Symbols and Units
| αh, αm, αn | transfer rate coefficients (Hodgkin-Huxley model) |
| βh, βm, βn | - " - |
| δs, δv | two-dimensional [m-2] and three-dimensional [m-3] Dirac delta functions |
| ε | permittivity [F/m] |
| E | electromotive force (emf) [V] |
| Θ | conduction velocity (of wave) [m/s] |
| λ | membrane length constant [cm] (~ √(rm/ri) = √(Rma/2ρi)) |
| µ | magnetic permeability of the medium [H/m = Vs/Am] |
| µ, µ0 | electrochemical potential of the ion in general and in the reference state [J/mol] |
| ν | nodal width [µm] |
| ρ | resistivity [Ωm], charge density [C/m3] |
| ρib, ρob | intracellular and interstitial bidomain resistivities [kΩ·cm] |
| ρmb | bidomain membrane resistivity [kΩ·cm] |
| ρtb | bidomain total tme impedance [kΩ·cm] |
| ρi, ρo | intracellular and interstitial resistivities [kΩ·cm] |
| σ | conductivity [S/m] |
| σib, σib | intracellular and interstitial bidomain conductivities [mS/cm] |
| σi, σo | intracellular and interstitial conductivities [mS/cm] |
| τ | membrane time constant [ms] (= rmcm in one-dimensional problem, = RmCm in two-dimensional problem) |
| φ, θ | longitude (azimuth), colatitude, in spherical polar coordinates |
| Φ | potential [V] |
| Φi, Φo | potential inside and outside the membrane [mV] |
| ΦLE | reciprocal electric scalar potential field of electric lead due to unit reciprocal current [V/A] |
| ΦLM | reciprocal magnetic scalar potential field of magnetic lead due to reciprocal current of unit time derivative [Vs/A] |
| Φ, Ψ | two scalar functions (in Green's theorem) |
| χ | surface to volume ratio of a cell [1/cm] |
| ω | radial frequency [rad] (= 2πf ) |
| Ω | solid angle [sr (steradian) = m2/m2] |
| a | radius [m], fiber radius [µm] |
 | unit vector |
| A | azimuth angle in spherical coordinates [ ° ] |
| A | cross-sectional area [m²] |
 | magnetic vector potential [Wb/m = Vs/m] |
 | magnetic induction (magnetic field density) [Wb/m2 = Vs/m2] |
| LM | reciprocal magnetic induction of a magnetic lead due to reciprocal current of unit time derivative [Wb·s/Am2 = Vs2/Am2] |
| c | particle concentration [mol/m3] |
 | lead vector |
| ci,co | intracellular and extracellular ion concentrations (monovalent ion) [mol/m3] |
| ck | ion concentration of the kth permeable ion [mol/m3] |
| cm | membrane capacitance per unit length [µF/cm fiber length] |
| C | electric charge [C (Coulomb) = As] |
| Cm | membrane capacitance per unit area (specific capacitance) [µF/cm²] |
| d | double layer thickness, diameter [µm] |
| di,do | fiber internal and external myelin diameters [µm] |
d | outward surface normal |
| D | Fick's constant (diffusion constant) [cm2/s = cm3/(cm·s)] |
| D | electric displacement [C/m2] |
| E | elevation angle in spherical coordinates [ ° ] |
 | electric field [V/m] |
| LE | reciprocal electric field of electric lead due to unit reciprocal current [V/Am] |
| LM | reciprocal electric field of magnetic lead due to reciprocal current of unit time derivative [Vs/Am] |
| F | Faraday's constant [9.649·104 C/mol] |
| F | magnetic flux [Wb = Vs] |
| gK, gNa, gL | membrane conductances per unit length for potassium, sodium, and chloride (leakage) [mS/cm fiber length] |
| GK, GNa, GL | membrane conductances per unit area for potassium, sodium, and chloride (leakage) [mS/cm2] |
| GK max, GNa max | maximum values of potassium and sodium conductances per unit area [mS/cm2] |
| Gm | membrane conductance per unit area [mS/cm2] |
| h | distance (height) [m] |
| h | membrane thickness [µm] |
| h, m, n | gating variables (Hodgkin-Huxley model) |
| Hct | hematocrit [%] |
 | magnetic field [A/m] |
| LM | reciprocal magnetic field of a magnetic lead due to reciprocal current of unit time derivative [s/m] |
| im | membrane current per unit length [µA/cm fiber length] (= 2πaIm) |
| ir | reciprocal current through a differential source element [A] |
| I | electric current [A] |
| Ia | applied steady-state (or stimulus) current [µA] |
| Ii, Io | axial currents [µA] and axial currents per unit area [µA/cm2] inside and outside the cell |
| iK, iNa, iL | membrane current carried by potassium, sodium, and chloride (leakage) ions per unit length [µA/cm fiber length] |
| IK, INa, IL | membrane current carried by potassium, sodium, and chloride (leakage) ions per unit area [µA/cm²] |
| IL | lead current in general [A] |
| Im | membrane current per unit area [µA/cm2] (= ImC + ImR), bidomain membrane current per unit volume [µA/cm³] |
| imC, imI, imR | capacitive, ionic, and resistive components of the membrane current per unit length [µA/cm fiber length] (= 2πaImC , = 2πaImI , = 2πaImR ) |
| ImC, ImI, ImR | capacitive, ionic, and resistive components of the membrane current per unit area [µA/cm²] |
| Ir | total reciprocal current [A] |
| Irh | rheobasic current per unit area [µA/cm2] |
| Is | stimulus current per unit area [µA/cm2] |
| j, jk | ionic flux, ionic flux due to the kth ion [mol/(cm2·s)] |
| jD, je | ionic flux due to diffusion, due to electric field [mol/(cm2·s)] |
 | electric current density [A/m2] |
| dv | source element |
| i | impressed current density [µA/cm2], impressed dipole moment per unit volume [µA·cm/cm3] |
| i, o | intracellular and interstitial current densities [µA/cm2] |
| iF, iV | flow (flux) and vortex source components of the impressed current density [µA/cm2] |
| ir, it | radial and tangential components of the impressed current density [µA/cm2] |
| L | lead field in general [A/m2] |
| LE | electric lead field due to unit reciprocal current [1/m2] |
| LI | lead field of current feeding electrodes for a unit current [1/m2] (in impedance measurement) |
| LM | magnetic lead field due to reciprocal current of unit time derivative [s/m2] |
| K | constant |
| K(k), E(k) | complete elliptic integrals |
 j | secondary current source for electric fields [µA/cm2] |
| l | length [m], internodal spacing [µm] |
 | liter |
| L | inductance [H = Wb/A = Vs/A] |
 | magnetic dipole moment of a volume source [Am2] |
| M | vector magnitude in spherical coordinates |
| M1, M2, M3 | peak vector magnitudes during the initial, mid, and terminal phases of the QRS-complex in ECG [mV] and MCG [pT] |
| n | number of moles |
 | surface normal (unit length) |
| j | surface normal of surface Sj directed from the primed region to the double-primed one |
| p | electric dipole moment per unit area [Am/m2 = A/m] |
 | electric dipole moment of a volume source [Am] |
| P | pressure [N/m²] |
| PCl, PK, PNa | membrane permeabilities of chloride, potassium and sodium iones [m/s] |
| r | radius, distance [m], vector magnitude in spherical polar coordinates |
| r | correlation coefficient |
 | radius vector |
| ri, ro | axial intracellular and interstitial resistances per unit length [kΩ/cm fiber length] (ri = 1/σi ρa2) |
| rm | membrane resistance times unit length [kΩ·cm fiber length] (= Rm/2ρa) |
| R | gas constant [8.314 J/(mol·K)] |
| Ri, Ro | axial resistances of the intracellular and interstitial media [kΩ] |
| Rm | membrane resistance times unit area (specific resistance) [kΩ·cm2] |
| Rs | series resistance [MΩ] |
| SCl, SK, SNa | electric current densities due to chloride, potassium and sodium ion fluxes [µA/cm2] |
| t | time [s] |
| T | temperature [ ° C], absolute temperature [K] |
| u | ionic mobility [cm2/(V·s)] |
| v | velocity [m/s] |
| v | volume [m3] |
| V | voltage [V] |
| V ' | deviation of the membrane voltage from the resting state [mV] (= Vm - Vr ) |
| Vc | clamp voltage [mV] |
| VL | lead voltage in general [V] |
| VLE | lead voltage of electric lead due to unit reciprocal current [V] |
| VLM | lead voltage of magnetic lead due to reciprocal current of unit time derivative [V] |
| VK, VNa, VL | Nernst voltages for potassium, sodium, and chloride (leakage) ions [mV] |
| Vm | membrane voltage [mV] (= Φi - Φo) |
| Vr , Vth | resting and threshold voltages of membrane [mV] |
| VR | reversal voltage [mV] |
| VZ | measured voltage (in impedance measurement) [V] |
| W | work [J/mol] |
| X, Y, Z | rectangular coordinates |
| z | valence of the ions |
| Z | impedance [Ω] |