181
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
These conclusions are consistent with the literature on the subject. Laboratory animals reportedly do not exhibit low impedance points (Matsumoto and Hayes 1973). Laboratory animals have a poorly developed stratum comeum. That laboratory animals do not exhibit low impedance points and have a poorly developed stratum comeum links the rupture of the stratum corneum to the existence of low impedance points. Our conclusions are also consistent with the contradictory data. in the literature. If low impedance points are interpreted in terms of the impedance of the stratum corneum, the contradictory data would be expected since the impedance of the stratum comeum depends on the impedance measuring technique and the condition of the stratum corneum of the individual from which the impedance data were collected. This is further supported by earlier attempts to locate acupuncture points by impedance which showed wide variation in measured impedance depending upon how the probe was manipulated (Noordergraaf and Silage, 1973). Finally, research indicates that acupuncture points do not represent specific points at all, but general areas in the body (Small 1974). If so, one would not expect low impedance points on the skin with diameters of the order of one millimeter to be the result of the anatomy of an acupuncture point. In short, the data presented and the literature reviewed in this study indicate that the electrical location of acupuncture points based on probe impedance is not an acceptable method. Low impedance points previously reported in the literature should be carefully reviewed in terms of the impedance of the epidermis of the skin, particularly the stratum corneum layer.
REFERENCES [1] Frost, E. and L. R. Orkin, "Localizations of acupuncture sites,"
[21 (3] [41 5]
[6]
Proceedings of the N.I.H. Acupuncture Research Conference, ed. H. P. Jenerick. Geddes, L. A., and M. F. Valentinuzzi, "Temporal changes in electrode impedance while recording the electrocardiogram with 'dry' electrodes," Annals of Biomedical Engineering, vol. 1, pp. 356-367, March, 1973. Kaslow, A. L., and 0. Lowenschuss, "Dragon chasing: a new technique for acupuncture point finding and stimulation," American Journal ofAcupuncture, vol. 3., No. 2, April-June, 1975. Matsumoto, I., and M. F. Hayes, "Acupuncture, electric phenomenon of the skin and postvagotomy gastrointestinal atony," 7he American Journal of Surgery, vol. 125, February, 1973. Noordergraaf, A., and D. Silage, "Electroacupuncture," IEEE Transactions on Biomedical Engineering, pp. 364-366, September, 1973. Small, T. L., "The neurophysiological basis for acupuncture," American Journal of Acupuncture, vol. 2, pp. 77-78, April-June,
1974. [7] Tan, L. T., M. T. C. Tan, I. Veith, Acupuncture Therapy (Temple University Press, Philadelphia), 1973.
Comments on "Laplace Plane Analysis of Transient Impedance Between Acupuncture Points Li-4 and Li-12" CHI- SANG POON In the above paperl the acupuncture system has been viewed
as an electrical transmission network consisting of a series impedance R, and a shunt impedance R2/(1 + jcwR2C) as a
Manuscript received June 1, 1978. The author is with the Biocybernetics Laboratory, Department of Engineering Systems, University of California, Los Angeles, CA 90024. 1M. Reichmanis, A. A. Marino, and R. 0. Becker, IEEE Trans. Biomed. Eng., vol. BME-24, pp. 402-405, 1977.
i
Ij,I i
4 0 jam "'--
-
-
-
-I) -
--
---~
epidermis dermis
Fig. 1. Current flux across the skin between two surface electrodes. A1
1/R2
A2
d
(joC)
2
R1
-AM
dermal pathway
Fig. 2. Equivalent electrical model for skin impedance.
single element defined by the acupuncture points. Using this analogy, results on transient measurements have led to the conclusion that the transmission line equivalent to the acupuncture network is capable of a higher signal transmission velocity and a lower characteristic impedance than other parts of the body surface. We note that the development of the equivalent transmission line model is basically a misleading concept totally irrelevant to our understanding of skin impedance and acupuncture, and is a reflection of the lack of electrophysiological committment in the design of the system model. To understand the situation better, the physiological significance of the observed skin impedance must first be fully identified. In experiments which involve progressive stripping of the skin, removing layers of the corneal cells from the skin surface, it has been asserted that the apparent resistance of the skin drops almost exponentially, showing that most of the resistivity of the skin is accountable by the epidermal stratum corneum [1] -[3]. When the epidermal part of the skin has been completely removed, the underlying dermal tissues are found to be relatively much more conductive and their contribution to the overall skin resistance are almost negligible. In Fig. 1, the current pathways between two surface electrodes placed on separate skin sites are shown to be directly across the corneum and running almost parallel to the skin surface in the sub-epidermal and dermal layers. For the thickness of the skin (- order of 100 ,um) to be much smaller than the dimension of the electrode, the current fluxes in the epidermal layers are expected to be almost perpendicular to the surface. The physical system is adequately described by the equivalent electrical network depicted in Fig. 2 where a frequency-dependent, constant-phase admittance element is used in place of the simple capacitive element C of the original model in order to account for the anomalous circular-arc complex impedance locus for the skin [4], [ 5 ]. Apparent enough, the network is far from being a transmission line system. It is noted that if the terminals A1 and A2 are connected by external circuits, transmission line theory will be applicable by treating each of the two impedances as an element of the line, but this unnecessary procedure can hardly be justified as far as internal signal propagation within the acupuncture network is concerned. REFERENCES 1. J. C. Lawler, M. J. Davis, and E. C. Griffith, "Electrical characteristics of the skin," J. Invest. Dermatol., 34, 1960.
001 8-9294/79/0300-0181$00.75 © 1979 IEEE
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
182
2. T. Yamamoto, Y. Yamamoto, "Electrical properties of the epidermal stratum corneum," Med. and Biol. Eng., Mar. 1976. 3. R. T. Tregear, Physical functions of skin, Academic Press, N.Y., 1966. 4. C. S. Poon, T. T. C. Choy, "Transient response studies of biological cell impedance," Med. and Biol. Eng., Nov. 1978. 5. K. S. Cole, Membranes, ions and impulses, University of Calif. Press,
Calif. 1968.
0S-
Comments on "Energy Flux Along High Voltage Transmission Lines"
Y. JO SETO AND JAMES A. CRONVICH Abstract-This communication is a critique of the above paper1 by Hart and Manno. The interpretation of their calculated Poynting vector as energy flux is disputed. ITe conclusion presented in their paper, based upon a comparison of their calculated Poynting vector induced by transmission line fields to microwave exposure standards, is examined.
In the above paper,1 Hart and Marino presented a calculation of the average, ground level, Poynting vector for a 765 kV, 60 Hz, three-phase overhead transmission line. The configuration of the transmission line used for the calculation is that for the proposed Ponnell Road-Sterling Volney line in New York. While the use of the image method for calculating ground level fields induced by overhead transmission lines is quite conventional, and thus acceptable, the interpretation of their calculated Poynting vector as energy flux, however, is conceptually questionable. Furthermore, their conclusions, implicit and explicit, based on a comparison of their calculated Poynting vector values to the U.S. and the Soviet microwave exposure standards as a measure of safety and hazardous exposure to electromagnetic fields under and near overhead transmission lines, are ill conceived. First, the original Poynting theorem is a statement of electromagnetic energy conservation in linear, isotropic media. In its differential form
aD aB V.S=E at at~H- a-E-J,(1 at the Poynting vector, S = E X H, has no convenient physical interpretation. But in its integral form
[
9fAS.dA=-f[E
at
at
-7+H- -+E-J]dv
conceptual difficulties in identifying S as "energy flux." The most obvious one is the nonuniqueness of S, since any arbitrary solenoidal vector can be added to E X H without affecting (1) and (2). Perhaps the most frequent application of the Poynting vector is in antenna theory, in which the radiation power flux is taken as E2/77, where q is the wave impedance of the medium [ 5 1. But this relation holds only in the far-field zone. Certainly the problem of the power transmission line given by Hart and Marino can hardly be considered as a far-field zone calculation. To many who are not familiar with electromagnetic field theory, the underlying difference in mathematical properties between dA and S might not seem readily apparent. In some respects the underlying difference between the energy absorbed S * dA and the "energy flux" S, is not unlike that between the more familiar quantities potential difference AO and potential function 0. Many persons tend to overlook the differences between the energy absorbed S* dA and "energy flux" S, just as they do between potential difference AO and the potential function 4. The potential difference is a unique and measurable quantity, but the potential function is not. (When analyzing a physical system, one should be careful to choose a unique and measurable quantity as the end point parameter lest one run the risk of not being able to compare analytical results with experimental measurements.) The numerical values calculated by Hart and Marino are for S = 151 in air, essentially a non-conductive medium. If the polarization of air molecules is neglected, which is allowed under the linearity and isotropicity constraint of the Poynting theorem, one expects that 5AS * dA 0 over any closed surface enclosing a volume of air. This means that no power is absorbed within this volume regardless of how large S is. On the other hand, if one wishes to find the power absorbed in biological tissues, one must perform the closed surface integration over the surface of the tissue in question. But then the vector S in this integral must be that in the tissue, not that calculated by Hart and Marino. The importance of recognizing that the Poynting vector depends strongly on the medium has been pointed out by Youmans and Ho [61. The second point to be discussed here is the conclusion
2
(2)
the integral on the left side of the equality sign has a meaningful interpretation as the net energy flow per unit time out of the volume V, bounded by the surface A. To facilitate a simple
explanation, some elementary textbooks on electromagnetic field theory identify S as a quantity which is related to electromagnetic energy flow density and term it energy flux; but
most advanced level textbooks caution the reader about such over-simplified interpretation [11-[4]. There are many
an
Manuscript received October 10, 1977; revised June 2, 1978. The authors are with the Department of Electrical Engineering and the Electroscience and Biophysics Research Laboratories, Tulane University, New Orleans, LA 701 18. 1 F. X Hart and A. A. Marino, IEEE Trans. Biomed. Eng., vol. BME24, no. 5, Sept. 1977.
reached by Hart and Marino by comparing their calculated values of S to those of the U.S. and the Soviet microwave exposure standards. Incidentally, these exposure standards are to be maintained by measurements in air using dosimeters (i.e., ( 1A)AS* dA ), not by calculating values of Poynting vectors. The distinction between the "energy flux" 9, and the energy flux (I1IA)fA. dA, is the very base for dosimeter designs. Aside from the inappropriate interpretation of S as true and measurable energy flux, the conclusion in the above paper1 failed to consider the frequency dependence of coupling electromagnetic energy from air to tissue and the frequency dependence of electromagnetic energy absorption in tissue. On the average, the permittivity of biological tissues at 60 Hz is about six orders of magnitude higher than that at microwave frequencies [7, [ 81. The percentage of electromagnetic energy coupled from air into tissue at 60 Hz is, therefore, many orders of magnitude smaller than that at microwave frequencies. In addition, tissue resistivity at 60 Hz, and thus the fraction of energy absorbed, is about an order of magnitude lower than that at microwave frequencies [9]. These phenomena simply reflect the dispersive nature of biological tissues. One may also point out that the mere consideration of energy flux is not necessarily the best means for investigating possible hazardous exposure to electromagnetic fields. Many other field parameters (e.g., frequency, field gradient, field polarization, etc.) may have more important effects on biological systems. Furthermore, the investigation is incomplete if one
0018-9294/79/0300-0182$00.75 i 1979 IEEE
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
These conclusions are consistent with the literature on the subject. Laboratory animals reportedly do not exhibit low impedance points (Matsumoto and Hayes 1973). Laboratory animals have a poorly developed stratum comeum. That laboratory animals do not exhibit low impedance points and have a poorly developed stratum comeum links the rupture of the stratum corneum to the existence of low impedance points. Our conclusions are also consistent with the contradictory data. in the literature. If low impedance points are interpreted in terms of the impedance of the stratum corneum, the contradictory data would be expected since the impedance of the stratum comeum depends on the impedance measuring technique and the condition of the stratum corneum of the individual from which the impedance data were collected. This is further supported by earlier attempts to locate acupuncture points by impedance which showed wide variation in measured impedance depending upon how the probe was manipulated (Noordergraaf and Silage, 1973). Finally, research indicates that acupuncture points do not represent specific points at all, but general areas in the body (Small 1974). If so, one would not expect low impedance points on the skin with diameters of the order of one millimeter to be the result of the anatomy of an acupuncture point. In short, the data presented and the literature reviewed in this study indicate that the electrical location of acupuncture points based on probe impedance is not an acceptable method. Low impedance points previously reported in the literature should be carefully reviewed in terms of the impedance of the epidermis of the skin, particularly the stratum corneum layer.
REFERENCES [1] Frost, E. and L. R. Orkin, "Localizations of acupuncture sites,"
[21 (3] [41 5]
[6]
Proceedings of the N.I.H. Acupuncture Research Conference, ed. H. P. Jenerick. Geddes, L. A., and M. F. Valentinuzzi, "Temporal changes in electrode impedance while recording the electrocardiogram with 'dry' electrodes," Annals of Biomedical Engineering, vol. 1, pp. 356-367, March, 1973. Kaslow, A. L., and 0. Lowenschuss, "Dragon chasing: a new technique for acupuncture point finding and stimulation," American Journal ofAcupuncture, vol. 3., No. 2, April-June, 1975. Matsumoto, I., and M. F. Hayes, "Acupuncture, electric phenomenon of the skin and postvagotomy gastrointestinal atony," 7he American Journal of Surgery, vol. 125, February, 1973. Noordergraaf, A., and D. Silage, "Electroacupuncture," IEEE Transactions on Biomedical Engineering, pp. 364-366, September, 1973. Small, T. L., "The neurophysiological basis for acupuncture," American Journal of Acupuncture, vol. 2, pp. 77-78, April-June,
1974. [7] Tan, L. T., M. T. C. Tan, I. Veith, Acupuncture Therapy (Temple University Press, Philadelphia), 1973.
Comments on "Laplace Plane Analysis of Transient Impedance Between Acupuncture Points Li-4 and Li-12" CHI- SANG POON In the above paperl the acupuncture system has been viewed
as an electrical transmission network consisting of a series impedance R, and a shunt impedance R2/(1 + jcwR2C) as a
Manuscript received June 1, 1978. The author is with the Biocybernetics Laboratory, Department of Engineering Systems, University of California, Los Angeles, CA 90024. 1M. Reichmanis, A. A. Marino, and R. 0. Becker, IEEE Trans. Biomed. Eng., vol. BME-24, pp. 402-405, 1977.
i
Ij,I i
4 0 jam "'--
-
-
-
-I) -
--
---~
epidermis dermis
Fig. 1. Current flux across the skin between two surface electrodes. A1
1/R2
A2
d
(joC)
2
R1
-AM
dermal pathway
Fig. 2. Equivalent electrical model for skin impedance.
single element defined by the acupuncture points. Using this analogy, results on transient measurements have led to the conclusion that the transmission line equivalent to the acupuncture network is capable of a higher signal transmission velocity and a lower characteristic impedance than other parts of the body surface. We note that the development of the equivalent transmission line model is basically a misleading concept totally irrelevant to our understanding of skin impedance and acupuncture, and is a reflection of the lack of electrophysiological committment in the design of the system model. To understand the situation better, the physiological significance of the observed skin impedance must first be fully identified. In experiments which involve progressive stripping of the skin, removing layers of the corneal cells from the skin surface, it has been asserted that the apparent resistance of the skin drops almost exponentially, showing that most of the resistivity of the skin is accountable by the epidermal stratum corneum [1] -[3]. When the epidermal part of the skin has been completely removed, the underlying dermal tissues are found to be relatively much more conductive and their contribution to the overall skin resistance are almost negligible. In Fig. 1, the current pathways between two surface electrodes placed on separate skin sites are shown to be directly across the corneum and running almost parallel to the skin surface in the sub-epidermal and dermal layers. For the thickness of the skin (- order of 100 ,um) to be much smaller than the dimension of the electrode, the current fluxes in the epidermal layers are expected to be almost perpendicular to the surface. The physical system is adequately described by the equivalent electrical network depicted in Fig. 2 where a frequency-dependent, constant-phase admittance element is used in place of the simple capacitive element C of the original model in order to account for the anomalous circular-arc complex impedance locus for the skin [4], [ 5 ]. Apparent enough, the network is far from being a transmission line system. It is noted that if the terminals A1 and A2 are connected by external circuits, transmission line theory will be applicable by treating each of the two impedances as an element of the line, but this unnecessary procedure can hardly be justified as far as internal signal propagation within the acupuncture network is concerned. REFERENCES 1. J. C. Lawler, M. J. Davis, and E. C. Griffith, "Electrical characteristics of the skin," J. Invest. Dermatol., 34, 1960.
001 8-9294/79/0300-0181$00.75 © 1979 IEEE
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
182
2. T. Yamamoto, Y. Yamamoto, "Electrical properties of the epidermal stratum corneum," Med. and Biol. Eng., Mar. 1976. 3. R. T. Tregear, Physical functions of skin, Academic Press, N.Y., 1966. 4. C. S. Poon, T. T. C. Choy, "Transient response studies of biological cell impedance," Med. and Biol. Eng., Nov. 1978. 5. K. S. Cole, Membranes, ions and impulses, University of Calif. Press,
Calif. 1968.
0S-
Comments on "Energy Flux Along High Voltage Transmission Lines"
Y. JO SETO AND JAMES A. CRONVICH Abstract-This communication is a critique of the above paper1 by Hart and Manno. The interpretation of their calculated Poynting vector as energy flux is disputed. ITe conclusion presented in their paper, based upon a comparison of their calculated Poynting vector induced by transmission line fields to microwave exposure standards, is examined.
In the above paper,1 Hart and Marino presented a calculation of the average, ground level, Poynting vector for a 765 kV, 60 Hz, three-phase overhead transmission line. The configuration of the transmission line used for the calculation is that for the proposed Ponnell Road-Sterling Volney line in New York. While the use of the image method for calculating ground level fields induced by overhead transmission lines is quite conventional, and thus acceptable, the interpretation of their calculated Poynting vector as energy flux, however, is conceptually questionable. Furthermore, their conclusions, implicit and explicit, based on a comparison of their calculated Poynting vector values to the U.S. and the Soviet microwave exposure standards as a measure of safety and hazardous exposure to electromagnetic fields under and near overhead transmission lines, are ill conceived. First, the original Poynting theorem is a statement of electromagnetic energy conservation in linear, isotropic media. In its differential form
aD aB V.S=E at at~H- a-E-J,(1 at the Poynting vector, S = E X H, has no convenient physical interpretation. But in its integral form
[
9fAS.dA=-f[E
at
at
-7+H- -+E-J]dv
conceptual difficulties in identifying S as "energy flux." The most obvious one is the nonuniqueness of S, since any arbitrary solenoidal vector can be added to E X H without affecting (1) and (2). Perhaps the most frequent application of the Poynting vector is in antenna theory, in which the radiation power flux is taken as E2/77, where q is the wave impedance of the medium [ 5 1. But this relation holds only in the far-field zone. Certainly the problem of the power transmission line given by Hart and Marino can hardly be considered as a far-field zone calculation. To many who are not familiar with electromagnetic field theory, the underlying difference in mathematical properties between dA and S might not seem readily apparent. In some respects the underlying difference between the energy absorbed S * dA and the "energy flux" S, is not unlike that between the more familiar quantities potential difference AO and potential function 0. Many persons tend to overlook the differences between the energy absorbed S* dA and "energy flux" S, just as they do between potential difference AO and the potential function 4. The potential difference is a unique and measurable quantity, but the potential function is not. (When analyzing a physical system, one should be careful to choose a unique and measurable quantity as the end point parameter lest one run the risk of not being able to compare analytical results with experimental measurements.) The numerical values calculated by Hart and Marino are for S = 151 in air, essentially a non-conductive medium. If the polarization of air molecules is neglected, which is allowed under the linearity and isotropicity constraint of the Poynting theorem, one expects that 5AS * dA 0 over any closed surface enclosing a volume of air. This means that no power is absorbed within this volume regardless of how large S is. On the other hand, if one wishes to find the power absorbed in biological tissues, one must perform the closed surface integration over the surface of the tissue in question. But then the vector S in this integral must be that in the tissue, not that calculated by Hart and Marino. The importance of recognizing that the Poynting vector depends strongly on the medium has been pointed out by Youmans and Ho [61. The second point to be discussed here is the conclusion
2
(2)
the integral on the left side of the equality sign has a meaningful interpretation as the net energy flow per unit time out of the volume V, bounded by the surface A. To facilitate a simple
explanation, some elementary textbooks on electromagnetic field theory identify S as a quantity which is related to electromagnetic energy flow density and term it energy flux; but
most advanced level textbooks caution the reader about such over-simplified interpretation [11-[4]. There are many
an
Manuscript received October 10, 1977; revised June 2, 1978. The authors are with the Department of Electrical Engineering and the Electroscience and Biophysics Research Laboratories, Tulane University, New Orleans, LA 701 18. 1 F. X Hart and A. A. Marino, IEEE Trans. Biomed. Eng., vol. BME24, no. 5, Sept. 1977.
reached by Hart and Marino by comparing their calculated values of S to those of the U.S. and the Soviet microwave exposure standards. Incidentally, these exposure standards are to be maintained by measurements in air using dosimeters (i.e., ( 1A)AS* dA ), not by calculating values of Poynting vectors. The distinction between the "energy flux" 9, and the energy flux (I1IA)fA. dA, is the very base for dosimeter designs. Aside from the inappropriate interpretation of S as true and measurable energy flux, the conclusion in the above paper1 failed to consider the frequency dependence of coupling electromagnetic energy from air to tissue and the frequency dependence of electromagnetic energy absorption in tissue. On the average, the permittivity of biological tissues at 60 Hz is about six orders of magnitude higher than that at microwave frequencies [7, [ 81. The percentage of electromagnetic energy coupled from air into tissue at 60 Hz is, therefore, many orders of magnitude smaller than that at microwave frequencies. In addition, tissue resistivity at 60 Hz, and thus the fraction of energy absorbed, is about an order of magnitude lower than that at microwave frequencies [9]. These phenomena simply reflect the dispersive nature of biological tissues. One may also point out that the mere consideration of energy flux is not necessarily the best means for investigating possible hazardous exposure to electromagnetic fields. Many other field parameters (e.g., frequency, field gradient, field polarization, etc.) may have more important effects on biological systems. Furthermore, the investigation is incomplete if one
0018-9294/79/0300-0182$00.75 i 1979 IEEE
