Assessment of Symptoms and Exercise Capacity in Cyanotic Patients With Congenital Heart Disease: Statistical Analysis

Assessment of Symptoms and Exercise Capacity in Cyanotic Patients With Congenital Heart Disease: Statistical AnalysisDuring the exercise period, Vo2AT (primarily according to the V-slope method and, if necessary, with further inspection of the Vo2, Vco2, Ve/Vo2, and Peto2 kinetics) and Ve vs Vco2 slope were determined, and at maximal exertion (peak Vo2), Peto2 and Petco2 were assessed. The terminal nonlinear part of the VE vs Vco2 relationship was excluded from the analysis of the VE vs Vco2 slope. Great effort was taken not to stop exercise prematurely. Blood was sampled in a capillary tube from a cut earlobe during rest and maximal exertion in 23 patients.
Unless stated otherwise, all data are presented as mean ± SD. Differences between groups were assessed using Kruskal-Wallis test and Mann-Whitney test; p < 0.05 was considered statistically significant.
Symptomatology and Exercise Gas Exchange

Eighteen patients were assigned to NYHA class II, 8 patients to NYHA class III, and 1 patient to NYHA class IV. Ability classification was II in 6 patients, III in 17 patients, and IV in 4 patients. Seven patients were unable to work professionally; the remaining 20 patients were able to do so with limitations (avoiding physical labor).
The changes in ventilatory parameters and differences in exercise capacity as compared to normal values are given in Table 2. The maximal aerobic capacity was markedly impaired in patients (Table 2). Patients reached a significantly lower maximal heart rate (145 ± 21 beats/min vs 177 ± 23 beats/ min, p < 0.05) and maximal exercise time: 9 min, 53 s (± 0 min, 50 s) vs 26 min, 18 s (± 6 min, 40 s) [p < 0.05]. Ve/Vco2 ratio and Ve vs Vco2 slope were markedly impaired. с

The extent of cyanosis, measured by the Pa02, did not significantly correlate with all parameters of symptomatic state assessed in this study. Pa02 at rest and under exercise were different for patients in NYHA class II vs III, and oxygen saturation showed a similar trend. However, the ability index was not related to Pa02 at rest as shown in Figure 1. Inspection of the exercise-related decline in Pa02 also failed to show an association with the ability index.
Figure 1. Mean Pao2 at rest and under maximal exercise for groups in different NYHA and ability classes.

Table 2—Results of CPX

Variables Vo2, mL O2/kg/min VE, L/min Ve/Vco2 Ratio VE vs Vco2 Slope
AT Peak 1Rest Rest 1 1Exercise
Mean 12.8 16.7 16.0 69.6 57.5
± SD 4.9 6.6 3.9 17.9 30.1
Control subjects
Mean 20.7 36.1 12.8 52.5 26.2
± SD 5.1 7.7 3.1 11.2 4.1
p Value < 0.005 < 0.005 < 0.005 < 0.005 < 0.005