Wei-Chih Hu

The effect of data reduction by independent component analysis and principal component analysis in hand motion identification

Both independent component analysis (ICA) and principal component analysis (PCA) were used in this study to evaluate their effects in data reduction in the hand motion identification using surface electromyogram (SEMG) and stationary wavelet transformation. The results indicate that both methods increase the number of training epochs of the artificial neural network. The unsupervised fast ICA reduces the number of SEMG channels from 7 to 4. However the hand motion identification rate using the reduced channels is significantly lower (p < 0.05). On the other hand, the PCA reduces the size of neural network by more than 70%. Moreover, the results of discrimination rate and neural network training epochs show no significant difference as compared to the results before PCA reduction. The result of this study demonstrates that using wavelet and PCA are effective pre-processing for surface EMG analysis. It can efficiently reduce the size of neural network and increase the discrimination rate for different hand motions.

Evaluation of changes in cardiac output from the electrical impedance waveform in the forearm

We tested the validity of regional impedance cardiography (RIC) for measuring changes in both cardiac output and stroke volume by comparing the values with a 2D ultrasound technique in response to the breath-hold manipulation. Among 13 subjects, changes in the maximum amplitude of the regional impedance waveform from the forearm conformed to those in stroke volume (r = 0.86, p < 0.001) and cardiac output (r = 0.76, p < 0.003) measured with the ultrasound technique in baseline and immediately after a 30 s breath-hold maneuver. We also found that the per cent change in cardiac output (r = 0.73, p < 0.005) and the per cent change in stroke volume (r = 0.84, p < 0.0003) by the echocardiography were both positively correlated with the per cent change in the peak impedance amplitude. In addition, both the change and the per cent change in the mean area under the impedance curve were consistent with those in the stroke volume, respectively. Accordingly, the regional electrical impedance waveform from lower limbs may be helpful in providing a non-invasive and continuous assessment of left ventricular output, especially during cardiac procedures.

Noninvasive determination of arterial pressure-dependent compliance in young subjects using an arterial tonometer

The objective of this study is to determine the pressure-dependent compliance of human radial artery in young subjects. The arterial blood pressure and the change in vessel volume of the radial artery in ten normotensive volunteers were simultaneously measured with an arterial tonometer. The arterial global compliance was calculated as the division of change in vessel volume by the difference between the systolic and the diastolic blood pressures. The arterial global compliance measured from the ten young volunteers was found to be 4.645 ± 2.739 uL/mmHg. When the arterial pressure-volume relation was assumed to be of natural logarithm, a correlation coefficient of 0.996 was yielded by curve-fit methods. Similarly, when the arterial compliance-pressure relation was fit in a natural logarithmic form, a correlation coefficient of 0.998 was obtained. In conclusion, the arterial vessel volume varies with the arterial blood pressure logarithmicly and positively, whereas a logarithmic and negative relation betwe...

On Measuring the Changes in Stroke Volume from a Peripheral Artery by Means of Electrical Impedance Plethysmography

In the study, we assessed the change in the left ventricular stroke volume from a radial artery by using an electrical impedance plethysmographic device. This device mainly incorporated tetra-polar electrodes, two of which were excited by an ac constant current source, and the other two are the sensing electrodes. In theory, the voltage difference between the two sensing electrodes was inversely proportional to the radial arterial blood flow of interest. In order to alter the stroke volume, 13 volunteers were recruited to undertake a thirty- second breath-hold maneuver. It was found that the impedance waveform registered in the lower arm had a significantly higher amplitude (2.24 plusmn 0.43 Volts) just after the 30-second breath-hold than in the steady state (1.81 plusmn 0.47 Volts) (p<0.001). In addition, a linear regression coefficient of 0.85 was found between the change in the stroke volume measured by a 2-D ultrasound system, and the change in the impedance amplitude before and after the breath-hold maneuver. In conclusion, we may non- invasively and continuously monitor the subjects stroke volume via a peripheral artery by means of the electrical impedance plethysmography.

Relationship between the Left Ventricular Elastance and the Effective Arterial Elastance in AMI Patients after Thrombolysis

The purpose of the study is to investigate the effect of thrombolysis on the relationship between the left ventricular (LV) maximum elastance (Emax) and effective arterial elastance (Eart) in 20 patients with acute myocardial infarction (AMI). LV pressures and volumes of the patients were measured with Millar and multi-electrode volume conductance catheters during catheterization examination, respectively, at the first week and 3 months after the thrombolytic treatment. Emax was represented by the slope of the LV end-systolic pressure-volume relation, and Eart by the slope of the arterial end-systolic pressure-stroke volume relation. The results showed a linear Emax to Eart relation (r = 0.59) at the 1st week, but not 3 months (r =0.20), in those post-AMI patients. Moreover, the Emax was found to be linearly proportional to the Emax/Eart ratio at both the 1st week (r = 0.88) and 3 months (r = 0.85) after thrombolytic therapy. In summary, a stunt hearts in the initial period after thrombolytic intervention reveals a linear relationship between the ventricular contractility and afterload, suggesting that the coupling of the left ventricle and arterial vasculature seems to be maintained

ABNORMAL MATCHING BETWEEN THE LEFT VENTRICLE AND THE ARTERIAL SYSTEM IN PATIENTS WITH ACUTE MYOCARDIAL INFARCTION AFTER THROMBOLYSIS PLUS ADJUVANT ANGIOPLASTY

The purpose of this study was to investigate the relationship between the left ventriculo–arterial coupling and the left ventricular (LV) mechanical efficiency in human hearts with acute myocardial infarction (AMI) after thrombolytic therapy combined with subsequent percutaneous coronary intervention. Twenty-six patients with post-AMI at cardiac catheterization were divided into two groups according to their resting ejection fraction (EF). The first group included 18 patients with EF greater than or equal to 50%, and the second group consisted of 8 patients with EF less than 50%. LV pressure–volume relations were measured by the conductance catheter method with preload altered by inferior vena cava obstruction in the 26 patients who received the thrombolytic therapy in 6 h and the percutaneous coronary intervention at first week after the AMI event. The ventriculo–arterial coupling relationship was determined by the ratio of the ventricular chamber elastance Ees (the slope of the LV end-systolic pressure relation) and the effective arterial elastance Ea (the slope of the arterial end-systolic pressure–stroke volume relation). The results showed no significant difference in the ratio of Ees/Ea between Group 1 (0.78 ± 0.34) and Group 2 (0.72 ± 0.22). Significant difference (p < 0.05) in the stroke work was found between Group 1 (7188 ± 1923 mmHg × ml) and Group 2 (5677 ± 670 mmHg × ml), although the potential energy in Group 1 was not significantly different from that in Group 2. We also found in the two patient groups that Ees but not Ea was linearly increased with the Ees/Ea ratio (Group 1: r = 0.84, p < 0.001 and Group 2: r = 0.76, p < 0.05). In addition, the ventricular mechanical efficiency in the infracted hearts with EF more than 50% (r = 0.71) was shown to be linearly increased with the Ees/Ea ratio, but not in those with EF of less than 50%. We concluded that in spite of no significant difference in the values of Ees/Ea between the infarct hearts with larger EF and those with smaller EF, all infarcted LV elastance but not their afterload depends linearly on Ees/Ea. Also, in myocardial infarcted patients with higher EF, their LV mechanical efficiency may tend to correlate linearly with the ventriculo–arterial coupling index, although the abnormal coupling between the left ventricle and arterial system still exists.

Primary Pharmocological Therapy May Improve Left Ventricular Diastolic Function in Patients with Acute Myocardial Infarction

The aim of this study was to investigate the effects of thrombolytic therapy and delayed percutaneous coronary intervention (PCI) on the time constant of left ventricular (LV) isovolumic relaxation. Of 38 patients with acute myocardial infarction (AMI) recruited in the study, 26 patients (TL group) received intravenously thrombolytic therapy within 12 hours after the AMI event, and 12 patients (PCI group) received delayed PCI at fifth or sixth day after the AMI event. LV pressure was measured with Millar catheters during diagnostic catheterization both at first week after admission and at 3-month follow-up. We found that in the patients with the thrombolytic therapy, the time constant of the isovolumic relaxation significantly decreases from 50.1 ±± 11.0 ms measured at the first week to 44.2 ±± 8.8 ms measured at the 3-month follow-up (p<0.05). In contrast, the time constant measured from the patients with PCI is significantly increased from 46.3 ±± 8.4 at the first week to 63.1 ±± 15.9 ms at the 3-month follow-up (p<0.05). In addition, the time constant was considerably smaller in the TL group patients than in the PCI group patients three months after occurrence of AMI (p<0.001). In conclusion, myocardial microvessels early reopened by the thrombolysis may dominantly contribute to the improvement in LV diastolic function, suggesting that the thrombolytic therapy may play a more progressive role in the AMI-related treatment as PCI equipment is not immediately available within 12 hours.

Myocardial Reperfusion Improves Ventricular Isovolumic Relaxation in Patients with Acute Myocardial Infarction

The study aimed to investigate the effects of thrombolytic therapy and percutaneous coronary intervention (PCI) on the time constant of left ventricular (LV) isovolumic relaxation. Of 38 patients with acute myocardial infarction (AMI) recruited in the work, 26 patients (treated group) received intravenously thrombolytic therapy within 12 hours after the AMI event, and 12 patients (controlled group) received PCI at fifth or sixth day after the AMI event. LV pressure was measured with Millar catheters during diagnostic catheterization both at first week after admission and at 3-month follow-up. We found that in the patients with the thrombolytic therapy, the time constant of the isovolumic relaxation significantly decreases from 50.1 plusmn 11.0 ms measured at the first week to 44.2 plusmn 8.8 ms measured at the 3-month follow-up (p < 0.05). In contrast, the time constant measured from the patients with PCI is significantly increased from 46.3 plusmn 8.4 at the first week to 63.1 plusmn 15.9 ms at the 3-month follow-up (p < 0.05). In addition, the time constant was considerably smaller in the treated patients than in the controlled patients three months after occurrence of AMI (p < 0.001). In conclusion, myocardial microvessels early reopened by the thrombolysis may dominantly contribute to the improvement in LV diastolic function, suggesting that the thrombolytic therapy may play a more progressive role in the AMI-related treatment as PCI equipment is not available.

Estimation of Left Ventricular Systolic Function Using Volume-Normalized Contractility Measures in Patients with Acute Myocardial Infraction

We propose three cardiac size-normalized contractility indexes in the work to investigate whether left ventricular (LV) systolic function in patients with acute myocardial infraction (AMI) after thrombolysis is enhanced or not. A cohort of 18 patients (17 men) aged 45-72 years received thrombolytic therapy within 24 hours after an AMI event, and their LV chamber function was determined using pressure-volume loops obtained by simultaneous conductance catheter volumetry and micromanometer pressure during catheterization examination at the first week and 3 months, respectively. A slope of the end-systolic pressure volume relation (Ees) was derived by reduced venous return. Three new contractility indexes (Esv, Edv, and Emv) were defined as the Ees divided by the end-systolic volume, end-diastolic and midrange of the LV volume, and then normalized to 100 ml, respectively. Using linear regression methods, we found high correlation coefficients of r = 0.835 at the first week and r = 0.826 at 3 months between the Ees and Esv after thrombolysis. Furthermore, Esv and Emv but not Ees were significantly higher measured at 3 months than at the first week after thrombolytic intervention. Thus, an increase in the volume- normalized contractility measures Esv and Emv implies the improvement of the left ventricular systolic function in the post- AMI human hearts long-term after thrombolytic treatment, in despite that there is a great coefficient of variation in cardiac chamber sizes at different recovery stages.

Equivalent Contractility Indexes for the Assessment of Left Ventricular Systolic Function in Post-AMI Human Hearts

We propose new contractility indexes, in the work, which are equivalent to the conventional contractility (Ees) determined with the slope of left ventricular (LV) end-systolic pressure-volume relation. Nineteen patients with acute myocardial infarction (AMI) were recruited in the study. They received thrombolytic therapy within 24 hours after the AMI event, and their LV pressures and volumes were measured with Millar and multi-electrode volume conductance catheters during catheterization examination at the first week and 3 months, respectively. The first equivalent contractility index (eEsv) submitted was defined as the Ees divided by the end-systolic volume (ESV) and normalized to 100 ml, the second (eEdv) as the Ees divided by the end-diastolic volume (EDV) and normalized to 100 ml, and the third (eEmv) as the Ees divided by the midrange of the LV volume and normalized to 100 m. Using linear regression methods, we found that a high correlation coefficient (r > 0.82) exists between the Ees and one of the three new contractility indexes. Furthermore, the eEsv but not Ees was significantly higher measured at 3 months than at one week after thrombolysis. In conclusion, an increase in the equivalent contractility eEsv implies the improvement of the left ventricular systolic function in the post-AMI human hearts long-term after thrombolytic intervention, as the size-dependence of contractility is taken into account