Sleep disordered breathing – a new component of syndrome x?

Sleep disordered breathing (SDB) is a complication of obesity estimated to occur in about 4–6% of overweight individuals. These respiratory disturbances during sleep incorporate a number of conditions including snoring, upper airway resistance syndrome and obstructive sleep apnoea syndrome (OSAS). It is thought that as well as having deleterious effects on sleep quality these conditions may also promote cardiovascular and hormonal changes leading to an elevated blood pressure and an increased incidence of cardiovascular morbidity. Evidence reviewed here points to an alteration in sympathovagal balance, baroreceptor sensitivity, insulin resistance and leptin, growth hormone and lipid levels. Whether these changes are a consequence of the associated obesity or the SDB itself remains to be proven.     

Regulation of ventilation before and after sleep in patients with obstructive sleep apnoea

The objective was to examine whether abnormal breathing during sleep may affect regulation of ventilation after awakening in patients with obstructive sleep apnoea (OSAS). In 19 patients with OSA and 12 normal subjects we examined ventilatory responses to hypoxia (HVR) and to hypercapnia (HCVR) before and after sleep (BS and AS), and compared the changes in ventilatory responses with respiratory events during sleep. In the OSA group, the values of resting ventilation were significantly smaller in AS than those in BS and end-tidal partial pressure of CO2 in arterial blood (Pco2) (PETCO2) rose significantly from BS to AS. The slopes of the HVR or HCVR did not differ between BS and AS. However, both the response lines shifted downward and minute ventilation (VE)80 (VE at arterial oxygen saturation (Sao2) of 80%) in HVR and VE60 (VE at PETCO2 of 60 mmHg) in HCVR decreased significantly from BS to AS. The percentage changes of VE80 and VE60 were significantly correlated with mean Sao2, total sleep time below Sao2 of 90% and lowest Sao2 during sleep. However, in normal subjects we observed no circadian variation in their ventilatory responses. These data support the hypothesis that repeated episodes of nocturnal hypoxia and hypercapnia may modify the regulation of ventilation after awakening in patients with OSA.     

Anaesthetic management of sleep‐disordered breathing in adults

Anaesthesia and sleep are different states of unconsciousness with considerable physiological common ground. Because of their shared depressant effects on muscle activation and ventilatory drive, patients with anatomically compromised airways will tend to obstruct in either state and those with impaired ventilatory capacity will tend to hypoventilate. Breathing behaviour in one state is predictive of that in the other. An essential difference is that while arousal responses are preserved during sleep, they are depressed during sedation and abolished by anaesthesia. This renders patients with sleep‐related breathing disorders vulnerable to hypoventilation and asphyxia when deeply sedated. Addressing this vulnerability requires a systematic approach to identification of patients and circumstances that magnify this risk, and methods of managing it that seek to reconcile the need for safety with cost‐effective use of resources.     

Sleep and breathing in Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a genetic disorder, with hypotonia being the predominant feature in infancy, and developmental delay, obesity, and behavioral problems becoming more prominent in childhood and adolescence. Children with this disorder frequently suffer from excessive daytime sleepiness and have a primary abnormality of the circadian rhythm of rapid eye movement sleep. They also have primary abnormal ventilatory responses to hypoxia and hypercapnia, and these abnormalities may be exacerbated by obesity. Children with PWS are at risk of a variety of abnormalities of breathing during sleep, including obstructive sleep apnea and sleep-related alveolar hypoventilation. Clinical evaluation should include a careful history of sleep-related symptoms and assessment of the upper airway and lung function. Polysomnography should be considered for those with symptoms suggestive of sleep-disordered breathing. Treatment options depend on the underlying problem, but may include behavioral interventions, weight control, adenotonsillectomy, and nocturnal ventilation.     

Sleep-disordered breathing in patients with symptomatic heart failure: a contemporary study of prevalence in and characteristics of 700 patients

AIM: Evaluation of the prevalence and nature of sleep-disordered breathing (SDB) in patients with symptomatic chronic heart failure (CHF) receiving therapy according to current guidelines. METHODS AND RESULTS: We prospectively screened 700 patients with CHF (NYHA class> or =II, LV-EF< or =40%) for SDB using cardiorespiratory polygraphy (Embletta). Furthermore, echocardiography, cardiopulmonary exercise and 6-min walk testing were performed. Medication included ACE-inhibitors and/or AT1-receptor blockers in at least 94%, diuretics in 87%, beta-blockers in 85%, digitalis in 61% and spironolactone in 62% of patients. SDB was present in 76% of patients (40% central (CSA), 36% obstructive sleep apnoea (OSA)). CSA patients were more symptomatic (NYHA class 2.9+/-0.5 vs. no SDB 2.57+/-0.5 or OSA 2.57+/-0.5; p<0.05) and had a lower LV-EF (27.4+/-6.6% vs. 29.3+/-2.6%, p<0.05) than OSA patients. Oxygen uptake (VO(2)) was lowest in CSA patients: predicted peak VO(2) 57+/-16% vs. 64+/-18% in OSA and 63+/-17% in no SDB, p<0.05. 6-min walking distances were 331+/-111 m in CSA, 373+/-108 m in OSA and 377+/-118 m in no SDB (p<0.05). CONCLUSIONS: This study confirms the high prevalence of SDB, particularly CSA in CHF patients. CSA seems to be a marker of heart failure severity.     

Sleep‐disordered breathing in spinal cord‐injured patients: A short‐term longitudinal study

Background and objective: Previous studies have demonstrated an increased incidence of sleep apnoea in spinal cord‐injured patients. Many of these studies were performed in long‐term, stable spinal cord injury (SCI). The aims of this study were: (i) to determine the prevalence of sleep‐disordered breathing (SDB) in acute SCI; (ii) to document the change in SDB over time during the rehabilitation period; and (iii) to correlate the degree of SDB with ventilatory parameters. Methods: Sixteen subjects with an acute SCI level T12 and above with complete motor impairment (American Spinal Injury Association impairment scale A or B) were recruited. Assessment, including polysomnography, respiratory function testing, and hypoxic and hypercapnic ventilatory responses, were performed 6–8 weeks post SCI, and repeated 6 months post SCI. Results: Eleven of 16 subjects (73%) had evidence of sleep apnoea, five of whom were moderate to severe. This high incidence persisted during the acute admission, with 9 of 12 subjects (75%) having sleep apnoea on polysomnography 20 weeks following injury. There was no correlation between the severity of SDB and other measures, such as level or completeness of injury, respiratory function tests or measures of ventilatory responses. Conclusions: We have demonstrated a high incidence of sleep apnoea in the acute phase of SCI that persisted during the acute admission. Despite the high incidence of sleep apnoea, patients were relatively asymptomatic. Screening of this population would appear worthwhile given the high prevalence, although the significance of the sleep apnoea and clinical impact is not known.     

Influence of cardiac resynchronisation therapy on different types of sleep disordered breathing

AIMS: This study investigates the influence of cardiac resynchronisation therapy (CRT) on sleep disordered breathing (SDB) in patients with severe heart failure (HF). METHODS AND RESULTS: Seventy-seven patients with HF (19 females; 62.6+/-10 years) eligible for CRT were screened for presence, type, and severity of SDB before and after CRT initiation (5.3+/-3 months) using cardiorespiratory polygraphy. NYHA class, frequency of nycturia, cardiopulmonary exercise, 6-minute walking test results, and echocardiography parameters were obtained at baseline and follow-up. Central sleep apnoea (CSA) was documented in 36 (47%), obstructive sleep apnoea (OSA) in 26 (34%), and no SDB in 15 (19%) patients. CRT improved clinical and haemodynamic parameters. SDB parameters improved in CSA patients only (apnoea hypopnoea index: 31.2+/-15.5 to 17.3+/-13.7/h, p<0.001; SaO2min: 81.8+/-6.6 to 84.8+/-3.3%, p=0.02, desaturation: 6.5+/-2.3 to 5.5+/-0.8%, p=0.004). Daytime capillary pCO2 was significantly lower in CSA patients compared to those without SDB with a trend towards increase with CRT (35.5+/-4.2 to 37.9+/-5.7 mm Hg, ns). After classifying short term clinical and haemodynamic CRT effects, improved SDB parameters in CSA occurred in responders only. CONCLUSIONS: In patients with severe HF eligible for CRT, CSA is common and can be influenced by CRT, this improvement depends on good clinical and haemodynamic response to CRT.     

High prevalence of previously unknown subclinical hypothyroidism in obese patients referred to a sleep clinic for sleep disordered breathing

BACKGROUND AND AIM: To evaluate the prevalence of previously unknown hypothyroidism in adult male and female patients with a wide range of body mass index (BMI) values, referred to a Sleep Clinic because of sleep disordered breathing (SDB). METHODS AND RESULTS: Serum concentrations of thyroid stimulating hormone (TSH) and free thyroxin (fT4), as well as forced vital capacity (FVC), PaO2, PaCO2, the Epworth sleepiness scale (ESS), respiratory disturbance index (RDI), loud snoring, and the percentage of total sleep time (TST) with <90% oxyhemoglobin saturation (TST(saO2<90%)) were measured in 78 overweight and obese adult subjects with no previous diagnosis of hypothyroidism (age: 18-72 years). The prevalence of previously undiagnosed subclinical hypothyroidism in the population as a whole was 11.5%. BMI, TSH and ESS were significantly higher in the hypothyroid than the euthyroid subjects, but there was no significant between-group difference in RDI, TST(saO2<90%) or the other investigated variables, including the prevalence of obstructive sleep apnea (OSA). Among the hypothyroid individuals, BMI, neck circumference, ESS, RDI and TST(Sao2<90%) were significantly higher in those with than in those without OSA. Furthermore, there was a clear trend towards a lower FVC% and higher snoring score in the OSA patients. CONCLUSIONS: Our results demonstrate a higher prevalence of hypothyroidism than that commonly reported in overweight and obese individuals referred to a Sleep Clinic for polysomnography because of SDB, thus suggesting that thyroid function should be evaluated in all obese patients suffering from SDB despite economic concerns.     

Strategies to augment adherence in the management of sleep‐disordered breathing

Continuous positive airway pressure (CPAP) is highly effective in treating sleep‐disordered breathing (SDB). However, unlike surgical interventions, this treatment modality relies heavily on patient acceptance and adherence. The current definition of adherence is largely arbitrary and is mainly used by third‐party payers to determine CPAP reimbursement but CPAP adherence remains sub‐optimal. Strategies to augment adherence, especially early in the course of a CPAP trial, are needed in the management of SDB. An understanding of the basis for observed differences in CPAP and oral appliance (OA) use is necessary in developing these strategies, but to date no single factor has been consistently identified. Consequently, a multidimensional approach using educational, behavioural, technological and potentially pharmacological strategies to target (i) disease characteristics, (ii) patient characteristics including psychosocial factors, (iii) treatment protocols and (iv) technological devices and side effects that may influence adherence, is likely required to augment the complex behaviour of CPAP and OA use. In the near future, we envision a personalized medicine approach to determine the risk of non‐adherence and set individualized adherence goals aimed at treating specific symptoms (e.g. excessive daytime sleepiness) and reducing the risk of patient‐specific SDB consequences (e.g. atherosclerosis). Resources for interventions to improve adherence such as educational programmes and telemedicine encounters could then be more efficiently allocated.