Diagnostic Sleep Apnea Monitoring. Current Methods and Promising Advances

Transcription

1 Diagnostic Sleep Apnea Monitoring Current Methods and Promising Advances

2 1 Abstract In the United States of America alone, an estimated 70 million adults suffer from a sleep disorder ( Sleep ). Over half of these disturbances are chronic. In a study by the CDC, 11.3% of adults reported that they did not receive adequate sleep in any of the past 30 days (Montgomery Downs). One of the most common sleep disorders worldwide is sleep apnea, with prevalence between 1.2 and 7.5% in the general population. In addition to causing poor quality of sleep during the night, daytime sleepiness, and the accidents associated with daytime sleepiness, sleep apnea can aggravate or cause a variety of heart problems, including stroke or heart failure (Polese). When diagnosing sleep disorders, the best accepted method is use of polysomnography during an overnight stay in a sleep laboratory or sleep clinic. However, the requirement of at least one overnight stay at a clinic is suspected to deter a significant number of people from proper diagnosis and treatment of sleep problems. Furthermore, most people do not typically sleep in a medical facility on a regular basis, and the change of environment and schedule involved in lab testing may drastically change the quality and quantity of sleep which a participant obtains. In order to make sure the greatest number of people are helped, portable monitoring devices and routines are being evaluated for use outside of sleep clinics. A number of studies have given promising results relating to the accuracy of alternative monitoring devices compared to polysomnography. These studies suggest that in the near future portable monitoring devices may be feasible for general use in sleep disorder outpatients. Introduction An estimated 70 million people annually suffer from a sleep disorder in the United States. Of these cases, 60% are chronic conditions ( Sleep ). As many as 25% of children under the age of 5 and 50% of adults over the age of 65 experience abnormal sleep at least occasionally ( Sleep ). These conditions include a number of distinct disorders including insomnia, the difficulty falling sleep or staying asleep; hypersomnia, sleeping more than typical without relief of fatigue; narcolepsy, characterized by falling asleep at inappropriate times without control; and many others. These disorders cause discomfort and potential danger to the patient and those around them, as daytime sleepiness can lead to drowsing off or becoming distracted at inopportune times, as well as mood swings and decreased brain function associated with tiredness. This produces a cumulative cost to society in sleep related accidents, injuries, and also a loss of productivity by those affected and their peers. Sleep disorders are also often associated with additional complications besides abnormal sleep. These are often genetic factors, a sequence of genes which negatively impacts one or more component of the

3 2 body, resulting in sleep problems and other negative results. However, the side effects can also be a direct result of the sleep disorder. In the latter case, these can be caused by an underlying symptom that causes the abnormal sleep, such as airway obstruction in sleep apnea, or as a result of the lack of sleep itself. In order to adequately treat sleep disorders, there must first be a diagnosis of the potential condition or its underlying causes. With diagnosis and proper treatment these conditions can be made less severe and associated complications and dangers could be avoided or guarded against in advance. Figure 1: This figure illustrates the difference in position of the palette during sleep in a sleep apnea patient and a normal patient. In sleep apnea the airway is blocked, preventing proper breathing. ( Sleep Apnea Treatment ) In this paper I will focus on diagnosis of one particular sleep disorder, obstructive sleep apnea (OSA). Sleep apnea is present in % of the general population (Polese). This condition is caused by abnormal positioning of the tongue, palate, or both during sleep. This completely or partially blocks the airway, often causing snoring, which may disturb the sufferer s bed sharing partners. The respiratory distress may also cause frequent waking for the patient, resulting in excessive daytime sleepiness. This sleepiness may be moderate, causing some discomfort throughout the day, to more severe, causing the patient to alter their lifestyle in order to accommodate more rest or to limit exertion. In the most severe of cases, the patient may even fall asleep at inappropriate places such as work or school, or at dangerous times, such as while driving. Overall the sleepiness alone is enough to cause decreased quality of life, and may be dangerous to the patient and those around them. Furthermore, if the airway is blocked, less oxygen is able to enter the blood stream, placing additional strain on the heart and circulatory system to deliver oxygen to cell throughout the body. The lack of available oxygen may also alter or impair metabolic processes in cells. Due to the additional strains on the circulatory system and the metabolic changes throughout the body, sleep apnea is also linked to major issues such as diabetes,

4 3 hypertension, stroke, and heart failure (Polese, Gay). Given the prevalence of sleep apnea and the serious nature of the risks associated with it, finding a way to easily diagnose this condition will affect many lives in a vital way. Current Diagnostic Methods Currently there are four categories under which diagnostic methods for sleep apnea are classified. However, only type one sleep studies are broadly accepted by insurance companies as a diagnostic tool (Polese). A type one sleep study consists of polysomnography done overnight in a sleep lab. In order for it to fully qualify as a type one sleep study, the polysomnograph must measure and record at least seven biological parameters including an electroencephalogram (EEG), an electromyogram (EMG) of the chin, an electro oculogram (EOG), airflow, respiratory effort, pulse oximetry, and an electrocardiogram (ECG) (Polese). The polysomnograph is simply a compilation of all of these readings, as well as any additional measurements made. An EEG requires an electrode array over the face and scalp, which measures brain activity. The EEG can help determine whether the patient is awake or asleep, and what stage of the sleep cycle they are in. Healthy sleep consists of 4 sleep stages, stages 1 3, defined by brain wave patterns, followed by rapid eye movement (REM), which is defined by motion of the eyes as well as unique brain wave patterns. A chin EMG requires electrodes on the chin. The motion here can help determine sleep versus wake, as well as sleep quality and respiratory distress. An EOG requires electrode placement around the eyes to measure eye movement. This is a useful indicator of sleep cycles, especially REM stage onset, and by extent sleep quality. Airflow is typically measured by a sensor strip placed under the nose, which tracks air motion in and out of the nostrils. Respiratory effort is measured by sensors which are linked to elastic bands placed around the abdomen. The forces applied to the bands are indicative of the muscle effort made to breathe, and how full the breaths taken are. Pulse oximetry determines blood oxygen level via a light based surface sensor on the finger or earlobe. An ECG involves electrodes on the arms, legs, and chest, which measure activity of the heart. The readings can be an indication of inadequate respiration, and also contribute to the determination of sleep versus wake. In order to ensure the sensors are not displaced, disrupting the reading, the patient must lie supine and stationary through the night (Polese). Between the variety of sensors, the unfamiliar environment of the sleep clinic where the test must be performed, and the requirement the patient maintains a particular position through the night, it is likely many patients experience a degree of disturbance to their sleep which is not normally experienced. Furthermore the

5 4 inconvenience of travelling to a sleep clinic and staying there overnight, typically at least twice, dissuades many potential patients from even trying to get a diagnosis. Furthermore, the staff, space, and equipment in a sleep clinic are expensive to maintain, and may not be used to capacity, decreasing the cost efficiency of the location. Figure 2: An illustration of the standard polysomnography array. The patient must lie supine through the night to prevent disturbance of the sensors which could reduce the validity of the test. ( What Are Sleep Studies? ) Type two sleep studies, alternatively, may be accepted for diagnosis by insurance companies under specific circumstances (Polese). While they still require a full polysomnography to be performed, they can be done in the patient s home under supervision by a trained sleep technician (Polese). In accordance with recommendation by the American Academy of Sleep Medicine, in order for diagnosis for OSA via home polysomnography to be valid under most insurance plans, the patient must be unable to attend a sleep clinic due to immobility or critical condition, likely have sleep apnea based on a pretest screening, or have special approval in the case that sleep apnea symptoms are present but comorbidities are not (Polese). This includes cases where symptoms such as daytime sleepiness and snoring are observed, but high blood pressure, diabetes, or other complications are not present. There are certain advantages to type two testing compared to type one testing, such as the presence of a specialist in the home to locate environmental factors which may alternatively be contributing to the sleep problem, and a sleep pattern which is more likely to resemble that experienced night to night, as the patient can follow their normal routine and sleep in a comfortable, familiar environment.

6 5 Furthermore, the average cost per test would decrease as much as $3000 $4000 from the roughly $13,000 cost of a type one test, since there would no longer be funding going toward renting a facility, and staff would only be hired according to demand (Polese). However, there still remain some problems with this option. The many sensors are still placed and the patient must still maintain still on their back during the night, making it potentially uncomfortable and disruptive to sleep. The patient must also remain under observation by a trained professional, adding another element of potential discomfort or anxiety during the study. Additionally, while the cost of a home polysomnography is less than an in lab polysomnography, it is still an expensive procedure. A final consideration is potential complications with obtaining a polysomnography device in certain areas. If transportation is not available to an existing sleep center, there may not be transportation available from the nearest polysomnograph machine site to the household which needs it. There are still two more types of sleep studies used in diagnosis of OSA, but without a polysomnograph most insurance companies will not accept the diagnosis as valid (Polese). However, some studies suggest that these types of studies may be adequate for diagnosis, and with more testing and communication with insurance providers they may one day be approved as diagnostic methods by insurance providers. A type three sleep study measures at least 4 biological parameters including heart rate or ECG and 2 measures of respiratory movement or airflow (Polese). These two measures might consist of sensors under the nostrils to detect airflow, a calibrated microphone to detect snoring, sensors on the chest or neck to detect muscle movement during breathing, or others. Detection of airflow is vital to indication of sleep apnea as opposed to other sleep disorders, as it affirms airway blockage is the cause of the disturbance. A type four sleep study, in contrast, measures any three or fewer biological parameters, or measures more than three parameters but fails to record two or more measures of airflow or respiratory effort (Polese). Neither of these requires a sleep specialist to be present (Polese). Either may be done at home, and they are potentially far less intrusive and more comfortable than the standard polysomnography array. These types of studies are frequently accompanied by less empirical measures of disturbance of sleep and disruption of lifestyle such as questionnaires or sleep diaries (Polese). Design Requirements Taking in to consideration the advantages and shortcomings of the current procedures, criteria for an ideal device can be formulated. Starting with the critical components which are seen in the current solution, the diagnostic monitoring tool must be approved by insurance companies. It may not

7 6 be already approved, but it must fulfill requirements that would make it possible for the device to be approved. These qualifications include high intradevice consistency and agreement with the established monitoring devices. Intradevice consistency refers to how reliable a device is when placed in the same circumstances. If a device meant to measure heart rate, for example, might read 20 bps or 60 bps when the rate is actually 50 bps, the results aren t very meaningful. On the same line, if two monitors of the same model give very different values, the line as a whole doesn t give meaningful results. While some amount of error is acceptable, as manufacturing problems and software bugs do occur, thorough testing to ensure a device and a line are reliable is important. Agreement with prior devices refers to the device s ability to produce comparable outputs to accepted device outputs. While a new device may have improved output, giving more accurate results, overall the output should be very similar to accepted standards to ensure it is correct. Without these assurances, the results given by the device cannot be trusted. The device should also be able to differentiate between sleep and wake. This is important in determining if there is sleep disruption, and how severe it is if it occurs. A device that doesn t indicate whether the patient is awake or asleep is not useful for determining if the patient is waking up during the night or how long they sleep for. Ideally the device would also be able to determine what stage of the sleep cycle the patient is in, as this will also help determine quality of sleep. For example, the patient is likely not experiencing high quality sleep if they do not enter the REM phase of the sleep cycle. For the purposes of diagnosing sleep apnea particularly, the device should also detect at least one measure of airway obstruction. These might include blood oxygen levels, airflow readings, or muscle tension indicative of a breathing disturbance. The most direct method of measuring obstruction of the airways would be to measure air flow outside the nose and/or mouth, however, it may not be the best option. A calibrated microphone to detect snoring can also detect airway obstruction in some patients, as might a sensor of muscle tension in the throat or chest. Blood oxygen levels are also indicative of airway blockage, as oxygen levels will decrease if airflow is lessened. Without some measure of airway obstruction, even if sleep disturbance is witnessed, sleep apnea cannot be diagnosed due to the plethora of other conditions that may disrupt sleep. The number of parameters an ideal diagnostic device would measure I suggest is purely speculative. Provided devices are proven reliable and accurate it seems one of each should suffice, but two indicators of each would be ideal. This would allow for enough data output for diagnosis, and if a second parameter is measured, an internal check for device reliability. One might make the argument that more outputs is better, but there are other parameters to consider which type one sleep studies do not fulfill. These include ability to be used at home without a professional present, a reasonable cost for the average user, and a level of

8 7 compaction which would render it comfortable and non obstructive during sleep. It is vital to the usefulness of these tools that they not disturb the user s sleep. Adding more parameters will increase the data available to specialists, but it will also increase the number of sensors tied to the patient and the bulkiness and cost of the device. Additionally, a small, unobtrusive enough device has added potential as a 24 hour monitoring device. Measuring biological parameters throughout the day can help determine how seriously the condition is affecting the patient s lifestyle. Continuous measures may reveal excessive daytime sleepiness and falling asleep, or other complications related to sleep apnea such as elevated blood pressure. Balancing sufficient data output with simplicity, affordability, and comfort renders a type three diagnostic device or a very reliable and accurate type four study device ideal for an OSA diagnostic tool. Potential Alternatives to Traditional In Lab Polysomnography A number of type three and four sleep study devices already exist. Many of them are currently in use and marketed for other purposes, or are used in combination with other monitors in traditional polysomnography. The following devices are not the only possibilities for diagnostic OSA monitors. For each device examined here, a summary of the study and its results will be presented, followed by an analysis of the advantages and disadvantages it has compared to polysomnography and how well it fulfills the criteria presented for an ideal monitoring device. Alternatives to polysomnography which are useful in the home without observation by a professional fall in to the general category of unattended limited monitoring (ULM). These encompass any monitoring procedure which does not have the patient under observation, and takes less data than a full polysomnograph. The devices under discussion in this paper are intended to be used in unattended limited monitoring. These offer an excellent potential balance between privacy, comfort, cost, and the amount of data recorded for diagnostic use. Apnea Risk Evaluation System Unicorder One particular ULM which has been developed and studied is the Apnea Risk Evaluation System (ARES) Unicorder. The ARES Unicorder is applied by the patient, and is worn on the forehead. It records oxygen saturation, pulse rate, airflow from a nasal cannula and pressure transducer, snoring levels (via a calibrated microphone), head movement actigraphy, and head position (derived from the accelerometers) (Masdeu). The entire device is contained in a small, flexible plastic box secured to the head by a single elastic band, with the exception of the flexible plastic tubing which hangs from the band

9 8 for placement below the nose. Because of its small, compact form, it can be worn comfortably in most sleep positions. The device also contains an audible alert system if the device is not positioned adequately for readings, which will signal the user to reposition it. It qualifies as a type 3 sleep device (Masdeu). Figure 3: A picture of the ARES unicorder device placed appropriately on a mannequin head. (Harte) In a study by Masdeu et al it was evaluated against full in laboratory polysomnography. All participants went through two nights of ULM and two nights of polysomnography. Sixty six were sleep apnea patients, 19 were non patient volunteers with no symptoms (Masdeu). Results from both nights of polysomnography or both nights of ULM were presented to 4 trained clinicians with experience. Over a period of several days all clinicians gave diagnosis for each set of data for each patient (Masdeu). Overall numerical agreement on relevant parameters between the polysomnography data and ARES data was 86% (Masdeu). Subjects with high respiratory distress were consistently diagnosed between and within clinicians, but those with low distress were less consistently diagnosed regardless of test method or clinician (Masdeu). That is, subjects with high respiratory distress received similar diagnoses from different clinicians, as well as from the same physician for both their polysomnograph and ULM results. However, in those with less distress, even with polysomnography, significant disagreements on diagnosis and treatment were seen between clinicians (Masdeu). The authors concluded that more

10 9 specific guidelines for diagnosis and treatment are needed before alternative devices can be seriously considered (Masdeu). This is a critical point when the question of approving a new device arises. While a device may be shown to be accurate and reliable, in order for successful analysis to be made and presented to patients, doctors, and insurance providers, a better set of guidelines is needed to differentiate what amount of sleep and respiratory distress experienced qualifies as OSA as opposed to normal sleep. While numerical output agreement suggests this device may be feasible for diagnosis, variation in actual diagnosis regardless of what method was used makes it unclear how useful this particular device or any device might be. This study reflects that even the standard of comparison for apnea diagnosis has questionable merit when populations with less respiratory distress are under analysis. Home Oximetry Another potential alternative to polysomnography is use of home oximetry. An oximeter typically works by shining red and infrared LEDs at a photodiode through the finger or earlobe. The device is calibrated to interpret the changes in the light absorption levels as the heart beats to determine the oxygen content of the blood (Hill). Most also give a pulse reading, and some can also display body temperature (Hill). While this is not important to determining airflow, it offers a potential path for differentiation of sleep and wake in the patient. There are some limitations to which patients an oximeter can be used on. The user must have a perceivable pulse in the finger and have the oximeter securely on the finger in order to obtain an accurate reading (Hill). Dark skin pigment, intravenous dyes, and dark nail polish may also cause problems with obtaining an accurate reading in some oximeter models, although not all models reflect these problems (Hill). Another potential source of error comes with sickle cell anemia. While pulse oximeters have been shown to detect low oxygen saturation accurately in sickle cell disease, there are still concerns about their accuracy in this case (Hill). This is because the algorithms used to determine blood oxygen content rely on the amount of oxygen normal hemoglobin can transport, but the deformation in sickle cell anemia makes the maximum amount of oxygen in their blood lower. This means that blood oxygen content is skewed in sickle cell anemia patients so that even when their blood is fully saturated with oxygen it seems low. Other varieties of anemia do not seem to cause problems with the reading, however (Hill). A feature that already exists in some devices which may help lower error is a system that can alert the user if an inadequate signal is being obtained for measurement due to placement or other complications. Oximetry is part of the

11 10 existing standard polysomnography array, demonstrating that its usefulness and reliability are at least somewhat accepted already, which might help the case for its use alone in diagnosis of sleep apnea. A study by Whitelaw, Brant, and Flemons concluded that oximetry alone is sufficient for diagnosis of moderate to severe sleep apnea. In this study of 288 participants, 132 received an in lab polysomnograph, while the remaining 156 received home oximetry (Whitelaw). Trained sleep clinicians were then asked to predict the likelihood of success with CPAP treatment, a common OSA treatment that opens the airways using increased air pressure. Because the only aid CPAP provides to the user is opening the airway, sleep apnea is the only sleep disorder it should make less severe. When predicting, there were four categories predicting likelihood of success less than 25%, 25 50%, 50 75%, and greater than 75%, where success was defined as a significant rise, 1.0 points or more, in Sleep Apnea Quality of Life Index (SALQI). The SALQI is a commonly used questionnaire in determining the seriousness of sleep apnea. As current diagnostic testing cannot continue through the day, quantitative indicators of how sleep apnea affects the life of the patient are difficult to obtain. The SALQI helps generate a numerical value indicating the sleep apnea severity based on the qualitative data a patient can provide. In this study, treatment success was evaluated after four weeks of treatment with CPAP (Whitelaw). The prediction of success implies that symptoms are severe enough to reduce quality of life, the symptoms are due to OSA, and that the patient will not experience more discomfort due to the CPAP device than they would due to their apnea (Whitelaw). Success was correctly predicted, implying the correct diagnosis would have been made, in 61% of patients with polysomnography and 64% of patients who used home monitoring (Whitelaw). Oximetry was not better than polysomnography in a statistically significant manner. However, Whitelaw and associates determined with a confidence of 95% based on this study that oximetry is no worse than polysomnography for purposes of diagnosis of sleep apnea when symptoms are severe enough to impact quality of life. While sleep apnea may be present in patients who do not see a clear decrease in their day to day quality of life, those who are most likely to seek help are those experiencing a negative impact, making this a reasonable diagnostic tool for most if not all patients. Oximeters are available in small, affordable, accurate models. Oximetry does not require professional monitoring for use, and is simple enough for use by patients at home. It evaluates blood oxygen well enough to determine if obstruction of the airway is causing problems, but fails to show sleep and wake definitively. This leaves anecdotal evidence alone, such as a sleep diary, patient recollection or questionnaire like SALQI, to determine if the apnea is serious enough to disturb sleep. An

12 11 algorithm could possibly be developed using the heart rate and body temperature to extrapolate this difference. During sleep, the heart rate is typically slower than during wake, and the heart rate tends to increase suddenly after waking. Subtle changes in heart rate can also be observed at different points during the sleep cycle. Similarly, body temperature tends to decrease during sleep, as the decrease in activity reduces stimulation of metabolic processes. Another option for differentiating sleep and wake would be use of this device in congruence with another monitor. Oximetry alone is not currently approved by insurance companies or the American Academy of Sleep Medicine for diagnosis, as it qualifies as a type four sleep test. However, more studies like the one done by Whitelaw, Brant, and Flemons which replicate the results could be used to make the claim that oximeters are sufficient for sleep apnea diagnosis. Additional tests would be needed to ensure quality control between devices of specific models, though, and to confirm that the output is accurate. Actigraphy Another possible procedure for sleep apnea diagnosis is actigraphy. Actigraphy uses an accelerometer to track motion, which is interpreted by algorithms programmed in to the device to determine if the wearer is awake or asleep (Ancoli Israel). Some devices, such as the ARES unicorder, have an accelerometer mounted on the head. Those which seem to be most comfortable and functional, however, are wrist mounted accelerometers. These models closely resemble a watch. Actigraphs have been shown as proficient at detecting sleep (98% of sleep recorded as sleep), but poor at recognizing wakefulness (48%). In other words, when the patient is asleep, the actigraph output is usually that the user is asleep. However, when the patient is awake, the device will report that the patient is asleep roughly half the time. This results in a serious shortcoming; there is dramatic overestimation of sleep time and quality (Ancoli Israel), because sleep quality is largely a function of how long one sleeps continuously. A potential solution exists, though, in better accelerometers or algorithms for differentiating between sleep and wake (Ancoli Israel). Existing algorithms take the output of the accelerometer and determine the difference in sleep and wake based on the duration, speed, and length of motion. However, as people are seldom immobile even during sleep, certain motion patterns are disregarded. With more observation of outputs while subjects are awake and asleep, there is potential for improvement in differentiation. Specialists might be able to find even more subtle differences in the types of motion made while asleep or awake and using this information improve the algorithms. Another possible path to better results would be to couple the actigraph algorithm with another monitoring device, providing the algorithm with more factors to take in to account. This might help the

13 12 device output the correct state when it wouldn t be obvious based on motion patterns. To their advantage, though, since actigraphs consistently overestimate sleep rather than underestimating it, actigraphs as they stand will give false negatives for a condition, but not false positives. They may not be suitable for diagnosis of persons with minor sleep apnea, but they are potentially sufficient in moderate to severe cases. As is, actigraphs are readily available on the market in unobtrusive, low cost models. They are capable of recording for days or even weeks, while it s difficult to record polysomnography for even 24 hours. The shear amount of data output means that even if you had a patient who could sit for a full day of polysomnography, another device would be needed to store all of the data. This makes them potential trackers during everyday activity, allowing for a measure of disruption to life as a result of sleep problems (Ancoli Israel). With a long term tracker, it may be possible to evaluate daytime sleepiness based on the readout of the device. The device could pick up on a patient drowsing off, jumpiness due to inability to remain alert to the surroundings, and how quickly the patient generally fatigues. Montgomery Downs, Insana, and Bond performed a study on one particular Actigraphy device, the FitBit. This small, wrist mounted sensor was measured against standard polysomnography and standard actigraphy via Actiwatch 64 (AW 64) (Montgomery Downs). The AW 64 is the current standard for actigraphs, as it has been shown to be relatively accurate and useful. This component is necessary in this particular study because the FitBit was a new device and had not been tested against a similar device. By having some patients wear a FitBit on each wrist, an intradevice reliability of 96.5% 99.1% was determined (Montgomery Downs). This was done by comparing the readouts of the two devices worn by the same patient to ensure they were giving consistent results. When compared to polysomnography, the FitBit overestimated sleep efficiency, or the amount of sleep obtained relative to how long the patient tried to sleep, by 14.5%, while the AW 64 overestimated by 9.3% (Montgomery Downs). The FitBit is more accurate at determining sleep stages than AW 64, and is 90% 100% accurate when determining sleep stages and sudden waking when compared against polysomnography (Montgomery Downs). Due to overestimation of quality and efficiency of sleep observed, it is currently suggested that the FitBit only be used on healthy populations, rather than as a diagnostic tool, similar to Ancoli Israel s assertion actigraphy is only appropriate for sleep studies in healthy individuals (Montgomery Downs). In other words, the current abilities of actigraphy are not quite good enough for use in diagnosing sleep disorders, although they can be a helpful tool for healthy individuals who are curious about how well they sleep and for how long. However, given technological advances increasing availability and quality of accelerometers and further development of the interpretation algorithms, is

14 13 seems there is potential for this to be used as a monitoring device. Thus, while the FitBit is cheaper than other actigraphy devices and has reasonable accuracy and consistency, as well as being compact, comfortable, and easy to use, neither it nor standard actigraphy are suitable on their own as they stand for diagnosis of sleep apnea. Actigraphy may serve as a good tool in combination with oximetry or other devices, though, to produce a still affordable, compact device for diagnosis. If coupled with other devices, as well, more information could be provided to the algorithm, which may help with differentiation between sleep and wake. Direct Airflow Measurement Another potential diagnostic monitoring device involves an airway monitor such as an automatic CPAP machine or a single channel nasal airflow transducer. CPAP is the standard OSA treatment both in and out of the home, making it relatively available for purchase (Polese). A CPAP machine consists of a face mask which covers the nose, secured to the head with elastic straps. Pressurized air is administered through the mask in to the airway, gently forcing it open (Skomro). This will help keep the patient s airway open, relieving respiratory distress and as a result reducing disruption to sleep. Machines may be set to give a continuous amount of pressure, or some systems may be set for automatic adjustment based on airflow readings (Skomro). Because auto CPAP machines must measure airflow anyway, it makes sense that they could be used as monitoring devices as well as treatment devices. This would allow for treatment and monitoring simultaneously, and would simplify ongoing monitoring of patients to ensure the therapy is helping. A study by Skomro et al demonstrated auto CPAP after diagnosis at home was just as effective as titrated CPAP in a laboratory following full polysomnography for improving quality of life over a four week period. From their 102 subject pool, 89 were diagnosed with sleep apnea, 45 of which had undergone polysomnography while 44 had undergone home monitoring with a device measuring airflow (nasal pressure), respiratory effort (thoracic and abdominal), oxygen saturation, heart rate, and body position (Skomoro). While this is not CPAP alone, these readouts could be easily gathered with an auto CPAP device, an oximeter, and an actigraph watch. The results of this home monitor or the polysomnograph were used to determine if a patient had apnea, and if they did what level of CPAP would be appropriate (Skomoro). Ten patients dropped out of the study, choosing not to undergo CPAP therapy (Skomoro). Those who had home monitoring diagnosis were given an auto CPAP machine, while those who had undergone polysomnography had optimal pressure for their CPAP machines titrated in the lab by sleep technicians (Skomoro). In CPAP titration, CPAP machines deliver a constant pressure

15 14 regardless of how well the airway is opened. Sleep technicians manually adjust the machine to output minimal pressure while still fully opening the airway (Skomoro). After four weeks of CPAP therapy, measures of sleep quality, quality of life, and blood pressure were taken to determine how effective it had been (Skomoro). Of polysomnography patients, 89% showed improvement, while 88% of home monitoring patients showed improvement, a difference which is not statistically significant (Skomoro). Of home monitoring patients who had also undergone polysomnography at one point, 76% reported they liked the home monitor more than polysomnography (Skomoro). These results imply that this particular limited monitoring array, and potentially others, is effective enough for diagnosis of sleep apnea. Furthermore, alternative monitoring device diagnosis does not result in lower quality results or less accuracy in diagnosis and prescription of treatment than polysomnography based diagnosis. Single Channel Nasal Airflow Pressure Transducers (SCNAPTs) consist of a small plastic tube drawn across the face below the nose with two nasal inserts, one per nostril (Rofail). SCNAPTs measure airflow, a crucial parameter in diagnosing sleep apnea. SCNAPTs are affordable, portable, and less obstructive than polysomnography or CPAP (Rofail). Unlike CPAP, SCNAPTs are not treatment devices; they only have potential as diagnostic tools (Rofail). The only thing for which they are used is detecting airflow. SCNAPTS are currently on the market at a far lower cost than polysomnographs, but are not often used in sleep apnea testing currently. In a study by Rofail and associates, 105 sleep clinic patients and 88 primary care patients were invited to the study, which compared SCNAPT and polysomnography. The Flow Wizard, a portable SCNAPT produced by DiagnoseIT, was used for the study, as well as standard in lab polysomnography (Rofail). All patients underwent one night of full polysomnography and three consecutive nights of home based SCNAPT (Rofail). Data over the three nights was comparable, suggesting the device is reliable from test to test (Rofail). After one night, 19.5% of patients had insufficient data for diagnosis, while after three nights only 6.5% lacked sufficient data for diagnosis. This is comparable to an 18% 20% lack of sufficiency after one night of full home polysomnography (Rofail). There was slight overestimation of obstruction of the airway compared to polysomnography, possibly due to the large number of participants who experienced a broader range of obstruction on a regular basis (Rofail). As the tests were not done on the same night, it is uncertain whether the reason SCNAPTs had a tendency to say the airways were more blocked than polysomnography was due to the airways being more obstructed on some nights or due to actual disagreement between the two devices. More nights of polysomnography testing may have helped confirm or deny this hypothesis.

16 15 While both SCNAPT and CPAP feedback are affordable, available on the market, and measure the critical parameter of airflow, indicative of airway blockage, they fail to identify sleep and wake, making it difficult to determine if the condition is actually disruptive to the patient s sleep. Like the other alternatives discussed above, SCNAPT or CPAP could be used in combination with other devices to create a more useful reading, but CPAP is significantly less comfortable than indirect airway obstruction measures are, such as oximetry. Additionally, both SCNAPT and CPAP are worn on the face, making them less likely candidates for a portable around the clock monitor to measure daytime sleepiness as a result of apnea, as they have a greater cosmetic off put. Conclusions: Testing Method Cost Comfortable/ Can be Used in Any Position Compact Measures Airflow Measures Sleep/Wake Lab About No No Yes Yes Polysomnography $13000 Home About No No Yes Yes Polysomnography $9000 ARES ULM About Somewhat Yes Yes Yes $1300 Oximetry < $150 Yes Yes Yes No Actigraphy < $250 Yes Yes No Yes Auto CPAP $150 Somewhat Somewhat Yes No $1000 SCNAPT $100 $200 Yes Yes Yes No Polysomnography gives an excellent standard for diagnosis, but is expensive, unwieldy, requires specialized staff, and currently must usually be used in a laboratory. Unattended limited monitoring appears to provide the best balance between cost, comfort, and adequate data gathering. In order for it to be realistically feasible and useful for the patient, an unattended limited monitoring device would need to have accuracy demonstrated in order for approval by insurance companies. While polysomnography is not perfect, any alternative device would need to demonstrate that the outputs are

17 16 very similar to that of polysomnography, that data is sufficient for accurate diagnosis, and that the line of devices tends to Without this, some patients will be unable to afford testing or treatment, negating the usefulness of having a compact, comfortable device which does not inconvenience the user. In order to correctly diagnose and treat the maximum number of people both cost and insurance coverage and reducing the hassle that prevents those affected from seeking proper help are critical. Unattended limited monitoring devices could consist of any combination of a large number of monitoring options. These include SCNAPTs, auto CPAP, oximetry, actigraphy, and others which were not explicitly discussed here. The most useful devices will be compact, affordable, accurate, and comfortable. While there are more options for a device that is only used during the night, as people are more willing to wear obvious pieces of equipment like the CPAP mask or SCNAPT sensor, a device that is also usable during the day has more applications. It can be used to more empirically evaluate severe effects on quality of life and productivity than the usual practice of questionnaire use. Ideally this device would be able to indicate if the user falls asleep during the day, using any of the addressed methods for differentiating between sleep and wake. It might also be useful if this device could look for side effects of apnea, such as hypertension, during the day, as this might help reveal the risk level of the patient for serious complications. They could also be more applicable for study of other sleep disorders, where the patient may be experiencing vital symptoms that are not occurring during the night, such as narcolepsy. The stability and comfort of wrist mounted devices makes them ideal for this purpose, making a combined device such as an oximeter paired with an actigraph a particularly promising option for further research and comparison with polysomnography. The data output supplied by this device should be satisfactory for diagnosis based on the results of studies using these devices alone, and the component devices are already available for other purposes individually at very low cost.

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