Automatic algorithm for correcting motion artifacts in time-resolved two-dimensional magnetic resonance angiography using convex projections.

Time-resolved contrast enhanced magnetic resonance angiography (MRA) may suffer from involuntary patient motion. It is noted that while MR signal change associated with motion is large in magnitude and has smooth phase variation in k-phase, signal change associated with vascular enhancement is small in magnitude and has rapid phase variation in k-space. Based upon this observation, a novel projection onto convex sets (POCS) algorithm is developed as an automatic iterative method to remove motion artifacts. The presented POCS algorithm consists of high-pass phase filtering and convex projections in both k-space and image space. Without input of detailed motion knowledge, motion effects are filtered out, while vasculature information is preserved. The proposed method can be effective for a large class of nonrigid motions, including through-plane motion. The algorithm is stable and converges quickly, usually within five iterations. A double-blind evaluation on a set of clinical MRA cases shows that a completely unsupervised version of the algorithm produces significantly better rank scores (P=0.038) when compared to angiograms produced manually by an experienced radiologist.     

Structure function interface with sequential shortening of basal and apical components of the myocardial band

Objective: To mechanically test the intact cardiac structure to determine the sequence of contraction within the myocardial mass to try to explain ejection and suction. Methods: In 24 pigs (30–85 kg), segment shortening at the site of sonomicrometer crystals was continuously recorded. The ECG evaluated rhythm, and Millar pressure transducers measured intraventricular pressure and dP/dt. Results: Study of segment shortening defined a sequence of contraction within the myocardial mass, starting at the free wall of the right ventricle and on the endocardial side of the antero-septal wall of the left. Crystal location defined underlying contractile trajectory; transverse in right ventricle followed by basal posterior left ventricle, and from the endocardial anterior wall to the posterior apical segment and finally to the epicardial side of the anterior wall. Mean shortening fraction averaged 18±3%, with endocardial exceeding epicardial shortening by 5±1%. Epicardial segment crystal displacement followed endocardial shortening by 82±23 ms in the anterior wall, and finished 92±33 ms after endocardial shortening stopped, time frame that matches the interval of fast drop of ventricular pressure and the start of suction. Conclusions: Crystal shortening fraction sequence followed the rope-like myocardial band model to contradict traditional thinking, with two starting points of excitation–contraction, the right anterior free wall of the right ventricle, and the endocardial side of the anterior wall. Active suction may be due to active shortening of the epicardial fibers of the anterior wall, because relaxation was not detected when both mitral and aortic valves were closed during the interval previously termed ‘isovolumetric relaxation’.     

Pre-adaptation, adaptation and de-adaptation to high altitude in humans: hormonal and biochemical changes at sea level

High altitude residence is known to modify body biochemistry and hormone status. However, the effects of such a sojourn on these status observed at sea level both immediately and later after return are not as well established as are the effects of an intermittent acclimation. The aim of this study was therefore to investigate these changes. To achieve our objectives, nine subjects received intermittent acclimation at low pressure in a barometric chamber (8?h daily for 5 days, day 1 at 4500 m, day 5 at 8500 m) before an expedition to the Himalayas. Hormonal and biochemical changes were studied using samples of venous blood taken at sea level before and after acclimation, after return from the expedition and 1 and 2 months after descent. Concentrations of thyroid hormones, adrenaline, noradrenaline (NA), hormones of hydromineral metabolism (aldosterone, renin, arginine vasopressin, atrial natriuretic peptide) as well as prolactin, cortisol, insulin and endothelin 1 were measured. Biochemical measurements made were plasma osmolality, and concentrations of glucose, total cholesterol, total proteins, pre-albumin, transferrin, complement 3C, apolipoproteins A₁ and B and serum iron. Acclimation induced no alteration in hormone (except for NA with increases of about 1.5, fold P<0.05) and biochemistry data. After the expedition, hormone responses were characterized by a higher total triidothyronine concentration (+18%, P<0.05) while other hormones did not vary. A linear relationship was found between thyroid-stimulating-hormone and body mass changes after the expedition (r=0.67, P<0.05). The observed increased concentrations of plasma proteins and total cholesterol (P<0.05) could be related to the restoration of lean body mass. At 1 and 2 months after return, no changes in hormones were observed but a significant decrease in transferrin concentration was noticed. The higher serum iron concentration reported after 1 month (P<0.05) could have been the result of a physiological haemolysis. It was concluded that both acclimation and the expedition in the Himalayas affected hormone status and body biochemistry status even though the observed changes were slight and rapidly reversed.     

Use of amniotic grafts in the repair of gastroschisis

This article describes the use of amniotic grafts (AG) in the repair of large abdominal wall defects in newborns with gastroschisis. From 1988 to 1995, 22 newborns with gastroschisis underwent surgical repair. In 12 primary closure (PC) was performed; in 10 the abdominal wall defect was covered with an AG. A double layer of AG was used and the graft was additionally covered with a silastic silo in 8 cases. The overall mortality was 14%; 3 children died from necrotizing enterocolitis or sepsis after AG. However, the difference in mortality of newborns with PC versus AG was not statistically significant. Patient characteristics, the postoperative courses, nd the frequency of complications were similar after PC and AG. It is concluded that AG has no negative impact on the postoperative course and yields a low overall mortality. In our opinion there are several advantages in using the AG technique: it is an autoplastic material that is readily available without costs, reefing and removal is unnecessary, and there is a potentially low rate of adhesions.     

Hormone changes induced by 37.5-h head-down tilt (−6°) in humans

Endocrine regulation of hormones and electrolytes during 37.5 h of –6° head down tilt (HDT) was studied in 13 men. The acute effects of simulated weightlessness are today well documented, but no study has been made concerning the hormone changes between 12 h and 2 days of HDT. Plasma volume showed a maximal increase of 9.23 (SEM 1.97) % after 6.5 h (P<0.01) and had returned to prestudy levels after 13.5 h of HDT. From 1.5 h to 4 h of HDT, C-terminus and N-terminus atrial natriuretic peptide (ANP) concentrations in plasma were increased by about 50% (P<0.01) and thereafter declined to pre-HDT levels. Plasma renin activity (PRA) was decreased by 47% (P<0.05) after 4 h of HDT; PRA increased after 23.5 h to 60%; noradrenaline concentration decreased immediately and remained low up to 37.5 h. Diuresis and natriuresis were evident during the 1st day of HDT, resulting in a marked increase in the urinary Na⁺. These results showed that the initial hormone (ANP, PRA) changes during HDT did not last more than 13.5 h and that after 24 h a new state would seem to have been established to adapt the body to hypovolaemia.     

Sympathetic nervous activity and cardiovascular variability after a 3-day tail suspension in rats

The effects of a 3-day tail suspension on central and peripheral sympathetic activity were studied in rats by determining the in vivo noradrenaline (NA) turnover in the brain cell groups involved in central blood pressure control (A1, A2, A5 and A6) and in two peripheral organs, heart and kidneys. In addition, cardiovascular parameters and their variabilities were investigated by recording blood pressure (BP) and heart rate (HR) before and after suspension. These measurements were processed by spectrum analysis to assess the influence of tail suspension on autonomic balance. The NA turnover in the suspended rats was markedly reduced in A2 (–49%, P<0.01) and A5 (–38%, P<0.01) nuclei but unchanged in A1 and A6 cell groups compared with the control rats. Peripheral NA turnover was decreased in cardiac atria (–44%, P<0.001) and ventricles (–27%, P<0.01) while it was unchanged in kidneys after suspension. The BP, HR and their variabilities were similar in both groups of animals and showed no changes after suspension compared with baseline values. Spectrum analysis of BP and HR in our conscious suspended rats revealed no changes in power spectrum density or in peak frequencies. The discrepancy between the decrease in central sympathetic activity and the absence of changes in cardiovascular parameters after tail suspension raises the question of the validity of the tail suspended rat model when studying the cardiovascular deconditioning observed in humans after an exposure to actual or simulated weightlessness.     

Skinfold thickness versus isotope dilution for body fat assessment during simulated microgravity: results from three bed-rest campaigns in men and women with and without countermeasures

Because body composition is altered during head-down bed rest (HDBR), body mass can not be used as an index of energy balance. Consequently diet allowances should not be based on body mass evolution but on fat mass changes. Though criticized, skinfold thickness (ST) is the costless, easiest and fastest method to use for such an objective. The aim of this study was to compare the percentage of body fat (%BF) estimated by ST with the isotope dilution of H₂¹⁸O. We compiled data from three HDBR campaigns, one on women (n=8) in November 1998 and two on the same men (n=8) in December 1997 (without countermeasure) and January 1998 (with thigh-cuffs countermeasure), according to a crossover design. Body composition was assessed before and after 6 days of HDBR. %BF was derived from the biceps, triceps, sub-scapular and sup-iliac ST according to Durnin and Wormersly (1974). Fat-free mass was measured on the same day by H₂¹⁸O dilution and fat mass was calculated by the difference with body mass and expressed as a percentage. Based on precision tests, the minimum measurable change by ST was 1.1%BF for single measurement point. Both intercepts (F _4,30=0.89, P=0.45) and slopes (F _4,30=0.74; P=0.57) of the ST versus dilution relationships were not affected by the periods (December vs January), experimental conditions (control vs HDBR vs HDBR + thigh cuffs) or sex allowing the derivation of a common relationship %BF_st=0.94 × %BF_dil (F _1,47=97.9, P<0.0001; non-significant intercept excluded) with a bias between methods of −1.7±2.0 %BF (95% CI: −5.8, 2.4 %BF). ST can be used to measure %BF during HDBR provided great care is placed on training and changes are higher than 1.1 %BF. If the method can be applied for in-flight energy balance monitoring given the high observed energy deficit, a tight monitoring of the individual nutritional status as needed during simulation appears, however, dubious based on this solely method.     

The role of 5-hydroxytryptophan (5-HTP) in the regulation of the sleep/wake cycle in parachlorophenylalanine (p-CPA) pretreated rat: a multiple approach study

Summary In the rat, the insomnia which follows the administration of parachlorophenylalanine (p-CPA), a serotonin synthesis inhibitor, is transiently reversed either by intra-cisternal injection of L-5-HTP or by an associated injection of 5-HTP and an L-aromatic-aciddecarboxylase inhibitor (benserazide). Histochemical, immunohistochemical and chemical investigations showed that 5-HTP administration does not lead to a detectable increase in cerebral 5-HT. These findings suggest that the restoration of sleep after p-CPA treatment could be mediated by the central action of 5-HTP.     

Dietary docosahexaenoic acid-enriched phospholipids normalize urinary melatonin excretion in adult (n-3) polyunsaturated fatty acid-deficient rats.

Melatonin (MEL) plays an essential role in physiologic functions associated with darkness. We examined the effects of docosahexaenoic acid (DHA)-enriched phospholipids from pig brains (BPL) or hen eggs (EPL), as sources of DHA, on lipid FA composition of pineal membranes and daytime and nighttime concentrations of 6-sulfatoxymelatonin (aMT6) in adult male control and (n-3)-deficient rats fed BPL and EPL diets for 5 wk. In two experiments, at 3 wk of age, rats were divided into subgroups and fed semipurified diets containing either peanut oil [(n-3)-deficient group] or peanut plus rapeseed oil (control group) and two dietary formulas containing either 3.5 g/100 g diet of BPL (Experiment 1) or 5.0 g/100 g diet of EPL (Experiment 2). BPL and EPL diets provided approximately 200 mg of DHA/100 g diet. During the daytime, aMT6 concentrations were not significantly different among groups. Conversely, the (n-3)-deficient rats had significantly lower nighttime aMT6 concentrations than the control rats. BPL and EPL did not affect urinary nighttime aMT6 concentration in the control group, whereas (n-3)-deficient + BPL or EPL groups exhibited significantly higher nighttime aMT6 concentrations than the (n-3)-deficient group (76 and 110%, respectively). The level of DHA was significantly higher in the pineal glands of control rats than in (n-3)-deficient rats. In rats fed EPL and BPL, the level of DHA reached a plateau, between 10 and 11 mg/100 mg total fatty acids in control + BPL or EPL and (n-3)-deficient + BPL or EPL groups. These findings suggest that new DHA-enriched formulas may be used as an efficient alternative source of (n-3) polyunsaturated fatty acids to normalize MEL secretion.