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N Pallikarakis

Publications and source records attributed to N Pallikarakis.

8 recordsLinked to original sources
PubMed1991

Influence of the bicarbonate pool and on the occurrence of 13CO2 in exhaled air.

In 13CO2 breath tests, based on 13C:12C ratio measurements, the appearance of 13C in exhaled CO2 was monitored after the administration of a 13C-labelled compound. Independently of the substrate used, the existence of a bicarbonate pool into which the CO2 produced enters before being exhaled, imposes a delay on the appearance of changes in the 13C:12C ratio. To estimate the nature and magnitude of this delay, we applied a two-compartment model to describe the kinetics of the body bicarbonate pool and we evaluated the 13C:12C ratio of CO2 entering that pool from the measured 13C:12C ratio in the exhaled CO2 after an oral intake of "naturally labelled" 13C-glucose. Our results demonstrated that discrepancies between total and exogenous glucose oxidation in relation to the peak occurrence time, as well as the absolute quantities, could be adequately explained by the interference of the bicarbonate stores.

Bicarbonates↗
PubMed1986

Remarkable metabolic availability of oral glucose during long-duration exercise in humans.

It was reported previously that glucose ingestion prior to or at the beginning of muscular exercise was a readily available metabolic substrate. The aim of this study was to see what percentage of carbohydrate utilization can be covered by glucose ingested regularly during exercise. Male healthy volunteers exercised for 285 min at approximately 45% of their individual maximal O2 uptake on a 10% uphill treadmill. After 15 min adaptation to exercise they received either 200 g (group G 200) or 400 g (group G 400) glucose (0.25 g X ml H2O-1) orally in eight equal doses repeated every 30 min (G 200 = 8 X 25 g, n = 4; G 400 = 8 X 50 g, n = 4). Indirect calorimetry was used to evaluate carbohydrate and lipid oxidation. Naturally labeled [13C]glucose was used to follow the oxidation of the exogenous glucose. Total carbohydrate oxidation was 341 +/- 22 and 332 +/- 32 g, lipid oxidation was 119 +/- 8 and 105 +/- 5 g, and exogenous glucose oxidation was 137 +/- 4 and 227 +/- 13 g (P less than 0.005) in groups G 200 and G 400, respectively. Endogenous glucose oxidation was about half in G 400 of what it was in G 200: 106 +/- 27 vs. 204 +/- 24 g (P less than 0.02). During the last hour of exercise, exogenous oxidation represented 55.3 and 87.5% of total carbohydrate oxidation for groups G 200 and G 400, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxybutyric Acid↗
PubMed1986

Utilization of oral sucrose load during exercise in humans. Effect of the alpha-glucosidase inhibitor acarbose.

We investigated the hormonal and metabolic response to a 100-g sucrose load given 15 min after adaptation to moderate-intensity (50% VmaxO2) long-duration (4-h) exercise in healthy volunteers. The effect of a 100-mg dose of the alpha-glucosidase inhibitor Acarbose ingested with the sucrose load was also investigated. "Naturally labeled [13C] sucrose" was used to follow the conversion to expired-air CO2 of the sugar ingested by isotope-ratio mass spectrometry. Circulating hormone and metabolite data were obtained in nine subjects, and indirect calorimetry and stable isotope methodology were applied to six of them. Under placebo, 93 +/- 4 g sucrose were entirely oxidized during the 4 h of exercise, total carbohydrate utilization was 235 +/- 14 g, endogenous carbohydrate utilization was 142 +/- 13 g, and total lipid oxidation was 121 +/- 7 g. A single oral dose of 100 mg Acarbose ingested with the sucrose load did not significantly modify total carbohydrate (239 +/- 2 g/4 h) or lipid (122 +/- 6 g/4 h) oxidation. In contrast, sucrose oxidation was reduced to 53 +/- 6 g/4 h and endogenous carbohydrate utilization increased to 186 +/- 7 g/4 h. Reduction of the rises in blood glucose and fructose and of the increases in plasma insulin and C peptide under Acarbose confirmed these effects, whereas lower circulating levels of alanine suggested a higher rate of gluconeogenesis. These data show that a 100-g glucose load ingested soon after initiation of exercise is a perfect available metabolic substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Acarbose↗
PubMedDate not supplied

A multiple projection method for digital tomosynthesis.

A new method of optimized efficiency for the retrospective reconstruction of tomograms is presented. The method has been developed for use with isocentric fluoroscopic units and is capable of performing digital tomosynthesis of anatomical planes of user selected orientation and distance from the isocenter. Optimization of efficiency has been achieved by segmenting the reconstruction process into discrete transformations that are specific to groups of pixels, rather than performing pixel by pixel operations. These involve a number of projections of the acquired image matrices as well as parallel translations and summing. Application of this method has resulted in a significant reduction of computing time. The proposed algorithm has been experimentally tested on a radiotherapy simulator unit with the use of a phantom and the obtained results are reported and discussed.

Algorithms↗