Dhanjoo N. Ghista

Heart rate variability power spectrogram as a potential noninvasive signature of cardiac regulatory system response, mechanisms, and disorders

SummaryThis paper attempts to provide evidence that the heart rate variability power spectrum (HRVPS) reflects the presence of neural control of cardiac regulation. A normal individual is seen to have a characteristic HRVPS (comprising a 0.1-Hz peak and a repiratory peak at 0.25–0.34 Hz), which is altered in a predictable manner in response to orthostatic stress and exercise, while in two patients with autonomic neuropathy, the HRVPS failed to demonstrate such a characteristic alteration in response to orthostatic stress. Postinfarct HRVPS signatures were studied in two patients with anterior and inferior infarcts so as to lend insight using non-invasive means into both the healing process and the dominant deliterious sympathetic or protective vagal tone due to the infarct. When subjects with transplanted hearts were studied, their HRVPS did not exhibit the characteristic pattern of a normal individual; rather, the HRVPS energy was spread over a wider and higher frequency range. However, one of the transplanted patients surprisingly but consistently revealed the characteristic HRVPS; the post-transplant time at the time of the study was 33 months and the patient had the typically high resting heart rate of a transplant recipient but a wide standard deviation like that of a normal individual. This could be the first noninvasively demonstrated evidence in humans of reinnervation of a transplanted heart. Thus, the HRVPS constitutes a simple non-invasive method to assess cardiac neuroregulatory response and disorders and it is proposed that it be referred to as the heart rate variability cardiogram (HRVC).

Biomechanical basis of optimal scoliosis surgical correction

For an optimal approach to surgical correction of scoliosis, it was deemed desirable to biomechanically simulate the set of corrective forces applied by alternative internal fixation systems, so as to determine and apply the internal fixation system producing the best correction under safe levels of forces applied by the fixation systems to the spinal structures. To this end, we have developed, and presented here, (1) a spinal finite-element model relating the applied corrective forces to the corrected spinal configurations, (2) a method for determining the stiffness of the patients spine prior to surgery, (3) computerized finite-element analysis simulation of alternative internal correction-fixation systems, so as to determine the most efficacious system, (4) instrumentations for surgically implementing the recommendations of the surgical simulation analysis and (5) comparisons of the model-simulated and surgically-obtained corrected spinal configurations. These procedures together constitute the biomechanical foundations of scoliosis surgical correction.

Performance assessment of the Terry Fox jogging prosthesis for above-knee amputees

The Terry Fox jogging (TFJ) prosthesis was developed at Chedoke-McMaster Hospital to alleviate the asymmetric jogging pattern experienced by above-knee amputees when attempting to jog with conventional walking prostheses. This prosthesis features a spring-loaded, telescoping shank designed to eliminate any vaulting action and control the trunk motion during stance. The spring is intended to attenuate the impact forces and release its stored energy at push-off to provide momentum transfer to the jogger. This prosthesis was comprehensively assessed in the gait laboratory, by evaluating the kinematics, energy and power flow patterns of an above-knee amputee jogger wearing the TFJ prosthesis. Included in the assessment is the ability of the prosthesis to satisfy a set of relevant design criteria that have been established from non-amputee jogging patterns. An increased swing phase time for the prosthetic limb and the need to have the knee hyperextended throughout the stance phase contributed to an asymmetric jogging style. The telescoping action did lower the amputees centre of mass, thereby reducing the vaulting effect. However, the spring only imparted a lifting action to the jogger and the ground reaction forces were double those of a non-amputee jogger. These findings clearly indicate a need to redesign the TFJ prosthesis and are being incorporated in the design of a new physiological jogging prosthesis.

Intrinsic indices of the left ventricle as a blood pump in normal and infarcted left ventricles.

To assess the left ventricle as a blood pump, data are collected from contrast angiograms and analysed by computer, using two-dimensional finite element analysis, to provide instantaneous distributions of intra-LV flow and differential pressure during the diastolic and ejection phases. Characteristic indices are derived for normal and infarcted LVs, and for cases before and after administration of nitroglycerin. These indices may be used to assess the degree and nature of dysfunction in coronary artery disease.

Presurgical finite element simulation of scoliosis correction

For surgical correction of scoliotic spinal deformity, internal fixation systems apply lateral and distractive corrective forces. In order to gain maximal correction, a finite--element analysis of the spinal deformity correction technique has been carried out preoperatively, after first employing the spinal deformity correction finite--element model to determine the in vivo spinal stiffness. The presurgical analysis also gives us an appreciation of how the parameters of deformity, stiffness and corrective forces jointly contribute to the value of the correction index. The paper presents the methodology and clinical application. It also summarizes the results for ten patients, whereby the efficacy of presurgical analysis is assessed by comparing the corrective index values by presurgical simulation with the surgical results for equivalent levels of corrective forces.

Detection of Myocardial Scars in Neonatal Infants from Computerized Echocardiographic Texture Analysis

It has been demonstrated that highly reflectile echoes (HREs) on standard echocardiograms may represent foci of myocardial fibrosis, calcification, or infiltration. A pilot study of the echocardiograms of premature infants by our group has indicated the presence of HREs in many stressed infants. We have subsequently shown that these HREs correspond to myocardial scarring or necrosis. By studying normal two-dimensional echocardiograms and those with visually observed highly reflectile echoes (HREs). we have been able to develop echo-intensity ranges for normal neonatal myocardium and suspected foci of necrosis. An amplitude analysis of the intensity levels of these highly reflectile areas (HREs) in the echocardiogram has indicated that their mean intensity was significantly higher than the surrounding healthy myocardial areas. Significant correlation was found between these highly reflectile echo zones and calcified or necrotic tissue based on postmortem pathological examination. An objective method of quantifying the ultrasonic reflection amplitude has thereby been developed by us, based on image analysis of the echograms available from the B-scan system. Algorithms have been developed for evaluating the greylevels (or echo intensities or reflection amplitudes) of the pixels, normalizing them with respect to the reflection amplitude of the pericardium, and then printing out the grey-level distribution over an image. Appropriate software has been developed to designate scarred myocardial segments, based on the mean and standard deviation of the selected region on the echo image in comparison with these values for the pericardium.

Microcomputerized on-line evaluation of heart rate variability power spectra in humans

The heart rate variability power spectra is computed using an on-line microcomputer system. In normal subjects (n = 10), standing and post-exercise states demonstrated statistically significant increases (p less than 0.05) in the peak power at 0.1 Hz. During exercise, the peak power at 0.1 Hz was reduced significantly (p less than 0.05). In patients with myocardial infarction, either the peak at 0.1 Hz or the peak associated with breathing frequency was augmented. Our system is mobile and is useful especially when on-line heart rate variability power spectra are required in experimental or clinical situations.

Spinal Fixator for the Management of Spinal Injury (the Mechanical Rationale)

The goal of successful treatment of spinal injury is to achieve a stable pain-free spine with no deformity and also the complete anterior decompression of the cord for maximum neurological recovery, the minimum bed-ridden time and hospitalization, and reduction of complications and expenses. A special ‘spinal fixator’ has been developed to fulfill these aims. It is a small apparatus with two components: a stabilizer to fix the adjacent vertebrae and a turn-buckle part to produce compression. Extensive biomechanical tests on cadavers confirmed that this appliance produced secure stability on the broken spine. It will simply replace the broken bodies through an anterolateral approach, restore the height of the body vertebrae for normal weight-bearing, and securely stabilize the broken spine for early mobility and rehabilitation; and finally, it will provide the chance to decompress the cord anteriorly for a better recovery. In this way the patient will be able to sit one day after the operation, to stand (w...

Computerized Cheirometer for Assessing Grip-Strength Indices and Classification of Rheumatoid Patients

A computerized Cheirometer has been developed to objectively assess grip strength indices (GSI) of normals and rheumatoid arthritis (RA) patients. The instrument consists of a hand-grip bladder, an LVDT pressure transducer (Schaevitz) interfaced through a 12 bit A/D converter to an Apple II + computer. Software has been developed for data acquisition, display and classification of measured GSI into moderately diseased and severely diseased and normal classes.During the developmental phase of the instrument, it was noted that maximum pressure (PM) and rate-of-rise (ROR) of pressure during the squeezing of the bladder were the most sensitive indices to distinguish and classify normal and patient hand-grip waveforms. The reproducibility of PM and ROR as useful GS indices was tested in 13 chronic RA patients in the morning, with two measurements per patient, within half-hour intervals. The results indicate that PM and ROR are stable indices with no significant variation between two measurements (p < 0.05). A ...

Mathematical simulation of impact of birth control policies on Indian population system.

A feedback control computer simulation model of the popula tion system of India is synthesized by using system dynamics methodology. The governing dynamic equations are solved us ing continuous system modelling program (CSMP) on IBM 370/155 computer. The model, for different birth control policies, reproduces the past history of the sytem accurately. It projects (up to the year 2026) the future growth of popula tion ; birth and death rates; age structure; and total couples to be covered for (1) different intensities of birth control, (2) in crease in marriage age, and (3) better distribution of income policies. The model could be used as a tool to evaluate alternate policies for long-term population planning and to make recommenda tions of suitable policies to reduce and stabilize the population within minimum time. This model provides national policy makers with a scientific basis to evaluate the impact of their policies and thus to select the optimal one.