Following respiratory, cardiac and peripheral vascular impairments, Sickle Cell Disease (SCD) patients can experience early second lactate threshold (S2) during low intensity exercise.

Through a comprehensive evaluation of exercise parameters we want to assess and find factors associated with an early reached of S2.

Homozygous SCD patients were prospectively included in this study. They performed physical exercise with a standardized protocol. Gaz exchange, capillary lactate concentration measurements and echocardiography were performed at baseline and throughout the exercise until S2 was reached. Baseline and exercise data of the bottom and top half of patients in terms of %predicted VO2 at S2 were compared to investigate the determinant of an early S2, adjusted over age, sex and body mass index (BMI).

Thirty patients were included (42±12 years old, 50% of female). Bottom half group reached 34,5% ±5,2 predicted VO2 at S2 (mean %predicted Watt=32% ±5,9) while top half group reached 46,2% ±6,8 predicted VO2 at S2 (mean %predicted Watt=42,8%±9,6) (Figure 1). Plasmatic hemoglobin concentration was the only baseline parameter associated with a lower %predicted VO2 at S2 (8.1±1 vs. 9.2 ±1g/dl, P=0.007). None of the baseline echocardiographic parameters were associated with a lower %predicted VO2 at S2. Diastolic adaptation through exercise was associated with a better power and VO2 at S2 (ratio S2/baseline of E’lateral wave and E/E’, respectively 1,39 vs. 1,63, P=0,039 and 1,2 vs. 0,99, P=0,004)

SCD patients with lower hemoglobin and impaired diastolic adaptation through exercise displayed earlier S2, independently of age, sex and BMI. This highlights the great vulnerability of these patients to low metabolic stress. They should benefit from low intensity physical therapy programs.