Biomedical subjects

R L Burr

Publications and source records attributed to R L Burr.

12 recordsLinked to original sources

PubMed2005

Relationship of cerebral perfusion pressure levels to outcome in traumatic brain injury.

This study examined the relationship of cumulative percent time that cerebral perfusion pressure (CPP) fell below set thresholds to outcome in individuals with traumatic brain injury (TBI). The sample included 157 patients (16 to 89 years of age, 79%, male) admitted to an intensive care unit at an academic medical center who underwent invasive arterial blood pressure and intracranial pressure monitoring. CPP levels were recorded continuously during the first 96 hours of monitoring. Initial neurologic status was assessed using the post-resuscitation Glasgow Coma Scale. Outcome was evaluated at hospital discharge and at six months post-injury using the Extended Glasgow Outcome Scale (GOSE). The relationship of cumulative periods of low CPP to outcome was evaluated using hierarchical and binary logistic regression analysis, controlling for age, gender, and injury severity. Patients experiencing less cumulative percent time below specific CPP thresholds were more likely to have better outcome at discharge (55 mm Hg, p = .004; 60 mm Hg, p = .008; 65 mm Hg, p = .024; 70 mm Hg, p = .016). Although differences in GOSE scores at six months were not significant, those with less time below CPP thresholds were more likely to survive. Accumulated episodes of low CPP had a stronger negative relationship with outcome in patients with more severe primary brain injury.

Adult↗

PubMed2002

Information technology and CPP management in neuro intensive care.

This study developed and tested the acceptability of a computer interface intended to provide better information about CPP to Neuro Intensive Care nurses. Maintaining adequate CPP is crucial in preventing secondary brain injury, yet current monitoring data displays have poor ergonomics that minimize usable information for clinicians. Information systems developmental methods were used to 1) formulate the model for CPP information display, 2) develop the system with end-users, and 3) install the system in the Neuro Intensive Care Unit. System testing for effects on clinicians and patient outcomes is occurring in a randomized clinical trial. Metaphor graphic and universal graphic displays were tested with 37 staff nurses from three intensive care units using continuous ICP monitoring. Nursing staff preferred an augmented universal data display to the metaphor graphics, endorsing a modified trend area graph with threshold-dependent properties. The preferred model was programmed in Visual Basic and installed on small computers that were randomly allocated as live or blank displays to beds of newly admitted head injury or aneurysmal subarachnoid hemorrhage patients with continuous monitoring. Nursing acceptability of the information interface was achieved through the use of end-user focus groups that resulted in modifying the metaphor graphic approach to a more readily understandable one.

Brain Injuries↗

PubMed2001

Cerebral autoregulation and outcome in acute brain injury.

The purpose of this study was to examine the relationship between Czosnyka and others' Pressure Reactivity Index (PRx) and neurologic outcome in patients with acute brain injury, including traumatic brain injury (TBI) and cerebrovascular pathology. PRx measures the correlation between arterial blood pressure and intracranial pressure waves and may reflect cerebral autoregulation in response to blood pressure changes. A negative PRx reflects intact cerebrovascular response, whereas a positive PRx reflects impaired response. Positive PRx has been shown to correlate with poorer outcome in individuals with TBI, but these findings have not been confirmed by replication in other studies, nor have PRx values been reported for individuals with cerebrovascular pathology. In this study, PRx was determined in 52 patients with TBI (n = 27) or cerebrovascular pathology (n = 25). Hierarchical linear regression was used to evaluate the contribution of PRx to outcome, controlling for age and Glasgow Coma Scale score. Analysis of all subjects together did not support the previously reported relationship between PRx and outcome. However, for those with TBI, positive PRx was a significant predictor of negative outcome (P = 0.03). For those with cerebrovascular pathology, the effect was not significant (P = 0.10) and was in the opposite direction. For individuals with TBI, PRx may provide useful information related to cerebral autoregulation that is predictive of outcome. The meaning of PRx in individuals with cerebrovascular pathology is unclear, and further study is needed to examine the paradoxical findings observed.

Adult↗

PubMed2000

Sleep disturbance influences gastrointestinal symptoms in women with irritable bowel syndrome.

This analysis evaluated the association between sleep disturbance and gastrointestinal symptoms in women with and without irritable bowel syndrome (IBS), and examined the role of psychological distress in this relationship. Women with IBS (N = 82) reported considerably higher levels of sleep disturbance compared to controls (N = 35), using both retrospective seven-day recall and daily diary recall for two menstrual cycles (P < 0.05 on 8 of 10 measures). We used daily diary data to estimate the association between sleep disturbance and gastrointestinal symptoms, both across women (ie, whether women with high average sleep disturbance have higher average gastrointestinal symptoms) and within woman (ie, whether poorer than average sleep on one night is associated with higher than average gastrointestinal symptoms the following day). The regression coefficients for the across-women effect are large and highly significant in both groups (IBS, beta +/- SE = 0.46 +/- 0.08, P < 0.001; controls, 0.57 +/- 0.13, P < 0.001). The regression coefficients for the within-woman effect are considerably smaller and statistically significant only in the IBS group (IBS, 0.06 +/- 0.02, P = 0.006; control, 0.01 +/- 0.03, P = 0.691). These regression coefficients showed little change when daily psychological distress or stress was controlled for, the one exception being the coefficient for the across-women effect in the IBS group, which decreased substantially but still remained highly significant. Because it is possible that gastrointestinal symptoms could, in fact, cause poor sleep, we also fitted the temporally reversed model to evaluate the association between gastrointestinal symptoms on one day and sleep disturbance that night. The within-woman regression coefficients were nonsignificant in both the IBS and control groups. In conclusion, these results are consistent with the hypothesis that poor sleep leads to higher gastrointestinal symptoms on the following day among women with IBS.

Adolescent↗

PubMed2000

Intracranial pressure waveform analysis: clinical and research implications.

Assessment of intracranial adaptive capacity is vital in critically ill individuals with acute brain injury because there is the potential that nursing care activities and environmental stimuli to result in clinically significant increases in intracranial pressure (ICP) in a subset of individuals with decreased intracranial adaptive capacity. ICP waveform analysis provides information about intracranial dynamics that can help identify individuals who have decreased adaptive capacity and are at risk for increases in ICP and decreases in cerebral perfusion pressure, which may contribute to secondary brain injury and have a negative impact on neurologic outcome. The ability to identify high-risk individuals allows nurses to initiate interventions targeted at decreasing adaptive demand or increasing adaptive capacity in these individuals. Changes in the ICP waveform occur under various physiologic and pathophysiologic conditions and may provide valuable information about intracranial adaptive capacity. Simple visual assessment of the ICP waveform for increased amplitude and P2 elevation is clinically relevant and has been found to provide a rough indicator of decreased adaptive capacity. Advanced ICP waveform analysis techniques warrant further study as a means of dynamically assessing intracranial adaptive capacity.

Adaptation, Physiological↗

PubMed2000

Comparison of autonomic nervous system indices based on abdominal pain reports in women with irritable bowel syndrome.

Abdominal pain is an important symptom in irritable bowel syndrome (IBS), but patients report typical pain intensities ranging from mild to very severe. In a sample of women, the authors sought to determine whether measures of systemic autonomic activity are related to self-reported pain intensity and the occurrence of pain in the postprandial period. One hundred and six women with IBS and 41 controls completed bowel symptom and psychological distress questionnaires and wore 24-h Holter electrocardiogram monitors to estimate global heart rate variability measures of parasympathetic activity and sympathetic nervous system/parasympathetic nervous system balance. About one-third of the IBS sample reported severe or very severe abdominal pain (n = 34/106), and about one-half of the IBS sample reported postprandial pain (n = 52/106). Even after statistically controlling for age, body mass index, and psychological distress, vagal heart rate variability measures were markedly lower in women reporting high pain (P < 0.01) and markedly higher in women reporting postprandial pain (P < 0.02). The vagal component of heart rate variability appears to be reduced in women with severe abdominal pain, especially in those whose pain is not postprandial.

Abdominal Pain↗

PubMed1998

Evidence for autonomic nervous system imbalance in women with irritable bowel syndrome.

Autonomic nervous system function was assessed in women with and without irritable bowel syndrome using frequency domain measures of heart rate variability. Women were interviewed and placed into the irritable bowel syndrome (N = 25) group based on history of diagnosis and self-report of current gastrointestinal symptoms. Women in the control group denied a history of chronic gastrointestinal symptoms (N = 15). Women were followed for one menstrual cycle with a symptom diary, and during mid-luteal phase they wore a Holter 24-hr electrocardiograph monitor. Women with irritable bowel syndrome demonstrated significantly lower vagal tone as measured by the high frequency spectrum relative to control women. In addition, women with irritable bowel syndrome had a flattened 24-hr pattern of heart rate variability, with significantly lower levels of vagal tone during sleep. These results suggest that systemic sympathovagal balance may be shifted in a subset of women with irritable bowel syndrome.

Adult↗

PubMed1994

Effects of gender and age on heart rate variability in healthy individuals and in persons after sudden cardiac arrest.

The purpose of this study was to describe the effects of gender and age on heart rate variability (HRV) in healthy volunteers (n = 111; 40 men and 71 women) and in persons after sudden cardiac arrest (SCA) (n = 95; 79 men and 16 women). Frequency-domain measurements and six time-domain measurements of HRV (SDANN, 24-hour SD, SD, RMSSD, RR50, and %RR50) were taken. Two-factor analysis of variance was performed. In general, HRV was significantly lower in healthy women compared with healthy men in all the time-domain and frequency-domain variables except for the high-frequency components, RMSSD, RR50, and %RR50. There were no significant gender differences in the SCA sample. All the time-domain and frequency-domain measurements decreased with age in the healthy sample, but only the frequency-domain measurements decreased with age in the SCA sample.

Aged↗

PubMed1993

Description of time- and frequency- domain-based measures of heart rate variability in individuals taking antiarrhythmics, beta blockers, calcium channel blockers, and/or antihypertensive drugs after sudden cardiac arrest.

Concomitant drug therapies after sudden cardiac arrest and their potential effect of altering heart rate variability (HRV) represent confounding factors in interpreting the outcome of nonpharmacologic therapies on HRV. The purpose of this study is to describe a broad spectrum of time-domain and frequency-domain measurements of HRV in 50 individuals after sudden cardiac arrest. Some of the individuals were taking antiarrhythmics (n = 9), beta blockers (n = 13), calcium channel blockers (n = 10), nitrates (n = 8), cardiac glycosides (n = 10), and/or antihypertensives (n = 12). Heart rate variability was measured using a Holter recorder for 24 hours and the SpaceLabs FT2000 Monitoring System (Redmond, WA). In those individuals taking antiarrhythmic drugs, the power density within the low-frequency range (.016-.04 Hz) was significantly decreased (P = .001) compared to those not taking antiarrhythmics (n = 41). However, 78% of the people taking antiarrhythmics also had congestive heart failure (New York Heart Association functional classes II and III), which also decreased HRV. Those individuals taking beta blockers tended to have slower heart rates (P < .01). The association between beta blocker use and HRV was positive, but not statistically significant except for the increased power density in the low-frequency range (P < .05). In general, the relationships between HRV and drug therapy--calcium channel blockers, antihypertensives, cardiac glycosides, or nitrates--were not statistically significant.

Adrenergic beta-Antagonists↗

PubMed1992

Comparison of heart rate variability in survivors and nonsurvivors of sudden cardiac arrest.

Imbalances in autonomic nervous system function have been posed as a possible mechanism that produces ventricular fibrillation and sudden cardiac arrest in patients with cardiovascular disease. Heart rate (HR) variability is described in survivors and nonsurvivors of sudden cardiac arrest within 48 hours after resuscitation using time and frequency domain analytic approaches. HR data were collected using 24-hour ambulatory electro-cardiograms in 16 survivors and 5 nonsurvivors of sudden cardiac arrest, and 5 control subjects. Survivors of sudden cardiac arrest were followed for 1 year, with recurrent cardiac events occurring in 4 patients who died within that year. Analysis of 24-hour electrocardiograms demonstrated that control subjects had the highest HR variability (standard deviation of all RR intervals = 155.2 +/- 54 ms), with nonsurvivors demonstrating the lowest HR variability (standard deviation of all RR intervals = 52.3 +/- 6.1 ms) and survivors of sudden cardiac arrest falling between the other 2 groups (standard deviation of all RR intervals = 78 +/- 25.5 ms, p less than or equal to 0.0000). Two other indexes of HR variability (mean number of beat to beat differences in RR intervals greater than 50 ms/hour and root-mean-square of successive differences in RR intervals) did not demonstrate the expected pattern in this sample, indicating that perhaps patterns of HR variability differ between groups of patients with cardiovascular disorders. Spectral analytic methods demonstrated that survivors of sudden cardiac arrest had reduced low- and high-frequency spectral power, whereas nonsurvivors demonstrated a loss of both low- and high-frequency spectral power.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1992

Autoregressive spectral models of heart rate variability. Practical issues.

Autoregressive time series model-based spectral estimates of heart period sequences can provide a parsimonious and visually attractive representation of the dynamics of interbeat intervals. While a corollary to Wold's decomposition theorem implies that the discrete Fourier periodogram spectral estimate and the autoregressive spectral estimate converge asymptotically, there are practical differences between the two approaches when applied to short blocks of data. Autoregressive spectra can achieve good frequency resolution and excellent statistical stability on short segments of heart period data of sinus origin. However, the order of the autoregressive model (number of free parameters to be estimated) must be explicitly chosen, a decision that influences the trade-off of frequency resolution with statistical stability. Akaike's Information Criterion (AIC), an information-theoretic rule for picking the optimum order, is sensitive to the aggregate amount of data in the analysis. Thus, the best model order for estimating the spectrum of a 4-minute segment of data will generally be lower than the best order for estimating an hourly spectrum based on averaging 15 4-minute spectra. A major advantage of the autoregressive model approach to spectral analysis is the ease with which it can be extended to handle messy data frequently seen in heart rate variability studies. A number of autoregressive-based robust-resistant techniques are available for the analysis of heart period sequences that contain a high volume of nonsinus and other unusual beats intervals. A theoretically satisfying framework is also available for spectral analysis of unevenly sampled data and missing data.

Fourier Analysis↗

PubMed1992

Comparison of autoregression and fast Fourier transform techniques for power spectral analysis of heart period variability of persons with sudden cardiac arrest before and after therapy to increase heart period variability.

Clinical studies have used two types of analysis of the power spectral estimates of heart period variability: autoregressive and fast Fourier transform techniques. Controversy exists regarding which method is the most valid. The specific aims of this study are: (1) to describe the power spectra of heart period variability before and after an intervention designed to increase heart period variability in persons after sudden cardiac arrest; (2) to compare the integral of power spectral density between autoregressive and fast Fourier transform techniques within low and high-frequency bands; (3) to compare the magnitude of the spectral peak values determined by autoregressive and fast Fourier transform techniques approaches within low and high-frequency bands; and (4) to compare the aforementioned parameters using 4-minute, 1-hour, and 24-hour blocks of heart period data. Results indicated high correlations between spectral estimations by autoregressive and fast Fourier transform techniques using integrals or peak values within either the low or high-frequency ranges. The autoregressive technique demonstrated better resolution of sharp peaks than the fast Fourier transform technique, and makes a smoother, more interpretable curve. Lastly, people can cognitively change their heart rate variability.

Biofeedback, Psychology↗