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A1257
October 15, 2007
2:00 PM - 4:00 PM
Room Hall D, Area I,
Vascular Impedance and Pulse Wave Velosity during Sympathetic Blockade
Noboru Saeki, M.D., Ryuuji Nakamura, M.D., Masahi Kawamoto, M.D., Ph.D., Toshio Tsuji, Ph.D., Kenji Shiba, Ph.D.
Anesthesia and Critical Care, Hiroshima Universty Faculty of Medcine, Hiroshima City, Hiroshima Pref, Japan
Introduction:

Pulse wave velocity (PWV) has been used for evaluation of arterial sfiffness or sclerosis, however its role as a monitor during anesthesia has not determined. We have proposed a beat-to-beat, a neural network (NN) judged vascular impedance [stiffness (K), viscosity (B) and inertia (M)] monitoring system, which revealed to be useful in both anesthesia induction and sympathetic block. In this study, we compared PWV with the vascular impedance during sympathetic blockade.

Methods:

Subjected were 41 patients receiving endoscopic thoracic sympathectomy for palmar hyperhidrosis. Waveforms from ECG, radial arterial pressure (AP), and finger plethysmogram were computed to display Lissajous figure, and analyzed beat-to-beat using a NN judging an impedance model [F(t)= Kdr(t)+Bdr'(t)+Mdr"(t), where F(t) is force exerted on arterial wall; r(t), r'(t) and r"(t) were position, velocity and acceleration of the wall, respectively]. PWV was calculated from the time difference between R wave in ECG and the feet of AP originated by the same QRS complex, and from the distance between mid sternum and distal end of radius.

Results:

The reliability of this model was evidenced, as correlation coefficient was more than 0.95 between computed Lissajous and measured wave data. K, B, M, PWV and systolic blood pressure (SBP) were reduced by general anesthesia, and increased by surgical insult. Sympathectomy reduced K, B, M and SBP but not PWV (K and PWV were displayed in Figure 1). The changes for K, B, M, SBP and PWV during surgery were increased 8.9, 7.5, 9.4, 1.5 and 1.2 folds, respectively. Sympathectomy reduced K, B, M and SBP significantly (14.6+/-11.8, 14.7+/-9.7, 18.1+/-12.9 and 77.9+/-10.4%, respectively), but not PWV (97.9+/-8.5%) (Figure 2).

Conclusions:

Vascular impedance parameters and SBP but not PWV reflected sympathetic activity. Since PWV is believed to be affected mainly by large or elastic arteries which contain less vascular smooth muscles, our result may be due to the limited effect by sympathetic nerve system via vascular smooth muscles contraction. We concluded that in anesthetic management, vascular impedance but not PWV is suitable for the monitoring of sympathetic nerve activity.[figure1][figure2]

Anesthesiology 2007; 107: A1257
Figure 1


Figure 2