Sleep-Disordered Breathing

Tonya D. Russell

General Principles

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

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 drzezo in RESPIRATORY | Comments Off

Thoracic Key