Peripheral arterial tonometry-PAT technology.

PAT Technology is a plethysmographic based measurement method which facilitates the accurate recording of the pulsatile volume changes of the arteries of peripheral vascular beds at the distal end of the fingers over sustained periods of time. It represents a departure from previously available plethysmographic methods, in so far as it applies a uniform pressure field which completely envelopes the measured part of a digit, including its distal-most tip. Applying near diastolic blood pressure levels of pressure within the PAT probe optimizes the dynamic range of the signal, prevents confounding veno-arteriolar reflex vasoconstriction at the measurement site, reduces respiratory and movement artifacts and thus facilitates accurate long term measurement. The vascular bed of the distal phalanx of the finger is a major site of sympathetic nervous system mediated vasoconstrictor activity, and the PAT response to sympathetic changes provides a platform for accurate and robust measurement in a number of sleep and sleep related clinical areas, foremost as a patient friendly and extensively validated home sleep testing device.

Detecting central sleep apnea in adult patients using WatchPAT-a multicenter validation study.

STUDY OBJECTIVES: To assess the accuracy of WatchPAT (WP-Itamar-Medical, Caesarea, Israel) enhanced with a novel systolic upstroke analysis coupled with respiratory movement analysis derived from a dedicated snoring and body position (SBP) sensor, to enable automated algorithmic differentiation between central sleep apnea (CSA) and obstructive sleep apnea (OSA) compared with simultaneous in-lab sleep studies with polysomnography (PSG). METHODS: Eighty-four patients with suspected sleep-disordered breathing (SDB) underwent simultaneous WP and PSG studies in 11 sleep centers. PSG scoring was blinded to the automatically analyzed WP data. RESULTS: Overall WP apnea-hypopnea index (AHI; mean ± SD) was 25.2 ± 21.3 (range 0.2-101) versus PSG AHI 24.4 ± 21.2 (range 0-110) (p = 0.514), and correlation was 0.87 (p < 0.001). Using a threshold of AHI ≥ 15, the sensitivity and specificity of WP versus PSG for diagnosing sleep apnea were 85% and 70% respectively and agreement was 79% (kappa = 0.867). WP central AHI (AHIc) was 4.2 ± 7.7 (range 0-38) versus PSG AHIc 5.9 ± 11.8 (range 0-63) (p = 0.034), while correlation was 0.90 (p < 0.001). Using a threshold of AHI ≥ 15, the sensitivity and specificity of WP versus PSG for diagnosing CSA were 67% and 100% respectively with agreement of 95% (kappa = 0.774), and receiver operator characteristic (ROC) area under the curve of 0.866, (p < 0.01). Using a threshold of AHI ≥ 10 showed comparable overall sleep apnea and CSA diagnostic accuracies. CONCLUSIONS: These findings show that WP can accurately detect overall AHI and effectively differentiate between CSA and OSA.

Peripheral arterial tonometry: a diagnostic method for detection of myocardial ischemia induced during mental stress tests: a pilot study.

BACKGROUND: Mental stress testing is considered a reliable method for diagnosing patients with coronary heart disease (CHD) who may be at risk for future events. It has been shown recently that myocardial ischemia induced during mental stress tests is specifically associated with peripheral arterial vasoconstriction. HYPOTHESIS: The study was undertaken to test the diagnostic capability of peripheral arterial tonometry (PAT) to detect peripheral arterial vasomotor changes. METHODS: We monitored pulsatile finger blood volume changes using a specially designed finger plethysmograph, PAT that can detect peripheral arterial vasomotor changes. Equilibrium radionuclide angiography (ERNA) was simultaneously performed in 18 male patients at rest and during a mental arithmetic stress test with harassment. All patients had previously diagnosed coronary disease and positive exercise tests. Myocardial ischemia was diagnosed by ERNA when global ejection fraction fell > or = 8% during mental stress or new (or worsened) focal wall motion abnormalities occurred. Peripheral arterial tonometry tracings were considered abnormal when the pulse wave amplitude decreased by > or = 20% from baseline. RESULTS: In 18 patients there were 16 usable studies. In eight patients, both ERNA and PAT were abnormal, and in six patients the tests were negative by both methods. In two cases, the results were discordant. Therefore, when considering an abnormal PAT tracing as indicative of mental stress-driven myocardial ischemia, concordance of the two methods was 88%. CONCLUSION: The use of PAT may facilitate both clinical testing and research during mental stress.

An automatic ambulatory device for detection of AASM defined arousals from sleep: the WP100.

OBJECTIVES AND BACKGROUND: Arousals from sleep are associated with increased sympathetic activation and therefore with peripheral vasoconstriction. Sleep fragmentation in the form of multiple arousals is associated with daytime somnolence and cognitive impairment; however, manual scoring of arousal is time consuming and problematic due to relatively high inter-scorer variability. We have recently shown that automated analysis of in-lab recorded peripheral arterial tone (PAT) signal and the pulse rate derived from it can accurately assess arousals from sleep as defined by the American Academy of Sleep Medicine (AASM). In the current study we sought to extend these findings to the Watch_PAT100 (WP100), an ambulatory device measuring PAT, oximetry and actigraphy. METHODS: Sixty-eight subjects (61 patients referred to the sleep lab with suspected obstructive sleep apnea and seven healthy volunteers, mean age 46.3+/-14.2 years) underwent a whole night polysomnography (PSG) with simultaneous recording of PAT signal by the ambulatory WP100 device. The PSG recordings were blindly manually analyzed for arousals based on AASM criteria, while PAT was scored automatically based on the algorithm developed previously. RESULTS: There was a significant correlation between AASM arousals derived from the PSG and PAT autonomic arousals derived from the WP100 (R=0.87, P<0.001), with a good agreement across a wide range of values. The sensitivity and specificity of PAT in detecting patients with at least 20 arousals per hour of sleep were 0.80 and 0.79, respectively, with a receiver operating characteristic curve having an area under the curve of 0.87. CONCLUSIONS: We conclude that automatic analysis of peripheral arterial tonometry signal derived from the ambulatory device Watch_PAT100 can accurately identify arousals from sleep in a simple and time saving fashion.

Assessment of peripheral vascular endothelial function with finger arterial pulse wave amplitude.

BACKGROUND: Abnormalities in pulse wave amplitude (PWA) have been described in subjects with atherosclerosis and may be a marker of future cardiac events. We evaluated the relationship between changes in PWA of the finger and peripheral endothelial function. METHODS: We performed measurements of PWA with a novel finger plethysmograph (peripheral arterial tonometry [PAT]) and compared the findings with a simultaneous noninvasive measurement of peripheral endothelial function with brachial artery ultrasound scanning (BAUS) in 89 subjects. The PAT hyperemia ratio was defined as the ratio of PWA during reactive hyperemia relative to the baseline. Flow-mediated dilation (FMD) was defined by BAUS as the ratio of the brachial artery diameter during reactive hyperemia relative to the baseline. Sixty-eight subjects underwent exercise myocardial perfusion imaging (ExMPI). RESULTS: Fifty-four men and 35 women were examined. There was a linear relationship between the PAT hyperemia ratio and FMD during the same episode of reactive hyperemia (r = 0.55, P <.0001). Subjects in the lowest FMD quartile had the lowest PAT hyperemia ratio, whereas subjects in the highest FMD quartile had the highest PAT hyperemia ratio (P <.001 for trend). Similar to BAUS, the PAT hyperemia ratio was more impaired in subjects with cardiovascular risk factors and in subjects with ExMPI studies that were indicative of coronary artery disease. CONCLUSIONS: Assessment of PWA with PAT demonstrates patterns of abnormality similar to that of BAUS assessment of FMD. PWA during reactive hyperemia is influenced by factors known to affect endothelial function, including cardiovascular risk factors and coronary artery disease. These findings support the concept that analysis of PWA with PAT during reactive hyperemia may be used to study peripheral vascular endothelial function.

Enhanced external counterpulsation improves endothelial function in patients with symptomatic coronary artery disease.

OBJECTIVES: The goal of this study was to examine the effect of enhanced external counterpulsation (EECP) on endothelial function. BACKGROUND: Enhanced external counterpulsation improves symptoms and exercise tolerance in patients with symptomatic coronary artery disease (CAD). However, the exact mechanisms by which this technique exerts its clinical benefit are unclear. METHODS: Reactive hyperemia-peripheral arterial tonometry (RH-PAT), a noninvasive method to assess peripheral endothelial function by measuring reactive hyperemic response in the finger, was performed in 23 patients with refractory angina undergoing a 35-h course of EECP. In each patient RH-PAT measurements were performed before and after the first, at midcourse, and the last EECP session. In addition, RH-PAT response was assessed one month after completion of EECP therapy; RH-PAT index, a measure of reactive hyperemia, was calculated as the ratio of the digital pulse volume during reactive hyperemia divided by that at rest. RESULTS: Enhanced external counterpulsation led to symptomatic improvement (>/=1 Canadian Cardiovascular Society class) in 17 (74%) patients; EECP was associated with a significant immediate increase in average RH-PAT index after each treatment (p < 0.05). In addition, average RH-PAT index at one-month follow-up was significantly higher than that before EECP therapy (p < 0.05). When patients were divided by their clinical response, RH-PAT index at one-month follow-up increased only in those patients who experienced clinical benefit. CONCLUSIONS: Enhanced external counterpulsation enhances peripheral endothelial function with beneficial effects persisting at one-month follow-up in patients with a positive clinical response. This suggests that improvement in endothelial function may contribute to the clinical benefit of EECP in patients with symptomatic CAD.

Evaluation of a portable device based on peripheral arterial tone for unattended home sleep studies.

BACKGROUND: Diagnosis of obstructive sleep apnea syndrome (OSAS) by ambulatory systems is a growing practice in view of the large number of patients awaiting correct diagnosis. The Watch PAT100 (WP100) [Itamar Medical; Caesarea, Israel] is a portable device based on the peripheral arterial tone (PAT) signal, and is designed for unattended home sleep studies. OBJECTIVES: To evaluate the efficacy, reliability, and reproducibility of the WP100 device for the diagnosis of OSAS as compared to in-laboratory, standard polysomnographic-based manual scoring. DESIGN AND METHODS: One hundred two subjects (78 men; 69 patients with OSAS and 33 normal volunteers; mean +/- SD age, 41.4 +/- 15.2 years; body mass index, 26.8 +/- 5.5) underwent in-laboratory full polysomnography simultaneously with WP100 recording. Fourteen subjects also underwent two additional unattended home sleep studies with the WP100 alone. The polysomnography recordings were blindly scored for apnea/hypopnea according to the American Academy of Sleep Medicine criteria (1999), and the polysomnography respiratory disturbance index (RDI) [PSG-RDI] was calculated. The WP100 data were analyzed automatically for the PAT RDI (PRDI) by a proprietary algorithm that was previously developed on an independent group of subjects. RESULTS: Across a wide range of RDI levels, the PRDI was highly correlated with the PSG-RDI (r = 0.88, p < 0.0001), with an area under the receiver operating characteristic curve of 0.82 and 0.87 for thresholds of 10 events per hour and 20 events per hour, respectively. The PRDI scores were also highly reproducible, showing high correlation between home and in-laboratory sleep studies (r = 0.89, p < 0.001). CONCLUSION: The WP100 may offer an accurate, robust, and reliable ambulatory method for the detection of OSAS, with minimal patient discomfort.

Assessment of peripheral artery tonometry in the detection of treadmill exercise-induced myocardial ischemia.

OBJECTIVES: We sought to assess the added diagnostic value of peripheral artery tonometric (PAT) measurements, based on finger pulsatile arterial volume changes, to standard 12-lead stress electrocardiography (ECG), for detecting exercise-induced myocardial ischemia, using single-photon emission computed tomography (SPECT) as the standard of comparison in a double-blinded, multicenter protocol. METHODS: An automated algorithm for identifying myocardial ischemia from PAT was derived from 345 training cases. The PAT outcome was combined with the ECG result (ischemic, nonischemic, or equivocal), giving a PAT-enhanced value. A threshold of normality was determined to optimize agreement with the SPECT results in the training sample. The PAT-enhanced analysis was then validated in 616 subjects, only two of whom had technically unacceptable PAT studies. RESULTS: In the validation cohort, receiver operating characteristic curve analysis of the PAT-enhanced diagnosis yielded an area under the curve of 0.72, a sensitivity of 63.5%, compared with 44.7% for ECG alone (p < 0.0001), and a specificity of 67.8% common to both ECG and PAT-enhanced diagnoses. Similar results were found in the training sample. Although over 10% of validation subjects had equivocal ECG results, with the aid of PAT, it was possible to provide diagnostic information for all but one subject. CONCLUSIONS: Peripheral artery tonometry may be useful for improving the diagnosis of exercise-induced myocardial ischemia by both enhancing the sensitivity without impairing the specificity and increasing the percentage of definitive test results.