Detection of cardiac pathologies using dimensional characteristics of RR intervals in electrocardiograms

The possibility of detecting pathologies in patients with various types of heart failure by analyzing the correlation dimension and embedding dimension of RR intervals in electrocardiograms is estimated. Limitations of the proposed approach and methods of overcoming them are discussed. It is demonstrated that these methods are suitable for provisional diagnosis.     

The microwave Rio-Hortega technique: a 24 hour method

Summary Application of microwaves in histochemistry and cytochemistry generally speeds up the technique. Microwaves stimulate diffusion into the tissue and influence the proteins and membrane of the cell. Silver impregnation techniques for the brain, such as the fast Rio—Hortega or the slow Golgi—Cox technique, normally require a minimum time period of 7 days and 20 days respectively. Using microwaves, the Rio—Hortega technique can be completed within 24 h. In sections prepared from mature brains, good silver impregnation of cell bodies, of axons and their terminals, and of dendrites and their spines are obtained. An explanation is given as to why the method cannot be further reduced in time. To our knowledge, this is the first report of the application of microwave irradiation for colouring pieces of tissue.     

Effect of daily oral omeprazole on 24 hour intragastric acidity.

Twenty four hour intragastric acidity was measured in nine patients with duodenal ulcer before and after one week of treatment with oral omeprazole 30 mg daily, a drug that inhibits gastric secretion by inhibition of parietal cell H+K+ adenosinetriphosphatase (ATPase). Omeprazole virtually eliminated intragastric acidity in all patients: the median 24 hour intragastric pH rose from 1.4 to 5.3 and the mean hourly hydrogen ion activity fell from 38.50 to 1.95 mmol(mEq)/1 (p less than 0.001). This inhibition of 24 hour intragastric acidity is more profound than that previously reported with either cimetidine 1 g daily or ranitidine 300 mg daily.     

Dimensional analysis revisited

The applicability of dimensional analysis (DA) is discussed in relation to the metabolic scaling laws. The evolution of different theories of biological similarity has shown that the calculated reduced exponents (b) of Huxley's allometric equation are closely correlated with the numerical values obtained from the statistical analysis of empirical data. Body mass and body weight are not equivalent as biological reference systems, since in accordance to Newton's second law, the former has a dimension of a mass, while the latter should be dimensionally considered as a force (W = MLT-2). This distinction affects the coefficients of the mass exponent (alpha). This difference is of paramount importance in microgravity conditions (spaceflight) and of buoyancy during the fetal life in mammals. Furthermore, the coefficients (beta) of the length dimension, and (gamma) of the time dimension do not vary when mass or weight are utilized as reference systems. Consequently, the "specific metabolic time," that results from the ratio of basal oxygen consumption and body mass or body weight yields the "biological meaning" of the time dimension, which is of fractal nature.     

Protein synthesis in skeletal muscle measured at different times during a 24 hour period

Six groups of 5 male rats (starting body weight 109 g) were allowed free access to a conventional rat diet. At 4 hourly intervals, starting at 10.00 h muscle protein synthesis was measured. By relating the weights of the gastrocnemius and soleus muscles to the initial body weights of the animals (i.e., at 09.30, day 1), a linear increase in muscle weight throughout the day was demonstrated. The fractional rate of muscle protein synthesis varied from 16.8% per day to 20.3% per day in gastrocnemius muscle and from 17.9% per day and 22.1% per day in the soleus. It was calculated that the maximum error incurred in estimating daily muscle protein synthesis by extrapolation of the value at any one time was 6% in gastrocnemius and 9% in soleus. It is concluded that calculations of the average rate of muscle protein degradation based on the difference between the rates of synthesis and deposition are generally valid in rats allowed free access to an adequate diet.     

Oral NG-nitro-L-arginine in conscious dogs: 24 hour hypertensive response in relation to plasma levels

Summary Haemodynamic changes after oral administration of 30 mg/kg N^G-nitro-L-arginine (L-NNA) were studied in conscious chronically instrumented mongrel dogs throughout a 24 h observation period in order to evaluate the long-term efficacy of L-NNA-induced inhibition of endothelium-dependent relaxation and its relation to plasma L-NNA level. Diastolic blood pressure remained elevated for the entire 24 h observation period, but systolic blood pressure was raised only up to the 6 h value. The hypertensive response was accompanied by bradycardia. The increase in blood pressure and the plasma L-NNA level both reached their maxima at 3 h. The plasma L-NNA level at the end of the observation period was diminished by only 21.7% with respect to the maximum increase, whilst the maximum increase in mean arterial blood pressure was attenuated by 72.2% at 24 h. These data show a dissociation between plasma L-NNA level and the respective blood pressure.     

Vital working hour schemes: The dynamic balance between various interests

“Balancing Interests”, the theme of the 17th International Symposium on Shift Work and Working Time held in Hoofddorp, The Netherlands (September 2005), refers to the ambition to reach an optimal balance between the various aspects of shift work. Economic, ergonomic, physical, and psychosocial factors all interact in determining the impact of shift work at the individual, organizational, and societal level. It is the challenge of this multidisciplinary field of research to model all relevant factors in such a way that it will allow us to optimize the dynamic trade-off between the yield and the risk of shift work. The organizers of the 17th International Symposium and the co-editors of these proceedings are convinced that the high quality of the contributions will bring us closer to this ultimate goal.     

Dimensional analysis of nerve models

General equations for (i) a uniform patch of nerve membrane, (ii) a continuous (unmyelinated) axon and (iii) a noded (myelinated) axon are analyzed using dimensional analysis. The original dimensioned equations are transformed to dimensionless equations. These equations contain dimensionless constants called similarity parameters which are functions of the physical constants or parameters of the system. (The similarity parameters are analogous to such quantities as the Reynolds number and Mach number used in fluid dynamics.) There is one similarity parameter for each of cases (i) and (ii), and four for case (iii). All dimensioned systems having the same values of all the similarity parameters form a similarity class.Once a quantity such as threshold stimulus or conduction velocity is computed for one member of any similarity class, the same quantity can be easily computed for any other member of the same class, by a simple formula containing the physical constants of the system, called a generating equation, or by an even simpler expression of proportionality, called a scaling relation.     

Quantitative analysis of variability of electrocardiograms typical for polymorphic arrhythmias

A new approach to the analysis of variability of electrocardiograms (ECGs) typical of polymorphic arrhythmias is developed. In these ECGs, separate QRS complexes can be often hardly identified. As a result, the mathematical methods that have been elaborated hitherto are not suitable for such arrhythmias. The approach presented here is based on the quantitative estimation of the variability of neighboring parts of the ECG. In this case, the necessity of the identification of separate QRS complexes ceases to be significant. Based on this approach, the analysis of normalized ECG variability is developed in the framework of which two indices that characterize the oscillation variability and its changes in time are related to a part of the ECG and/or the ECG as a whole. Variations of these indices allow both the polymorphism of a separate ECG to be estimated and different ECGs to be compared with each other. The method presented may be useful in studies of the mechanisms and in the diagnosis of polymorphic arrhythmias.     

Automatic estimation of the correlation dimension for the analysis of electrocardiograms

The main purpose of the present work is the definition of a fully automatic procedure for correlation dimension (D₂) estimation. In the first part, the procedure for the estimation of the correlation dimension (D₂) is proposed and tested on various types of mathematical models: chaotic (Lorenz and Henon models), periodical (sinusoidal waves) and stochastic (Gaussian and uniform noise). In all cases, accurate D₂ estimates were obtained. The procedure can detect the presence of multiple scaling regions in the correlation integral function. The connection between the presence of multiple scaling regions and multiple dynamic activities cooperating in a system is investigated through the study of composite time series. In the second part of the paper, the proposed algorithm is applied to the study of cardiac electrical activity through the analysis of electrocardiographic signals (ECG) obtained from the commercially available MIT-BIH ECG arrhythmia database. Three groups of ECG signals have been considered: the ECGs of normal subjects and ECGs of subjects with atrial fibrillation and with premature ventricular contraction. D₂ estimates are computed on single ECG intervals (static analysis) of appropriate duration, striking a balance between stationarity requisites and accurate computation requirements. In addition, D₂ temporal variability is studied by analyzing consecutive intervals of ECG tracings (dynamic analysis). The procedure reveals the presence of multiple scaling regions in many ECG signals, and the D₂ temporal variability differs in the three ECG groups considered; it is greater in the case of atrial fibrillation than in normal sinus rhythms. This study points out the importance of considering both the static and dynamic D₂ analysis for a more complete study of the system under analysis. While the static analysis visualizes the underlying heart activity, dynamic D₂ analysis insights the time evolution of the underlying system. Received: 11 April 1997 / Accepted in revised form: 19 March 1999     

Dimensional analysis in mathematical biology. II

The application of dimensional analysis in biology is further illustrated by functional equations composed of dimensionless numbers and dealing with renal physiology, lung physiology and plant leaf shape. Dimensional variables and dimensionless numbers are examined from the viewpoint of numerical invariant properties of a certain physical system. Utilization of the method for problems such as design of an artificial kidney is considered briefly. A tabulation of variables useful in biology is given, with suggestions for a number of new dimensional entities. A continuation of the list of dimensionless invariants from Part I (Bull. Math. Biophysics,23, 355–376, 1961) is provided and includes terms pertaining to general physiology, geometric growth, metabolism, ecological interactions, muscle kinetics and other areas. It is pointed out that use of dimensionless ratios (similarity criteria) makes possible a direct comparison of form or shape factors and relative growth ratios with a variety of physical ratios, through the use of functional equations containing only dimensionless entities. Organismal similarity during growth and development, and between genetically related species, may be analyzed in terms of “automodel” or “self-similar” systems governed by certain dimensionless invariants. Tables of biological variables and dimensionless groupings are included.