Abstract
.In a pilot study of 11 healthy adults (24 to 39 years, all male), we characterize the influence of external probe pressure on optical diffuse correlation spectroscopy (DCS) measurements of pulsatile blood flow obtained on the forearm and forehead. For external probe pressure control, a hand inflatable air balloon is inserted between the tissue and an elastic strap. The air balloon is sequentially inflated to achieve a wide range of external probe pressures between 20 and 250 mmHg on the forearm and forehead, which are measured with a flexible pressure sensor underneath the probe. At each probe pressure, the pulsatility index (PI) of arteriole blood flow on the forehead and forearm is measured with DCS (2.1-cm source-detector separation). We observe a strong correlation between probe pressure and PI on the forearm (, ), but not on the forehead (, ). The forearm measurements demonstrate the sensitivity of the DCS PI to skeletal muscle tissue pressure, whereas the forehead measurements indicate that DCS PI measurements are not sensitive to scalp tissue pressure. Note, in contrast to pulsatility, the time-averaged DCS blood flow index on the forehead was significantly correlated with probe pressure (, ). This pilot data appears to support the initiation of more comprehensive clinical studies on DCS to detect trends in internal pressure in brain and skeletal muscle.
Highlights
Diffuse correlation spectroscopy (DCS) utilizes photon correlation techniques to noninvasively measure blood flow in deep tissues continuously and at the bedside.[1,2,3,4,5,6] It has been used in a variety of clinical applications, including stroke and muscle disease
Previous research based on transcranial Doppler ultrasound (TCD) measurements has shown that the shape of pulsatile arterial blood flow waveforms during the cardiac cycle is influenced by the tissue pressure (e.g., intracranial pressure (ICP)) compressing the arteries.[14,17,38,39]
We investigated the influence of pressure on the DCS pulsatility index (PI) measurements on the forearm and forehead acquired at 2.1-cm source-detector separation on eleven healthy adults
Summary
Diffuse correlation spectroscopy (DCS) utilizes photon correlation techniques to noninvasively measure blood flow in deep tissues continuously and at the bedside.[1,2,3,4,5,6] It has been used in a variety of clinical applications, including stroke and muscle disease. Doppler ultrasound techniques have been dominantly used for noninvasive assessment of flow pulsatility in the clinic. Doppler ultrasound measures blood velocity in major feeder arteries of the brain and peripheral tissues. The relation of Doppler waveforms to ICP and arterial stenosis has been investigated, and encouraging preliminary results were observed.[14,15,16] In traumatic brain-injured adults, for example, a transcranial Doppler ultrasound (TCD) derived pulsatility index (PI) was proportionally correlated with intrasubject trends in invasively measured ICP (R 1⁄4 0.61).[17] This TCD PI was defined as the difference of systolic flow velocity (FVsys) and diastolic flow velocity (FVdia) divided by mean flow velocity (hFVi), i.e., ðFVsys − FVdiaÞ∕hFVi
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