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1 2 . e l e c t r O t H e r a P y t H e O ry
95 EN WIRELESS PROFESSIONAL
We will therefore need to understand the fundamental law that it must observe in order to find the
optimum qualities of this current.
This first chapter aims to provide a reminder and explanation of this law.
This is followed by a second chapter which, on the basis of this fundamental law and ideas surrounding it,
determines the qualities of the optimum current.
At the turn of the last century, well-known physiologists such as Weiss, Hoorweg, Du Bois Reymond and
Lapicque managed to discover the fundamental law of electrostimulation and its mathematical expression.
Based on Hoorweg’s work, Weiss (a Parisian doctor and physiologist) emphasised the importance of the
quantity of electrical charges created by the stimulation current. His experiments led to the fundamental
observation that to achieve stimulation, it is not the type of current that is significant, but the quantity
of current in a specified period of time. In other words, if the stimulation threshold values are given as a
quantity of electricity (in electrical charges) that must be created to achieve these, the values are similar
even if the electrical pulse with the same overall duration is a different shape.
Fig. 2
As a reminder:
the quantity of electrical charges (
𝑄
) supplied by an electric current with intensity (
𝐼
)
in a given time (
𝑡
) is the product of the intensity multiplied by the time.
𝑄 = 𝐼 𝑥 𝑡
Since the quantity of electrical charges provided by the stimulation current is the fundamental factor,
Weiss studied the way in which the necessary quantity of charges is modified in order to achieve the
threshold (i.e. to cause stimulation) based on the duration of the current being applied.
He performed a series of measures to determine the relationship between the quantity of current and the
duration of the pulse for durations ranging from 0.23 to 3 ms.
From his experiments, Weiss found that there is a linear relationship between the quantity of charges
required to reach the stimulation threshold and the duration of the pulse (Fig. 2).
Quantity
of current
required to
reach the
stimulation
threshold
Duration of the pulse
Linear relationship between the duration of the electrical pulse and the amount of
electricity applied to reach the stimulation threshold:
𝑄 = 𝑞 + 𝑖𝑡