Electromyographic effects of fatigue and task repetition on the validity of estimates of strong and weak muscles in applied kinesiological muscle-testing procedures.

The study investigated the effects of fatigue and task repetition on the relationship between integrated electromyogram and force output during subjective clinical testing of upper extremity muscles. Muscles were studied under two conditions differing in the nature and duration of constant force production (SHORT-F) and (LONG-F). The findings included a significant relationship between force output and integrated EMG, a significant increase in efficiency of muscle activity with task repetition, and significant difference between Force/integrated EMG ratios for muscles labeled "Strong" and "Weak" in the LONG-F condition. This supports Smith's 1974 notion that practice results in increased muscular efficiency. With fatigue, integrated EMG activity increased strongly and functional (force) output of the muscle remained stable or decreased. Fatigue results in a less efficient muscle process. Muscles subjectively testing "Weak" or "Strong" yield effects significantly different from fatigue.

Receiver operating characteristic analysis of regional cerebral blood flow in Alzheimer's disease.

Receiver operating characteristic (ROC) curves were used to quantitatively assess the ability of individual detectors in a 32-detector 133Xe inhalation system to discriminate between two populations over the range of regional cerebral blood flow (rCBF) values. These populations were clinically evaluated as normal (age 63.1 +/- 13.1, n = 23) and presumed Alzheimer's disease (age 72.7 +/- 7.0, n = 82). Summary statistics showed that for homologous detectors the average value of blood flow in the normal group was greater than the flow value in the group of subjects with Alzheimer's disease. Conclusions drawn from single values of flow or mean hemispheric flow can lead to erroneous conclusions about hemisphere asymmetries. However, the dynamic relationship between the correct identifications (true positives) compared with incorrect identifications (false positives) of Alzheimer's disease at each detector varies over the range of blood flow values, and quantitative characterization of this relationship in terms of an ROC curve provides more insight into the structure of the data. Detectors approximating the speech, auditory and association cortex were most effective in discriminating between groups. Frontal detectors were marginally useful diagnostically.

Survival in Alzheimer's disease and vascular dementias.

Over 5 years, we followed 199 patients with dementia of the Alzheimer type (DAT), 69 with multi-infarct dementia (MID), and 43 with mixed dementia (MIX). All three diagnostic categories had comparable progression of behavioral and cognitive impairment and need for home care or institutionalization at follow-up. However, 50% survival from diagnosis was 2.6 years for MID and 2.5 years for MIX, compared with 3.4 years for DAT. The 50% survivals from onset were longer than previous reports would suggest (8.1 years for DAT, 6.7 for MID, and 6.2 for MIX). Vascular dementias have higher mortality than DAT, even when associated with comparable cognitive and behavioral impairment.

Cerebral blood flow decrements in chronic head injury syndrome.

Global and regional cerebral blood flow (CBF) has been reported to be decreased immediately after head injury. Since neuropsychological deficits in patients with chronic head injury syndrome persist long after the initial trauma, we studied CBF, which reflects cerebral metabolism and activity, and evaluated the results of neuropsychological tests in 12 alert, responsive patients aged 18-26, both 2-13 months after head injury and 1-12 months after they regained consciousness. Global CBF was significantly decreased in patients with head injury relative to age-matched normal controls. Four patients had well-localized injury; in three of these, CBF over the affected region was significantly decreased relative to the same region in the opposite hemisphere and relative to the same region in an age-matched normal control. In one patient with right frontal injury, cognitive improvement on repeat testing was associated with a relative increase in right frontal CBF. The remaining eight patients had diffuse bilateral injury. Asymmetry ratios (larger value of mean hemispheric CBF divided by the smaller) were significantly higher for the group with localized dysfunction (1.2 +/- 0.08 vs. 1.0 +/- 0.01, p less than 0.01), suggesting homolateral decrease in CBF in this group. Three patients with diffuse injury underwent repeat studies 5-14 weeks later; all improved on psychological tests, and two had a significant increase in global CBF. These results suggest that the chronic sequelae of head injury include decreased CBF, presumably reflecting decreased cerebral metabolism, which correlates with the neuropsychological impairment.

Factors associated with duration of survival in Alzheimer's disease.

With a computerized data base, a data retrieval system, and a computer program using the actuarial method of life-table analysis, we compared survival rates in different subgroups of patients with dementia of the Alzheimer type (DAT; n = 199). Men (n = 71) had a shorter duration of survival than women (n = 128), with 500-day survival (mean +/- SEM) 84 +/- 5% vs. 99 +/- 3%, p less than 0.01; 1000-day survival 49 +/- 10% vs. 96 +/- 8%, p less than 0.001; 50% survival 1000 days vs. 1550 days. Patients younger than 65 years at onset had a decreased relative duration of survival compared with patients over 65 at onset, suggesting a more malignant course. Patients with a longer duration of illness tended to die sooner, but this effect was not statistically significant. The Kahn-Goldfarb mental-status quotient was not a predictor of survival. Patients with high Haycox behavioral score (greater than 20; n = 50), indicating more severe behavioral impairment, had lower survival rates at 500 days than patients with low scores (less than 12; n = 65) (80 +/- 6% vs. 95 +/- 3%, p less than 0.05). Hachinski ischemic score, measuring signs and symptoms of vascular disease, had no correlation with survival. Factors associated with decreased duration of survival in DAT include male sex, presenile onset, and increased severity of behavioral impairment.

Clinical classification of regional cerebral blood flow (RCBF) by partitioning.

An algorithm is proposed to classify the regional cerebral blood flow (RCBF) of two groups of subjects. A 32-tuple training vector is defined corresponding to 32 detectors used to measure 133Xe washout following inhalation. For any index of 133Xe washout, each detector is associated with two cumulative distributions (cds) each corresponding to a population. The 32 index values at which the differences between cds are maximum are defined as partition values. All index values are then compared to their partitions and are designated binary values of 1 or 0 for being above or below the partitions. A representative sum of the binary numbers (0 to 16) indicates the number of detectors in each hemisphere which exceed their respective threshold. In the example, a normal group of subjects (n = 40) is compared to an abnormal group (n = 82). The abnormal group was identified independently of RCBF by clinical testing as having Alzheimer's disease, a subcategory of dementing diseases. The classification algorithm defined a training vector to which the two populations were compared. The normal subjects had higher representative scores than the abnormals with a tight clustering of these scores. Although some abnormals scored well, the great majority had representative scores well below 12 for each cerebral hemisphere. The training vector can be used to classify new studies or can be updated by new studies until no significant changes result. At this point, the new tracing vector is used as a reference set of partition values.

Rates of decrease of cerebral blood flow in progressive dementias.

To determine whether cerebral blood flow (CBF) progressively decreases as dementia progresses, we studied 133Xe washout at two or three different times in 23 demented patients. All 15 patients with Alzheimer's and 5 of 8 patients with vascular dementias had more rapid declines of CBF than did nondemented age-matched controls. Mean rate of change in Alzheimer's disease was -0.60 per month, compared with +0.29 per month in four controls tested twice. Regression analysis of CBF with age in 30 controls tested once showed a decline of CBF with aging at a rate of -0.013 per month. The rates of CBF decline in dementia were significantly correlated with rates of change of behavioral score measuring functional impairment.

Computerized data base for evaluation and follow-up of demented outpatients.

In the course of evaluating and following more than 600 geriatric outpatients referred to a subspecialty clinic because of cognitive impairment, standardized computer-compatible evaluation and follow-up forms were developed, as well as a computerized data base. The forms cover medical, neurologic, psychiatric, psychometric, and clinical laboratory examinations; they help health professionals to perform thorough, standardized, and efficient examinations focused on those characteristics relevant to dementias. The computerized data base facilitates follow-up and other clinical studies. This article presents both the forms and their translation into query-language terminology.

Alzheimer's disease. A metabolic systems degeneration?

Alzheimer's disease can be considered a late-onset system degeneration, characteristically involving certain populations of cholinergic neurons but eventually involving other cells as well. Decreases in cerebral metabolic rate occur in it and may reflect not only decreased neuronal activity, but also deficiencies in metabolic enzymes. Abnormalities reported in nonneural Alzheimer tissues suggest that at the molecular level it is a systemic disease whose biochemical aspects can usefully be studied in nonneural tissues. Alzheimer's disease can be formulated as one of a number of metabolic encephalopathies that impair central cholinergic function.

Regional decline of cerebral blood flow with age in cognitively intact subjects.

Cerebral blood flow was measured by the 133Xenon washout method in 44 cognitively intact subjects. Regression analysis of cerebral blood flow with age was performed on data from 33 subjects without arteriosclerotic cardiovascular disease, hypertension, or chronic obstructive pulmonary disease, factors which have been previously shown to lower cerebral blood flow. Changes with normal aging were significant in the left and right hemispheres with bilateral changes in temporal, parietal, and occipital regions. An additional group of 11 cognitively intact subjects with arteriosclerotic cardiovascular disease but no accompanying dementing disease had lower mean flow values at each detector position than did age- and sex-matched controls, although the differences did not always reach statistical significance. Decreased flows in temporal regions seem to be a concomitant of normal aging, and are not related to the presence of vascular disease.