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Kenji Sunagawa

Publications and source records attributed to Kenji Sunagawa.

113 records · Page 7Linked to original sources
PubMed2002

High-cut characteristics of the baroreflex neural arc preserve baroreflex gain against pulsatile pressure.

A transfer function from baroreceptor pressure input to sympathetic nerve activity (SNA) shows derivative characteristics in the frequency range below 0.8 Hz in rabbits. These derivative characteristics contribute to a quick and stable arterial pressure (AP) regulation. However, if the derivative characteristics hold up to heart rate frequency, the pulsatile pressure input will yield a markedly augmented SNA signal. Such a signal would saturate the baroreflex signal transduction, thereby disabling the baroreflex regulation of AP. We hypothesized that the transfer gain at heart rate frequency would be much smaller than that predicted from extrapolating the derivative characteristics. In anesthetized rabbits (n = 6), we estimated the neural arc transfer function in the frequency range up to 10 Hz. The transfer gain was lost at a rate of -20 dB/decade when the input frequency exceeded 0.8 Hz. A numerical simulation indicated that the high-cut characteristics above 0.8 Hz were effective to attenuate the pulsatile signal and preserve the open-loop gain when the baroreflex dynamic range was finite.

Animals↗
PubMed2002

Estimation of baroreflex gain using a baroreflex equilibrium diagram.

Two types of closed-loop perturbations can be applied to the arterial baroreflex system. The first (P(D1)) is introduced into the baroreceptors without a direct effect on arterial pressure (AP), whereas the second (P(D2)) initially affects AP. Neck suction and hemorrhage are examples of P(D1) and P(D2), respectively. To estimate the baroreflex open-loop gain (G(Baro)) without knowing the absolute magnitudes of P(D1) and P(D2), we explored a new strategy to estimate G(Baro) by combining P(D1) and P(D2) in a baroreflex equilibrium diagram. In this diagram, the neural arc presents the input-output relationship between baroreceptor pressure input and sympathetic nerve activity (SNA). The peripheral arc presents the input-output relationship between SNA and AP. In 8 anesthetized rabbits, we estimated G(Baro) by multiplying the slopes of the peripheral arc determined from P(D1) and the neural arc determined from P(D2). We also estimated G(Baro) by a conventional open-loop analysis. The G(Baro) values estimated by the equilibrium diagram and the open-loop analysis showed a positive correlation (y = 0.80x + 0.22, r(2) = 0.95) and a standard error of estimate of 0.21 across the animals. We conclude that G(Baro) was estimated well by combining P(D1) and P(D2) in the equilibrium diagram.

Animals↗
PubMed2002

Convenient automated conductance volumetric system.

Conventional conductance volumetric systems require ex-vivo calibrations for blood conductivity and parallel conductance. It is often impractical to repeat blood sampling and hypertonic saline infusion for these calibrations. To overcome these limitations, we developed a useful, self-calibrating conductance volumetric system that does not require ex-vivo calibrations. On a conventional 6-electrode catheter, we added an extra electrode close to one of the recording electrodes to estimate blood conductivity. These two electrodes were placed close (0.5 mm) enough so that conductance between them reflected only blood conductivity regardless of cardiac volume. We estimated parallel conductance by the dual-frequency excitation (2 and 20 kHz) method. In 18 anesthetized rabbits, blood conductivity (sigma(est)) thus estimated agreed well with that (sigma(conv)) measured by the conventional ex-vivo blood sampling method (sigma(est) = 1.04sigma(conv)-0.25, R(2) = 0.98, SEE = 0.01 mS/cm, 1.2% error). Parallel conductance (G(p est)) estimated by dual-frequency excitation also agreed well with that (G(p conv)) estimated by the saline injection method (G(p est) = 0.95G(p conv)+4.25, R(2) = 0.87, SEE = 4.0 mS, 6.0% error). Estimated ventricular volume (V(est)) by our system agreed reasonably well with that (V(conv)) by the conventional method (V(est) = 0.93V(conv)+0.01, R(2) = 0.86, SEE = 0.22 ml, 14.7% error). The fact that this self-calibrating conductance volumetric system drastically simplifies volume measurement makes it an attractive tool for the assessment of cardiac function where significant changes in blood conductivity and parallel conductance are inevitable, such as in cardiac surgery.

Animals↗
PubMed2002

[New algorithm for oscillometric noninvasive automatic arterial pressure measurement in patients with atrial fibrillation].

Oscillometric noninvasive arterial pressure monitoring devices frequently fail to measure pressure precisely in patients with arrhythmia, such as atrial fibrillation, because beat-by-beat changes in pulse pressure and mean pressure level distort the relation between cuff pressure and oscillometric wave amplitude. To overcome this problem, we developed a new algorithm for oscillometric measurement in which oscillometric wave amplitude is corrected according to changes in pulse pressure and mean arterial pressure level. In 7 patients with atrial fibrillation, we compared systolic pressure thus estimated with that simultaneously measured invasively in the radial artery and averaged during oscillometric measurement. Correction based on invasively obtained beat-by-beat pulse pressure and mean pressure level decreased the ratio of unmeasurable cases from 11 to 4%. Correction based on plethysmographically estimated pulse pressure decreased unmeasurable cases to 6% (P < 0.01). Standard error of systolic pressure estimates was 6.44 +/- 1.83, 4.10 +/- 0.85, and 4.75 +/- 1.26 mmHg with no, invasive, and plethysmographical correction in this order (P < 0.01). We conclude that oscillometric wave amplitude correction based on beat-by-beat pulse pressure and mean arterial pressure level lessened the number of unmeasurable cases and improved measurement precision in patients with atrial fibrillation.

Algorithms↗