Abstract
Completely noninvasive monitoring of hemoglobin concentration has not yet been fully realized in the clinical setting. This study investigates the viability of measuring hemoglobin concentration noninvasively by evaluating the performance of two types of sensor using a tissue phantom perfused with a blood substitute. An electrical sensor designed to measure blood volume changes during the cardiac cycle was used together with an infrared optical sensor for detection of erythrocyte-bound hemoglobin. Both sensors demonstrated sensitivity to changes in pulse volume (plethysmography). The electrical sensor produced a signal referred to as capacitance plethysmograph (CPG) a quantity which was invariant to the concentration of an infrared absorbing dye present in the blood substitute. The optical sensor signal (photoplethysmograph) increased in amplitude with increasing absorber concentration. The ratio PPG:CPG is invariant to pulse pressure. This quantity is discussed as a possible index of in vivo hemoglobin concentration.
Highlights
Anemia is a common condition affecting approximately 2 billion people worldwide [1]
250 mmHg and the dye concentration was equivalent to a hemoglobin concentration of 5 g/dL, while
PPG and capacitance plethysmograph (CPG) amplitude, resulting in relatively large variation in these quantities. This in vitro investigation demonstrated that simultaneous measurements of optical absorbance and capacitance can yield useful information regarding the composition of a blood substitute, namely the concentration of dye, which like hemoglobin and other chromophores is readily detectable using photoplethysmography
Summary
Anemia is a common condition affecting approximately 2 billion people worldwide [1]. It is defined as a less than normal quantity of hemoglobin in the blood or a reduction in size and/or the number of red blood cells. The main function of hemoglobin is to carry oxygen from the lungs to the tissues, so anemia leads to hypoxia (lack of oxygen) in organs. Mild anemia is usually symptomless but in Sensors 2012, 12 moderate cases, sufferers exhibit symptoms of tiredness and lethargy. The clinical definition of anemia in adults is a blood concentration of hemoglobin of less than 12–13 mg/L of blood, usually manifested as a lack of red blood cells [2]
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