New strategies of screening and treatment for sleep apnea syndrome

Prevalence of complex sleep apnea among Japanese patients with sleep apnea syndrome

Sleep apnea syndrome (SAS) is basically divided into two types: obstructive and central SAS. Recently, the concept of complex SAS has been advocated. Complex SAS is defined as SAS that initially manifests as primarily obstructive SAS, but is characterized by the frequent central apneas after the removal of upper airway obstruction. To determine the prevalence and clinical significance of complex SAS among Japanese patients with SAS, 1,312 patients with SAS were enrolled in this study. Diagnosis of central SAS was made based on diagnostic polysomnography, and differentiation of obstructive SAS from complex SAS was made from polysomnographic findings for treatment with continuous positive airway pressure, which resolved upper airway obstruction. As a result, obstructive SAS was found in 1,232 of 1,312 patients with SAS (93.9%) and central SAS was found in 14 patients (1.1%). The overall prevalence of complex SAS was 5.0% (n = 66). The prevalence of complex SAS among 1,218 male and 94 female patients with SAS were 5.3% and 1.1%, respectively. Patients with complex SAS had significantly higher apnea/hypopnea indices than patients with either obstructive or central SAS, but were similar in both mean age and average body mass index to obstructive SAS patients. There were no significant between-group differences in numbers of patients with clinical complications including hypertension, cardiac diseases, or cerebrovascular diseases. In conclusion, the prevalence of complex SAS in Japanese SAS patients is 5.0%, which is lower than previously reported prevalence of complex SAS in the USA and Australia.

Mice with Blunted Hypoxic Ventilatory Response are Susceptible to Respiratory Disturbance during Hypoxia

Hypoxia causes a life-threatening situation, and the ventilatory response to hypoxia plays an important role in preventing death. We have hypothesized that persons with a blunted hypoxic ventilatory response may have a weak defense response to hypoxic episodes and be susceptible to fatal respiratory disturbances. However, precise correlations between the hypoxic ventilatory response and respiratory disturbances are not well understood. In the present study we examined the hypoxic and hypercapnic ventilatory responses in nine inbred mouse strains (A/J, AKR/N, BALB/c, C3H/He, C57BL/6, DBA/2, NZW, SWR/J, and 129Sv). Breathing frequency, tidal volume and minute ventilation of unanesthetized and unrestrained mice were assessed by whole body plethysmography. Age-matched mice were exposed for 3 min to 10% O(2) in N(2) gas or 10% CO(2) in hyperoxic gas to determine the acute ventilatory response to chemical stimuli. Basal respiratory variables and hypoxic ventilatory responses differed among the strains, but the hypercapnic ventilatory response did not differ. The hypoxic ventilatory response was the highest in AKR/N mice and the lowest in SWR/J mice. These findings suggest that genetic factors may have influenced the hypoxic ventilatory response but not the hypercapnic ventilatory response. To examine the effects of severe hypoxic stress on the respiratory cycle, we exposed the strain with the highest or lowest hypoxic ventilatory response to 6% O(2) in N(2) until the onset of apnea. The "appearance time of apnea", which is defined as the time from the hypoxic loading to the onset of apnea, was shorter in the SWR/J strain than in the AKR/N strain. We suggest that a lower hypoxic ventilatory response may be a risk factor for apnea under hypoxia.

Ageing, soft-palate tone and sleep-related breathing disorders

We compared the tissue tone of the soft palate in 10 young (18-29 years) and 15 middle-aged (30-70 years) apnoeics with 10 young and 10 middle-aged non-snorers and healthy volunteers of the same ages. The obstructive sleep apnoea syndrome (OSAS) was diagnosed by means of the self-reported questionnaire about the medical history of the subjects and polysomnography (PSG) with overnight pulse oximetry. Computerized endopharyngeal myotonometry (CEM) was used to measure the tissue tone of the soft palate. The CEM study is performed while the subjects are awake. CEM records and analyses the biomechanical properties of tissue in response to a brief mechanical impact. Tissue stiffness is expressed as a frequency and elasticity as a logarithmic decrement of damped oscillation.

RESULTS

The values of the tissue stiffness (13.5, SD 2.5 Hz) and elasticity (1.2, SD 0.4) of the soft palate in young adults with OSAS reveal no important differences in comparison with the tissue stiffness (12.7, SD 2.4 Hz) and elasticity (0.9, SD 0.2) in non-snoring young adults. The difference in the value of the tissue stiffness of the soft palate is significant among middle-aged patients with OSAS (20.3, SD 4.7 Hz) and non-snoring middle-aged persons (13.9, SD 2.3 Hz). A non-significant difference was observed in the value of the tissue elasticity among middle-aged patients with OSAS (1.7, SD 0.8) and non-snoring middle-aged persons (1.6, SD 0.3). The tissue tone of the soft palate in young and middle-aged healthy subjects differs by elasticity but not by stiffness.

CONCLUSIONS

We found that some biomechanical properties of the tissues of the soft palate may be changed by OSAS and some by age.