Extracting 1/f fluctuation from the arterial blood pressure of an artificial heart

Temporal dynamics and statistical characteristics of the microfluctuations of accommodation: dependence on the mean accommodative effort

Microfluctuations of accommodation have been the subject of many studies. New technological developments now permit us to study the dynamics of the microfluctuations with unprecedented resolution and accuracy. We aim to characterise their temporal statistics for different levels of accommodative effort, using a custom-built aberrometer. We conducted 46 s long measurements on the dominant eye of 9 young, healthy subjects. The ocular wavefront was sampled every 250 microm across the 3.9 mm measured pupil, at a frame rate of 173 Hz. This enabled us to obtain high resolution estimates of the Power Spectral Density (PSD). Results show that the shape of the estimated PSD for a 4 D effort is distinct from the shape for the two extrema of the accommodation range. The autocorrelation function of the increments of the accommodation signal is also affected by the level of effort, regardless of the refractive error of the subject.

Lighter General Anesthesia Causes Less Decrease in Arterial Pressure Induced by Epinephrine Scalp Infiltration During Neurosurgery

Scalp infiltration with epinephrine-containing lidocaine solution can elicit significant hypotension before craniotomy under general anesthesia. A prospective randomized controlled study was designed to observe whether a lighter depth of general anesthesia could prevent the unintentional hypotension induced by the epinephrine scalp infiltration during neurosurgery or not. Fifty patients undergoing scheduled neurosurgery involving craniotomy were randomly allocated into 2 groups. After anesthesia induction, anesthesia was maintained with propofol 2 mug/mL and rimifentanil 2 ng/mL by target-controlled infusion in group 1, and propofol 4 microg/mL and rimifentanil 4 ng/mL in group 2 (control group), respectively. All the patients received epinephrine scalp infiltration with 1% lidocaine 16 mL containing epinephrine 5 microg/mL. Mean arterial pressure (MAP) and heart rate were recorded at 30-second interval from the baseline to 5 minutes after the beginning of local infiltration. Bispectral index readings indicated group 1 had the lighter general anesthesia than group 2 (P<0.05). MAP was higher (P<0.05) and heart rate was lower (P<0.05) at 1.5 minutes time point in group 1 than group 2. The mean percentage of maximal decrease in MAP was group 1 (13%) <group 2 (24%) (P<0.05). The mean percentage of maximal increase in MAP was group 1 (10%)> group 2 (4%) without significant difference (P>0.05). The results implied that keeping a lighter general anesthesia caused less decrease in arterial blood pressure and was a relative effective method to prevent hypotension episode induced by epinephrine scalp infiltration.

Hemodynamic changes due to infiltration of the scalp with epinephrine-containing lidocaine solution: a hypotensive episode before craniotomy

Epinephrine-containing lidocaine solution is commonly infiltrated on the scalp before craniotomy. But the hemodynamic changes caused by epinephrine-containing lidocaine solution have been less intensely studied. A prospective randomized double blind control study was designed to observe hemodynamic changes caused by epinephrine-containing lidocaine solution in neurosurgical operations under general anesthesia. One hundred twenty patients undergoing scheduled craniotomy were allocated randomly to 4 groups. All the patients received 1% lidocaine 16 mL with different dose (concentration) epinephrine: group 1 with 40 microg (2.5 microg/mL); group 2 with 80 microg (5 microg/mL); group 3 with 160 microg (10 microg/mL); and group 4 (control group) without epinephrine. mean arterial pressure (MAP) and heart rate were recorded at 30-second interval in 5 minutes after the beginning of local infiltration. In group 1, group 2, and group 3, the lowest MAP and the highest MAP during this period also were recorded. Bleeding was assessed after raising the craniotomy flap. Compared with the baseline, significant hemodynamic changes, particularly decrease in MAP with increase in heart rate at 1.5 minutes after the beginning of local infiltration, were observed in group 1, group 2, and group 3 (P<0.001), but not in group 4. The highest MAP increased significantly compared with the baseline in group 3 (P<0.05), but not in group 1 or group 2. Epinephrine-containing lidocaine solution reduced bleeding significantly (P<0.01). Infiltration with epinephrine-containing lidocaine solution elicits temporary but significant hemodynamic changes including hypotension before craniotomy. Commonly clinically used concentrations of epinephrine (2.5 to 10 microg/mL) can reduce the bleeding on the scalp.

Chaotic dynamics in circulation with Tohoku University vibrating flow pump

For the development of a totally implantable ventricular assist system (VAS), we have been developing the vibrating flow pump (VFP), which can generate oscillated blood flow with a relative high frequency (10-50 Hz) for a totally implantable system. In this study, the effects of left ventricular assistance with this unique oscillated blood flow were analyzed by the use of nonlinear mathematics for evaluation as the whole circulatory regulatory system, not as the decomposed parts of the system. Left heart bypasses using the VFP from the left atrium to the descending aorta were performed in chronic animal experiments using healthy adult goats. The ECG, arterial blood pressure, VFP pump flow, and the flow of the descending aorta were recorded in the data recorder during awake conditions and analyzed in a personal computer system through an A-D convertor. By the use of nonlinear mathematics, time series data were embedded into the phase space, the Lyapunov numerical method, fractal dimension analysis, and power spectrum analysis were performed to evaluate nonlinear dynamics. During left ventricular assistance with the VFP, Mayer wave fluctuations were decreased in the power spectrum, the fractal dimension of the hemodynamics was significantly decreased, and peripheral vascular resistance was significantly decreased. These results suggest that nonlinear dynamics, which mediate the cardiovascular dynamics, may be affected during left ventricular (LV) bypass with oscillated flow. The decreased power of the Mayer wave in the spectrum caused the limit cycle attractor of the hemodynamics and decreased peripheral resistance. Decreased sympathetic discharges may be the origin of the decreased Mayer wave and fractal dimension. These nonlinear dynamic analyses may be useful to design optimal VAS control.