Activation of peripheral nerve fibers by electrical stimulation in the sole of the foot

BMC Neuroscience

Table 1 Electrical and geometric parameters in the model

	Electrical properties		Source	Thickness (mm)				Source
				Location (sole/rest of foot)
Tissue					Heel	Arch	Forefoot
Bone	ϵ_r	10,000	[23]	Sole & rest	10	10	10
marrow	σ (S/m)	0.09
Cortical	ϵ_r	3,000	[23]	Sole & rest	6	6	6	[15]
bone	σ (S/m)	0.02
Muscle	ϵ_r	1.5×10⁶	[24]	Rest	3	3	3	[25]
	σ (S/m)	0.5		Sole	0	2	0	US ^*
Fat	ϵ_r	10,000	[24]	Rest	4	4	4	[16]
	σ (S/m)	0.025		Sole	9.7	5.3	6.1	US
Dermis	ϵ_r – r	1.26×10⁶	[22]	Rest	1.3	1.3	1.3	[16]
	ϵ_r – z	4.01×10⁵		Rest	1.3	1.3	1.3	[16]
	σ (S/m) - r	2.57		Sole	5.1	4.3	4.6	US-SB ^**
	σ (S/m) - z	1.62		Sole	5.1	4.3	4.6	US-SB ^**
Vital	ϵ_r - r	2.71×10⁵	[22]	Rest	0.042	0.042	0.042	SB
epidermis	ϵ_r - z	7.30×10⁴		Rest	0.042	0.042	0.042	SB
	σ (S/m) - r	0.95		Sole	0.213	0.094	0.107	SB
	σ (S/m) - z	0.15		Sole	0.213	0.094	0.107	SB
Stratum	ϵ_r	1,500	[21]	Rest	0.033	0.033	0.033	SB
corneum	σ (S/m)	5×10^-4		Sole	0.748	0.161	0.253	SB

The relative permittivity (ϵ_r) and conductivity (σ) were adopted from literature. The geometry values for the sole of the foot were determined from ultrasound (US) scans and the skin biopsies (SB) used for the Na_v1.7 immunochemistry. Since the US scans provided only a bulk measure for the entire skin, and the SB provided only an estimate of the thickness of the stratum corneum and vital epidermis (*), the thickness of the dermis was calculated as the thickness of the entire skin subtracted the thickness of the entire epidermis (**, Stratum corneum + Vital epidermis).

ISSN: 1471-2202