Michael Khoo

Abnormal autonomic cardiac response to transient hypoxia in sickle cell anemia

The objective of this study was to non-invasively assess cardiac autonomic control in subjects with sickle cell anemia (SCA) by tracking the changes in heart rate variability (HRV) that occur following brief exposure to a hypoxic stimulus. Five African-American SCA patients and seven healthy control subjects were recruited to participate in this study. Each subject was exposed to a controlled hypoxic stimulus consisting of five breaths of nitrogen. Time-varying spectral analysis of HRV was applied to estimate the cardiac autonomic response to the transient episode of hypoxia. The confounding effects of changes in respiration on the HRV spectral indices were reduced by using a computational model. A significant decrease in the parameters related to parasympathetic control was detected in the post-hypoxic responses of the SCA subjects relative to normal controls. The spectral index related to sympathetic activity, on the other hand, showed a tendency to increase the following hypoxic stimulation, but the change was not significant. This study suggests that there is some degree of cardiovascular autonomic dysfunction in SCA that is revealed by the response to transient hypoxia.

Patients with sickle cell anemia on simple chronic transfusion protocol show sex differences for hemodynamic and hematologic responses to transfusion

Chronic transfusion therapy (CTT) is a mainstay for stroke prophylaxis in sickle cell anemia, but its effects on hemodynamics are poorly characterized. Transfusion improves oxygen‐carrying capacity, reducing demands for high cardiac output, while decreasing hemoglobin (Hb)S%, reticulocyte count, and hemolysis. We hypothesized that transfusion would improve oxygen‐carrying capacity, but that would be counteracted by a decrease in cardiac output due to increased hematocrit (Hct) and vascular resistance, leaving oxygen delivery unchanged.