- Email: [email protected]
Re: “electrical maturation trajectory of human tissues identified by bioelectrical impedance vector analysis”
LETTERS TO THE EDITOR
319
think this is an important point because, in my view, Geelhoed responds well7 to the main criticisms leveled by Sugarman3 and Daly.4 Why, then, was his response not incorporated into a reworked version of his original manuscript before it was sent to the second set of reviewers or, especially, before it was published? In publishing it the way you have, it appears that an unnecessary amount of controversy is created that leaves egg on the faces of Geelhoed, Sugarman, and Daly. Have I been mistakenly placated by Geelhoed’s response?7 If so, that is what deserves the editorial/commentary process, rather than what appears to be the unnecessary vilification of an unpolished manuscript instead of an unethical project.
Stephen Cunnane, PhD Department of Nutritional Sciences University of Toronto Toronto, Canada REFERENCES 1. Meguid MM. A glimpse into the process . . . . Nutrition 1999;15:933 2. Geelhoed GW. Metabolic maladaptation: individual and social consequences of medical intervention in correcting endemic hypothyroidism. Nutrition 1999;15: 908 3. Sugarman J. Moral maladaptation? Reflections on a report of research involving the correction of endemic hypothyroidism in Africa. Nutrition 1999;15:934 4. Daly RW. Medical imperialism in the Congo? Nutrition 1999;15:936 5. MacFie J. Informed consent and other ethical issues: a clinician’s view. Nutrition 1999;15:937 6. Dobson JE. On “metabolic maladaptation: individual and social consequences of medical intervention in correcting endemic hypothyroidism” by Glenn William Geelhoed, MD, DTMH, MPH, FACS. Nutrition 1999;15:939 7. Geelhoed GW. An author’s editorial: health care advocacy in world health. Nutrition 1999;15:940
PII S0899-9007(00)00224-0
Editor’s Response As mentioned in my editorial,1 none of the six reviewers were invited to write a contributory editorial. In view of the controversial reviews of the papers which were received and which reflected a wide spectrum of opinion, the Editor, in consultation with Editorial Board members, invited editorials from ethicists, surgeons, and others. Dr. Geelhoed did have an opportunity to review the editorials and did have an opportunity to respond to them in an editorial format.2 Geelhoed also revised the manuscript according to the extensive review/critique provided to him from the six reviewers, which constituted the final manuscript. There is no perfect way to this process, only a fair way, which this Editor believes was used.
Michael M. Meguid, MD, PhD Professor Editor-In-Chief Department of Surgery SUNY Upstate Medical University Syracuse, New York, USA REFERENCES
Re: “Electrical Maturation Trajectory of Human Tissues Identified by Bioelectrical Impedance Vector Analysis” To the Editor: We read with interest the recent letter to the editor by Piccoli et al.1 concerning the “electrical maturation” of human tissues in which Piccoli et al. reported a preliminary bioelectrical impedance vector analysis (BIVA) of bioelectrical impedance data for 150 Caucasian children, ranging in age from 1 mo to 6 y. In BIVA, data are presented as “R-Xc” plots2 in which the resistive and reactive components of impedance, standardized for height, are plotted as vectors on either gender-specific bivariate tolerance ellipses for individual data or confidence ellipses for group means. Reference ellipses for healthy subjects are constructed as normative data against which data for individuals or subject groups may be compared.3 The method has previously proved valuable in adults for discriminating healthy, obese, and edematous subjects.4,5 The stated aim of the present work by Piccoli et al. was to extend the reference data back to birth. Two features of the present study are worthy of comment. First, it is clear, from the data presented by Piccoli et al. in Figure 1 of their paper, that the confidence ellipses for the adults, both male and female, are considerably smaller than those for the children, stratified into the age bands younger than 1 y, 1 to 3 y, and 4 to 6 y. It should be noted that the confidence interval, or ellipse, is critically dependent on sample size. Unfortunately, Piccoli et al. did not provide the precise numbers of children in each of the age strata. Presumably these approximate 50 per group compared with adult group sizes of about 350 subjects. Furthermore, the visually striking separation of confidence ellipses for the different groups tends to obscure the fact that the data are drawn from an age continuum that has been stratified by the researcher into specific age bands and, hence, inevitably yielding discrete and separate 95% confidence ellipses. Second, Piccoli et al. speculate that the left downward trajectory of the impedance vectors toward the origin with increasing age represents an electrical maturation process of human tissues. An alternative, more prosaic explanation is that it simply represents increasing body size independent of any inherent change in the electrical properties of body tissues.6 The adult population studied by Piccoli et al. ranged in body mass index (BMI) from 16 to 31 kg/m2, whereas the BMIs of the children ranged from 10.2 to 19.3 kg/m2. Stratification of subjects, even within a general adult population, according to BMI irrespective of age produces a similar downward trajectory of ellipses to that presented by Piccoli et al. In Figure 1, we show R-Xc plots for 1051 males and 1039 females, ranging in BMI from 17 to 47.5 and from 15.6 to 48 kg/m2, respectively, stratified in BMI bands: less than 20, from 20 to less than 25, from 25 to less than 30, from 30 to less than 35, and more than 35 kg/m2 (data taken from the Danish MONICA study7). These data indicate that the impedance vector in overtly healthy subjects is closely related to body size, as indicated by BMI. In further support of this notion, even the slight downward vertical displacement of the ellipse for the children 1 to 3 y old may reflect the non-linear growth development seen in this age group.8 Because the BIVA method has proved useful in distinguishing subjects with altered hydration status from the general healthy population,4,5 the discriminatory power of the method may be
1. Meguid MM. A glimpse into the process. Nutrition 1999;15:933 2. Geelhoed GW. An author’s editorial: health care advocacy in world health. Nutrition 1999;15:940
PII S0899-9007(00)00261-6
Correspondence to: Leigh C. Ward, PhD, Department of Biochemistry, University of Queensland, Brisbane, Australia QLD 4072.
320
LETTERS TO THE EDITOR
FIG. 1. R-Xc plot of 95% confidence ellipse for healthy male and female subjects (40 –70 y) stratified by gender and body mass index. R is whole body electrical resistance (ohm), Xc electrical reactance (ohm) and H height (m). Numbers in parentheses in the legend are the numbers of subjects in each group.
enhanced by presenting data not simply as gender-specific ellipses for adults or children but as a continuum of ellipses across BMI bands.
Leigh C. Ward, PhD Department of Biochemistry University of Queensland Brisbane, Australia Berit L. Heitmann, PhD The Copenhagen County Center for Preventive Medicine Glostrup University Hospital Copenhagen, Denmark REFERENCES 1. Piccoli A, Pillon L, Pisanello L, Zachello G. Electrical maturation trajectory of human tissues identified by bioelectrical impedance vector analysis. Nutrition 1999;15:77 2. Piccoli A, Rossi B, Pillon L, Bucciante G. A new method for monitoring body fluid variation by bioimpedance analysis: the RXc graph. Kidney Int 1994;46:534 3. Piccoli A, Nigrelli S, Caberlotto A, et al. Bivariate normal values of the bioelectrical impedance vector in adult and elderly populations. Am J Clin Nutr 1995; 61:269 4. Piccoli A, Brunani A, Savia G, et al. Discriminating between body fat and fluid changes in the obese adult using bioimpedance vector analysis. Int J Obes 1998; 22:97 5. Piccoli A. Identification of operational clues to dry weight prescription in hemodialysis using bioimpedance vector analysis. Kidney Int 1998;53:106 6. Ward L, Heitmann BL. Multiple frequency bioelectrical impedance (MFBIA) and R-Xc plots in the assessment of obesity. Proc Austral Soc Study Obes 1998;7:20 7. Heitmann BL. Body fat in the adult Danish population aged 35– 65 years. Int J Obes 1991;15:535 8. Rolland-Cachera MF, Deheeger M, Akrout M, Bellisle F. Influence of macronutrients on adiposity development: a follow-up study of nutrition and growth from 10 months to 8 years of age. Int J Obes 1995;19:573
PII S0899-9007(00)00225-2
Author’s Response Re: “Electrical Maturation Trajectory of Human Tissues Identified by Bioelectrical Impedance Vector Analysis” To the Editor: Our preliminary study1 consisted of 150 white subjects divided into three age groups: 70 children were ages 1 mo–1 y, 47 were 1–3 y, and 33 were 4 – 6 y. The 95% confidence ellipse of the mean vector from children of younger than 1 y was larger than that of the other two groups, despite the double sample size, because of a greater variability of vector components. It was also different in shape because of a different correlation coefficient between vector components (age ⬍ 1 y, r ⫽ ⫺0.11; 1–3 y, r ⫽ 0.40; and 4 – 6 y, r ⫽ 0.54). The body mass index (BMI) of the children ranged from 10.2 to 19.3 kg/m2, with averages of 16.3 (SD 1.4), 16.3 (SD 1.3), and 15.7 (SD 1.2) kg/m2 in children younger than 1 y, 1–3 y, and 4 – 6 y, respectively. The difference among groups was not statistically significant (F ⫽ 2.3, one-way analysis of variance). With twoway analysis of variance, there was no significant influence by either 1-y age classes (F ⫽ 2.0) or gender (F ⫽ 0.1) on BMI averages. The correlation coefficients between BMI and age (r ⫽ ⫺0.18) as well as between BMI and vector components (r ⫽ ⫺0.06 with R/H, and r ⫽ ⫺0.16 with Xc/H) were low. Therefore, we could not explain the observed trend of impedance vectors over age with BMI variations, as suggested by Ward and Heitmann in their Letter to the Editor.2 Instead, the pattern of negative correlation of age (6-y range) with vector components, namely r ⫽ ⫺0.62 with R/H and r ⫽ ⫺0.23 with Xc/H, was consistent with
Correspondence to: Antonio Piccoli, MD, BSc, Istituto di Medicina Interna, Via Giustiniani, 2, I-35128 Padova, Italy. E-mail: apiccoli@ ux1.unipd.it
319
think this is an important point because, in my view, Geelhoed responds well7 to the main criticisms leveled by Sugarman3 and Daly.4 Why, then, was his response not incorporated into a reworked version of his original manuscript before it was sent to the second set of reviewers or, especially, before it was published? In publishing it the way you have, it appears that an unnecessary amount of controversy is created that leaves egg on the faces of Geelhoed, Sugarman, and Daly. Have I been mistakenly placated by Geelhoed’s response?7 If so, that is what deserves the editorial/commentary process, rather than what appears to be the unnecessary vilification of an unpolished manuscript instead of an unethical project.
Stephen Cunnane, PhD Department of Nutritional Sciences University of Toronto Toronto, Canada REFERENCES 1. Meguid MM. A glimpse into the process . . . . Nutrition 1999;15:933 2. Geelhoed GW. Metabolic maladaptation: individual and social consequences of medical intervention in correcting endemic hypothyroidism. Nutrition 1999;15: 908 3. Sugarman J. Moral maladaptation? Reflections on a report of research involving the correction of endemic hypothyroidism in Africa. Nutrition 1999;15:934 4. Daly RW. Medical imperialism in the Congo? Nutrition 1999;15:936 5. MacFie J. Informed consent and other ethical issues: a clinician’s view. Nutrition 1999;15:937 6. Dobson JE. On “metabolic maladaptation: individual and social consequences of medical intervention in correcting endemic hypothyroidism” by Glenn William Geelhoed, MD, DTMH, MPH, FACS. Nutrition 1999;15:939 7. Geelhoed GW. An author’s editorial: health care advocacy in world health. Nutrition 1999;15:940
PII S0899-9007(00)00224-0
Editor’s Response As mentioned in my editorial,1 none of the six reviewers were invited to write a contributory editorial. In view of the controversial reviews of the papers which were received and which reflected a wide spectrum of opinion, the Editor, in consultation with Editorial Board members, invited editorials from ethicists, surgeons, and others. Dr. Geelhoed did have an opportunity to review the editorials and did have an opportunity to respond to them in an editorial format.2 Geelhoed also revised the manuscript according to the extensive review/critique provided to him from the six reviewers, which constituted the final manuscript. There is no perfect way to this process, only a fair way, which this Editor believes was used.
Michael M. Meguid, MD, PhD Professor Editor-In-Chief Department of Surgery SUNY Upstate Medical University Syracuse, New York, USA REFERENCES
Re: “Electrical Maturation Trajectory of Human Tissues Identified by Bioelectrical Impedance Vector Analysis” To the Editor: We read with interest the recent letter to the editor by Piccoli et al.1 concerning the “electrical maturation” of human tissues in which Piccoli et al. reported a preliminary bioelectrical impedance vector analysis (BIVA) of bioelectrical impedance data for 150 Caucasian children, ranging in age from 1 mo to 6 y. In BIVA, data are presented as “R-Xc” plots2 in which the resistive and reactive components of impedance, standardized for height, are plotted as vectors on either gender-specific bivariate tolerance ellipses for individual data or confidence ellipses for group means. Reference ellipses for healthy subjects are constructed as normative data against which data for individuals or subject groups may be compared.3 The method has previously proved valuable in adults for discriminating healthy, obese, and edematous subjects.4,5 The stated aim of the present work by Piccoli et al. was to extend the reference data back to birth. Two features of the present study are worthy of comment. First, it is clear, from the data presented by Piccoli et al. in Figure 1 of their paper, that the confidence ellipses for the adults, both male and female, are considerably smaller than those for the children, stratified into the age bands younger than 1 y, 1 to 3 y, and 4 to 6 y. It should be noted that the confidence interval, or ellipse, is critically dependent on sample size. Unfortunately, Piccoli et al. did not provide the precise numbers of children in each of the age strata. Presumably these approximate 50 per group compared with adult group sizes of about 350 subjects. Furthermore, the visually striking separation of confidence ellipses for the different groups tends to obscure the fact that the data are drawn from an age continuum that has been stratified by the researcher into specific age bands and, hence, inevitably yielding discrete and separate 95% confidence ellipses. Second, Piccoli et al. speculate that the left downward trajectory of the impedance vectors toward the origin with increasing age represents an electrical maturation process of human tissues. An alternative, more prosaic explanation is that it simply represents increasing body size independent of any inherent change in the electrical properties of body tissues.6 The adult population studied by Piccoli et al. ranged in body mass index (BMI) from 16 to 31 kg/m2, whereas the BMIs of the children ranged from 10.2 to 19.3 kg/m2. Stratification of subjects, even within a general adult population, according to BMI irrespective of age produces a similar downward trajectory of ellipses to that presented by Piccoli et al. In Figure 1, we show R-Xc plots for 1051 males and 1039 females, ranging in BMI from 17 to 47.5 and from 15.6 to 48 kg/m2, respectively, stratified in BMI bands: less than 20, from 20 to less than 25, from 25 to less than 30, from 30 to less than 35, and more than 35 kg/m2 (data taken from the Danish MONICA study7). These data indicate that the impedance vector in overtly healthy subjects is closely related to body size, as indicated by BMI. In further support of this notion, even the slight downward vertical displacement of the ellipse for the children 1 to 3 y old may reflect the non-linear growth development seen in this age group.8 Because the BIVA method has proved useful in distinguishing subjects with altered hydration status from the general healthy population,4,5 the discriminatory power of the method may be
1. Meguid MM. A glimpse into the process. Nutrition 1999;15:933 2. Geelhoed GW. An author’s editorial: health care advocacy in world health. Nutrition 1999;15:940
PII S0899-9007(00)00261-6
Correspondence to: Leigh C. Ward, PhD, Department of Biochemistry, University of Queensland, Brisbane, Australia QLD 4072.
320
LETTERS TO THE EDITOR
FIG. 1. R-Xc plot of 95% confidence ellipse for healthy male and female subjects (40 –70 y) stratified by gender and body mass index. R is whole body electrical resistance (ohm), Xc electrical reactance (ohm) and H height (m). Numbers in parentheses in the legend are the numbers of subjects in each group.
enhanced by presenting data not simply as gender-specific ellipses for adults or children but as a continuum of ellipses across BMI bands.
Leigh C. Ward, PhD Department of Biochemistry University of Queensland Brisbane, Australia Berit L. Heitmann, PhD The Copenhagen County Center for Preventive Medicine Glostrup University Hospital Copenhagen, Denmark REFERENCES 1. Piccoli A, Pillon L, Pisanello L, Zachello G. Electrical maturation trajectory of human tissues identified by bioelectrical impedance vector analysis. Nutrition 1999;15:77 2. Piccoli A, Rossi B, Pillon L, Bucciante G. A new method for monitoring body fluid variation by bioimpedance analysis: the RXc graph. Kidney Int 1994;46:534 3. Piccoli A, Nigrelli S, Caberlotto A, et al. Bivariate normal values of the bioelectrical impedance vector in adult and elderly populations. Am J Clin Nutr 1995; 61:269 4. Piccoli A, Brunani A, Savia G, et al. Discriminating between body fat and fluid changes in the obese adult using bioimpedance vector analysis. Int J Obes 1998; 22:97 5. Piccoli A. Identification of operational clues to dry weight prescription in hemodialysis using bioimpedance vector analysis. Kidney Int 1998;53:106 6. Ward L, Heitmann BL. Multiple frequency bioelectrical impedance (MFBIA) and R-Xc plots in the assessment of obesity. Proc Austral Soc Study Obes 1998;7:20 7. Heitmann BL. Body fat in the adult Danish population aged 35– 65 years. Int J Obes 1991;15:535 8. Rolland-Cachera MF, Deheeger M, Akrout M, Bellisle F. Influence of macronutrients on adiposity development: a follow-up study of nutrition and growth from 10 months to 8 years of age. Int J Obes 1995;19:573
PII S0899-9007(00)00225-2
Author’s Response Re: “Electrical Maturation Trajectory of Human Tissues Identified by Bioelectrical Impedance Vector Analysis” To the Editor: Our preliminary study1 consisted of 150 white subjects divided into three age groups: 70 children were ages 1 mo–1 y, 47 were 1–3 y, and 33 were 4 – 6 y. The 95% confidence ellipse of the mean vector from children of younger than 1 y was larger than that of the other two groups, despite the double sample size, because of a greater variability of vector components. It was also different in shape because of a different correlation coefficient between vector components (age ⬍ 1 y, r ⫽ ⫺0.11; 1–3 y, r ⫽ 0.40; and 4 – 6 y, r ⫽ 0.54). The body mass index (BMI) of the children ranged from 10.2 to 19.3 kg/m2, with averages of 16.3 (SD 1.4), 16.3 (SD 1.3), and 15.7 (SD 1.2) kg/m2 in children younger than 1 y, 1–3 y, and 4 – 6 y, respectively. The difference among groups was not statistically significant (F ⫽ 2.3, one-way analysis of variance). With twoway analysis of variance, there was no significant influence by either 1-y age classes (F ⫽ 2.0) or gender (F ⫽ 0.1) on BMI averages. The correlation coefficients between BMI and age (r ⫽ ⫺0.18) as well as between BMI and vector components (r ⫽ ⫺0.06 with R/H, and r ⫽ ⫺0.16 with Xc/H) were low. Therefore, we could not explain the observed trend of impedance vectors over age with BMI variations, as suggested by Ward and Heitmann in their Letter to the Editor.2 Instead, the pattern of negative correlation of age (6-y range) with vector components, namely r ⫽ ⫺0.62 with R/H and r ⫽ ⫺0.23 with Xc/H, was consistent with
Correspondence to: Antonio Piccoli, MD, BSc, Istituto di Medicina Interna, Via Giustiniani, 2, I-35128 Padova, Italy. E-mail: apiccoli@ ux1.unipd.it