Sleep-related breathing disorders following discharge from intensive care

Objectives: To determine the incidence of sleep-related breathing disorders and nocturnal hypoxaemia in patients discharged from ICU following prolonged mechanical ventilation.¶Design: Prospective, consecutive patient observational study.¶Setting: The medical and surgical wards of a University Hospital.¶Patients and participants: Fifteen consecutive, adult patients discharged from the ICU who had received more than 48 h of mechanical ventilation were studied. Ten healthy volunteers acted as controls.¶Measurements and results: Overnight, multi-channel pneumographic studies were performed on all patients and controls. Chest and abdominal wall movement, air flow, oxygen saturation and snoring were continuously recorded. Data was analysed by both visual inspection of the traces and by computer-based algorithms. An apnoea/hypopnoea index was calculated for each patient and volunteer. Volunteers had an apnoea/hypopnoea index of less than 5 and had no episodes of nocturnal oxygen desaturation (SaO₂ < 90 %). Despite oxygen therapy 13/15 patients had episodes of desaturation and 9/15 spent more than 2 h with an SaO₂ < 90 %. Eleven patients had an abnormal apnoea/hypopnoea index (range 5–34 events/h). Four patients had predominantly obstructive events while 7 primarily had hypopnoeas.¶Conclusions: Significant overnight oxygen desaturation is common in patients discharged from ICU who have received prolonged mechanical ventilation. This group also has a significant incidence of sleep-related breathing disorders and this mechanism is likely to be important in the pathogenesis of the hypoxaemia.     

Pattern recognition of obstructive sleep apnoea and Cheyne-Stokes respiration

The aim of this study was to assess the validity of an artificial neural network based on flow-related spectral entropy as a diagnostic test for obstructive sleep apnoea and Cheyne-Stokes respiration. A data set of 37 subjects was used for spectral analysis of the airflow by performing a fast Fourier transform. The examined intervals were divided into epochs of 3 min. Spectral entropy S was applied as a measure for the spread of the related power spectrum. The spectrum was divided into several frequency areas with various subsets of spectral entropy. We studied 11 subjects with obstructive apnoeas (n = 267 epochs), 10 subjects with obstructive hypopnoeas (n = 80 epochs), 11 subjects with Cheyne-Stokes respiration (n = 253 epochs) and 5 subjects with normal breathing in non-REM sleep (n = 174 epochs). Based on spectral entropy an artificial neural network was built, and we obtained a sensitivity of 90.2% and a specificity of 90.9% for distinguishing between obstructive apnoeas and Cheyne-Stokes respiration, and a sensitivity of 91.3% and a specificity of 94.6% for discriminating between obstructive hypopnoeas and normal breathing in non-REM sleep. This resulted in an accuracy of 91.5% for identifying flow patterns of obstructive sleep apnoea, Cheyne-Stokes respiration and normal breathing in non-REM sleep. It is concluded that the use of an artificial neural network relying on spectral analysis of the airflow could be a useful method as a diagnostic test for obstructive sleep apnoea and Cheyne-Stokes respiration.     

Breathing during sleep in patients with myotonic dystrophy and non-myotonic respiratory muscle weakness.

Sleep apnoea and hypopnoea have been reported in myotonic dystrophy, but it is unclear whether this is simply attributable to the respiratory muscle weakness which is common in this condition. We therefore investigated whether breathing and oxygenation during sleep were more abnormal in patients with myotonic dystrophy than in patients with non-myotonic muscle weakness. Seven subjects were studied in each of three groups: normal controls, myotonic dystrophy and non-myotonic weakness. Patients in the latter group were chosen to represent a similar range of severity of respiratory muscle weakness to those with myotonic dystrophy. Detailed polysomnography was performed; the severity of breathing disorders during sleep was quantified in terms of the frequencies of apnoea and hypopnoea and the degree of arterial desaturation. The myotonic patients showed more frequent apnoea and hypopnoea and more severe desaturation than the other two groups; the results in the non-myotonic patients were generally intermediate. The results suggest that abnormal breathing during sleep is common in myotonic dystrophy and is not due solely to the direct effects of respiratory muscle weakness. Somnolence, which is a well recognized symptom of myotonic dystrophy, was not clearly attributable to the sleep apnoea/hypopnoea syndrome nor to abnormal sleep architecture in the myotonic patients.     

Respiratory monitoring using an air-mattress system

This paper describes a non-invasive respiratory monitoring system using an air mattress. The air-mattress system features multiple air compartments to monitor movements of the thorax and the abdomen separately. To evaluate the performance of the air-mattress system, four subjects were selected for the study and their separate ribcage and abdominal movements were monitored simultaneously by respiratory inductive phlethysmography belts and the air-mattress system. The sensitivity and accuracy indices of the air-mattress system for the detection of hypopnoeas scored remarkably well (above 90%). In addition, it was noted that the mean error in the measurement of the respiratory rate between the two systems was very small. This paper shows that the air-mattress system can be a reliable non-invasive respiratory monitoring system to detect simple abnormalities in breathing, such as respiration rate and hypopnoeas.     

Breathing During Sleep in Patients with Myotonic Dystrophy and Non-myotonic Respiratory Muscle Weakness

Sleep apnoea and hypopnoea have been reported in myotonic dystrophy,but it is unclear whether this is simply attributable to therespiratory muscle weakness which is common in this condition.We therefore investigated whether breathing and oxygenationduring sleep were more abnormal in patients with myotonic dystrophythan in patients with non-myotonic muscle weakness. Seven subjectswere studied in each of three groups: normal controls, myotonicdystrophy and non-myotonic weakness. Patients in the lattergroup were chosen to represent a similar range of severity ofrespiratory muscle weakness to those with myotonic dystrophy.Detailed polysoranography was performed; the severity of breathingdisorders during sleep was quantified in terms of the frequenciesof apnoea and hypopnoea and the degree of arterial desaturation.The myotonic patients showed more frequent apnoea and hypopnoeaand more severe desaturation than the other two groups; theresults in the non-myotonic patients were generally intermediate.The results suggest that abnormal breathing during sleep iscommon in myotonic dystrophy and is not due solely to the directeffects of respiratory muscle weakness. Somnolence, which isa well recognized symptom of myotonic dystrophy, was not clearlyattributable to the sleep apnoea/hypopnoea syndrome nor to abnormalsleep architecture in the myotonic patients.     

Pitot-tube flowmeter for quantification of airflow during sleep

The gold-standard pneumotachograph is not routinely used to quantify airflow during overnight polysomnography due to the size, weight, bulkiness and discomfort of the equipment that must be worn. To overcome these deficiencies that have precluded the use of a pneumotachograph in routine sleep studies, our group developed a lightweight, low dead space 'pitot flowmeter' (based on pitot-tube principle) for use during sleep. We aimed to examine the characteristics and validate the flowmeter for quantifying airflow and detecting hypopneas during polysomnography by performing a head-to-head comparison with a pneumotachograph. Four experimental paradigms were utilized to determine the technical performance characteristics and the clinical usefulness of the pitot flowmeter in a head-to-head comparison with a pneumotachograph. In each study (1-4), the pitot flowmeter was connected in series with a pneumotachograph under either static flow (flow generator inline or on a face model) or dynamic flow (subject breathing via a polyester face model or on a nasal mask) conditions. The technical characteristics of the pitot flowmeter showed that, (1) the airflow resistance ranged from 0.065 ± 0.002 to 0.279 ± 0.004 cm H(2)O L(-1) s(-1) over the airflow rates of 10 to 50 L min(-1). (2) On the polyester face model there was a linear relationship between airflow as measured by the pitot flowmeter output voltage and the calibrated pneumotachograph signal a (β(1) = 1.08 V L(-1) s(-1); β(0) = 2.45 V). The clinically relevant performance characteristics (hypopnea detection) showed that (3) when the pitot flowmeter was connected via a mask to the human face model, both the sensitivity and specificity for detecting a 50% decrease in peak-to-peak airflow amplitude was 99.2%. When tested in sleeping human subjects, (4) the pitot flowmeter signal displayed 94.5% sensitivity and 91.5% specificity for the detection of 50% peak-to-peak reductions in pneumotachograph-measured airflow. Our data validate the pitot flowmeter for quantification of airflow and detecting breathing reduction during polysomnographic sleep studies. We speculate that quantifying airflow during sleep can differentiate phenotypic traits related to sleep disordered breathing.     

Does propofol and alfentanil‐induced sedation cause periodic apnoea in chronic renal failure patients?

Aims: There is evidence suggesting that the respiratory response to sedation is different in patients with sleep apnoea, which is common in patients with chronic renal failure (CRF). This study examined the respiratory response of sedation with propofol and alfentanil, whose pharmacokinetics are not affected by the renal function, in CRF patients. Methods: Chronic renal failure patients who underwent arteriovenous‐fistular surgery (CRF group) and patients who underwent chemoport insertion (control group) were enrolled in this study. Sedation was induced by infusing propofol 1.5 μ/ml and alfentanil 0.2 μ/kg/min continuously in both groups. In the desaturation study, the respiratory rate and peripheral oxygen saturation in room air were checked. In the apnoea–hypopnoea study, the patient's sedation (Observer's Assessment of Alertness/Sedation) score, apnoea–hypopnoea index (AHI) was recorded using a portable ventilation effort recorder (microMesam) while applying 5 l/min of oxygen through a facial mask. Results: The desaturation event was more common (21.5/h vs. 2/h, p = 0.001) in the CRF patients. Apnoea and hypopnoea (AHI: 13.0 vs. 1.6, p = 0.012, per cent of patients with an AHI > 5: 53.3% vs. 7.1%, p = 0.014) occurred more frequently in the CRF patients but the sedation score was not different. Conclusion: Chronic renal failure patients have a higher risk of developing apnoea and hypopnoea during sedation, which highlights the need for careful monitoring and management in these patients.     

Sleep apnoea in alcoholic patients after withdrawal

Respiration during sleep was studied in 16 withdrawn alcoholic patients and in 12 control subjects. The alcoholic patients had increased numbers of central (P less than 0.01) and of obstructive (P less than 0.05) apnoea and of hypopnoea episodes (P less than 0.01) as compared with controls. Significant positive associations were found between the frequencies of central apnoea (P less than 0.05) or hypopnoea (P less than 0.01) and clinical evidence of central nervous system damage in the alcoholic patients. Hypopnoea also showed a significant association with vagal neuropathy (P less than 0.05), assessed by tests of cardioreflexes. We conclude that abnormal respiratory events are common in abstinent alcoholic patients and that they are likely to be at least partly related to nervous damage.     

Eszopiclone increases the respiratory arousal threshold and lowers the apnoea/hypopnoea index in obstructive sleep apnoea patients with a low arousal threshold

Recent insights into sleep apnoea pathogenesis reveal that a low respiratory arousal threshold (awaken easily) is important for many patients. As most patients experience stable breathing periods mediated by upper-airway dilator muscle activation via accumulation of respiratory stimuli, premature awakening may prevent respiratory stimuli build up as well as the resulting stabilization of sleep and breathing. The aim of the present physiological study was to determine the effects of a non-benzodiazepine sedative, eszopiclone, on the arousal threshold and the AHI (apnoea/hypopnoea index) in obstructive sleep apnoea patients. We hypothesized that eszopiclone would increase the arousal threshold and lower the AHI in patients with a low arousal threshold (0 to -15 cm H(2)O). Following a baseline overnight polysomnogram with an epiglottic pressure catheter to quantify the arousal threshold, 17 obstructive sleep apnoea patients, without major hypoxaemia [nadir SaO(2) (arterial blood oxygen saturation) >70%], returned on two additional nights and received 3 mg of eszopiclone or placebo immediately prior to each study. Compared with placebo, eszopiclone significantly increased the arousal threshold [-14.0 (-19.9 to -10.9) compared with -18.0 (-22.2 to -15.1) cm H(2)O; P<0.01], and sleep duration, improved sleep quality and lowered the AHI without respiratory event prolongation or worsening hypoxaemia. Among the eight patients identified as having a low arousal threshold, reductions in the AHI occurred invariably and were most pronounced (25±6 compared with 14±4 events/h of sleep; P<0.01). In conclusion, eszopiclone increases the arousal threshold and lowers the AHI in obstructive sleep apnoea patients that do not have marked overnight hypoxaemia. The greatest reductions in the AHI occurred in those with a low arousal threshold. The results of this single night physiological study suggest that certain sedatives may be of therapeutic benefit for a definable subgroup of patients. However, additional treatment strategies are probably required to achieve elimination of apnoea.     

The nurse role in managing and treating sleep disorders

Obstructive sleep apnoea/hypopnoea syndrome affects a significant number of middle-aged people. By causing the person with the condition to wake repeatedly during the night in order to restart breathing, it causes excessive daytime sleepiness and impairs cognitive function and driving ability. It can also adversely affect family relationships, particularly with partners whose sleep may also be disturbed. Nurses have a role in the diagnosis and management of the condition through appropriate questioning, observation, advice on lifestyle choices, and support for treatment. The article also focuses on narcolepsy.     

Forced oscillation technique in the sleep apnoea/hypopnoea syndrome: identification of respiratory events and nasal continuous positive airway pressure titration

Sleep breathing disorders (SBD) are related to obstructions resulting from repetitive narrowing and closure of the pharyngeal airway. Their diagnoses and treatment are critically dependent on an accurate identification of and discrimination between types of respiratory events. However, these disorders have been diagnosed using indirect or invasive measurements, which resulted in serious doubts concerning the correct evaluation of breathing events. The forced oscillation technique (FOT) has recently been suggested as a clinical tool able to accurately and non-invasively quantify respiratory obstruction during sleep. The present study investigates the morphology of the impedance signal during different sleep respiratory events and evaluates the ability of impedance measurements in providing adequate nasal continuous positive airway pressure (nCPAP) titration. The results evidenced characteristic patterns in impedance signal morphology that are useful in the identification and classification of abnormal respiratory events. Moreover, significantly higher impedance values were obtained during apnoea and hypopnoea events when compared with normal values (p < 0.01). Studies using impedance measurements to adjust nCPAP showed a significant reduction (p < 0.01) of abnormal respiratory events, and a consequent normalization of the patients. These findings support the use of the FOT as a versatile clinic diagnostic tool helping SBD diagnosis and treatment.     

Autonomic cardiovascular regulation in patients with obstructive sleep apnoea: a study based on spectral analysis of heart rate variability

The aim of this study was to assess the function of the autonomic nervous system in patients with obstructive sleep apnoea syndrome (OSAS). The study was designed as a cross‐sectional case–control study. Fifty‐one patients were included, and the findings were compared with those in 66 controls. Spectral analysis of heart rate variability (HRV) during supine rest, during controlled breathing and after tilting was performed in each patient and control case. The patients performed overnight sleep recordings the night before the HRV recordings. Individuals with an apnoea–hypopnoea index (AHI) above 20 were regarded as OSAS patients and those with AHI lower than 20 as snorers. Differences in HRV and blood pressure between patients and controls were analysed by multiple linear regression with age, body mass index and sex as independent variables. During free and controlled breathing there was a significant decrease in indices reflecting vagal modulation, indicating parasympathetic dysfunction in OSAS patients compared with controls. The mid‐frequency component was also significantly reduced in OSAS patients after tilting but not in the lying position. This may be related to the parasympathetic dysfunction, but could also indicate a decreased sympathetic reserve capacity. We found no significant relation between AHI and indices of vagal modulation in the patient group. Our findings show an autonomic dysfunction in patients with OSAS. The dysfunction involves the parasympathetic system, and may be related to the increased cardiovascular mortality and malignant arrhythmia described in OSAS.     

Imposed work of breathing during ventilator failure

INTRODUCTION: Ventilators possess an anti-asphyxia valve that allows spontaneous breathing of ambient air during ventilator failure. This study examined the imposed work of breathing and pressure-time product of 8 critical care and 9 portable ventilators, using a laboratory simulation of spontaneous breathing during ventilator failure. METHODS: A test lung was modified to simulate spontaneous breathing with a tidal volume of 0.5 L and peak inspiratory flow of 60 L/min. A pneumotachograph and pressure tap were placed at the proximal airway between the breathing circuit and endotracheal tube. Flow was derived from the pressure drop across the pneumotachograph. Signals were amplified, integrated, and saved to a spreadsheet program, and imposed work of breathing and pressure-time product were calculated. Also measured were the inspiratory pressure required to open the anti-asphyxia valve (cracking pressure), time to cracking pressure, maximum negative inspiratory pressure, and time to maximum negative inspiratory pressure. RESULTS: For the critical care ventilators the mean +/- SD imposed work of breathing ranged from 213.07 +/- 3.53 to 890.63 +/- 0.88 mJ/L and the pressure-time product ranged from 2.67 +/- 0.01 to 13.37 +/- 0.01 cm H(2)O x s/L. For the portable ventilators the mean +/- SD imposed work of breathing ranged from 361.37 +/- 1.22 to 969.60 +/- 22.70 mJ/L and the pressure-time product ranged from 4.52 +/- 0.01 to 16.70 +/- 0.37 cm H(2)O x s/L. CONCLUSIONS: Spontaneous breathing during ventilator failure may impose work approximating the physiologic work of breathing. This imposed work may prevent effective breathing through the anti-asphyxia valve during mechanical ventilator failure due to electrical failure. These results reinforce the need to properly monitor mechanically ventilated patients and to have in place sufficient back-up power supplies and a method of manual ventilation.     

Flow-regulated continuous positive airway pressure to minimize imposed work of breathing

We have developed a new continuous positive airway pressure (CPAP) system, which consists of an electropneumatic regulator, a microcomputer, and a pneumotachograph placed between the endotracheal tube and the breathing circuit of the CPAP apparatus. This flow-regulated CPAP (FR-CPAP) system delivers a basal flow and also regulates this flow every 20 msec to match the patient's flow demand. To evaluate the performance of this FR-CPAP system, we compared the imposed work of breathing of the FR-CPAP and continuous flow CPAP (CF-CPAP) systems. A model lung was used to simulate spontaneous breathing. The imposed work of breathing of the FR-CPAP system was less than that of the CF-CPAP system. These results indicate that the FR-CPAP system could minimize the imposed work of breathing of a patient receiving CPAP.     

Clinical Significance of Sleep-Related Breathing Disorders in Patients with Implantable Cardioverter Defibrillators

The prevalence and clinical significance of sleep-related breathing disorders (SRBDs) in patients with cardiac disease and a history of life-threatening ventricular tachyarrhythmias is unclear. Forty consecutive recipients of implantable cardioverter defibrillators (ICDs) with cardiac disease and a documented history of spontaneous, life-threatening, ventricular tachyarrhythmias underwent full night polysomnography. SRBDs were diagnosed if the apnea/hypopnea index was > 10. SRBD were diagnosed in 16 of 40 patients (40%): central sleep apnea (CSA) was present in 9 of these 16 patients (56%), 8 of whom had associated Cheyne-Stoke respiration. Seven of the 16 patients with SRBD (44%) had obstructive sleep apnea (OSA). Patients with and without SRBDs were comparable with respect to left ventricular ejection fraction, NYHA classification, underlying heart disease, ICD indications, and concomitant antiarrhythmic drug and beta-blocker therapy. Patients were followed prospectively for 2 years. ICD-treated ventricular tachyarrhythmias occurred in 10 of 24 patients (42%) without SRBD, in 4 of 9 patients (44%) with CSA, and in 3 of 7 patients (44%) with OSA (NS). The numbers and circadian distributions of episodes recorded during follow-up in patients without SRBD versus with CSA or OSA were not significantly different (14 ± 25, median = 4 vs 4 ± 5, median = 2.5 vs 15 ± 15, median = 7, respectively). The 2-year mortality, which was entirely attributable to nonsudden cardiac events, was highest in patients with CSA (4/9 [44%], vs 0/7 [0%] with OSA, vs 3/24 patients (12.5%) without SRBD; P < 0.05).     

椎-基动脉缺血发作与睡眠呼吸障碍

Therelationshipbetweencerebro－vasculardiseases（CVD）andSRBDhasattractedpeople’sattentionmoreandmoreinthepastyears．WepresentinthispapertherelationshipofVBIandSRBDwhichhasnoteverbeenreportedbefore．１Subjectandmethod１．１SubjectFortyfivepatients，male３２，female１３，withanageof２７～７４yearsandanaveragedurationofillnessof２．１years（５daysto１０years）．１．２Criteriaofdiagnosis犤１犦（１）Transientvertigoattacksaccom－paniedbyotherVBIsymptomssuchasdiplopia，scintillation，visua…     

Automated detection of sleep apnea from electrocardiogram signals using nonlinear parameters

Sleep apnoea is a very common sleep disorder which can cause symptoms such as daytime sleepiness, irritability and poor concentration. To monitor patients with this sleeping disorder we measured the electrical activity of the heart. The resulting electrocardiography (ECG) signals are both non-stationary and nonlinear. Therefore, we used nonlinear parameters such as approximate entropy, fractal dimension, correlation dimension, largest Lyapunov exponent and Hurst exponent to extract physiological information. This information was used to train an artificial neural network (ANN) classifier to categorize ECG signal segments into one of the following groups: apnoea, hypopnoea and normal breathing. ANN classification tests produced an average classification accuracy of 90%; specificity and sensitivity were 100% and 95%, respectively. We have also proposed unique recurrence plots for the normal, hypopnea and apnea classes. Detecting sleep apnea with this level of accuracy can potentially reduce the need of polysomnography (PSG). This brings advantages to patients, because the proposed system is less cumbersome when compared to PSG.     

Clinical Features of the Sleep Apnoea/Hypopnoea Syndrome

The sleep apnoea/hypopnoea syndrome has been reported to berare in Britain. We have offered a clinical service for thediagnosis and treatment of this condition in Scotland for fouryears during which there has been an increase in referral ratefrom 19 patients in year 1 to 61 in year 4. We report the clinicalfeatures of the 80 patients. Seventy-eight snored and 70 weresomnolent, each falling asleep at least once each day when notin bed. Ten reported falling asleep whilst driving or flying.Twenty-nine slept restlessly, 28 were not refreshed by sleepand 21 had nocturnal choking attacks. Ankle swelling was reportedby 26 and 25 were hypertensive (diastolic BP > 95 mmHg).Two had hyperthyroidism and one acromegaly. Nineteen have beensuccessfully treated by continuous positive airway pressuretherapy at home. The data suggest that regional centres shouldbe established in Britain to diagnose and treat this condition.     

Validation of indirect calorimetry for measurement of energy expenditure in healthy volunteers undergoing pressure controlled non-invasive ventilation support

The aim of this validation study was to assess the reliability of gas exchange measurement with indirect calorimetry among subjects who undergo non-invasive ventilation (NIV). Oxygen consumption (VO₂) and carbon dioxide production (VCO₂) were measured in twelve healthy volunteers. Respiratory quotient (RQ) and resting energy expenditure (REE) were then calculated from the measured VO₂ and VCO₂ values. During the measurement period the subjects were breathing spontaneously and ventilated using NIV. Two different sampling air flow values 40 and 80 l/min were used. The gas leakage from the measurement setup was assessed with a separate capnograph. The mean weight of the subjects was 93 kg. Their mean body mass index was 29 (range 22–40) kg/m². There was no statistically significant difference in the measured values for VO₂, VCO₂, RQ and REE during NIV-supported breathing and spontaneous breathing. The change of sampling air flow had no statistically significant effect on any of the above parameters. We found that REE can be accurately measured with an indirect calorimeter also during NIV-supported breathing and the change of sampling air flow does not distort the gas exchange measurement. A higher sampling air flow in indirect calorimetry decreases the possibility for air leakages in the measurement system and increases the reliability of REE measurement.     

Obstructive sleep apnoea/hypopnoea as the initial presentation of relapsing polychondritis

Relapsing polychondritis (RP) is a relatively rare rheumatological condition, which can affect the upper airway and prove potentially life threatening. We report the first case of RP presenting initially as the obstructive sleep apnoea/hypopnoea syndrome, discuss management and review the extant literature.