A CARDIOTACHOMETER WITH LINEAR INDICATION OF BEAT-TO-BEAT FREQUENCY

The instrument described has a linear indication of beat-to-beat heart rate with an overall accuracy of ±1 beat per minute. A linear output response over the range of 30 to 270 beats per minute is achieved with a square law discharge network. Input clipping and filter circuits permit reliable operation with moderately active subjects. Details of the circuit design and its performance are discussed.     

Ventricular arrhythmias and changes in heart rate preceding ventricular tachycardia in patients with an implantable cardioverter defibrillator

The objective was to determine the characteristics of heart rate variability and ventricular arrhythmias prior to the onset of ventricular tachycardia (VT) in patients with an implantable cardioverter defibrillator (ICD). Sixty-eight beat-to-beat time series from 13 patients with an ICD were analyzed to quantify heart rate variability and ventricular arrhythmias. The episodes of VT were classified in one of two groups depending on whether the sinus rate in the 1 min preceding the VT was greater or less than 90 beats per minute. In a subset of patients, increased heart rate and reduced heart rate variability was often observed up to 20 min prior to the VT. There was a non-significant trend to higher incidence of premature ventricular complexes (PVCs) before VT compared to control recordings. The patterns of the ventricular arrhythmias were highly heterogeneous among different patients and even within the same patient. Analysis of the changes of heart rate and heart rate variability may have predictive value about the onset of VT in selected patients. The patterns of ventricular arrhythmia could not be used to predict onset of VT in this group of patients.     

Short-term variability of systolic blood pressure and heart rate in normotensive subjects

Short-term fluctuations in systolic blood pressure (SBP) and heart rate (HR) and their inter-relationship were analysed in a group of normotensive middle-aged men (n = 16) using a multivariate autoregressive modelling technique. This study is the first to evaluate the beat-to-beat variability of SBP and HR in a group of real normotensive subjects. Direct intra-arterial blood pressure was registered together with ECG using an ambulatory tape recording technique (the Oxford method). Power spectrum density estimated (PSD) were used as a measure of the variability. PSDs were calculated over 3-min periods for four basic physiological conditions: during sleep and in the supine, sitting and standing positions. The inter-relationship between the blood pressure and heart rate variabilities was analysed using a closed-loop model. In agreement with results presented earlier in the literature, the beat-to-beat variation in SBP and HR was concentrated in three typical power spectrum regions: the high-frequency (HF = 0.15-0.35 Hz) region (respiration), the mid-frequency (MF = 0.075-0.15 Hz) region (vasomotor oscillation) and the low-frequency (LF = 0.02-0.075 Hz) region (thermoregulation). The variability changes considerably between different situations, especially that of the MF region. The variability was most prominent in the MF region and in the standing position. The variability was generally smallest in the HF region and in sleep. The results also demonstrate that the beat-to-beat variability in SBP and HR can considerably affect one another.     

Relationships between short-term blood-pressure fluctuations and heart-rate variability in resting subjects I: a spectral analysis approach

A method to attribute the short-term variability of blood pressure and heart rate of resting subjects to their various causes, using spectral techniques, is presented. Power spectra and cross-spectra are calculated for beat-to-beat values of R-R interval and blood pressure from subjects who were seated in a comfortable chair. Interval values as well as systolic, mean and pulse pressures show variations linked to respiration and to the so-called 10 s rhythm. The diastolic pressure values are scarcely influenced by respiration in the normal respiratory range (0·20–0·35 Hz), but do show 10 s variability. Relationships between pressure and interval variability which indicate that the 10 s variability in systolic pressure leads the interval variation by two to three beats become manifest in cross-spectra; however, no such lag is found between the respiration-linked variations in systolic pressure and intervals. It is argued that the technique presented provides a critical test for models of the fast regulation of the cardiovascular system.     

Cardiac vulnerability assessment from electrical microvariability of high-resolution electrocardiogram

Patients susceptible to malignant arrhythmias often have an increased beat-to-beat variation of the T-wave of the electrocardiogram. Variability analysis of the T-wave is increasingly used for non-invasive risk assessment. The aim of this study is to evaluate intra-QRS beat-to-beat signal variation and to compare it to ST-T variation. The beat-to-beat, microvolt variation of the QRS and the ST-T segment from 44 patients with coronary heart disease at high risk of suffering from malignant arrhythmias and from 51 healthy volunteers are compared. Variation analysis is carried out on 250 consecutive sinus beats from high-resolution electrocardiograms. The individual beats are filtered using a waveform-independent, cubic spline-filter. A variability index of the QRS and ST-T segments is calculated as the integrated standard deviation of corresponding samples inside the area of interest. Patients at risk of suffering from malignant arrhythmias have a significantly higher variability index of both the QRS (median 44.5 ms against 34.7 ms, p<0.001) and the ST-T segment (median 20.5 ms against 9.8 ms, p<0.001) compared to the group of healthy subjects. The discriminative ability of the odds variability indices of the QRS and ST-T segments are not statistically different, the ratios being 7.8 (QRS) and 12.6 (ST-T). We conclude that patients at high risk of suffering from malignant arrhythmias are characterised by an increased beat-to-beat microvolt variation of both the QRS and the ST-T segment. Further studies are necessary to evaluate the prognostic potential of depolarisation variability.     

Noninvasive beat-to-beat detection of ventricular late potentials

The detection of ventricular late potentials is a subject of some clinical interest. Most techniques currently being investigated rely on signal averaging to extract the microvolt signals from the considerable amounts of noise which are present. Although this approach produces useful results, it does remove any beat-to-beat variations from the signal, and also requires that the signal be present for a considerable number of beats. The paper describes a technique for detecting ventricular late potentials from the body surface, which preserves beat-to-beat variations. The most important aspect of this technique is the use of an adaptive signal enhancer to minimise random noise. Representative results for one normal and two pathological subjects are presented and discussed. A comparison with signal averaging is made and the effectiveness of adaptive signal enhancement is illustrated.     

Non-invasive methods for evaluating the importance of heart rate and atrial activity in cardiac pacing. Results of ballistocardiography and digital plethysmography studies in six patients with heart block

Ultralow frequency ballistocardiography (UFB) and digital pulse plethysmography (DPP) were performed in six patients with an external artificial pacemaker system. UFB was used mainly to evaluate the force of contraction of the left ventricle (IJ amplitude) and DPP for evaluating relative changes in the peripheral pulse volume. Four patients were studied at 40, 50, 60, 70, 80, 90 and 100 beats/min. There was a significant decrease (p less than 0.001) in LJ and pulse amplitudes when the heart rate increased from 40 to 100 beats/min. A positive correlation between relative IJ and pulse amplitude was observed in all cases studied. In beat-to-beat analysis it was found that the importance of the PR interval for the IJ and pulse amplitudes varied between patients. It is concluded that both UFB and DPP may be of value in clinical practice for evaluating hemodynamics in patients with slow spontaneous heart rate. The methods may be of help in selecting the most effective type of pacemaker for the individual patient.     

On the variability of QRS time-duration in magnetocardiographic recordings

High resolution electrocardiography (HRECG) recordings have already shown an increased beat-to-beat microvariability of the QRS duration of the terminal QRS in patients with a history of ventricular tachycardia (VT). The purpose of this study is to detect QRS-duration microvariability with magnetocardiographic (MCG) recordings in normals, patients with coronary heart disease (CHD), patients with a history of myocardial infarction (MI), and VT patients. QRS microvariability is calculated as the variance of time-shifts of single beats respectively to the average of all beats. The average over all channels of the MCG is performed. QRS microvariability was evaluated from 55-channel MCG in 15 normal persons, in 12 patients with CHD, in 13 patients with MI, and in 10 patients with VT. We found a significantly higher microvariability in patients with MI compared to normals. The highest microvariability was found in VT patients.     

On the variability of QRS time-duration in magnetocardiographic recordings

High resolution electrocardiography (HRECG) recordings have already shown an increased beat-to-beat microvariability of the QRS duration of the terminal QRS in patients with a history of ventricular tachycardia (VT). The purpose of this study is to detect QRS-duration microvariability with magnetocardiographic (MCG) recordings in normals, patients with coronary heart disease (CHD), patients with a history of myocardial infarction (MI), and VT patients. QRS microvariability is calculated as the variance of time-shifts of single beats respectively to the average of all beats. The average over all channels of the MCG is performed. QRS microvariability was evaluated from 55-channel MCG in 15 normal persons, in 12 patients with CHD, in 13 patients with MI, and in 10 patients with VT. We found a significantly higher microvariability in patients with MI compared to normals. The highest microvariability was found in VT patients.     

High-resolution determination of the R-R interval.

A preprocessor is described that determines the time interval between successive R waves of the electrocardiogram with an error of less than 0.2 ms. It accomplishes this by sepearting in hardware the function of determining the approximate location of the R wave from the function of localizing with great accuracy the peak of the wave form. With this device it is possible to detect abnormal heart rate patterns characterized by exceedingly small beat-to-beat variability. The approach may be useful for other bioelectric signals.     

Digital socially acceptable monitoring instrument (s.a.m.i.)

The design of an instrument is described for the purpose of counting the heart beat of a subject while undergoing ‘out-of-the-laboratory experiments’. The instrument consists basically of two units one of which is small, is worn by the subject and counts the subjects heart beats during the experimental period. The other unit is used to display the magnitude of the count at the end of the experimental time. The instrument has a capacity to count over two million heart beats over an experimental period of one week. The theme of the design has been to use commonly available and inexpensive components throughout. The extensive use of integrated circuits also facilitates ease of construction.     

缺血性心脏病患者运动引发T波交替作为危险因素价值的探讨

目的:探讨微伏T波交替(TWA)可否作为一项缺血性心脏病患者伴室性心律失常危险因素的预测指标。方法:选择经Holter心电图监测检出阵发性室速及/或有室速病史的23例缺血性心脏病患者、30例无室速的缺血性心脏病患者和39例正常人进行运动中TWA检测。TWA采用微机化6353心电图检测系统,在受检者运动至心率95~110bpm时,波间T波变异差超过1.9微伏并在心率阈值内持续出现即为阳性。结果:23例缺血性心脏病室速组中,TWA阳性14例,占60.7%,非室速缺血组阳性出现率为10%(3/30),正常对照组0%(0/39);TWA电压三组分别是2.3±1.1uV、1.1±0.6uV和0.8±0.3uV,组间差异非常显著(P<0.05或P<0.01)。结论:运动微伏TWA测定可作为缺血性心脏病室性心律失常危险因素的参考指标之一。     

Analysis of heart rate control to assess thermal sensitivity responses in Brazilian toads

In anurans, changes in ambient temperature influence body temperature and, therefore, energy consumption. These changes ultimately affect energy supply and, consequently, heart rate (HR). Typically, anurans living in different thermal environments have different thermal sensitivities, and these cannot be distinguished by changes in HR. We hypothesized that Rhinella jimi (a toad from a xeric environment that lives in a wide range of temperatures) would have a lower thermal sensitivity regarding cardiac control than R. icterica (originally from a tropical forest environment with a more restricted range of ambient temperatures). Thermal sensitivity was assessed by comparing animals housed at 15° and 25°C. Cardiac control was estimated by heart rate variability (HRV) and heart rate complexity (HRC). Differences in HRV between the two temperatures were not significant (P=0.214 for R. icterica and P=0.328 for R. jimi), whereas HRC differences were. All specimens but one R. jimi had a lower HRC at 15°C (all P<0.01). These results indicate that R. jimi has a lower thermal sensitivity and that cardiac control is not completely dependent on the thermal environment because HRC was not consistently different between temperatures in all R. jimi specimens. This result indicates a lack of evolutive trade-offs among temperatures given that heart rate control at 25°C is potentially not a constraint to heart rate control at 15°C.     

Heart rate during haemorrhagic shock.

In a prospective study, heart rate and mean arterial pressure were related to estimated blood loss in 34 consecutive patients aged 23-92 years during resuscitation from haemorrhagic shock. Eighteen patients with a blood loss of less than 31 (1.9 [0.9-3.0] l) (median and range), corresponding to 34 (16-46) % of estimated blood volume, had a heart rate of 83 (60-160) beats min-1 and a mean arterial pressure of 62 (35-73) mmHg. In 16 patients with a blood loss of more than 3 l (4.0 [3.3-5.0] l) corresponding to 89 (35-100) % of the estimated blood volume, heart rate was 120 (110-160) beats min-1 (P < 0.05) and mean arterial pressure 52 (0-70) mmHg (P < 0.05). Six patients died due to severe bleeding (3.1 [2.5-5.0] l) with a heart rate of 129 (110-160) beats min-1 and a mean arterial pressure of 40 (0-70) mmHg. It is concluded that reversible hypovolaemic shock is associated with a relatively low heart rate (approximately 80 beats min-1) and that tachycardia (approximately 120 beats min-1) is associated with profound bleeding. Hypovolaemic shock with tachycardia may represent a transition to an irreversible stage.     

Computerized blood pressure and heart rate recording system interfaces standard chart recorder with any micro-computer.

The designed inexpensive blood pressure recording system (BPRS) gives any microcomputer direct on-line blood pressure and heart rate recording capability that will save research time and increase the accuracy of collected data. The data is automatically stored in a file compatible with most graphic and statistical processing software. In vitro testing, over a range of 0-200 mmHg and 0-360 beats per minute showed a 0.999 intraclass correlation. In vivo testing of the BPRS used anaesthetized rats whereby their systolic and diastolic pressures were measured simultaneously with heart rate. The blood pressures and heart rate data, measured by the BPRS demonstrated excellent stability, sensitivity and accuracy when compared to those measured by standard pressure transducers in conjunction with a Grass polygraph and a sphygmomanometer.     

老年人心房颤动临床及心电图分析

87—94年收治的老年心房颤动(以下简称房颤)患者100例。年龄60—79岁。房颤的病因,冠心病68例,风心病11例,肺心病4例,病因不明1例。房颤持续一年以上72例,病程短于一年28例,心室率大于130次/分的快速型房颤17例,小于60次/分缓慢型房颤6例。心电图特点,fv_1≥1mm为粗颤波,占21％,以风心病多见;fv_1<1mm为细颤波,占79％,以冠心病多见。     

Beat-to-beat heart rate detection in multi-lead abdominal fetal ECG recordings

Reliable monitoring of fetal condition often requires more information than is provided by cardiotocography, the standard technique for fetal monitoring. Abdominal recording of the fetal electrocardiogram may offer valuable additional information, but unfortunately is troubled by poor signal-to-noise ratios during certain parts of pregnancy. To increase the usability of abdominal fetal ECG recordings, an algorithm was developed that enhances fetal QRS complexes in these recordings and thereby provides a promising method for detecting the beat-to-beat fetal heart rate in recordings with poor signal-to-noise ratios. The method was evaluated on generated recordings with controlled signal-to-noise ratios and on actual recordings that were performed in clinical practice and were annotated by two independent experts. The evaluation on the generated signals demonstrated excellent results (sensitivity of 0.98 for SNR≥1.5). Only for SNR<2, the inaccuracy of the fetal heart rate detection exceeded 2 ms, which may still suffice for cardiotocography but is unacceptable for analysis of the beat-to-beat fetal heart rate variability. The sensitivity and positive predictive value of the method in actual recordings were reduced to approximately 90% for SNR≤2.4, but were excellent for higher signal-to-noise ratios.     

The variability of muscle nerve sympathetic activity in resting recumbent man

1. Pulse synchronous bursts of multi-unit sympathetic activity was recorded from median or peroneal muscle nerve fascicles in fourteen subjects resting in the recumbent position. The neural activity was quantitated in terms of burst incidence, i.e. the number of bursts in the mean voltage neurogram/100 heart beats, during successive rest periods of 2-4 min.2. For each individual the burst incidence was fairly constant between different rest periods but the mean burst incidence varied widely between individuals, the range being from less than 10 to more than 90 bursts/100 heart beats.3. Simultaneous double nerve recordings were made on one subject from median and peroneal nerves and on eight subjects from the two peroneal nerves. There was always close similarity between the two records in such experiments regardless of which muscles the nerve fascicles innervated. When analysed separately the difference in burst incidence between the two sides ranged from 0.7 to 5.1 bursts/100 heart beats. The findings suggest that sympathetic neurones destined to skeletal muscles are subjected to a homogenous central drive and that contributions to the activity from ganglionic or segmental sources are of lesser importance.4. On seven subjects repeated recordings at rest were made with intervals of 3 weeks-21 months between recordings. In each subject mean burst incidences were similar in all recordings (range of differences 0.5-11.2 bursts/100 heart beats) suggesting an individually constant level of sympathetic activity in muscle nerves.5. For each individual the variability of burst amplitudes in the mean voltage neurogram was described by burst amplitude spectra. Most subjects had a relatively larger proportion of small than high amplitude bursts, but there was a tendency for more even amplitude distributions in subjects with high burst incidence. The finding may be an indication of interindividual differences in the average number of impulses/burst.6. It is concluded that the multi-unit recording technique can be used for comparisons of the level of muscle nerve ;sympathetic tone' between different subjects.     

Accuracy of the LifeShirt (Vivometrics) in the detection of cardiac rhythms

The use of heart rate measures in research requires accurate detection and timing of beat-to-beat values. Numerous technologies are available to researchers; however, benchmarking of a specific apparatus is seldom conducted. Since heart rate variability provides a portal to the neural regulation of the heart, accurate detection and timing of beat-to-beat values is essential to both basic physiological research and the clinical application of heart rate variability measures. The current study evaluated the accuracy of an ambulatory system, the LifeShirt (Vivometrics), relative to a standard laboratory-based heart rate monitoring equipment (Biopac), during baseline and exercise conditions. LifeShirt performed equivalently to the Biopac during both conditions, experienced few errors of detection, generated similar times between sequential heart periods, and produced similar summary indices of heart rate and heart rate variability.