Red Blood Cells
© Discovery Institute.
Medical researchers Gregory Sloop, Gheorghe Pop, and John St. Cyt published an article in the journal BIO-Complexity that describes how their design-based framework for studying the circulatory system led to a breakthrough in understanding the regulation of blood viscosity. Sloop is a pathology professor at Idaho College of Osteopathic Medicine, Pop is a professor emeritus at the Radboud University Medical Center in the Netherlands, and St. Cyr is a medical and surgical consultant. The authors also explain how the standard evolutionary framework misdirected earlier researchers.

The article is titled "The Hematocrit and Blood Viscosity are Modulated to Maintain Constant Wall Shear Stress in the Carotid Sinus." It reports how the investigators experimentally demonstrated that the circulatory system regulates the proportion of blood composed of red blood cells (aka the hematocrit) to maintain a constant shear stress on the blood vessels. Increasing the hematocrit increases the viscosity which increases the shear stress. This insight explained previously unexpected observations.

Limitations of the Reductionist View

The authors' design-based framework inspired them to study blood flow from a systems or holistic perspective, which allowed them to consider variables that were less directly connected to the hematocrit. Earlier researchers employed a reductionist or evolutionary framework that led them to overemphasize O2 transport since that factor directly affects survival. The investigators explain the limitations of the reductionist view:
In this view [reductionism], the impact of the hemoglobin concentration on factors other than O2 transport, such as blood viscosity or wall shear stress, are given secondary importance. The historic view of the hematocrit is now known to have overestimated tissue O2 needs.
They also explain how the insight that a systems perspective was required led to the breakthrough:
That deeper insight requires a holistic approach. Holism is the view that full understanding of a system requires analyzing its components while they are acting in concert. The heart, blood vessels and blood are seen as an integrated unit. Holism is necessary to understand complex quantities — such as blood pressure, systemic vascular resistance and endothelial wall shear stress — which arise from the interaction of the heart, blood vessels and blood.
The authors also describe how identifying shear stress as the key variable directing hematocrit regulation explains observed differences in normal hematocrit based on such factors as sex and age:
The key insight contained in this paper is that wall shear stress is maintained in Homo sapiens by modulating the hematocrit, and thus, blood viscosity. This insight was made possible by the recent description of the "viscometer function" of the carotid sinus. Maintaining normal wall shear stress in the carotid sinus explains the sex difference in normal hematocrit, the increasing hematocrit with growth, and the heretofore poorly understood condition called "sports anemia." It also explains the differences between the normal, native, and optimal hematocrits.
This research is another example of how the design framework advances scientific research while denying design slows progress.