Key result
Excessive erythrocytosis is linked to ~28% lower FMD, which improves after isovolemic hemodilution.
Why the study?
Excessive erythrocytosis is associated with increased cardiovascular risk in highlander Andeans, prompting investigation into shear stress and endothelial function via flow-mediated dilation.
Does excessive erythrocytosis impair endothelial function, and does isovolemic hemodilution improve it in male Andeans?
Observational (n=42)
No
Does excessive erythrocytosis impair endothelial function, and does isovolemic hemodilution improve it in male Andeans?
Effect estimate: 28% lower
p-value: p=0.013
Hyperviscosity and high hemoglobin in excessive erythrocytosis actively contribute to acutely reversible impairments in endothelial function, suggesting a pathogenic role in the increased cardiovascular risk among highlanders.
Excessive erythrocytosis may impair endothelial function in Andeans; hypothesis-generating for hemodilution trials before any practice change.
Excessive erythrocytosis (EE; hemoglobin concentration [Hb] ≥21 g/dL in adult males) is associated with increased cardiovascular risk in highlander Andeans. We sought to quantify shear stress and assess endothelial function via flow-mediated dilation (FMD) in male Andeans with and without EE. We hypothesized that FMD would be impaired in Andeans with EE after accounting for shear stress and that FMD would improve after isovolemic hemodilution. Brachial artery shear stress and FMD were assessed in 23 male Andeans without EE (age: 40±15 years [mean±SD]; Hb<21 g/dL) and 19 male Andeans with EE (age: 43±14 years; Hb≥21 g/dL) in Cerro de Pasco, Peru (4330 m). Shear stress was quantified from Duplex ultrasound measures of shear rate and blood viscosity. In a subset of participants (n=8), FMD was performed before and after isovolemic hemodilution with blood volume replaced by an equal volume of human serum albumin. Blood viscosity and Hb were 48% and 23% higher (both P <0.001) and FMD was 28% lower after adjusting for the shear stress stimulus ( P =0.013) in Andeans with EE compared to those without. FMD was inversely correlated with blood viscosity ( r 2 =0.303; P<0.001) and Hb ( r 2 =0.230; P =0.001). Isovolemic hemodilution decreased blood viscosity by 30±10% and Hb by 14±5% (both P <0.001) and improved shear stress stimulus-adjusted FMD from 2.7±1.9% to 4.3±1.9% ( P =0.022). Hyperviscosity, high Hb, or both, actively contribute to acutely reversible impairments in FMD in EE, suggesting that this plays a pathogenic role in the increased cardiovascular risk.
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Tremblay et al. (2019) conducted an observational in Excessive erythrocytosis (n=42). Excessive erythrocytosis vs. Male Andeans without excessive erythrocytosis was evaluated on Shear stress stimulus-adjusted flow-mediated dilation (FMD) (28% lower, p=0.013). Excessive erythrocytosis in male Andeans was associated with 28% lower adjusted flow-mediated dilation (P=0.013), which improved from 2.7% to 4.3% after isovolemic hemodilution (P=0.022).
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