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• Neuro-endocrine - effects on 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

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)

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)

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

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Field penetration in tissue in near field

Plane wave

Near field

Neubar et al. 1999

Antenna

Antenna

Effective penetration at 900MHz for human and rat brain

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-1 is needed

• Humans start to sweat at 1-2oC above normal - about 2-4Wkg-1

Advised levelsWhole body:Workers - 0.4Wkg-1 (above 10MHz)Public - 0.08Wkg-1

Localized (including head) ,,

10Wkg-1 NRPB (av. over 10g, 10MHz-10GHz)or 2Wkg-1 ICNIRP (av. over 10g for general public)Both averaged over any 6 min. period

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)

Phone type Field strengthin brain

SAR (W/kg)in brain

Nokia 5110 18.84 0.37Nokia 2110 20.47 0.44Bosch World 718 17.78 0.33Nokia 6110 16.59 0.29Ericsson GA628 15.88 0.26Hagenuk Global 5.12 0.03Motorola V3688 4.58 0.02Motorola Star Tac 70 4.56 0.02

Summary

Highest brain SAR from GSM (0.25W) = 0.44Wkg-1

Range of SAR from analogue = 0.9 - 1.76Wkg-1

Thermal estimates

Worst case for head:4Wkg-1 for 30mins = 7200J = 1714 caloriesthat 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)

Neubar et al. 1999

Dielectric property of head tissues

Tissue Type Fat 5.5 1.8

Skull 12.5 3.4Skin 39.5 14.0Brain 56.8 22.0Eye 52.3 23.2

Muscle 55.0 22.0(Air-way) (1) (0)

Human Cognitive Function Tests Standard tests used to assess effects of drugs e.g. opiates, psychotropics for medico-legal purposes

1. Immediate Word Recall2. Picture Presentation3. Simple Reaction Time4. Digit Vigilance Task5. Choice Reaction Time

6. Spatial Working Memory7. Numeric Working Memory8. Delayed Word Recall9. Delayed Word Recognition10. Delayed Pict. Recognition

Effect at 50Hz - 600T 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

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

Volunteers

Group 1. Hospital staff aged 24 to 60No control over alcohol, caffeine, sleep, drugs

Group 2. Medical, dental or postgrad. science students aged 18-28 Controlled for alcohol, caffeine, sleep, drugsAll were given two training sessions, and 30mins exposure each visit

915MHz

217Hz

To Coding switch

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

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

Variable(1st four)

P-Value(3-waycomp-arison)

MeanAna-loguefield

MeanDig-italfield

MeanContcond-itions

Simplereaction time(msec)

0.559 225.9 228.6 227.3

Choicereaction time(msec)

0.003 373.4 384.4 387.9

Vigilancereaction time(msec)

0.377 385.8 382.2 388.1

Vigilanceaccuracy (%)

0.164 99.0%

99.1%

98.3%

Results (MANOVA):

Outcomevariable

p-value for 3simulations

p-value forvisit order

Reaction time onattentional tasks

0.007 NS

Speed on working& secondarymemory

NS 0.000

Accuracy on workingand secondarymemory tasks

NS NS

Accuracy onattentional tasks

NS NS

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

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

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

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 leftRecord 15 min with one phone activatedRecord 15 min recovery

Blood flow / 2Watts/kg

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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?)

Blood flowA 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???

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

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

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*