Analysis and processing of laser Doppler perfusion monitoring signals recorded from the beating heart

Laser Doppler perfusion monitoring (LDPM) can be used for monitoring myocardial perfusion in the non-beating heart. However, the movement of the beating heart generates large artifacts. Therefore the aim of the study was to develop an LDPM system capable of correlating the laser Doppler signals to the cardiac cycle and to process the signals to reduce the movement artifacts. Measurements were performed on three calves, both on the normal beating heart and during occlusion of the left anterior descending coronary artery (LAD). The recorded LDPM signals were digitally processed and correlated to the sampled ECG. Large variations in the output (perfusion) and DC signals during the cardiac cycle were found, with average coefficients of variation of 0.36 and 0.14 (n-14), respectively. However, sections with a relatively low, stable output signal were found in late diastole, where the movement of the heart is at a minimum. Occlusion of the LAD showed the importance of recording the laser Doppler signals at an appropriate point in the cardiac cycle, in this case late systole, to minimise movement artifacts. It is possible to further reduce movement artifacts by increasing the lower cutoff frequency when calculating the output signal.     

Myocardial perfusion monitoring during coronary artery bypass using an electrocardiogram-triggered laser Doppler technique

Electrocardiogram (ECG)—triggered laser Doppler perfusion monitoring (LDPM) was used to assess myocardial perfusion, with minimum myocardial tissue motion influence, during coronary artery bypass grafting (CABG). Thirteen subjects were investigated at six phases: pre- and post-CABG; post aorta cross-clamping; pre and post left internal mammary artery (LIMA) graft declamping; and post aorta declamping. The perfusion signal was calculated in late systole and late diastole, with expected minimum tissue motion, and compared with arrested heart measurements. Patient conditions or artifacts caused by surgical activity made it impossible to perform and analyse data in all six phases for some patients. No significant (n=5) difference between perfusion signals pre- and post-CABG was found. Diastolic perfusion signal levels were significantly (p<0.02) lower compared with systolic levels. After aorta cross-clamping, the signal level was almost zero. A distinct perfusion signal increase after LIMA and aorta declamping, compared with pre-LIMA declamping, was found in ten cases out of 13. A significantly (p<0.04) lower perfusion signal in the arrested heart compared with in the beating heart was registered. Influence from mechanical ventilation was observed in 14 measurements out of 17. In conclusion, ECG-triggered LDPM can be used to assess myocardial perfusion during CABG. Perfusion signals were lower in the arrested heart compared with in the beating heart and in late diastole compared with late systole. No significant difference between pre- and post-CABG was found.     

552例正常胎儿房室环运动的组织多普勒分析

目的探讨组织多普勒成像（TDI）检测胎儿房室环运动的可行性并测量其正常值。方法应用TDI技术观察552正常胎儿四腔心切面的二、三尖瓣环运动，测量其收缩、舒张期运动的峰值速度并进行比较。结果TDI技术可清晰显示二、三尖瓣环运动情况。收缩、舒张期二、三尖瓣环运动的峰值速度均随孕周增加而增大。收缩、舒张期三尖瓣环运动的峰值速度均大于二尖瓣环（P〈0．01）。结论TDI可用于检测胎儿二、三尖瓣环运动及其随孕周的变化，进而评价胎儿心功能。     

Baseline tissue Doppler imaging-derived echocardiographic parameters and left ventricle reverse remodelling following cardiac resynchronization therapy introduction

Introduction

The aim of the study was to assess the relation of baseline mechanical dyssynchrony with the left ventricular end-systolic volume (LVESV) decrease following cardiac resynchronization (CRT) therapy introduction.

Material and methods

Sixty consecutive patients (aged 66.3 ± 8.7 years; 57 men) with chronic heart failure (71.7% of ischaemic and 28.3% of non-ischaemic origin) and current indications for CRT were assessed before and 3 months after biventricular heart stimulator implantation. Longitudinal movements of twelve segments of the left ventricle (LV) (6 basal and 6 midlevel) and two segments of the right ventricle (RV) were analysed using tissue Doppler imaging (TDI) techniques with time from onset of Q wave in ECG to peak systolic velocity in colour-coded TDI (T_TDI), time to peak strain (T_strain) and time to peak strain rate (T_{strain rate}). Minimal and maximal time differences within LV and between LV and RV walls were calculated.

Results

In the study group LVEF and 6-min walk test distance increased, while NYHA class, NT-proBNP level, left ventricular end-diastolic volume and LVESV decreased. Significant correlations between the magnitude of LVESV reduction with maximal time differences between T_strain of 12 LV segments (r=0.34, p = 0.017) and time differences between T_TDI basal LV-RV segments (r = –0.29, p=0.041) were found.

Conclusions

Only a few TDI-derived parameters such as maximal time differences between T_strain of 12 LV segments and T_TDI difference of LV-RV basal segments can be useful to predict the magnitude of left ventricle reverse remodelling after CRT introduction.     

Evaluation of left ventricular dyssynchrony using combined pulsed wave and tissue Doppler imaging

Introduction

The combination of pulsed wave (PW) and tissue Doppler imaging (TDI) has been proposed as a new method to assess left ventricular (LV) mechanical dyssynchrony (LVMD), but results have not been validated. We investigated the correlation of a combination of PW and TDI with a positive response to cardiac resynchronization therapy (CRT).

Material and methods

We studied 108 consecutive patients who received CRT. Patients with atrial fibrillation were excluded. The time difference (T_PW-TDI) between onset of QRS to the end of LV ejection by PW (T_PW) and onset of QRS to the end of the systolic wave in LV basal segments with greatest delay by TDI (T_TDI) was measured before CRT and during short-term and long-term follow-up.

Results

The T_PW-TDI interval before CRT was 74 ±48 ms. Intra-observer variabilities for T_PW and T_TDI were 1.5 ±0.24% and 1 ±0.17%. Inter-observer variabilities for T_PW and T_TDI were 1 ±0.36% and 1 ±0.64%, respectively. T_PW-TDI > 50 ms was defined as the cutoff value for diagnosis of LVMD by receiver operating curve (ROC) analysis. During follow-up of 15 ±11 months, the sensitivity and specificity of TP_PW-TDI to predict a positive response to CRT were 98% and 82%, respectively. The area under the ROC curve was 0.92. There was a significant agreement between LVMD determined by T_PW-TDI and the positive response to CRT (κ=0.80).

Conclusions

Left vertricular dyssynchrony detected by the method combining PW and TDI demonstrated a high reproducibility, sensitivity, specificity and agreement with a positive response to CRT.     

Modulation of the human nociceptive flexion reflex across the cardiac cycle

Carotid baroreceptor stimulation has been shown to dampen pain. This study tested, in 40 normotensive adults, the hypothesis that pain is lower during systole when arterial baroreceptor stimulation is maximal than diastole when stimulation is minimal. The sural nerve was stimulated electrocutaneously to obtain a nociceptive flexion reflex (NFR) threshold, and then stimulation was delivered for 28 trials at 100% NFR threshold at seven intervals after the R-wave. Nociceptive responding was indexed by electromyographic (EMG) activity elicited in the biceps femoris. Significant variations in EMG activity occurred across the cardiac cycle, with less activity midcycle, indicating that the NFR response was attenuated during systole compared to diastole. Stimulation of baroreceptors by natural changes in blood pressure during the cardiac cycle dampened nociception, and accordingly, the data support the arterial baroreflex mechanism of hypertensive hypoalgesia.     

Electrocutaneous pain thresholds are higher during systole than diastole

Arterial baroreceptors may modulate pain. Evidence suggests the neurophysiological correlates of pain are dampened during systole, when baroreceptors are stimulated, compared to diastole, when stimulation is minimal. However, the influence of the cardiac cycle on perception of pain remains unclear. This study examined pain thresholds in 49 healthy adults at seven intervals after the R-wave of the electrocardiogram, using an interleaved up-down staircase procedure. Electrocutaneous stimuli were delivered to the hand and participants indicated the presence or absence of pain. Pain thresholds were higher mid-cycle, indicative of pain attenuation during systole compared to diastole. Moderation analyses revealed no relationship between the magnitude of cardiac cycle-related modulation and tonic blood pressure. These findings suggest fluctuations in arterial baroreceptor activity across the cardiac cycle may influence pain in normotensive individuals; however, tonic blood pressure may not affect the magnitude of this pain modulation.     

Cardiac cycle time effects on selection efficiency in vision

The effect of cardiac cycle time on attentional selection was investigated in an experiment in which participants classified target letters in a visual selection task. Stimulus onsets were aligned to the R wave of the electrocardiogram and stimuli presented either during the ventricular systole or diastole. Selection efficiency was operationalized as difference in target selection performance under conditions of homogeneous and heterogeneous distractors. Differences in performance (i.e., the impact selection difficulty had on the ability to select the target) were attenuated for stimuli presented during the ventricular systole compared to the diastole. Increased baroafferent signal transmission during the systole appears to reduce interference of highly distracting stimuli on visual selection efficiency.     

组织多普勒成像超声检测在胎儿心律失常诊断中的应用

目的探讨组织多普勒成像超声检测在胎儿心律失常诊断中的价值。方法采用组织多普勒成像（TDI）对100例孕妇进行组织多普勒成像超声检测,测量房室传导时间（AV）及心室开始收缩至下一心动周期心房开始收缩的时间间期（VA）。均测量3个心动周期,取平均值。对于偶发心律失常的胎儿,测量AV、VA时,取心律失常前或后至少3个窦性心动周期以外开始测量;同时测量心律失常时的AV、VA并与自身窦性心率进行比较。结果 （1）100例胎儿的心脏传导时间均被成功测量,心脏结构均正常,心律正常88例,偶发心律失常12例。AV、VA与心率呈负相关,AV在不同心率胎儿的比较差异无统计学意义（P〉0.05）,VA在不同心率胎儿的比较差异有统计学意义（P〈0.05）。（2）AV、VA与心率呈负相关。AV在不同心率胎儿的比较差异无统计学意义（P〉0.05）,VA在不同心率胎儿的比较差异有统计学意义（P〈0.05）。（3）12例偶发心律失常胎儿心脏结构正常。4例为心动过缓胎儿中,1例表现为AV、VA均明显延长,l例AV明显延长,2例VA明显延长。8例为房型期前收缩,其中2例为二联律,早搏周期VA均较窦性心率时缩短,其后代偿间歇周期的VA除2例外均明显延长,早搏周期AV、代偿间歇周期AV与窦性心动周期的AV相比无明显改变。结论组织多普勒成像超声检测对产前超声筛查胎儿心律失常方面具有重要的作用和临床意义。结论组织多普勒成像可简单快速地定量测定胎儿心脏传导时间,对产前超声筛查胎儿心律失常方面具有重要的作用和临床意义。     

Artificial neural network-based classification of body movements in ambulatory ECG signal

Abstract

Ambulatory ECG monitoring provides electrical activity of the heart when a person is involved in doing normal routine activities. Thus, the recorded ECG signal consists of cardiac signal along with motion artifacts introduced due to a person’s body movements during routine activities. Detection of motion artifacts due to different physical activities might help in further cardiac diagnosis. Ambulatory ECG signal analysis for detection of various motion artifacts using adaptive filtering approach is addressed in this paper. We have used BIOPAC MP 36 system for acquiring ECG signal. The ECG signals of five healthy subjects (aged between 22–30 years) were recorded while the person performed various body movements like up and down movement of the left hand, up and down movement of the right hand, waist twisting movement while standing and change from sitting down on a chair to standing up movement in lead I configuration. An adaptive filter-based approach has been used to extract the motion artifact component from the ambulatory ECG signal. The features of motion artifact signal, extracted using Gabor transform, have been used to train the artificial neural network (ANN) for classifying body movements.     

Polarized laser Doppler perfusion imaging--reduction of movement-induced artifacts

Laser Doppler perfusion imaging (LDPI) enables superficial tissue perfusion assessment, but is sensitive to tissue motion not related to blood cells. The aim was to investigate if a polarization technique could reduce movement-induced artifacts. A linearly polarized laser and a cross-polarized filter, placed in front of the detectors, were used to block specular reflection. Measurements were performed with, and without, the polarization filter, at a single site during horizontal and vertical movement of skin tissue (index finger, twelve subjects, n = 112) and of a flow model (n = 432), with varying surface structures. Measurements were repeated during different flow conditions and at increased skin specular reflection. Statistical analysis was performed using ANOVA models. The perfusion signal was lower (p < 0.001, skin and p < 0.05, flow model) using the polarization filter, due to movement artifact reduction. No significant influence from surface structure was found when using the polarization filter. Movement artifacts were lower (p < 0.05) in the vertical movement direction, however, depending on flow conditions for skin measurements. Increased skin specular reflection gave rise to large movement artifacts without the polarization filter. In conclusion, the polarized LDPI technique reduces movement artifacts and is particularly appropriate when assessing, e.g., ulcers and burns, where specular reflection is high.     

The effect of averaging cardiac Doppler spectrograms on the reduction of their amplitude variability

The effect of averaging cardiac Doppler spectrograms on the reduction of their amplitude variability was investigated in 30 patients. Beat-to-beat variations in the amplitude of Doppler spectrograms were also analysed. The quantification of amplitude variability was based on the computation of the area under the absolute value of the derivative function of each spectrum composing mean spectrograms. Fast Fourier transform using a Hanning window was used to compute Doppler spectra. Results obtained over systolic and diastolic periods showed that the reduction of amplitude variability followed an exponentially decreasing curve characterised by the equation f(r)=100e^−β(r−1), where r is the number of cardiac cycles, β the exponentially decreasing rate, and 100 the normalised variability for r=1. In systole, the decreasing rate β was 0·165, whereas in diastole it was 0·225. Reductions of the variability in systole for a number of cardiac cycles of 5, 10, 15, and 20 were 48, 77, 90 and 96 per cent, respectively. In diastole, reductions of the variability for the same numbers of cardiac cycles were 59, 87, 96 and 99 per cent, respectively. Based on these results, it can be concluded that no significant improvement in the reduction of amplitude variability may be obtained by averaging more than 20 cardiac cycles.     

Basis for phase relations between baroreceptor and sympathetic nervous discharge.

The phase relations between the cardiac cycle and sympathetic nervous discharge (SND) were studied with an average-response computer in the anesthetized cat. Maximum SND occurred during early diastole at heart rates between 3 and 4 beats/s. Dramatic shifts in the phase relations between SND and the cardiac cycle accompanied the decrease in heart rate produced by stimulation of the distal end of the cut right vagus nerve. The point of maximum SND was shifted from early diastole to near peak systole and then into the late diastolic phase of the preceding cardiac cycle as heart rate was progressively lowered to 2 beats/s. These observations indicate that synchronization of SND during each cardiac cycle is not the simple consequence of the waxing and waning of baroreceptor nerve activity. Rather, 1:1 locking of bursts of SND to the cardiac cycle is explained on the basis of entrainment by the baroreceptor reflexes of a sympathetic rhythm of central origin. An inhibitory-phasing hypothesis is proposed to account for entrainment. In addition, two components (spinal and brainstem) of sympathoinhibition associated with the pulse-synchronous discharge of the carotid sinus nerve were revealed when the 1:1 relationship between bursts of SND and the cardiac cycle was disrupted at heart rates below 2 beats/s.     

Optimum control of the Hemopump as a left-ventricular assist device

A general framework for designing an optimum control strategy for the Hemopump is described. An objective function was defined that includes four membership functions, each constructed based on the desired values of one of the four members: stroke volume, mean left atrial pressure, aortic diastolic pressure and mean pump rotation speed. The Hemopump was allowed to operate either at a constant speed or at two different speeds during a cardiac cycle. The goal was to maximise the objective function by varying the magnitude and timing of the pump speed. Using a canine circulatory model, it was demonstrated that, in general, different cardiac conditions or different clinical objectives require different operation parameters. For example, when a left ventricle with minor ischaemia was simulated, and the main objective was to increase stoke volume, the objective function was maximised, from a value of 0.877 when the pump was off, to 0.946 when the pump was operated at speed 2 (18 500-revolutions min⁻¹). On the other hand, for a severely ischaemic heart, the optimum pump speed became speed 3 (20 000 revolutions min⁻¹), which maximized the objective function to 0.943 (from 0.707 when the pump was off). The results also suggest that it is more beneficial to operate the Hemopump at two different speeds during a cardiac cycle (a higher speed during systole and early diastole, and a lower speed during late diastole) than to maintain a constant speed throughout the cardiac cycle.     

An approach of in vivo measurement for ultrasonic myocardial tissue characterization

The purpose of this study is to characterize regional myocardial alternations of reflected ultrasound throughout a cardiac cycle in normal and ischemic myocardium. Integrated ultrasonic backscatter (2-5 MHz) gated R wave of ECG was measured at the base, middle and apex in 4 dogs, and the apex before and after ischemia in other 4 dogs. Quantitative ultrasonic backscatter (IB) was reflected to a steel reflector. At the apex and middle, where a cyclic pattern of IB was discernible, maximum values were recorded near end diastole and minimum near end systole. The amplitude of the variation of IB throughout a cardiac cycle for each region increase progressively from base to middle to apex. Time-averaged IB over a cardiac cycle (averaged IB) was similar for each area of the heart (base = -50.6 +/- 0.5 dB (mean +/- SE), middle -49.4 +/- 0.5 dB, apex -49.7 +/- 0.6 dB. p = NS for comparison of any two regions). After occluding left anterior descending coronary artery for 30 minutes, the variation of IB was markedly blunted and averaged IB increased significantly (-47.5 +/- 0.5 dB. p less than 0.01 compared with preocclusion (-50.8 +/- 0.5 dB]. These results suggested that IB and averaged IB may permit assessment of intrinsic geometrical changes throughout a cardiac cycle (contractile properties) and histological changes respectively.     

Simultaneous assessment of left-ventricular infarction size, function and tissue viability in a murine model of myocardial infarction by cardiac manganese-enhanced magnetic resonance imaging (MEMRI)

Owing to its signal-enhancing characteristics in viable well-perfused tissue, divalent manganese (Mn2+) has been used as a myocardial imaging contrast agent. Because Mn2+ can enter excitable cells through the voltage-gated L-type calcium channels, manganese-enhanced MRI (MEMRI) has been used to determine the viability and the inotropic state of the heart. In this study, we examined the correlation between left ventricular infarction zone as assessed by cardiac MEMRI and function in mice with permanent coronary artery occlusion. At an Mn2+ infusion dose of 1.72+/-0.47 nmol/min/g body weight, the steady-state signal intensity (SI) enhancement 20-26 min post-Mn2+ infusion of the normal septum and left-ventricular wall during diastole was 128.2+/-14.4 and 127.9+/-26.5%, respectively, whereas the infarction zone was 56.0+/-7.1%. During systole, the SI enhancement was 144.6+/-33.0, 116.0+/-18.7 and 48.3+/-20.0% for the normal septum, left-ventricular wall and infarction zone, respectively. A good correlation was obtained between the MEMRI determined infarction volume and conventional histological TTC staining (r = 0.9582, p<0.01). There was also a strong negative correlation between MEMRI determined infarction percentage (compared with whole left ventricle) and ejection fraction (r = -0.94, p<0.05). These data suggest that the Mn2+ concentration at steady state in the heart may reflect altered tissue viability in the infarcted tissue as well as surrounding region following myocardial infarction. In conclusion, in vivo cardiac MEMRI offers a manner in which functional, pathologic and viability data may be obtained simultaneously in myocardial tissue.     

Geometrical variations of the canine superior vena cava: Relationship between diameter,segment length and transmural venous pressure

The dimensional variations of the superior vena cava throughout the cardiac cycle were investigated by means of angiographic and ultrasonic techniques. Results obtained by both methods were largely in agreement. In frontal direction the diameter curve resembled the transmural pressure variations, the sagittal diameter curve was not related to the venous pressure variations during certain phases of the cardiac cycle and compressional and/or stretching forces exerted by respectively the distending aorta and/or pulmonary artery and the contracting heart may have been responsible. Also segment length variations occurred: during atrial contraction, ventricular systole and early diastole the vein elongated, indicating the varying longitudinal traction forces, possibly exerted by the rotational movement of the contracting heart. Assuming elliptical symmetry the vena caval cross-section could be reconstructed, and the cross-sectional area, perimeter and segmental volume could be calculated throughout the cardiac cycle. Despite the high venous distensibility, no extreme collapse of the vein was observed during the cardiac cycle at low transmural pressures.     

In vivo imaging of the cyclic changes in cross‐sectional shape of the ventricular segment of pulsating embryonic chick hearts at stages 14 to 17: A contribution to the understanding of the ontogenesis of cardiac pumping function

The cardiac cycle‐related deformations of tubular embryonic hearts were traditionally described as concentric narrowing and widening of a tube of circular cross‐section. Using optical coherence tomography (OCT), we have recently shown that, during the cardiac cycle, only the myocardial tube undergoes concentric narrowing and widening while the endocardial tube undergoes eccentric narrowing and widening, having an elliptic cross‐section at end‐diastole and a slit‐shaped cross‐section at end‐systole. Due to technical limitations, these analyses were confined to early stages of ventricular development (chick embryos, stages 10–13). Using a modified OCT‐system, we now document, for the first time, the cyclic changes in cross‐sectional shape of beating embryonic ventricles at stages 14 to 17. We show that during these stages (1) a large area of diminished cardiac jelly appears at the outer curvature of the ventricular region associated with formation of endocardial pouches; (2) the ventricular endocardial lumen acquires a bell‐shaped cross‐section at end‐diastole and becomes compressed like a fireplace bellows during systole; (3) the contracting portions of the embryonic ventricles display stretching along its baso‐apical axis at end‐systole. The functional significance of our data is discussed with respect to early cardiac pumping function. Developmental Dynamics 238:3273–3284, 2009. © 2009 Wiley‐Liss, Inc.     

In vivo quantification of blood velocity in mouse carotid and pulmonary arteries by ECG‐triggered 3D time‐resolved magnetic resonance angiography

Blood flow velocity is a functional parameter of fundamental importance in diagnosis and follow‐up of various vascular diseases. Vascular pathologies can be efficiently studied in animal models, especially in small rodents. ECG‐gated magnetic resonance imaging (MRI) assessment of blood velocity in small animals is a challenge because of limited spatial resolution and high‐frequency physiological parameters. Here it is shown that a bright‐blood cine‐3D‐MRI method can be used to measure blood velocity at specific times of the cardiac cycle in mouse pulmonary and carotid arteries. The method used a series of time‐of‐flight (TOF) acquisitions in a volume of interest at different times after signal cancellation in the same volume. This scheme was repeated at different periods of the cardiac cycle by varying the delay between the ECG R‐wave peak and signal cancellation. Velocity values in mouse pulmonary artery varied from 35 cm/s in systole to 0–10 cm/s in diastole. A similar pattern was displayed in carotid arteries (18 and 2.5 cm/s, in systole and diastole, respectively). Results are discussed in terms of efficiency, limitation, and comparison with other methods. Copyright © 2009 John Wiley & Sons, Ltd.