Cardiopulmonary bypass (CPB) provides cerebral oxygenation and blood flow (CBF) during neonatal congenital heart surgery, but the impacts of CPB on brain oxygen supply and metabolic demands are generally unknown. To elucidate this physiology, we used diffuse correlation spectroscopy and frequency-domain diffuse optical spectroscopy to continuously measure CBF, oxygen extraction fraction (OEF), and oxygen metabolism (CMRO₂) in 27 neonatal swine before, during, and up to 24 h after CPB. Concurrently, we sampled cerebral microdialysis biomarkers of metabolic distress (lactate–pyruvate ratio) and injury (glycerol). We applied a novel theoretical approach to correct for hematocrit variation during optical quantification of CBF in vivo. Without correction, a mean (95% CI) +53% (42, 63) increase in hematocrit resulted in a physiologically improbable +58% (27, 90) increase in CMRO₂ relative to baseline at CPB initiation; following correction, CMRO₂ did not differ from baseline at this timepoint. After CPB initiation, OEF increased but CBF and CMRO₂ decreased with CPB time; these temporal trends persisted for 0–8 h following CPB and coincided with a 48% (7, 90) elevation of glycerol. The temporal trends and glycerol elevation resolved by 8–24 h. The hematocrit correction improved quantification of cerebral physiologic trends that precede and coincide with neurological injury following CPB.

Pressure injuries (PIs) originate beneath the surface of the skin at the interface between bone and soft tissue. We used diffuse correlation spectroscopy (DCS) and diffuse near-infrared spectroscopy (DNIRS) to predict the development of PIs by measuring dermal and subcutaneous red cell motion and optical absorption and scattering properties in 11 spinal cord injury subjects with only nonbleachable redness in the sacrococcygeal area in a rehabilitation hospital and 20 healthy volunteers. A custom optical probe was developed to obtain continuous DCS and DNIRS data from sacrococcygeal tissue while the subjects were placed in supine and lateral positions to apply pressure from body weight and to release pressure, respectively. Rehabilitation patients were measured up to four times over a two-week period. Three rehabilitation patients developed open PIs (POs) within four weeks and eight patients did not (PNOs). Temporal correlation functions in the area of redness were significantly different ($p<0.01$) during both baseline and applied pressure stages for POs and PNOs. The results show that our optical method may be used for the early prediction of ulcer progression.

Significance: The critical closing pressure (CrCP) of cerebral circulation, as measured by diffuse correlation spectroscopy (DCS), is a promising biomarker of intracranial hypertension. However, CrCP techniques using DCS have not been assessed in gold standard experiments.Aim: CrCP is typically calculated by examining the variation of cerebral blood flow (CBF) during the cardiac cycle (with normal sinus rhythm). We compare this typical CrCP measurement with a gold standard obtained during the drops in arterial blood pressure (ABP) caused by rapid ventricular pacing (RVP) in patients undergoing invasive electrophysiologic procedures.Approach: Adults receiving electrophysiology procedures with planned ablation were enrolled for DCS CBF monitoring. CrCP was calculated from CBF and ABP data by three methods: (1) linear extrapolation of data during RVP (CrCPRVP; the gold standard); (2) linear extrapolation of data during regular heartbeats (CrCPLinear); and (3) fundamental harmonic Fourier filtering of data during regular heartbeats (CrCPFourier).Results: CBF monitoring was performed prior to and during 55 episodes of RVP in five adults. CrCPRVP and CrCPFourier demonstrated agreement (R = 0.66, slope = 1.05 (95%CI, 0.72 to 1.38). Agreement between CrCPRVP and CrCPLinear was worse; CrCPLinear was 8.2 ± 5.9 mmHg higher than CrCPRVP (mean ± SD; p < 0.001).Conclusions: Our results suggest that DCS-measured CrCP can be accurately acquired during normal sinus rhythm.