INSPIRATORY AIRFLOW DYNAMICS, METABOLIC SYNDROME, AND HYPERAROUSAL IN PATIENTS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In this study, we propose to compare the effect of therapeutic nasal CPAP to placebo nasal CPAP on functional complaints of Upper Airway Resistance Syndrome (UARS) patients (i.e., fatigue, daytime sleepiness, sleep problems, gastrointestinal irritability, headache, anxiety and body pain). A second goal of this research is to gather pilot data examining the effect of preventing upper airway collapse during sleep upon the metabolic function of UARS patients. Disorders of sleep have been associated with metabolic disorders. One such metabolic disorder, metabolic syndrome (MTS), is a common syndrome characterized by central obesity, dyslipidemia, insulin resistance and hypertension.5 MTS is known to be a risk factor for myocardial infarction, stroke and renal failure.5 Several recently published investigations have demonstrated that MTS is associated with snoring (inspiratory flow limitation during sleep)6 and sleep apnea.7, 8 Patients who experience snoring, sleep fragmentation or apnea have a higher prevalence/incidence of MTS,9 cardiovascular disease 10-12 and insulin resistance/diabetes.13-16 There is also evidence that patients with fragmented sleep have higher systolic and diastolic blood pressures that normalize when sleep fragmentation is decreased with nasal CPAP.17 No research has been conducted to date examining these relationships in UARS, a milder form of sleep disordered breathing than apnea. Therefore, we hypothesize that preventing upper airway collapse during sleep in UARS patients with nasal CPAP will decrease the levels of the parameters that characterize MTS. A second question that we are seeking to answer is whether UARS patients are in a state of metabolic hyperarousal. Hyperarousal20 is a state of increased metabolic activity reflected in oxygen consumption, 21 heart rate22, 23 and body temperature. 24, 25 Evidence of hyperarousal has been demonstrated in patients with chronic insomnia and may account for their inability to sleep at night. Patients with UARS, unlike patients with sleep apnea, have a high prevalence of insomnia (35%).2 We hypothesize that metabolic hyperarousal is present in UARS patients, and that it serves to stabilize the upper airway during sleep, resulting in the mild level of inspiratory airflow limitation observed in UARS.26 Based upon this hypothesis, we anticipate that splinting the upper airway during sleep with nasal CPAP will decrease metabolic hyperarousal and result in decreases in oxygen consumption, resting heart rate and body temperature in UARS patients.