Understanding Arterial Pressure Waveforms

Abstract

• their relation to the cardiac cycle • the difference in waveforms recorded from different body sites The arterial pulse is the result of a wave of vascular disten-tion, initiated by the impact of the stroke volume ejected into a closed system with every heartbeat. The forward-propagat-ing pressure wave has both a fast-moving (10m/sec) and slower (0,5m/sec) component. 5 The wave is reflected back mostly by the arteriole, which provides the majority of peripheral vas-cular resistance. 6 Peak aortic blood flow acceleration produces the initial rise of the pressure pulse, whereas the ejection of the ventricular volume fills out and sustains the pulse wave-form. The systolic components follow the ECG R wave. The interval between the two reflects the time required for the spread of a depolarisation wave, isovolumic left ventricular contraction, aortic valve opening, left ventricular ejection, transmission of the aortic pressure wave to the radial artery and of the pressure signal from catheter to transducer. The incisura is the dicrotic notch recorded directly from the central aorta and relates to aortic valve closure. 7 The pe-ripheral arterial waveform has a later, smoother dicrotic notch that rather reflects arterial wall properties. Simultaneous re-cording of pressure waveforms from different arterial sites have different morphologies because of the impedance and harmonic resonance of the vascular tree. Predominantly pressure wave reflection influences the shape of the waveform as it travels peripherally, 6 because the high resistance to flow in the arteri-oles diminishes pressure pulsations in small downstream ves-Introduction Direct arterial pressure monitoring of patients under anaes-thesia began more than fifty years ago. 1 Even though analysis of the morphology and detail of the arterial pressure (ART) waveform can provide useful diagnostic information, modern physicians seemingly pay little attention to it. 2 This change in practice is attributed to the reliance on cuff sphygmomanom-etry providing " numbers which can be linked in a simplistic way to cardiac strength (systolic pressure) and arteriolar tone (diastolic pressure). " 3