Cardiac and autonomic responses to change in posture or vitamin C supplementation in sickle cell anemia subjects

Change in posture significantly decreased QRS amplitude, QRS duration, PR interval, RR interval and MABP but increased HR and rate pressure product (RPP) in both groups of subjects. The HR and RPP responses were significantly higher in NSCA than in SCA subjects (p < 0.001, respectively). Vitamin C caused greater reductions in QRS duration (p < 0.01), PR duration p < 0.001) in the NSCA subjects than in SCA subjects. It caused, however, greater reduction in RR duration (p < 0.001) and MABP in SCA subjects than in NSCA subjects. It also caused significantly greater increases in HR and RPP (p < 0.001, respectively) in the SCA subjects than in NSCA subjects. After vitamin C supplementation, change in posture decreased RR interval (p < 0.001), QT interval (p < 0.01) and MABP (p < 0.05) but increased RPP (p < 0.01) in NSCA subjects. In SCA subjects, there was a fall in RR interval (p < 0.001) and MABP (p < 0.01), but elevated RPP (p < 0.001). Changes (Δ) in MABP, HR and RPP were similar between NSCA and SCA subjects. In conclusion, these findings indicate a blunted cardiovascular autonomic response to change in posture in sickle cell anemia subjects. Chronic, oral, low-dose vitamin C supplementation equilibrates this response with those of non-sickle cell anemia subjects.