Juha Töyräs

University of Eastern Finland | UEF · Department of Applied Physics

Background Major cardiovascular events (MACE) and mortality in obstructive sleep apnea (OSA) patients have been frequently reported. However, there is an ongoing debate regarding biomarkers predicting MACE and mortality in OSA. The Apnoea Hypopnea Index (AHI) has been used to assess the severity of Obstructive Sleep Apnea (OSA) despite poor associa...

Optical properties of biological tissues, such as refractive index, are fundamental properties, intrinsically linked to a tissue’s composition and structure. This study aims to investigate the variation of refractive index (RI) of human articular cartilage along the tissue depth (via collagen fibril orientation and optical density) and integrity (b...

Cartilage and synovial fluid are challenging to observe separately in native computed tomography (CT). We report the use of triple contrast agent (bismuth nanoparticles, CA4+, and gadoteridol) to image and segment cartilage in cadaveric knee joints with a clinical CT scanner. We hypothesize that bismuth nanoparticles will remain in synovial fluid w...

Oxygen saturation (SpO2 )-based parameters are more strongly linked to impaired daytime vigilance than the conventional diagnostic metrics in patients with obstructive sleep apnea (OSA). However, whether the association between SpO2 -based parameters and impaired daytime vigilance is modulated by sex, remains unknown. Hence, we investigated the int...

Sleep recordings are increasingly being conducted in patients' homes where patients apply the sensors themselves according to instructions. However, certain sensor types such as cup electrodes used in conventional polysomnography are unfeasible for self-application. To overcome this, self-applied forehead montages with electroencephalography and el...

Mid-infrared spectroscopy (MIR), near-infrared spectroscopy (NIR), and Raman spectroscopy are all well-established analytical techniques in biomedical applications. Since they provide complementary chemical information, we aimed to determine whether combining them amplifies their strengths and mitigates their weaknesses. This study investigates the...

Osteoarthritis degenerates cartilage and impairs joint function. Early intervention opportunities are missed as current diagnostic methods are insensitive to early tissue degeneration. We investigated the capability of visible light-near-infrared spectroscopy (Vis-NIRS) to differentiate normal human cartilage from early osteoarthritic one. Vis-NIRS...

Objective To differentiate healthy from artificially degraded articular cartilage and estimate its structural, compositional, and functional properties using Raman spectroscopy (RS). Design Visually normal bovine patellae ( n = 12) were used in this study. Osteochondral plugs ( n = 60) were prepared and artificially degraded either enzymatically (...

To assess whether articular cartilage changes in an equine model of post traumatic osteoarthritis (PTOA), induced by surgical creation of standard (blunt) grooves, and very subtle sharp grooves, could be detected with ex vivo T1 relaxation time mapping utilizing 3-D readout sequence with zero echo time. Grooves were made on the articular surfaces o...

There is increasing research on the potential application of diffuse optical spectroscopy and hyperspectral imaging for characterizing the health of the connective tissues, such as articular cartilage, during joint surgery. These optical techniques facilitate the rapid and objective diagnostic assessment of the tissue, thus providing unprecedented...

Introduction Commonly utilised metrics such as apnoea-hypopnoea index show limited correlation to excessive daytime sleepiness (EDS). Oxygen desaturation parameters show better predictive power, however oxygen resaturation parameters have not yet been investigated. Oxygen resaturation may represent increased cardiovascular fitness and thus we hypot...

Introduction: Visual sleep scoring has several shortcomings, including inter-scorer inconsistency, which may adversely affect diagnostic decision-making. Although automatic sleep staging in adults has been extensively studied, it is uncertain whether such sophisticated algorithms generalize well to different pediatric age groups due to distinctive...

Objective/background: Previous studies have shown that obstructive sleep apnoea (OSA) is associated with reduced delta EEG and increased beta EEG power and increased EEG slowing ratio. There are however no studies that explore differences in sleep EEG between positional obstructive sleep apnoea (pOSA) and non-positional obstructive sleep apnoea (n...

In the above article [1] , Table 2 partially showed erroneous values for the absolute skin-electrode impedances while the correct median absolute impedances were presented in Figure 2. The authors regret the error and apologize for the possible inconvenience. The corrected Table 2 is presented below.

Artificial neural networks show great success in sleep stage classification, with an accuracy comparable to human scoring. While their ability to learn from labelled electroencephalography (EEG) signals is widely researched, the underlying learning processes remain unexplored. Variational autoencoders can capture the underlying meaning of data by e...

Obstructive sleep apnea (OSA) is related to the progression of cardiovascular diseases (CVD); it is an independent risk factor for stroke and is also prevalent post-stroke. Furthermore, heart rate corrected QT (QTc) is an important predictor of the risk of arrhythmia and CVD. Thus, we aimed to investigate QTc interval variations in different sleep...

Obstructive sleep apnea (OSA)‐related intermittent hypoxaemia is a potential risk factor for different OSA comorbidities, for example cardiovascular disease. However, conflicting results are found as to whether intermittent hypoxaemia is associated with impaired vigilance. Therefore, we aimed to investigate how desaturation characteristics differ b...

Introduction The mechanism underlying the development of excessive daytime sleepiness (EDS) in obstructive sleep apnea (OSA) remains unclear. Thus, we characterised the association between sleep architecture and EDS in individuals with and without OSA. Methods 1876 suspected OSA patients reporting daytime sleepiness underwent in-lab polysomnograph...

Introduction Impaired daytime vigilance is common in obstructive sleep apnoea (OSA) patients. However, the apnoea-hypopnea index (AHI) has been shown to have a weak correlation with daytime vigilance. This may be because the AHI only quantifies respiratory event frequency. Thus, we aimed to test our hypothesis that increased airflow limitation duri...

Background and objective Many sleep recording software used in clinical settings have some tools to automatically analyze the blood oxygen saturation (SpO2) signal by detecting desaturations. However, these tools are often inadequate for scientific research as they do not provide SpO2 signal-based parameters which are superior in the estimation of...

Pulse oximeters are routinely used in various medical-grade and consumer-grade applications. They can be used to estimate, for example, blood oxygen saturation, autonomic nervous system activity and cardiac function, blood pressure, sleep quality, and recovery through the recording of photoplethysmography signal. Medical-grade devices often record...

Objectives/Background Interest in using blood oxygen desaturations in the diagnostics of sleep apnea has risen in recent years. However, no standardized criteria for desaturation scoring exist which complicates the drawing of solid conclusions from literature. Patients/methods We investigated how different desaturation scoring criteria affect the...

Sleep research often relies on large retrospective clinical datasets. However, as the data is usually stored in proprietary formats specific for each sleep software, the raw data cannot be easily accessed and analyzed with external tools. While the raw data can usually be exported to more common data formats, this is often a cumbersome and labor-in...

Purpose To develop the means to estimate cartilage histologic grades and proteoglycan content in ex vivo arthroscopy using near-infrared spectroscopy (NIRS). Methods In this experimental study, arthroscopic NIR spectral measurements were performed on both knees of 9 human cadavers, followed by osteochondral block extraction and in vitro measuremen...

Background: Obstructive sleep apnoea (OSA) causes, among other things, intermittent blood oxygen desaturations, increasing the sympathetic tone. Yet the effect of desaturations on heart rate variability (HRV), a simple and noninvasive method for assessing sympathovagal balance, has not been comprehensively studied. We aimed to study whether desatu...

Injuries to the ligaments of the knee commonly impact vulnerable and physically active individuals. These injuries can lead to the development of degenerative diseases such as post-traumatic osteoarthritis (PTOA). Non-invasive optical modalities, such as infrared and Raman spectroscopy, provide means for quantitative evaluation of knee joint tissue...

In this study, we mapped and quantified changes of proteoglycan (PG) content and biomechanical properties in articular cartilage in which either blunt or sharp grooves had been made, both close to the groove and more remote of it, and at the opposing joint surface (kissing site) in equine carpal joints. In nine adult Shetland ponies, standardized b...

Obstructive sleep apnea is linked to severe health consequences such as hypertension, daytime sleepiness, and cardiovascular disease. Nearly a billion people are estimated to have obstructive sleep apnea with a substantial economic burden. However, the current diagnostic parameter of obstructive sleep apnea, the apnea–hypopnea index, correlates poo...

Background: Obstructive sleep apnea (OSA) is associated with vascular diseases from which stroke and sudden cardiac death are the most significant ones. It is known that disturbances of the autonomic nervous system and electrocardiographic changes are seen in patients with a previous cerebrovascular event. However, the pathophysiological cascade b...

Background: Post-traumatic osteoarthritis is a frequent joint disease in the horse. Currently, equine medicine lacks effective methods to diagnose the severity of chondral defects after an injury. Objectives: To investigate the capability of dual-contrast-enhanced computed tomography (dual-CECT) for detection of chondral lesions and evaluation o...

Objective To evaluate the feasibility of Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy to detect cartilage degradation due to osteoarthritis and to validate the methodology with osteochondral human cartilage samples for future development towards clinical use. Design Cylindrical (d = 4 mm) osteochondral samples (n...

Novel diagnostic markers for obstructive sleep apnea beyond the apnea–hypopnea index (AHI) have been introduced. There are no studies on their association with markers of subclinical myocardial injury. We assessed the association between novel desaturation parameters and elevated cardiac troponin I and T. Participants with polysomnography (498) fro...

Knee ligaments and tendons play an important role in stabilizing and controlling the motions of the knee. Injuries to the ligaments can lead to abnormal mechanical loading of the other supporting tissues (e.g., cartilage and meniscus) and even osteoarthritis. While the condition of knee ligaments can be examined during arthroscopic repair procedure...

Subchondral bone structure has been observed to change in osteoarthritis (OA). However, it remains unclear how the early-stage OA changes affect the mechanics (stresses and strains) of the osteochondral unit. In this study, we aim to characterize the effect of subchondral bone structure and mechanical properties on the osteochondral unit mechanics....

The aims of this case‐control study were to: (1) Identify cartilage locations and volumes at risk of osteoarthritis (OA) using subject‐specific finite element (FE) models; (2) Quantify the relationships between the simulated biomechanical parameters and T2 and T1ρ relaxation times of magnetic resonance imaging (MRI). We created subject‐specific FE...

Introduction Excessive daytime sleepiness (EDS) is a common but not universal-accompanying symptom of obstructive sleep apnea (OSA). The mechanisms explaining the presence of EDS in OSA subjects are not fully understood. We hypothesised that characteristic differences in sleep architecture can be quantified with more comprehensive descriptors of sl...

Introduction Sleep disorders are widespread in children and associated with a myriad of detrimental health sequelae. Accurate identification of sleep stages is crucial in diagnosing various sleep disorders; however, manual sleep stage scoring can be subjective, laborious, and costly. To tackle these shortcomings, we aimed to develop an accurate dee...

Sleep disorders form a massive global health burden and there is an increasing need for simple and cost-efficient sleep recording devices. Recent machine learning-based approaches have already achieved scoring accuracy of sleep recordings on par with manual scoring, even with reduced recording montages. Simple and inexpensive monitoring over multip...

Optical properties of biological tissues in the NIR spectral range have demonstrated significant potential for in vivo diagnostic applications and are critical parameters for modelling light interaction in biological tissues. This study aims to investigate the optical properties of articular cartilage as a function of tissue depth and integrity. Th...

Intermittent hypoxaemia is a risk factor for numerous diseases. However, the reverse pathway remains unclear. Therefore, we investigated whether pre‐existing hypertension, diabetes or cardiovascular diseases are associated with the worsening of intermittent hypoxaemia. Among the included 2,535 Sleep Heart Health Study participants, hypertension (n...

Changes in the fibril-reinforced poroelastic (FRPE) mechanical material parameters of human patellar cartilage at different stages of osteoarthritis (OA) are not known. Further, the patellofemoral joint loading is thought to include more sliding and shear compared to other knee joint locations, thus, the relations between structural and functional...

To prevent the progression of posttraumatic osteoarthritis, assessment of cartilage composition is critical for effective treatment planning. Posttraumatic changes include proteoglycan (PG) loss and elevated water content. Quantitative dual‐energy computed tomography (QDECT) provides a means to diagnose these changes. Here, we determine the potenti...

Study Objectives Obesity, older age, and male sex are recognized risk factors for sleep apnea. However, it is unclear whether the severity of hypoxic burden, an essential feature of sleep apnea, is associated with the risk of sleep apnea worsening. Thus, we investigated our hypothesis that the worsening of sleep apnea is expedited in individuals wi...

Photon-counting detector computed tomography (PCD-CT) is a modern spectral imaging technique utilizing photon-counting detectors (PCDs). PCDs detect individual photons and classify them into fixed energy bins, thus enabling energy selective imaging, contrary to energy integrating detectors that detects and sums the total energy from all photons dur...

PurposeHypertension is a common finding in patients with obstructive sleep apnea (OSA), but it has remained unclear whether or not the amount of disturbed breathing and characteristics of individual respiratory events differ between hypertensive and normotensive patients with severe OSA.Methods Full polysomnographic recordings of 323 men and 89 wom...

PurposeObstructive sleep apnoea (OSA) is a prevalent sleep disorder with significant health consequences. Sleep fragmentation is a feature of OSA and is often determined by the arousal index (ArI), a metric based on the electroencephalograph (EEG). The ArI has a weak correlation with neurocognitive outcomes in OSA patients. In this study, we examin...

Knee joint ligaments and patellar tendon are rope-like tissues that enable the proper function of the knee by connecting the bones that form the joint. A better understanding of ligament structure-function relationships is needed to develop objective and reliable diagnostic methods for ligaments. Recently, arthroscopic near infrared spectroscopy (N...

Objective Joint injuries may lead to degeneration of cartilage tissue and initiate development of posttraumatic osteoarthritis. Arthroscopic surgeries can be used to treat joint injuries, but arthroscopic evaluation of articular cartilage quality is subjective. Fourier transform infrared spectroscopy combined with fiber optics and attenuated total...

Background Supine sleeping position and obesity are well-known risk factors for obstructive sleep apnea (OSA) and modulate the risk for OSA-related daytime sleepiness. Although respiratory event durations are associated with OSA-related severe health consequences, it is unclear how sleeping position, obesity, and daytime sleepiness affect respirato...

Tissue-level stress-relaxation of ligaments and tendons in the toe region is characterized by fast and long-term relaxations and an increase in relaxation magnitude with strain. Characterizing the compositional and structural origins of these phenomena helps in the understanding of mechanisms of ligament and tendon function and adaptation in health...

Finite element analysis (FEA) provides a powerful approach for estimating the in-vivo loading characteristics of the hip joint during various locomotory and functional activities. However, time-consuming procedures, such as the generation of high-quality FE meshes and setup of FE simulation, typically make the method impractical for rapid applicati...

Near-infrared (NIR) spectroscopy is a powerful analytical method for rapid, non-destructive and label-free assessment of biological materials. Compared to mid-infrared spectroscopy, NIR spectroscopy excels in penetration depth, allowing intact biological tissue assessment, albeit at the cost of reduced molecular specificity. Furthermore, it is rela...

Raman spectroscopy is promising in vivo tool in various biomedical applications; moreover, in recent years, its use for characterizing articular cartilage degeneration has been developing. It has also shown potential for scoring the severity of cartilage lesions, which could be useful in determining the optimal treatment strategy during cartilage r...

This study aimed to quantify the long‐term progression of blunt and sharp cartilage defects and their effect on joint homeostasis and function of the equine carpus. In nine adult Shetland ponies, the cartilage in the radiocarpal and middle carpal joint of one front limb was grooved (blunt or sharp randomized). The ponies were subjected to an 8‐week...

Low long-term heart rate variability (HRV), often observed in obstructive sleep apnea (OSA) patients, is a known risk factor for cardiovascular diseases. However, it is unclear how the type or duration of individual respiratory events modulate ultra-short-term HRV and beat-to-beat intervals (RR intervals). We aimed to examine the sex-specific chang...

Purpose: Obstructive sleep apnea (OSA) is associated with increased risk for stroke, which is known to further impair respiratory functions. However, it is unknown whether the type and severity of respiratory events are linked to stroke or transient ischemic attack (TIA). Thus, we investigate whether the characteristics of individual respiratory e...

Knee osteoarthritis (OA) is a painful joint disease, causing disabilities in daily activities. However, there is no known cure for OA, and the best treatment strategy might be prevention. Finite element (FE) modeling has demonstrated potential for evaluating personalized risks for the progression of OA. Current FE modeling approaches use primarily...

Objective To assess the potential of near-infrared spectroscopy (NIRS) for in vivo arthroscopic monitoring of cartilage defects. Method Sharp and blunt cartilage grooves were induced in the radiocarpal and intercarpal joints of Shetland ponies and monitored at baseline (0 weeks) and at three follow-up time points (11, 23, and 39 weeks) by measurin...

Current diagnostics of sleep apnea relies on the time-consuming manual analysis of complex sleep registrations, which is impractical for routine screening in hospitalized patients with a high probability for sleep apnea, e.g. those experiencing acute stroke or transient ischemic attacks (TIA). To overcome this shortcoming, we aimed to develop a con...

Absorption and reduced scattering coefficients (μa, μ′s ) of biological tissues have shown significant potential in biomedical applications. Thus, they are effective parameters for the characterization of tissue integrity and provide vital information on the health of biological tissues. This study investigates the potential of optical properties (...

Objectives Besides hypoxemia severity, heart rate variability has been linked to cognitive decline in obstructive sleep apnea (OSA) patients. Thus, our aim was to examine whether the frequency domain features of nocturnal photoplethysmogram (PPG) can be linked to poor performance in psychomotor vigilance task (PVT). Methods PPG signals from 567 su...

Purpose To determine the accuracy of scoring masticatory muscle activity (MMA) events in seven different polysomnography (PSG) setups. Methods Nineteen volunteers (13 females, 6 males, age 31.1 ± 12.9 years, 12 self-proclaimed bruxers) attended one-night PSG recording, supplemented with audio, video, and a separate frontal electroencephalography e...

Contrast-enhanced magnetic resonance imaging (MRI) is a promising method for estimating myocardial blood flow (MBF). However, it is often affected by noise from imaging artefacts, such as dark rim artefact obscuring relevant features. Machine learning enables extracting important features from such noisy data and is increasingly applied in areas wh...