Tests
1st tests to order
overnight polysomnography
Test
Because the severity of CSA may be linked to the severity of underlying conditions, ideally patients should be under optimal and stable medical management prior to polysomnography.[1]
The polysomnogram consists of close observation and recording of several channels of data during an entire night of sleep in a specialized facility.[38]
Measures include airflow, chest and abdominal movements, electroencephalogram, ECG, submental and anterior tibialis electromyogram, oxygen saturation, and eye movements.[38]
The test is best performed at a center specializing in sleep medicine when CSA is suspected, as treatment is not as straightforward as in the more common disorder obstructive sleep apnea. In general, home sleep test (HST) devices should not be selected as diagnostic tools in this population with complex pathology.[39]
A central apnea is defined as a cessation of respiratory flow of at least 10 seconds in duration, not accompanied by any chest or abdominal respiratory movements. They are usually more common in nonrapid eye movement (NREM) sleep and in supine sleeping positions. Therefore, adequate sleep to observe sleep during REM and NREM in both supine and nonsupine postures is desirable. If this is not achieved and a diagnosis is not certain, a repeat test with better conditions or with the help of a sleeping aid should be considered.
CSA due to opioids can be diagnosed on a polysomnogram in a person who has been on an opioid or other respiratory depressant, typically for at least 2 months.
Result
≥5 central apneas or hypopneas per hour of sleep (called the apnea-hypopnea index) and the total number of central apneas and/or central hypopneas is >50% of the total number of apneas and hypopneas. Breathing patterns are: (1) Cheyne-Stokes breathing (≥3 consecutive central apneas and/or central hypopneas, separated by a crescendo and decrescendo change in breathing amplitude, with a cycle length of ≥40 seconds); or (2) ataxic breathing with variable amplitude of tidal volume, breathing rate, and length of CSAs. Periodic breathing due to high altitude: recurrent central apneas during sleep with a cycle length of 12 to 34 seconds.
Tests to consider
serum thyroid stimulating hormone
Test
Patients who present with symptoms of cold intolerance, weight gain, muscle aches, constipation, menstrual irregularities, dry skin, bradycardia, coarse or brittle hair, or edema (especially periorbital), especially in the setting of sleep complaints, should be tested for hypothyroidism.
A serum thyroid stimulating hormone (TSH) is the best screening test for hypothyroidism.
A normal TSH excludes primary hypothyroidism. An abnormal TSH should be followed up by determination of thyroid hormone levels and additional testing as indicated.
Result
normal; abnormal in presence of thyroid dysfunction
serum creatinine
Test
Unexplained edema should prompt consideration to measure a serum creatinine.
Result
normal; elevated with renal dysfunction
ECG
Test
If heart failure is suspected and not previously known or explained, an ECG should be obtained.
Previously unsuspected atrial fibrillation or ECG findings suggesting cardiomyopathy or ischemia should prompt further evaluation.
Result
normal; may show previously unsuspected atrial fibrillation, or evidence of ischemia or cardiomyopathy
serum insulin-like growth factor 1 (acromegaly testing)
Test
Patients suspected of having acromegaly should have serum insulin-like growth factor 1 (IGF-I) measured. Elevated IGF-I should prompt consideration of acromegaly as a diagnosis.
Result
normal; serum insulin-like growth factor 1 concentrations that are elevated for age may indicate acromegaly
echocardiogram
Test
Patients with CSA and other symptoms or signs of congestive heart failure may benefit from measurements using echocardiogram to determine systolic and diastolic function, valvular pathology, and intracardiac and intravascular pressure estimates.
Result
systolic dysfunction (left ventricular ejection fraction [LVEF] ≤40%) and evidence of diastolic dysfunction are common findings; LVEF ≤45% will exclude the use of adaptive servoventilation in congestive heart failure with predominant CSA
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