Streamlining fluid pathways lessens flow energy dissipation: relevance to atriocavopulmonary connections.

Flow energy dissipation reduces cardiac efficiency, particularly in the Fontan-modified, single-ventricle heart. To provide insight into flow energetics relevant to Fontan-type anatomy, a simple, analytical description of fluid motion was employed. Mechanical energy balance and the force-momentum relationship were used to describe theoretical pressure changes and flow energy losses.

Pressure loss from flow energy dissipation: relevance to Fontan-type modifications.

Pressure loss from flow energy dissipation may impair cardiac performance when a heart with a single ventricle must support the circulation. Therefore, the goal of this study was to use a simple description of fluid motion to provide insight into flow energetics relevant to Fontan-type procedures. Our findings indicate that when either the cross-sectional area or the axial direction of flow changes "abruptly," disturbances are set up within the fluid that lead to dissipation of available energy.

Mechanical and metabolic characterization of ischemic contracture in the neonatal pig heart.

Isolated, paced, isovolumetrically beating piglet hearts (n = 37) underwent retrograde aortic perfusion with a crystalloid solution during three periods: 1) baseline (coronary perfusion pressure 60 mm Hg), 2) ischemia (coronary flow 10% of baseline for approximately 80 min), and 3) reperfusion (perfusion pressure returned to baseline). In one group of hearts, glycolysis (using 3H2O formation from [3H]glucose) was assessed. During baseline, peak systolic pressure (PSP) was 101.

Vasoactive intestinal peptide: electrophysiologic activity in the newborn heart.

We performed intracardiac electrophysiologic studies of the effects of vasoactive intestinal peptide (VIP, 0.125 micrograms/kg/min) on sinus and atrioventricular (AV) nodal function, intracardiac conduction, and myocardial refractoriness in two groups of neonatal dogs (aged 6-16 d). Group I consisted of eight neonates in whom VIP was administered after bilateral vagotomy and beta-blockade with propranolol.

Pituitary adenylate cyclase activating polypeptide: a neuropeptide with potent inotropic and coronary vasodilatory effects in neonatal pig hearts.

Cardiac effects of the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) have not previously been reported. We investigated the influence of PACAP, vasoactive intestinal polypeptide (68% homology with PACAP) and the beta-adrenergic receptor agonist isoproterenol on contractile function and coronary vascular tone in isolated piglet hearts (1 to 5 d of age). Paced (180 beats/min) isovolumically beating hearts underwent retrograde aortic perfusion at constant coronary flow (approximately 3 mL.

Proton NMR spin grouping and exchange in dentin.

The nuclear magnetic resonance spin-grouping technique has been applied to dentin from human donors of different ages. The apparent T2, T1, and T1 rho have been determined for natural dentin, for dentin which has been dried in vacuum, and for dried dentin which has been rehydrated in an atmosphere with 75% relative humidity. All apparent spin relaxation has been analyzed for exchange between the spin groups in which the dentin protons exist; the analyses incorporate the results of selective inversion recovery T1 measurements which better probe the effects of exchange.

Water molecule dynamics in hydrated lysozyme. A deuteron magnetic resonance study.

Proton nuclear magnetic resonance relaxation investigations of water dynamics in hydrated protein powders have the serious drawback that protein-water intermolecular dipolar interactions make the unambiguous interpretation of the results difficult. To circumvent this difficulty, deuteron spin-lattice and spin-spin relaxation times in lysozyme powder hydrated with deuterium oxide were measured as a function of temperature and at two frequencies. Although the deuteron relaxation results are compatible with a water molecule dynamics model based on either a bimodal distribution of correlation times or anisotropic motion, a comparison of the present results with proton data suggests than an anisotropic motion model is more likely to provide a reasonable description of the water molecule motion.

Characterization of normal and malignant mouse tissue by NMR lineshape-relaxation correlations in the rotation frame.

With the NMR lineshape-relaxation correlation technique the relaxation times and the relative magnitudes of the proton spin groups characterized by these respective relaxation times are obtained. In most tissues the spin-lattice relaxation in the rotating frame is nonexponential. The magnetization evolution can be represented as the sum of three exponential decays characterized by three T1rho relaxation times.

Composition and relaxation of the proton magnetization of human enamel and its contribution to the tooth NMR image.

The spin-spin, T2, and spin-lattice, T1, relaxation times and the magnetization of protons were measured in human enamel. The proton free induction decay was analyzed into solid-like interstitial water, enamel apatite, and semiliquid-like water components. The solid-like interstitial water was evaluated to be approximately 5 wt% and the semiliquid-like water to be approximately 1 to 2%.

Improved characterization of healthy and malignant tissue by NMR line-shape relaxation correlations.

We performed a relaxation-line-shape correlation NMR experiment on muscle, liver, kidney, and spleen tissues of healthy mice and of mouse tumor tissue. In each tissue studied, five spin groups were resolved and characterized by their relaxation parameters. We report a previously uncharacterized semi-solid spin group and discuss briefly the value of this method for the identification of malignant tissues.

Nuclear magnetic resonance analysis of water in natural and deuterated mouse muscle above and below freezing.

Measurements of absolute proton signal intensities, free induction decays, spin-spin relaxation times, and local fields in the rotating frame in natural and fully deuterated mouse muscle at five temperatures in the range 293-170 K are reported. The analysis is carried out at three time windows on the free induction decay. The contribution to the magnetization from protons on large molecules and water are analyzed.

A study of molecular dynamics and freezing phase transition in tissues by proton spin relaxation.

Muscle, spleen, and kidney tissues from 4-wk-old C57 black mice were studied by proton magnetic resonance. Spin-lattice relaxation times at high fields and in the rotating frame, as well as the spin-spin relaxation times, are reported as a function of temperature in the liquid and frozen phase. Motions of large molecules and of water molecules and their changes at the freezing phase transition are studied.