Endemicity change of hepatitis A infection necessitates vaccination in food handlers: An Indian perspective

In the last two decades, outbreaks due to the foodborne hepatitis A virus (HAV) have been frequently reported in India, with adolescents and adults primarily affected. In India, most food handlers are adolescents and young adults who might be exposed to unsatisfactory environmental conditions and poor water quality. This increases the risk of HAV infection and consequently compounds the risk of HAV transmission from food handlers to susceptible populations. Given the shift in hepatitis A endemicity from high to intermediate levels in India, implementing the vaccination of food handlers has become important as it can also contribute to the elimination of hepatitis A in India. This narrative review makes a case for hepatitis A immunization of food handlers in India considering the growing food industry, evolving food culture, and the substantial burden caused by hepatitis A outbreaks.

What is the context?

Hepatitis A disease is a common form of viral hepatitis and is transmitted through contaminated food and water or through close contact with an infected person. The virus with stands high temperature and can survive on surfaces for long periods of time.

In India, the burden of hepatitis A has shifted from children to adolescents and adults who are more culnerable to infection. They present a high risk of complications, often requiring hopitalization.

The prevention of the disease has often bee neglected, inadequate safety measures for the preparation of food (via food handlers) is a known risk factor for the transmission of hepatitis A.

What is new?

Our review highlights the relationship between food handling and hepatitis A infection among adolescents and adults in Inida.

The lack of knowledge of food safety regulations and hygiene measures among food handlers and the organizations that guide them may contribute to the spread of hepatitis A.

What is the impact?

Sanitation efforts, awareness and educational programs for food are needed to help reduce the transmission of hepatitis A virus and disease, yet these measures alone may not be sufficient.

Vaccination among high-risk populations such as food handlers can prevent hepatitis A infection and its complications as well as transmission.

A phase I, pharmacokinetic and pharmacodynamic study of GSK2256098, a focal adhesion kinase inhibitor, in patients with advanced solid tumors

BACKGROUND

Focal adhesion kinase (FAK) is important in cancer growth, survival, invasion, and migration. The purpose of this study was to determine the maximum tolerated dose (MTD), safety, pharmacokinetics (PK), and pharmacodynamics (PD) of the FAK inhibitor, GSK2256098, in cancer patients.

PATIENTS AND METHODS

The dose of GSK2256098 was escalated, in cohorts of patients with advanced cancer, from 80 to 1500 mg, oral twice daily (BID), until the MTD was determined. Serial blood samples were obtained from all patients, and the PK was determined. Paired tumor biopsies were obtained in select patients, and the level of phospho-FAK (pFAK) was determined.

RESULTS

Sixty-two patients (39 males, 23 females; median age 61 y.o., range 21-84) received GSK2256098. Dose-limiting toxicities of grade 2 proteinuria (1000 mg BID), grade 2 fatigue, nausea, vomiting (1250 mg BID), and grade 3 asthenia and grade 2 fatigue (1500 mg BID) were reported with the MTD identified as 1000 mg BID. The most frequent adverse events (AEs) were nausea (76%), diarrhea (65%), vomiting (58%), and decreased appetite (47%) with the majority of AEs being grades 1-2. The PK was generally dose proportional with a geometric mean elimination half-life range of 4-9 h. At the 750, 1000, and 1500 mg BID dose levels evaluated, the pFAK, Y397 autophosphorylation site, was reduced by ∼80% from baseline. Minor responses were observed in a patient with melanoma (-26%) and three patients with mesothelioma (-13%, -15%, and -17%). In the 29 patients with recurrent mesothelioma, the median progression-free survival was 12 weeks with 95% CI 9.1, 23.4 weeks (23.4 weeks merlin negative, n = 14; 11.4 weeks merlin positive, n = 9; 10.9 weeks merlin status unknown, n = 6).

CONCLUSIONS

GSK2256098 has an acceptable safety profile, has evidence of target engagement at doses at or below the MTD, and has clinical activity in patients with mesothelioma, particularly those with merlin loss.

Neonatal Empyema Thoracis

Empyema thoracis, is a rare cause of respiratory distress in neonates. Only a few cases of neonatal empyema thoracis are described in medical literature. Empyema thoracis is not a well known entity in the neonates. It is fulminant with rapid progression with a high mortality. Compounding the problem is its uncertain etiopathogenesis and lack of definite treatment guidelines. We shall describe one case of neonatal empyema in a newborn aged five days caused by Pseudomonas aeruginosa. The neonate died subsequently. DOI: http://dx.doi.org/10.3126/jnps.v34i1.8233   J Nepal Paediatr Soc 2014;34(1):65-67  

Burden of respiratory tract infections among paediatric in and out-patient units during 2010-11

INTRODUCTION

Respiratory tract infections due to viral etiology were studied with an objective to identify and compare the pathogens between Hospital Indoor and Outdoor Units.

MATERIALS AND METHODS

A hospital-based cross-sectional study was conducted among children below 12 years over a period of one year. The throat and nasal swabs were collected from both the Units and screened for viral infections by real time RT-PCR technique.

RESULTS

Out of 880 samples collected, 87% and 13% were from outdoor and indoor Department with total viral positivity rate of 30% and 25% respectively. Influenza B virus (IBV) (n=126, 16%) was more prevalent in Outdoor Unit, whereas respiratory syncytial virus (RSV) (n=18, 16%) among indoor admitted cases. The multinomial logistic regression analysis revealed that both RSV and Influenza viruses were predominant in children of pre-school age groups < 5 years. In the year 2010-11, the prevalence of human metapneumovirus (HMPV) was low. The pandemic influenza A virus (pH1N1/2009) accounted for 4% (n=29) and 0.8% (n=1) cases among Outdoor and Indoor Units respectively.

CONCLUSIONS

The Outdoor Department outnumbered the Indoor Unit in terms of patient attendees and the rate of viral infections. An effective vaccination and continuous surveillance program is the need of the hour.

Surveillance in Eastern India (2007-2009) revealed reassortment event involving NS and PB1-F2 gene segments among co-circulating influenza A subtypes

BACKGROUND

Influenza A virus encodes for eleven proteins, of which HA, NA, NS1 and PB1-F2 have been implicated in viral pathogenicity and virulence. Thus, in addition to the HA and NA gene segments, monitoring diversity of NS1 and PB1-F2 is also important.

METHODS

55 out of 166 circulating influenza A strains (31 H1N1 and 24 H3N2) were randomly picked during 2007-2009 and NS and PB1-F2 genes were sequenced. Phylogenetic analysis was carried out with reference to the prototype strains, concurrent vaccine strains and other reference strains isolated world wide.

RESULTS

Comparative analysis of both nucleotide and deduced amino acid sequences, revealed presence of NS gene with A/PR/8/34(H1N1)-like mutations (H4N, Q21R, A22V, K44R, N53D, C59R, V60A, F103S and M106I) in both RNA-binding and effector domain of NS1 protein, and G63E, the HPAI-H5N1-like mutation in NEP/NS2 of five A/H1N1 strains of 2007 and 2009. NS1 of other A/H1N1 strains clustered with concurrent A/H1N1 vaccine strains. Of 31 A/H1N1 strains, five had PB1-F2 similar to the H3N2 strains; six had non-functional PB1-F2 protein (11 amino acids) similar to the 2009 pandemic H1N1 strains and rest 20 strains had 57 amino acids PB1-F2 protein, similar to concurrent A/H1N1 vaccine strain. Interestingly, three A/H1N1 strains with H3N2-like PB1-F2 protein carried primitive PR8-like NS gene. Full gene sequencing of PB1 gene confirmed presence of H3N2-like PB1 gene in these A/H1N1 strains.

CONCLUSION

Overall the study highlights reassortment event involving gene segments other than HA and NA in the co-circulating A/H1N1 and A/H3N2 strains and their importance in complexity of influenza virus genetics. In contrast, NS and PB1-F2 genes of all A/H3N2 eastern India strains were highly conserved and homologous to the concurrent A/H3N2 vaccine strains suggesting that these gene segments of H3N2 viruses are evolutionarily more stable compared to H1N1 viruses.

Dynamic matrix composition in engineered cartilage with stochastic supplementation of growth factors

Dynamic extracellular matrix (ECM) synthesis is explored in a hypothesized engineered cartilage construct. Growth (alpha) and decay (beta) rate parameters are developed from a previous engineered cartilage model. The presented mathematical model was constructed from the parameterized experimental data using a deterministic and stochastic examination of ECM synthesis based on a negative feedback control mechanism. A growth factor supplementation is incorporated in a probabilistic mathematical approach. The growth factor component modified an initial deterministic model through a Gaussian white noise fluctuation. As the primary constituents of ECM, the mathematical tool is intended to characterize the probable steady state distribution of glycosaminoglycan (GAG) and collagen molecules as well as mean mass accumulation at homeostasis. Computer simulation of the models is applied to reported data from four similar chondrocyte-polymer construct culture systems. The range in rate ratios reflect the differing nature of GAG and collagen synthesis (alphaGAG/betaGAG = 4.2 to 148.6; alphacollagen/betacollagen = 8.1 to 2590.4). This technique reduced the influencing synthesis factors to a few key descriptive parameters. Additional anabolic and catabolic factors may further be built into the models.

A genetic algorithm based nearest neighbor classification to breast cancer diagnosis

This paper presents an application of a hybrid approach (the genetic algorithms and the k-nearest neighbour) proposed by Ishbuchi to Wisconsin breast cancer data. For the diagnosis of breast cancer, the determination of the presence of benign/malignant breast tumors represents a very complex problem (even for an experienced cytologist). Therefore the automatic classification of benign and malignant symptoms is highly desirable as a valuable aid to assist oncologists in the decision making of the diagnosis of breast cancer. In this paper, the genetic algorithm based k-nearest neighbour method for classification of benign and malignant breast tumors is presented. The genetic-algorithm (GA) is used for finding a compact reference set by selecting a small number of reference patterns from a large number of training patterns in nearest neighbor classification. The GA simultaneously performs feature selection and pattern selection and prunes unnecessary features. The goal is to maximize the classification performance of the reference set and minimize the number of selected patterns and features. Results are also compared with a fuzzy-genetic approach where each reference patten represents a fuzzy if-then rule with a circular-cone-type membership function.

Unsteady stenosis flow prediction: a comparative study of non-Newtonian models with operator splitting scheme

This paper presents a comparative study of non-Newtonian and Newtonian models of blood. A non-Newtonian incompressible 2-D Navier-Stokes (N-S) solver has been developed using Fasttalk language within the Fastflo environment. It is based on the method of operator splitting with artificial compressibility technique. The Power law and Casson models have been used as the constitutive equations for blood with a hematocrit of approximately 45%. These two non-Newtonian models and the Newtonian model are used to simulate unsteady flow through a hypothetical stenotic geometry over an aperiodic time interval of 1 s. Through comparison of the results of the three models, it was found that the wall shear stress (WSS) distribution over the time interval was comparable for both non-Newtonian models. The peak WSS for the Newtonian model had the lowest value. The peak wall shear stress gradient (WSSG) for the Power law was the highest, followed by the Casson and Newtonian models. Flow characteristics such as higher pressure drop across the stenosis, location and movement of vortex were similar in all three models. Non-Newtonian effects were most significant in the vicinity of the stenosis.

Effects of multiple stenoses and post-stenotic dilatation on non-Newtonian blood flow in small arteries

Fully-developed one-dimensional Casson flow through a single vessel of varying radius is proposed as a model of low Reynolds number blood flow in small stenosed coronary arteries. A formula for the resistance-to-flow ratio is derived, and results for yield stresses of tau 0 = 0, 0.005 and 0.01 Nm-2, viscosities of mu = 3.45 x 10(-3), 4.00 x 10(-3) and 4.55 x 10(-3) Pa.s and fluxes of 2.73 x 10(-6), x 10(-5) and x 10(-4) m3 s-1 are determined for segment of 0.45 mm radius and 45 mm length, with 15 mm abnormalities at each end where the radius varies by up to +/- 0.225 mm. When tau 0 = 0.005 N m-2, mu = 4 x 10(-3) Pa.s and Q = 1, the numerical values of the resistance-to-flow ratio vary from lambda = 0.525, when the maximum radii of the two abnormal segments are both 0.675 mm, to lambda = 3.06, when the minimum radii are both 0.225 mm. The resistance-to-flow ratio moves closer to unity as yield stress increases or as blood viscosity or flux decreases, and the magnitude of these alterations is greatest for yield stress and least for flux.

Mathematical modelling of peristaltic transport of a non-Newtonian fluid

The paper considers the phenomena of peristaltic transport of a non-Newtonian fluid represented as a power law fluid. The governing equations are the modified Navier-Stokes equations and the continuity equation in axisymmetric form. A solution is sought in terms of a perturbation series and it is shown the close proximity between analytical and numerical solutions when considering stream functions for various values of the flow behaviour index.

Application of fuzzy-classifier system to coronary artery disease and breast cancer

This paper presents an application of a genetic-algorithm-based representation of fuzzy rules for the classification of coronary artery disease data and breast cancer data. The performance of this fuzzy classifier for classification of coronary artery disease and breast cancer data is evaluated. In this study the concept of fuzzy if-then has been applied of rules proposed by Ishibuchi et al. for a multi dimensional data classification problem which leads to higher classification power. The fitness value of each fuzzy if-then rule was determined by the numbers of correctly and wrongly classified training patterns for that rule. The classification power on real world data for coronary artery disease and breast cancer was thus demonstrated by computer simulations.

Classification of heart rate variability in patients with mild hypertension

The diagnostic performance of two pattern classification methods to detect hypertension was evaluated in a population of 29 mildly hypertensive and 20 normal subjects. The heart rate variability (HRV) signal of each subject was recorded during rest and isometric handgrip exercise. Feature vectors composed of up to 6 features from both the time and frequency domain representation of the HRV signal were constructed and applied to a Bayes' likelihood classifier and a voting k-nearest neighbours classifier. Each subject was classified as hypertensive or normal, and the classification compared to the clinical diagnosis for each subject. The diagnostic performance of each classifier/feature vector combination was evaluated using the leave-one-out method. The best performance of 90% correct classifications was achieved using a nearest neighbour classifier, a Euclidean distance metric and 3 features. The Bayes' classifier achieved a best performance of 84% correct classification. The work shows promise for the detection of the autonomic disturbance which precedes and accompanies the hypertensive state.

A computational model for blood flow through highly curved arteries with asymmetric stenoses

In this paper, we develop a three dimensional model of blood flow through curved arteries with asymmetric stenoses. Firstly, the Navier-Stokes equations representing Newtonian flow are solved using PHOENICS, a computational fluid dynamics package which utilises the Finite Volume method of solution. The severity of the stenoses considered in this study vary from about 40% to about 70%. Subsequently, the model is solved for Reynolds numbers ranging from 100 to 1200. The pressure drop results show good agreement with published results. The results also show that stenoses on a bent artery has a significant effect on blood flow characteristics.

Spectral analysis of an acoustic respiratory signal with a view to developing an apnoea monitor

The movement of air through the air passages during normal respiration generates an acoustic signal which can be detected from the surface of the body at suitable sites with the aid of a microphone applied to the skin. The spectral characteristics of these sounds were analysed to see if they could be differentiated from other sources of sound. During normal respiration the other major source of sound was that transmitted from the heart, and this could be filtered out with a band pass filter. A prototype apnoea monitor was built which utilised these sound signals as an indicator of respiration and underwent preliminary testing. Although such acoustic signals have the potential to indicate respiration, and cardiac sounds can be effectively filtered, further work would be required to recognise and reject other extraneous sources of sound interfering with the respiratory signal.

Mathematical modelling of triple arterial stenoses

This paper examines the effects of triple stenoses (ie. three stenoses in series) in a reasonably large artery. The model developed is axi-symmetric and blood is assumed to be a Newtonian fluid. The governing equations are the Navier-Stokes equations and the continuity equation. These equations are solved using the Finite Element Method and the FIDAP computational fluid dynamics (C.F.D.) package. Various combinations of differing degrees of stenosis in the triplet are considered. Pressure drop profiles and streamline plots of the solutions to these models show that the effects of milder stenoses are diminished in the presence of more severe ones. Also, a pressure recovery is observed whenever a mild stenosis follows a more severe stenosis in multiply stenosed arteries.

A profile of heart disease risk factors and their relation to parents' education, fathers' occupation and family history of heart disease in 843 South Australian families: the Adelaide Children's WHO Collaborative Study

OBJECTIVE

A study was conducted to determine whether the prevalence of risk factors among pre-adolescent children is associated with their parents' risk factor status and what influence family history of ischaemic heart disease (IHD) and socio-economic status (SES) had.

METHODOLOGY

This was a cross-sectional study of 856 children, mean age 8.6 years, and their parents who underwent the World Health Organization and National Heart Foundation protocols for the study of arteriosclerosis precursors. Historical, demographic, anthropometric, clinical and biochemical outcome measures were used.

RESULTS

There was the expected burden of illness reported for the grandparents and parents, with the latter conforming to their expected age group's heart disease risk factor status. The mean serum total cholesterol (TC) level for boys was 4.43 (+/- 0.79) mmol/L and girls 4.62 (+/- 0.84) mmol/L, with the 95th percentile for boys and girls combined being 5.88 mmol/L. The level corresponding to two standard deviations above the mean was 6.0 mmol/L. Childrens' IHD risk factor status reflected their parents' with TC, skin fold thickness and body mass index most closely correlated, followed by blood pressure. The greatest correlation was between the childrens' TC and their mothers'. Socio-economic status as assessed by the parents' education level and fathers' occupational status produced differences in their childrens' risk factors, with mother's level of education having the major influence. There was no impact of family history of IHD.

CONCLUSIONS

From these results it would appear that screening of the pre-adolescent may be appropriate but longitudinal study will be important to establish this by documenting persistence of risk factor status. Also, it would appear that a child's future risk from IHD morbidity may be due to environmental influences mediated through differences in SES. As the level of IHD risk factors is reduced within the community, the extent of parent-child transmission of measurable IHD risk factors in families of high IHD risk may be reduced.

Asymmetrical loads and lateral bending of the human spine

The human spine is modelled as a cantilever-type beam column. Under the influence of static asymmetrical loads, muscle and low-back forces are predicted from a hypothetical but revealing model. Such forces produced by asymmetrical loads are much larger than for a corresponding symmetrical load. Asymmetrical loads can encourage, especially in young schoolchildren, lateral bending of the spine by alleviating muscle and low-back forces. This could possibly be a factor contributing to the surprisingly high percentage of schoolchildren with measurable scoliotic curves. The wearing of knapsack-type bags is advocated.

Biomechanical simulations of scoliotic spinal deformity and correction

A new approach to surgical correction of scoliosis has been advanced by us, in the form of simulation of the surgical correction system and technique. For this purpose, we developed a finite-element model of the spinal column (SFEM), applied tractions to it and determined the model stiffness so as to watch the actual spinal geometry. Having patient-simulated this SFEM, we applied to this SFEM corrective forces and determined the optimal set of forces to gain the best correction of the spinal deformity. We then developed a special instrumentation to measure the applied corrective forces during surgery using a particular fixation system. The SFEM corrected geometry was shown to compare favourably with the post-surgical curve. We have now developed an elastic beam-column model (EBCM) to which muscle activation forces, representing asymmetrical paralysis of the vertebral column muscles, can be applied to generate a given scoliotic curve. In that process the stiffness properties of the patient-simulated EBCM are determined. Now on these patient-simulated EBCM(s), identical corrective force systems are applied as developed by the finite-element model (SFEM) and implemented surgically for these patients. It is shown that the EBCM corrected geometries compare favourably with both SFEM corrected geometries as well as with the post-surgical curves for similar corrective force systems. Thus the EBCM can be employed to presurgically simulate scoliolic correction, specify the optimal corrective system of forces so as to gain the best surgical correction.

Computational fluid mechanical evaluation of steady-flow energy losses in cardiac valve prostheses

A form of the general integral energy conservation equation is applied to the case of steady flow through a rigid control volume bounded by stationary walls and fixed inflow and outflow control surfaces. The total energy loss due to viscous dissipation in the control volume is then defined as the change in mean (pressure + kinetic energy + shear stress energy) quantities between the inflow and outflow surfaces. Computational fluid mechanical modelling can then be used to provide the extensive flow field data necessary to calculate the integral means of the total energy components--not only at the inflow/outflow surfaces, but throughout the control volume via a series of "cutting surfaces" progressing from the inlet to the outlet. This allows interchanges between the various forms of energy to be examined and provides an insight into the mechanisms responsible for these interchanges. Two illustrative examples are presented: laminar flow through a specially designed ball-occluded conduit valve in a long conduit run, and through a caged-ball annulus valve mounted in a ventricle-aorta model. Analysis of the results suggests that a new energy loss parameter be defined--a "valve only" loss, calculated by subtracting the total energy loss for the system with the valve absent, from the total energy loss for the same system with the valve in place. This developed concept of "valve only" energy loss has the potential of standardising the findings of different research groups by removing the arbitrary selection of measurement points from reported results.

A mathematical study of simple exponential modelling in biochemical processes

This paper discusses the application of simple exponential functions for analyses of complex biochemical processes such as transport phenomena in a mammalian system. The main aim is to identify these exponential function models using various curve fitting techniques. The experimental data used is based on transport of a radio-active tracer 32P (Radio-phosphorus) from a central compartment of blood plasma to subsidiary organ compartments in insulin-treated diabetic rats. The data has been analysed with a view to fitting exponential functions. A graphical method of exponential peeling and six (I to VI) computer programs based on iterative methods for solving single, as well as, multiple exponential functions have been used. The method of exponential peeling has also been compared with the least squares method for simple linear regression. The sum of two exponential functions has been found to be the most preferred Goodness of Fit by the computer programs. This model indicates that the transport of 32P in blood plasma in rats is governed by two major metabolic parameters. Further interpretations of the fitted equations are discussed.

Continuous model of the human scoliotic spine

The human scoliotic spine is mathematically modelled by employing the classical non-linear theory of curved beam-columns. A realistically representative muscle force system is included in the model. Scoliosis due to asymmetrical bi-lateral muscular contractions has been studied and arbitrary large displacements and curvatures are allowed. The two-dimensional model allowing curvature in the frontal plane can show the progression of a scoliotic curve from an initially straight configuration. For various parameter values, particularly muscle asymmetry, the model attempts to simulate the progression of actual scoliotic curves. Once these curves have been simulated, forces corresponding to corrective surgical systems are applied to the scoliotic spine. The corresponding corrected curves are then compared with those produced by a finite element model and also to the actual clinical curve. The comparisons were very favourable, considering the simplicity of the continuous model. The commonly observed phenomenon of the scoliotic curve lying to the weaker side of the back in terms of muscle strength is reproduced and explained by the model. The possible usefulness of continuous spinal models to analyse the overall deformation of the spine under various loading conditions can then be deduced.

A mathematical study of non-Newtonian blood flow through elastic arteries

Existing models of blood flow through arteries are revisited. Non-Newtonian and viscous properties are also considered. Treating blood as a non-Newtonian, pseudoplastic fluid obeying the power law, the flow equations are rigorously derived, using the same principles applied in existing models. An appropriate and more physically and physiologically correct model is obtained. Another model in exponential form is also derived. The resulting equations are solved numerically for a range of parameters and the various graphs are compared.

Developmental and corrective biomechanics for scoliosis

The developmental mechanism for scoliosis and its surgical correction are studied by modeling the spinal column as a curved nonlinear (large-deformation-sustaining) beam column to which are applied (a) muscle forces to simulate scoliosis development due to asymmetrical bilateral muscle contractions and (b) corrective forces to simulate the action of surgically implanted corrective systems. The two-dimensional model permits curvature in the frontal plane and can simulate and demonstrate the progression of a scoliotic curve from an initially straight configuration for various model parameter values. The calculation of the bonding moments is treated, and a simple algorithm for solving the model equations is presented. Results for an actual clinical case are given.

Assessment of haemolytic and thromboembolic potentials--from CFD studies of Starr-Edwards cardiac valve prostheses

Quantitative assessments of haemolysis, thromboembolism and endothelial damage are established using computational fluid dynamics and documented threshold values. The régime studied was steady forward (systolic) flow through a fully open Starr-Edwards model 1260 ball valve, in an aortic shaped chamber. Modelling was carried out using finite difference techniques for turbulent, Newtonian flow. Haemolysis was not predicted "in-bulk", but a haemolytic potential as high as 30% was suggested at prosthetic surfaces. Also a 10% thromboembolic potential and a 6% potential for endothelium damage were noted.

A study of the first heart sound spectra in normal anesthetized cats: possible origins and chest wall influences

Heart sound recordings were taken from cats. The heart sounds were recorded directly from the chest wall and through an esophageal tube. The phono transducer and the esophageal tube were both placed over the base of the heart. Ultrasound M-mode, or motion-mode, recordings were taken to study the mitral valve dynamics. After analogue to digital conversion, electrocardiogram gated first heart sounds of each phono record were analyzed by the fast Fourier transform to obtain a frequency spectrum. Relative energies in 15 Hz bandwidths up to 150 Hz were correlated with the mitral valve closing velocity of the anterior mitral leaflet, obtained from the M-mode echocardiograms. The closing velocity correlated best with the energy in the 30-45 Hz bandwidth and 60-75 Hz bandwidth for the externally and internally monitored phonocardiogram respectively. The chest wall acted as a low pass filter, that is, the wall favoured the transmission of low frequencies and the energy transmitted decreased as wall thickness increased.

A mathematical study of semilunar valve vibration

A simple mathematical model to describe the valvular vibrations and their role in the production of the second heart sound is presented. The closed semilunar valve is considered as a vibrating stretched membrane secured around a circular edge. An exponential function is used to represent the actual pressure gradient across the closed valve, which is the force that drives the membrane to vibrate. The displacement and the rate of displacement of the centreline are calculated and are found to be similar to the experimental and numerical results given earlier in the literature by Stein and his co-workers.