The microcirculatory disturbances in sepsis have prompted micropore bu
lk-filtration studies of red blood cell (RBC) mechanical behavior (i.e
., deformability). However, these prior reports may not solely reflect
RBC behavior because of possible white blood cell (WBC) occlusion of
the filter pores. The present study was designed to examine RBC mechan
ical alterations in human and experimental sepsis using techniques tha
t are not affected by WBC artifacts. RBC were obtained from adult pati
ents with sepsis and from healthy control donors. RBC were also obtain
ed from Swiss-albino rats in which experimental sepsis was induced via
cecal ligation-puncture. Red cell mechanical behavior was tested usin
g a computerized micropore filtration system (CTA) and a laser-diffrac
tion shearing device (LORCA); the latter provides the extent of RBC de
formation at various stresses and the time constant for RBC shape reco
very. Salient findings include: (1) for human RBC, significantly decre
ased deformability at fluid shear stresses < 5 Pa (LORCA) yet no diffe
rences from control with the CTA; (2) for rat RBC in experimental seps
is, significant decreases of deformability and shape-recovery time con
stant (LORCA) but no differences with the CTA. We conclude that RBC de
formability is reduced in sepsis but that micropore bulk-filtration me
thods may not be appropriate for detecting these changes.