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Biomedical subjects

J A Helpern

Publications and source records attributed to J A Helpern.

60 records · Page 4Linked to original sources
PubMed1984

Anoxia followed by hyperoxia: in vivo 31-P NMR of cat brain.

In vivo 31P NMR spectroscopy was performed on a cat brain subjected to an extended period of anoxia followed by restoration of oxygen. High energy phosphate spectra were continuously obtained and pH measured. Following the onset of anoxia, phosphocreatine and ATP peaks decreased with a concomitant increase in inorganic phosphate. Following 34 min ventilation on 100% N2, the animal was ventilated on 100% O2. The spectral content progressively changed, inorganic phosphate decreased and ATP increased with the spectrum closely resembling that of control. Our results suggest that the absence of NMR detectable ATP signal cannot be interpreted as an irreversable change in cellular metabolic function.

Adenosine Triphosphate↗
PubMedDate not supplied

Assessment of magnesium concentrations by 31P NMR in vivo.

31P NMR spectra obtained in vivo reveal the presence of a few reasonably well defined chemical species, namely, ATP, orthophosphate (Pi), and, in brain, phosphocreatine. The chemical shifts of these resonances respond to changes in concentrations of ions such as H+ and Mg2+ in a manner that depends on both the chemical shifts intrinsic to individual complexes and the formation or binding constants for the several complexes. Values of the appropriate formation constants are well established in the literature. We have derived estimates of the chemical shifts intrinsic to the individual complexes by analyzing high resolution spectra of solutions whose composition brackets the domain of physiological relevance. This provides information sufficient to estimate intracellular concentrations of H+ and Mg2+ from chemical shifts seen with in vivo spectra. The primary finding is an estimate of 0.3 mM for the concentration of free magnesium in human brain. Differing values are obtained from other tissues.

Adenosine Triphosphate↗
PubMedDate not supplied

Neuropsychiatric applications of DTI - a review.

Psychiatric disorders are common throughout the world and are a leading cause of disability. There is a growing appreciation of the importance of connectivity to brain function. Disruption of this connectivity can result in brain dysfunction manifested in impaired cognitive functioning and the development of clinical symptoms. White matter forms the basis of anatomical connectivity. Diffusion tensor imaging (DTI) is a useful tool for examining and quantifying white matter microstructure. Clinical research studies in alcoholism, HIV-1 infection, geriatric depression and schizophrenia using DTI have revealed abnormalities in white matter microstructure. The use of complementary imaging methods may be helpful in further characterizing these abnormalities. Other psychiatric disorders may also have white matter involvement amenable to study with DTI. Advances in acquisition and analysis methods will be necessary to further advance work in this field. The study of animal models and postmortem tissue may be helpful in elucidating the neurobiological underpinnings of abnormalities observed with DTI.

Aged↗
PubMedDate not supplied

In vivo 31-P NMR of photoactivated hematoporphyrin derivative in cat brain.

In vivo 31-P nuclear magnetic resonance (NMR) spectroscopy was performed on cat brains injected with hematoporphyrin derivative (HpD). A 2-cm-diam region of the right parietal lobe was photoactivated with red light. The 31-P NMR spectra of the photoactivated hemisphere revealed increased inorganic phosphate and decreased phosphocreatine and adenosine triphosphate (ATP) levels, compared to spectra obtained from the control hemisphere. In the absence of drug, no difference in spectra was observed between the photoradiated and control lobes. Our studies suggest that in vivo 31-P NMR spectroscopy may be used to monitor the effects of phototherapy on tissue high-energy phosphate metabolism.

Animals↗
PubMedDate not supplied

Pathophysiological correlates of cerebral ischemia the significance of cellular acid base shifts.

In vivo 31-Phosphorus nuclear magnetic resonance (31PNMR) spectroscopy was used to study regional high energy phosphate, and phospholipid metabolism together with intracellular pH in patients with acute hemispheric ischemic stroke. The pH of ischemic brain progressed from acidosis to alkalosis. Acidosis was correlated with metabolic deterioration. Alkalosis was correlated with poor neurological outcome. Hyperglycemia worsened acidosis and metabolic breakdown. Therapeutic control of systemic glucose levels and cerebral acidosis should be evaluated in acute stroke.

Acid-Base Equilibrium↗