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PubMed1995

Ligand-induced changes in the conformational stability of bovine trypsinogen and their implications for the protein function.

Bovine trypsinogen was used as a model protein for studying changes in the conformational stability induced by pH or binding of the calcium ion. Spectrophotometrically monitored thermal unfolding of trypsinogen and beta-trypsin in the acidic pH range yielded substantial differences in the stability parameters. Compared to beta-trypsin, trypsinogen exhibits lower enthalpy of denaturation delta Hden, higher denaturational heat capacity change delta Cp,den, but very similar temperature of denaturation Tden. pH-dependence of the conformational stability of the ligand-free trypsinogen, measured also by GdnCl-induced unfolding, is bell shaped with the maximum free energy of unfolding delta Gden = 10.9 kcal/mole at pH 5.5 (4.5 pH units below its isoelectric point). At pH 8.3 the conformational stability of the zymogen drops to delta Gden = 3.2 kcal/mole, but increases by delta delta Gden = 6.1 kcal/mole in the presence of Ca2+. This significant stabilization of the zymogen by the calcium ion is also pH-dependent. To assess the effect of Ca2+ on the trypsinogen molecule, the spectrophotometric titrations and NOESY spectra were carried out. Based on the structural analysis, the long range effects between Ca2+-->Ile73-->Trp141 and the interdomain His40-Asp194 ion pair are proposed to be partially responsible for trypsinogen stabilization. Additionally, the steady-state parameters for hydrolysis of the oligopeptide amide substrate catalysed by free trypsinogen, its complexes with Ca2+ and the IleVal dipeptide and by beta-trypsin were measured. It appears that in the pH range 5.5 to 8.3 the stability and the catalytic activity/ligand binding properties are fully separated. Whereas the deprotonation of His57 accounts for the increase of kcat/km parameter, deprotonation of His40 is involved in the huge decrease of the conformational stability. Similarly, a large stabilization by the calcium ion is not accompanied by changes in enzymatic activity. Presented data are encouraging for an enzyme design directed toward improved stability.

Animals↗
PubMed1988

Goal-directed vestibulo-ocular function in man: gaze stabilization by slow-phase and saccadic eye movements.

Vestibular function was examined during passive head movements having profiles that approximated low-to-intermediate range of natural self-generated movements (10-220 degrees/s peak velocity, about 0.5 s duration). A seated subject looked at a point target on the wall, the lights were extinguished and the chair was briefly turned while the subject tried to "look" at the just-viewed point. The chair was stopped, the lights were turned on again and the target was re-fixated, if necessary. Ocular stabilization was characterized (1) by "net stabilization" that was due to the combined effects of both slow-phase and rapid (saccadic or quick-phase) eye movements, (2) by "cumulative-slow-phase stabilization" that was due to slow-phase eye movements, and (3) by "cumulative-saccadic stabilization" that was due to effects of all rapid eye movements. It was found that both slow-phase and saccadic eye movements tended to keep the eyes on the actual unseen target. During repeatedly applied head movements, net and cumulative-slow-phase stabilization tended to be almost perfect. However, the average magnitude of the error in net stabilization (i.e., deviation from perfection) was always less than the corresponding error in slow-phase stabilization. This occurred because in a given turn, saccadic movements tended to supplement deficient slow-phase movements and to decrement excessive slow-phases. In 4 of 5 subjects, cumulative-saccadic stabilization tended to equal the error in cumulative-slow-phase stabilization. All results were unaffected by head velocities up to +/- 220 degrees/s. It was concluded that these saccades tended to stabilize gaze (eye + head) in space during head movements in total darkness.

Eye Movements↗
PubMed1989

mRNA stabilizing signals encoded in the genome of the bacteriophage phi x174.

In Escherichia coli cells infected with bacteriophage phi x174, mRNAs initiated by promoters PB and PD terminate after genes J, F, G, or H (TJ, TF, TG, or TH). These RNAs are relatively stable and contain mRNA-stabilizing signals at their 3' ends. These signals were cloned after gene D of phi x174 in an expression vector plasmid. The cloned signals stabilize mRNA of the upstream gene D and the stabilized mRNA is translationally functional. When these signals are inserted in reverse, no stabilizing effect on mRNA is observed indicating that the correct sequences at the 3' ends of transcripts determine their stability. When a stabilizing signal (+) and a mutated stabilizing signal (-) which has reduced stabilizing activity are tandemly inserted after gene D, two sets of 3' termini of the transcript are observed indicating that both signals also function as terminators. The amount of gpD synthesized from these constructs varies depending upon the relative positions of the (+) or (-) signals after gene D. The stabilizing function seems to act by preventing mRNA degradation from the 3' to 5' direction. Several common features of these stabilizers are described.

Bacteriophage phi X 174↗
PubMed1986

Stability of teacher temperament ratings over 6 and 12 months.

Six and 12-month stability of teacher ratings of temperament was studied in four samples. For the two samples retested after a 6-month interval, the same teacher provided the original and retest ratings. For the two samples retested after a 12-month interval, different teachers provided the retest ratings than provided the original ratings. Four indices of stability were investigated for each sample: cross-rank stability, within-person stability , absolute score stability, and factorial stability. Factorial stability was demonstrated for all samples. For the other three indices of stability, 6-month stability was moderate to high, and significantly higher than the 12-month stability. The general pattern of results is comparable to temperament rating data from parents, with specific coefficients being somewhat higher.

Child↗
PubMed1989

Stabilization of halophilic malate dehydrogenase.

Malate dehydrogenase from the extreme halophile, Halobacterium marismortui, is stable only in highly concentrated solutions of certain salts. Previous work has established that its physiological environment is saturated in KCl; it remains soluble is saturated NaCl or KCl solutions; also it unfolds in solutions containing less than 2.5 M-NaCl or -KCl, salt concentrations which are still relatively high. New data show that the structure of this enzyme can be stabilized in a range of high concentrations of Mg2+ or other "salting-in" ions, also with exceptional protein-solvent interactions. "Salting-in" ions, contrary to stabilizing protein structure, usually favour unfolding. These, and most other results concerning the structure, stability and solvent interactions of the protein cannot be understood in terms of the usual effects of salts on protein structure. In this paper, a novel stabilization model is proposed for halophilic malate dehydrogenase that can account for all observations so far. The model results from experiments on the protein in salt solutions chosen for their different effects on protein stability (potassium phosphate, a strongly "salting-out" agent, and MgCl2, which is "salting-in"), and previously published data from NaCl and KCl solutions (mildly "salting-out"). Enzymic activity and stability measurements were combined with neutron scattering, ultracentrifugation and quasi-elastic light-scattering experiments. The analysis showed that the structure of the protein in solution as well as the dominant stabilization mechanisms were different in different salt solutions in which this enzyme is active. Thus, in molar concentrations of phosphate ions, stabilization and hydration are similar to those of non-halophilic soluble proteins, in which the hydrophobic effect dominates. In high concentrations of KCl, NaCl or MgCl2, on the other hand, solution particles are formed in which the protein dimer interacts with large numbers of salt and water molecules (the mass of solvent molecules involved depends on the nature of the salt but it is approximately equivalent to the protein mass). It is proposed that, under these conditions, the hydrophobicity of the protein core is too weak to stabilize the folded structure and the main stabilization mechanism is the formation of co-operative hydrate bonds between the protein and hydrated salt ions. Model predictions are in agreement with all experimental results, such as the different numbers of solvent molecules found in the solution particles formed with different salts, the loss of the exceptional solvent interactions concomitant with unfolding at non-physiological salt concentrations, and the different temperature denaturation curves observed for different salt solutions.(ABSTRACT TRUNCATED AT 400 WORDS)

Buffers↗
PubMed1994

Plasmid stability and ecological competence in recombinant cultures.

The instability of cell cultures containing plasmid vectors is a major problem in the commercial exploitation of molecular cloning techniques. Plasmid stability is influenced by the nature of the host cell, the type of plasmid and/or environmental conditions. Plasmid encoded properties may confer a selective advantage on the host cell but can be an energy drain due to replication and expression. Stability of recombinant cultures ultimately may be determined by the cost to benefit ratio of plasmid carriage. The relative competition between plasmid containing and plasmid-free or indigenous populations can determine the degree of dominance of recombinant cultures. The use of inocula in biotechnological processes in which dynamic environmental conditions dominate may also result in instabilities resulting from the characteristics of the ecosystem. In such dynamic conditions plasmid stability is just one contribution to culture stability. Strategies to enhance plasmid stability, within such environments, based on manipulation of physiological state of host cells, must consider the responsiveness or plasticity of both cells and populations. The robustness of cells or the responses to stresses or transient environmental conditions can influence the levels of instability detected; for example, instability or mutation in the host genome may lead to enhanced plasmid stability. Competition among subpopulations arising from unstable copy number control may determine the levels of recombinant cells in open versus closed fermenter systems. Thus the ecological competence (ability to survive and compete) of recombinant cells in dynamic or transient environments is fundamental to the understanding of the ultimate dominance or survival of such recombinant cultures and may form the basis of a strategy to enhance or control stability either in fermenter systems or dynamic process environments. The creation of microniches in time and/or space can enhance plasmid stability. Transient operation based on defined environmental stresses or perturbations in fermenter systems or in heterogeneous or dynamic environments found in gel immobilized cultures have resulted in enhanced stability. Spatial organization resulting from immobilization has the additional advantage of regulated cell protection within defined microenvironments and controlled release, depending on the nature of the gel, from these microenvironments or microcosms. This regulation of ecological competence allied to the advantages of microbial cell growth in gel microenvironments combined with the spatial organization (or juxtapositioning of cells, selective agents, nutrients, protectants, etc.) possible through immobilization technology offers new strategies to enhance plasmid and culture stability.

Journal Article↗
PubMed2005

PKCalpha is involved in phorbol ester TPA-mediated stabilization of p14ARF.

We generated A21-13 cells expressing p14(ARF) in the presence of doxycycline in order to examine the stability of p14(ARF) protein. The effects of proteasome inhibitor MG132 on p14(ARF) protein stabilization were detectable using our experimental procedure. Introduction of mutant p53 did not affect MG132-mediated p14(ARF) protein stabilization. We found that phorbol ester TPA (12-o-tetradecanoyl-phorbol 13-acetate) stabilized p14(ARF) protein and that p53 status had no effect on TPA-mediated stabilization. TPA-mediated stabilization was abolished by staurosporine but not by lovastatin or U0126. We further investigated which isoforms of PKC were involved in TPA-mediated p14(ARF) stabilization using short-interference RNA. Knockdown of PKCalpha, but not PKCdelta, attenuated TPA-mediated p14(ARF) stabilization. These findings suggest that PKCalpha is involved in TPA-mediated stabilization of p14(ARF) protein, and this effect of TPA was not affected by the Ras/MAPK pathway or p53 status. Our results are indicative of a novel role of PKC in p14(ARF) protein stability.

Butadienes↗
PubMed2005

Influence of cortical bone thickness and implant length on implant stability at the time of surgery--clinical, prospective, biomechanical, and imaging study.

This clinical study is the first to quantitatively evaluate both regional bone structure by computed tomography preoperatively and dental implant stability by resonance frequency analysis at the time of surgery to explore the relation between local bone structure and dental implant stability in humans. Implant stability at the time of installation is often difficult to achieve in lower density bone and implant stability might influence treatment efficacy. Few clinical studies have reported detailed bone characteristics obtained using computed tomography prior to surgery and comprehensive implant stability measurements at the time of surgery. We hypothesized that thicker cortical bone would improve the stability of the dental implant at the time of placement. Before radiographic examination, diagnostic radiographic templates were made by incorporating radiopaque indicators. Computed tomography scans were obtained for 50 edentulous subjects prior to surgery. Preoperatively, the thickness of the cortical bone at the sites of implant insertion was measured digitally, and then implant insertion surgery was performed. A total of 225-implant stability measurements were made using a resonance frequency analyzer. There was a strong linear correlation between cortical bone thickness and resonance frequency (r = 0.84, P < 0.0001). The implant length had a weak negative correlation with stability (r = -0.25, P < 0.0005). These results suggest that the initial stability at the time of implant installation is influenced more by cortical bone thickness than by implant length. The cortical and cancellous ratio of local bone is extremely important for implant stability at the time of surgery and determining the local bone condition is critical for treatment success.

Adult↗
PubMed2005

Muscle force-stiffness characteristics influence joint stability: a spine example.

BACKGROUND: The muscle force-stiffness relationship has often been modeled as linear, while in situ muscle research has clearly demonstrated non-linearity. Estimation of rotational joint stability relies on both a muscle's instantaneous pre-perturbation force and stiffness. Under conditions of static equilibrium, a muscle's stiffness will function in a stabilizing manner, while its force can function in either a stabilizing or destabilizing manner depending on the muscle's orientation about the joint. METHODS: A single muscle (rectus abdominis) was modeled and its individual direct stabilizing potential about the L4-L5 spine joint was analyzed. Three force-stiffness relationships were examined: (1) linear; (2) non-linear with moderate stiffness magnitudes; (3) non-linear with higher stiffness magnitudes. FINDINGS: With a linear force-stiffness relationship, stability increased proportional to muscle force; with a non-linear relationship, stability peaked and subsequently decreased at submaximal muscle forces. When considering the lower, as opposed to the higher non-linear stiffness magnitudes, the stabilizing potential of the muscle peaked at a lower muscle force level and actually became negative (destabilizing) at a critical stiffness magnitude. INTERPRETATION: It was concluded that a non-linear muscle force-stiffness relationship greatly alters the individual stabilizing potential of the muscle throughout its progression of force development. A muscle's stabilizing contribution may actually peak at and subsequently decrease above a critical submaximal force level. Incorporating this knowledge into stability models may assist in recognizing unstable events that lead to injury at higher levels of muscle activation.

Biomechanical Phenomena↗
PubMed2006

DNA stability in the gas versus solution phases: a systematic study of thirty-one duplexes with varying length, sequence, and charge level.

We report herein a systematic mass spectrometric study of a series of thirty-one non-self-complementary, matched, DNA duplexes ranging in size from 5- to 12-mers. The purpose of this work is threefold: (1) to establish the viability of using mass spectrometry as a tool for examining solution phase stabilities of DNA duplexes; (2) to systematically assess gas-phase stabilities of DNA duplexes; and (3) to compare gas and solution phase stabilities in an effort to understand how media affects DNA stability. These fundamental issues are of importance both on their own, and also for harnessing the potential of mass spectrometry for biological applications. We have found that ion abundances do not always track with solution phase stability; GC content must be taken into account. Two duplexes with the same Tm yet with differing GC content can yield different ion abundances. That is, if two duplexes have the exact same melting temperature, yet one has a higher GC content, the duplex with the higher GC content yields a higher ion abundance. It thus appears that not only is a GC base pair stronger than an AT base pair, but the relative strengths of each differ in the gas phase versus in solution, such that the electrospray process can differentiate between them. We also characterize the gas-phase stabilities of the duplexes, using collision-induced dissociation (CID) as a method to assess stability. We focus on two aspects of this CID experiment. One, we examine what factors appear to control whether the duplexes dissociate into single strands or covalently fragment; we are able to utilize a charge state normalization we coin "charge level" to compare our results with others' and establish generalities regarding dissociation versus fragmentation patterns. Two, we examine those duplexes that primarily dissociate and use CID to assess the gas-phase stabilities. We find that correlation of gas-phase to solution-phase stabilities is more likely to occur when duplexes of varying GC content are examined. Duplexes with the same GC content tend to have stabilities that do not parallel those in solution. We discuss these results in light of the different roles that hydrogen bonding and base stacking play in solution versus the gas phase. Ultimately, we apply what we learn to lend insight into the biological problem of how the carcinogenic, damaged nucleobase O6-methylguanine causes mutations.

Chemical Phenomena↗
PubMed2004

Mechanical and metabolic requirements for active lateral stabilization in human walking.

Walking appears to be passively unstable in the lateral direction, requiring active feedback control for stability. The central nervous system may control stability by adjusting medio-lateral foot placement, but potentially with a metabolic cost. This cost increases with narrow steps and may affect the preferred step width. We hypothesized that external stabilization of the body would reduce the active control needed, thereby decreasing metabolic cost and preferred step width. To test these hypotheses, we provided external lateral stabilization, using springs pulling bilaterally from the waist, to human subjects walking on a force treadmill at 1.25 m/s. Ten subjects walked, with and without stabilization, at a prescribed step width of zero and also at their preferred step width. We measured metabolic cost using indirect calorimetry, and step width from force treadmill data. We found that at the prescribed zero step width, external stabilization resulted in a 33% decrease in step width variability (root-mean-square) and a 9.2% decrease in metabolic cost. In the preferred step width conditions, external stabilization caused subjects to prefer a 47% narrower step width, with a 32% decrease in step width variability and a 5.7% decrease in metabolic cost. These results suggest that (a). human walking requires active lateral stabilization, (b). body lateral motion is partially stabilized via medio-lateral foot placement, (c). active stabilization exacts a modest metabolic cost, and (d). humans avoid narrow step widths because they are less stable.

Adult↗
PubMed2006

The effects of sensory loss and walking speed on the orbital dynamic stability of human walking.

Peripheral sensory feedback is believed to contribute significantly to maintaining walking stability. Patients with diabetic peripheral neuropathy have a greatly increased risk of falling. Previously, we demonstrated that slower walking speeds in neuropathic patients lead to improved local dynamic stability. However, all subjects exhibited significant local instability during walking, even though no subject fell or stumbled during testing. The present study was conducted to determine if and how significant changes in peripheral sensation and walking speed affect orbital stability during walking. Trunk and lower extremity kinematics were examined from two prior experiments that compared patients with significant neuropathy to healthy controls and walking at multiple different speeds in young healthy subjects. Maximum Floquet multipliers were computed for each time series to quantify the orbital stability of these movements. All subjects exhibited orbitally stable walking kinematics, even though these same kinematics were previously shown to be locally unstable. Differences in orbital stability between neuropathic and control subjects were small and, with the exception of knee joint movements (p=0.001), not statistically significant (0.380p0.946). Differences in knee orbital stability were not mediated by differences in walking speed. This was supported by our finding that although orbital stability improved slightly with slower walking speeds, the correlations between walking speed and orbital stability were generally weak (r(2)16.7%). Thus, neuropathic patients do not gain improved orbital stability as a result of slowing down and do not experience any loss of orbital stability because of their sensory deficits.

Algorithms↗
PubMed2004

Rational engineering of enzyme stability.

During the past 15 years there has been a continuous flow of reports describing proteins stabilized by the introduction of mutations. These reports span a period from pioneering rational design work on small enzymes such as T4 lysozyme and barnase to protein design, and directed evolution. Concomitantly, the purification and characterization of naturally occurring hyperstable proteins has added to our understanding of protein stability. Along the way, many strategies for rational protein stabilization have been proposed, some of which (e.g. entropic stabilization by introduction of prolines or disulfide bridges) have reasonable success rates. On the other hand, comparative studies and efforts in directed evolution have revealed that there are many mutational strategies that lead to high stability, some of which are not easy to define and rationalize. Recent developments in the field include increasing awareness of the importance of the protein surface for stability, as well as the notion that normally a very limited number of mutations can yield a large increase in stability. Another development concerns the notion that there is a fundamental difference between the "laboratory stability" of small pure proteins that unfold reversibly and completely at high temperatures and "industrial stability", which is usually governed by partial unfolding processes followed by some kind of irreversible inactivation process (e.g. aggregation). Provided that one has sufficient knowledge of the mechanism of thermal inactivation, successful and efficient rational stabilization of enzymes can be achieved.

Biotechnology↗
PubMed2005

Stabilization of the cold shock protein CspB from Bacillus subtilis by evolutionary optimization of Coulombic interactions.

The bacterial cold shock proteins (Csp) are used by both experimentalists and theoreticians as model systems for analyzing the Coulombic contributions to protein stability. We employ Proside, a method of directed evolution, to identify stabilized variants of Bs-CspB from Bacillus subtilis. Proside links the increased protease resistance of stabilized protein variants to the infectivity of a filamentous phage. Here, three cspB libraries were used for in vitro selections to explore the stabilizing potential of charged amino acids in Bs-CspB. In the first library codons for nine selected surface residues were partially randomized, in the second one random mutations were introduced non-specifically by error-prone PCR, and in the third one the spontaneous mutation rate of the phage in Escherichia coli was used. Stabilizing mutations were found at the surface positions 1, 3, 46, 48, 65, and 66. The contributions of these mutations to stability were characterized by analyzing them individually and in combination. The best combination (M1R, E3K, K65I, and E66L) increased the midpoint of thermal unfolding of Bs-CspB from 53.8 to 85.0 degrees C. The effects of most mutations are strongly context dependent. A good example is provided by the E3R mutation. It is strongly stabilizing (DeltaDeltaGD=11.1kJ mol(-1)) in the wild-type protein, but destabilizing (DeltaDeltaGD=-4.0kJ mol(-1)) in the A46K/S48R/E66L variant. The stabilizations by charge mutations did not correlate well with the corresponding changes in the protein net charge, and they could not be ascribed to the formation of ion pairs. Previous theoretical analyses did not identify the stabilization caused by the mutations at positions 1, 46, and 48. Also, electrostatics calculations based on protein net charge or charge asymmetry did not predict well the stability changes that occur when charged residues in Bs-CspB are mutated. It remains a challenge to model the Coulombic interactions of charged residues in a protein and to determine their contributions to the Gibbs free energy of protein folding.

Bacillus subtilis↗
PubMed2001

Shared dynamics of attentional cost and pattern stability.

This paper examines the informational activity devoted by the CNS to couple oscillating limbs in order to sustain and stabilize bimanual coordination patterns. Through a double-task paradigm associating a bimanual coordination task and a reaction time (RT) task, we investigated the relation between the stability of preferred bimanual coordination patterns and the central cost expended by the CNS for their stabilization. Ten participants performed in-phase and anti-phase coordination patterns in a dual task condition (coordination + RT) at several frequencies (0.5, 0.75, 1.0, 1.5, and 2.0 Hz), thereby decreasing the stability of the bimanual patterns. Results showed a U-shaped evolution of pattern stability and attentional cost, as a function of oscillation frequency, exhibiting a minimum value at the same frequency. These findings indicate that central cost and pattern stability covary and may share common, high order dynamics. Moreover, the attentional focus given to the bimanual coordination and the RT task was also manipulated by requiring either shared attention or priority to the coordination task. Such a manipulation led to a tradeoff between pattern stability and RT performance: The more stable the pattern, the more costly it is to stabilize. This suggests that stabilizing a coordination pattern incurs a central cost that depends on its intrinsic stability. Conceptual consequences of these results for understanding the relationship between attention and coordination are drawn, and the mechanisms putatively at work in dual tasks are discussed.

Adult↗
PubMed1997

Functional stability limits while holding loads in various positions.

Stability of the body during manual material handling is an important issue in the prevention of falls and over-exertion injuries. This research investigated stability limits while standing and holding loads in different positions relative to the body. Theoretically, the stability region is the full base of support defined by the perimeter of the foot contact area. However, the functional stability region may be smaller. The purpose of this study was to locate functional stability limits with respect to the base of support. Fifteen male subjects leaned as far as possible in four directions in the sagittal and frontal planes. Their center of gravity location at these extremes determined the stability limit. The results showed that functional stability limits reached only about 60% of the distance to the maximum base of support limits under the conditions of this study. The sway angles reached at the stability limits averaged 9.2 degrees anteroposteriorly and 15.3 degrees laterally. External load positions which lowered the center of gravity of the body-and-load system extended those stability limits. This study provides a postural stability perspective of load-holding which may be applied in establishing safe lifting and reach limits.

Accident Prevention↗
PubMed2002

Relative contribution of trunk muscles to the stability of the lumbar spine during isometric exertions.

OBJECTIVE: To compare the relative contribution of various trunk muscles to the stability of the lumbar spine. DESIGN: Quantification of spine stability with a biomechanical model. BACKGROUND: Modern low back rehabilitation techniques focus on muscles that stabilize the lumbar spine. However, the relative contribution of various trunk muscles to spine stability is currently unknown. METHODS: Eight male subjects performed isometric exertions in trunk flexion, extension, lateral bending, and axial rotation, and isometric exertions under vertical trunk loading and in a lifting hold. Each isometric trial was repeated three times at 20%, 40%, and 60% of the maximum trunk flexion force or with a load of 0%, 20%, 40%, and 60% of body weight for the latter two exertions. Surface EMG data from 12 major trunk muscles were used in the biomechanical model to estimate stability of the lumbar spine. A simulation of each trial was performed repeatedly with one of the 10 major trunk muscle groups removed from the model. RESULTS: Relative contribution of each muscle to spine stability was significantly affected by the combination of loading magnitude and direction (3-way interaction). None of the removed muscles reduced spine stability by more than 30%. CONCLUSIONS: A single muscle cannot be identified as the most important for the stability of the lumbar spine. Rather, spine stability depends on the relative activation of all trunk muscles and other loading variables. RELEVANCE: This study will improve our understanding of individual trunk muscles' contribution to overall stability of the lumbar spine.

Adult↗
PubMed1998

The effects of mechanical cardiac stabilization on left ventricular performance.

OBJECTIVE: Mechanical cardiac stabilization is beneficial for precise coronary anastomoses on the beating heart. However, the effect of mechanical cardiac stabilization on hemodynamics, left ventricular performance, and the degree of injury to underlying tissue are uncertain. METHODS: Twelve swine (20-30 kg) underwent median sternotomy and a mechanical stabilizing device (United States Surgical, Norwalk, CT) was positioned astride a segment of left anterior descending coronary artery (LAD). Coronary blood flow was measured by Doppler. Sonomicrometry crystals were placed distal to the stabilizer in a region of myocardium subtended by the LAD, and a left ventricular micromanometer was inserted. Regional myocardial function was determined using the preload recruitable stroke work (PRSW) relationship. Data were acquired at three time points: 20 min before (PRE) and after placing the stabilizer (EXPT); and 20 min after removing the stabilizer (POST). Tissue subjacent to the stabilizer was then biopsied. Means +/- standard deviation are reported. RESULTS: The mechanical stabilizer caused a decrease in cardiac output from 4.2+/-1.5 to 3.6+/-1.3 l/min (P < 0.05), which returned to baseline values after its removal. Regional myocardial function (percent systolic shortening and MW and x-intercept of the PRSW relationship) was unchanged. Blood pressure, heart rate, and LAD blood flow remained constant. Histologic findings included a layer of myocyte necrosis less than 1 mm in depth immediately beneath the stabilizer. CONCLUSIONS: These data demonstrate that mechanical stabilization of the LAD may temporarily decrease cardiac output. This is not attributed to impaired contractility or ischemia, but is secondary to direct ventricular compression with reduced stroke volume. Injury to underlying tissue is negligible.

Animals↗