In
2012 at the 14th International Congress of
Biorheology, the Poiseuille Gold was
bestowed on Herbert Lipowsky. Professor
Lipowsky established a distinguished and
highly innovative record of accomplishments
with major impact on the field of
Biorheology. All of his contributions to
Biorheology were made in the context of true
in-vivo studies at the cellular and
molecular level and these studies
established a scientific standard. He made
major contributions to the development and
application of
techniques for studying the microcirculation
in the living animal by direct intravital
microscopy, and interpretation of
experimental data with engineering analyses
and modeling.
Some of his earliest studies provided
precise information on the resistance to
flow within single unbranched microvessels,
and within the framework of Poiseuille�s
equation, this making possible estimates of
the effective viscosity of blood. These
studies affirmed the important role of
microvessel diameter, and its inverse fourth
power relationship to resistance, as a
determinant of flow resistance throughout
successive microvascular divisions (Circ.
Res. 1978). Subsequent studies clarified the
roles of microvessel hematocrit as a
determinant of the effective viscosity of
blood in microvessels and the resistance to
flow, as well as the roles of red cell
aggregation and white cell adhesion in
modulating microvascular flow.
By applying his innovative in vivo
microvascular measurements, Dr. Lipowsky
made seminal contributions to the rheology
of pathological disorders, such as sickle
cell disease and inflammation. His
laboratory was the first to demonstrate that
blood viscosity may increase dramatically in
small microvessels when perfused with
deoxygenated human sickle cells (Blood
Cells, 1982). He also applied the techniques
of nailfold microscopy to quantitate for the
first time the adverse effects of onset of a
vaso-occlusive crisis in the sickle cell
patient (J Clinical Invest, 1987), which
prolonged the time for flow to return to
normal following an intermittent vaso-occlusion
as characterized by the response to
post-occlusive reactive hyperemia.
Subsequent studies revealed the extent to
which reductions in capillary shear rates my
promote sequestration of red cells in
nailfold capillaries (Microcirculation,
1997).
Dr. Lipowsky and his co-workers also made
outstanding contributions to the role of
leukocyte (WBC) adhesion to endothelial cell
(EC) as a determinant of the resistance to
flow. His quantitative studies on the
effects of fMLP in stimulating WBC-EC
adhesion revealed that the resistance to
flow in single unbranched venules may double
when as few as 12 WBCs adhere per 100 �m
length of venule (Microvasc Res, 1987).
Using the dual micropressure system, he
deduced the drag force acting upon adhered
WBCs by application of the laws of
conservation of momentum to measurements of
pressure drops and flows (Circ. Res. 1988).
Studies of the mechanics of WBC adhesion
subsequently shed new light on the
alterations in the mechanical properties of
WBCs during adhesion (Biorhelogy, 1991), the
sequestration of WBCs in the microvascular
network (Am J
Physiol, 1994; Microvasc Res 1996), rolling
velocity of WBCs (Am J Physiol, 1996) and
their adhesive contact with the EC (Annals
of Biomedical Eng, 1997).
Dr. Lipowsky�s studies of the rheological
behavior of blood during the inflammatory
process focused on the role of the
endothelial glycocalyx as a barrier to WBC-EC
adhesion. These studies explicitly showed
for the first time that shedding of the
glycocalyx served to expose ICAM-1 on the
surface of the EC (Am J Physiol. 2002) and
that this shedding occurs during
inflammation and ischemia (Am J Physiol.
2004). It was also demonstrated that
shedding may be modulated by the activation
of extracellular matrix metalloproteinases
on the surface of the EC (Microcirculation,
2009). Most recently, with measurements of
the resistance to flow within single
capillaries of the mesentery that during
activation of the EC with fMLP resistance to
flow be reduced by 26% due to shedding of
glycans from the EC surface layer (Am. J.
Physiol, 2011).
The title of his Poiseuille Award
lecture at the Congress was "In vivo
studies of the rheology of blood flow in the
microcirculation in an in vitro
world." |
