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Biomedical subjects

Lewis A Lipsitz

Publications and source records attributed to Lewis A Lipsitz.

At least 37 records · Page 2Linked to original sources
PubMed2004

Cerebral pressure-flow relations in hypertensive elderly humans: transfer gain in different frequency domains.

The dynamics of the cerebral vascular response to blood pressure changes in hypertensive humans is poorly understood. Because cerebral blood flow is dependent on adequate perfusion pressure, it is important to understand the effect of hypertension on the transfer of pressure to flow in the cerebrovascular system of elderly people. Therefore, we examined the effect of spontaneous and induced blood pressure changes on beat-to-beat and within-beat cerebral blood flow in three groups of elderly people: normotensive, controlled hypertensive, and uncontrolled hypertensive subjects. Cerebral blood flow velocity (transcranial Doppler), blood pressure (Finapres), heart rate, and end-tidal CO(2) were measured during the transition from a sit to stand position. Transfer function gains relating blood pressure to cerebral blood flow velocity were assessed during steady-state sitting and standing. Cerebral blood flow regulation was preserved in all three groups by using changes in cerebrovascular resistance, transfer function gains, and the autoregulatory index as indexes of cerebral autoregulation. Hypertensive subjects demonstrated better attenuation of cerebral blood flow fluctuations in response to blood pressure changes both within the beat (i.e., lower gain at the cardiac frequency) and in the low-frequency range (autoregulatory, 0.03-0.07 Hz). Despite a better pressure autoregulatory response, hypertensive subjects demonstrated reduced reactivity to CO(2). Thus otherwise healthy hypertensive elderly subjects, whether controlled or uncontrolled with antihypertensive medication, retain the ability to maintain cerebral blood flow in the face of acute changes in perfusion pressure. Pressure regulation of cerebral blood flow is unrelated to cerebrovascular reactivity to CO(2).

Aged↗
PubMed2004

Spectral indices of human cerebral blood flow control: responses to augmented blood pressure oscillations.

We set out to fully examine the frequency domain relationship between arterial pressure and cerebral blood flow. Oscillatory lower body negative pressure (OLBNP) was used to create consistent blood pressure oscillations of varying frequency and amplitude to rigorously test for a frequency- and/or amplitude-dependent relationship between arterial pressure and cerebral flow. We also examined the predictions from OLBNP data for the cerebral flow response to the stepwise drop in pressure subsequent to deflation of ischaemic thigh cuffs. We measured spectral powers, cross-spectral coherence, and transfer function gains and phases in arterial pressure and cerebral flow during three amplitudes (0, 20, and 40 mmHg) and three frequencies (0.10, 0.05, and 0.03 Hz) of OLBNP in nine healthy young volunteers. Pressure fluctuations were directly related to OLBNP amplitude and inversely to OLBNP frequency. Although cerebral flow oscillations were increased, they did not demonstrate the same frequency dependence seen in pressure oscillations. The overall pattern of the pressure-flow relation was of decreasing coherence and gain and increasing phase with decreasing frequency, characteristic of a high-pass filter. Coherence between pressure and flow was increased at all frequencies by OLBNP, but was still significantly lower at frequencies below 0.07 Hz despite the augmented pressure input. In addition, predictions of thigh cuff data from spectral estimates were extremely inconsistent and highly variable, suggesting that cerebral autoregulation is a frequency-dependent mechanism that may not be fully characterized by linear methods.

Adult↗
PubMed2004

Physiological complexity, aging, and the path to frailty.

Healthy physiological processes require the complex interaction of multiple control systems operating over multiple time scales. The output of these processes (for example, heart rate, blood pressure, hormonal rhythms, or postural sway) demonstrates complex variability that can be quantified using the concept of fractals, derived from the field of nonlinear dynamics. Complex physiological dynamics enable an organism to rapidly respond to the internal and external perturbations of everyday life. Aging and disease are associated with a loss of complexity in the dynamics of many physiological systems. This loss of complexity may reduce the ability to adapt to stress and lead to the syndrome of frailty.

Aged↗
PubMed2004

Is pulse pressure a predictor of cardiovascular complications in a frail elderly nursing home population?

BACKGROUND AND AIMS: Previous studies have focused on systolic blood pressure (SBP), diastolic pressure (DBP), and more recently pulse pressure (PP) as risk factors for adverse cardiovascular (CV) endpoints in elderly people. However, the relation between these pressures and CV complications in the frail nursing home population has not been well studied. The aims of this project are to determine the value of PP in predicting CV complications in a nursing home population, and to compare its predictive value with SBP, DBP, and mean arterial pressure (MAP). METHODS: This study is a retrospective 2-year review of the medical charts of 248 residents of the Hebrew Rehabilitation Center for the Aged, a long-term care facility in Boston, MA, USA. During the review process, data were collected about past medical history and new onset CV events, in addition to blood pressure and medication use. RESULTS: The results showed, with 95% confidence, that within a 2-year period, the odds ratio for the occurrence of the selected CV outcomes (myocardial infarction, congestive heart failure, angina, stroke, renal failure, syncope, death) included 1.0 for PP, SBP, DBP, MAP, and changes in these values. After adjusting for medication use, pulse pressure was still not an independent risk factor for CV complications. CONCLUSIONS: PP, SBP, DBP or MAP cannot serve as predictors of CV outcomes in the nursing home population. The presence of multiple medical problems in this frail population may have resulted in CV morbidity and mortality, independent of blood pressure effects.

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PubMed2004

Effect of blood pressure on cognitive functions in elderly persons.

BACKGROUND: Little is known about what specific cognitive functions are affected by elevated blood pressure (BP) and how orthostatic BP change is related to cognitive impairment. The aim of this study was to determine the effect of BP and its postural change on cognitive functions in otherwise healthy elders. METHODS: In 70 healthy persons (mean age, 72 +/- 4 years), supine systolic BP (SBP) was assessed 3 times using a sphygmomanometer, and the average values were obtained for the analysis. After 1, 3, and 5 minutes of standing, 3 BP measurements were obtained and the orthostatic SBP changes were determined by subtracting these values from the supine average. Neuropsychological tests were administered to assess short-term and long-term verbal and visual memory, visuospatial skills, and frontal-executive functions. Participants were considered impaired in the specific cognitive performance if their scores fell below the 25th percentile of the study population. Multiple logistic regression models were used to evaluate the relation of SBP and the magnitude of orthostatic SBP decline to risk for impairment in each of the cognitive tests. RESULTS: Controlling for potential confounders, each 10 mmHg increase in supine SBP was associated with a 2.31-fold increase (95% confidence interval, 1.14 to 4.66) in risk for impairment in psychomotor speed and set shifting as measured using the Trailmaking Part-B test. There was no significant association between cognitive functions and orthostatic SBP decline at 1, 3, and 5 minutes of standing. CONCLUSION: Elevation of BP is associated with a selective impairment in executive function in otherwise healthy community-dwelling elders.

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PubMed2004

Cerebral white matter changes and geriatric syndromes: is there a link?

Cerebral white matter lesions (WMLs), also called "leukoaraiosis," are common neuroradiological findings in elderly people. WMLs are often located at periventricular and subcortical areas and manifest as hyperintensities in magnetic resonance imaging. Recent studies suggest that cardiovascular risk factors are associated with the development of WMLs. These lesions are associated with different geriatric syndromes such as falls, executive cognitive impairment, depressive symptoms, and urinary incontinence. Damage to associative pathways in frontal and subcortical regions due to hypoperfusion may disrupt frontal executive, motor control, and other systems, resulting in these manifestations. WMLs are associated with substantial disability and should not be considered a benign and silent condition as once believed. Interventions addressing cardiovascular risk factors should be undertaken in early or mid-life in order to prevent late-life functional impairment associated with WMLs. After these lesions develop and impair executive cognitive functions, the patient's ability to comply with a complex risk reduction program may be significantly compromised.

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PubMed2004

Persistent nonmalignant pain and analgesic prescribing patterns in elderly nursing home residents.

OBJECTIVES: To determine the prevalence of analgesics used, their prescribing patterns, and associations with particular diagnoses and medications in patients with persistent pain. DESIGN: Cross-sectional study. SETTING: Nursing homes from 10 U.S. states. PARTICIPANTS: A total of 21,380 nursing home residents aged 65 and older with persistent pain. MEASUREMENTS: Minimum Data Set (MDS) assessments on pain, analgesics, cognitive, functional, and emotional status were summarized. Logistic regression models identified diagnoses associated with different analgesic classes. RESULTS: Persistent pain as determined using the MDS was identified in 49% of residents with an average age of 83; 83% were female. Persistent pain was prevalent in patients with a history of fractures (62.9%) or surgery (63.6%) in the past 6 months. One-quarter received no analgesics. The most common analgesics were acetaminophen (37.2%), propoxyphene (18.2%), hydrocodone (6.8%), and tramadol (5.4%). Only 46.9% of all analgesics were given as standing doses. Acetaminophen was usually prescribed as needed (65.6%), at doses less than 1,300 mg per day. Nonsteroidal antiinflammatory drugs (NSAIDs) were prescribed as a standing dose more than 70% of the time, and one-third of NSAIDs were prescribed at high doses. CONCLUSION: In nursing home residents, persistent pain is highly prevalent, there is suboptimal compliance with geriatric prescribing recommendations, and acute pain may be an important contributing source of persistent pain. More effective provider education and research is needed to determine whether treatment of acute pain could prevent persistent pain.

Activities of Daily Living↗
PubMed2003

Vibrating insoles and balance control in elderly people.

Somatosensory function declines with age, and such changes have been associated with diminished motor performance. Input noise can enhance sensory and motor function. We asked young and elderly participants to stand quietly on vibrating gel-based insoles, and calculated sway parameters and random-walk variables. In our 27 participants, application of noise resulted in a reduction in seven of eight sway parameters in young participants and all of the sway variables in elderly participants. Elderly participants showed greater improvement than young people in two variables, mediolateral range (p=0.008), and critical mean square displacement (p=0.012). Noise-based devices, such as randomly vibrating insoles, could ameliorate age-related impairments in balance control.

Adult↗
PubMed2003

Predicting the dynamic postural control response from quiet-stance behavior in elderly adults.

Human postural sway, as measured by fluctuations of the center of pressure (COP) under the feet of a quietly standing individual, can be characterized as a stochastic process. The fluctuation-dissipation theorem (FDT) provides a linear relationship between the fluctuations of a quasi-static, stochastic system to the same system's relaxation to equilibrium following a perturbation. We applied a similar linear relationship, based on the FDT, to the human postural control system to explore whether anterior-posterior (AP) fluctuations of the COP during quiet stance can be used to predict the AP response of the postural control system to a weak posteriorly directed mechanical perturbation (tug or pull at the waist). We tested 10 healthy elderly (mean age of 69yr) and 10 healthy young (mean age of 25yr) adult subjects. We found that this linear relationship was applicable to the postural control system of all 10 young and eight of the 10 elderly adult subjects. These results suggest that it is possible to predict an individual's dynamic response to a mild perturbation using quiet-stance data, regardless of age. The existence of this FDT-based linear relationship with respect to the human postural control system suggests that, for a given individual, the postural control system may use the same control mechanisms during quiet stance and mild-perturbation conditions, regardless of age.

Adult↗
PubMed2003

Aging, muscle activity, and balance control: physiologic changes associated with balance impairment.

Older adults demonstrate increased amounts of postural sway, which may ultimately lead to falls. The mechanisms contributing to age-related increases in postural sway and falls in the elderly remain unclear. In an effort to understand age-related changes in posture control, we assessed foot center-of-pressure (COP) displacements and electromyographic data from the tibialis anterior, soleus, vastus lateralis, and biceps femoris collected simultaneously during quiet-standing trials from elderly fallers, elderly non-fallers, and healthy young subjects. Both traditional measures of COP displacements and stabilogram-diffusion analysis were used to characterize the postural sway of each group. Regression analyses were used to assess the relationship between the COP measures and muscle activity. Elderly fallers demonstrated significantly greater amounts of sway in the anteroposterior (AP) direction and greater muscle activity during quiet standing compared with the young subjects, while elderly non-fallers demonstrated significantly greater muscle activation and co-activation compared with the young subjects. No significant differences were found between elderly fallers and elderly non-fallers in measures of postural sway or muscle activity. However, greater postural sway in both the AP and mediolateral (ML) directions and trends of greater muscle activity were found in those older adults who demonstrated lower scores on clinical measures of balance. In addition, short-term postural sway was found to be significantly correlated with muscle activity in each of these groups. This work suggests that high levels of muscle activity are a characteristic of age-related declines in postural stability and that such activity is correlated with short-term postural sway. It is unclear whether increases in muscle activity preclude greater postural instability or if increased muscle activity is a compensatory response to increases in postural sway.

Accidental Falls↗
PubMed2003

Selective impairment of frontal-executive cognitive function in african americans with cardiovascular risk factors.

OBJECTIVES: To determine whether a summary cardiovascular risk score is associated with an increased risk of frontal-executive cognitive impairment. DESIGN: Cross-sectional study. SETTING: Subjects were recruited from senior centers, senior housing complexes, and communities in the Boston metropolitan area. PARTICIPANTS: Forty-three predominantly female elderly African Americans. MEASUREMENTS: Cardiovascular risk factors were assessed during an interview and clinical examination. For each subject, the total number of cardiovascular (CV) risk factors was summed to compute a CV risk score. A battery of neuropsychological tests was administered that examined memory, visuospatial abilities, and frontal-executive functions. Cognitive test scores were transformed into domain-specific (memory, visuospatial, frontal-executive) composite z scores. Cognitive impairment for each composite z score was defined as performance less than the median for the study group. Multivariate logistic regression was used to examine the relationship between the CV risk score and the risk for cognitive impairment in the three cognitive domains of interest. RESULTS: After controlling for age and education, the CV risk score was associated only with frontal-executive cognitive impairment (odds ratio (OR)=2.44, 95% confidence interval (CI)=1.06-5.65). The CV risk score was not associated with the risk of memory (OR=1.30, 95% CI=0.64-2.67) or visuospatial impairment (OR=1.49, 95% CI=0.66-3.36). Greater CV risk scores were associated with an increased likelihood of having frontal-executive cognitive impairment. CONCLUSION: CV risk factors may exert a specific deleterious effect on frontal-executive cognitive abilities as opposed to memory or visuospatial functions. Associated executive dysfunction may compromise the ability of patients with CV risk factors to comply with recommendations for risk reduction.

Aged↗
PubMed2003

The value of cardiac enzymes in elderly patients presenting to the emergency department with syncope.

BACKGROUND: Most patients admitted to the hospital from the emergency department (ED) with syncope do not have a myocardial infarction (MI), yet a common practice is to draw serial cardiac enzymes. METHODS: To assess the value of serial cardiac enzymes in elderly patients who present to the ED with syncope, a retrospective chart review was performed on consecutive patients aged 65 and older with syncope in an urban teaching hospital ED between July 1, 1998 and June 30, 1999. Charts were screened for presenting history, cardiac risk factors, testing, and outcomes including acute coronary syndromes, MI, death, and patients returning to the ED or admitted within 72 hours of discharge. RESULTS: 319 patients met the study criteria of syncope with confirmed loss of consciousness in the absence of seizure or stroke. 141 of 228 admitted patients (62%) had creatine phosphokinase (CPK) drawn and 5% of these had Troponin I (TnI). 3 of 141 patients, or 2.1% (95% CI [confidence interval]: 0.04%-6.09%), had positive cardiac enzymes during their hospitalization. CPK was positive in all 3, and TnI, drawn in 1 patient, was also positive. Two of these patients had chest discomfort and ST segment and T-wave abnormalities on electrocardiogram (ECG) in addition to a syncopal event. The third patient had dementia and could not recall the details surrounding her syncopal event. In addition, her baseline ECG demonstrated a left bundle branch block, limiting ECG interpretation. CONCLUSIONS: Cardiac enzymes may be of little additional value if drawn routinely on elderly patients with syncope who are admitted to the hospital from the ED, unless they have other signs or symptoms suggestive of myocardial ischemia.

Aged↗
PubMed2003

Effect of systolic blood pressure and carotid stiffness on baroreflex gain in elderly subjects.

BACKGROUND: Aging is associated with diminished baroreflex sensitivity (gain), which predisposes elderly people to orthostatic hypotension, syncope, and cardiovascular morbidity. Aging is also associated with systolic blood pressure (SBP) elevation and carotid artery stiffness, which may both affect baroreflex gain. METHODS: We examined the relation between SBP, carotid artery stiffness, and baroreflex gain in 34 healthy elderly (71 +/- 4 years) and 10 healthy young (31 +/- 3 years) subjects. SBP (Finapres) and carotid artery stiffness (ultrasound measures of relative carotid artery diameter changes during each blood pressure pulse) were measured. The gain of the transfer function relating the R-R interval to SBP fluctuations at a frequency of 0.05-0.15 Hz was used to assess cardiovagal baroreflex gain. RESULTS: Elderly subjects had higher carotid artery stiffness (14.2 +/- 5.1 vs 6.6 +/- 1.8, p <.05), higher SBP (146 +/- 24 vs 125 +/- 8 mmHg, p =.012), and lower baroreflex gain (8.2 +/- 6.4 vs 16.3 +/- 7.4, p <.05) than young subjects. Among all subjects, SBP and carotid artery stiffness both correlated with baroreflex gain (r = -.39, p =.02 for both). Although SBP was related to stiffness across all subjects, this relation was not present among the elderly subjects. Within the elderly group, only SBP was independently related to baroreflex gain (R(2) =.51, p =.009). CONCLUSIONS: SBP elevation in elderly people may affect the neural or cardiac response to blood pressure fluctuations, independent of the mechanical properties of barosensory regions in the carotid artery. Future studies should examine the effect of pharmacologic treatment of hypertension on baroreflex gain in elderly people.

Adult↗
PubMed2002

Noise-enhanced human balance control.

Noise can enhance the detection and transmission of weak signals in certain nonlinear systems, via a mechanism known as stochastic resonance. Here we show that input noise can be used to improve motor control in humans. Specifically, we show that the postural sway of both young and elderly individuals during quiet standing can be significantly reduced by applying subsensory mechanical noise to the feet. We further demonstrate with input noise a trend towards the reduction of postural sway in elderly subjects to the level of young subjects. These results suggest that noise-based devices, such as randomly vibrating shoe inserts, may enable people to overcome functional difficulties due to age-related sensory loss.

Adult↗
PubMed2002

Noise-enhanced balance control in older adults.

Somatosensory information is critical to balance control and fall prevention in older adults. Recently, it has been shown that low-level input noise (electrical or mechanical) can enhance the sensitivity of the human somatosensory system. In this study, we tested the effect of low-level electrical noise, applied at the knee, on balance control in 13 healthy elderly volunteers. Subjects performed multiple single-legged stance trials with imperceptible electrical noise applied at the knee during half of the trials. Balance performance was characterized using a force platform to measure the displacement of the center of pressure (COP) under the subject's stance foot. Seven sway parameters were extracted from the COP time series. Improved balance was defined as a reduction in postural sway as indicated by decreases in the COP measures. Six of the seven sway parameters decreased with electrical noise. Three of these parameters decreased significantly ( < 0.05), and a fourth parameter was borderline significant. Averaged across subjects, the application of electrical noise resulted in a 3.8% reduction in mediolateral COP standard deviation ( = 0.04), a 5.4% decrease in the maximum anteroposterior COP excursion ( = 0.03), a 3.1% reduction in the COP path length ( = 0.04), and a 7.8% decrease in swept area ( = 0.05). The results suggest that imperceptible electrical noise, when applied to the knee, can enhance the balance performance of healthy older adults. These findings suggest that electrical noise-based devices may be effective in improving balance control in elderly people.

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PubMed2002

Enhancing tactile sensation in older adults with electrical noise stimulation.

Older adults often suffer from diminished somatosensation stemming from age-related neuropathy. Recently, localized low-level electrical noise stimulation was shown to enhance tactile sensitivity in healthy young subjects. Here, we hypothesized that fine-touch sensitivity in older adults can be similarly improved. Semmes-Weinstein monofilaments were used to evaluate fine-touch sensitivity on the first metatarsal phalangeal joint with four electrical stimulus conditions and a null (no-noise) condition in nine healthy elderly subjects. Electrical noise stimulation resulted in a statistically significant increase in the number of detections below the null-condition detection threshold, for five of the nine subjects, as well as across the entire population. This work suggests that electrical noise-based techniques may enable people to overcome functional difficulties due to age-related sensory loss.

Aged↗
PubMed2002

Orthostatic hypotension.

A common problem among elderly people, orthostatic hypotension is associated with significant morbidity and mortality, which may be caused by medications, the cumulative effects of age- and hypertension-related alterations in blood pressure regulation, or age-associated diseases that impair autonomic function. Evaluation requires multiple blood pressure measurements taken at different times of the day and after meals or medications. Central and peripheral nervous system disorders should be sought, and the laboratory evaluation should concentrate on ruling out diabetes mellitus, amyloidosis, occult malignancy, and vitamin deficiencies. If orthostatic hypotension is detected, it should be considered a risk factor for adverse outcomes and treated first with nonpharmacologic interventions, including the withdrawal of potentially hypotensive medications. In patients with hypertension and orthostatic hypotension, the judicious treatment of hypertension may be helpful. For persistent, symptomatic orthostatic hypotension caused by autonomic failure, pharmacologic interventions include fludrocortisone, midodrine, and a variety of other agents. The careful evaluation and management of orthostatic hypotension will hopefully result in a significant reduction in falls, syncope, and fractures, and an attenuation of functional decline in elderly patients.

Adult↗