Premium
Simultaneous Monitoring of the Cerebral and Skeletomuscular Microcirculation using Hyperspectral Near Infrared Spectroscopy and Intravital Video Microscopy
Author(s) -
Mawdsley Laura,
Rajaram Ajay,
Yip Lawrence,
Abayomi Naomi,
Li Natalie,
Milkovich Stephanie,
Carson Jeffrey,
St. Lawrence Keith,
Ellis Christopher,
Diop Mamadou
Publication year - 2021
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2021.35.s1.00289
Subject(s) - phenylephrine , microcirculation , bolus (digestion) , medicine , intravital microscopy , skeletal muscle , biomedical engineering , anesthesia , anatomy , blood pressure
Phenylephrine is a vasoconstrictor commonly used in cardiac surgery to increase mean arterial pressure without affecting cardiac output; however, its effects on the microcirculation of the brain and in skeletal muscle are unclear. In the current study, the timing and effects of a phenylephrine bolus on brain and skeletal muscle microvasculature were investigated using hyperspectral near infrared spectroscopy ( h ‐NIRS) and intravital video microscopy (IVVM. The objective of this study is to compare the effects of a timed phenylephrine bolus in the brain microvasculature, to the effects of the same bolus on the skeletal muscle microvasculature using both invasive (IVVM) and non‐invasive ( h ‐NIRS) methods. Methods The IVVM system uses an inverted Olympus microscope and two Rolera XR cameras to record 20X videos of individual capillaries in the Sprague Dawley rat (n=8, 158±10g) extensor digitorum longus muscle. The h ‐NIRS system uses two Ocean Insight spectrometers (MayaPro and QE65000) and an Ocean Insight HL‐2000 halogen light source. 3‐D printed probe‐holders were positioned on the left hind limb and the top of the skull, with a source‐detector distance of 10mm. Seven microvascular challenges were monitored with the h ‐NIRS system by recording a two‐minute baseline, then injecting 0.1mL of phenylephrine (0.1ug/mL) or 0.1mL of saline intravenously, then collecting data for 8 minutes. The same challenges were also monitored using IVVM simultaneously, by recording 1 minute at baseline and 2 minutes post‐IV injection. One representative phenylephrine bolus was chosen for this abstract. Results The h ‐NIRS system measured a 3.75% decrease in deoxygenated hemoglobin (Hb) and a 0.87% increase in oxygenated hemoglobin (HbO) in the brain microcirculation ( Fig .1A), as well as a 2.78% decrease in Hb and a 1.13% decrease in HbO the skeletal muscle microcirculation ( Fig .1B) in the seconds following the phenylephrine bolus. Total hemoglobin (tHb) decreased by 2.88% in the brain and 3.91% in the skeletal muscle. Results obtained from IVVM show an increase in optical density for frequencies reflecting microvascular activity immediately following the phenylephrine bolus ( Fig . 2), followed by a gradual return to baseline activity. Discussion This is the first report of the use of h ‐NIRS and IVVM to monitor the effects of phenylephrine on multiple microvascular beds in a healthy animal. Phenylephrine caused a decrease in Hb and tHb in both the brain and skeletal muscle microvasculature, but did not cause a prolonged decrease as both microvascular beds returned to baseline levels by the end of the 10‐minute collection. The same pattern was measured in the optical density ( Fig . 2). Unlike Hb, HbO levels increase in the brain after the phenylephrine bolus but decrease in skeletal muscle. This may be due to the oxygen requirements of the brain. Future work includes incorporating diffuse correlation spectroscopy into the methodology to provide insight into blood flow during the vascular challenge.