Brain oxidative phosphorylation following alteration in head position in preterm and term neonates

Systematic review of 31P-magnetic resonance spectroscopy studies of brain high energy phosphates and membrane phospholipids in aging and Alzheimer's disease

Many lines of evidence suggest that mitochondria have a central role in aging-related neurodegenerative diseases, such as Alzheimer's disease (AD). Mitochondrial dysfunction, cerebral energy dysmetabolism and oxidative damage increase with age, and are early event in AD pathophysiology and may precede amyloid beta (Aβ) plaques. In vivo probes of mitochondrial function and energy metabolism are therefore crucial to characterize the bioenergetic abnormalities underlying AD risk, and their relationship to pathophysiology and cognition. A majority of the research conducted in humans have used ¹⁸F-fluoro-deoxygluose (FDG) PET to image cerebral glucose metabolism (CMRglc), but key information regarding oxidative phosphorylation (OXPHOS), the process which generates 90% of the energy for the brain, cannot be assessed with this method. Thus, there is a crucial need for imaging tools to measure mitochondrial processes and OXPHOS in vivo in the human brain. ³¹Phosphorus-magnetic resonance spectroscopy (³¹P-MRS) is a non-invasive method which allows for the measurement of OXPHOS-related high-energy phosphates (HEP), including phosphocreatine (PCr), adenosine triphosphate (ATP), and inorganic phosphate (Pi), in addition to potential of hydrogen (pH), as well as components of phospholipid metabolism, such as phosphomonoesters (PMEs) and phosphodiesters (PDEs). Herein, we provide a systematic review of the existing literature utilizing the ³¹P-MRS methodology during the normal aging process and in patients with mild cognitive impairment (MCI) and AD, with an additional focus on individuals at risk for AD. We discuss the strengths and limitations of the technique, in addition to considering future directions toward validating the use of ³¹P-MRS measures as biomarkers for the early detection of AD.

Supine vs. Prone Position With Turn of the Head Does Not Affect Cerebral Perfusion and Oxygenation in Stable Preterm Infants ≤32 Weeks Gestational Age

Intraventricular hemorrhage (IVH) is a frequent major damage to the brain of premature babies ≤32 weeks gestational age, and its incidence (20–25%) has not significantly changed lately. Because of the intrinsic fragility of germinal matrix blood vessels, IVH occurs following disruption of subependymal mono-layer arteries and is generally attributed to ischemia-reperfusion alterations or venous congestion, which may be caused by turn of the head. Therefore, supine position with the head in a midline position is considered a standard position for preterm infants during their first days of life. We asked whether a change in body position (supine vs. prone) linked with a turn of the head by 90° in the prone position would change blood flow velocities and resistance indices in major cerebral arteries and veins of stable premature babies at two different time points (t0, day of life 2, vs. t1, day 9). Moreover, we assessed cerebral tissue oxygenation (cStO2) by near-infrared spectroscopy and determined correlations for changes in velocities and oxygenation. Twenty one premature infants [gestational age 30 (26–32) weeks] with sufficiently stable gas exchange and circulation were screened by ultrasonography and near-infrared spectroscopy. Peak systolic and end-diastolic blood flow velocities in the anterior cerebral arteries (29 ± 6 m/s vs. 28 ± 7 peak flow at t0, 36 ± 8 vs. 35 ± 7 at t1), the basilar artery, the right and the left internal carotid artery, and the great cerebral vein Galen (4.0 ± 0.8 m/s vs. 4.1 ± 1.0 maximum flow at t0, 4.4 ± 0.8 vs. 4.4 ± 1.0 at t1) did not show significant differences following change of body and head position. Also, there were no differences in cStO₂ (83 ± 7% vs. 84 ± 7 at t0, 76 ± 10 vs. 77 ± 11 at t1) and in vital signs such as heart rate and blood pressure. We conclude that change in body position with turn of the head in the prone position does not elicit significant alterations in cerebral blood flow velocities or in oxygenation of cerebral tissues. Maturational changes in arterial flow velocities and cStO₂ are not correlated. For this subgroup of premature infants at low risk of IVH our data do not support the concept of exclusive preterm infant care in supine position.

The prone sleeping position and SIDS. Historical aspects and possible pathomechanisms

The incidence of SIDS decreased during the previous 25 years significantly. This is mainly due to epidemiological research identifying important risk factors such as prone sleeping position and subsequent campaigns to reduce this risk factor.Originally, the prone sleeping position for babies had been strongly recommended in the sixties and seventies despite previous publications pointed to the associated risk. Worldwide, many infants died of SIDS whose deaths could have been avoided. Today, the recommendation that infants should sleep in supine position has been scientifically verified. In supine sleeping position, pathophysiological mechanisms can be avoided which may lead to hypoxia and death in prone position. Such mechanisms could be occlusion of airways (in particularly associated with face-down position), elevated diaphragm, positional cerebral hypoxia caused by constriction of arteries, rebreathing CO2, and overheating.Irrespective of the specific pathomechanism leading to death in individual cases, it has been established that the prone position is the most important risk factor for SIDS and therefore should be incorporated in the definition of the term SIDS.

Magnetic resonance spectroscopy (MRS) in the investigation of cancer at The Royal Marsden Hospital and The Institute of Cancer Research

Developments in magnetic resonance spectroscopy (MRS) at The Royal Marsden Hospital and The Institute of Cancer Research are reviewed in the context of preceding developments in nuclear magnetic resonance (NMR) and MRS, and some of the early developments in this field, particularly those leading to human measurements. The early development of technology, and associated techniques for human measurement and assessment will be discussed, with particular reference to experience at out institutions. Applications using particular nuclei will then be described and related to other experimental work where appropriate. Contributions to the development of MRS that have been published in Physics in Medicine and Biology will be discussed.

Sudden infant death—focus subject of medico-legal research

The compilation of research activities concerning SID in the field of legal medicine could only choose those out of a great abundance of high-quality examinations which represent applied research. By this they have contributed either to the clarifying of the aetiology which has not been cleared up or to the prophylaxis. For this looking through in a widest sense the basic approach was to consider SID being the result of an intrinsic and/or extrinsic disturbance of the modulation of respiratory regulation of the infant. This namely means a metabolic disturbance of respiratory neurons. One must not share this opinion even if it is given a certain plausibility by newer physiological examinations. But this also means that some examinations did not receive the acknowledgement which they would have received if there had been an immunological approach. The compilation was completely done without a presentation of the primary crisis intervention and the long-term care as being a fundamental medico-legal approach. Altogether may be summarized that legal medicine has completely fulfilled its duty to take care of the problem SID and that the examinations did not remain without success.

Body position-dependent changes in cerebral hemodynamics during apnea in preterm infants

The objective of the present study was to evaluate sleeping position-dependent effects on cerebral hemodynamics during apnea in preterm infants. To this end, polygraphic studies were performed on 15 stable preterm infants lying prone and lying supine. Changes in cerebral blood volume (DeltaCBV) and in cerebral hemoglobin oxygenation ((Delta)cHbD) in association with apnea were measured by near infrared spectroscopy. For comparison, apnea in the prone position was matched for duration to apnea in the supine position. A total number of 98 pairs of apnea were compared. The mean duration of apnea was 8.2+/-3 s. In both positions there was a predominance of decrease in CBV and cHbD in association with apnea. The mean decrease of cHbD (-1.57+/-1.82 micromol/l) and of CBV (-0.120+/-0.137 ml/100g brain) in the supine position was significantly pronounced compared to prone position (DeltacHbD: -1.18+/-1.77 micromol/l, DeltaCBV: -0.080+/-0.095 ml/100 g brain). The degree of DeltaCBV and DeltaHbD did not correlate with postconceptional or postnatal age (r2<0.01). In both positions there was a similar small decrease of SaO2 in association with apnea. In the supine position heart rate decreased slightly during apnea, whereas in the prone position no change in heart rate could be observed. The present study revealed a position-dependent different impact of apnea on cerebral hemodynamics. With regard to cerebral blood volume and oxygenation in association with apnea no negative effects of prone sleeping position could be observed in preterm infants.

Study of the maturation of the child's brain using 31P-MRS

The maturation of human cerebrum and cerebellum in 37 normal children aged 4 months to 13 years 8 months was evaluated by 31P-magnetic resonance spectroscopy using two different conditions of repetition time (TR) (TR = 3 seconds and 15 seconds) in each region. The results were as follows. First, the PME/PDE, PCr/gamma-ATP and Pi/PCr ratios differed between the cerebrum and the cerebellum. The PME/PDE and PCr/gamma-ATP ratios were greater in the cerebellum than in the cerebrum. However, the Pi/PCr ratio was smaller in the cerebellum than in the cerebrum. At TR = 3 seconds, the ratio of (PME/PDE ratio in the cerebellum)/(PME/PDE ratio in the cerebrum) and the ratio of (PCr/gamma-ATP ratio in the cerebellum)/(PCr/gamma-ATP ratio in the cerebrum) manifested a nearly constant value independent of age. Second, the phosphomonoester peak in the cerebrum contained a substance with a longer relaxation time than 3 seconds; this substance was present in large amounts in the early period, then gradually decreased during maturation.

High-energy phosphate metabolism in a neonatal model of hydrocephalus before and after shunting

The authors studied the effects of hydrocephalus on the high-energy phosphate metabolism of the brain and the impact of ventriculoperitoneal (VP) shunting on these changes in an experimental model of hydrocephalus. High-energy phosphate metabolism was analyzed using in vivo magnetic resonance (MR) imaging and 31P MR spectroscopy. Hydrocephalus was produced in 34 1-week-old kittens by cisternal injection of 0.05 ml of a 25% kaolin solution. Sixteen litter mates were used as controls. A VP shunt with a distal slit valve was implanted in 17 of the 34 hydrocephalic animals 10 days after induction of hydrocephalus. Both MR imaging and 31P MR spectroscopy were obtained 1 and 3 weeks after either kaolin or distilled water injection. Untreated hydrocephalic animals had marked dilatation of the lateral ventricles and periventricular edema. Magnetic resonance spectroscopy showed a significant decrease in the energy index ratio of phosphocreatine (PCR): inorganic phosphate (PI) and an increase in the PI:adenosine triphosphate (ATP) ratio. There was a direct correlation between the decrease in the energy index and ventricular size. Compared with preoperative scans, shunted animals showed no periventricular edema, and the ventricles decreased in size. Also, PCR:PI and PI:ATP ratios were within the levels of controls. This study suggests that neonatal hydrocephalus results in a mild hypoxic/ischemic insult that is treatable by VP shunting.

New noninvasive techniques for assessing brain oxygenation and hemodynamics

Infants who require intensive care are at considerable risk of death or long-term neurodevelopmental disability. Therefore, noninvasive methods have been sought for assessing the structure and function of the brain in the immediate newborn period. The major aims are to investigate the prevalence and mechanisms of brain-damaging lesions, to test preventive strategies and treatment, and to assign the prognosis of the infants. Several methods have proved their worth, e.g., ultrasound imaging, electroencephalography, including the testing of evoked potentials, and Doppler ultrasonography for measuring flow velocity in intracerebral vessels.