Medical application of millimetre waves
M.A. ROJAVIN and M.C. ZISKIN
From the Richard J. Fox Center for Biomedical Physics, Temple University School of Medicine, Philadelphia, USA
Introduction
The biological effects of millimetre waves (MWs) at power levels <20 mW/cm2 were first discovered in the late 1960s, and within 10 years were studied in various countries including the former USSR,1–4Canada,5,6 France7 and Germany.8,9 These early studies used a wide variety of objects ranging from biomolecules to bacteria to tissues of higher organ- isms. Poor reproducibility of some of the experi- mental results and the lack of acceptable theoretical models resulted in a significant delay to research activity in this area in the USA.10–12
In the meantime, based on the biological experi- ments, medical applications of MWs began in the former Soviet Union in the 1970s,13,14 and since the mid–1980s, have been in widespread usage. Use of MWs for medical purposes is known as ‘Millimetre Wave Therapy’ (MW therapy), ‘Extremely High Frequency (EHF) therapy’, or, less frequently, ‘Microwave Resonance Therapy’. With numerous medical MW generators now employed in hospitals and clinics in the former USSR and some other European states (some estimates range as high as 50000 units15), thousands of patients undergo treatment with MWs every year. Some authors16,17claim that there are several hundred thousand patients who have been treated with MWs. The reported success rate of MW therapy for various pathologies is astonishingly high. However, this treat- ment modality is almost unknown to Western med- ical scientists and practitioners. There is only one publication on this subject in Western peer-reviewed medical journals.
We present an overview of the available informa- tion regarding MW therapy. The majority of information resides in Soviet/Russian/Ukrainian reports on this topic published as conference abstracts. However, their analysis allows us to reveal some general features of MW therapy. Upon comparing the clinical information with the existing experi- mental results, we can better understand the possible mechanisms involved, as well as the most potentially beneficial applications of MW therapy.
Physical characteristics of millimetre waves
MWs belong to a relatively narrow range of electro- magnetic waves with wavelengths from 1 to 10 mm (corresponding to frequencies from 300 to 30 GHz, with 1 GHz=109 oscillations per second). MW gen- erators and related equipment were produced primar- ily for military purposes (short-range radar), which, to a large extent, explains the secrecy and predomin- ance of incomplete publications on this topic in the former USSR.
The penetration depth of MWs into biological tissues is very small. Unlike centimetre and decimetre waves, MWs are absorbed in water and water- containing media (including biological structures) within the first 0.3–0.5mm from the surface, depending on the frequency used.18–20 With energy insufficient to break chemical bonds directly,21,22and a low average incident power density of <20 mW/cm2, MWs usually produce an average heating of an irradiated surface on the order of several tenths of a degree C, which is usually imperceptible.
Obviously the range of reported biological and medical effects of MWs cannot be explained by such a small bulk heating of structures. H. Fro ̈hlich21,23–25suggested that such effects might occur through a resonance-type interaction, since some of the biomo- lecules and structural elements of the cells have their own theoretically calculated resonant frequency within the range of 1010–1011 Hz. Several experi- ments showing narrow resonant frequency depend- ence of biological effects of MWs seem to support this hypothesis.3,6–9,26,27
However, other physical mechanisms may also be responsible for the biological effects of MWs. It has been shown, both theoretically 28 and experiment- ally, 29, 30 that not only the absolute value, but the rate of heating is of critical importance for biological effects. The initial rate of heating due to MW exposure is usually very high, reaching 0.1–0.5°C/s,30–32 and is sufficient to produce some biological effects, such as an increase in neuronal firing rates.
Another important characteristic of MWs is their heterogeneous distribution on the surface of exposed objects. As shown by infrared thermography,33so-called ‘localized hot spots’ with a temperature elevation several degrees Celsius higher than the average can be formed on the surface of the skin.
Therapeutic potential of MW therapy
During the past 20 years, MW therapy has been used for a broad spectrum of diseases and conditions, some of which are listed in Table 1. The list of pathological conditions treated with MW therapy includes: some gastrointestinal diseases (peptic ulcer, gastroduodenitis);34−39 diabetes;41 coronary artery disease and some other blood circulation dis- orders;42–45 cerebral palsy;46 chronic non-specific pulmonary diseases;47 skin diseases such as psoriasis and atopic dermatitis;16,48,49 enhancement of bone and wound healing.50–54 MW therapy has also been used to treat cancer patients, as a means of increasing their non-specific immunity and alleviating the toxic side effects of chemo- and radiotherapy.55–57 There have been some promising results in the use of MW therapy for treating opioid, alcohol and nicotine dependencies.16,58,59
In all of the above cases, MW therapy seems to enhance regulatory effects, restoring a patient’s homoeostasis.17,39 This means that, depending on the condition of a patient, MW therapy can cause such changes as an increase or decrease of blood pres- sure,45 stimulation of inhibited (or suppression of excessive) immune activity,16,39,60,61 etc. For more data on efficacy of MW therapy in various diseases see Table 1.
Instead of sorting information according to disease, we will analyse it by the types of effect generated.
Physicians using MW therapy, irrespective of the disease being treated, have observed some general features which form three main groups. They are: (i) sedative/analgesic effects; (ii) anti-inflammatory action and enhancement of tissue regeneration pro- cesses; and (iii) immune stimulation.
Sedative and analgesic effects
These are the most common effects of MW therapy which are cited by the majority of physicians and patients. Usually, after the first 2–3 sessions of MW therapy, 73–100% of patients report alleviation of, or even total relief from, the pain accompanying the disease, whether peptic ulcer,34,36,62,63 heart dis- ease64,65 or a pruritic skin condition.48,49 This is followed by normalization of sleep and improvement of general condition. Sleepiness sometimes develops during the MW therapy sessions.65 Efficacy of MW therapy in treatment of males with psychogenic sexual dysfunction66 can probably also be attributed to a general sedative action.
Pain relief is considered among the most general purposes of MW therapy application: in one of the largest cardiology centres in Russia, a clinical study is underway in which the decreased level of blood endorphins in patients with acute cardiac disorders is regarded as an indication for performing MW therapy.67
Some recent experiments confirmed that low- power MWs are capable of interacting with neurons affecting the electrical characteristics of neuronal functioning27,30 and the production of some neuro- peptides.39 In vitro, MW directly affected such func- tions of neurons as firing rate, amplitude and form of the signal in marine skates,68 frogs,27,69 and snails.30 In vivo exposure of mice to MWs increased by 40–50% the duration of anaesthesia caused by several non-opioid anesthetics.70 The additional anaesthetic effect of MW was completely blocked by pre-treatment with the opioid antagonist naloxone, suggesting that MW therapy causes a release of opiate substances in the exposed organism. It is too early at this stage to make definite statements that opioids are being released in the body during MW therapy based on this one experiment, but some of the clinical data given below make such a possibility quite plausible.
A clinical study of 70 opioid drug abusers58revealed that MW therapy alone can significantly improve the conditions of patients suffering from withdrawal symptoms. After the first session of MW therapy, symptoms of abstinence were relieved for 2hin33.8%patients,upto6hin50.7%,upto12h in 15.8%. Full relief usually developed after 3–12 sessions (days) of MW therapy. Drug abusers reported the sensory feelings comparable with those from
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