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Vol. 75, No. 2, 2008
Issue release date: March 2008
Respiration 2008;75:170–177
(DOI:10.1159/000097772)

Breathing Pattern Adopted by Children with Cystic Fibrosis with Mild to Moderate Pulmonary Impairment during Exercise

Keochkerian D.a · Chlif M.a · Delanaud S.b · Gauthier R.c · Maingourd Y.a, d · Ahmaidi S.a
aEA 3300, APS et Conduites Motrices: ‘Adaptations et Réadaptations’, Faculté des Sciences du Sport, Université Picardie Jules Verne, bEA 2088, Unité de Recherches sur les Adaptations Physiologiques et Comportementales, Faculté de Médecine, cUnité d’Explorations Fonctionnelles Respiratoires Pédiatriques, and dUnité d’Explorations Fonctionnelles Cardio-pédiatriques, CHU Amiens Nord, Amiens, France
email Corresponding Author

Abstract

Background: It is well known that severe lung impairment in cystic fibrosis (CF) may compromise respiratory muscle function at rest. Even though patients with CF and severe obstructive lung disease exhibit an abnormal breathing pattern during exercise (due to expiratory flow limitation), patients with CF and normal lung function reportedly have a normal breathing pattern. Objectives: The aim of the study was to assess the precise characteristics of the ventilatory pattern adopted during exercise by children with CF and mild to moderate lung disease. Methods: Nine children diagnosed as having mild to moderate CF and 9 healthy children with a similar age distribution participated in this study. Both groups performed a continuous incremental cycling protocol. Breathing and timing components were assessed during exercise. Results: Differences in the breathing pattern between children with CF and controls during exercise are illustrated in Hey plot which described a rapid shallow breathing pattern in children with CF. During exercise, children with CF showed a significantly lower mean inspiratory flow than healthy children (p < 0.001), whereas the mean expiratory flow was higher (p < 0.001). Children with CF also showed a significant increase in the end-tidal carbon dioxide pressure, which may indicate the emergence of hypercapnia. Conclusions: During exercise, children with CF (even those not suffering from advanced disease) showed signs of rapid, shallow breathing and an increase in the ventilatory response. This was essentially due to an increase in the mean inspiratory flow, which in turn suggests an expiratory flow limitation. The children were also predisposed to hypercapnia.


 Outline


 goto top of outline Key Words

  • Cystic fibrosis
  • Pulmonary impairment during exercise
  • Respiratory muscle function

 goto top of outline Abstract

Background: It is well known that severe lung impairment in cystic fibrosis (CF) may compromise respiratory muscle function at rest. Even though patients with CF and severe obstructive lung disease exhibit an abnormal breathing pattern during exercise (due to expiratory flow limitation), patients with CF and normal lung function reportedly have a normal breathing pattern. Objectives: The aim of the study was to assess the precise characteristics of the ventilatory pattern adopted during exercise by children with CF and mild to moderate lung disease. Methods: Nine children diagnosed as having mild to moderate CF and 9 healthy children with a similar age distribution participated in this study. Both groups performed a continuous incremental cycling protocol. Breathing and timing components were assessed during exercise. Results: Differences in the breathing pattern between children with CF and controls during exercise are illustrated in Hey plot which described a rapid shallow breathing pattern in children with CF. During exercise, children with CF showed a significantly lower mean inspiratory flow than healthy children (p < 0.001), whereas the mean expiratory flow was higher (p < 0.001). Children with CF also showed a significant increase in the end-tidal carbon dioxide pressure, which may indicate the emergence of hypercapnia. Conclusions: During exercise, children with CF (even those not suffering from advanced disease) showed signs of rapid, shallow breathing and an increase in the ventilatory response. This was essentially due to an increase in the mean inspiratory flow, which in turn suggests an expiratory flow limitation. The children were also predisposed to hypercapnia.

Copyright © 2007 S. Karger AG, Basel


goto top of outline Introduction

Patients with pulmonary disease caused by cystic fibrosis (CF) are known to have reduced exercise tolerance [1]. An early clinical feature of lung disease in CF is the development of hyperinflation, which increases with further lung injury [2], and progressive, severe airway obstruction. Firstly, this is due to viscous secretions in the bronchial lumen, and secondly, to inflammatory processes in the bronchial wall and lung parenchyma [3]. Such changes may compromise respiratory muscle function during exercise, and as a result, patients with CF are more susceptible to respiratory failure or expiratory flow limitation (EFL) [4, 5]. It has been variously suggested that alterations in the thoracopulmonary mechanical properties of the respiratory system might modify the ventilatory response to a given neural output, the breathing pattern [6], the mouth occlusion pressure [7], the maximal inspiratory strength [8] and the work of breathing [9].

In children and young adults with advanced CF – as judged by forced expiratory volume in 1 s (FEV1) less than 40% of the predicted value – Hart et al. [10] reported changes in breathing patterns at rest. Specifically, patients adopted a rapid, shallow breathing pattern associated with further impairment of gas exchange. However, even though patients with CF and severe obstructive lung disease clearly exhibit an abnormal breathing pattern during exercise (due to EFL), CF sufferers with normal lung function reportedly have a normal breathing pattern [4, 5]. In children with less advanced forms of CF, Hayot et al. [7] showed that in order to ensure the same level of ventilation (at rest) as in healthy children, the load imposed by the disease had to be counterbalanced by an increase in neural drive, but that this did not result in rapid, shallow breathing. Nevertheless, even though children with CF and mild to moderate obstructive lung disease reportedly have a normal breathing pattern at rest, we hypothesized that these individuals might exhibit an altered ventilatory pattern, characterized by a rapid shallow breathing which, in turn, might indicate an EFL.

The aim of our study was to assess the precise ventilatory pattern adopted during exercise by children with CF and mild to moderate obstructive lung disease.

 

goto top of outline Methods

goto top of outline Subjects

Nine children with CF (2 girls and 7 boys, aged 11–14 years), diagnosed as having mild to moderate lung disease and who had not been hospitalized for at least 1 month before study, were compared with 9 healthy children with a similar age distribution (2 girls and 7 boys). The diagnosis of CF had been confirmed by sweat test and CF gene mutation analysis. Subjects were recruited on the basis of their willingness to take part in this study. Written informed consent was obtained from the parents. The study was approved by the local University Ethics Committee in accordance with the ethical standards of the 1975 Helsinki Declaration. Spirometric and anthropometric measurements are listed in table 1.

TAB01
Table 1. Anthropometric, spirometric and ventilatory parameters in children with CF and controls

goto top of outline Spirometry

Spirometry was performed using a pneumotachometer in a Jaeger Masterscreen body plethysmograph (Erich Jaeger AG, Würzburg, Germany) by skilled pediatric pulmonary function technicians who regularly work with children with CF. The calibration of the plethysmograph was performed daily before each test. FEV1 and forced vital capacity (FVC) were measured. The reproducibility and criteria of measurements were those recommended by the American Thoracic Society [11].

The residual volume (RV), total lung capacity (TLC) and the functional residual capacity were determined in the body plethysmograph as the mean of three tests. Reference values from Zapletal et al. [12] were used for spirometry and lung volumes.

goto top of outline Measurements

Oxygen uptake (VO2) and carbon dioxide output (VCO2) were analyzed by a mass spectrometer (Marquette). End-tidal CO2 tension (PCO2) was measured in the mouthpiece by mass spectrometry. The mass spectrometer was calibrated before each test by use of certified medical gases of known concentrations. Ventilatory flow was determined by a turbine flowmeter in a ventilatory measurement module (Interface Associates, Inc., Aliso Vieijo, Calif., USA) that was calibrated before each test with a 3-liter calibration syringe. The data of tidal volume (VT), breathing frequency, minute ventilation (VE), and duty cycle were averaged during the last 30 s of each workload.

goto top of outline Oxygen Saturation and End-Tidal PCO2

Arterial oxygen saturation (SaO2) was measured continuously using a pulse oximeter (Sat-Trak Finger Pulse Oximeter; SensorMedics, Yorba Linda, Calif., USA) at rest and during exercise. Mild exercise-induced arterial hypoxemia (EIAH) is defined as an SaO2 of 93–95% (or 3–4% <rest), moderate EIAH as 88–93% and severe EIAH as <88% [13].

CO2 retention was arbitrarily defined as a rise of 5 mm Hg or more in end-tidal PCO2 from the first workload until the final workload, or to an absolute value >50 mm Hg during the test. We chose to use the end-tidal PCO2 value during the first workload to lessen the chance of a falsely low resting end-tidal PCO2 that may have been the result of anticipatory anxiety and hyperventilation.

goto top of outline Protocol

All tests were performed at the same time of day. Subjects underwent first spirometric measurements at rest. Subjects then sat on the electromagnetic braked cycle ergometer (ER 900, Jaeger) to perform a continuous incremental cycling protocol. Workload increments were individualized for each patient based on clinical factors (i.e. history, pulmonary function test results and comorbidities) to provide an estimated exhaustion between 8 and 10 min of exercise. After a stable respiratory ratio was attained, subjects started the exercise by a 2-min warm-up period. The workload was then increased every 60 s until exhaustion. The child had to maintain a regular pedaling rhythm of 60 revolutions per minute. The following criteria for maximal exercise were those used in progressive incremental cardiopulmonary exercise testing in adults [14]: (1) exhaustion of the subject or inability to maintain the required pedaling speed (60 revolutions per minute) despite strong verbal encouragement; (2) VO2 plateau reached – the VO2 plateau is considered to have been reached if the final increase in VO2 does not exceed 2 ml/kg/min for an increase in work of 5–10% [15], and peak VO2 is the highest VO2 elicited during the exercise test if a VO2 plateau is not observed (we considered the predicted maximal VO2 to have been reached if the maximal VO2 value recorded was >85% of the predicted value); (3) predicted maximum heart rate achieved [210 – (0.65 × age) ± 10%] (we considered the predicted maximum heart rate to have been achieved if the heart rate recorded was >90% of the predicted value); and (4) maximal respiratory exchange ratio of >1 [16] (in adults, the maximal respiratory exchange ratio must be >1.1). Three of these criteria must be satisfied for maximal exercise to be considered to have been achieved.

goto top of outline Statistical Analysis

The values are reported as means ± standard deviation. Data at rest were compared between CF and healthy children using an unpaired Student’s test or the Mann-Whitney test when both normality (Kolmogorov-Smirnov) and equality of the variance (Levene median test) tests failed.

Exercise data were compared at the same percentage of maximal VO2, using a two-way analysis of variance for repeated measures (ANOVA), i.e. a fixed factor (group) and a repeated factor (percent of maximal VO2), or the ANOVA on rank test when the normality test of the distribution failed. When the ANOVA F ratio was significant (F group, F power and F group/power), the post hoc Bonferroni test was used to perform pairwise multiple comparisons.

Linear regression analysis was performed using the least squares method. This analysis was carried out using lung functions as dependent variables and VE versus VT slope as independent variables. A p value <0.05 was considered statistically significant.

 

goto top of outline Results

goto top of outline Anthropometric and Spirometric Data

Anthropometric and spirometric data for the children with CF and controls are listed in table 1. There was no statistical difference between the two groups in age, height and weight. Children with CF showed a significant decrease in FEV1, FCV and FEV1/FVC ratio. Children with CF showed a range of values from 58 to 78% for FEV1, from 75 to 83% for FVC and from 61 to 80% for the FEV1/FVC ratio. The RV/TLC ratio was significantly increased in children with CF (p < 0.001), indicating higher hyperinflation compared with healthy children.

goto top of outline Exercise Performance

Compared with the control group, children with CF had significantly lower maximum workload, maximum heart rate, maximal VO2 and maximal VCO2 (table 2). Children with CF had similar SaO2 at rest compared with the control group (98 ± 1 vs. 99 ± 1%; p < 0.05). The fall in SaO2 during exercise was significantly greater in children with CF compared with the control group but did not attest exercise-induced arterial hypoxemia (table 2). End-tidal PCO2 increased in children with CF whereas it decreased in control children during exercise. Figure 1 demonstrates the change in end-tidal PCO2 for all subjects at 40, 60, 80 and 100% of maximal VO2. End-tidal ΔPCO2 between the first workload until the final workload was significantly different between both groups (table 2). Children with CF exhibited a higher ventilatory equivalent for O2 (fig. 2a) and CO2 (fig. 2b) during exercise than healthy children.

TAB02
Table 2. Exercise data and breathing pattern parameters at maximal exercise in children with CF and controls

FIG01
Fig. 1. Individual changes in end-tidal PCO2 at rest and during exercise at the same percentage of maximal VO2 in children with CF (closed symbols) and healthy children (open symbols).

FIG02
Fig. 2. Changes in ventilatory equivalents for O2 (VE/VO2; a) and CO2 (VE/VCO2; b) during exercise at the same percentage of maximal VO2 in children with CF (closed circles) and healthy children (open circles). * Statistically significant difference at p < 0.001.

goto top of outline Breathing Pattern Components

Children with CF exhibited a lower VT (at 40, 60, 80 and 100% of maximal VO2) (fig. 3a) and VE (at 60, 80 and 100% of maximal VO2) (fig. 3b), whereas breathing frequencies were higher (fig. 3c) during exercise compared with healthy children.

FIG03
Fig. 3. Changes in VT (a), VE (b), breathing frequency (f; c), mean inspiratory flow (VT/tI; d), mean expiratory flow (VT/tE; e), tI (f), tE (g), ratio of tI/tTOT (h), ratio of tE/tTOT (i) and the ratio of tI/tE (j) during exercise at the same percentage of maximal VO2 in children with CF (closed circles) and healthy children (open circles). * Statistically significant difference at p < 0.05; ** statistically significant difference at p < 0.01; *** statistically significant difference at p < 0.001.

During exercise, children with CF showed a significantly lower mean inspiratory flow (at 80 and 100% of maximal VO2) (fig. 3d) and mean expiratory flow (at 40, 60, 80 and 100% of maximal VO2) (fig. 3e) than healthy children.

The inspiratory time (tI) was significantly lower in children with CF during exercise (fig. 3f) than in healthy children, whereas the expiratory time (tE) did not show any difference between the two groups (fig. 3g).

Children with CF exhibited a significantly lower duty cycle and tI/tE (fig. 3h, j), and a higher tE/tTOT (fig. 3i) during exercise than healthy children.

The Hey plot [17] (fig. 4) illustrates the individual VE versus VT slopes and shows that children with CF depend more on increases in breathing frequency to mediate an increase in VE than controls from the outset of exercise.

FIG04
Fig. 4. VE versus VT (Hey plot) during exercise in children with CF (black lines = FEV1 50–60% predicted; dashed lines = FEV1 65–80% predicted) and healthy children (grey lines). Dotted lines are isopleths indicating overall breathing frequency (min–1).

 

goto top of outline Discussion

Even in the absence of severe lung disease, children with CF showed signs of rapid shallow breathing during exercise, together with an increase in their ventilatory response. This was essentially due to an increase in mean inspiratory flow, which in turn suggests an EFL. The severity of airway obstruction and hyperinflation were found to be determinants of rapid shallow breathing.

During the initial stages of exercise, healthy subjects recruit inspiratory and expiratory reserve volumes to increase VT. Next, as exercise continues, they increase the respiratory rate. In contrast, patients with chest hyperinflation (such as the children with CF studied here) are unable to recruit significant inspiratory and expiratory reserve volumes, and therefore, maintain a relatively high respiratory rate throughout the exercise period [18]. CF patients are known to suffer from EFL during exercise [4, 5, 19]. Hence, when these individuals have to increase ventilation, they can neither increase their expiratory flow nor decrease their lung volume; they can only increase the lung volume (end expiratory lung volume, EELV) and/or inspiratory flow. In general, patients with CF and normal spirometry results do not exhibit EFL during exercise and are able to decrease EELV in a manner similar to that described in normal subjects [4, 5]. Not only does this decrease in EELV optimize diaphragm length but, in addition, the abdominal wall recoil following expiration aids inspiration [20, 21]. In contrast, CF sufferers with severe lung disease exhibit EFL both at rest and during exercise, despite the progressive increase in EELV (dynamic hyperinflation) that is also observed in patients with chronic obstructive pulmonary disease [22] or congestive heart failure [23]. An important mechanical consequence of dynamic hyperinflation is the severe restriction of VT expansion during exercise: to increase VE, the patients must rely on increasing their breathing frequency. However, as a result, this tachypnea causes further dynamic hyperinflation in a vicious cycle [24]. To date, no study has provided evidence of dynamic hyperinflation in CF patients with mild to moderate lung disease. Regnis et al. [5] observed that EFL was not apparent in the 2 studied patients with mild lung disease, either at rest or during light exercise. Their breathing pattern was normal, as characterized by an increase in both VT (with a decrease in EELV) and breathing frequency. These patients were obliged to increase EELV when EFL occurred during heavier exercise workloads.

In contrast to Regnis et al. [5], we observed that in children with CF and mild to moderate obstructive lung disease, the ventilatory pattern responsible for the increase in minute ventilation was unusual from the very start of the exercise, with the increase stemming more from an increase in respiratory rate than from an increase in VT (fig. 3). Differences in the breathing pattern between children with CF and controls during exercise are illustrated in the Hey plot [17] (fig. 4), which described total ventilation versus VT. The VE/VT slope was significantly steeper for children with CF (compared with healthy controls), especially for the 5 most severely affected individuals (fig. 4, black lines), attesting a rapid shallow breathing pattern. This observation implies that in order to mediate an increase in VE, children with CF rely more heavily on increases in breathing frequency from the start of the exercise; in fact, this could suggest dynamic hyperinflation, since the latter places severe mechanical constraint on VT expansion during exercise. Furthermore, children with CF demonstrated a significantly lower mean expiratory flow during exercise than healthy children, whereas the two groups did not significantly differ in terms of mean inspiratory flow during submaximal exercise (fig. 3d). Hence, the children with CF adopted a ventilatory pattern which corresponded to increased inspiratory activity. This finding suggests that children with CF and mild to moderate obstructive lung disease can develop EFL even during light exercise.

Rapid shallow breathing has a lower energetic cost than deep breathing [25] but is less efficient in terms of alveolar ventilation (due to the relative increase in dead space ventilation). Indeed, Thin et al. [26] observed that dead space ventilation increased during exercise in patients with CF and thus contributed to a high proportion of wasted ventilation – even though the volume of the airway dead space in CF patients was not higher than that in the control subjects. Nevertheless, set against the context of a blunted VT response to exercise (as was the case for our CF subjects), high dead space ventilation could compromise CO2 elimination by altering the ventilation/perfusion (V/Q) balance within the lung [27]. During exercise, children with CF showed an increase in end-tidal PCO2 (fig. 1), suggesting that much of the benefit of increased ventilation starts to be wasted and is likely to result in increased dead space ventilation [18]. Normally, end-tidal PCO2 is slightly lower than PaCO2 at rest. However, end-tidal PCO2 rises above PaCO2 during exercise in normal individuals. However, in lung disease, the influence of lung regions with increased V/Q means that end-tidal PCO2 may remain below PaCO2 even during exercise – which may possibly lead to the underestimation of VD/VT [28, 29]. Furthermore, our result demonstrated that the slope of the VE/VO2 and VE/VCO2 relationships, indexes of ventilatory ‘inefficiency’ [14], were higher in children with CF during exercise. A high VE/VCO2 without a fall in end-tidal PCO2, as we observed in children with CF, also suggests more increased dead space ventilation than hyperventilation [30].

The ventilation-perfusion abnormalities and alveolar hypoventilation observed in patients with CF could also predispose the latter to hypoxemia [31, 32]. In our study, children with CF showed a decrease in SaO2 during exercise (ΔSaO2 = 4 ± 2%) (table 2). Only the 2 patients with the lowest FEV1/FVC ratios and the highest RV/TLC ratios showed significant oxygen arterial hypoxemia induced by moderate exercise [13]. Indeed, Henke and Orenstein [31] found that only 1 out of 62 patients with a FEV1/FVC ratio >50% of the predicted value showed a drop of more than 5% in SaO2 at maximal exercise. Versteegh et al. [33] have shown that desaturation during exercise and sleep was only found in patients with FEV1 <65% of the predicted value. Hence, our results confirm previous reports, and our patients were not sufficiently affected by the disease (i.e. mild airway obstruction only) to show exercise-induced arterial hypoxemia.

In conclusion, children with CF and mild to moderate obstructive lung disease showed rapid, shallow breathing during exercise. They increased ventilation mainly by an increase in the mean inspiratory flow. These results could suggest EFL.

 

goto top of outline Acknowledgments

This work was supported by grant No. 99/10 from the Regional Council of Picardie ‘Pôle GBM Périnalité-Enfance’. The authors would like to thank Dr. Pautard and the medical staff of the Pediatric Department and the Pediatrics Cardiopulmonary Explorations Department of the University Hospital of Amiens for their technical assistance, especially Mr. and Mrs. Goin. We would also like to thank Eric Sanniez for his precious help in writing journals in English.


 goto top of outline References
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 goto top of outline Author Contacts

Mr David Keochkerian
Faculté des Sciences du Sport, Allée P. Grousset
Université de Picardie Jules Verne, Campus le Bailly
FR–80025 Amiens Cedex (France)
Tel. +33 3 22 82 79 03, Fax +33 3 22 82 79 10, E-Mail david.keochkerian@u-picardie.fr


 goto top of outline Article Information

Received: September 7, 2005
Accepted after revision: September 20, 2006
Published online: December 4, 2006
Number of Print Pages : 8
Number of Figures : 4, Number of Tables : 2, Number of References : 33


 goto top of outline Publication Details

Respiration (International Journal of Thoracic Medicine)

Vol. 75, No. 2, Year 2008 (Cover Date: March 2008)

Journal Editor: Bolliger, C.T. (Cape Town)
ISSN: 0025–7931 (Print), eISSN: 1423–0356 (Online)

For additional information: http://www.karger.com/RES


Copyright / Drug Dosage / Disclaimer

Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher or, in the case of photocopying, direct payment of a specified fee to the Copyright Clearance Center.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in goverment regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
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Abstract

Background: It is well known that severe lung impairment in cystic fibrosis (CF) may compromise respiratory muscle function at rest. Even though patients with CF and severe obstructive lung disease exhibit an abnormal breathing pattern during exercise (due to expiratory flow limitation), patients with CF and normal lung function reportedly have a normal breathing pattern. Objectives: The aim of the study was to assess the precise characteristics of the ventilatory pattern adopted during exercise by children with CF and mild to moderate lung disease. Methods: Nine children diagnosed as having mild to moderate CF and 9 healthy children with a similar age distribution participated in this study. Both groups performed a continuous incremental cycling protocol. Breathing and timing components were assessed during exercise. Results: Differences in the breathing pattern between children with CF and controls during exercise are illustrated in Hey plot which described a rapid shallow breathing pattern in children with CF. During exercise, children with CF showed a significantly lower mean inspiratory flow than healthy children (p < 0.001), whereas the mean expiratory flow was higher (p < 0.001). Children with CF also showed a significant increase in the end-tidal carbon dioxide pressure, which may indicate the emergence of hypercapnia. Conclusions: During exercise, children with CF (even those not suffering from advanced disease) showed signs of rapid, shallow breathing and an increase in the ventilatory response. This was essentially due to an increase in the mean inspiratory flow, which in turn suggests an expiratory flow limitation. The children were also predisposed to hypercapnia.



 goto top of outline Author Contacts

Mr David Keochkerian
Faculté des Sciences du Sport, Allée P. Grousset
Université de Picardie Jules Verne, Campus le Bailly
FR–80025 Amiens Cedex (France)
Tel. +33 3 22 82 79 03, Fax +33 3 22 82 79 10, E-Mail david.keochkerian@u-picardie.fr


 goto top of outline Article Information

Received: September 7, 2005
Accepted after revision: September 20, 2006
Published online: December 4, 2006
Number of Print Pages : 8
Number of Figures : 4, Number of Tables : 2, Number of References : 33


 goto top of outline Publication Details

Respiration (International Journal of Thoracic Medicine)

Vol. 75, No. 2, Year 2008 (Cover Date: March 2008)

Journal Editor: Bolliger, C.T. (Cape Town)
ISSN: 0025–7931 (Print), eISSN: 1423–0356 (Online)

For additional information: http://www.karger.com/RES


Copyright / Drug Dosage

Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher or, in the case of photocopying, direct payment of a specified fee to the Copyright Clearance Center.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in goverment regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
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