Determinants of Age Related Breathing Instability During Non-Rapid-Eye-Movement (NREM) Sleep

Sleep apnea-hypopnea syndrome (SAS) is a relatively common disorder in the US population with significant adverse health consequences. Despite the high prevalence of SAS in elderly individuals, the underlying mechanisms have remained elusive. Specifically, the investigators do not know whether the high prevalence of sleep apnea in older adults is due to increased central breathing instability. This proposal focused on investigating age-specific differences in the susceptibility to central breathing instability in adults.

This project had the following specific objectives:

• To determine age-specific changes in the hypocapnic apneic threshold during NREM sleep in elderly vs young individuals.
• To determine age-specific changes in long-term facilitation during sleep in elderly versus young individuals.

Procedure: The investigators determined the susceptibility to central breathing instability by mechanically ventilating the subjects during NREM sleep using non-invasive pressure support ventilation. The investigators compared the hypocapnic apneic threshold in old (age>60 years) and young (age 18-50 years) individuals who were healthy. The investigators also measured the parameters over a continuum of age from 18 to 89 years.

• The investigators investigated whether there was a difference in the susceptibility to long term facilitation of ventilation between young and old healthy individuals in response to episodic hypoxia, while maintaining isocapnia.

Sleep apnea is very common in older Veterans and is associated with significant cardiovascular complications. Greater insight into the pathogenesis will have a positive impact on the health of Veterans suffering from this condition. This study furthers the understanding of the pathogenesis of breathing instability leading to sleep-disordered breathing during sleep. The investigators anticipate findings will provide a basis for new approaches to prevention and management of SAS in Veterans.

Inclusion criteria

• Healthy older and young adults

Exclusion criteria

• Pregnancy,
• history of active coronary artery disease-including stable and unstable angina,
• recent myocardial infarction,
• history of congestive heart failure,
• stroke,
• excessive daytime sleepiness with Epworth Sleepiness Scale of >15
• patient with OSA- (Obstructive sleep apnea) on therapy
• depression,
• schizophrenia,
• untreated hypothyroidism,
• diabetes on insulin,
• seizure disorder,
• intrinsic renal and liver disorders,
• failure to give informed consent,
• patients with evidence of pulmonary diseases based on history and abnormal pulmonary function testing, including obstructive (ratio of predicted forced expiratory volume to forced vital capacity, <80% predicted) or restrictive lung disorders (total lung capacity <80% predicted) with resting oxygen saturation of <96% and kyphoscoliosis (chest wall deformities)
• patients on certain medications including, opiates derivatives, stimulants, antidepressants, tranquilizers, anti-psychotic agents, theophylline and other central nervous system altering medications
• history of alcohol or recreational drug use will also serve as grounds for exclusion,
• patients with body mass index (BMI) >34kg/m2
• subjects with sleep apnea are already using continuous positive airway pressure for more than 7 days as therapy