Arterial pulse wave analysis. With special reference to vasoactive and anaesthetic drugs and to heart lung interactions

Abstract

In the young systolic arterial pressures (SAP) are higher in the radial artery than in the proximal aorta. Due to increased large artery stiffness and early pulse wave reflection aortic SAP increases more with age than peripheral SAP. Some vasodilators like nitroglycerin can delay wave reflection and reduce aortic SAP while early diastolic pressure and coronary perfusion are increased. These effects are mainly unseen when blood pressure is measured in the radial artery. We therefore chose to study simultaneous radial and aortic blood pressures during anaesthesia-related interventions, and also validated a synthesised aortic pressure wave. Alterations in intrathoracic pressures by means of large tidal volumes (LTV) were studied as a less invasive method for assessment of preload independent left ventricular systolic function in a porcine model.Methods. Ascending aortic pressure (catheter-tip manometer) and invasive radial arterial pressure were studied in 30 elderly and/or hypertensive coronary patients. Interventions were midazolam, nitroglycerin, a Valsalva manoeuvre, prostacyklin, induction of anaesthesia with fentanyl 20 µg/kg, volume loading, nitrous oxide, and positive pressure ventilation with LTV. In 18 of these patients blood flow was measured by thermodilution. In 12 patients aortic pressures were synthesised through application of a generalised transfer function to the radial pressure wave. In 7 anaesthetised pigs preload independent measures of left ventricul-ar function were studied through conductance volumetry. Preload was altered through infe-rior vena cava occlusion (IVCO) or LTV during halothane, phenylefrine or adrenaline.Results. Nitroglycerin increased the difference between SAP in the aorta and the radial artery. Prostacyklin did not affect this difference, despite similar decreases in mean pressure. Fentanyl like nitroglycerin reduces aortic SAP and wave reflection, but in contrast to nitro-glycerin, it leaves stroke volume unchanged. Preload recruitable stroke work changed similarly with LTV and IVCO.Conclusions. Effects of wave reflection on aortic SAP in the elderly are clinically relevant and can be traced through monitoring of the radial waveform. Wave reflection is influenced by some, but not all, vasodilating drugs. Clinically useful aortic waveforms can be synthesised from a radial pulse wave. LTV is an alternative to IVCO in studies of preload independent cardiac function.