Abnormal submaximal cardiopulmonary exercise parameters predict impaired peak exercise performance in sickle cell anemia patients

Abstract

Purpose: Sickle cell anemia (SCA) patients frequently have many comorbidities, including diastolic dysfunction (DD) and exercise intolerance. SCA patients often cannot reach maximal effort on exercise testing; little is known regarding whether submaximal exercise parameters can predict abnormal maximal exercise results in SCA patients and if there are any possible associations with DD.

Methods: A prospective longitudinal study was performed in SCA patients. All patients had a resting cardiac MRI (CMR), cardiopulmonary exercise test (CPET) with cycle ergometry using a ramp protocol, and an echocardiogram. Exercise data were compared with age-, gender-, and size-matched normal controls.

Results: Compared with normal controls, the SCA group (n = 19) had lower mean max oxygen consumption (VO2 ; 1378 ± 412 mL/min vs 2237 ± 580, P < 0.01) and workload (117 ± 37.6 watts vs 175 ± 50.5 watts, P = 0.0003). When evaluating the submaximal exercise parameters, there was lower VO2 at the anaerobic threshold (AT; 950 ± 311.7 vs 1460 ± 409.9, P < 0.01) and oxygen uptake efficiency slope (OUES) at AT (1512 ± 426.2 vs 2080 ± 339, P < 0.01). The max VO2 strongly correlated with VO2 at AT (r = 0.9, P < 0.01) and OUES (r = 0.83, P < 0.01) at AT. The VO2 at AT correlated with hematocrit (r = 0.77, P < 0.05). The OUES correlated with left ventricular ejection fraction by CMR (r = 0.55, P = 0.01), hematocrit (r = 0.52, P = 0.02), and lateral E/e' (r = -0.54, P = 0.01).

Conclusions: SCA patients have abnormal submaximal exercise measures compared with controls, which is strongly associated with abnormal maximal exercise results. The degree of submaximal abnormality correlates with DD abnormalities by echocardiography. These data expand the scope of functional cardiovascular abnormalities in SCA.

Keywords: cardiopulmonary exercise test; sickle cell disease; submaximal exercise.

Conflict of interest statement

CONFLICTS OF INTEREST

None.

© 2019 Wiley Periodicals, Inc.

Figures

FIGURE 1

Comparison data between the SCA (blue) and control (red) patients at peak exercise (A) and submaximal exercise. SCA, sickle cell anemia; % Pred, percentage of predicted; VO2, oxygen consumption; O2 pulse, oxygen pulse; VE/VCO2 slope, ventilatory efficiency; AT, anaerobic Threshold

FIGURE 2

Data from SCA and control groups plotted on a graph. Solid line is less than 2 standard deviations from the mean derived by the regression equation for calculating the VO2 @ RER 1.0 described by Chin et al, 2009. SCA, sickle cell anemia; VO2, oxygen consumption;RER, respiratory exchange ratio

FIGURE 3

Comparison data between the SCA patients with (purple) and without (orange) diastolic dysfunction at peak exercise (A) and submaximal exercise. SCA, sickle cell anemia; % Pred, percentage of predicted; VO2, oxygen consumption; O2Pulse, oxygen pulse; VE/VCO2 slope, ventilatory efficiency; AT, anaerobic threshold