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Mobile phone-Human in-vivo studies

Mobile phone-Human in-vivo studies. Alan W Preece Medical Physics Research Centre UNIVERSITY of BRISTOL. Existing Effects. Pacemakers - (disturbances to the pacing mode in range 0.1 -2m - but not when implanted) ITU - safety critical equipment - MDA guidelines

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Mobile phone-Human in-vivo studies

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  1. Mobile phone-Human in-vivo studies Alan W Preece Medical Physics Research Centre UNIVERSITY of BRISTOL

  2. Existing Effects • Pacemakers - (disturbances to the pacing mode in range 0.1 -2m - but not when implanted) • ITU - safety critical equipment - MDA guidelines • Neuro-endocrine - effectson animals, but not humans • VEP - no effect • Subjective effects - Hocking and Hansson-Mild • DNA fragmentation - Lai • Long term potentiation - Tattersall • Blood pressure changes - Braune • Brain permeability - Salford

  3. Selection of key animal studies • Seaman and Lebowitz ‘89 - acoustic effects of low power 915MHz pulses • Chou etal ‘85 - no acoustic effect of low power 2.45GHz pulses • Thuroczy ‘94 - effects on the EEG and brain blood flow • Lai and Singh ‘96 - neurotransmitters and DNA • Salford ‘94 - blood-brain barrier decrease • Repacholi ‘97 - increased lymphoma incidence (All below 10W/kg SAR)

  4. Selection of key human studies • Borbeley et al ‘99 - Effect of GSM on sleep - increase EEG activity - deeper sleep • Freude et al ‘98 - Effect of GSM on VEP during visual tasks (on slow wave activity) - left ear • Urban et al ‘98 - No effect of GSM on VEP • Preece et al ‘99 - No effect on memory - but changes in response speed • Mild et al ‘98 - Subjective stress and warmth effects (epi.) • Hardell ‘99 - No increase in absolute no. of tumours, but association with side of use (recall bias, handedness) (epi)

  5. WTR output - (Summary of letter to Chairman of AT&T corporation from G Carlo - head of WTR) • Rate of death from brain Ca. higher in mobile than portable phone users • Acoustic neuroma 50% higher in phone users of >6 years use • Risk of neuro-epithelial tumours 2x higher in phone users • Correlation between side of use and incidence of tumours • Confirmation of genetic damage

  6. Plane wave Near field Field penetration in tissue in near field

  7. Neubar et al. 1999

  8. Antenna Antenna Effective penetration at 900MHz for human and rat brain

  9. Thermal effects • Human cells will stand up to 43C for only a short time--above this cell killing becomes very rapid. Probably about 41C is tolerable. • To reach this (41o) an SAR of about 10Wkg-1is needed • Humans start to sweat at 1-2oC above normal - about 2-4Wkg-1

  10. Advised levels Whole body: Workers - 0.4Wkg-1 (above 10MHz) Public - 0.08Wkg-1 Localized (including head) ,, 10Wkg-1NRPB (av. over 10g, 10MHz-10GHz) or 2Wkg-1ICNIRP (av. over 10g for general public) Both averaged over any 6 min. period

  11. Mobile phones - SAR estimates Max values (referenced to 1Watt) Dimbylow (‘94) 3 - 4Wkg-1 Excell (‘98) - 4.2 (900MHz) - 8.2Wkg-1(1.8GHz) Brain values (referenced to 0.25W GSM) CSELT (‘99) - 0.3Wkg-1(Computed standard design) Measured - 0.44Wkg-1(Helical and quarter wave ant.) to 0.02Wkg-1(Flip-out design)

  12. Summary Highest brain SAR from GSM (0.25W) = 0.44Wkg-1 Range of SAR from analogue = 0.9 - 1.76Wkg-1

  13. Thermal estimates Worst case for head: 4Wkg-1 for 30mins = 7200J = 1714 calories that could be 1.7o Worst case for brain: 0.44Wkg-1 for 30min - 0.20 1.6Wkg-1 for 30min - 0.70 With blood flow, half these values or less are to be expected (Rui and Foster 1999)

  14. Neubar et al. 1999

  15. Dielectric property of head tissues

  16. Human Cognitive Function TestsStandard tests used to assess effects of drugs e.g. opiates, psychotropics for medico-legal purposes 1.Immediate Word Recall 2. Picture Presentation 3. Simple Reaction Time 4. Digit Vigilance Task 5. Choice Reaction Time 6. Spatial Working Memory 7. Numeric Working Memory 8. Delayed Word Recall 9. Delayed Word Recognition 10. Delayed Pict. Recognition

  17. Effect at 50Hz - 600T applied to the head (about 6mA/sq.m) • Reaction time - no effect • Choice reaction - no effect • Spatial memory - no effect • Vigilance - no effect • Picture recall - small effect • Number recall - intermediate effect • Word recall - large effect

  18. Simulated 915MHz phone Exposure • 1Watt CW to antenna, or • Modulated at 217Hz square wave at 0.125 duty cycle (mean power 0.125 W) • Mounted on ear defender with antenna 2-3cm from head, over left squamous temple bone

  19. Volunteers • Group 1. Hospital staff aged 24 to 60 • No control over alcohol, caffeine, sleep, drugs • Group 2. Medical, dental or postgrad. science students aged 18-28 • Controlled for alcohol, caffeine, sleep, drugs • All were given two training sessions, and 30mins exposure each visit

  20. To Coding switch 217Hz 915MHz

  21. Result 1: • Group 1 showed no effect on memory but “Choice reaction time” was decreased - i.e. the speed went up!! • is this a Type 1 error? • or, did some volunteers have no sleep, too much alcohol or too much coffee? Reason for the second, tightly controlled, group

  22. Result 2: • Second group showed exactly the same result! • No effect of alcohol (even after 15 units the night before) • Coffee/tea uniformly distributed • Sleep unrelated to performance • Drugs (legal or otherwise) not a factor

  23. Results (MANOVA):

  24. Conclusions: • There is an effect on the brain of a 915MHz transmission • Greater for analogue than GSM type • mean effect is a 15msec reduction in transit between visual and speech centre - this has to be a synaptic effect not transmission one • Big question is whether this is thermal or non-thermal

  25. Possibilities: • An effect on the angular gyrus - this is a processing centre between visual and speech centres • Normally on the left • Is affected by heat or blood flow - (measurable) • Could be protein effect - (effect will persist) These are all testable hypotheses

  26. Brain blood flow measurement methods MRI - difficult without contrast, but Diffusion-perfusion sequence possible (extra large imaging gradient). Metal antenna a nuisance PET - Involves radioactive materials (need about 4mSv) and specialised centre to carry it out, and expensive Ultrasound - Direct colour-Doppler studies on the middle cerebral artery which perfuses the cortex NIRS - transillumination of the skull and brain

  27. Flow measurement protocol • Dual channel 2Mhz ultrasound colour Doppler with time-average-max and resistance-index measurement • Two dummy phones on right and left side, one activated with 915Mhz analogue to give SAR of 1WKg-1 in brain • Ten volunteers on two visits each, randomly assigned to right or left activation, contralateral side on second visit • Record 15 min baseline flows on right and left • Record 15 min with one phone activated • Record 15 min recovery

  28. Possible mechanism via HSP • Brophy (1998) - HSP in intimal epithelium causes vasodilatation • Used to precondition vessels before vascular surgery • If waves can induce HSP in absence of heat then this may explain vasodilatation at very low RF levels - (Chronic effects?)

  29. Blood flow A change in blood flow in the middle cerebral artery can be detected at power levels 2 - 3x usual phone power Similar experiments with NIRS show changes in perfusion (but are these SKIN and SKULL changes only) Changes in BRAIN perfusion may be more difficult to pin down - in which case are they even significant???

  30. Summary and Conclusions • Some evidence for a direct electro-physiological effect on brain of pulsed RF (i.e.GSM systems) • Some evidence for short term physiological effects (perfusion, temperature) • Some animal and cellular evidence for heat-shock (stress) protein at non-thermal levels • Confusing evidence for genotoxic damage • No sound evidence as yet for human carcinogenicity

  31. Needs for future study • Epidemiology of cognitive changes (i.e. long term memory effects) • Epidemiology of neural tumours (already under way with IARC) • Correlation of SAR’s from phones and “normal” limits for physiological changes in the brain • Study of other critical organ exposure (salivary, thyroid, eye) • Resolution of the genotoxicity (Lai and Singh) issue and confirmation of stress protein production • New technology - Tetra, satellite, environment

  32. Science and Technology Select Committee Report - September 1999 • Change limits to ICNIRP (2W/kg instead of 10W/kg)* • Set up Independent Expert Group • Industry should be involved, but in minority • Lay members on study groups • Confirm or deny work on DNA fragmentation* • Further research on subjective and cognitive symptoms • Large increase in publicly-funded research • Academically led research programme • Publish SAR’s and give consumers choice*

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