Estimation of cerebral blood flow velocity during breath-hold challenge using artificial neural networks.

The effect of untreated Obstructive Sleep Apnoea (OSA) on cerebral haemodynamics and CA impairment is an active field of research interest. A breath-hold challenge is usually used in clinical and research settings to simulate cardiovascular and cerebrovascular changes that mimic OSA events. This work utilises temporal arterial oxygen saturation (SpO2) and photoplethysmography (PPG) signals to estimate the temporal cerebral blood flow velocity (CBFv) waveform. Measurements of CBFv, SpO2, and PPG, were acquired concurrently from volunteers performing two different protocols of breath-hold challenge in the supine position. Past values of the SpO2 and PPG signals were used to estimate the current values of CBFv using different permutations and topologies of supervised learning with shallow artificial neural networks (ANNs). The measurements from one protocol were used to train the ANNs and find the optimum topologies, which in turn were tested using the other protocol. Data collected from 10 normotensive, healthy subjects (four females, age 28.5 ±â€¯6.1 years, Body Mass Index (BMI) 24.0 ±â€¯4.7 kg/m2) were used in this study. The results show that different subjects have different optimum topologies for ANNs, thus indicating the effects of inter-subject variability on ANNs. Successfully reconstructed blind waveforms for the same subject group in the second protocol showed a reasonable accuracy of 60-80% estimation compared to the measured waveforms. HYPOTHESIS: Temporal waveforms for SpO2 and PPG contain adequate information to estimate the temporal CBFv waveform using ANNs. METHODOLOGY: Concurrent measurements of SpO2 and PPG using pulse oximetry from the forehead and CBFv from the middle cerebral artery (MCA) using transcranial Doppler (TCD) were recorded from healthy, normotensive subjects performing a breath-hold challenge. The breath-hold challenge mimicked the cerebrovascular response to apnoea, and was recorded by measuring CBFv in MCA. Two protocols were used, each consisting of five breath-holding manoeuvres and differing in terms of the time between the five successive breath-holds. Using data from one protocol, several permutations of the temporal values of SpO2 and PPG signals were used as inputs to different ANN topologies, in order to train and find the optimum model. The optimum model was evaluated using the data from the other protocol as a blind dataset. RESULTS: Using the first protocol for training, optimum ANN configurations were found to be different for each subject, and accuracy of 75-87% was achieved. When these optimum ANN models were tested using the second protocol as a blind dataset, the accuracy achieved was around 60-80%. CONCLUSIONS: A novel approach employing temporal records of SpO2 and PPG can be used to estimate the CBFv waveform using ANNs with acceptable accuracy. Increases in the size and diversity of the population dataset and the use of features extracted from SpO2 and PPG signals are needed for generalisation of the method and potential future clinical applications.

An investigation of simultaneous variations in cerebral blood flow velocity and arterial blood pressure during sleep apnea.

Obstructive Sleep Apnea (OSA) is a major sleep disorder with a prevalence of about 15 % among US adult population and can lead to cardiovascular diseases and stroke. In this study, we have investigated the OSA-induced concurrent rise in cerebral blood flow velocity and blood pressure in 5 positively diagnosed sleep apnea subjects. The subject population had a mean AHI of 57.94±25.73 and BMI of 33.66±7.27 kg/m(2). The results of this preliminary study yielded a relatively high correlation between rise in blood pressure and rise in cerebral blood flow velocity during apnea episodes (r=0.61±0.16) compared to normal breathing (r=0.28±0.26). These findings suggest that cerebral autoregulation may be less effective during apnea episodes.

Upper airway occlusion detection using a novel ultrasound technique.

Obstructive sleep apnea/hypopnea Syndrome (OSAHS) is the most common form of Sleep Disordered Breathing (SDB) and it is estimated to affect approximately 15% of US adult population. In this paper, we report on the results of in vivo experiments of an ultrasonic device for the non-invasive detection of obstructive sleep apnea/hypopnea (OSAH). A description of the ultrasonic system used is presented, followed by the results of a full night sleep study. The findings show a significant difference in the spectral features extracted from the received ultrasonic waveform during apneic breathing, compared to the hyperventilation that follows. Therefore, the findings indicate the feasibility of developing an ultrasonic detection device for low cost diagnosis of SDB.

Relation between arterial blood pressure and cerebral blood flow velocity in simulated sleep apnea.

Obstructive Sleep Apnea (OSA) is one of the most common breathing disorder, affecting approximately 27% of U.S. adults. Limited data have suggested that OSA causes cerebral autoregulation impairment, thus being an important risk factor to stroke. The objective of this paper is to investigate and measure the relation between arterial blood pressure (BP) and cerebral blood flow velocity (CBFV) in simulated apnea. Sixteen healthy subjects (9 male, 7 female) of 29±4.89 yrs age and body mass index of 24.07±4.84 kg/m(2) participated in the study. Four protocols were used; sitting 30 seconds, 90 s, and supine 30 s and 90 s. Our results showed that systolic BP and peak CBFV were correlated with average r=0.672 +0.265. Also, CBFV exhibited a significantly higher percent rise than BP. Thus, our findings suggest that cerebral autoregulation may be impaired during apnea episodes.

In vivo characterization of ultrasonic transducers for the detection of airway occlusion in Sleep Disordered Breathing.

Obstructive Sleep Apnea/Hypopnea Syndrome (OSAHS) is the most common form of Sleep Disordered Breathing (SDB) and it is estimated to affect approximately 15% of US adult population. Various methods have been proposed for the development of inexpensive screening methods to detect SDB to reduce the need for costly nocturnal polysomnography (NPSG). In this paper, a description of the ultrasonic transducer design and characterization is presented, followed by the results of a full night sleep study. The findings show a significant difference in the temporal features extracted from the received ultrasonic waveform during apneic breathing, compared to the hyperventilation that follows. Therefore, the findings indicate the feasibility of developing an ultrasonic detection device for low cost diagnosis of SDB.

Concurrent variations of cerebral blood flow and arterial blood pressure in simulated sleep apnea.

Obstructive Sleep Apnea (OSA) is one of the most common sleep disordered breathing which affects about 15 % of US adult population. OSA is considered to be an important risk factor for the development of cardiac dysfunction and stroke. In this paper, we present the initial results of our investigation of the relationship between arterial blood pressure and cerebral blood flow velocity in simulated apnea. Sixteen healthy subjects (9 male, 7 female) of 29 ± 4.89 yrs age and body mass index of 24.07 ± 4.84 kg/m(2) participated in the study. Our findings indicate that cerebral blood flow velocity variations has a relatively high correlation to changes in blood pressure during simulated apnea (r = 0.74 ± 0.06), suggesting that cerebral autoregulation may not compensate for the pressure changes during apnea.

Detection of airway occlusion in simulated obstructive sleep apnea/hypopnea using ultrasound: an in vitro study.

Obstructive sleep apnea/hypopnea Syndrome (OSAHS) is the most common form of Sleep Disordered Breathing (SDB) and it is estimated to affect approximately 6% of US adult population. Various methods have been proposed for the development of inexpensive screening methods to detect SDB to reduce the need for costly nocturnal polysomnography (NPSG). By using the existing air in the airway as an ultrasonic contrast agent, we propose a method to examine the narrowing or occlusion of the airway associated with OSAHS events. We describe here an in vitro study that approximates the anatomical and acoustic characteristics of the airway and neck. In this experiment, we simulate the fully open airway as well as apnea and hypopnea events. These in vitro studies results show significant differences in the ultrasonic signals acquired from the open airway model versus those from the model depicting apnea and hypopnea events. Therefore, the findings provide a foundation for development of an ultrasound system to detect SDB in vivo.

Sleep disordered breathing detection using heart rate variability and R-peak envelope spectrogram.

We report that combining the interbeat heart rate as measured by the RR interval (RR) and R-peak envelope (RPE) derived from R-peak of ECG waveform may significantly improve the detection of sleep disordered breathing (SDB) from single lead ECG recording. The method uses textural features extracted from normalized gray-level cooccurrence matrices of the time frequency plots of HRV or RPE sequences. An optimum subset of textural features is selected for classification of the records. A multi-layer perceptron (MLP) serves as a classifier. To evaluate the performance of the proposed method, single Lead ECG recordings from 7 normal subjects and 7 obstructive sleep apnea patients were used. With 500 randomized Monte-Carlo simulations, the average training sensitivity, specificity and accuracy were 100.0%, 99.9%, and 99.9%, respectively. The mean testing sensitivity, specificity and accuracy were 99.0%, 96.7%, and 97.8%, respectively.