Blood flow velocity comparison in the eye capillaries and postcapillary venules between normal pregnant and non-pregnant women

Abstract

Background: There is no consensus on how much and at what diameters the blood flow velocity changes in the female microcirculation during normal pregnancy.

Methods: A non-contact, digital slit-lamp biomicroscopy system was used to measure axial blood velocity (Vax) and diameter (D) in the conjunctival microcirculation of 28 normal non-pregnant women (Control Group), 17 women in the first semester of their normal pregnancy (Group 1) and 16 women in the third trimester of their normal pregnancy (Group 2). Blood volume flow (Q) was estimated from Vax and D. Microvessels were classified as "capillaries" (CAP) with D < 9 μm, "postcapillary venules of size 1" (PC1) with 9 ≤ D < 14 μm and "postcapillary venules of size 2" (PC2) with 14 ≤ D ≤ 24 μm.

Results: The women groups did not differ significantly in age, diastolic and systolic pressure and diameter of each size. Taking as baseline the capillary Vax of 0.51 mm/s of the Control Group, there was a statistically significant (p < 0.001) increase to 0.74 mm/s (45%) in Group 1 and to 0.95 mm/s (86%) in Group 2. This significant Vax increase in capillaries (CAP) was a consistent finding irrespective of the exact vessel size cut-off value for discriminating CAP from PC1. There was no statistical difference in Vax among groups at postcapillary venules of size 2 (PC2). Statistical conclusions for blood volume flows were similar to velocities.

Conclusions: Normal pregnancy increases significantly axial blood velocity (Vax) in capillaries (CAP) with diameter <9 μm.

Keywords: Blood flow velocity; Blood volume flow; Capillaries; Diameter; Hemodynamics; Human conjunctiva; Human microcirculation; Normal pregnancy; Postcapillary venules; Slit-lamp biomicroscopy.