Biomedical subjects

M Farach

Publications and source records attributed to M Farach.

4 recordsLinked to original sources

PubMed1998

[The evaluation of patients with ischemic cerebral lesions by CT, SPECT and qEEG in acute, subacute and chronic phases].

INTRODUCTION: SPECT, EEG AND CT scan offer information with several pathophysiologic meanings. Their results vary with time and according to the vascular affected territory. OBJECTIVE: We wanted to study how the sensibility varies and the relationship with the clinic of SPECT, qEEG and CT scan in the acute, subacute and chronic stages and according to the vascular affected territory. We also wanted to analyze the several pathophysiologic aspects of the cerebral ischemia. METHODS: Thirty-six patients with symptoms of hemispheric stroke were evaluated with CT scan, qEEG, SPECT99mTc-HMPAO during the acute (0-5 days), subacute (0-15 days) and chronic (16 days to 1 year) stages. RESULTS: The decrease of ipsilateral CBF depend on the time (p = 0.0061), being not very frequent during the two first weeks. The qEEG was the most sensitive study in the first phase, its sensibility did not depend on the vascular affected territory and was dependent on the time (p = 0.0011), diminishing in the chronic phase. The slow activity was habitually ipsilateral. The CT scan was the less sensitive study. CONCLUSION: After 24 hours and until the second week, there is habitually an increase of the ipsilateral rCBF. The luxury perfusion could explain the fogging effect in the CT scan. The slow activity of the qEEG represents the alteration of the oxygen metabolism. The interpretation of the variation of the CBF and the qEEG allow us to define oligemia of the ischemia and between reactive hyperemia and the increase of CBF due to the necrotic tissue.

Acute Disease↗

PubMed1997

Recognizing circular decomposable metrics.

Circular decomposable metrics (CDMs) have been used in phylogenetic studies. The fastest algorithm for recognizing a CDM runs in time O(n5), given an n x n table of pairwise distances. We give an O(n2) time algorithm for this problem.

Algorithms↗

PubMed1997

Local rules for protein folding on a triangular lattice and generalized hydrophobicity in the HP model.

We consider the problem of determining the three-dimensional folding of a protein given its one-dimensional amino acid sequence. We use the HP model for protein folding proposed by Dill (1985), which models protein as a chain of amino acid residues that are either hydrophobic or polar, and hydrophobic interactions are the dominant initial driving force for the protein folding. Hart and Istrail (1996a) gave approximation algorithms for folding proteins on the cubic lattice under the HP model. In this paper, we examine the choice of a lattice by considering its algorithmic and geometric implications and argue that the triangular lattice is a more reasonable choice. We present a set of folding rules for a triangular lattice and analyze the approximation ratio they achieve. In addition, we introduce a generalization of the HP model to account for residues having different levels of hydrophobicity. After describing the biological foundation for this generalization, we show that in the new model we are able to achieve similar constant factor approximation guarantees on the triangular lattice as were achieved in the standard HP model. While the structures derived from our folding rules are probably still far from biological reality, we hope that having a set of folding rules with different properties will yield more interesting folds when combined.

Algorithms↗

PubMed1997

Numerical taxonomy on data: experimental results.

We consider the problem of fitting an n x n distance matrix D by a tree metric T. This problem is NP-hard for most reasonable distance functions between D and T. Recently, an approximation algorithm was presented (Agarwala et al., 1996) which achieves a factor of 3 approximation to the L infinity best fitting tree. We call this method the Single Pivot (SP) heuristic. Within the biology community, the so-called Neighbor-Joining (NJ) heuristic (Saitou and Nei, 1987) has wide acceptance. In this paper, we introduced a new Double Pivot (DP) heuristic, which is an extension of the SP heuristic, and show that DP outperforms NJ on biological and random data.

Classification↗