Downregulation of DNA topoisomerase I in old versus young human diploid fibroblasts.

DNA topoisomerase I (Topo I) is an enzyme that alters the superhelicity of DNA. It has been implicated in such critical cellular functions as transcription, DNA replication, and recombination. Roles for Topo I in DNA repair following DNA damage have also been studied extensively. In the present investigation, we examined the regulation of Topo I expression and activity during cellular replicative senescence. We found that the capacity of Topo I to relax supercoiled DNA molecules is significantly decreased in senescent diploid fibroblasts when compared to young (early passage) fibroblasts. We also found that the steady-state expression level of Topo I mRNA is correlated with enzyme activity, i.e., decreased in early vs. late passage cells. We also treated early and late passage cells with agents that may modulate the process of cellular senescence: UV light, retinoic acid, and interleukin-1 beta. We found that all three agents decreased the activity of Topo I in young fibroblasts and increased the activity of Topo I in senescent fibroblasts. This effect was most striking following exposure of the cells to retinoic acid, so to analyze this effect, we postulated an age-dependent kinetics of Topo I mRNA induction in response to retinoic acid. Consistent with this postulate, we found that whereas exposure of early passage cells to retinoic acid results, in a matter of hours, in a decrease in the expression of Topo I mRNA, exposure of the senescent cells to retinoic acid results in an increased expression. These observations suggest that processes that are altered in senescent fibroblasts, such as DNA replication and repair, may be due, in part, to alteration in the expression and activity of DNA Topo I.

Effects of head-down bed rest on complex heart rate variability: response to LBNP testing.

Head-down bed rest is used to model physiological changes during spaceflight. We postulated that bed rest would decrease the degree of complex physiological heart rate variability. We analyzed continuous heart rate data from digitized Holter recordings in eight healthy female volunteers (age 28-34 yr) who underwent a 13-day 6 degree head-down bed rest study with serial lower body negative pressure (LBNP) trials. Heart rate variability was measured on 4-min data sets using conventional time and frequency domain measures as well as with a new measure of signal "complexity" (approximate entropy). Data were obtained pre-bed rest (control), during bed rest (day 4 and day 9 or 11), and 2 days post-bed rest (recovery). Tolerance to LBNP was significantly (P < 0.02) reduced on both bed rest days vs. pre-bed rest. Heart rate variability was assessed at peak LBNP. Heart rate approximate entropy was significantly (P < 0.05) decreased at day 4 and day 9 or 11, returning toward normal during recovery. Heart rate standard deviation and the ratio of high- to low-power frequency did not change significantly. We conclude that short-term bed rest is associated with a decrease in the complex variability of heart rate during LBNP testing in healthy young adult women. Measurement of heart rate complexity, using a method derived from nonlinear dynamics ("chaos theory"), may provide a sensitive marker of this loss of physiological variability, complementing conventional time and frequency domain statistical measures.

Two-dimensional electrophoretic profile of human sperm membrane proteins.

The purpose of this study was to characterize highly enriched human spermatozoa membrane proteins by two-dimensional electrophoresis and computer image analysis. Sperm membrane proteins were extracted by detergent solubilization from three different preparations: 1) washed semen cells following centrifugation and three wash steps in Ham's F-10 medium (the standard sperm preparation, which is contaminated with seminal immature germ cells, white blood cells, and acellular material), 2) the motile sperm fraction following centrifugation of diluted semen cells through a Percoll density gradient to enrich (> 98%) the viable mature sperm population, and 3) sperm membrane vesicles isolated from Percoll-purified motile mature sperm by nitrogen cavitation followed by differential centrifugation. The two-dimensional gel profiles of extracts of washed semen cells and motile spermatozoa contained more than 600 protein spots between pH 4 and 7 and apparent molecular mass ranging from 7.9 to 93.5 kDa. Only 73% of the major proteins in these two samples matched by computer image analysis. The highly enriched sperm membrane vesicle extract showed a much simpler protein pattern, with only 64 major protein spots, 61 of which could be matched with proteins detected in extracts from purified motile sperm. The isoelectric point and molecular weight coordinates of these major human sperm membrane proteins could serve as a foundation for systematic isolation and further characterization of human sperm antigens for studies of mechanisms of fertilization and the development of contraceptive vaccines.

Increased walking variability in elderly persons with congestive heart failure.

OBJECTIVES: To determine the effects of congestive heart failure on a person's ability to walk at a steady pace while ambulating at a self-determined rate. SETTING: Beth Israel Hospital, Boston, a primary and tertiary teaching hospital, and a social activity center for elderly adults living in the community. PARTICIPANTS: Eleven elderly subjects (aged 70-93 years) with well compensated congestive heart failure (NY Heart Association class I or II), seven elderly subjects (aged 70-79 years) without congestive heart failure, and 10 healthy young adult subjects (aged 20-30 years). MEASUREMENTS: Subjects walked for 8 minutes on level ground at their own selected walking rate. Footswitches were used to measure the time between steps. Step rate (steps/minute) and step rate variability were calculated for the entire walking period, for 30 seconds during the first minute of the walk, for 30 seconds during the last minute of the walk, and for the 30-second period when each subject's step rate variability was minimal. Group means and 5% and 95% confidence intervals were computed. MAIN RESULTS: All measures of walking variability were significantly increased in the elderly subjects with congestive heart failure, intermediate in the elderly controls, and lowest in the young subjects. There was no overlap between the three groups using the minimal 30-second variability (elderly CHF vs elderly controls: P < 0.001, elderly controls vs young: P < 0.001), and no overlap between elderly subjects with and without congestive heart failure when using the overall variability. For all four measures, there was no overlap in any of the confidence intervals, and all group means were significantly different (P < 0.05).

Conventional heart rate variability analysis of ambulatory electrocardiographic recordings fails to predict imminent ventricular fibrillation.

OBJECTIVES: The purpose of this report was to study heart rate variability in Holter recordings of patients who experienced ventricular fibrillation during the recording. BACKGROUND: Decreased heart rate variability is recognized as a long-term predictor of overall and arrhythmic death after myocardial infarction. It was therefore postulated that heart rate variability would be lowest when measured immediately before ventricular fibrillation. METHODS: Conventional indexes of heart rate variability were calculated from Holter recordings of 24 patients with structural heart disease who had ventricular fibrillation during monitoring. The control group consisted of 19 patients with coronary artery disease, of comparable age and left ventricular ejection fraction, who had nonsustained ventricular tachycardia but no ventricular fibrillation. RESULTS: Heart rate variability did not differ between the two groups, and no consistent trends in heart rate variability were observed before ventricular fibrillation occurred. CONCLUSIONS: Although conventional heart rate variability is an independent long-term predictor of adverse outcome after myocardial infarction, its clinical utility as a short-term predictor of life-threatening arrhythmias remains to be elucidated.

bpshape wk4: a computer program that implements a physiological model for analyzing the shape of blood pressure waveforms.

We describe the theory and computer implementation of a newly-derived mathematical model for analyzing the shape of blood pressure waveforms. Input to the program consists of an ECG signal, plus a single continuous channel of peripheral blood pressure, which is often obtained invasively from an indwelling catheter during intensive-care monitoring or non-invasively from a tonometer. Output from the program includes a set of parameter estimates, made for every heart beat. Parameters of the model can be interpreted in terms of the capacitance of large arteries, the capacitance of peripheral arteries, the inertance of blood flow, the peripheral resistance, and arterial pressure due to basal vascular tone. Aortic flow due to contraction of the left ventricle is represented by a forcing function in the form of a descending ramp, the area under which represents the stroke volume. Differential equations describing the model are solved by the method of Laplace transforms, permitting rapid parameter estimation by the Levenberg-Marquardt algorithm. Parameter estimates and their confidence intervals are given in six examples, which are chosen to represent a variety of pressure waveforms that are observed during intensive-care monitoring. The examples demonstrate that some of the parameters may fluctuate markedly from beat to beat. Our program will find application in projects that are intended to correlate the details of the blood pressure waveform with other physiological variables, pathological conditions, and the effects of interventions.

Cocaine effects on neonatal heart rate dynamics: preliminary findings and methodological problems.

Cocaine use by pregnant women has been reported to cause fetal and neonatal morbidity and mortality. We hypothesized that human neonates exposed to cocaine via maternal use during pregnancy might manifest changes in beat-to-beat heart rate variability, similar to those described in experimental animals. In this preliminary report, we present findings from the first systematic analysis of heart rate dynamics in a small group of (n = 5) neonates exposed in utero to cocaine compared to gestationally age matched controls (n = 6) without known drug exposure. Overall heart rate spectral power during ten minute periods of quiescent sleep was significantly reduced (p < 0.01) in the cocaine-exposed group, reminiscent of the changes recently reported in an animal model. In two other cocaine-exposed newborns, a quiescent sleep period could not be found. We discuss the special methodological problems associated with collection and interpretation of such data.

A new technique for simultaneous monitoring of electrocardiogram and walking cadence.

A new technique for simultaneously recording continuous electrocardiographic (ECG) data and walking step rate (cadence) is described. The ECG and gait signals are recorded on 2 channels of an ambulatory Holter monitor. Footfall is detected using ultrathin, force-sensitive foot switches and is frequency modulated. The footfall signal provides an indication of the subject's activity (walking or standing), as well as the instantaneous walking rate. Twenty-three young and elderly subjects were studied to demonstrate the use of this ECG and gait recorder. High-quality gait signals were obtained in all subjects, and the effects of walking on the electrocardiogram were assessed. Initial investigation revealed the following findings: (1) Although walking rates were similar in young and elderly subjects, the elderly had both decreased heart rate (HR) variability (p < 0.005) and increased cadence variability (p < 0.0001). (2) Overall, there was an inverse relation between HR and cadence variability (r = -0.73). Three elderly subjects with no known cardiac disease had HR and cadence variability similar to those of the young, whereas elderly subjects with history of congestive heart failure were among those with the lowest HR variability and the highest cadence variability. (3) Low-frequency (approximately equal to 0.1 Hz) HR oscillations (frequently observed during standing) persisted during walking in all young subjects. (4) In some subjects, both step rate and HR oscillated at the same low frequency (approximately equal to 0.1 Hz) previously identified with autonomic control of the baroreflex.(ABSTRACT TRUNCATED AT 250 WORDS)

Personal computer interface and software for the ZONAX microscope attachment controller.

We describe the hardware and software of a general-purpose interface that permits a personal computer (PC) running MS-DOS to control cytometric devices, e.g., a scanning stage, shutters, and focus motor attached to a microscope. This note explains how to use the interface to convert the ZONAX microscope attachment controller from 8080-based hardware control to PC-based control.

Nonlinear mechanics of the heart's swinging during pericardial effusion.

When excessive fluid accumulates in the pericardial space, the heart, suspended by the great vessels, is then free to swing as a pendulum. The swinging may occur at either the same frequency as the heart rate (1:1 oscillation) or at half the heart rate (2:1 oscillation), the latter frequency often arising during cardiac tamponade. We show that these two frequencies of oscillation may be explained by the nonlinearity of Newton's equation of motion as applied to the heart. Terms in the equation correspond to gravitational and buoyancy forces, forces due to ejection of blood into the great vessels, and damping forces. A transition between the 1:1 and 2:1 swinging is found to occur when particular parameters of the model are changed, notably when there is an increase of heart rate. This finding is compatible with previous clinical reports.

Note on the dispersion of generations among cells in senescing diploid fibroblast populations.

The cells in a cultured diploid fibroblast population have heterogeneous intermitotic times--even cells derived from the same mitosis may divide at different ages. This heterogeneity of inter-mitotic times results in asynchronous population growth and a dispersion of generations among members of the cell population. Because the appearance of non-dividing cells in middle-age populations has been attributed to the presence of lineages with more generations than average, we estimated the magnitude of the dispersion of cell generations as functions of the population doubling level and of the coefficient of variation of inter-mitotic times. For some data, such as that of Macieira-Coelho and Azzarone (Exp. Cell Res., 141 (1982) 325, the rate at which such non-proliferating lineages appear could be explained by a reasonable coefficient of variation of inter-mitotic times (25%). Most other data, however, would be fit only if the coefficient of variation of inter-mitotic times were 50% or greater, a variability that exceeds what has been observed in microcinematography experiments.

Nonlinear dynamics in sudden cardiac death syndrome: heartrate oscillations and bifurcations.

Patients at high risk of sudden cardiac death show evidence of nonlinear heartrate dynamics, including abrupt spectral changes (bifurcations) and sustained low frequency (.01-.04 Hz) oscillations in heartrate.

A novel motion detection method for improving the quality of two-dimensional echocardiographic images.

Two-dimensional echocardiographic pictures from elderly patients are often technically unsatisfactory. It may be helpful or even necessary to improve the signal-to-noise ratio of these images before interpreting them. A novel picture-averaging method for obtaining the improved image is described here. The procedure may be performed with either live video or video taped two-dimensional echocardiograms and does not require an electrocardiogram signal for triggering images from the same cardiac phase of successive heart beats. Instead, the triggering is performed by comparing video frames with a reference image, automatically selecting only the frames that are most nearly equivalent to the reference picture and averaging the selected images to obtain an enhanced, time-averaged picture. Frames that are rejected by the method are those in which motion has been detected relative to the reference image, often caused by slight beat-to-beat image changes that accompany breathing. This enhancement may facilitate the interpretation and measurement of echocardiographic data, thus improving the diagnosis and management of heart disease in these patients.

Multiple-transition cell cycle models that exhibit transition probability kinetics.

Cell cycle models that allow multiple random transitions and asymmetric cell division may exhibit a property that has been used to support the transition probability model of the cell cycle: that the absolute value of the difference between sibling cell inter-mitotic times varies from one sibling pair to another and is described by an exponential statistical distribution. Three models that show this property are described, each of which postulates the existence of objects that are partitioned between daughter cells during cell division and whose number influences the duration of the subsequent cell cycle, e.g., surface receptors for growth factors or transcriptional complexes that are carried by sister chromatids. In the first model, sibling cells receive identical numbers of the objects, which are used to perform multiple random transitions that constitute part of the cell cycle. The second model is like the first, except that the partitioning of objects between the newly-formed sibling cells is random. The third model is also like the first, except that all of the objects are passed to one of the sibling cells. These results show that the general mechanisms that are responsible for the dispersion of inter-mitotic times, the correlation between sibling generation times and the apparently exponentially distributed difference between sibling generation times, could be a combination of unequal cell division, multiple random cell cycle transitions and heterogeneity of mitotic cells.