Relationship of Effective Circulating Volume with Sublingual Red Blood Cell Velocity and Microvessel Pressure Difference: A Clinical Investigation and Computational Fluid Dynamics Modeling

Abstract

The characteristics of physiologic hemodynamic coherence are not well-investigated. We examined the physiological relationship between circulating blood volume, sublingual microcirculatory perfusion, and tissue oxygenation in anesthetized individuals with steady-state physiology. We assessed the correlation of mean circulatory filling pressure analogue (Pmca) with sublingual microcirculatory perfusion and red blood cell (RBC) velocity using SDF+ imaging and a modified optical flow-based algorithm. We also reconstructed the 2D microvessels and applied computational fluid dynamics (CFD) to evaluate the correlation of Pmca and RBC velocity with the obtained pressure and velocity fields in microvessels from CFD (pressure difference, (Δp)). Twenty adults with a median age of 39.5 years (IQR 35.5–44.5) were included in the study. Sublingual velocity distributions were similar and followed a log-normal distribution. A constant Pmca value of 14 mmHg was observed in all individuals with sublingual RBC velocity 6–24 μm s−1, while a Pmca < 14 mmHg was observed in those with RBC velocity > 24 μm s−1. When Pmca ranged between 11 mmHg and 15 mmHg, Δp fluctuated between 0.02 Pa and 0.1 Pa. In conclusion, the intact regulatory mechanisms maintain a physiological coupling between systemic hemodynamics, sublingual microcirculatory perfusion, and tissue oxygenation when Pmca is 14 mmHg.

Association between mean arterial pressure and sublingual microcirculation during major non‐cardiac surgery: Post hoc analysis of a prospective cohort

“…Previous studies of sublingual microcirculation during noncardiac surgery also reported considerable heterogeneity in microcirculatory flow among individuals, as well as substantial interindividual variability. 8,26,27 In general, available evidence suggests that microcirculatory perfusion is preserved during general anesthesia and elective non-cardiac surgery when MAP is maintained within a normal range or slightly higher. 28 In contrast, there may be an association between microcirculatory tissue perfusion and outcome in high-risk non-cardiac surgery patients.…”

“…Within this range, microcirculation can be highly adaptive to its cellular environment and can be autoregulated independent of changes in systemic blood pressure. 8,26 However, monitoring of sublingual microcirculation can yield important physiologic information in patients with hypotension, comorbidities, or those with high levels of chronic systemic inflammation. 27 The latter can decrease capillary perfusion and vascular integrity and impair the ability of the microvasculature to coordinate a vasodilatory response.…”

“…Although the expansion of intraoperative hemodynamic monitoring to include monitoring of the microcirculation can be helpful in optimizing cardiovascular dynamics, our findings suggest that sublingual microcirculation is insensitive to MAP ranges between 65 and 120 mmHg. Within this range, microcirculation can be highly adaptive to its cellular environment and can be autoregulated independent of changes in systemic blood pressure 8,26 . However, monitoring of sublingual microcirculation can yield important physiologic information in patients with hypotension, comorbidities, or those with high levels of chronic systemic inflammation 27 .…”

General Critical Care, Temperature Control, and End-of-Life Decision Making in Patients Resuscitated from Cardiac Arrest

“…Although extreme hyperoxia is associated with poor neurologic outcomes [ 70 , 71 , 72 , 73 ], “critical” hypoxia does not equate to a specific oxygen concentration. Of note, many tissues function physiologically at levels equivalent to an atmosphere of 5% oxygen, and some at levels as low as 1% oxygen [ 74 , 75 ], and therefore, optimizing perfusion may be more important than setting a specific oxygenation target in anesthetized patients [ 76 , 77 , 78 ].…”

Cutting-Edge Approaches in Respiratory and Critical Care Medicine

“…Inflammation and increased reactive oxygen species formation may affect all organ systems, including the lungs. Thus, the attenuation of NO exhalation by propofol and sevoflurane reported by Vekrakou et al may imply the preservation of bronchial microcirculatory perfusion and decreased NO synthesis, due to the immunomodulatory effects and the effects on microcirculation mediated by anesthetics in steady states [ 30 , 31 ] and in disease [ 32 , 33 ]. All the aforementioned factors can improve heart–lung interactions and facilitate the application of lung-protective ventilation strategies, preventing injurious mechanical stretching of lung parenchyma, and subsequent progression to fibrosis in patients with ARDS [ 34 ].…”