Using near infrared spectroscopy and diffuse correlation spectroscopy to determine the microvascular effects of phenylephrine in vivo

Phenylephrine is commonly used in cardiac surgery is common to increase mean arterial pressure without affecting cardiac output; however, its effects on the microcirculation of the brain and in skeletal muscle are unclear. The objective of this study is to use hyperspectral near infrared spectroscopy (h-NIRS) and diffuse correlation spectroscopy (DCS) to monitor the microcirculation during a phenylephrine bolus would be able to discern the timing and effects of a phenylephrine bolus on brain and skeletal muscle microvasculature. The h-NIRS subsystem uses two spectrometers and a halogen light source, and the DCS subsystem uses a long coherence diode laser (785 nm) and a single photon counting module. Probes were positioned on the left hind limb and the top of the skull, with a source-detector distance of 10mm. Data were collected from Sprague Dawley rats (n = 1, 158 g). Nine microvascular challenges were monitored by recording a two-minute baseline, then injecting 0.1mL of phenylephrine (0.1 ug/mL) intravenously, followed by collecting data for 4 additional minutes. Oxygen saturation increased by 9% in the brain and 2% in the muscle. Blood flow increased by 60% in the brain, and 17% in the muscle. This study is the first report on the use of h-NIRS and DCS to investigate the effects of phenylephrine in the microvasculature. Dissimilitude in flow response may be due to differences in regulation mechanisms. Future work will include acquiring data from both subsystems simultaneously to provide further insight into the relationship between oxygen saturation and blood flow.