In several new studies presented at this week's Associated Professional Sleep Societies (APSS) meetings, researchers from Harvard, Johns Hopkins School of Medicine, the Technion-Israel Institute of Technology and other major institutions from around the world have shown that sleep-related conditions such as obstructive sleep apnea, sleep fragmentation due to microarousals, and abnormal respiratory patterns associated with congestive heart failure are reflected by changes in an individual's peripheral arterial tone (PAT). These studies also indicate that the PAT signal can offer new insights into the relationship between sleep and cardiovascular health.

PAT is a newly detected physiological signal that reflects arterial pulsatile volume changes in the fingertip. The PAT signal mirrors changes or anomalies in autonomic nervous system activity; a variety of medical conditions can trigger this activity, causing vascular events that can be independent of the patient's blood pressure, heart rate or ECG changes. The PAT signal can be measured using a non-invasive finger mounted optical sensor and is analyzed with specialized signal processing algorithms. The FDA recently approved a PAT based device that uses the PAT signal to increase the sensitivity and yield of ECG exercise stress testing in the detection of myocardial ischemia.

Obstructive Sleep Apnea (OSA)

The PAT signal may also be useful in the diagnosis and treatment of OSA. According to the National Institutes of Health, OSA affects over 18 million people in the US; it is associated with irregular heartbeat, high blood pressure, heart attack, stroke, cognitive and behavioral impairment, daytime fatigue and related motor vehicle and work accidents. Clinicians typically use polysomnographic (PSG) measures to evaluate patients with OSA; PSG testing requires an overnight stay in a sleep lab, connected to multiple devices that monitor heart, respiratory and brain functions.

Alan R. Schwartz, MD, Associate Professor of Pulmonary Medicine and Co-Director of the Sleep Disorders Center at Johns Hopkins School of Medicine, demonstrated in his study(1) how the PAT signal may help to improve diagnosis and management of OSA .

"OSA is significantly underdiagnosed and its consequences are a burden on the healthcare system," noted Dr. Schwartz. "Our study showed that the PAT is a sensitive indicator of arousal induced by acute periods of airflow obstruction, such as associated with OSA."

Sleep Fragmentation

In other studies(2,3), a PAT-based index of sleep arousals was compared to standard PSG measures in evaluating patients with sleep fragmentation.

"Sleep fragmentation in the form of frequent 'microarousals' i.e. transient changes in autonomic parameters which may not be associated with any visible brain wave activities -- has been implicated in daytime impairment of alertness plus cognitive and psychomotor performance," noted Professor Peretz Lavie, PhD, Director of the Sleep Laboratory at the Technion-Israel Institute of Technology, and author of The Enchanted World of Sleep (Yale University Press, 1996). "Our study(2) demonstrates that the PAT can be very valuable for screening of autonomic arousals during sleep."

David P. White, MD, Associate Professor of Medicine at Harvard University School of Medicine and Director, Sleep Disorders Program at Brigham and Women's Hospital added "Our data(3) suggest that a PAT-based index of sleep disruption may be better at predicting subjective and objective sleepiness, plus decrements in performance than standard PSG measures such as respiratory and electroencephalographic monitoring. The PAT seems to provide more subtle data than other tools, which may offer new useful information about the impact of sleep disorders on waking function. It may also be useful for early diagnosis of sleep disorders and their consequences."

Congestive Heart Failure

In patients with advanced congestive heart failure (CHF), abnormal respiratory patterns during sleep called Cheyne-Stokes breathing (CSB) are related to poor prognosis and therefore are important to diagnose. Typically, once suspected, CSB is diagnosed through monitoring of respiratory effort, oral-nasal airflow and blood oxygen saturation. Professor Lavie and a colleague, in a study of 20 congestive heart failure patients(4) conducted at the Technion-Israel Institute of Technology found that the PAT signal was shown to be a sensitive and specific marker of CSB when compared to current standard techniques (90% sensitivity/87% specificity).

Professor Lavie observed that, "In view of the prognostic value of CSB in CHF patients and the high potential of correction through intervention, ambulatory screening of CHF patients for CSB could become routine clinical practice using the convenient, noninvasive PAT-based technology."

REM Sleep and Cardiovascular Health

Professor Lavie also presented PAT signal data(5) in which the relationship between phases of REM sleep stage, (the stage of dreaming) and peripheral vasoconstriction were explored. Previous findings showed blood pressure surges during REM sleep, suggesting elevated sympathetic activation. Based on his analyses, Professor Lavie was able to demonstrate that the change in sympathetic activation during REM sleep is phasic in nature, increasing through the night and reaching a peak in early morning. Professor Lavie suggested that these data can be used to develop appropriate algorithms to automatically identify episodes of REM sleep using only the PAT signal.

"This next step will allow us to examine, by using PAT, whether the early morning peak in REM-related sympathetic activation is related to the early morning peak in cardiovascular events," added Dr. Lavie. "By demonstrating a physiologic relationship between REM and autonomic activation, we may be able to identify and intervene early in the case of those patients most at risk for cardiovascular events."

The PAT signal technology -- including the non-invasive finger probe, hardware, software, and application-specific signal processing algorithms -- was developed by Itamar Medical, a medical technology company based in Caesarea, Israel. The studies reported at APSS were supported in part by grants from Itamar Medical. To learn more about the PAT signal and Itamar Medical, visit http://www.itamar-medical.com. For further information, email contact@itamar-medical.com or phone 1-800-206-6952 ext 204.

References:

1. O'Donnell CP, Allan L, Atkinson P, Schwartz AR Peripheral Arterial Tonometry (PAT) is a Sensitive Indicator of Acute Arousal Responses to

Obstructive Sleep Apnea (OSA). SLEEP, Vol. 24, Abstract Supplement, 2001, 717R.

2. Pillar G, Shlitner A, Lavie P Autonomic Activation Index (AAI) -- A New Marker of Sleep Disruption. SLEEP, Vol. 24, Abstract Supplement, 2001, 176R.

3. Ayas N, Pittman SD, Malhotra A, Pillar G, Stanchina M, Winkelma, JW White DP Do Indices of Autonomic Arousal Predict Sleepiness Better than Standard Polysomnographic (PSG) Measures? SLEEP, Vol. 24, Abstract Supplement, 2001, 146J.

4. Lavie P, Freimark D, Adler Y, Sheffy K, Schechter D, Schwammenthal E, Motro M Oscillations in Peripheral Arterial Tone in CHF Patients: A New Marker for Cheyne-Stokes Breathing. SLEEP, Vol. 24, Abstract Supplement, 2001, 700R.

5. Likhtik E, Lavie P REM-related Peripheral Vasoconstriction -- Association with Rapid Eye Movement Density. SLEEP, Vol. 24, Abstract Supplement, 2001, 131R.