Heterogeneity and Variability in Pressure Autoregulation of Organ Blood Flow: Lessons Learned Over 100+ Years.

OBJECTIVES: Pressure autoregulation is an organ's intrinsic ability to maintain blood flow despite changes in perfusion pressure. The purpose of this review is to discuss autoregulation's heterogeneity among different organs and variability under different conditions, a very clinically relevant topic. DATA SOURCES: Systematic search of Ovid MEDLINE; nonsystematic search of PubMed, Google Scholar, and reference lists. STUDY SELECTION: Animal or human studies investigating the potency or variation of pressure autoregulation of any organs or the association between autoregulation and outcomes. DATA EXTRACTION: Two authors screened the identified studies independently then collectively agreed upon articles to be used as the basis for this review. DATA SYNTHESIS: Study details, including subjects, organ investigated, methods of blood pressure intervention and blood flow measurement, and values of the lower limit, upper limit, and plateau were examined. Comparative canine studies were used to demonstrate the heterogeneity of pressure autoregulation among different organs and validate the proposed scale for organ categorization by autoregulatory capacity. Autoregulatory variability is discussed per organ. The association between cerebral autoregulation and outcome is summarized. CONCLUSIONS: The organs with robust autoregulation are the brain, spinal cord, heart, and kidney. Skeletal muscle has moderate autoregulation. Nearly all splanchnic organs including the stomach, small intestine, colon, liver, and pancreas possess weak autoregulation. Autoregulation can be readily affected by a variety of clinically relevant factors. Organs with weak or weakened autoregulation are at a greater risk of suboptimal perfusion when blood pressure fluctuates. Cerebral autoregulation and outcomes are closely related. These lessons learned over 100+ years are instructive in clinical care.