Impedance cardiography-derived hemodynamic responses during baroreceptor testing with amyl nitrite and phenylephrine: A validity and reliability study

Baroreflex (BR) testing with phenylephrine (PE) and amyl nitrite (AN) provi ded an opportunity to evaluate the ability of impedance cardiography (IC) t o track the rapid hemodynamic (HD) changes elicited by these drugs. The AN response was measured after inhalation and the PE response was measured aft er a bolus injection in 19 subjects on two occasions. High reliability was observed for all of the HD measures. Blood pressure (BP), peripheral resist ance (PR), and preejection period (PEP) decreased significantly after admin istration of AN, whereas heart rate (HR) and cardiac output (Q over dot) in creased. BP and total PR increased significantly after administration of PE ; HR and Q over dot decreased and PEP did not change significantly. Stroke volume did not change significantly with either drug. The BR slope was reli ably elicited with AN and PE. The IC and Finapres BP consistently detected short-term changes in HD responses to AN and PE. The pharmacological interv entions demonstrated that IC measures followed the course predicted by the actions of the drugs. Change in PEP and dZ/dt reflected increased contracti lity. The BR sensitivity was also reproducible.