This page aims to put together some answers to frequently asked clinical questions.
Stowood takes no responsibility for the accuracy of anything on this page, please consult a skilled practitioner for confirmation before acting on any of these suggestions.
Please contact us if you have anything you’d like us to add.
Sleep recorders for personal use
Q: I need to have a sleep study performed as soon as possible as I suspect I may have a problem that is affecting my job/ relationships/ life. Can I buy a sleep recorder from Stowood and use it on myself?
A: There is no law about us selling you a device in the UK, but we highly discourage individuals from purchasing devices. This is because you will not be able to get treatment unless your study has been performed and analysed by a recognised sleep professional. Instead, we recommend you talk to your local sleep service, who may offer fast-track sleep screening for those who need it. See the Sleep Apnoea Trust (SATA) website for more consumer-level information.
Q: Does oximetry alone allow recognition of sleep apnoea?
A: From Thorax, “Oximetry alone allowed recognition of a moderate or severe sleep apnoea syndrome”.
From Am J Respir Crit Care Med. “the ability of physicians to predict the outcome of continuous positive airway treatment in individual patients is not significantly better with polysomnography than with home oximeter based monitoring”
From Western Journal of Medicine, “screening for obstructive sleep apnea using only oximetry will not obviate the need for further study in a symptomatic patient. The electroencephalogram may not be essential, but, in addition to oximetry and clinical assessment, a measurement of respiratory activity and of leg movements is probably needed in the evaluation for this disorder as further refinement of the interpretation of the oximetry tracing is undertaken.”
Q: Does it matter which oximeter I choose to perform a sleep test?
A: From Chest, “…oximeter choice affected whether the AHI reached the critical cutoff …”
Polygraphy (PG) (limited channel/ ambulatory) studies
Q: Is polysomnography better than polygraphy for diagnosis of obstructive sleep apnoea?
A: From Ann Intern Med., “PSG confers no advantage over the ambulatory approach in terms of diagnosis and CPAP titration.”
Q: Are nasal prongs as good or better than a thermistor?
A: From Chest, “The incorporation of nasal prongs in routine full-night studies is an attainable technical option that provides adequate recordings in most cases. Additionally, relevant information not scored by thermistors is obtained on flow-related respiratory events, thus increasing diagnostic accuracy.”
Q: How does Respiratory Inductive Plethysmography compare to nocturnal esophageal pressure for the Diagnosis of Upper Airway Resistance Syndrome?
A: From Chest, “The sensitivities and specificities, respectively, of RIP to distinguish UARS patients from non-UARS patients are from stage 2 sleep (67%, 80%), immediately prior to arousals (100%, 100%).”
Q: Are sleep studies worth doing on children suspected of having sleep related upper airway obstruction?
A: From the BMJ Journal Archives of Disease in Childhood, “In children with suspected SRUAO, sleep studies do contribute to assessing the need for operation, the likelihood of postoperative respiratory failure, or as a baseline or outcome measure in intervention studies.”
Q: Can you suggest reference values for home PG in primary schoolchildren?
A: Consult this article in Pediatric Research
Q: How can I measure obstructive events in children?
A: Polygraphy and pulse transit time- from Pediatric Research, “in children, PTT arousals are a more sensitive measure of obstructive events than visible EEG arousals”.
From Arch Otolaryngol Head Neck Surg. , “for mild OSAHS, PTT was barely adequate and did not significantly outperform pulse oximetry. Pulse transit time may be a useful tool to evaluate moderate to severe sleep-related breathing disorders in children”
Q: What information can I get from the pulse oximeter derived photoplethysmographic (PPG) signals?
A: Vertical narrowing (systolic to diastolic) of the beat-to-beat photoplethysmographic signal occurs on arousal as the sympathetic activity to the peripheral arterioles increases and reduces the amplitude with which the blood vessels pulsate with the arrival of each pulse. From J Clin Sleep Med., “PPG-derived data compare well with simultaneous in-lab PSG in the diagnosis of suspected OSA among patients with and without cardiopulmonary comorbidities”.
From Medicine (Baltimore). “The tested PPG approach yielded acceptable results compared to the gold standard PSG among moderate to severe OSA patients.”
Notes: The Black series and Visi-Download display PPG.
Stowood’s range of ambulatory monitors are here
Polysomnography (PSG) studies
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Stowood’s range of polysomnography/ lab systems is here
Q: How many times do I need to perform an Osler test on a patient in a day?
A: Fig1 in J. Sleep Res. (1997) 6, 142-145 “A behavioural test to assess daytime sleepiness in obstructive sleep apnoea” may show that the results at each time of the four runs during the day are very similar. The MWT and original Osler were 4/day.
Page 1622 (top right) in Am J Respir Crit Care Med. 2001 Jun;163(7):1619-25 “Microsleep during a Simplified Maintenance of Wakefulness Test: A Validation Study of the OSLER Test” suggests two is as good as four but did not look at one.
Page 476 (line 11 discussion) and the abstract in Am J Respir Crit Care Med. 2002 Aug 15;166(4):474-8 “Analysis of Error Profiles Occurring during the OSLER Test: a sensitive mean of detecting fluctuations in vigilance in patients with obstructive sleep apnea syndrome.” claim that one at 9am is a good as the four averaged.