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INTRODUCTION: The maintenance of cerebral perfusion during shoulder surgery performed in the beach chair position is controversial. The aim of this report is to present the first case in Mexico of a total shoulder arthroplasty performed with interscalene block and monitoring of the cerebral oxygen saturation. This monitoring was described in 1977, but only until the last decade has it reached relevance from the clinical point of view. CLINICAL CASE: We present an 84-year-old patient scheduled for total shoulder arthroplasty in beach chair position under regional anesthesia (ultrasound-guided interscalene block) in which the regional oxygen saturation (CrSO2) was monitored. DISCUSSION: Monitoring of cerebral oximetry is a suitable tool that allows us to have a continuous assessment throughout the transanesthetic, so we can make decisions more expeditiously. On this basis, we believe that this type of monitoring should be fundamental in patients placed in a beach chair position, as well as predominantly use regional anesthesia. In cases where it cannot be used, this monitor is absolutely essential.

INTRODUCCIÓN: Desde hace algún tiempo es tema de controversia el mantenimiento de la perfusión cerebral durante la cirugía de hombro realizada en posición de silla de playa. El objetivo de este reporte es presentar el primer caso en México de una artroplastía total de hombro realizada con bloqueo interescalénico y monitoreo de la saturación cerebral de oxígeno. Este monitoreo se describió en 1977, pero sólo hasta la última década ha alcanzado relevancia desde el punto de vista clínico. CASO CLÍNICO: Paciente de 84 años programado para artroplastía total de hombro en posición de silla de playa bajo anestesia regional tipo bloqueo interescalénico guiado por ultrasonido, en la cual se monitoreó la saturación regional de oxígeno (CrSO2). DISCUSIÓN: El monitoreo de la oximetría cerebral es una herramienta adecuada que nos permite tener una valoración continua durante todo el transanestésico, con lo que podemos tomar decisiones de forma más expedita. Con base en esto consideramos que este tipo de monitoreo debe ser básico en pacientes colocados en posición de silla de playa, así como el uso preponderante de anestesia regional; en los casos donde ésta no se pueda utilizar, este monitor es primordial.

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In this paper, we study the dependence of the Tm (melting temperature) of complexes formed between double-stranded deoxypolynucleotides and pure destabilizer nonspecific ligands on Kc (intrinsic association constant), nc (apparent site size), and wc (cooperativity constant). Using the Sequence Generating Function (SGF) method, we have found a simple, analytical relationship between the Tm and these interaction parameters. The validity of this relationship depends strongly on the sigma value (sigma being the nucleation parameter of the deoxypolynucleotide). Through the equation so obtained, it is possible to evaluate Kc, nc, and wc from the melting temperature of three experimental thermal denaturation profiles at different r (ligand/deoxypolynucleotide ratio) values. However, when wc greater than 100, a degeneration in the wc and Kc values appears, and the study of the free deoxypolynucleotide region in the melting profile is necessary in order to accurately evaluate these two parameters. The method has been checked using complexes formed with poly(d(A-T].poly(d(A-T] and both bovine pancreatic ribonuclease and protein GP32 of phage T4 as experimental models. The applicability of the method here developed is discussed in relation to the nature of the ligands and the sigma and wc values.

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We have studied the interaction of the isolated C-terminal domain of histone H1 with linear DNA using precipitation curves and electron microscopy. The C-terminal domain shows a salt-dependent transition towards cooperative binding, which reaches completion at 60 mM NaCl. At this salt concentration, the C-terminal domain binds to some of the DNA molecules, leaving the rest free. A binding site of 22 base-pairs can be calculated from the stoichiometry of the precipitated fractions. The C-terminal domain condenses the DNA in toroidal particles. The average inner radius of the particles is of the order of 195 A. Consideration of the value of the inner radius of the toroids in the light of counterion condensation theory suggests that in these complexes the isolated C-terminal domain is capable of nearly full electrostatic neutralization of the DNA phosphate charge.

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In this paper we have studied the kinetics of psi-DNA structure formation induced by H1 and H1 peptides containing the C-terminal domain, namely the CTB peptide, obtained by thrombin digestion, and the CNBS peptide, derived from N-bromosuccinimide treatment of H1. The time course for the formation of the psi structure has been followed by measuring the changes in ellipticity at 270 nm as a function of time under different experimental conditions. In all cases studied here, we have observed the existence of two elementary processes: one fast, the other slow. Kinetic experiments performed with high molecular weight DNA showed that the greater the salt concentration, the higher was the apparent rate of psi structure formation. In complexes formed with sonicated DNA and H1, CNBS and CTB, we observed that the greater the content of the C-terminal domain, the higher was the apparent rate at which the final psi structure was reached. Thus, the presence of increasing amounts of either salt or C-terminal domain facilitates the formation of the psi structure. The molecular basis for these phenomena is discussed. The influence of the order of addition of the different components of the complex on the kinetics of psi structure induction is also studied.

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We have semiempirically studied the thermal denaturation profiles of complexes formed between double strand polynucleotides and pure stabilizer nonspecific binding ligands. By using the McGhee model (J. D. McGhee, (1976) Biopolymers 15, 1345-1375) we have found a simple, analytical relationship between the melting temperature (Tm) and the Kh (intrinsic association constant), nh (apparent site size), and wh (cooperativity constant) values of the interaction. The validity of this approach strongly depends on the sigma value (sigma being the nucleation parameter of the DNA). Through the equation so obtained it is possible to calculate the Kh, nh, and wh values from the melting temperature of three experimental thermal denaturation profiles at different r (ligand/polynucleotide ratio) values. The method has been checked by studying the thermal denaturation profiles of daunomycin-poly(d(A-T)).poly(d(A-T)) complexes in two different salt concentrations. The results so obtained are compared with those previously described using other techniques. The applicability of the method here developed is discussed in relation with both the nature of the ligands and the value of the nucleation parameter (sigma).

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We have studied the interactions of the high-mobility-group-like proteins (C1a1, C1a2 and C1b) from the fruit fly Ceratitis capitata with DNA. Nitrocellulose filter binding assays, thermal denaturation studies and spectrofluorimetry of the complexes revealed the existence of specific and nonspecific interactions. Thermal denaturation curves showed that the three proteins stabilized the DNA, thus suggesting a preferential binding to double-stranded DNA. The calculation of the thermodynamic parameters of the interactions showed that the nonspecific bindings were characterized by low association constants (Ka) with values ranging from 2.7 X 10(4) M-1 to 2.0 X 10(6) M-1. Also, the cooperativity of these interactions was relatively high (cooperativity factor, w, values ranging over 20-35), and the number of nucleotides involved was low (1-3 base pairs). On the other hand, the existence of specific interactions between C1 proteins and DNA was suggested by two facts: the retention of C. capitata [3H]DNA in nitrocellulose filters was only a low percentage of total input DNA and there was a marked size dependence of the binding (25% retention of a 40-kb DNA and only 3% retention with a DNA of 1 kb). The specific bindings had higher Ka values than the nonspecific ones, and they also were cooperative. Some differences were observed between C1b and the C1a proteins about the way they interact with C. capitata DNA.

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