Lawrence H. Larsen

Sleep/wake patterns In Alzheimer's disease: relationships with cognition and function

SUMMARY  Alzheimers disease (AD), the most common dementing disorder of aging, is a progressive neurodegenerative disease of unknown etiology. Two of the common clinical features of AD are progressive cognitive and functional impairment, and disturbed sleep/wake patterns. We examined sleep/wake patterns and cognitive and functional status measures in a large sample of AD subjects ranging from mild to moderate‐severe in impairment. All subjects survived at least 2 years after initial diagnosis. Regression analyses revealed that sleep/wake variables were highly correlated with and explained significant variance in cognitive and functional measures. More wakefulness during the night and longer REM latencies were associated with impaired cognition and function while more REM and slow‐wave sleep were associated with preserved cognition and function. These results indicate that with advancing severity of the disease, sleep/wake patterns are disrupted in parallel with the disturbances in cognition and function that are the hallmarks of AD. Further, they suggest that the neural substrates underlying each process degenerate at somewhat comparable rates.

Dim light melatonin onset and circadian temperature during a constant routine in hypersomnic winter depression

The onset of melatonin secretion under dim light conditions (DLMO) and the circadian temperature rhythm during a constant routine were assessed in 6 female controls and 6 female patients with winter depression (seasonal affective disorder, SAD) before and after bright light treatment. After sleep was standardized for 6 days, the subjects were sleep‐deprived and at bedrest for 27 h while core temperature and evening melatonin levels were determined. The DLMO of the SAD patients was phase‐delayed compared with controls (2310 vs 2138); with bright light treatment, the DLMO advanced (2310 to 2135). The minimum of the fitted rectal temperature rhythm was phase‐delayed in the SAD group compared with the controls (0542 vs 0316); with bright light treatment, the minimum advanced (0542 vs 0336).

Healthy Elderly Women and Men Have Different Entrained Circadian Temperature Rhythms

Body core temperature was measured in healthy elderly men and women under entrained conditions. Female subjects showed a larger amplitude and a higher peak temperature than male subjects. In addition, acrophase was advanced for females by an average of 49 minutes. Variability in acrophase was greater for males than females. This pattern of gender differences varies considerably from the pattern others have observed in young subjects, suggesting that aging may affect the circadian timing system of males and females differently.

Reverse sediment transport induced by amplitude-modulated waves

Abstract Amplitude-modulated waves can induce bedload and suspended-load transports of sediment in the reverse direction of the wave propagation. The reverse transport rate is mainly controlled by the magnitude of the bottom orbital velocity. The mechanism is most effective in transporting silts and fine sands offshore, but not clays. The sorting characteristic may be amplified when non-uniform size sediments are present in the sea bed. The mechanism provides a feasible explanation for two shelf sedimentation patterns difficult to understand using conventional seaward sediment-transport models.

Field investigations of the threshold of grain motion by ocean waves and currents

Abstract Instrumented tripods were deployed on three occasions at continental shelf sites: twice in the United States (December, 1978, and March, 1979) and once in Australia (December, 1979). A total of 37 days of data were collected. Data included measurements of current speed and direction 100 cm off the seabed; mean bottom pressure and pressure fluctuations; water turbidity with nephelometer or transmissometer; and photographs of the seabed. Bottom sediment samples were also collected prior to each deployment. These data were analyzed to estimate the vector-averaged velocity (U100), tides, gravity waves, near-bottom sediment concentration, bed configuration, and bottom sediment texture. During the sampling period, sediment resuspension occurred frequently as a result of oscillatory currents due to surface gravity waves. The field data have been used to evaluate several existing relationships for predicting the threshold of grain motion under oscillatory flow conditions. The first method is an evaluation of the Shields (1936) entrainment function for unidirectional flows in which the boundary shear stress is computed using the wave friction factor of Jonsson (1966). The second is an equation presented by Komar and Miller (1973, 1975) that is based on the laboratory investigations of Bagnold (1946) and Manohar (1955). The third method computes the boundary shear stress as a nonlinear combination of stresses due to waves and currents as proposed by Grant and Madsen (1979) and further developed in this paper. The results show that the Shields diagram, in which the Shields entrainment function for unidirectional currents is plotted with respect to a grain Reynolds number, adequately predicts the threshold of grain motion on the continental shelf. Although the results of all three computational methods were within the scatter of results of the laboratory studies upon which the predictive relationships were based, the wave-current model of Grant and Madsen is preferred because it includes the influence of currents in the computation of boundary shear stress.

EEG markers of early Alzheimer's disease in computer selected tonic REM sleep ☆

All night sleep/wake EEGs were examined for diagnostic features sensitive to early Alzheimers disease (AD) using computer automated techniques. Thirty-nine mild AD patients and 43 normal controls underwent 9 h of EEG recording in the sleep laboratory. All-night EEGs were screened for ideal, low artifact tonic REM sleep using autoregressive and power spectral techniques. The frequency spectra during tonic REM sleep revealed a significant shift towards slower wave forms in AD vs. control subjects. Beta (greater than 12 Hz) was reduced and theta and delta (2-8 Hz) increased in AD compared to control groups. This frequency shift was demonstrated by several analytic techniques, including binned spectral energies and unique zones in the frequency spectra. Discriminant analyses using optimal binned EEG variables correctly classified 74% of AD and 98% of control subjects, and unique zone scores correctly classified 92% of AD and 95% of control subjects, indicating that these sleep EEG changes are apparently predictive of AD status.

Frequency of sediment movement on the Washington continental shelf: A note

Abstract Several independent sets of field data have been analyzed in order to estimate the frequency of sediment movement on the continental shelf off Washington over an annual period and to identify the major components of the bottom velocity field causing this motion. Sediment motions resulting from: (1) bottom currents caused by surface wind stress and tides, and (2) wave-induced oscillatory bottom currents have been investigated. Analysis of a 260-day current record from 3 m off the seabed at 80 m depth on the continental shelf and a 205-day open-ocean wave record collected on Cobb Seamount 465 km west of the Washington coast suggest that the threshold of sediment motion was exceeded for approximately 22 days per year as a result of mean currents (20 min time averaged) and approximately 53 days per year from wave-induced oscillatory currents. Substantial variations can be expected from year to year, so these values represent order of magnitude estimates.

Threshold of sediment movement by open ocean waves: observations☆

Between 8 and 25 March, 1973, a sequence of bottom photographs, sediment samples, bottom current measurements, and bottom pressure measurements was recorded continuously at several locations on the Washington continental shelf. Concurrently, wave conditions were recorded at 35-m depth on the summit of Cobb Seamount 465 km west of the shelf experiment. During the sampling period the bottom turbidity at 167 m on the shelf varied significantly in response to the magnitude of wave activity, and these data are used to evaluate the threshold wave conditions necessary to iniatiate the observed sediment movement. The bottom oscillatory velocity, orbital diameter of wave motion, and the mean sediment size occurring at the shelf location are compared. For unconsolidated silt-sized sediment the expression ρU2110(ρ8 − ρ)gD = 0.13 d0D12 where ϱ8 and ϱ are the sediment and fluid densities, d0 is the horizontal excursion of water particles at the sea floor, D is the grain diameter, and U110 the higher 10% of bottom oscillatory velocities, describes the threshold of grain motion as observed.

Predicting suspended sediment concentration on continental shelves

Field observations of the near-bottom suspended sediment concentration, current and wave at a depth of 90 m on the Washington Shelf and at a depth of 1.5 m on the coastal Beaufort Sea show that wave-induced oscillatory flow plays a dominant role in resuspending bottom sediment. The suspended sediment concentration can be reasonably predicted from the measured flow data by applying a diffusion model. Good agreement between the predicted and observed concentrations is obtained by using a reference concentration proportional to the square root of the excess boundary shear stress. For a sediment bed consisting of multiple grain sizes, the differential rate at which material is eroded leads to a significant change in the surfacial grain-size composition. The fraction of the fine-grain sediment in the surface layer decreases sharply with increasing boundary shear stress. A procedure is presented to model this change of the grain-size distribution in the surface layer. The analysis indicates that neglecting the change of the surfacial grain-size distribution with flow may overestimate the erosion depth by a factor of 10 at bottom orbital velocities exceeding 70 cm s−1.

Age trends in the sleep EEG of healthy older men and women.

SUMMARY  The all‐night sleep EEGs of 314 (191 women, 123 men) healthy older subjects between the ages of 45 and 90 were studied for age trends in the power spectra of the all‐night NREM sleep EEG. Power spectra of the unnormalized EEG of the women show a power loss in the delta band and a power increase in the beta band with increasing age. For the men no significant trends in the power spectra of the unnormalized EEG were in evidence. A normalization of the power spectra was performed by referencing each logarithmically expressed spectra to its area between 2 Hz and 30 Hz. For both genders the normalized spectra show significant decreases in power at many frequencies below 16 Hz and significant increases in power at frequencies above 18 Hz with increasing age. The age trends observed in the spectra of this population (45‐90y age group) are about a third of the magnitude of those reported in the literature for subjects between the ages of 20y and 40y.