Barbara Waag Carlson

EVALUATION OF A NON-INVASIVE RESPIRATORY MONITORING SYSTEM FOR SLEEPING SUBJECTS

In a previous paper we introduced a non-invasive respiratory monitoring system (NIRMS) for monitoring respiratory movements during sleep. Unlike standard sleep laboratory methods, the NIRMS can be used in frail older adults to describe breathing patterns during sleep that will mark individuals with declining neurological function. The present study evaluates the use of the NIRMS as a respiratory monitor and identifies variables that can reliably detect changes in breathing patterns and the presence of other body movements. Data were obtained from eleven healthy adults (six women, five men) whose body mass indices ranged from 20 to 47 kg m(-2), and whose baseline respiratory rates ranged from 4 to 19 breaths per minute. We evaluated three variables derived from frequency and amplitude measurements of the NIRMS: (1) the interval between breathing cycles (the interbreath interval or IBI); (2) the period between breathing cycles (the interbreath frequency or IBF); and (3) the amplitude of breath cycles (AMP). The frequency of NIRMS waveform deflections correlated highly with the frequency of visually observed chest movements (r = 0.99). Compared with a subjects baseline, a standard deviation of IBI > 3.0 s consistently identified time segments with three or more apnoeic events. The IBF and AMP differentiated respiratory from other body movements. An IBF > 20 cycles/s or an AMP > 0.4 V identified experimentally introduced body movements much more accurately than wrist accelerometry (NIRMS detected 99% of events, kappa = 0.90; WA detected 50%, kappa = 0.70). These findings support the use of the NIRMS in monitoring changes in breathing patterns during sleep, especially in frail and cognitively impaired subjects.

Cerebral Oxygenation in Wake and During Sleep and Its Relationship to Cognitive Function in Community-Dwelling Older Adults Without Sleep Disordered Breathing

BACKGROUND This descriptive cross-sectional study investigated the relationships between cerebral oxygen reserve and cognitive function in community-dwelling older adults. METHODS Participants (72 women and 40 men) underwent standard polysomnography, including regional measures of percent oxyhemoglobin saturation (rcSO(2)) determined by cerebral oximetry. Two variables were used to calculate cerebral oxygen reserve: (a) awake rcSO(2) (mean presleep rcSO(2)) and (b) the change in rcSO(2) from before sleep to the end of the first non-rapid-eye movement cycle. General linear models, adjusted for the effects of education and occupation, tested differences in performance on standard tests of memory, attention, and speed of mental processing. RESULTS Awake rcSO(2) values were normal (60%-79.9%) in 64 participants, marginal (50%-59.9%) in 41, and low (43%-49.9%) in 7. Participants with normal awake levels had higher cognitive function than those with low levels (p < .05). Changes in rcSO(2) were greatest in participants with marginal awake rcSO(2) values; among whom, those who increased rcSO(2) during sleep (n = 17) had better memory function than the 24 who did not (p < .05). CONCLUSIONS Low awake rcSO(2) values mark individuals with low cerebral oxygen reserves and generally lower cognitive function; marginal awake rcSO(2) values that fall during sleep may indicate loss of cerebral oxygen reserve and an increased risk for cognitive decline. Further studies may clarify the significance of and mechanisms underlying individual differences in awake rcSO(2) and the changes that occur in rcSO(2) while asleep.

The relationship between body mass index/body composition and survival in patients with heart failure

PurposeThe purpose of this review was to summarize the literature on the relationship between obesity and survival in persons with heart failure (HF). In particular, the article examines the ways in which studies define body size/composition (body mass index [BMI], body composition, weight, cachexia, fluid retention, or albumin) and the relationship of BMI and survival after controlling for factors such as HF severity, etiology of the HF, gender, race, age, and/or time since HF diagnosis. Data sourcesThe keywords heart failure and body mass index, heart failure and obesity, and heart failure and body composition were indexed in PubMed. Articles published from 1999 to 2006 that used multivariate analyses to examine the relationship between obesity and survival in persons with HF were included in the review. ConclusionsBMI is the standard most often used for measuring body weight in patients with HF. Yet, BMI does not address other major components of body weight (fat, lean body mass, and fluid) that may factor into the mortality of patients with HF. Four of the six studies reviewed reported a positive relationship between obesity and improved survival. However, the studies are limited by design, with the majority being cross-sectional. Furthermore, most of the data were collected through secondary data analysis from patient records in the 1990s, before contemporary HF treatment was used. Implications for practiceUntil further research solidifies a clear association between higher BMIs and improved survival in patients with HF, nurse practitioners and others should continue to counsel their patients with HF who are overweight to lose weight. Assessing BMI alone as a predictor of survival for patients with HF may be misleading and should be performed in the context of other factors. Moreover, care should be taken in managing patients with HF who are cachexic because these patients have a worrisome prognosis.

Psychological stress and arterial stiffness in Korean Americans

OBJECTIVE Arterial stiffness is identified as a causative factor for hypertension. The purpose of this study was to explore the relationship between psychological stress and arterial stiffness in Korean Americans. METHODS A convenience sample of 102 Korean Americans (aged 21-60 years, 60% women) was recruited from North Carolina. Psychological stress was measured by the Perceived Stress Scale, the Social, Attitudinal, Familiar, and Environmental (SAFE) Acculturative Stress Scale, and the Spielbergers State-Trait Anxiety Inventory. Arterial stiffness was measured by carotid-femoral pulse wave velocity (cfPWV) using the SphygmoCor system (AtCor Medical, Australia). RESULTS This study shows that the emotional stress response, measured by anxiety, significantly predicted arterial stiffness (β=.25, p=.008), independently of such confounding factors as age, mean arterial pressure (MAP), gender, body mass index, smoking, education, and income. Anxiety was neither related to age (r=.12, p=.212) nor MAP (r=.14, p=.151). Additionally, this sample of Korean Americans had higher levels of psychological stress when compared to previous findings from studies of other racial/ethnic groups in the U.S. CONCLUSION Findings demonstrate that anxiety is a significant and independent determinant of arterial stiffness. Given that anxiety was not related to MAP, these findings suggest that arterial stiffness may be a pathway to explain the connection between anxiety and hypertension risk. Studies that scrutinize the relationship between anxiety and arterial stiffness are an important next step for future research. Further studies are also recommended to explore cultural factors and individual characteristics that may affect anxiety in Korean Americans.

Cerebrovascular disease and patterns of cerebral oxygenation during sleep in elders.

Purpose: The aim of this descriptive exploratory study was to describe patterns of cerebral oxygen reserves during sleep and their association with cerebrovascular risk factors in elders. Method: Participants—115 elders, age 70 + years—were monitored overnight using standard polysomnography. Measures included arterial oxyhemoglobin (SaO2) and regional measures of percentage of cerebral oxyhemoglobin saturation (rcSO2) via cerebral oximetry. Participants were classified based on the magnitude of change in rcSO2 from resting baseline to the end of the first nonrapideye-movement (NREM) period. One-way ANOVA and Chi-square were used to test group differences in SaO2 and the prevalence of cerebrovascular risk factors. Findings: 20 participants (Group 1) experienced an increase in rcSO2 during sleep along with sleeping rcSO2 levels !55%; 95 participants experienced a decline in rcSO2; 72 participants (Group 2) had sleeping rcSO2 levels !55%; and 23 participants had sleeping rcSO2 levels <55% (Group 3). Although all three groups had equivalent declines in SaO2 levels during sleep, Group 3 had more cardiovascular comorbidity than Groups 1 and 2. Conclusions: Although SaO2 levels decline in most people during sleep, compensatory vascular responses to these drops in SaO2 are important for preventing rcSO2 from falling during sleep. Those entering sleep with lower baseline rcSO2 levels and those with greater declines in cerebral oxygenation during sleep may have greater cardiovascular burden and be at greater risk for stroke and other forms of disabling cerebrovascular disease.

Tailoring protocols to successfully recruit and retain older adults in a longitudinal study of sleep and cognition.

Many studies attest to the challenges of recruiting and retaining older adults in longitudinal studies. This article presents the methods used by the Physiological Research to Improve Sleep and Memory project to recruit and retain 115 adults (age 70 and older) in a 2-year study that involved annual administrations of two neurocognitive test batteries and two nights of polysomnography. Strategies built on knowledge obtained from participant informants and the use of tailored, individualized protocols are described. Together, these strategies enabled participants to become vested in the research process and to fully participate in all aspects of the study.

Exploratory analysis of cerebral oxygen reserves during sleep onset in older and younger adults.

OBJECTIVES: To explore differences in cerebral oxygen reserves during sleep in old and young adults.

Evaluation of variables to characterize respiratory periodicity during sleep in older adults.

Reliable markers of early neurological decline might guide interventions to prevent or reverse cognitive decline in older adults. Because cognitive decline is associated with hypoxemia during sleep, the authors examined 3 respiratory periodicity variables in 5 older adults. Subjects were monitored overnight using standard polysomnography. From the inductance band signal, the authors calculated the variability in duration of breathing cycles measured by standard deviation of interbreath intervals (sdIBI), frequency of breathing cycles measured by standard deviation of interbreath frequencies (sdIBF), and amplitude of breathing cycles measured by standard deviation of breathing cycle amplitudes (sdAMP). Logistic regression analysis and kappa coefficients identified variables that reliably detected 5-minute segments having central or obstructive apneas or body movements. An sdIBF 4.5 cpm identified body movements (sensitivity= 0.96, specificity = 0.96, kappa = 0.90). An sdIBI > 1.2 seconds identified central apneas (sensitivity = 0.86, specificity = 0.99, kappa= 0.86), and an sdIBI 1.68 seconds identified segments with 3 central apneas (sensitivity = 0.90, specificity = 0.89, kappa = 0.89). An sdAMP 0.1 V and an sdIBF 1.5 cpm identified obstructive apneas (kappa = 0.91). Data support the potential of these variables to identify central and obstructive apneas and to classify individuals according to different patterns of respiratory periodicity.

Respiratory Periodicity and Electroencephalogram Arousals During Sleep in Older Adults

The aim of this exploratory study was to examine the relationship of electroencephalogram (EEG) arousals to breathing patterns and the relationship of both arousals and breathing patterns to arterial oxygenation during sleep in older adults. Five older adults were monitored using standard polysomnography. Records were divided into 5-min segments and breathing patterns identified based on the level of respiratory periodicity and the variability in the frequency of breathing cycles. Standard criteria were used to determine sleep states and occurrence of EEG arousals. High respiratory periodicity was seen in 23% of the segments, whereas 24% had low respiratory periodicity with minimal variability in the frequency of breathing (Type A low respiratory periodicity) and 53% had low respiratory periodicity with high variability in the frequency of breathing (Type B low respiratory periodicity). Nearly all (97%) segments with high respiratory periodicity had EEG arousals, whereas fewer segments (33%) with low respiratory periodicity had arousals, regardless of the stage of sleep. Desaturations occurred more often in segments with high respiratory periodicity, F (2,4) = 57.3, p < .001, but overall, the mean SaO2 of segments with high respiratory periodicity did not differ from levels seen in segments with low respiratory periodicity, F( 2,4) = 0.77, ns. Our findings suggest that high respiratory periodicity is a common feature of EEG arousals and, in older adults, may be important for maintaining oxygen levels during desaturations during sleep.