By Robert C. Basner, MD
Obstructive sleep apnea (OSA) and nocturnal asthma are two distinct entities that come under the broad classification of "sleep-disordered breathing." Each of these disorders maybe mistaken for the other, since both may involve repetitive arousals associated with changes in oronasal airflow, respiratory effort and/or decreases in SaO2 during sleep. Thus, patients with asthma may not only have similar presentations to those with OSA, including daytime sleepiness secondary to sleep disruption, but nocturnal asthma may closely mimic OSA even on standard polysomnography.
COMMON FACTORS
Asthma and OSA may overlap in a significant number of patients. This may be due to the prevalence of each disorder in the population, but there are common pathophysiologic factors. Congestion of the nasopharynx and sinuses may predispose to worsening bronchoconstriction as well as OSA, as might the resultant mouth breathing, which itself could be a factor in both bronchoconstriction and OSA. Similarly, the presence of one of these entities may cause or worsen the other.
Irritation of the upper airways may predispose to decreased lung function at night. Sleep disruption secondary to asthma could cause periodic breathing and decreased upper airway muscle activity, two factors that may lead to upper airway obstruction during sleep. Finally, hypoxemia itself may predispose to increased bronchial reactivity.
TREATMENT
It has been shown that nasal CPAP is effective therapy for patients with concomitant OSA and asthma. In a small group of patients, CPAP improved both nocturnal and diurnal peak expiratory airflow up to two weeks after beginning therapy. When CPAP was applied in patients with nocturnal asthma only, nocturnal expiratory airflow was not improved, and sleep quality worsened.
The use of supplemental oxygen alone has been found to be beneficial in a limited number of patients with nocturnal hypoxemia due to asthma, but more studies need to be done to assess its safety and efficacy in this setting. These data illustrate the importance of accurate diagnostic assessment both clinically and in the sleep laboratory. Polysomnography in the patient with known or suspected asthma and OSA with and without CPAP titration is ideally done by a sleep technologist with credentials in respiratory care, and with meaningful supervision from a pulmonary or sleep physician.
During a nasal CPAP titration in a patient with known asthma, technicians need to be careful not to increase CPAP for respiratory events that are not upper airway obstruction. Assessing the patients for wheezing or obvious expiratory airflow limitation is particularly helpful in this regard. It is perferable to study such patients when asthma is relatively stable, since a fair assessment of the need for OSA treatment during a night of symptomatic asthma is difficult to achieve, and effective long-term CPAP levels are difficult to adjust under such circumstances. Providing bronchodilator therapy under the supervision of an RCP and physician can be very helpful in increasing patient comfort and ability to sleep, as well as in delineating asthma vs. upper airway obstruction.
PATIENT EDUCATION AND FOLLOW-UP
Education and follow-up are important for patients with concomitant asthma and OSA who have begun receiving CPAP. RCPs are in an excellent position to be of benefit in this setting. Peak expiratory airflow, symptoms of shortness of breath, wheezing, snoring, worsening sleep quality and/or daytime sleepiness should be routinely monitored. Chest pain or dyspnea during CPAP use should be immediately reported to the supervising physician. The need for warm air humidification in conjunction with the CPAP circuit should always be considered in the asthmatic patient.
The patient with asthma is at risk for sleep disruption secondary to medications commonly used for this condition. In particular, theophylline, beta adrenergic agents and systemic steroids have been associated with fragmented and generally non-restorative sleep. On the other hand, effective use of agents has been shown to improve sleep quality in nocturnal asthma. Patients should not withdraw themselves from asthma medications because they are feeling better on CPAP; such withdrawal can only be made in consultation with the supervising physician.
When asthma and OSA co-exist, successful treatment of one is dependent upon the accurate identification and effective treatment of the other. All RCPs have a role to play in the successful diagnosis and ongoing management of such patients.
Dr. Basner is associate professor of medicine in the respiratory and critical care section of the University of Illinois at Chicago College of medicine, and director of the Center for Sleep and Ventilatory Disorders at University of Illinois Hospital. He is also a member of the ASAA medical and research advisory committee.
Sleep Notes is produced in conjunction with the American Sleep Apnea Association. For information about the ASAA, contact them at 1424 K Street NW Ste. 302, Washington, DC 20005;
202-293-3650.
Sleep Tracks, Advance for Managers of Respiratory Care, April, 1996.
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