Biomedical subjects

T Roebuck

Publications and source records attributed to T Roebuck.

11 recordsLinked to original sources

PubMed2004

Increased long-term mortality in heart failure due to sleep apnoea is not yet proven.

Previous small-scale studies of the effect of sleep-disordered breathing (SDB) on prognosis in congestive heart failure (CHF) are either lacking or conflicting. The aim of this study was to assess the impact of the presence and type of SDB on mortality in a patient group with severe CHF referred to a specialised heart failure centre. Out of 78 patients ((mean +/- SD) 53 +/- 9 yrs, left ventricular ejection fraction 19.9 +/- 7.2% and pulmonary capillary wedge pressure 16.5 +/- 8.3 mmHg) followed-up over a median period of 52 months, 29% had no apnoea (CHF-N), 28% had obstructive sleep apnoea (CHF-OSA) and 42% had central sleep apnoea (CHF-CSA). At 52 months, their overall mortality was 40%, and combined mortality and transplantation was 72%. Mortality rates were similar between the three apnoea groups. Survivors had a similar prevalence of SDB (71%) as the nonsurvivors (70%). Although a significant increase in mortality was evident at 500 days in those patients with either CHF-SDB or CHF-CSA as compared with CHF-N, this was not significant at final follow-up (52 months) using Kaplan Meier analysis. Multivariate analysis identified transplantation but not SDB type or severity as a significant predictor of survival. In conclusion, sleep-disordered breathing impacts upon early (500 day), but not long-term (52 month), mortality in a specialised heart failure centre.

Adult↗

PubMed2002

Cardiac diastolic function and hypercapnic ventilatory responses in central sleep apnoea.

Hyperventilation is the key factor contributing to the development of idiopathic nonhypercapnic central sleep apnoea (ICSA), where left ventricular systolic function is normal. ICSA is reported to occur in 20% of patients with left ventricular diastolic dysfunction, in whom elevated pulmonary vascular pressures and resultant increased pulmonary vagal afferent traffic may contribute to hyperventilation. The contribution of the two potential mechanisms responsible for the hyperventilation seen in the following ICSA was measured: 1) left ventricular diastolic dysfunction-induced pulmonary hypertension; and 2) increased peripheral and central hypercapnic ventilatory responses (HCVR). The pulmonary artery pressure, left ventricular diastolic function and chemosensitivity to hypercapnia were measured during wakefulness in 16 subjects with ICSA. All subjects had systolic pulmonary artery pressures <3.99 kPa (<30 mmHg) and only four had diastolic dysfunction. All subjects had elevated peripheral and central HCVR compared with historical normal control subjects. Diastolic dysfunction correlated with increasing age but not with HCVR or markers of central sleep apnoea severity. Idiopathic nonhypercapnic central sleep apnoea is likely to be dependent upon raised hypercapnic ventilatory responses, and not pulmonary hypertension due to left ventricular diastolic dysfunction.

Adolescent↗

PubMed2001

Working memory in schizophrenia: transient "online" storage versus executive functioning.

Working memory has been described as the temporary "online" storage and the subsequent manipulation and retrieval of information. It has been suggested that the prefrontal cortex is a primary site of working memory. Schizophrenia patients, who are thought to have prefrontal cortical dysfunction, have demonstrated inconsistent deficits on a variety of verbal and spatial working memory tests. This has led to questions about how to define and measure working memory, whether these deficits are distinct to one cognitive domain, and what role factors such as intelligence and symptoms play in working memory performance. We compared schizophrenia patients to normal comparison subjects in four separate studies. Based upon the results we recommend that working memory tests be characterized as either transient "online" storage and retrieval tasks (where short-term storage and retrieval of information is required) or executive-functioning working memory tasks (where storage, manipulation, and retrieval of information is required). The importance of clearly identifying which distinct aspects of working memory are assessed is discussed.

Adolescent↗

PubMed2000

Peripheral and central ventilatory responses in central sleep apnea with and without congestive heart failure.

Given that the apnea-ventilation cycle length during central sleep apnea (CSA) with congestive heart failure (CHF) is approximately 70 s, we hypothesized that rapidly responsive peripheral CO(2) ventilatory responses would be raised in CHF-CSA and would correlate with the severity of CSA. Sleep studies and single breath and rebreathe hypercapnic ventilatory responses (HCVR) were measured as markers of peripheral and central CO(2) ventilatory responses, respectively, in 51 subjects: 12 CHF with no apnea (CHF-N), 8 CHF with obstructive sleep apnea (CHF-OSA), 12 CHF-CSA, 11 CSA without CHF ("idiopathic" CSA; ICSA), and 8 normal subjects. Single breath HCVR was equally elevated in CHF-CSA and ICSA groups compared with CHF-N, CHF-OSA, and normal groups (0.58 +/- 0.09 [mean +/- SE] and 0. 58 +/- 0.07 versus 0.23 +/- 0.06, 0.25 +/- 0.04, and 0.27 +/- 0.02 L/min/PET(CO(2)) mm Hg, respectively, p < 0.001). Similarly, rebreathe HCVR was elevated in both CHF-CSA and ICSA groups compared with CHF-N, CHF-OSA, and normal groups (5.80 +/- 1.12 and 3.53 +/- 0. 29 versus 2.00 +/- 0.25, 1.44 +/- 0.16, and 2.14 +/- 0.22 L/min/PET(CO(2)) mm Hg, respectively, p < 0.001). Furthermore, in the entire CHF group, single breath HCVR correlated with central apnea-hypopnea index (AHI) (r = 0.63, p < 0.001) and percentage central/total apneas (r = 0.52, p = 0.022). Rebreathe HCVR correlated with awake Pa(CO(2)) (r = -0.61, p < 0.001), but not with central AHI or percentage central/total apneas independent of its relationship with single breath HCVR. In conclusion, in subjects with CHF, raised central CO(2) ventilatory response predisposes to CSA promoting background hypocapnia and exposing the apnea threshold to fluctuations in ventilation, whereas raised and faster-acting peripheral CO(2) ventilatory response determines the periodicity and severity of CSA.

Analysis of Variance↗

PubMed2000

Effect of moderate alcohol upon obstructive sleep apnoea.

Moderate-to-large quantities of alcohol are known to aggravate severe obstructive sleep apnoea (OSA), however, the reported effects of moderate alcohol consumption upon mild-to-moderate OSA are inconsistent. Given the reported benefits of moderate alcohol consumption on cardiovascular mortality, recommendations regarding the management of patients with OSA are difficult to formulate. The aim of this study was to evaluate the effects of moderate alcohol on sleep and breathing in subjects with mild-to-moderate OSA. Twenty-one male volunteers, who snored habitually, underwent polysomnography with and without 0.5 g alcohol x kg body weight (BW)(-1) consumed 90 min prior to sleep time, in random order. The mean blood alcohol concentration (BAC) following alcohol at the time of lights out was 0.07 g x dL(-1). The distribution amongst the various sleep stages was not significantly altered by alcohol. The mean apnoea/hypopnoea index rose from 7.1+/-1.9 to 9.7+/-2.1 events x h(-1) (mean+/-SEM, p=0.017); however, there was no significant change in the minimum arterial oxygen saturation measured by pulse oximetry Sp,O2, apnoea length or snoring intensity. Mean sleep cardiac frequency rose significantly from 53.9+/-1.4 to 59.9+/-1.9 beats x min(-1) (P<0.001) and overnight urinary noradrenalin increased from 14.9+/-2.3 to 18.8+/-2.3 nmol x mmol creatinine(-1) (p=0.061) on the alcohol night compared to the nonalcohol night. To conclude, modest alcohol consumption, giving a mean blood alcohol concentration of 0.07 g x dL(-1), significantly increases both obstructive sleep apnoea frequency and mean sleep cardiac frequency.

Adult↗

PubMed1998

Improvement of mild sleep-disordered breathing with CPAP compared with conservative therapy.

The aim of this randomized controlled trial was to assess the effects of treatment with continuous positive airway pressure versus conservative therapy (CT) on well-being, mood, and functional status in subjects with mild sleep-disordered breathing (SDB). One hundred and eleven subjects, aged 25 to 65 yr, with a respiratory disturbance index (RDI) of 5 to 30 and without subjective pathologic sleepiness, were randomized to nasal CPAP or to CT. Ninety-seven subjects were followed-up after 8 wk. Treatment response was assessed from changes between baseline and follow-up measures of mood, energy/fatigue, and functional status/general health. Of the 51 subjects randomized to CPAP, 25 (49%) experienced an improved outcome, as compared with 12 of 46 of subjects (26%) randomized to CT (p < 0.05). The odds of experiencing a treatment response in the CPAP as compared with the CT group were 2.72 (OR: 1.18 to 6.58, 95% CI). A beneficial effect of CPAP over CT was most evident among individuals without sinus problems and among subjects with hypertension or diabetes. Differential treatment responses were not related to degree of baseline sleepiness or SDB. This suggests that middle-aged snorers with relatively low levels of SDB (RDI < 30) may benefit more from nasal CPAP than from less specific therapy directed at improving breathing during sleep. CPAP therapy may be beneficial to a broader group of subjects than previously appreciated.

Activities of Daily Living↗

PubMed1998

Effects of cardiac dysfunction on non-hypercapnic central sleep apnea.

INTRODUCTION: Non-hypercapnic central sleep apnea (CSA) commonly occurs during nonrapid eye movement (non-REM) sleep in adults with congestive heart failure (CHF) and in some subjects without signs or symptoms of CHF. Hyperventilation, reduced lung volume, and circulatory delay are known to contribute to CSA, but to differing degrees depending on presence or absence of CHF. AIM: To determine whether the pattern of ventilation during sleep could be used to determine the presence of CHF. METHODS: Full polysomnographs demonstrating CSA were examined in 10 consecutive subjects with CHF and in 10 without CHF. Ventilatory, apnea, and cycle lengths, and circulation time (from the onset of ventilatory effort to the nadir of oximeter trace) were measured from cyclic apneas during non-REM sleep. RESULTS: The non-CHF group had a greater left ventricular ejection fraction (LVEF) (59.7+/-1.9% vs 19.2+/-2.2%). Circulation time (11.8+/-0.5 s vs 24.9+/-1.7 s; p < 0.001) and cycle length (35.1+/-2.8 s vs 69.5+/-4.5 s; p < 0.001) were significantly greater in the CHF group compared with the non-CHF group, but not apnea length (21.3+/-1.8 s vs 26.8+/-2.0 s; p=0.06). Ventilatory length to apnea length ratio (VL:AL) was uniformly > 1.0 in the CHF group (mean, 1.65; range, 1.02 to 2.33), and in the non-CHF group < 1.0 (mean, 0.66; range, 0.54 to 0.89). LVEF correlated negatively with both circulation time (r=-0.86; p < 0.001) and cycle length (r=-0.79; p < 0.001). CONCLUSION: The VL:AL ratio > 1.0, as well as both circulation time > 15 s and cycle length > 45 s, can be used to recognize the presence of CHF in subjects with CSA.

Adolescent↗

PubMed1997

Asymmetric interference between concurrent tasks: an evaluation of competing explanatory models.

According to Kinsbourne's functional cerebral distance model, asymmetric interference between concurrent cognitive and manual tasks reflects the functional specialization of the cerebral hemispheres. However, alternative explanations include initial-values artifact (statistical bias model), motor asymmetry (manual dominance model), and a combination of functional cerebral distance and manual dominance (two-factor model). We evaluated the competing models in four experiments with right- and left-handed university students for whom manual dominance was in effect reversed by requiring the dominant hand to perform the more difficult manual task. The cognitive load of the nonmanual task was varied within each experiment. The results did not support any of the models but, instead, reflected only tradeoffs between manual and nonmanual performance. The primary implications for future research are that performance on both tasks must be measured, and each task must be sensitive to interference from the other task, if observed asymmetries are to be interpretable.

Adult↗

PubMed1997

Webster's scattergram method: usefulness for assessing the asymmetry of interference between concurrent tasks.

Webster (1988) described a means of using scattergrams to represent the manual and nonmanual data from dual-task laterality experiments in a composite analysis. We used Webster's method and the conventional approach (i.e., separate analyses) to analyze the results of an experiment in which 40 right-handed adults performed a verbal and a manual task concurrently. Whereas separate analyses yielded dissimilar outcomes for the two tasks, the scattergram analysis showed that overall interference was greater when the right hand performed the manual task than when the left hand performed the manual task. Advantages of the scattergram method for analyzing dual-task data are discussed.

Adult↗

PubMed1997

Neuropsychological function in mild sleep-disordered breathing.

Although a broad range of neuropsychological deficits has been reported in patients with severe sleep disordered breathing (SDB), little is known about the impact of mild SDB on neuropsychological performance. In this study, we compared neuropsychological test performance in two groups of carefully screened volunteers who differed clearly according to the respiratory disturbance index (RDI). Controls (n = 20) were identified on the basis of an RDI < 5; cases (n = 32) had an RDI in the range of 10-30. Cases and controls were well matched with regard to IQ, age, and sex. Cases had significantly more self-reported snorting and apneas and a higher body mass index than controls but did not differ according to sleepiness as measured by either the multiple sleep latency test or the Epworth sleepiness scale. An extensive battery of neuropsychological and performance tests was administered after an overnight sleep study. Cases performed significantly more poorly on a visual vigilance task (perceptual sensitivity, d': 2.24 +/- 0.64 vs. 2.70 +/- 0.53, p = 0.01, for cases and controls, respectively) and a test of working memory, the Wechsler adult intelligence scale-revised digits backwards test (6.12 +/- 2.20 vs. 7.55 +/- 2.22, p = 0.02), than controls. The groups did not differ in their performance on other tests of memory, information processing, and executive functioning. In summary, subjects with mild SDB may manifest a vigilance deficit in the absence of substantial sleepiness. Subjects with a mildly elevated RDI (10-30) without sleepiness do not appear to suffer appreciable deficits in more complex neuropsychological processes (e.g. executive functions).

Cognition Disorders↗

PubMed1996

Relationship between sleepiness and general health status.

One commonly used instrument for evaluating general health and functional status is the medical outcomes survey short form 36 (MOS). Scores obtained from this instrument are known to vary with chronic diseases and depression. However, the degree to which these health dimensions may be influenced by sleep quality or sleepiness is not well understood. A cross-sectional study was performed on the association between general health status, as determined by the MOS, with sleepiness, assessed using a standardized questionnaire [the Epworth sleepiness scale (ESS)] and the multiple sleep latency test (MSLT). One hundred twenty-nine subjects (68 women), aged 25-65 years, without severe chronic medical or psychiatric illnesses, underwent an overnight sleep study, followed by an MSLT (consisting of a series of four attempts at napping at 2-hour intervals), and completed the MOS and the ESS. The mean MSLT score was 11 +/- 2 minutes, (range 2-20) and the mean ESS score was 10 +/- 5 (range 0-24). Scores for the MOS dimensions "general health perceptions", "energy/fatigue", and "role limitations due to emotional problems" were correlated significantly with ESS scores (r = -0.30, -0.41, and -0.30, respectively; p values were all < 0.001). The MSLT was also significantly correlated with "energy/fatigue" (r = -0.19; p < 0.05). After considering the effects of chronic illness and/or body mass index in a multiple hierarchical regression analysis, sleepiness, as assessed by the ESS score, explained 8% of the variance in general health perceptions, 17% of the variance in energy/fatigue, 6% of the variance in the summary measure of well-being, and 3% of the variance in the summary measure of functional status. The variation of MOS scores with sleepiness, unrelated to age or chronic disease, suggests that measures of general health status may be broadly influenced by sleepiness and sleep quality. These data suggest that 1) sleepiness has an important impact on general health and functional status, specifically influencing self-perceptions regarding energy/fatigue; 2) a more specific assessment of sleepiness in general health evaluations may help explain some of the observed variability in these measures across subjects; and 3) general health measures may be useful in the evaluations of patients with sleep disorders.

Adult↗