A GENERALIZED LEAST SQUARES APPROACH TO BLIND SEPARATION OF SOURCES WHICH HAVE VARIANCE DEPENDENCIES

ABSTRACT We discuss the blind source separation problem where the sources are not independent but are dependent only through their variances. Some estimation methods have been proposed on this line. However, most of them require some additional assumptions, a parametric model for their dependencies or a temporal structure of the sources, for example. In this article, we propose a generalized least squares approach to the blind source separation problem in the general case where those additional assumptions do not hold

Effect of atherothrombotic aorta on outcomes of total aortic arch replacement

ObjectiveThe effect of an atherothrombotic aorta on the short- and long-term outcomes of total aortic arch replacement, including postoperative neurologic deficits, remains unknown. We evaluated this relationship and also elucidated the synergistic effect of multiple other risk factors, in addition to an atherothrombotic aorta, on the neurologic outcome.MethodsA group of 179 consecutive patients undergoing total aortic arch replacement were studied. An atherothrombotic aorta was present in 34 patients (19%), more than moderate leukoaraiosis in 71 (39.7%), and significant extracranial carotid artery stenosis in 27 (15.1%). In-hospital deaths occurred in 2 patients, 1 (2.9%) of 34 patients with and 1 (0.7%) of 145 patients without an atherothrombotic aorta (P = .26). Permanent neurologic deficits occurred in 4 (2.2%) and transient neurologic deficits in 17 (9.5%) patients. Multivariate analysis demonstrated that the risk factors for transient neurologic deficits were an atherothrombotic aorta (odds ratio, 4.4), extracranial carotid artery stenosis (odds ratio, 5.5), moderate/severe leukoaraiosis (odds ratio, 3.6), and cardiopulmonary bypass time (odds ratio, 1.02). To calculate the probability of transient neurologic deficits, the following equation was derived: probability of transient neurologic deficits = {1 + exp [7.276 − 1.489 (atherothrombotic aorta) − 1.285 (leukoaraiosis) − 1.701 (extracranial carotid artery stenosis) − 0.017 (cardiopulmonary bypass time)]}−1. An exponential increase occurred in the probability of transient neurologic deficits with presence of an atherothrombotic aorta and other risk factors in relation to the cardiopulmonary bypass time. Survival at 3 years after surgery was significantly reduced in patients with vs without an atherothrombotic aorta (75.0% ± 8.8% vs 89.2% ± 3.1%, P = .01).ConclusionsPatients with an atherothrombotic aorta and associated preoperative comorbidities might be predisposed to adverse short- and long-term outcomes, including transient neurologic deficits

Cellular biology of cryopreserved allograft valves

Although analyzing the precise mechanisms of cryopreserved allograft valve failure may be difficult due to a number of crucial reasons and the interrelationships between the overlapping mechanisms, there is some evidence that cryopreservation is currently the best method of storing allograft valves. The present review shows the basic cellular biology of cryopreserved allograft valves for long-term durability, particularly relevant to allograft valve cellular viability, the immune response mainly caused by viable donor cells, and the preservation and regeneration of the intrinsic extracellular matrix. The present findings are as follows. First, cryopreservation produces serious damage to cytosolic and mitochondrial functions of both endothelial cells and fibroblasts, which may cause valve failure after implantation. Second, although the collagen synthesis of cryopreserved valves was relatively maintained, total protein synthesis was highly diminished and the collagenolytic ability was activated immediately after the thawing process. These findings imply that the cryopreservation itself may cause the collagen metabolism to become degradable, which will lead to valve failure. Further examination of collagen metabolism and modulation of the collagenolytic activity will be necessary to improve the tissue preservation for improved clinical use

Plasticity of microvascular oxygenation control in rat fast-twitch muscle: effects of experimental creatine depletion

Aging, heart failure and diabetes each compromise the matching of O2 delivery (QO2)-to-metabolic requirements (O2 uptake, VO2) in skeletal muscle such that the O2 pressure driving blood-myocyte O2 flux (microvascular PO2, PmvO2) is reduced and contractile function impaired. In contrast, β-guanidinopropionic acid (β-GPA) treatment improves muscle contractile function, primarily in fast-twitch muscle (Moerland and Kushmerick, 1994). We tested the hypothesis that β-GPA (2% wt/BW in rat chow, 8 wk; n=14) would improve QO2-to-VO2 matching (elevated PmvO2) during contractions (4.5 V @ 1 Hz) in mixed (MG) and white (WG) portions of the gastrocnemius, both predominantly fast-twitch). Compared with control (CON), during contractions PmvO2 fell less following β-GPA (MG -54%, WG -26%, p<0.05), elevating steady-state PmvO2 (CON, MG: 10±2, WG: 9±1; β-GPA, MG 16±2, WG 18±2 mmHg, P<0.05). This reflected an increased QO2/VO2 ratio due primarily to a reduced VO2 in β-GPA muscles. It is likely that this adaptation helps facilitate the β-GPA-induced enhancement of contractile function in fast-twitch muscles