Noninvasive optical monitoring of critical closing pressure and arteriole compliance in human subjects

Abstract

The critical closing pressure ( CrCP) of the cerebral circulation depends on both tissue intracranial pressure and vasomotor tone. CrCP defines the arterial blood pressure ( ABP) at which cerebral blood flow approaches zero, and their difference ( ABP - CrCP) is an accurate estimate of cerebral perfusion pressure. Here we demonstrate a novel non-invasive technique for continuous monitoring of CrCP at the bedside. The methodology combines optical diffuse correlation spectroscopy (DCS) measurements of pulsatile cerebral blood flow in arterioles with concurrent ABP data during the cardiac cycle. Together, the two waveforms permit calculation of CrCP via the two-compartment Windkessel model for flow in the cerebral arterioles. Measurements of CrCP by optics (DCS) and transcranial Doppler ultrasound (TCD) were carried out in 18 healthy adults; they demonstrated good agreement (R = 0.66, slope = 1.14 ± 0.23) with means of 11.1 ± 5.0 and 13.0 ± 7.5 mmHg, respectively. Additionally, a potentially useful and rarely measured arteriole compliance parameter was derived from the phase difference between ABP and DCS arteriole blood flow waveforms. The measurements provide evidence that DCS signals originate predominantly from arteriole blood flow and are well suited for long-term continuous monitoring of CrCP and assessment of arteriole compliance in the clinic.

High-density speckle contrast optical tomography of cerebral blood flow response to functional stimuli in the rodent brain

“…Combining both contributions, this technology provides new opportunities for the study of the rodent brain after an injury. For example, it would be possible to monitor not only pathological changes in the brain due to a stroke, but also to study the evolution of the functional brain activity after the injury 51,53,54 and in the long term, it would also be possible to study longitudinal effects 17,30,34 such as those due to rehabilitation. The unique innovation of HD-SCOT is that these studies can be carried out with the same imaging platform in a noninvasive manner.…”

Influence of probe pressure on the pulsatile diffuse correlation spectroscopy blood flow signal on the forearm and forehead regions

“…18,19,42 Recently, DCS measurement of blood flow pulsatility in the microvasculature has emerged as a potential complementary and alternative approach to Doppler ultrasound. [7][8][9][10][11] The DCS measurement is robust to the particular placement and orientation of its sensors, which can be held on the head with clinical tape or an elastic strap. 11,19 Accordingly, DCS is well-suited for continuous prolonged monitoring.…”

“…In future work, arterial blood pressure measurements and DCS PI measurements utilized in combination with a model of the arterial vascular tree may be more predictive of tissue pressure. 10 Steady-state BFI was modestly less correlated with muscle tissue pressure than the PI (i.e., R ¼ −0.57). Thus the BFI can also potentially be used as a biomarker of tissue pressure.…”

“…We chose to use first harmonic Fourier filtering to calculate PI because this approach is less affected by measurement noise than the difference between systolic and diastolic BFI. 10,34 Exemplar mean intensity autocorrelation curves at two discrete probe pressures obtained on the forearm, along with their respective temporal BFI traces in the time domain and Fourier spectral amplitudes in the frequency-domain, are shown in Fig. 3.…”

“…Recently, improvements in DCS measurement speed have been exploited to resolve the pulsatile heartbeat fluctuations of arterial blood flow. [7][8][9][10][11] DCS measurement of blood flow pulsatility has generated considerable interest in new clinical applications for the optical technology, which include assessment of intracranial pressure (ICP) 10,12,13 and arterial stiffness. 10,11 To date, Doppler ultrasound techniques have been dominantly used for noninvasive assessment of flow pulsatility in the clinic.…”