Noninvasive pulse wave analysis for the determination of central artery stiffness.

Central artery stiffness predicts cardiovascular structural damage and clinical outcome. It is controversial whether central artery stiffness can be determined by noninvasive measurements. We compared noninvasive determination of central artery stiffness obtained from applanation tonometry of the peripheral radial artery waveform with invasive measurements of the ratio of pulse-pressure-to-stroke-volume. A total of 112 invasive measurements of the ratio of pulse-pressure-to-stroke-volume and noninvasive determinations of central artery stiffness were performed in 49 patients on the intensive care unit. In 13 out of 112 attempts of noninvasive measurements (12%) radial pulse could not be obtained using applanation tonometry because of cardiac arrhythmia or radial pulse could not be detected. These 13 failing noninvasive measurements were attempted in 7 patients. In the remaining cases we found a significant correlation between noninvasively obtained central artery stiffness and invasive measurements of the ratio of pulse-pressure-to-stroke-volume (Spearman r=0.40; p<0.0001). The association between invasive and noninvasive measurements was confirmed using Bland-Altman plots. Furthermore, a norepinephrine-induced increase of arterial stiffness was detected both invasively and noninvasively. Noninvasive determination of central artery stiffness obtained from peripheral radial artery waveform should be useful in clinical practice although it cannot be performed in every patient.

Noninvasive cardiac output determination using applanation tonometry-derived radial artery pulse contour analysis in critically ill patients.

Conventional thermodilution cardiac output (CO) monitoring is limited mainly to intensive care units and operating rooms because it requires the use of invasive techniques. To reduce the potential for complications and to broaden the applicability of hemodynamic monitoring, noninvasive methods for CO determination are being sought. Applanation tonometry allows noninvasive CO estimation through pulse contour analysis, but the method has not been evaluated in critically ill patients. We therefore performed noninvasive radial artery applanation tonometry in 49 critically ill medical intensive care unit patients and compared CO estimates to invasive CO measurements obtained using a pulmonary artery catheter or the PiCCO transpulmonary thermodilution system. One-hundred-sixteen measurements were performed, and patients were receiving vasopressor support during 78 measurements. When the data were analyzed with bias and precision statistics, a large bias of 2.03 L x min(-1) x m(-2) and a high percentage error of 85% were found between the invasive measurements and applanation tonometry-derived CO estimates, with the noninvasive CO results being significantly lower than the invasive ones (P < 0.001). There was no significant difference in bias between the patients who were receiving vasopressor support and those who were not (P = 0.874) or between patients with good and poor applanation tonometry pressure waveform signal quality (P = 0.071). Whereas a significant increase in the invasively determined CO was observed when a fluid bolus was administered (n = 7, P = 0.016), these changes were not reflected by the noninvasive method. We conclude that radial artery applanation tonometry is not suitable to determine CO in critically ill hemodynamically unstable patients.