significant differences were measured between the groups.

Figure 4

(a) Correlation between baseline glucose concentration in blood (mmol/l) and cutaneous blood cell flux directly after shear combined with pressure loading (time point 0) in patients with type 2 DM (-0.5, 95% CI -0.8 to –0.01, P = 0.04). Correlation was tested with the Spearman rank test. (b) Correlation between CNE score and cutaneous blood cell flux directly after shear combined with pressure loading (time point 0) in patients with a CNE score of ≥1 (0.2, 95% CI –0.4 to 0.7, P = 0.4). Correlation was tested with the Spearman rank test. (c) Correlation between IL-1α concentration (pg/ml) and cutaneous blood cell flux (AU) directly after shear combined with pressure loading (time point 0) (0.2, 95% CI -0.2 to 0.5, P = 0.4). Correlation was tested with Spearman rank test (P > 0.05). (d) Correlation between baseline glucose concentration in blood (mmol/l) and IL-1α concentration (pg/ml) directly after shear combined with pressure loading (time point 0) in patients with type 2 DM (-0.1, 95% CI -0.5 to 0.4, P = 0.6). Correlation was tested with the Spearman rank test (P > 0.05). (e) Correlation between VALK score and IL-1α concentration (pg/ml) directly after shear combined with pressure loading (time point 0) (95% CI -0.6 to 0.5, P = 0.7). Correlation was tested with the Spearman rank test (P > 0.05). Only participants with a VALK score of ≥1 were included in the analysis.