Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 27
Identification of Research Needs Relating to Potential Biological or Adverse Health Effects of Wireless Communication Devices Human Laboratory Studies The third session of the workshop focused on human laboratory studies. Human laboratory studies of radiofrequency (RF) exposure investigate the effects of RF exposure to humans in a controlled laboratory environment to determine potential RF effects on relevant biological endpoints including changes in electroencephalogram (EEG) amplitudes, increase in blood pressure, sleep disturbances, cardiac arrhythmia, changes in cognitive performance, and headaches. This report section is organized into neurophysiological and cognitive effects, effects on the ear and hearing, effects on heart rate and blood pressure, and subjective symptoms and electromagnetic hypersensitivity (EHS). NEUROPHYSIOLOGICAL AND COGNITIVE EFFECTS In spite of the large number of investigations, RF-induced neurophysiological effects need further study. While several studies have focused on spectral power of EEG, regional cerebral blood flow (rCBF),1 and event-related (evoked) potentials (ERP),2 most of the present data are collected by investigations evaluating acute effects on healthy adults during short 1 Cerebral blood flow (CBF) is the blood supply to the brain in a given time, being about 15percent of the cardiac output. An increase or decrease in normal CBF will cause an increase or decrease in cerebral arterial blood volume because of arterial dilatation or constriction. 2 An event-related potential (ERP) is any stereotyped electrophysiological response to an internal or external stimulus. More simply, it is any measured brain response that is directly the result of a thought or perception.
OCR for page 28
Identification of Research Needs Relating to Potential Biological or Adverse Health Effects of Wireless Communication Devices exposures to RF fields. Dosimetric measurements for different cortical functional subregions can be conducted inside a head phantom filled with liquid having tissue-equivalent dielectric properties. A calibrated RF field scanning probe, moved by a robotic arm, records the spatial values of electric field strengths and Specific Absorption Rates (SARs) within cubic volumes in the head phantom. It is generally recognized that the interpretation of EEG findings is difficult because of the high intra-individual variability in attention and waking state of volunteers. Some of the waking EEG studies reveal an enhancement of cortical activity, as measured by the increase of spectral power in the alpha band3 during RF exposure. Also, the most convincing effects of RF exposure on the sleep EEG indicate an increase of the power of the alpha waves, while studies on ERPs have given mixed and inconclusive results (Hamblin and Wood, 2002; Cook et al. 2006). For other spectral ranges,4 reduction of beta band, attenuation in the theta activity, and increase of gamma response have been reported, as well as reduced amplitude and latency of N100 waves5 and an increased P300 latency.6 However, these findings could not be replicated with an experiment that had more statistical power (Hamblin et al. 2006). The inconsistency with the previous studies was attributed to the small sample size or the lack of a double blind protocol of the previous study. Cognitive performance was assessed using several cognitive tasks, but no statistically significant effects were found on task performances in a recent study on effects on cognitive performance of exposure to 888 MHz signals using 168 volunteers (Russo et al. 2006). Another comprehensive study focused on cognitive performance of 120 subjects exposed to 900 MHz mobile phones (Keetley et al. 2006). Cognitive performance was assessed using eight cognitive tests. After adjusting for gender, age and education, simple and choice reaction times showed significant impairment, whereas performance on the trail-making task,7 which involves working memory, significantly improved. 3 The alpha band is the spectral component in the EEG signal, which falls between 8-13 Hz. 4 EEG has usually been described in terms of frequency bands: GAMMA (greater than 30Hz), BETA (13-30 Hz), ALPHA (8-13 Hz), THETA (4-8 Hz), and DELTA (less than 4 Hz). 5 N100 is an ERP component, characterized as a negative deflection in voltage, peaking approximately 100 ms after the stimulus. Anomalies in N100 may give rise to cognitive deficits (i.e., impairments of memory and learning abilities). 6 P300 is an ERP potential component, characterized as a positive deflection in voltage, peaking approximately 300 ms after the stimulus. 7 This test consists of two parts, A and B. Part A consists of encircled numbers from 1 to 25 spread across a sheet of paper. The object of the test is for the subject to connect the numbers in order, beginning with 1 and ending with 25, whereas Part B requires the subject to connect numbers and letters in an alternating pattern (1-A-2-B-3-C, etc.), both in as little time as possible.
OCR for page 29
Identification of Research Needs Relating to Potential Biological or Adverse Health Effects of Wireless Communication Devices EFFECTS ON THE EAR AND HEARING Because of the close proximity of mobile phones to human ears, the area around the ear receives the highest RF exposure, and a lot of interest has focused on possible effects on auditory perception or on acoustic evoked potentials.8 However, in the majority of experiments on hearing threshold levels or transient evoked otoacoustic emissions,9 no significant effects have been reported. Accordingly, no effects of RF exposure on auditory functions of the cochlea or auditory brainstem responses have been found by several research groups (Pau et al. 2005; Sievert et al. 2005; Parazzini et al. 2005). While there is no evidence on adverse effects on hearing, there are anecdotal reports on interaction of cell phones with hearing aids and cochlear implants. At present, however, there are very few experimental data from human volunteer studies concerning health problems with auditory prostheses. EFFECTS ON HEART RATE AND BLOOD PRESSURE Acute changes in the blood pressure and in other cardiophysiological parameters during RF exposure have been studied using healthy adult volunteers. In a study of 32 volunteers, an extensive set of test conditions including controlled and spontaneous breathing, head-up tilt table test, and deep breathing tests was applied during real and sham exposure (Tahvanainen et al. 2004). The results indicated no statistically significant effects on heart rate or blood pressure. Also a later comprehensive study with 125 volunteers concluded that RF exposure from cellular phones does not cause noticeable effects on heart rate regulation in healthy adults (Barker et al. 2007). Although there is no clear evidence concerning the negative cardiovascular, inflammatory, or respiratory health effects of the electromagnetic field (EMF) produced by wireless communications tools at the macro-physiological level, further studies focusing on the early phase of potentially harmful changes are needed. The new techniques focusing on endothelial dysfunction or prolonged oxidative stress have not been extensively used 8 Evoked potentials are brain reactions on stimulus with amplitude much lower than EEG voltage measured during regular brain activity. While different evoked potentials occur as a result of different stimuli, acoustic evoked potentials (AEP) are a result of acoustic stimuli. 9 An otoacoustic emission (OAE) is a sound that is generated from within the inner ear. Broadly speaking, there are two types of otoacoustic emissions: Spontaneous Otoacoustic Emissions (SOAEs) and Evoked Otoacoustic Emissions (EOAEs). As their names suggest, SOAEs arise spontaneously and EOAEs require an evoking stimulus.
OCR for page 30
Identification of Research Needs Relating to Potential Biological or Adverse Health Effects of Wireless Communication Devices in the human studies. Also, the rapidly developing salivary biochemical analysis techniques offer new possibilities. SUBJECTIVE SYMPTOMS AND ELECTROMAGNETIC HYPERSENSITIVITY During recent years, numerous individuals have reported a variety of health problems that they relate to exposure to RF fields from mobile phones. While some perceive only mild symptoms and react by avoiding phones, others are so severely affected that they change their entire lifestyle. This reported sensitivity has been generally termed “electromagnetic hypersensitivity” or EHS (WHO 2005). A number of studies have been conducted where EHS individuals were exposed to RF fields similar to those emitted by cellular phones. In one provocation study,10 20 EHS volunteers were exposed to cellular phone signals, which they attributed to the cause of their symptoms (Hietanen et al. 2002). The aim was to elicit symptoms under controlled conditions with low-background fields. The number of reported symptoms was higher during sham exposure than during RF exposure, which could have been due to higher postural and mental tension at the beginning of the experiment when subjects were not yet adapted to the experimental conditions. In another study, persons with self-reported sensitivity to mobile phone signals did not react to RF exposure with any increased severity of perceived symptoms (Rubin et al. 2006). Hence there is little support in the research community for the perception that RF fields can be related to EHS or symptoms (Roosli 2007). The conclusion of the Fact Sheet on EHS published by the World Health Organization’s (WHO’s) EMF project is that “EHS is characterized by a variety of non-specific symptoms that differ from individual to individual. The symptoms are certainly real and can vary widely in their severity. Whatever its cause, EHS can be a disabling problem for the affected individual. EHS has no clear diagnostic criteria and there is no scientific basis to link EHS symptoms to EMF exposure. Further, EHS is not a medical diagnosis, nor is it clear that it represents a single medical problem” (WHO 2005). The committee’s evaluation of presentations and discussions at the workshop has resulted in the identification of research needs and gaps. Because of the paucity of data from identically replicated experiments, any future studies would benefit from experiments focusing on possible adverse effects on EEG activity, as well as on cognitive performance functions, and should include an increased number of subjects (Croft 2007). 10 An investigation into the basis of symptoms attributed to RF emissions.
OCR for page 31
Identification of Research Needs Relating to Potential Biological or Adverse Health Effects of Wireless Communication Devices For further research, the workshop attendees noted the following important considerations: appropriate exposure regimes, multi-center collaborations using identical research protocols, large sample sizes, and reliable EEG analysis techniques. In addition, most human studies have examined healthy young adults, a group not necessarily representing the most susceptible part of the population. Therefore, future research needs to include children, the elderly, and people with underlying diseases. While the basic thermoregulatory physiology of healthy people in relation to external heat stress and internal heat load generated by RF radiation is well known, elderly people may be particularly vulnerable to the effects of heat stress (coronary and cerebral thrombosis); therefore, a gap exists in the study of this population. Current research gaps include little existing information about neurophysiological changes duringheavy (occupational) use of cellular phones for several years. A second gap is that no studies using elderly volunteersare available, but could be performed. Finally, there is a continuing need for experiments focusing on possible adverse RF effects identified by changes in cognitive performance functions. Research Needs There are some considerable research needs for human laboratory studies. Due to the paucity of data from identically replicated experiments, There is a need for experiments focusing on possible adverse RF effects identified by changes in EEG activity, as well as a need to include a larger number of subjects. Research Gaps Research Ongoing Little or no information is available on possible neurophysiologic effects developing during long-term exposure to RF fields. Risks of exposure to RF fields in elderly volunteers arenot well explored. There is a continuing need for experiments focusing on possible adverse RF effects identified by changes in cognitive performance functions.
OCR for page 32
Identification of Research Needs Relating to Potential Biological or Adverse Health Effects of Wireless Communication Devices Judged to Be of Lower Priority Because the use of cell phones by individuals with auditory prostheses is increasing, there is a need to conduct human volunteer studies to investigate potential health implications arising from interaction of cell phones with hearing aids and cochlear implants.