Abstract
In this work we introduce a modified form of laser speckle imaging (LSI) referred to as affixed transmission speckle analysis (ATSA) that uses a single coherent light source to probe two physiological signals: one related to pulsatile vascular expansion (classically known as the photoplethysmographic (PPG) waveform) and one related to pulsatile vascular blood flow (named here the speckle plethysmographic (SPG) waveform). The PPG signal is determined by recording intensity fluctuations, and the SPG signal is determined via the LSI dynamic light scattering technique. These two co-registered signals are obtained by transilluminating a single digit (e.g. finger) which produces quasi-periodic waveforms derived from the cardiac cycle. Because PPG and SPG waveforms probe vascular expansion and flow, respectively, in cm-thick tissue, these complementary phenomena are offset in time and have rich dynamic features. We characterize the timing offset and harmonic content of the waveforms in 16 human subjects and demonstrate physiologic relevance for assessing microvascular flow and resistance.
Highlights
Photoplethysmography is a well-established technique in which light is transmitted through tissue in order to interrogate vascular fluctuations caused by the cardiac cycle [1, 2]
In this work we introduce a modified form of laser speckle imaging (LSI) referred to as affixed transmission speckle analysis (ATSA) that uses a single coherent light source to probe two physiological signals: one related to pulsatile vascular expansion (classically known as the photoplethysmographic (PPG) waveform) and one related to pulsatile vascular blood flow (named here the speckle plethysmographic (SPG) waveform)
The PPG signal is determined by recording intensity fluctuations, and the SPG signal is determined via the LSI dynamic light scattering technique
Summary
Photoplethysmography is a well-established technique in which light is transmitted through tissue in order to interrogate vascular fluctuations caused by the cardiac cycle [1, 2] These fluctuations are due to volumetric expansion of blood caused by variations in pressure which modulate the attenuation of transmitted light [3, 4]. PPG has failed to achieve wide-spread clinical adoption in other important applications such as continuous noninvasive arterial pressure, arterial stiffness characterization, and noninvasive cardiac output monitoring [7, 8]. One reason for this is the tendency of the PPG waveform to deteriorate in situations of low peripheral blood flow such as hypovolemia or thermoregulatory vasoconstriction [1]. PPG may lack sufficient information content to properly characterize the cardiovascular system
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