Ventilatory response during exercise among chronic Chagas cardiopathy patients

ABSTRACT CONTEXT AND OBJECTIVE: The change in slope of the V˙E/V˙CO2 curve with time during exercise (V˙E/V˙CO2 slope) has been recommended as a parameter for analyzing the ventilatory response during exercise among patients with heart failure of different etiologies. The aim of this work was to evaluate the ventilatory response among patients with chronic Chagas cardiopathy. METHODS: Forty-eight patients, divided into four groups according to the Los Andes clinical/hemodynamic classification, were studied. They were also classified according to peak oxygen uptake (peak V˙O2) for a second analysis. The results from the patients were compared with results from a control group consisting of 21 healthy male volunteers (no Chagas disease). Exercise was performed on a cycle ergometer with loads increasing at the rate of 12.5 watts/min, and exercise duration was symptom-limited. Gas concentration and flow rate data were fed into a computer, which produced a real-time report on ventilatory and gas exchange parameters. (breath-by-breath). The ventilatory parameters of V˙E/V˙CO2 slope and V˙E/V˙CO2 ratio computed at different times of the test were adopted. RESULTS: Although there were no significant differences in V˙E/V˙CO2 ratio and V˙E/V˙CO2 slope when patients were grouped using the Los Andes clinical/hemodynamic classification, these parameters varied significantly when peak V˙O2 was used to define patient groups. CONCLUSION: Our results indicate that progressive deterioration in ventilatory response among chronic Chagas cardiopathy patients during exercise is more evident when the functional capacity (peak V˙O2) is reduced, than when changes are related to the Los Andes classification.


INTRODUCTION
The change in slope of the V .E/V .CO 2 curve with time during exercise (V .

E/V
. CO 2 slope) has been recommended as a parameter for analyzing the ventilatory response during exercise among patients with heart failure of different etiologies. 1

OBJECTIVE
The aim of the present study was to evaluate ventilatory response among chronic Chagas cardiopathy (CCC) patients.

MATERIALS AND METHODS
This study was a cross-sectional and descriptive analysis of 48 male patients with CCC (mean age: 51 ± 11 years).These patients were living in Rio de Janeiro and were not taking part in any systematic physical training program.All of these patients had been clinically stable over the three-month period preceding the study.They presented positive indirect hemagglutination reaction and indirect immunofl uorescence for Trypanosoma cruzi, and no other associated disease.They were grouped according to the Los Andes clinical/hemodynamic classifi cation, 2 and the diagnosis of congestive heart failure met the criteria of the Framingham Heart Study. 3 Selection of the patients for the study was performed among the 200 patients followed up in Hospital Universitário Clementino Fraga Filho, Universidade Federal do Rio de Janeiro, over the period from 1999 to 2000, and the data were analyzed in 2002.The exclusion criteria were: systemic arterial hypertension, chronic obstructive pulmonary disease, cardiomyopathy of any other type or cause, thyroid dysfunction, known immunological dysfunction, rheumatic valve disease, congenital heart diseases, obstructive coronary artery disease, use of heart pacemaker, neuro-muscular disorders, practicing of sports, and inability to reach the anaerobic threshold when undergoing the test.
The patients were grouped in two ways: fi rstly, using the Los Andes clinical/hemodynamic classifi cation 2 ; secondly, to determine whether alterations in the functional capacity of the cardiovascular system were associated with the ventilatory response to exercise, the patients were redistributed into four groups according to their peak V .O 2 independent of their degree of heart failure.
The exercise test was performed on a mechanically braked cycle ergometer (Monarch) and the patients using medications were instructed to suspend their use 48 hours prior to the test.
The exercise was begun with two minutes of warm-up (zero Watts).The workload was increased at a rate of 12.5 watts/min, with 60 rotations per minute, until the appearance of limiting symptoms.All of the patients and also a control group consisting of 21 healthy male volunteers performed the same test protocol.
The reproducibility of the exercise test in our laboratory was verifi ed by means of test and retest of ten volunteers and there were no signifi cant differences (paired and simple Student's t test, p < 0.05) between the results.
A rapid gas analyzer (Airspec MGA 2000) was utilized on a breath-by-breath basis, with a Fleisch pneumotachograph and a differential pressure transducer (Microswitch 163PC01D36).Equipment calibration was performed on a daily basis before each test.
We analyzed V .

E/V
. CO 2 slope) has been recommended as a parameter for analyzing the ventilatory response during exercise among patients with heart failure of different etiologies.The aim of this work was to evaluate the ventilatory response among patients with chronic Chagas cardiopathy.

METHODS:
Forty-eight patients, divided into four groups according to the Los Andes clinical/hemodynamic classifi cation, were studied.They were also classifi ed according to peak oxygen uptake (peak V .O 2 ) for a second analysis.The results from the patients were compared with results from a control group consisting of 21 healthy male volunteers (no Chagas disease).Exercise was performed on a cycle ergometer with loads increasing at the rate of 12.5 watts/min, and exercise duration was symptom-limited.Gas concentration and fl ow rate data were fed into a computer, which produced a real-time report on ventilatory and gas exchange parameters (breath-by-breath).The ventilatory parameters of V .

E/V
. CO 2 slope and V .

E/V
. CO 2 ratio computed at different times of the test were adopted.

RESULTS:
Although there were no signifi cant differences in V .

E/V
. CO 2 ratio and V .

E/V
. CO 2 slope when patients were grouped using the Los Andes clinical/hemodynamic classifi cation, these parameters varied signifi cantly when peak V

DISCUSSION
This study demonstrated an inverse relationship between the degree of heart disease in CCC and the patients' functional capacity (peak V .O 2 and anaerobic threshold, Table 3).Both controls and patients in the initial phase of the disease (group IA) were more tolerant of exercise than were patients in advanced stages of CCC (Table 1).
No signifi cant differences in ventilatory effi ciency could be seen between the patient during exercise period was also analyzed (li near regression analysis). 4The results from the patients were compared with the results from the 21 healthy male volunteers.
The local Ethics Committee approved this study and the patients and the control group underwent the tests only after providing written informed consent.
The statistical treatment (Pearson's correlation coeffi cient, one-way analysis of variance, ANOVA, post-hoc Tukey, HSD) were performed using the Statistical Analysis System (SAS), considering signifi cant values of p < 0.05.

RESULTS
The functional capacity of patients in the initial phase (IA) of CCC was superior to that of patients in an advanced phase (group III) (Table 1, Figure 1).There was great variability in the peak  O 2 = oxygen uptake in the last seconds of exercise; V .
groups organized according to the Los Andes classifi cation (Table 1).This contrasted with the classifi cation according to functional capacity (Table 4).Results of this nature have also been found via another mathematical method that considers ventilation and functional capac ity. 5 The variations in peak V .O 2 values (Table 2) among patients with the same Los Andes classifi cation who are characterized clinically as having severe heart involvement were probably due to the development of compensatory muscle adaptations.These muscle adaptations result in better exercise tolerance and reduce the impact of cardiopathy consequences.Certainly these patients were in a better condition: a few of the participants had V .O 2 > 20 ml/kg/min.Analysis of V .

E/V
. CO 2 slope refl ect ventilatory effi ciency throughout the exercise period (Table 4).Chagas patients with reduced functional capacity exhibited greater V .

E/V
. CO 2 slope, thus reproducing the results obtained from non-Chagas cardiopathies. 1 These results indicate that the patients needed greater ventilatory effort for the equivalent quantity of CO 2 produced during exercise than did individuals with better functional capacity (Figure 1).
Grouping patients according to peak V .O 2 also served to emphasize differences in ventila-tory response at the beginning of the exercise (V .

E/V
. CO 2 , at 0.5 liter/min of V .CO 2 ).At this exercise level, aerobic metabolism probably predominates, thereby eliminating any need for an altered ventilatory response that would compensate for an increase in lactic acid.A likely candidate for such alterations at this phase of the effort is the change in V D /V T (fraction of the tidal volume that contributes to the dead space), which some authors have detected during exercise in patients with heart failure. 6he usefulness of V .

E/V
. CO 2 in predicting survival rates for patients with congestive heart failure has been demons trated: 1 after 18 months, the survival rate was 95% for patients that attained V .

CO 2 (
liter/min) by considering the average from the last fi ve cycles at six different times: (a) at rest; (b) when V .CO 2 reached 0.5 liter/min; (c) when V .CO 2 reached 1.0 liter/min; (d) at the exercise peak; (e) after the fi rst minute of recovery; and (f ) after the third minute of recovery.The V .E/V .CO 2 slope CONTEXT AND OBJECTIVE: The change in slope of the V .E/V .CO 2 curve with time during exercise (V . defi ne patient groups.CONCLUSION: Our results indicate that progressive deterioration in ventilatory response among chronic Chagas cardiopathy patients during exercise is more evident when the functional capacity (peak V .O 2 ) is reduced, than when changes are related to the Los Andes classifi cation.KEY WORDS: Chagas disease.Oxygen consumption.Ventilation.Carbon dioxide.Exercise test.Sao Paulo Med J. 2006;124(5):280-4.Fátima Palha de Oliveira Roberto Coury Pedrosa Sao Paulo Med J. 2006;124(5):280-4.
between some groups of patients and controls.
C = control group; Peak V .

Table 4 )
, there were signifi cant differences

Table 1 .
2ean results (mean ± standard deviation) for all variables measured in Chagas patients, grouped according to the Los Andes clinical/hemodynamic classifi cation2

Table 2 .
Distribution of Chagas patients among Los Andes groups versus classifi cation 2 and V .E/V .CO 2 slope is a by V .O 2 attained at exercise peak