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Biomedical subjects

D R Rigney

Publications and source records attributed to D R Rigney.

14 recordsLinked to original sources
PubMed1994

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).

Adult↗
PubMed1994

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.

Adult↗
PubMed1992

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)

Adult↗
PubMed1990

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.

Computer Peripherals↗
PubMed1989

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.

Cell Cycle↗
PubMed1989

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.

Heart↗
PubMed1986

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.

Cell Cycle↗
PubMedDate not supplied

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.

Aged↗
PubMedDate not supplied

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.

Adult↗