calculated blood vessel dilation force reduction measurement concentration of acetylcholine at which the reduction in force during dilation of a blood vessel is half the maximum value (EC50) 2012-03-14T04:23:57Z A calculated value for the concentration of acetylcholine (ACh), the ester of acetic acid and choline with chemical formula CH3C=OO(CH2)2-N(+)-(CH3)3 and IUPAC name 2-acetoxy-N,N,N-trimethylethanaminium, which acts as a neurotransmitter, at which the energy exerted during the active expansion in the diameter of a blood vessel in response to the application of ACh is halfway between the highest value, that is the force at greatest constriction (often measured in a pre-constricted blood vessel), and the lowest achievable value of such contractile energy during ACh-induced relaxation of the vessel wall (i.e. the maximum effect of Ach which is the minimum contractile energy). CHEBI:15355 CMO:0000724 JSmith VT:0000197 acetylcholine half maximal effective concentration (EC50) clinical_measurement_ontology acetylcholine response/sensitivity measurement