|
|
||||||||
Original Research Communications |
1 From the Klinik I für Innere Medizin der Universität zu Köln, Cologne, Germany, and Addenbrooke's Hospital, Cambridge, United Kingdom.
2 Address reprint requests to A Schwenk, Department of Infectious Disease, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, United Kingdom. E-mail: a.schwenk{at}sghms.ac.uk.
| ABSTRACT |
|---|
|
|
|---|
Objective: Our objective was to assess the prognostic ability of the phase angle in HIV-infected patients in the era of HAART.
Design: Two cross-sectional observation studies were conducted in 1996 and 1997 at a German university outpatient HIV clinic. In the 1996 and 1997 cohorts, HAART was prescribed to 17 of 212 and 168 of 257 patients at baseline and to 179 of 212 and 234 of 257 patients during observation, respectively. Whole-body BIA was assessed at 50 KHz. Time to clinical progression and survival were calculated by using Cox proportional hazard models with time-dependent covariates. Median observation times were 1000 and 515 d for the 1996 and 1997 cohorts, respectively.
Results: Higher phase angle was associated with a lower relative mortality risk, adjusted for viral load and CD4+ cell count, of 0.49 (95% CI: 0.30, 0.81) per degree in 1996 and of 0.33 (95% CI: 0.18, 0.61) in 1997. The influence of phase angle on time to clinical progression, adjusted for viral load and CD4+ cell count, was not significant in 1996 but the relative risk was 0.58 (0.36, 0.83) in 1997.
Conclusion: Despite the favorable effects of HAART on the nutritional status of HIV-infected persons, low phase angle remains an independent adverse prognostic marker of clinical progression and survival.
Key Words: Acquired immunodeficiency syndrome AIDS biological markers body fluid compartments body composition bioelectrical impedance HIV infection survival analysis
| INTRODUCTION |
|---|
|
|
|---|
The current study was undertaken to determine whether a low phase angle with BIA is still associated with a poor prognosis if considered together with other state-of-the-art prognostic markers and their changes during antiretroviral treatment. The phase angle is defined as the relation between the 2 vector components of impedance: resistance and reactance. It may be interpreted as an indicator of water distribution between the extra- and intracellular spaces. However, the relation of impedance to body composition is indirect and incompletely understood (11). Therefore, the phase angle, rather than derived body-composition estimates, was examined for its prognostic weight in the current study.
This study was part of a series of cross-sectional and longitudinal BIA measurements in a defined population of HIV-infected outpatients in the era of rapid improvements in antiretroviral therapy. Data on the effect of protease inhibitors on weight and BIA data have been published elsewhere (9, 12). In this article, we report the prognostic weight of phase angle for survival and progression-free survival in the same population, before and after the introduction of HAART.
| SUBJECTS AND METHODS |
|---|
|
|
|---|
500 d apart. Patients were excluded from the analysis if they were receiving enteral or parenteral nutrition or any drug treatment for wasting, lacked documentation of HIV viremia or CD4+ cell count, or had had follow-up of <2 wk, unless progression or death occurred during this period.
During the period in 1996, 250 of 254 clinic patients consented to BIA measurement. The current analysis was restricted to 212 patients because 3 patients received parenteral nutrition, 20 had an insufficient length of follow-up, and 15 had missing data. During the period in 1997, 266 of 276 patients participated but 9 patients were excluded because their follow-up periods were too short. Baseline characteristics of the remaining 212 and 257 patients are given in Table 1
.
|
= (Xc x 180°)/(R x
). Estimates for intracellular water (ICW), total body water (TBW), and FFM were calculated by using regression equations resulting from the comparison of BIA with reference methods in HIV-infected and healthy subjects (14). Extracellular water was calculated by subtraction as ECW = TBW ICW, and fat mass as FM = body weight - FFM. All measurements were made by the same investigator (AB) using standard electrode positions (15). HIV viral load was assessed at the Institute of Virology, University of Cologne, by using quantitative polymerase chain reaction (PCR; Roche Amplicor; Hoffmann-La Roche, Germany). Detection limits for this test were 300 copies/mL before March 1997 and 20 copies/mL afterward. All results with undetectable copy numbers were set to these detection limits. Results obtained by the ultrasensitive PCR were retested with the less sensitive assay if they were above the linear range of the assay (>10000 copies). Routine methods were used for all other laboratory tests.
Statistics were calculated by using SPSS version 7.5 (16). Comparisons were made with Pearson's chi-square for dichotomous variables and Student's t test for continuous variables. The prognostic influence of BIA and other independent variables on survival and time to clinical progression were tested with the Kaplan-Meier method for monovariate analysis. Proportional hazards were calculated in mono- and multivariate Cox models. Viral load and CD4+ cell counts were used as time-dependent covariates by using their mean log10-transformed results within 100-d periods after the periods in 1996 and 1997, respectively (16). Variables in the multivariate models were selected with the backward elimination log-likelihood method and with thresholds of
< 0.05 for entry and
0.10 for removal of variables. Phase angle was the principal BIA-derived independent variable in these models but was replaced by the 3 body compartments body fat, ICW, and ECWor by the ECW-ICW ratio in other explorative models. Time to clinical progression was defined as the time between baseline and the first episode of any disease listed in the Centers for Disease Control and Prevention case definition for AIDS (category C) (17), or death. Recurrence of diseases that had occurred before the period in 1996 were counted as new episodes if the period without symptoms or specific induction treatment was
1 mo. Interactions between the phase angle and other independent variables were further explored by using general linear models (16). The 1996 cohort was observed for 1000 (281203) d [median (range)], and the 1997 cohort for 515 (28704) d. The 2 cohorts overlapped with 132 patients, but only 3 deaths and 1 clinical progression event were counted twice. Omission of these events from the 1996 cohort data did not alter the overall results (data not shown). The study was conducted in accordance with the Declaration of Helsinki.
| RESULTS |
|---|
|
|
|---|
|
In multivariate Cox models, survival time after 1996 was predicted only by the CD4+ cell count, HIV viral load, and the phase angle (Table 2
). Survival after 1997 was predicted only by phase angle and CD4+ cell count, not by viral load. Time to clinical progression was predicted by the CD4+ cell count in both cohorts, together with a prior AIDS diagnosis in 1996, and together with the phase angle in 1997 (Table 2
). Viral load did not contribute significantly to the prediction of clinical progression in either cohort.
|
|
| DISCUSSION |
|---|
|
|
|---|
What pathogenic effects are represented in the phase angle? Although BIA is an established technique for assessment of body composition in health and disease (11), the relation of measured impedance to body composition is indirect and not fully clarified. Phase angle describes the relation between the 2 vector components of impedance (reactance and resistance) of the human body to an alternating electric current. Because the current passes only through the ionized water compartments within the body, the volume of TBW can be estimated from resistance (11). Reactance reflects the ability of cell membranes to act as imperfect capacitors. Therefore, phase angle is an indicator of the distribution of water between the intra- and extracellular spaces (18). A high phase angle corresponds to a low ECW-ICW ratio.
In the current study, the prognostic power of the phase angle was much stronger than that of any of the 3 body compartments estimated from BIA. In HIV-negative patients with bacteremia, our study group also found the ratio of 2 other impedance parameters [resistance at zero (R0) and resistance at infinite frequency of alternate current (Rinf)] to be superior to the calculated ECW-ICW ratio as a marker of adverse prognosis (19). These findings indicate that it may be easier to define normal and pathologic ranges for crude BIA data than for derived estimates of body composition. More importantly, bioelectrical impedance may reflect pathogenic events beyond its correlation with body composition. Expansion of ECW and loss of ICW are typical features of systemic illness (2022) but unlikely candidates for a direct pathogenic effect. Rather, they accompany protein leakage into the extracellular space and loss of intracellular protein in critical illness (23). Tumor necrosis factor
elicits capillary leakage in animal models (24), partly mediated by nitric oxide (25).
Other surrogate markers for these pathogenic events are more widely known to predict survival than is the phase angle. Loss of intracellular potassium and extracellular accumulation of sodium result in an increased whole-body exchangeable Na+-K+ ratio, which is a strong predictor of mortality in surgical patients (26). Hypoalbuminemia results largely from protein leakage (23) and is an adverse prognostic marker in systemic illness, such as bacteremia (27), HIV infection (28), and tuberculosis (29). Like the Na+-K+ ratio and serum albumin, phase angle can be interpreted as a global marker of the systemic reaction that forms an integral part of the host defense to systemic infection but may eventually result in malnutrition (30). Further studies comparing the phase angle with more direct assessment of metabolic distress will be needed to test this hypothesis.
If one accepts this interpretation of the phase angle, our findings indicate that the systemic response that predisposes patients to malnutrition and wasting is an independent risk factor in HIV infection together with viral load and immunodeficiency. Malnutrition, when more strictly defined by a low body mass index, was not significantly associated with prognosis in the current study. Effective antiretroviral treatment reduces the risk of wasting, controls viremia, and restores immune competence. Although statistically independent, these 3 effects are inseparable in patients. Different associations between phase angle and other measures of disease severity were found between 1996 and 1997. In the 1996 cohort, the patients' nutritional status was largely determined by their history of opportunistic infections, reflecting the episodic nature of malnutrition in HIV infection (31, 32). Effective antiretroviral treatment not only led to a lower incidence of opportunistic infections before 1997 but may also have reduced the severity of episodes and their metabolic consequences. This may have unmasked the metabolic effect of chronic HIV infection, as reflected in the CD4+ cell count.
Metabolic adverse effects of HAART may have confounded our data. Because this prospective study was designed before the first description of the fat redistribution syndrome, or lipodystrophy (33, 34), incidence of this syndrome could be determined only retrospectively in a subset (n = 111) of this population. As described elsewhere (9), the fat redistribution syndrome was associated with a greater increase of the phase angle between 1996 and 1997. Diagnosis of the fat redistribution syndrome did not have a detectable influence on prognosis in this subset (data not shown), but the statistical power of this finding is small. A protective effect of the syndrome is unlikely, apart from its association with low viral load (34, 35); hence, it could either have no effect or lead to underestimation of the prognostic power of phase angle.
Because of the close association between metabolic status and other manifestations of HIV infection, our data do not provide a causal link between reversal of catabolism and improved prognosis. However, they do underline the importance of monitoring the patient's metabolic status alongside viral load and CD4+ cell count in assessing prognosis. Phase angle with BIA may become a useful surrogate marker for the systemic response to chronic HIV infection.
| ACKNOWLEDGMENTS |
|---|
| REFERENCES |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
J. C K Wells and M. S Fewtrell Is body composition important for paediatricians? Arch. Dis. Child., February 1, 2008; 93(2): 168 - 172. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. Aghdassi, B. Arendt, I. E. Salit, and J. P. Allard Estimation of Body Fat Mass Using Dual-Energy X-Ray Absorptiometry, Bioelectric Impedance Analysis, and Anthropometry in HIV-Positive Male Subjects Receiving Highly Active Antiretroviral Therapy JPEN J Parenter Enteral Nutr, March 1, 2007; 31(2): 135 - 141. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Mulligan, R. Zackin, J. H. Von Roenn, M. A. Chesney, M. J. Egorin, F. R. Sattler, C. A. Benson, T. Liu, T. Umbleja, S. Shriver, et al. Testosterone Supplementation of Megestrol Therapy Does Not Enhance Lean Tissue Accrual in Men with Human Immunodeficiency Virus-Associated Weight Loss: A Randomized, Double-Blind, Placebo-Controlled, Multicenter Trial J. Clin. Endocrinol. Metab., February 1, 2007; 92(2): 563 - 570. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. Bosy-Westphal, S. Danielzik, R.-P. Dorhofer, W. Later, S. Wiese, and M. J. Muller Phase Angle From Bioelectrical Impedance Analysis: Population Reference Values by Age, Sex, and Body Mass Index JPEN J Parenter Enteral Nutr, July 1, 2006; 30(4): 309 - 316. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. B. Cole, B. Langkamp-Henken, B. S. Bender, K. Findley, K. A. Herrlinger-Garcia, and C. R. Uphold Oxidative Stress and Antioxidant Capacity in Smoking and Nonsmoking Men With HIV/Acquired Immunodeficiency Syndrome Nutr Clin Pract, December 1, 2005; 20(6): 662 - 667. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. Villamor, E. Saathoff, K. Manji, G. Msamanga, D. J Hunter, and W. W Fawzi Vitamin supplements, socioeconomic status, and morbidity events as predictors of wasting in HIV-infected women from Tanzania Am. J. Clinical Nutrition, October 1, 2005; 82(4): 857 - 865. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. C. G Barbosa-Silva, A. J. Barros, J. Wang, S. B Heymsfield, and R. N Pierson Jr Bioelectrical impedance analysis: population reference values for phase angle by age and sex Am. J. Clinical Nutrition, July 1, 2005; 82(1): 49 - 52. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Mulligan, R. Zackin, R. A. Clark, B. Alston-Smith, T. Liu, F. R. Sattler, T. B. Delvers, J. S. Currier, and for the AIDS Clinical Trials Group 329 Study Team Effect of Nandrolone Decanoate Therapy on Weight and Lean Body Mass in HIV-Infected Women With Weight Loss: A Randomized, Double-blind, Placebo-Controlled, Multicenter Trial Arch Intern Med, March 14, 2005; 165(5): 578 - 585. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. Gupta, C. A Lammersfeld, J. L Burrows, S. L Dahlk, P. G Vashi, J. F Grutsch, S. Hoffman, and C. G Lis Bioelectrical impedance phase angle in clinical practice: implications for prognosis in advanced colorectal cancer Am. J. Clinical Nutrition, December 1, 2004; 80(6): 1634 - 1638. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. Heckmann, C. Waltzinger, P. Jolicoeur, M. Dreano, M. H. Kosco-Vilbois, and Y. Sagot IKK2 Inhibitor Alleviates Kidney and Wasting Diseases in a Murine Model of Human AIDS Am. J. Pathol., April 1, 2004; 164(4): 1253 - 1262. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. L. Cox-Reijven, B. van Kreel, and P. B Soeters Bioelectrical impedance measurements in patients with gastrointestinal disease: validation of the spectrum approach and a comparison of different methods for screening for nutritional depletion Am. J. Clinical Nutrition, December 1, 2003; 78(6): 1111 - 1119. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Shah, C. Whalen, D. P. Kotler, H. Mayanja, A. Namale, G. Melikian, R. Mugerwa, and R. D. Semba Severity of Human Immunodeficiency Virus Infection Is Associated with Decreased Phase Angle, Fat Mass and Body Cell Mass in Adults with Pulmonary Tuberculosis Infection in Uganda J. Nutr., November 1, 2001; 131(11): 2843 - 2847. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |