A tissue compression/transillumination approach to noninvasive hemoglobinometry

The measurement of blood hemoglobin concentration is among the most common clinical laboratory assessments made. Current methods for measuring hemoglobin concentration require direct blood access. Numerous disadvantages associated with collecting blood, including patient pain and risk of infection, make a noninvasive hemoglobinometry method desirable. This dissertation evaluates tissue compression/transillumination (TCTI) hemoglobinometry, a noninvasive opto-mechanical technique in which vascularized tissue is compressed to diminish tissue blood volume while measuring the change in transmitted near-infrared (NIR) light intensity.; The feasibility of TCTI hemoglobinometry was established using Monte Carlo computer simulations of near-infrared light transmission through a tissue model comprised of blood and nonblood layers. The computer simulations indicated that the technique was feasible, although the measurement range for the method was limited due to the nonlinear relationship between the optical density of blood and the blood hematocrit (directly related to hemoglobin concentration).; A microprocessor-based opto-mechanical device was developed to collect TCTI data. An in vitro investigation was conducted on a physical model of vascularized tissue consisting of a thin layer of canine blood positioned between two layers of nonblood tissue phantom material (Intralipid and India ink). The blood layer hemoglobin concentration was varied between 0 and 28 g/dl. In vivo canine studies were conducted using the tongue as the tissue bed for analysis. Hemoglobin concentration in each animal was incrementally decreased by normovolemic hemodilution from 17.2 g/dl (s.d. 1.3) to 5.3 g/dl (s.d. 2.2). TCTI data and reference hemoglobin measurements were collected at each hemoglobin level.; Results from the in vitro and in vivo experiments generally agreed with computer simulation results, and exhibited the predicted nonlinear relationship between hemoglobin concentration and optical transmission data. For data with hemoglobin concentrations up to 15 g/dl, 80% limits of agreement between the TCTI hemoglobinometer and reference measurements were +/−0.83 g/dl for the in vitro experiments, and ranged from +/−2.03 to +/−3.06 g/dl for the in vivo experiments. These results indicate that TCTI technique is capable of noninvasive hemoglobin determination, although its precision is not yet adequate for some clinical applications. Venous occlusion and impedance plethysmography offer potential alternatives to tissue compression and NIR transillumination.