United States Environmental Protection Agency Health Effects Research Laboratory Research Triangle Park NC 27711 Research and Development EPA/600/S1 -86/006 Dec. 1986 Project Summary Effects of 60-Hz Fields on Human Health Parameters Mary R. Cook, Carl M. Maresh, and Harvey D. Cohen Research on the effects of exposure to 60-Hz electric and magnetic fields has provided contradictory evidence for both increases and decreases in physio- logical and metabolic functioning, and specific results have often been difficult to replicate. If biological responses to powerline fields occur, they are un- doubtedly subtle, and research strate- gies must be specifically designed to enhance and clarify subtle effects. The study reported here used quanti- tative exercise testing techniques to evaluate whether increases in metabolism, caused by moderate steady-state exercise prior to exposure to real or sham fields, would clarify po- tential field effects. This research showed that physical recovery processes following moderate steady-state exercise were the same in real and sham fields. Of the variables examined, only heart rate (cardiac in- terbeat interval) was altered by 2 hr of field exposure. A small, statistically sig- nificant decrease in heart rate (3 beats/ min) was found when subjects were ex- posed to the real field after sitting quietly prior to exposure. This repli- cates our earlier research, in which heart rate showed a similar decrease after a total of 6 hr of field exposure. The results suggest that future studies should examine a broader range of the continuum of human arousal and phys- iological activation. This Project Summary was devel- oped by EPA's Health Effects Research Laboratory, Research Triangle Park, NC, to announce key findings of the re- search project that is fully documented in a separate report of the same title (see Project Report ordering informa- tion at back). Introduction Public concern has been expressed about possible health risks arising from exposure to the electric and magnetic fields generated by overhead power transmission lines. Previous research results have often been contradictory and difficult to replicate, suggesting that field effects, if real, are subtle. Fur- thermore, the literature suggests that 60-Hz fields might interact with neural mechanisms important in the control of levels of arousal. Research strategies. specifically designed to elucidate subtle effects are needed, and such strategies should be used to directly investigate the effects of field exposure over the continuum of human arousal. Quantitative exercise testing tech- niques have been quite helpful in im- proving the understanding of mecha- nisms associated with adaptation to other environmental conditions. Con- trolled exercise can be used to raise physiological and metabolic function to a higher level; at this higher level, sub- tle changes in function may be more ap- parent and therefore more easily mea- sured. This research was based on the idea that exercise testing methods might be particularly promising in re- search on 60-Hz field effects, since re- sults of previous studies on the effects of field exposure have provided support for both increases and decreases in physiological functioning, as well as for a dampening or shifting of normal circa- dian variations. The research reported here had two objectives: to evaluate the efficacy of the approach by determining the feasi- bility of combining exercise and field exposure techniques; and to evaluate whether increases in metabolism. ------- caused by moderate steady-state exer- cise prior to exposure to real or sham fields, would clarify potential field ef- fects. Procedures Experimental Design Each of eleven subjects participated in a maximal exercise test, one familiar- ization session, and four experimental sessions. During the four experimental sessions, which were held at weekly in- tervals, four conditions were presented in counterbalanced order: (1) exercise on a bicycle ergometer at 50% of VO2 max for 45 min, followed by exposure to sham fields for 2 hr; (2) exercise fol- lowed by exposure to real fields (9 kV/ m, 16 A/m) for 2 hr; (3) sitting quietly for 45 min, followed by exposure to sham fields for 2 hr; and (4) sitting quietly fol- lowed by exposure to real fields. All four sessions were conducted under double- blind conditions. Measure of cardiac activity, rectal temperature, and biochemistry were obtained at the end of a 30-min equili- bration period and during the 45-min pre-exposure period (exercise or sitting quietly). Ratings of perceived exertion also were collected at 2-min intervals during exercise. All measures except rectal temperature and perceived exer- tion were obtained during recovery in the real and sham fields. In addition, continuous dosimetry measures were taken throughout exposure. At the end of each session, both the experimenter and the subject judged whether the real or sham fields had been presented. Exposure Facility and Double- Blind Control System The exposure room is positioned in- side a parallel plate system. A set of ca- pacitively coupled, copper gradient rings is located behind the walls to in- crease field uniformity. The magnetic field is generated by six Helmholtz coils, surrounding the room in both the verti- cal and horizontal axes. Dedicated equipment is used to maintain ambient temperature and relative humidity at controlled levels, and the exposure area is continuously monitored from two ad- jacent control rooms via closed-circuit television and audio intercommunica- tion equipment. Uniform electric and magnetic fields can be generated in the subject test area (0-16 kV/m, ± 5.6%; 0- 32 A/m, ± 4.8%). The vertical axis of the magnetic field is in phase with the elec- tric field, and the horizontal axis is phase shifted 90° with the electric field. Additional equipment provides continu- ous monitoring of electric and magnetic field status, and individual short circuit current (Isc) throughout the exposure period. During exposure periods in this study the E field was set at 9 kV/m and the magnetic field components set at 16 A/m. The double-blind experimental con- trol system allows presentation of real and sham fields without either the sub- ject or the experimenters being aware of which field condition is in effect at any given time. Experimenters are kept unaware of exposure conditions through a system of hardware and soft- ware interlocks under the control of a master computer program. The inter- locks blank, mask, or disguise all field- related cues in the control room equip- ment. Our previous research indicated that subjects could often perceive the fields when they raised their hands in the air. The double-blind system was designed to counteract this major perceptual cue. It uses the continuous Isc monitoring circuit to detect arm and hand move- ment. Whenever continuous Isc ex- ceeds an individually set reference value, the strength of the electric field is immediately decreased by 75% for 30 sec, and then gradually returns to the original 9 kV/m level. When the original level is attained, the Isc comparison is again made. If the hands are still raised, field strength again decreases; if Isc is below the reference value, field strength continues to be maintained at 9 kV/m. Once an experimental session is started, operation of the double-blind system is completely automatic. Subjects Twelve men between 21 and 29 years of age volunteered to participate in the study, but only 11 subjects completed all of the experimental sessions. All were in good health and had not partic- ipated during the past year in a formal aerobic conditioning program. Each subject's daily activity pattern remained consistent throughout the duration of the study. After a complete and accurate verbal description of the procedures, risks, and benefits associated with the study, each subject provided written in- formed consent. Subjects were paid for their participation. Maximal Exercise Test In addition to measuring each sub- ject's aerobic power, the maximal exer- cise test was designed to determine the workload and heart rate that most closely corresponded with 50% of the VO2 max. Metabolic measurements were assessed using a breath-by-breath system. The subject wore a Hans- Rudolph respiratory mask (Hans Rudolph, Incorporated) connected to a Medical Graphics Wave-Form analyzer (Medical Graphics Corporation); 02 and C02 percentages were determined using a Perkin-Elmer MGA 1100 mass spectrometer. The subject cycled continuously on a bicycle ergometer (Monark A.B.) at 60 rpm beginning with a 2-min workload of 0 kgm-min~1 followed by incremental increases of 180 kgnvmin"1 every 3 min until volitional exhaustion. To ascertain that V02 max had been attained, each subject was required to meet at least three of the following criteria: (1) no fur- ther increase in oxygen uptake, despite an increase in workload (plateau crite- rion); (2) attainment of the age- predicted maximal heart rate; (3) a res- piratory exchange ratio (VC02/VO2) greater than 1.10; and (4) a blood lactic acid value of at least 8 mM-L~1 at 4 min after exercise. Experimental Sessions When a subject arrived at the labora- tory, he changed into a sweatsuit and cotton socks. Electrodes for recording heart rate were attached, a rectal tem- perature probe inserted, and a 20-gauge cannula maintained patent with a hep- arin lock inserted into a forearm vein. After a 30-min equilibration period, a blood sample was drawn; the standard- ized 45-min exercise/no-exercise period then began. Under the no-excercise condition, the subject sat quietly read- ing for the remainder of the period. Under exercise conditions, the subject cycled continuously (60 rpm) at appro- priately adjusted workload settings to maintain the desired 50% of his previ- ously determined V"O2 max. Heart rate and core temperature were monitored, and differentiated ratings of perceived exertion were recorded every 5 min. A 3-mL blood sample was drawn via the cannula after 30 min of exercise for measurement of lactic acid. Prior to con- clusion of the exercise test, another blood sample was drawn for measure- ment of all blood variables. Identical physiological and biochemical meas- ures were obtained under the no- exercise condition, except that the 30- min lactate sample was not required. After the exercise period, the subject ------- immediately entered the exposure facil- ity. The rectal probe and the subject's shoes were removed, the subject put the sweatshirt back on, and the electric field dosimetry "ground" was attached to both ankles. This transition required approximately 2 min. The real or sham field was then activated by initiating the computer program. Cardiac measures were obtained continuously during the exposure period. Blood pressure and blood samples for all blood variables were obtained at 10, 30, 60, 90, and 120 min after exercise. Approximately 2 min of field deactivation was required each time blood pressure readings and blood samples were obtained. Results The first goal of statistical analysis was to verify that the conditions speci- fied in the experimental design were met. No difference in temperature or humidity was found between real and sham exposure days. Subjects were un- able to distinguish between real and sham conditions at better than chance levels. All subjects met criteria for max- imal exercise tests, and increased metabolic steady-state was associated with the 45-min exercise regimen. Analysis of Experimental Variables Each dependent measure was sub- mitted to three analyses. The first ad- dressed the question of whether exer- cise, as compared to sitting quietly, altered the measure significantly. The other two analyses examined exercise and no-exercise conditions separately to determine whether exposure to 60-Hz fields had a significant effect. This strat- egy was chosen since a major hypothe- sis was that any field effects observed would show higher levels of statistical significance after exercise. Data at 10, 30, 60, 90, and 120 min from the end of the exercise or resting period were used for these analyses. An effect was considered to be statistically significant if probability was .05 or less. The Greenhouse-Geisser correction was used to adjust for inflated degrees of freedom due to repeated measures. Although exercise produced the ex- pected changes in the physiological and biochemical measures, the variables were not different under real and sham field conditions subsequent to exercise. However, when subjects rested quietly prior to exposure, heart rate was slower during exposure to the real fields than during exposure to sham fields. Com- parison between heart rate at the end of the first 10 min of exposure and after 120 min of exposure indicated that, on real field exposure days, subjects showed a significant decrease in heart rate, while on sham exposure days no change was found. This decrease in heart rate associated with exposure to the real fields occurred for 9 of the 11 subjects; the magnitude of the change was correlated with total exposure to the electric field as measured with short circuit current (r = .49, df 9, p < .10). No other differences in response between real and sham field exposure were found. Conclusions and Recommendations The feasibility of the methods and procedures used was clearly estab- lished. Exercise at 50% of maximal oxy- gen uptake produced the expected changes in plasma volume and in hor- mone, electrolyte, and lactic acid levels. When subjects were subsequently ex- posed to real and sham fields, the double-blind control procedures used were effective in preventing the sub- jects from distinguishing between the two conditions at better than chance levels. If subjects sat quietly instead of exercising during the preexposure pe- riod, heart rate significantly decreased during subsequent exposure to the real fields. This phenomenon was also ob- served in our previous study of field ex- posure effects. However, the use of moderate, steady-state exercise prior to exposure did not serve to clarify field effects. The recovery process was the same under real versus sham exposure conditions. These results suggest that future work should focus on evaluation of the effects of 60-Hz fields on the entire proc- ess of exercise-induced activation and recovery (pre-exercise, exercise, and re- covery). Ideally, such studies should: (1) contrast exercise results with results obtained after periods of very low phys- iological arousal; (2) vary the duration of exposure to fields before exercise; and (3) examine the effects of different intensities of exercise in the fields. ------- MaryR. Cook, Carl M. Maresh, and Harvey D. Cohen are with Midwest Research Institute, Kansas City. MO 64110. Carl F. Blackman is the EPA Project Officer (see below). The complete report, entitled "Effects of 60-Hz Fields on Human Health Parameters," (Order No. PB 86-231 297/AS; Cost: $ 11.95. subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Health Effects Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency Center for EnviroRrffSntal Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 EPA/600/S1-86/006 ------- |