Sleep-related breathing disorders and cardiovascular disease

Peripheral vasoconstriction and abnormal parasympathetic response to sighs and transient hypoxia in sickle cell disease

RATIONALE

Sickle cell disease is an inherited blood disorder characterized by vasoocclusive crises. Although hypoxia and pulmonary disease are known risk factors for these crises, the mechanisms that initiate vasoocclusive events are not well known.

OBJECTIVES

To study the relationship between transient hypoxia, respiration, and microvascular blood flow in patients with sickle cell.

METHODS

We established a protocol that mimics nighttime hypoxic episodes and measured microvascular blood flow to determine if transient hypoxia causes a decrease in microvascular blood flow. Significant desaturations were induced safely by five breaths of 100% nitrogen.

MEASUREMENTS AND MAIN RESULTS

Desaturation did not induce change in microvascular perfusion; however, it induced substantial transient parasympathetic activity withdrawal in patients with sickle cell disease, but not controls subjects. Marked periodic drops in peripheral microvascular perfusion, unrelated to hypoxia, were triggered by sighs in 11 of 11 patients with sickle cell and 8 of 11 control subjects. Although the sigh frequency was the same in both groups, the probability of a sigh inducing a perfusion drop was 78% in patients with sickle cell and 17% in control subjects (P < 0.001). Evidence for sigh-induced sympathetic nervous system dominance was seen in patients with sickle cell (P < 0.05), but was not significant in control subjects.

CONCLUSIONS

These data demonstrate significant disruption of autonomic nervous system balance, with marked parasympathetic withdrawal in response to transient hypoxia. They draw attention to an enhanced autonomic nervous system–mediated sigh–vasoconstrictor response in patients with sickle cell that could increase red cell retention in the microvasculature, promoting vasoocclusion.

Correlation between severity of sleep apnea and upper airway morphology: Cephalometry and MD-CT study during awake and sleep states

CONCLUSION

The data show that the evaluation of obstruction site in patients with obstructive sleep apnea (OSA) should be performed in the sleep state rather than in wakefulness.

OBJECTIVE

The aim of this study was to identify correlation between severity of OSA as measured by the apnea-hypopnea index (AHI) and upper airway morphology examined by cephalometry and dynamic multidetector computed tomography (MD-CT) in awake and sleep states.

METHODS

Polysomnography and cephalometry were performed in 94 patients with snoring or OSA. Among them, 64 patients underwent MD-CT study. Thirteen cephalometric variables were measured. We analyzed the correlations between AHI and MD-CT measurements - minimal cross-sectional area (mCSA) and collapsibility index (CI) in high retropalate (HRP), low retropalate (LRP), high retroglossal (HRG), and low retroglossal (LRG) areas.

RESULTS

Statistically significant correlations between the AHI and inferior displacement of the hyoid bone and pharyngeal length were identified in the cephalometric study. In wakefulness, AHI had a negative correlation with mCSA in the LRP area and a significant correlation with CI in LRP and HRG in MD-CT measurements. However, in the sleep state, the AHI had a negative correlation with mCSA in LRP, HRG, and LRG areas and a meaningful correlation with CI for the whole upper airway (HRP, LRP, HRG, and LRG).

Sensitivity and specificity of telemedicine-based long-term pulse-oximetry in comparison with cardiorespiratory polygraphy and polysomnography in patients with obstructive sleep apnoea syndrome

We investigated the feasibility of night-time pulse-oximetry telemedicine. We compared polysomnography (PSG) as the gold standard with simultaneously recorded pulse-oximetry from a wrist pulse-oximeter. The results were evaluated by a sleep specialist and compared with outpatient polygraphy. A total of 135 consecutive patients (mean age 55 years, mean body mass index 31.6 kg/m2) were studied. Patients with minor, moderate and severe PSG findings were grouped together and compared to those without PSG findings; the resulting sensitivity was 1 and specificity 0.35. In addition, patients with and without minor PSG findings were grouped together and compared to those with moderate and severe PSG findings; the resulting sensitivity was 0.66 and the specificity was 0.98. The receiver operating characteristic (ROC) of telemedically-evaluated oximetry was superior to that of outpatient polygraphy. In contrast, the automatic assessment of severity based on the Oxygen Desaturation Index was unsatisfactory. For patients suspected of sleep related breathing disorders (SRBD), telemedically-evaluated pulse-oximetry is able to identify those who should be referred to a sleep laboratory for definitive diagnosis and treatment. The technique appears to be suitable for first screening in all patients at risk for SRBD.

In vivo characterization of ultrasonic transducers for the detection of airway occlusion in Sleep Disordered Breathing

Obstructive Sleep Apnea/Hypopnea Syndrome (OSAHS) is the most common form of Sleep Disordered Breathing (SDB) and it is estimated to affect approximately 15% of US adult population. Various methods have been proposed for the development of inexpensive screening methods to detect SDB to reduce the need for costly nocturnal polysomnography (NPSG). In this paper, a description of the ultrasonic transducer design and characterization is presented, followed by the results of a full night sleep study. The findings show a significant difference in the temporal features extracted from the received ultrasonic waveform during apneic breathing, compared to the hyperventilation that follows. Therefore, the findings indicate the feasibility of developing an ultrasonic detection device for low cost diagnosis of SDB.

Use of high-frequency peak in spectral analysis of heart rate increment to improve screening of obstructive sleep apnoea

PURPOSE

Several studies have correlated the ratio of the very low frequency power spectral density of heart rate increment (%VLFI) with obstructive sleep apnoea syndrome (OSAS). However, patients with impaired heart rate variability may exhibit large variations of heart rate increment (HRI) spectral pattern and alter the screening accuracy of the method.

METHODS

To overcome this limitation, the present study uses the high-frequency increment (HFI) peak in the HRI spectrum, which corresponds to the respiratory influence on RR variations over the frequency range 0.2 to 0.4 Hz. We evaluated 288 consecutive patients referred for snoring, observed nocturnal breathing cessation and/or daytime sleepiness. Patients were classified as OSAS if their apnoea plus hypopnoea index (AHI) during polysomnography exceeded 15 events per hour. Synchronized electrocardiogram Holter monitoring allowed HRI analysis.

RESULTS

Using a %VLFI threshold >2.4% for identifying the presence of OSAS, sensitivity for OSAS was 74.9%, specificity 51%, positive predictive value 54.9% and negative predictive value 71.7% (33 false negative subjects). Using threshold for %VLFI >2.4% and HFI peak position >0.4 Hz, negative predictive value increased to 78.2% while maintaining specificity at 50.6%. Among 11 subjects with %VLFI <2.4% and HFI peak >0.4 Hz, nine demonstrated moderate to severe OSAS (AHI >30).

CONCLUSIONS

HFI represents a minimal physiological criterion for applying %VLFI by ensuring that heart rate variations are band frequency limited.

Prediction of obstructive sleep apnea syndrome in a large Greek population

PURPOSE

We aimed to evaluate the predictive value of anthropometric measurements and self-reported symptoms of obstructive sleep apnea syndrome (OSAS) in a large number of not yet diagnosed or treated patients. Commonly used clinical indices were used to derive a prediction formula that could identify patients at low and high risk for OSAS.

METHODS

Two thousand six hundred ninety patients with suspected OSAS were enrolled. We obtained weight; height; neck, waist, and hip circumference; and a measure of subjective sleepiness (Epworth sleepiness scale--ESS) prior to diagnostic polysomnography. Excessive daytime sleepiness severity (EDS) was coded as follows: 0 for ESS ≤ 3 (normal), 1 for ESS score 4-9 (normal to mild sleepiness), 2 for score 10-16 (moderate to severe sleepiness), and 3 for score >16 (severe sleepiness). Multivariate linear and logistic regression analysis was used to identify independent predictors of apnea-hypopnea index (AHI) and derive a prediction formula.

RESULTS

Neck circumference (NC) in centimeters, body mass index (BMI) in kilograms per square meter, sleepiness as a code indicating EDS severity, and gender as a constant were significant predictors for AHI. The derived formula was: AHIpred = NC × 0.84 + EDS × 7.78 + BMI × 0.91 - [8.2 × gender constant (1 or 2) + 37]. The probability that this equation predicts AHI greater than 15 correctly was 78%.

CONCLUSIONS

Gender, BMI, NC, and sleepiness were significant clinical predictors of OSAS in Greek subjects. Such a prediction formula can play a role in prioritizing patients for PSG evaluation, diagnosis, and initiation of treatment.

Quantitative spectral analysis of vigilance EEG in patients with obstructive sleep apnoea syndrome: EEG mapping in OSAS patients

INTRODUCTION

Sleep disruption and blood gas abnormalities, observed in patients with obstructive sleep apnoea (OSA) syndrome, prevent sleep-related restorative processes and induce chemical or structural central nervous system cellular injury. The aim of the study was to determine electroencephalogram (EEG) alterations related to the severity of OSA in patients with OSAS and the effect of the nasal continuous positive air pressure (nCPAP) treatment.

MATERIALS AND METHODS

Polysomnography and vigilant EEGs were performed in subjects with possible OSA. The mean relative power was calculated for delta, theta, alpha and beta frequency bands. Thirty subjects without and 131 with OSA participated in this study. In 29 male patients with severe OSA, quantitative EEGs were re-evaluated after 6 months of CPAP treatment.

RESULTS

Compared to subjects without OSA, patients with severe OSA showed an increase in relative theta and delta power (occipital, temporal and parietal areas). Six months of nCPAP treatment improved daytime sleepiness of OSA patients. EEG demonstrated a decrease in alpha (frontal, central and temporal areas) and theta (frontal areas) relative power. However, beta relative power was increased mainly in central, and delta relative power, in all brain areas.

DISCUSSION

In conclusion, EEG slowing was observed in OSA patients. CPAP treatment improved daytime sleepiness of OSA patients in contrast to the alterations in alpha (decreased) and delta (increased) relative power suggesting a possible persistent brain dysfunction.

Detection of airway occlusion in simulated obstructive sleep apnea/hypopnea using ultrasound: an in vitro study

Obstructive sleep apnea/hypopnea Syndrome (OSAHS) is the most common form of Sleep Disordered Breathing (SDB) and it is estimated to affect approximately 6% of US adult population. Various methods have been proposed for the development of inexpensive screening methods to detect SDB to reduce the need for costly nocturnal polysomnography (NPSG). By using the existing air in the airway as an ultrasonic contrast agent, we propose a method to examine the narrowing or occlusion of the airway associated with OSAHS events. We describe here an in vitro study that approximates the anatomical and acoustic characteristics of the airway and neck. In this experiment, we simulate the fully open airway as well as apnea and hypopnea events. These in vitro studies results show significant differences in the ultrasonic signals acquired from the open airway model versus those from the model depicting apnea and hypopnea events. Therefore, the findings provide a foundation for development of an ultrasound system to detect SDB in vivo.

Obstructive sleep apnea among adults in Nigeria

INTRODUCTION

Obstructive sleep apnea syndrome (OSAS) is a common medical condition with significant adverse medical and public health consequences, but OSAS remains undiagnosed in many individuals. The Berlin questionnaire is a validated instrument that is used to identify individuals who are at risk for OSAS.

OBJECTIVES

To determine the prevalence of high risk of OSAS in an adult population in Nigeria.

DESIGN

A cross-sectional survey was done of 370 young adults and adults living in Abuja, Nigeria, using the Berlin questionnaire. This instrument includes questions about snoring; witnessed apneas, self-reported hypertension, and daytime sleepiness. Data were collected on sociodemographic characteristics. Excessive daytime sleepiness was determined using Epworth Sleepiness scale. Body mass index (BMI) and blood pressure were calculated and measured, respectively.

RESULTS

Of the 370 respondents, 218 (59%) were females. The overall prevalence of snoring was 31%. Overall, 19% of participants (22% of men and 16% of women) met the Berlin questionnaire criteria indicating a high risk of OSAS. The highest prevalence of risk of OSAS occurred in ages 50 to 59 years for male. Respondents with a high risk for OSAS were more likely to be obese (BMI >30 kg/m2), have a higher mean ESS score, and a chronic medical condition than those who were at lower risk.

CONCLUSIONS

OSAS may be more common a medical problem than ever imagined among Nigerians.

Preliminary results from a telemedicine referral network for early diagnosis of sleep apnoea in sleep laboratories

We conducted a feasibility study to find out whether a simple preliminary examination using telemedicine for diagnosis was sufficient to identify sleep-related breathing disorders (SRBD). Night-time pulse oximetry recordings were made in normal home surroundings on patients suffering from sleep apnoea/SRBD by doctors with a range of non-specialist backgrounds. The readings were transmitted to the relevant sleep laboratory, examined and the results returned to the referring doctor. From 80 patients (aged 29 to 60 years), 58 complained about characteristic symptoms (snoring, daytime sleepiness); 33 of these patients showed additional symptoms of associated diseases. In eight patients associated diseases were found without any symptoms. The findings were compatible with SRBD in 58 cases (73%); 12 of these were asymptomatic patients. A total of 57 patients had to be referred to a sleep laboratory for differential diagnosis by full polysomnography. Of the 22 patients (28%) without pathological findings following pulse-oximetry, 12 were symptomatic. The system described here is suitable for the creation of referral networks and for the identification of patients from institutions not trained in sleep medicine, who would otherwise not have been referred for specific diagnosis to a sleep laboratory.

The impact of chronic primary insomnia on the heart rate--EEG variability link

OBJECTIVE

To determine if chronic insomnia alters the relationship between heart rate variability and delta sleep determined at the EEG.

METHODS

After one night of accommodation, polysomnography was performed in 14 male patients with chronic primary insomnia matched with 14 healthy men. ECG and EEG recordings allowed the determination of High Frequency (HF) power of RR-interval and delta sleep EEG power across the first three Non Rapid Eye Movement (NREM)-REM cycles. Interaction between normalized HF RR-interval variability and normalized delta sleep EEG power was studied by coherency analysis.

RESULTS

Patients showed increased total number of awakenings, longer sleep latency and wake durations and shorter sleep efficiency and REM duration than controls (p<.01). Heart rate variability across first three NREM-REM cycles and sleep stages (NREM, REM and awake) were similar between both groups. In each group, normalized HF variability of RR-interval decreased from NREM to both REM and awake. Patients showed decreased linear relationship between normalized HF RR-interval variability and delta EEG power, expressed by decreased coherence, in comparison to controls (p<.05). Gain and phase shift between these signals were similar between both groups.

CONCLUSIONS

Interaction between changes in cardiac autonomic activity and delta power is altered in chronic primary insomniac patients, even in the absence of modifications in heart rate variability and cardiovascular diseases.

SIGNIFICANCE

This altered interaction could reflect the first step to cardiovascular disorders.

The effect of gender on the prevalence of hypertension in obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) causes systemic hypertension. However, there is conflicting data on the effect of gender on susceptibility to hypertension in OSA. Some show no gender differences in the prevalence of hypertension while others report either female or male propensity to have hypertension in the context of OSA. The inconsistencies in the results appear to be due to lack of full range of sleep apnea severity and insufficient number of women in the studies. We examined the effect of gender on prevalent hypertension in a cohort with a large representation of females with OSA.

METHODS

A cross-sectional study of a large cohort of subjects referred for sleep disorder evaluation.

RESULTS

The cohort comprised of 736 with OSA and 315 without OSA. OSA was defined as apnea-hypopnea index (AHI) of 5/h. There were 529 men and 207 women in the OSA group with mean+/-SD age of 50+/-13 and 51+/-14 years, respectively. The control group consisted of 154 men and 161 women with mean+/-SD age of 44+/-15 and 43+/-14 years, respectively. The AHI in the OSA group varied from 5 to 197 with a median of 24 and a mean of 36 (interquartile range: 11-53). Multiple logistic regression analyses, modeling the association between AHI and hypertension and considering other covariates, showed that odds of hypertension increased with increasing age, BMI, and AHI. There was evidence that men were at higher risk for hypertension than women OR 1.82 (95%CI 1.01, 3.20) at the highest quartile of BMI.

CONCLUSIONS

We have shown that the prevalence of hypertension increases with increasing age and severity of OSA, and markedly obese men may have a nearly 2-fold greater risk for hypertension than women in this clinic-based population.

Plasma thioredoxin, a novel oxidative stress marker, in patients with obstructive sleep apnea before and after nasal continuous positive airway pressure

Obstructive sleep apnea (OSA) is associated with increased cardiovascular mortality, and oxidative stress was suggested to play an important role. We hypothesized that the plasma TRX level, a novel oxidative stress marker, is elevated in OSA patients. Plasma TRX and adiponectin levels, which are significantly associated with cardiovascular mortality, were measured in 41 patients with severe OSA before (n = 41) and after (n = 27) nasal continuous positive airway pressure therapy (nCPAP) for 1 month and in 12 subjects without OSA (non-OSA group). The TRX level was significantly higher (p = 0.02) and the adiponectin level was significantly lower (p = 0.02) in the OSA group than in the non-OSA group. After 1 month of nCPAP (n = 27), the TRX level significantly decreased (p = 0.03), and the adiponectin level significantly increased (p = 0.03). Among the 14 patients with untreated OSA, the TRX and adiponectin levels did not significantly change over a 1-month interval. Among the 53 (41 OSA + 12 non-OSA) subjects, the TRX level was positively correlated with the respiratory disturbance index (p = 0.001) and percentage of time with SaO(2) <90% (p = 0.0002). The adiponectin level, but not the TRX level, was correlated with the BMI (n = 53; p = 0.02). Plasma TRX may be a unique marker for evaluating oxidative stress and monitoring the effectiveness of nCPAP in OSA patients.

Modeling of autonomic control in sleep-disordered breathing

There is ample evidence to support the notion that chronic exposure to repetitive episodes of interrupted breathing during sleep can lead to systemic hypertension, heart failure, myocardial infarction and stroke. Recent studies have suggested that abnormal autonomic control may be the common factor linking sleep-disordered breathing (SDB) to these cardiovascular diseases. We have developed a closed-loop minimal model that enables the delineation of the major physiological mechanisms responsible for changes in autonomic system function in SDB, and also forms the basis for a noninvasive technique that enables the early detection of cardiovascular control abnormalities. The model is "minimal" in the sense that all its parameters can be estimated through analysis of the data measured noninvasively from a single experimental procedure. Parameter estimation is enhanced by broadening the frequency content of the subject's ventilatory pattern, either through voluntary control of breathing or involuntary control using ventilator assistance. Although the original form of the model is linear and time-invariant, extensions of the model include the incorporation of nonlinear dynamics in the autonomic control of heart rate, and allowing the transfer functions of the model components to assume time-varying characteristics. The various versions of the model have been applied to different populations of subjects with SDB under different conditions (e.g. supine wakefulness, orthostatic stress, sleep). Our cumulative findings suggest that the minimal model approach provides a more sensitive means of detecting abnormalities in autonomic cardiovascular control in SDB, compared to univariate analysis of heart rate variability or blood pressure variability.

Detection of compressed tracheal sound patterns with large amplitude variation during sleep

The objective of the present work was to develop automated methods for the compressed tracheal breathing sound analysis. Overnight tracheal breathing sound was recorded from ten apnoea patients. From each patient, three different types of tracheal sound deflection pattern, each of 10 min duration, were visually scored, viewing the compressed tracheal sound curve. Among them, high deflection patterns are of special interest due to the possible correlation with apnoea-hypopnoea sequences. Three methods were developed to detect patterns with high deflection, utilizing nonlinear filtering in local characterization of tracheal sounds. Method one comprises of local signal maximum, the second method of its local range, and the third of its relative range. The three methods provided 80% sensitivity with 57, 91 and 93% specificity, respectively. Method three provided an amplitude-independent approach. The nonlinear filtering based methods developed here offer effective means for analysing tracheal sounds of sleep-disordered breathing.

Sleep apnea and dialysis therapies: things that go bump in the night?

Sleep apnea has been linked to excessive daytime sleepiness, depressed mood, hypertension, and cardiovascular disease in the general population. The prevalence of severe sleep apnea in the conventional thrice-weekly hemodialysis population has been estimated to be more than 50%. Sleep apnea leads to repetitive episodes of hypoxemia, hypercapnia, sleep disruption, and activation of the sympathetic nervous system. The hypoxemia, arousals, and intrathoracic pressure changes associated with sleep apnea lead to sympathetic activation, endothelial dysfunction, oxidative stress, and inflammation. Because sleep apnea has been shown to be widespread in the conventional dialysis population, it may be that sleep apnea contributes substantially to the sleepiness, poor quality of life, and cardiovascular disease found in this population. The causal links between conventional dialysis and sleep apnea remain speculative, but there are likely multiple factors related to volume status and azotemia that contribute to the high rate of severe sleep apnea in dialysis patients. Both nocturnal automated peritoneal dialysis and nocturnal hemodialysis have been associated with reduced severity of sleep apnea. Nocturnal dialysis modalities may provide tools to increase our understanding of the uremic sleep apnea and may also provide therapeutic alternatives for end-stage renal disease patients with severe sleep apnea. In conclusion, sleep apnea is an important, but overlooked, public health problem for the dialysis population. The impact of sleep apnea treatment in this high-risk population may include reduced sleepiness, better mood and blood pressure, and lowered risk of cardiovascular disease.

Selective impairment of central mediation of baroreflex in anesthetized young adult Fischer 344 rats after chronic intermittent hypoxia

Baroreflex control of heart rate (HR) is impaired after chronic intermittent hypoxia (CIH). However, the location and nature of this response remain unclear. We examined baroreceptor afferent, vagal efferent, and central components of the baroreflex circuitry. Fischer 344 (F344) rats were exposed to room air (RA) or CIH for 35-50 days and were then anesthetized with isoflurane, ventilated, and catheterized for measurement of mean arterial blood pressure (MAP) and HR. Baroreceptor function was characterized by measuring percent changes of integrated aortic depressor nerve (ADN) activity (Int ADNA) relative to the baseline value in response to sodium nitroprusside- and phenylephrine-induced changes in MAP. Data were fitted to a sigmoid logistic function curve. HR responses to electrical stimulation of the left ADN and the right vagus nerve were assessed under ketamine-acepromazine anesthesia. Compared with RA controls, CIH significantly increased maximum baroreceptor gain or maximum slope, maximum Int ADNA, and Int ADNA range (maximum - minimum Int ADNA), whereas other parameters of the logistic function were unchanged. In addition, CIH increased the maximum amplitude of bradycardic response to vagal efferent stimulation and decreased the time from stimulus onset to peak response. In contrast, CIH significantly reduced the maximum amplitude of bradycardic response to left ADN stimulation and increased the time from stimulus onset to peak response. Therefore, CIH decreased central mediation of the baroreflex but augmented baroreceptor afferent function and vagal efferent control of HR.

Screening, diagnosis & monitoring of depression/distress in CHF patients

Objective and validated measures of depression/distress (anxiety and anger) are available and readily usable at the bedside or in clinic. Foremost among these is the Patient's Health Questionnaire--an adaptation of DSM IV criteria for Major Depressive Disorder that permits administration and scoring by nursing or physician personnel, and quantification of the intensity of depression. A score of 10 or greater indicates a need for evaluation/treatment. Because of patient denial/minimization/alexithymia, PHQ negatives should undergo further screening by having a spouse or friend complete a depression/distress rating scale. The only standardized, normed, and validated spouse/friend scale presently available is the Ketterer Stress Symptom Frequency Checklist, which is available by internet.

Chronic intermittent hypoxia impairs baroreflex control of heart rate but enhances heart rate responses to vagal efferent stimulation in anesthetized mice

Chronic intermittent hypoxia (CIH) leads to increased sympathetic nerve activity and arterial hypertension. In this study, we tested the hypothesis that CIH impairs baroreflex (BR) control of heart rate (HR) in mice, and that decreased cardiac chronotropic responsiveness to vagal efferent activity contributes to such impairment. C57BL/6J mice were exposed to either room air (RA) or CIH (6-min alternations of 21% O(2) and 5.7% O(2), 12 h/day) for 90 days. After the treatment period, mice were anesthetized (Avertin) and arterial blood pressure (ABP) was measured from the femoral artery. Mean ABP (MABP) was significantly increased in mice exposed to CIH (98.7 +/- 2.5 vs. RA: 78.9 +/- 1.4 mmHg, P < 0.001). CIH increased HR significantly (584.7 +/- 8.9 beats/min; RA: 518.2 +/- 17.9 beats/min, P < 0.05). Sustained infusion of phenylephrine (PE) at different doses (0.1-0.4 microg/min) significantly increased MABP in both CIH and RA mice, but the ABP-mediated decreases in HR were significantly attenuated in mice exposed to CIH (P < 0.001). In contrast, decreases in HR in response to electrical stimulation of the left vagus nerve (30 microA, 2-ms pulses) were significantly enhanced in mice exposed to CIH compared with RA mice at low frequencies. We conclude that CIH elicits a sustained impairment of baroreflex control of HR in mice. The blunted BR-mediated bradycardia occurs despite enhanced cardiac chronotropic responsiveness to vagal efferent stimulation. This suggests that an afferent and/or a central defect is responsible for the baroreflex impairment following CIH.

Prediction of obstructive sleep apnea in patients presenting to a tertiary care center

The objective of this prospective observational clinical study is to derive and validate a diagnostic model for prediction of obstructive sleep apnea (OSA) in subjects presenting with non-sleep-related complaints in a tertiary care center in north India. We included 102 subjects (group I, range 31-70 years) presenting to the hospital with non-sleep-related complaints. None of the subjects had any significant comorbid illness such as respiratory or congestive cardiac failure. All subjects underwent detailed evaluation including polysomnography (PSG). Various parameters were compared between the cases (apnea-hypopnea index, AHI > or =15/h) and controls (AHI <15/h). Using multivariate logistic regression analysis, a diagnostic model for prediction of OSA was derived. Subsequently, using similar selection criteria, 104 subjects (group II, range 32-68 years) were included for validation of the newly derived diagnostic model. Body mass index [BMI; OR (95% CI), 1.14(1.1-1.2)], male gender 5.0(1.4-27.1), relative-reported snoring index (SI) 2.8(1.7-5.0), and choking index (ChI) 8.1(1.4-46.5) were significant, independent predictors of OSA. Diagnostic model was computed as score = [1.61 x (gender)] + [1.01 x (S1)] + [2.09 x (ChI)] + [0.1 x (BMI)] where, gender: 0 = female, 1 = male and SI, ChI, BMI are actual values. The diagnostic model had an area under the receiver operator characteristics curve of 89.6%. A cutoff of 4.3 for the score was associated with sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 91.3, 68.5, 70.5, and 92.3%, respectively. Misclassification rate with the application of the diagnostic model on group II subjects was 13.5% (14/104). Sensitivity, specificity, PPV, and NPV of the model for predicting OSA in this group were 82, 90.7, 89.1, and 84.5%, respectively. BMI, male gender, SI, and ChI are independent predictors of OSA. Diagnostic model derived from these parameters is useful for predicting presence of OSA and screening subjects for PSG.

Sleep‐Disordered Breathing and the Association With Cardiovascular Risk

Breathing-related sleep disorders, particularly obstructive sleep apnea, have been largely undiagnosed in people with cardiovascular disease, probably due to limited health care provider awareness of the association between the two conditions. Solid evidence is emerging that the apneic events that occur during sleep lead to acute and chronic hemodynamic changes during wake time, including elevated sympathetic tone, decreased stroke volume and cardiac output, increased heart rate, and changes in circulating hormones that regulate blood pressure, fluid volume, vasoconstriction, and vasodilation. Obstructive sleep apnea is associated with known cardiovascular risk factors such as obesity and hyperlipidemia, and is considered by many sleep clinicians to be an independent risk factor for hypertension. Additionally, sleep apnea has been implicated in the pathogenesis of heart failure and stroke. Treatment with positive airway pressure during sleep eliminates the apneic events and the ensuing acute hemodynamic changes. Improvements in daytime blood pressure and left ventricular function also have been noted in persons with hypertension and heart failure. Because effective treatment is available for sleep apnea, this condition needs to be diagnosed and treated in persons with cardiovascular disease.

Cardiovascular manifestations seen in obstructive sleep apnea

Patients with obstructive sleep apnea (OSA) have an increased prevalence of systemic and pulmonary hypertension, left ventricular (LV) hypertrophy, LV systolic and diastolic dysfunction, and congestive heart failure, increased platelet aggregability, and increased susceptibility to thrombotic and embolic cardiac and cerebrovascular events. Patients with OSA have an increased prevalence of coronary artery disease, myocardial infarction, nocturnal angina, and myocardial ischemia, arrhythmias, and sudden cardiac death. Patients with OSA also have an increased prevalence of stroke. Treatment of OSA with continuous positive airway pressure improves cardiac efficiency in patients with heart failure, causes a reduction in the frequency of nocturnal ischemic ST-segment depression, relieves nocturnal angina, and causes a reduction in the occurrence of new cardiovascular events and an increase in the time to such events.

Circulating ICAM-1 and VCAM-1 levels in patients with obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS)-induced hypoxic stress modulates circulating inflammatory mediators causing accelerated atherogenesis.

OBJECTIVES

We hypothesized that OSAS-induced hypoxia might result in cardiovascular disease due to increased expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on the endothelial surface.

METHODS

Thirty-nine subjects with moderate-to-severe OSAS and 34 non-apneic controls matched for age, gender, body mass index (BMI), smoking history, and cardiovascular disease were included in this prospective study. Overnight polysomnography was performed. Circulating ICAM-1 and VCAM-1 levels in the serum were measured by enzyme-linked immunosorbent assay.

RESULTS

Circulating levels of both ICAM-1 (480.1 +/- 216.7 vs. 303.4 +/- 98.6 ng/ml, p < 0.0001) and VCAM-1 (1,156.6 +/- 79.8 vs. 878.8 +/- 71.1 ng/ml, p = 0.002) were significantly increased in the OSAS group compared to the control group. For an ICAM-1 cutoff level of 375 ng/ml, predictive sensitivity and specificity for OSAS were 69.2% (95% confidence interval, CI: 52.4-83.0%) and 82.4% (95% CI: 65.5-93.2%), respectively. For a VCAM-1 cutoff level of 859 ng/ml, predictive sensitivity and specificity for OSAS were 74.4% (95% CI: 57.9-86.9%) and 64.7% (95% CI: 46.5-80.2%), respectively. There was a significant positive correlation between circulating levels of ICAM-1 and ln of AHI (r = 0.276, p = 0.018). Multiple logistic regression analyses showed that OSAS was associated with high ICAM-1 and high VCAM-1 levels independent of age, gender, BMI, smoking status and cardiovascular disease.

CONCLUSION

We conclude that OSAS can independently increase circulating levels of adhesion molecules

Validation of a questionnaire instrument for prediction of obstructive sleep apnea in Hong Kong Chinese children

To develop and validate a questionnaire scale that can be used as a screening tool to investigate for the presence of childhood obstructive sleep apnea syndrome (OSAS) in Hong Kong Chinese children. Subjects suspected to have OSAS and controls were recruited. Parents completed a Hong Kong children sleep questionnaire (HK-CSQ) and all recruited subjects underwent at least one overnight polysomnographic study (PSG). An obstructive apnea index (OAI) >or= 1/h was diagnostic of OSAS. Receiver-operating characteristics (ROC) curve was constructed to determine optimal sensitivity and specificity. Reliability and validity of the questionnaire scale were also assessed. Two hundred twenty-nine children (149 boys and 80 girls) with a mean age of 10.0 years (SD = 2.1) were recruited. Their mean body mass index (BMI) and OAI were 19.8 (SD = 5.1) and 2.6 (SD = 7.6), respectively. Fifty-four boys and 12 girls were found to have OSAS. Three questions were found to be highly significant in predicting for the presence of OSAS-snoring, nocturnal mouth breathing, and sweating. A composite score of 7 from the three questions (range 0-12) was found to discriminate the OSAS cases best [ROC curve, AUC = 0.8 (95% CI = 0.8-0.9)]. The sensitivity, specificity, positive predictive values (PPVs), and negative predictive values (NPVs) were 75.4, 80.5, 61.3, and 88.9%, respectively. Test-retest reliability was undertaken in 51 subjects and the measurement of agreement (Kappa value) was 0.6. This HK-CSQ is a useful, valid, and reliable screening instrument for the presence of OSAS in children.

[Sleep apnea-hypopnea syndrome and the heart]

Cardiovascular and cerebrovascular diseases are the most common diseases in industrialized societies. The main objectives of this article were to summarize the physiological effects of sleep apnea on the circulatory system and to review how treatment of this condition influences cardiovascular disease. Acute sleep apnea has a number of hemodynamic consequences, such as pulmonary and systemic hypertension, increased ventricular afterload and reduced cardiac output, all of which result from sympathetic stimulation, arousal, alterations in intrathoracic pressure, hypoxia and hypercapnia. When chronic, sleep apnea-hypopnea syndrome is associated with systemic hypertension, ischemic heart disease, congestive heart failure, and Cheyne-Stokes respiration in patients with congestive heart failure. Nocturnal treatment with continuous positive airway pressure decreases both the number of central apneic episodes and blood pressure in patients with sleep apnea-hypopnea syndrome and arterial hypertension.

Sleep Apnea in Patients on Conventional Thrice-Weekly Hemodialysis: Comparison with Matched Controls from the Sleep Heart Health Study

Sleep-disordered breathing (SDB) has been noted commonly in hemodialysis (HD) patients, but it is not known whether this is related directly to the treatment of kidney failure with HD or to the higher prevalence of obesity and older age. Forty-six HD patients were compared with 137 participants from the Sleep Heart Health Study (SHHS) who were matched for age, gender, body mass index (BMI), and race. Home unattended polysomnography was performed and scored using similar protocols. The study sample was 62.7 +/- 10.1 yr, was predominantly male (72%) and white (63%), and had an average BMI of 28 +/- 5.3 kg/m(2). The HD sample had a higher systolic BP (137 versus 121 mmHg; P < 0.01) and a higher prevalence of diabetes (33 versus 9%; P < 0.01) and cardiovascular disease (33 versus 13%; P < 0.01) compared with the SHHS sample. The HD group had significantly less sleep time (320 versus 379 min; P < 0.0001) but similar sleep efficiency. HD patients had a higher frequency of arousals per hour (25.1 versus 17.1; P < 0.0001) and apnea-hypopneas per hour (27.2 versus 15.2; P < 0.0001) and greater percentage of the total sleep time below an oxygen saturation of 90% (7.2 versus 1.8; P < 0.0001). HD patients were more likely to have severe SDB (>30 respiratory events per hour) compared with the SHHS sample (odds ratio 4.07; 95% confidence interval 1.83 to 9.07). There was a strong association of HD with severe SDB and nocturnal hypoxemia independent of age, BMI, and the higher prevalence of chronic disease. The potential mechanisms for the higher likelihood of SDB in the HD population must be identified to provide specific prevention and therapy.

Sleep disorders in end-stage renal disease: ‘Markers of inadequate dialysis?’

Excessive daytime sleepiness and sleep disorders, including sleep apnea syndrome, restless legs syndrome, and periodic limb movement disorder, occur with increased frequency in patients with end-stage renal disease (ESRD). The detection and management of sleep disorders in ESRD patients is often challenging but may have significant clinical benefits. Some of the poor quality of life in ESRD may be attributed to the presence of concomitant sleep disorders, yet the classical symptoms of sleep disorders (poor concentration, daytime sleepiness, and insomnia) are often ascribed to the uremic syndrome itself. Conventional risk factors and screening tools used in the diagnosis of sleep disorders seem to have limited applicability in dialysis patients implicating the unique pathophysiology of sleep disorders in ESRD. Emerging evidence suggests that sleep apnea may contribute to the augmented cardiovascular event rates and to the accelerated development of atherosclerosis in ESRD. Whether treatment of sleep disorders in ESRD patients can affect the high morbidity and mortality of ESRD patients has yet to be elucidated. To date, conventional renal replacement therapies do not appear to have a significant impact on the treatment of sleep disorders in ESRD. The promising therapeutic effects of optimal uremia control in the forms of nocturnal hemodialysis and renal transplantation on sleep disorders require further mechanistic and clinical studies.

Consequences of subchronic and chronic exposure to intermittent hypoxia and sleep deprivation on cardiovascular risk factors in rats

Since studies suggest that both hypoxia and sleep fragmentation are related to cardiovascular alterations induced by obstructive sleep apnea, the present study was designed to evaluate the effects of hypoxia, sleep deprivation, and their combination on biochemical blood parameters in rats. In subchronic experiments (4 days), rats were exposed to intermittent hypoxia (IH) during the light period (2min room air-2min 10% O(2) for 12h/day) and/or paradoxical sleep deprivation (PSD, 24h/day). Consequences of chronic intermittent hypoxia (CIH) exposure were examined after 21 consecutive days of hypoxia protocol from 10:00 to 16:00 followed by a sleep restriction (SR) period of 18h (16:00-10:00). Rats were randomly assigned to seven treatment groups: (1) control (2) IH (3) PSD (4) IH-PSD (5) SR (6) CIH and (7) CIH-SR. PSD reduced triglycerides and very low-density lipoprotein (VLDL) cholesterol concentrations and increased total cholesterol and high-density lipoprotein (HDL) cholesterol. IH did not alter any of these parameters. The combination of IH-PSD did not modify the values of total cholesterol and HDL compared to control group. In the chronic experiment, the animals exposed to CIH displayed a reduction of Vitamin B(6) and an increase of triglycerides and VLDL. Our findings show a duration-dependent effect of hypoxia on triglycerides. Rats in the SR and CIH-SR groups showed a diminished concentration of triglycerides and VLDL. SR rats showed a reduction in the concentration of homocysteine but the animals in the CIH-SR treatment condition did not display any alterations in this parameter. In this latter group, an augmentation of cysteine concentration was observed. These results suggest that sleep deprivation and hypoxia modify biochemical blood parameters in distinct ways.

The link between cardiac autonomic activity and sleep delta power is altered in men with sleep apnea-hypopnea syndrome

We hypothesize that sleep apnea-hypopnea alters interaction between cardiac vagal modulation and sleep delta EEG. Sleep apnea-hypopnea syndrome (SAHS) is related to cardiovascular complications in men. SAHS patients show higher sympathetic activity than normal subjects. In healthy men, non-rapid eye movement (NREM) sleep is associated with cardiac vagal influence, whereas rapid eye movement (REM) sleep is linked to cardiac sympathetic activity. Interaction between cardiac autonomic modulation and delta sleep EEG is not altered across a life span nor is the delay between appearances of modifications in both signals. Healthy controls, moderate SAHS, and severe SAHS patients were compared across the first three NREM-REM cycles. Spectral analysis was applied to ECG and EEG signals. High frequency (HF) and low frequency (LF) of heart rate variability (HRV), ratio of LF/HF, and normalized (nu) delta power were obtained. A coherency analysis between HFnu and delta was performed, as well as a correlation analysis between obstructive apnea index (AI) or hypopnea index (HI) and gain, coherence, or phase shift. HRV components were similar between groups. In each group, HFnu was larger during NREM, while LFnu predominated across REM and wake stages. Coherence and gain between HFnu and delta decreased from controls to severe SAHS patients. In SAHS patients, the delay between modifications in HFnu and delta did not differ from zero. AI and HI correlated negatively with coherence, while HI correlated negatively with gain only. Apneas-hypopneas affect the link between cardiac sympathetic and vagal modulation and delta EEG demonstrated by the loss of cardiac autonomic activity fluctuations across shifts in sleep stages. Obstructive apneas and hypopneas alter the interaction between both signals differently.

Rhinitis and snoring as risk factors for hypertension in post-menopausal women

OBJECTIVE

Several studies have suggested an association between snoring and hypertension. An association between rhinitis and hypertension has been recently indicated in men but not in women. Since menopausal status is an important determinant of blood pressure, we evaluated the relationship between rhinitis, snoring and blood pressure taking into account the modifying effect of menopausal status.

DESIGN

Cross-sectional survey.

SETTINGS

Four areas of Italy: the Po river Delta, Pisa (Tuscany), Viterbo (Lazio) and Rome.

MAIN OUTCOME MEASURES

Data were collected by a questionnaire and a medical visit.

PARTICIPANTS

One thousand five hundred and fifty-four female non-smokers.

RESULTS

Systolic blood pressure (SBP) was significantly related to both occasional and habitual snoring in the overall sample. No associations were found between SBP, snoring, and rhinitis in pre-menopausal women. Both occasional and habitual snoring, but not rhinitis, were significant risk factors for increased SBP in women who stopped menstruating fewer than 11 years previously (beta=10.27 mmHg, 95% confidence interval (CI)=3.5, 17.01 and beta=9.91 mmHg, 95% CI=2.3, 17.5, respectively). However, women who had been menopausal for more than 11 years were found to have an increased SBP if they were occasional snorers (beta=8.94 mmHg 95% CI=1.2, 16.6) or habitual snorers (beta=8.01 mmHg, 95% CI=0.10, 15.9). The increase in SBP was even greater in these women when habitual snoring was associated with rhinitis (beta=11.96 mmHg, 95% CI=1.01, 22.9).

CONCLUSION

We suggest that the association of snoring with rhinitis may facilitate the development of apnea during sleep, which in post-menopausal women may increase the risk of developing hypertension.

Lymphocyte activation as a possible measure of atherosclerotic risk in patients with sleep apnea

Obstructive sleep apnea (OSA), a breathing disorder in sleep characterized by intermittent hypoxia and sleep fragmentation, constitutes an independent risk factor for cardiovascular morbidity. Investigating how this breathing disorder modulates immune responses may facilitate understanding one of the risk factors for atherosclerosis. T cells play a significant role in atherogenesis and plaque development via cytokine production and by directly contributing to vascular injury. Using flow cytometry and chromium release assays, we found that CD4 and CD8 T cells of OSA patients undergo phenotypic and functional changes and acquire cytotoxic capabilities. Thus, a shift in CD4 and CD8 T cells toward type 2 cytokine dominance with increased IL-4 expression was noted. IL-10 expression in T cells was negatively correlated with the severity of OSA, as determined by the apnea-hypopnea index (AHI), whereas TNF-alpha was positively correlated. CD8 T cells of OSA patients expressed a fourfold increase in TNF-alpha and CD40 ligand (CD40L), and exhibited an increased OSA severity-dependent cytotoxicity against endothelial cells. The percentage of CD4(+)CD28(null) and cytotoxicity of CD4 T lymphocytes were also significantly higher in OSA patients than in controls. Nasal continuous positive airway pressure (nCPAP) treatment, which ameliorated the severity of OSA, significantly lowered TNF-alpha and CD40L expression, and decreased cytotoxicity in CD8 T cells. In conclusion, increased cytotoxicity and cytokine imbalance in CD4 and CD8 T cells may be involved in atherogenesis in OSA. Nasal CPAP treatment ameliorates some lymphocyte dysfunctions and thus may moderate some atherogenic pathways.

Heritable and pharmacological influences on pauses and apneas in inbred mice during anesthesia and emergence

Inherited differences in response to hypercapnia are augmented by volatile anesthetics. Therefore, the authors tested the hypotheses that (1) the incidence of pauses and apneas also increase under anesthesia; (2) there is a difference in the incidence between mouse strains; and (3) there is a difference in the incidence of pauses and apneas depending on the volatile agent. The authors assessed respiratory pauses and apneas at rest; during anesthesia with isoflurane, sevoflurane, and desflurane; and at recovery in C3, B6, and F1 mice. The results are compared using analysis of variance (ANOVA) (P<.05). Awake, there was no difference between mouse strains (Bb, 0.3+/-0.7 P min(-1), C3, 0.4+/-0.7 P min(-1) and F1, 0.4+/-0.5 P min(-1)). In contrast, during anesthesia C3 mice showed a significantly higher incidence of pauses and apneas. There was no increase for B6 and F1 mice. There was no difference depending on the volatile agent. These results indicate an inheritance of a susceptibility to pauses and apneas under the influence of volatile anesthetics, albeit independent of the agent used. This response seems to be independent from the inherited response to hypercapnia.

Chronic intermittent hypoxia activates nuclear factor-κB in cardiovascular tissues in vivo

Obstructive sleep apnea (OSA) is an important risk factor for cardiovascular morbidity and mortality. The mechanisms through which OSA promotes the development of cardiovascular disease are poorly understood. In this study, we tested the hypotheses that chronic exposure to intermittent hypoxia and reoxygenation (CIH) is a major pathologic factor causing cardiovascular inflammation, and that CIH-induces cardiovascular inflammation and pathology by activating the NF-kappaB pathway. We demonstrated that exposure of mice to CIH activated NF-kappaB in cardiovascular tissues, and that OSA patients had markedly elevated monocyte NF-kappaB activity, which was significantly decreased when obstructive apneas and their resultant CIH were eliminated by nocturnal CPAP therapy. The elevated NF-kappaB activity induced by CIH is accompanied by and temporally correlated to the increased expression of iNOS protein, a putative and important NF-kappaB-dependent gene product. Thus, CIH-mediated NF-kappaB activation may be a molecular mechanism linking OSA and cardiovascular pathologies seen in OSA patients.

Antidepressant therapy in patients with ischemic heart disease

Depressive disorders are common in patients with ischemic heart disease and have serious consequences in terms of the risk of further cardiac events and cardiac mortality. Among survivors of acute myocardial infarction, up to one fifth meet diagnostic criteria for major depression, and the presence of major depression carries a >5-fold increased risk for cardiac mortality within 6 months. This article reviews clinical trial data on the cardiac safety profiles of antidepressant agents with the aim of discussing clinical considerations in selecting the most appropriate treatment of comorbid depression in patients with ischemic heart disease. Tricyclic antidepressants are effective against depression but are associated with cardiovascular side effects including orthostatic hypotension, slowed cardiac conduction, antiarrhythmic activity, and increased heart rate. Selective serotonin reuptake inhibitors, by contrast, have benign cardiovascular profiles and are well tolerated in patients with cardiac disease. The safety of dual-acting serotonin and noradrenaline reuptake inhibitors has not been well studied. Intervention with a selective serotonin reuptake inhibitors has the potential to provide the depressed patient with ischemic heart disease relief from their depressive symptoms and may offer a potential improvement in their cardiovascular risk profile.

Automatic detection of spiking events in EMFi sheet during sleep

In this paper we present a new method for detection of spiking events caused by the increased respiratory resistance (IRR) from ballistocardiographic (BCG) data recorded with EMFi sheet. Spiking is a phenomenon where BCG wave complexes increase in amplitude during IRR. In this study data from six patients with a total of 1503 visually scored spiking events were studied. The algorithm monitors amplitude levels of BCG complexes and detects large relative increases. In this work 10 different variations of the algorithm were compared in order to find the best variation, which can cope with different recordings. The best variation of the algorithm was able to detect spiking events with 80% true positive and 19% false positive rates. The detection is not dependent on absolute waveform amplitudes and therefore does not require any recording-specific tuning prior to application. It is important to recognize spiking events in order to evaluate the severity of respiratory disturbance during sleep.

A stepped approach for prediction of obstructive sleep apnea in overtly asymptomatic obese subjects: a hospital based study

BACKGROUND AND PURPOSE

Prevalence of obstructive sleep apnea (OSA) is high in obese subjects, many of whom may not be overtly symptomatic. Polysomnography (PSG) is a costly and time-consuming investigation. Since it is not feasible to subject all obese individuals to PSG, it is useful to define predictors of OSA among these subjects.

PATIENTS AND METHODS

One hundred and eighteen obese subjects [body mass index (BMI)> or =25 kg/m(2)] presenting to the hospital with non-sleep related complaints were included, of which 53 subjects with PSG evidence of OSA [apnea-hypopnea index (AHI)> or =15/h] were defined as cases and 65 subjects without any evidence of OSA (AHI<15/h) were defined as controls. Anthropometry, biochemical investigations, blood gas analysis, pulmonary function tests, and PSG were performed for all subjects.

RESULTS

Waist hip ratio (WHR) (as percentage of a standard) [odds ratio (95% CI): 1.07 (1.00-1.14); P = 0.049] male gender [odds ratio (95% CI): 3.97 (0.99-15.81); P = 0.046] and neck circumference (NC) [odds ratio (95% CI): 1.23 (1.03-1.47); P = 0.023] were found to be independent predictors of OSA. Overnight oxygen desaturation data were evaluated in patients selected as having OSA on the basis of these clinical markers, and the best cut-off for level of desaturation (10%) was defined. The stepped approach had a specificity, sensitivity, positive and negative predictive value of 89.2, 88.5, 86.8 and 90.6%, respectively, for the diagnosis of OSA.

CONCLUSIONS

Male gender, WHR and NC are independent predictors of OSA in overtly asymptomatic obese subjects. A stepped approach to diagnose OSA should be used, as it is accurate and cost-effective.

Positive pressure ventilation in the management of acute and chronic cardiac failure: a systematic review and meta-analysis

Chronic heart failure (CHF) is a common condition and is associated with excess morbidity and mortality, in spite of the many advances in its treatment. Chronic stable heart failure is also associated with an increased incidence of sleep-related breathing disorders, such as central sleep apnoea (CSA) and Cheyne Stokes respiration (CSR). Continuous positive airways pressure (CPAP) has been shown to alleviate the symptoms of CHF, improve left ventricular function and oxygenation. To a certain extent, CPAP also abolishes sleep-related breathing disorders in patients with chronic heart failure. In patients with acute pulmonary oedema, the use of positive pressure ventilation improves cardiac haemodynamic indices, as well as symptoms and oxygenation, and is associated with a lower need for intubation. However, some studies have cast doubts about its safety and suggest a higher rate of myocardial infarction associated with its use. In our opinion, non-invasive positive pressure ventilation and CPAP offers an adjunctive mode of therapy in patients with acute pulmonary oedema and chronic heart failure, who may not be suitable for intubation and in those not responsive to conventional therapies. Non-invasive ventilation also helps to improve oxygenation in those patients with exhaustion and respiratory acidosis. Many trials are still ongoing and the results of these studies would throw more light on the present role of non-invasive ventilation in the management of CHF.

Radial basis function approach to nonlinear Granger causality of time series

We consider an extension of Granger causality to nonlinear bivariate time series. In this frame, if the prediction error of the first time series is reduced by including measurements from the second time series, then the second time series is said to have a causal influence on the first one. Not all the nonlinear prediction schemes are suitable to evaluate causality; indeed, not all of them allow one to quantify how much knowledge of the other time series counts to improve prediction error. We present an approach with bivariate time series modeled by a generalization of radial basis functions and show its application to a pair of unidirectionally coupled chaotic maps and to physiological examples.

Determinants of heart rate variability in obstructive sleep apnea syndrome during wakefulness and sleep

Heart rate variability (HRV) is mediated by at least three primary mechanisms: 1) vagal feedback from pulmonary stretch receptors (PSR), 2) central medullary coupling between respiratory and cardiovagal neurons (RCC), and 3) arterial baroreflex (ABR)-induced fluctuations. We employed a noninvasive experimental protocol in conjunction with a minimal model to determine how these sources of HRV are altered in obstructive sleep apnea syndrome (OSAS). Respiration, heart rate, and blood pressure were monitored in eight normal subjects and nine untreated OSAS patients in relaxed wakefulness and stage 2 and rapid eye movement sleep. A computer-controlled ventilator delivered inspiratory pressures that varied randomly from breath to breath. Application of the model to the corresponding subject responses allowed the delineation of the three components of HRV. In all states, RCC gain was lower in OSAS patients than in normal subjects (P < 0.04). ABR gain was also reduced in OSAS patients (P < 0.03). RCC and ABR gains increased from wakefulness to sleep (P < 0.04). However, there was no difference in PSR gain between subject groups or across states. The findings of this study suggest that the adverse autonomic effects of OSAS include impairment of baroreflex gain and central respiratory-cardiovascular coupling, but the component of respiratory sinus arrhythmia that is mediated by lung vagal feedback remains intact.

Sleep-disordered breathing: implications in cerebrovascular disease

Stroke and sleep-disordered breathing (SDB) are both common and are associated with significant morbidity and mortality. Several recent large epidemiologic studies have shown a strong association between these two disorders independent of known risk factors for stroke. This review will outline the scientific basis for this relationship and suggest SDB as a modifiable risk factor for stroke. Several studies have shown a characteristic circadian rhythmicity in stroke. The authors discussed the influence of normal sleep states as well as the effect of SDB on cerebral hemodynamics. The hemodynamic, metabolic, and hematologic changes during SDB in the form of decreased cerebral perfusion and increased coagulability are the possible pathogenetic mechanisms for stroke. There are accumulating lines of evidence that SDB may indeed cause diurnal hypertension. However, the increased risk of stroke in patients with SDB appears to be independent of coexisting hypertension, but the presence of hypertension would greatly increase the risk even further. Furthermore, several studies have documented high prevalence of sleep apnea in patients with transient ischemic attacks and stroke. SDB appears to contribute as a risk factor for stroke through hemodynamic and hematologic changes. Because of high prevalence of SDB in this population, patients with transient ischemic attacks and stroke should be screened for these disorders.

Obstructive sleep apnea presenting as pseudopheochromocytoma: a case report

Sudden arousal from sleep causes a transient surge in sympathetic nervous activity. Repeated arousals, as occur in obstructive sleep apnea (OSA), are well documented to cause a more prolonged sympathetic overactivity and consequent elevations in 24-h urinary catecholamine levels. We describe here a series of five patients, each presenting with a clinical and biochemical picture indistinguishable from that of pheochromocytoma. Thorough investigations have failed to find catecholamine-secreting tumor in any of these subjects, but all have been diagnosed with OSA. Primary treatment of OSA with nasal continuous positive airways pressure has led to normalization of systemic blood pressure and urinary catecholamines. Pseudopheochromocytoma is therefore a rare, but treatable, presentation of obstructive sleep apnea.

What's “Unstable” in Unstable Angina?

The role of emotional distress (e.g., anger, depression, and anxiety) in anginal chest discomfort (ACD) may have been underestimated. The authors review the empirical studies in this area, which are inconsistent with the standard theory on the ischemia-angina relationship; summarize the substantial evidence indicating a strong and consistent cross-sectional/prospective epidemiological association of emotional distress and ischemia/ACD; review the distress-targeted, interventional evidence confirming a causal relationship (i.e., reduced chest discomfort and health system utilization), thus confirming clinical utility of such interventions; and explore the possible mechanisms that might account for the relationship between emotional distress and chest discomfort. Substantial clinical benefit may be achieved by aggressively detecting and treating emotional distress in ACD patients.