Sleep-Disordered Breathing



Sleep-Disordered Breathing


Tonya D. Russell



General Principles

Sleep-disordered breathing (SDB) is comprised of multiple different entities:



  • Obstructive sleep apnea (OSA)


  • Central sleep apnea (CSA)


  • Sleep-related hypoventilation


Definitions



  • An apnea is defined as ≥90% decrease in airflow as measured by thermistor, lasting at least 10 seconds in duration.


  • An hypopnea is a ≥30% decrease in airflow as measured by pressure transducer lasting at least 10 seconds in duration and associated with a ≥4% desaturation.


  • A respiratory effort-related arousal (RERA) is a sequence of breaths lasting at least 10 seconds with increased respiratory effort or change in airflow which is associated with an arousal.


  • The apnea–hypopnea index (AHI) is the number of apneas and hypopneas per hour of sleep.


  • The respiratory disturbance index (RDI) is the number of apneas, hypopneas, and RERAs per hour of sleep.


  • Sleep-related hypoventilation is defined as an increase in PaCO2 during sleep by at least ≥10 mm Hg when compared to an awake supine value.


  • Morbid obesity is defined by a body mass index (BMI) ≥40.


Classification



  • Apneas can be obstructive, central, or mixed in nature.1



    • Apneas are classified as obstructive when there is no airflow, but continued respiratory effort.


    • Central apneas have no airflow and no respiratory effort.


    • Mixed apneas have no airflow associated with a lack of respiratory effort during the first part of the event but resumption of respiratory effort during the latter part of the event.


  • Severity of sleep apnea based on AHI1



    • An AHI <5 is normal.


    • Mild sleep apnea has an AHI of 5–15.


    • Moderate sleep apnea has an AHI of >15 and <30.


    • Severe sleep apnea has an AHI ≥30.


  • Severity of sleepiness1



    • Mild sleepiness is when sleepiness occurs in sedentary situations such as watching TV or reading.


    • Moderate sleepiness is when sleepiness occurs in settings such as meetings or the theater.


    • Severe sleepiness is when sleepiness occurs with activities such as talking, eating, or driving.



Epidemiology



  • OSA is the most common form of SDB.



    • OSA associated with daytime sleepiness (OSA-hypopnea syndrome) occurs in 2–4% of the general population.2


    • This percentage likely underestimates current prevalence due to the increasing prevalence of obesity in the United States and the strong association between obesity and OSA.


  • Prevalence of SDB increases with age.3,4



    • The prevalence of OSA increases with age but CSA also becomes more prevalent.


    • The prevalence of SDB in postmenopausal women is higher than in premenopausal women.


  • As BMI increases, obesity hypoventilation (OHV) is more likely to occur.4 In patients with a BMI >50, ∼50% of patients have evidence of hypoventilation.5,6


Etiology



  • OSA occurs due to narrowing of the upper airway either due to excessive soft tissue or structural abnormalities.


  • CSA can have a variety of causes



    • Stroke


    • Brain tumor


    • Congestive heart failure


    • Use of positive airway pressure devices can result in treatment-emergent central apneas.


  • Sleep-related hypoventilation can be due to a variety of causes



    • Morbid obesity-OHV


    • Severe OSA


    • Neuromuscular disease with respiratory muscle weakness


    • Severe kyphoscoliosis or thoracic cage deformity


    • Diaphragmatic paralysis


    • Severe obstructive lung disease


Pathophysiology



  • OSA: Narrowing of the upper airway leads to recurrent arousals.


  • CSA



    • Central apneas can occur due to direct effects on the medullary respiratory centers (stroke or brain tumor).


    • In addition, central apneas may be due to increased sensitivity to small changes in carbon dioxide levels (congestive heart failure).


    • Central apneas can occur in the setting of using positive airway pressure to treat OSA.


  • OHV



    • OHV may be due to frequent obstructive apneas or hypopneas that lead to a decrease in minute ventilation.6


    • Impairment of respiratory mechanics due to morbid obesity can also contribute to OHV.6


    • Leptin resistance in morbidly obese patients may impair their ability to increase their minute ventilation appropriately.6,7,8


Risk Factors



  • Risk factors for OSA include the following: obesity, macroglossia, micrognathia, retrognathia, neck circumference >17 in in men and >16 in in women, enlarged tonsils, increasing age, male gender, family history, use of alcohol or sedatives, and concomitant medical conditions such as hypothyroidism.1,2,3,4,9


  • Risk factors for CSA include the following: use of positive airway pressure, severe congestive heart failure, and stroke or brain injury.1



  • Risk factors for sleep-related hypoventilation include the following: very severe OSA, respiratory muscle weakness, morbid obesity, severe obstructive lung disease, and thoracic cage abnormalities.1


Prevention



  • The following factors help in the prevention of OSA:



    • Weight loss can be beneficial. However, weight loss alone may not prevent OSA if there are craniopharyngeal structural abnormalities.


    • Avoidance of alcohol and sedatives may help prevent OSA as these substances contribute to muscle relaxation and impaired arousal threshold.


    • Treatment of underlying conditions such as hypothyroidism may help prevent OSA. Hypothyroidism can result in weight gain and decreased upper airway muscle tone.


  • The following factors help in the prevention of CSA:



    • Medical treatment of severe congestive heart failure may improve CSA.


    • Avoiding over titration of continuous positive airway pressure (CPAP) may help prevent CSA, as treatment-emergent CSA is more likely to occur at higher pressure settings.


  • The following factors may help in the prevention of sleep-related hypoventilation: weight loss in the morbidly obese may improve underlying OSA, respiratory muscle dysfunction, and leptin resistance which can all contribute to OHV.


Associated Conditions

Nov 20, 2018 | Posted by in RESPIRATORY | Comments Off on Sleep-Disordered Breathing
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