The ringed esophagus

Abdominal Radiology -     

Therapeutic vaccination for closed head injury

Closed head injury often has a devastating outcome, partly because the insult, like other injuries to the central nervous system (CNS), triggers self-destructive processes. During studies of the response to other CNS insults, it was unexpectedly discovered that the immune system, if well controlled, provides protection against self-destructive activities. Here we show that in mice with closed head injury, the immune system plays a key role in the spontaneous recovery. Strain-related differences were observed in the ability to harness a T cell-dependent protective mechanism against the effects of the injury. We further show that the trauma-induced deficit could be reduced, both functionally and anatomically, by post-traumatic vaccination with Cop-1, a synthetic copolymer used to treat patients with multiple sclerosis and found (using a different treatment protocol) to effectively counteract the loss of neurons caused by axonal injury or glutamate-induced toxicity. We suggest that a compound such as Cop-1 can be safely developed as a therapeutic vaccine to boost the body's immune repair mechanisms, thereby providing multifactorial protection against the consequences of brain trauma.     

Parametric description of cardiac vagal control

Heart rate variability (HRV) indices that reflect the magnitude of respiratory sinus arrhythmia (RSA) are commonly applied as non-invasive measures of cardiac vagal control. Recently, however, serious doubts have been raised about the accuracy and validity of such assessments. To evaluate these methods, we derived a theoretical model for the dependence of mean heart rate and RSA on gradual vagal blockade by atropine, and compared its predictions to actual experimental results. The experiment involved the injection of nine consecutive intravenous bolus doses of atropine to eight young healthy male subjects. Seven-minute recordings of ECG and respiration were made for each atropine dose. The heart rate (HR) signal was derived from the ECG recording, and mean heart rate and the power of the high frequency peak of HRV (which measures the magnitude of RSA) were computed. The experimental data were fitted to the model's equations, and optimal values were obtained for the model's parameters. A tight agreement is observed between the theoretical fitted curves and the experimental data. The parameters that were computed from fitting the experimental data to the mean heart rate equation display a surprisingly small variance among the different subjects. The parameters that were computed from fitting the experimental data to the RSA equation, and the resulting shape of these fitted curves, explain many of the conflicting results previously published, and provide a new quantitative insight to cardiac vagal activity.     

Estimation of autonomic response based on individually determined time axis

The analysis of the time-dependence of autonomic response requires: 1. A reliable procedure for the quantification of autonomic activity under nonsteady conditions, such as an algorithm for time-frequency decomposition (ex. SDA. Wigner-Ville, or others). 2. The choice of an adequate time scale for focusing on the data: (a) the regular, universal time scale, independent of the unsteady physiological conditions, or (b) a time axis defined by specific events related to an applied perturbation, as the indicators of specific experimental or physiological conditions, so that each individual is considered according to his own intrinsic time scale. The alignment of the various subjects according to their intrinsic time scale, reflecting their individual response mechanisms, may help to disclose a common pattern of autonomic function. Using an absolute time scale to align and average results for different subjects may obscure the underlying mechanisms. Several examples of autonomic challenges are presented, in which the use of an individual time scale contributes to unveil a typical response pattern: tilt test in vasovagal syncope, the autonomic effect of active standing on hypertension, and the autonomic response to acute hypoxia.     

Nonlinear dynamics applied to blood pressure control

Hypertension is a very frequent disease, known to trigger a range of severe cardiovascular problems. The elucidation of its pathophysiology requires investigation of the mechanisms responsible for the maintenance of blood pressure in the normal system, and their possible failure in hypertension. Some of these control mechanisms display nonlinear features, indicating that the blood pressure signal might be characterized by nonlinear dynamics. Our aim was thus to investigate the nonlinear properties of the blood pressure signal under normal conditions, and in a cardiovascular system prone to hypertension. Blood pressure was investigated in young spontaneously hypertensive rats (SHR), versus their age-matched normotensive progenitors (WKY). The correlation dimension was computed as quantification of blood pressure control complexity. The parameters required for the calculation procedure of the correlation dimension were carefully determined. The results were tested with surrogate data statistics. assuming linear autocorrelated Gaussian noise as the null hypothesis. Non-integer correlation dimension values were found in both strains, with lower values for SHR than for WKY, in particular following alpha-blockade. In all cases, a statistically significant difference was found between the real and surrogate data. These results show that the nonlinear dynamics parameter D, can be used to detect differences in BP control between prehypertensive SHR and WKY rats as early as 6-7 weeks after birth.     

Evaluation of autonomic dysfunction in familial dysautonomia by power spectral analysis

We examined the nature and extent of the autonomic control defect in patients with autonomic dysfunction using power spectral analysis of heart rate fluctuations. Heart rate variability and respiratory patterns were monitored and discrete blood pressure measurements were made during supine and standing positions in 10 ambulatory patients with familial dysautonomia and in controls. Postural hypotension without compensatory tachycardia was confirmed in the patients upon standing. The balance between sympathetic and parasympathetic activity was compared in both positions by quantifying the power of the low (0.04-0.095 Hz) and high (respiratory) frequency fluctuations in instantaneous heart rate. After changing from supine to standing position there was a small decrease in the low frequency power of heart rate fluctuations in the patients as opposed to a significant increase in controls. The mean power of fluctuations occurring at high frequency decreased only slightly in the patients compared to a marked decrease in the controls. We conclude that the fall in blood pressure, lack of appropriate heart rate modulation, and failure to increase low frequency heart rate power which occurred in the patients upon standing, are all due to lack of increased sympathetic output under the influence of gravity. The failure to decrease power in the respiratory frequency peak in the patients, suggests an abnormal retention of parasympathetic activity. This may be explained by parasympathetic compensation for the substantial sympathetic loss, or by a lack of appropriate inhibition of parasympathetic tone from baroreceptors or supraspinal structures.     

Effects of coronary occlusion on high-frequency content of the epicardial electrogram and body surface electrocardiogram

The very high-frequency content (150 to 250 Hz) of epicardial electrogram waveforms was studied in 19 anesthetized dogs subjected to occlusion of left anterior descending coronary artery. Computer techniques of digital averaging and digital band-pass filtering were applied. Signals were obtained from epicardial electrodes placed in the ischemic left ventricular region and on the noninjured right ventricular surface, and from the body surface electrocardiogram. All recordings were made simultaneously before, during, and after coronary occlusion and subjected to the same analysis. The waveforms obtained from the ischemic left ventricular region showed a considerable decrease in high-frequency content, while those obtained from the noninjured right ventricular surface remained unchanged. The results correlated with the appearance of a zone of reduced amplitude in the body surface high-frequency QRS complex. Therefore, this macroscopic phenomenon measured noninvasively from the body surface is explained by local reduction of high-frequency activity in the ischemic region of the myocardium.     

Development of a gamma-gamma-perturbed angular correlation one-detector method (1-PAC) for investigation of physico-chemical properties of matter.

A new method of the perturbed angular gamma-gamma-correlation (PAC) measurements was developed using one HPGe detector only (1-PAC). For quantifying the perturbation factor, the ratio R gamma 1 + gamma 2 of the summing peak composed of two cascade gamma-rays (the perturbation-affected parameter) to the summing peak composed of one gamma-ray and one X-ray (the perturbation non-affected parameter) was used. This method was demonstrated for the radionuclides 111In and 111mCd, identifying the chemical status of the radionuclides in aqueous solutions.     

Application of a semiautomatic boundary detection algorithm for the assessment of amniotic fluid quantity from ultrasound images.

The aim of this study was to develop a computer-assisted method to evaluate amniotic fluid volume (AFV). This was done by automatically detecting the boundaries of the amniotic fluid portion in 2-D ultrasonographic images. The study population consisted of 36 low-risk patients that were selected at random from a healthy population undergoing routine pregnancy follow-up. For each patient, images of the four quadrants of the uterus were digitized into a PC. The amniotic fluid portion in each ultrasonographic image was automatically detected, and its area was calculated. Its area was also manually determined by an expert physician (R. T.). The areas automatically detected by the algorithm were highly correlated with the areas manually delimited by the expert: r2 = 0.9722 (p < 0.01). The areas calculated by the program provide a good measure for the areas determined by the expert and may, therefore, be used for calculating the actual amniotic fluid volume.     

Mapping strain exerted on blood vessel walls using deuterium double-quantum-filtered MRI

A technique is described for displaying distinct tissue layers of large blood vessel walls as well as measuring their mechanical strain. The technique is based on deuterium double-quantum-filtered (DQF) spectroscopic imaging. The effectiveness of the double-quantum filtration in suppressing the signal of bulk water is demonstrated on a phantom consisting of rat tail tendon fibers. Only intrafibrillar water is displayed, excluding all other signals of water molecules that reorient isotropically. One- and two-dimensional spectroscopic imaging of bovine aorta and coronary arteries show the characteristic DQF spectrum of each of the tissue layers. This property is used to obtain separate images of the outer layer, the tunica adventitia, or the intermediate layer, the tunica media, or both. To visualize the effect of elongation, the average residual quadrupole splitting <Δν_q> is calculated for each pixel. Two-dimensional deuterium quadrupolar splitting images are obtained for a fully relaxed and a 55% elongated sample of bovine coronary artery. These images indicate that the strong effect of strain is associated with water molecules in the tunica adventitia whereas the DQF NMR signal of water in the tunica media is apparently strain-insensitive. After appropriate calibration, these average quadrupolar splitting images can be interpreted as strain maps.