Assessing skeletal muscle variations in microvascular pressure and unstressed blood volume at the bedside.
OBJECTIVE
Quantitative NIRS measurements for MBV partitioning inside microvessels are of current physiologic and clinical interest. In this study, in healthy subjects, we sought new bedside NIRS variables for noninvasively measuring Vu and Pi changes.


METHODS
Fifteen healthy subjects underwent graded venous congestion for MBV measurements with NIRS and the reference technique strain-gauge plethysmography. From ΔMBV we calculated vascular compliance, blood flow, and new NIRS variables including V(u) and P(it) and P(crit).


RESULTS
Extrapolating MBV changes to 0 yielded Pit 4.19 ± 0.5 mmHg corresponding to a Vu of 2.53 ± 0.43 mL/100 mL T. The slope for MBV began steeper at values below 18 mmHg (P(crit)). Microvascular compliance measured with NIRS or with strain gauge gave matching results. The change in MBV depended on the oxyhemoglobin increase. No correlation was found between Vu and microvascular compliance or the overall ΔMBV. Cumulative pressure steps showed higher linearity in ΔMBV than that induced by discontinuous steps.


CONCLUSIONS
The new NIRS variables we report could be a practical bench-to-bedside tool to assess venous driving pressure for systemic perfusion and measure changes in Vu within the microvascular bed.
Department of Medical & Surgical Sciences and Translational Medicine, Faculty of Medicine and Psychology, University of Rome "Sapienza", Rome, Italy.
Roberto Alberto
RA
De Blasi
Roberto
R
Arcioni
D000328:Adult; D001794:Blood Pressure; D001795:Blood Pressure Determination / Q000379:methods*; D001810:Blood Volume; D001811:Blood Volume Determination / Q000379:methods*; D003187:Compliance; D005260:Female; D006452:Hemoglobinometry / Q000379:methods; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D008297:Male; D008833:Microcirculation; D018482:Muscle, Skeletal / Q000098:blood supply*; D009211:Myoglobin / Q000032:analysis; D010101:Oxygen Consumption; D010108:Oxyhemoglobins / Q000032:analysis; D010991:Plethysmography / Q000379:methods; D019095:Point-of-Care Systems; D012016:Reference Values; D012039:Regional Blood Flow; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D014655:Vascular Resistance; D055815:Young Adult
D006454:Hemoglobins; D009211:Myoglobin; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin
blood flow; critical pressure; healthy subjects; microcirculation; microvascular compliance; near-infrared spectroscopy; skeletal muscle; strain-gauge plethysmography; unstressed blood volume; venous congestions