Cooling-controlled and reliable driving module for low-level light therapy LED helmet

Highlights

• Developed a LED-based low level light therapy helmet for treating brain dysfunction.

• Reliable, stable, and cooling-controlled driving module

• The effective control, cooling effect, and stability of the helmet are fully testified.

Abstract

Stroke is a horrible disease of high incidence, which is the second leading cause of disability worldwide. Thousands of people are suffering from stroke sequelae. Therefore, how to rehabilitate from stroke sequela is an urgent research field benefiting human beings. The traditional and experience-based treatment methods not only have an uncertain treatment effect, but were also unsuitable to be widely used due to its unstable therapeutic effect. Transcranial low level light/laser therapy (LLLT) of neurological diseases and brain trauma has gained momentum due to the character of high-efficient, safe and non-invasive in the past decade. In this study, we developed a LLLT helmet with cooling-controlled and reliable driving module for treating stroke depending on near-infrared light. An application of integrated constant-current driving solution under high power is introduced in this paper. In order to reduce the large heat release of instrument and voltage drift of reference source, the major factors of current fluctuation, we proposed an integral thermal cooling solution and a multi-element parallel reference sources with temperature compensation to enhance the stability and robustness of the LLLT helmet. A series of experiments were performed to quantitatively testify the robustness and stability of our instrument.

Introduction

Stroke becomes the second leading cause of death and the major cause of disability in adults worldwide, due to the advent of worldwide aging population [1]. China, a nation with the world's most rapidly aging population, has more than ten million stroke patients. World Health Organization suggests that though most patients who undergo timely and proper treatment, can save their lives, still they will suffer from severe negative sequela, such as dyskinesia, cognitive disorder, swallowing disorders and so on [2]. Therefore, the rehabilitation of apoplectic sequelae is an urgent research field benefiting human beings.

There are many stroke rehabilitations, however, most of them are based on a long period of clinical experience, which make limited treatment effect. The neurological rehabilitation (Bobath, Brunnstrom, Rood, and Proprioceptive Neuromuscular Facilitation) is the most commonly applied for stroke [3], [4]. This approach not only requires active participation from both the patient and the therapist, but also takes quite a long time and constant treatment. Recently, combinations of acupuncture and neurological rehabilitation are considered as rapid and effective treatment or stroke rehabilitation in China, compared with traditional treatment schemes [5], [6]. However, experience-based treatment methods are unsuitable to be massively applied due to the poor reliability and stability of methods.

Transcranial LLLT has been demonstrated as a novel, high-efficiency, safe, and non-invasive therapy for stroke treatments by employed in multiple validated animal experiments (in rats and dogs) and few human experiment in vivo [7], [8], [9]. During LLLT, absorption of red or near-infrared (NIR) photons by cytochrome c oxidase in the mitochondrial respiratory chain causes an increase in cellular respiration that continues for much longer than the light is present when delivered at appropriate flounce and exposure durations [1], [10]. However, LLLT, a potentially unexceptionable and incomparable treatment has not been commercially deployed worldwide until now. This may attribute to one key reason that there is no unitive, high reliable, high-robust and high-stable LLLT instrument.

The driving current of LED is the vital parameter of our instrument. Adopting a current source with temperature compensation or replacing current source with high driving capability are the most common methods to steady current. However, these methods have some limited effects. A current source with temperature compensation is implemented as a voltage follower with series negative feedback driven by a constant input voltage source (i.e., a negative feedback voltage stabilizer) [11], [12]. The voltage follower is loaded by a constant (current sensing) resistor acting as a simple current-to-voltage converter connected in the feedback loop. The external load of this current source is connected somewhere in the path of the current supplying the current sensing resistor but out of the feedback loop [13], [14]. Though this method is effective in some cases, current sources implement as circuits with series negative feedback have the disadvantage that the voltage drop across the current sensing resistor decreases the maximal voltage across the load (the compliance voltage). Therefore, this method is flawed. The reason for current fluctuation is diversification. In order to fundamentally solve this problem, we must find out the origin and propose solutions.

In our study, we developed a LLLT helmet with cooling-controlled and reliable driving module for treating stroke based on LED arrays. In order to improve robustness and stability of current driving module, we practiced and verified an integral thermal cooling solution which contained a solution associated air-cooling and water-cooling, a multi-element parallel reference source with temperature compensation. We tested the whole instrument and software for 100 min to verify the robustness and stability of our instrument. The analyzed data demonstrated that the current of driving module had high reliability and our instrument had great uniformity, stability, and robustness in the process of stroke rehabilitation.