Forehead Sensors Research Articles

Assessing the accuracy of photoplethysmography for wearable heart rate monitoring based on body location and body motion in uncontrolled outdoor environments

Introduction
 Reflective photoplethysmography (PPG) is the dominant method for heart rate (HR) monitoring consumer wearables. However, motion artifacts and sensor placement impact the accuracy of these HR measurements. Here, we present a study on how these two factors affect the accuracy of PPG-based HR measurements and compare them to ground-truth measurements from electrocardiography (ECG). Our study investigated these measurements in outdoor environments outside controlled laboratory settings.
 Methods
 Our study collected a dataset of 16 participants, each for 13 hours wearing four reflective PPG sensing devices placed at the forehead, sternum, ankle (supramalleolar), and wrist. Participants traveled by train from downtown Zurich to the Jungfraujoch railway station at 3,460 m above sea level in the mountains. PPG measurements were obtained using a MAX86141 optical analog front-end coupled with a green LED and photodiode from an SFH7072 module. Motion was quantified using two accelerometers (LIS2DH, ADXL355). A Lead I ECG was obtained by the device at the sternum using a MAX30003 biopotential sensor connected to gel electrodes on the chest. All devices were synchronized by aligning recorded signals post-hoc (33ms accuracy, Meier & Holz, 2023). The HR was extracted from the ECG by time-domain peak detection. The HR extraction from PPG was both performed by time-domain peak detection and frequency-domain analysis. The HR was computed every 5 seconds (30 seconds window size) resulting in 152,000 HR measurements across the whole dataset.
 Results
 The forehead and chest locations exhibited the highest HR measurement accuracy (median error 7.1% and 7.7%, respectively), while lower accuracies were observed for ankle and wrist placements (9.9% and 18.4% error). At rest, all median errors were below 5% while movements influenced readings at all locations negatively. Adjusted for motion, the HR obtained from the forehead sensor was most accurate. In terms of processing method, time-domain analysis produced better accuracy during periods of low motion while frequency-domain analysis was more reliable during movements.
 Discussion/Conclusion
 The accuracy of PPG-based HR measurements in uncontrolled outdoor settings is affected both by body location and motion artifacts with a clear ranking of site suitability: forehead >> chest >> ankle >> wrist. This is consistent with prior studies in controlled environments, though our study found a higher impact of motion than body location on HR accuracy (Longmore et al., 2019). This may be because participants’ motions in uncontrolled environments are more irregular and diverse, resulting in deteriorated signal quality. Our study shows the importance of further investigations in everyday conditions on the path toward more reliable PPG-based HR monitoring in wearable devices.
 References
 Longmore, S. K., Lui, G. Y., Naik, G., Breen, P. P., Jalaludin, B., & Gargiulo, G. D. (2019). A comparison of reflective photoplethysmography for detection of heart rate, blood oxygen saturation, and respiration rate at various anatomical locations. Sensors, 19(8), Article 1874. https://doi.org/10.3390/s19081874
 Meier, M., & Holz, C. (2023). BMAR: Barometric and Motion-based Alignment and Refinement for offline signal synchronization across devices. Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies, 7(2), Article 69. https://doi.org/10.1145/3596268

Self-applied somnography: technical feasibility of electroencephalography and electro-oculography signal characteristics in sleep staging of suspected sleep-disordered adults.

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 electro-oculography sensors have been developed. We evaluated the technical feasibility of a self-applied electrode set from Nox Medical (Reykjavik, Iceland) through home sleep recordings of healthy and suspected sleep-disordered adults (n = 174) in the context of sleep staging. Subjects slept with a double setup of conventional type II polysomnography sensors and self-applied forehead sensors. We found that the self-applied electroencephalography and electro-oculography electrodes had acceptable impedance levels but were more prone to losing proper skin-electrode contact than the conventional cup electrodes. Moreover, the forehead electroencephalography signals recorded using the self-applied electrodes expressed lower amplitudes (difference 25.3%-43.9%, p < 0.001) and less absolute power (at 1-40 Hz, p < 0.001) than the polysomnography electroencephalography signals in all sleep stages. However, the signals recorded with the self-applied electroencephalography electrodes expressed more relative power (p < 0.001) at very low frequencies (0.3-1.0 Hz) in all sleep stages. The electro-oculography signals recorded with the self-applied electrodes expressed comparable characteristics with standard electro-oculography. In conclusion, the results support the technical feasibility of the self-applied electroencephalography and electro-oculography for sleep staging in home sleep recordings, after adjustment for amplitude differences, especially for scoring Stage N3 sleep.

0546 Patient-reported experience with a wireless patch-based polysomnography system – results from a pilot study

Abstract Introduction Sleep is critical for health and wellbeing. Left untreated, sleep disorders negatively impact daily functioning and quality of life. The gold-standard for sleep monitoring and diagnosis is in-lab polysomnography (PSG). Though PSG provides a comprehensive overview of sleep, it is uncomfortable due to the amount of sensors, which prohibit movement and disturb sleep. A wireless patch-based PSG system, the Onera Sleep Test System (STS), consisting of four body-worn sensors, was recently introduced to overcome these limitations. The objective of this study is to evaluate patient-reported experience when using the Onera STS. Methods Forty-two patients were enrolled in Germany as part of an ongoing validation study. Participants were asked to fill in two questionnaires. The first, administed before the Onera STS sleep study, asked open-ended questions on their first impression of the device. The second, administered after the Onera STS sleep study, focused on the ease of use of the device and comfort of wearing it during the night using a 5-point Likert scale. Results Thirty-six patients completed the first questionnaire (85%) and 39 (93%) the second. First impression of the Onera STS was positive by 86% of patients. The size of the sensors was described as acceptable by 72%. Participants stated that the device looked more comfortable than in-lab PSG and they expected improved sleep quality and a more accurate diagnosis. After completing the PSG with the Onera STS system, 69% found wearing the four sensors comfortable, and no participant expressed strong discomfort during the sleep study. The Forehead sensor was considered the most comfortable (based on 77% stating strongly agree or agree), followed by the Abdomen sensor (74%), the Leg sensor (72%), and the Chest sensor (69%). Most participants (72%) expressed confidence in their ability to fit the sensors by themselves at home. Only one participant preferred to be supported by a technician for the application of the system. Conclusion The first impression of the Onera STS device were positive, and participants found it comfortable during sleep. The majority considered the application simple enough for unsupervised self-application, which can allow patients to undergo a PSG in the comfort of their own home. Support (if any)

A Forehead Wearable Sensor for the Objective Measurement of Chronic Pain

Chronic pain impacts one in five Americans and is difficult to manage, costing ~USD 600 billion annually. The subjective experience of pain is a complex processing of central nervous system input. Recent advances in magnetic resonance imaging revealed the prefrontal cortex as vital to the perception of pain and that changes in the cerebral hemodynamics can be used to detect painful sensations. Current pain monitoring is dependent on the subjective rating provided by patients and is limited to a single time point. We have developed a biomarker for the objective, real-time and continuous chronic pain assessment using proprietary algorithms termed ROPA and cerebral optical spectrometry. Using a forehead sensor, the cerebral optical spectrometry data were collected in two clinical sites from 41 patients (19 and 22, respectively, from sites 1 and 2), who elected to receive an epidural steroid injection for the treatment of chronic pain. Patients rated their pain on a numeric rating scale, ranging from 0-10, which were used to validate the ROPA objective pain scoring. Multiple time points, including pre- and post-procedure were recorded. The steroid injection was performed per standard medical practice. There was a significant correlation between the patient's reported numeric rating scale and ROPA, for both clinical sites (Overall ~0.81). Holding the subjective pain ratings on a numeric rating scale as ground truth, we determined that the area under the receiver operator curves for both sites revealed at least good (AUC: 64%) to excellent (AUC > 98%) distinctions between clinically meaningful pain severity differentiations (no/mild/moderate/severe). The objective measure of chronic pain (ROPA) determined using cerebral optical spectrometry significantly correlated with the subjective pain scores reported by the subjects. This technology may provide a useful method of detection for the objective and continuous monitoring and treatment of patients with chronic pain, particularly in clinical circumstances where direct assessment is not available, or to complement the patient-reported pain scores.

Intraoperative Hypothermia Is Not Associated with Surgical Site Infections after Total Hip or Knee Arthroplasty.

Maintaining perioperative normothermia decreases the post-surgery surgical site infection (SSI) rate. We investigated whether SSI is associated with intraoperative hypothermia in total hip (THA) and total knee (TKA) arthroplasties by retrospectively analyzing 297 THA and TKA cases. The patients' intraoperative core body temperature (BT) was measured by bladder catheter or forehead sensor. We evaluated the associations between SSI and intraoperative BT and other variables and patient characteristics. Fifty-six patients (18.8%) had hypothermia (BT <36°C); 43 developed SSI (14.5%); only five had hypothermia (11.6%). Intraoperative hypothermia and SSI were not significantly associated. The SSI group had more men (34.9% vs. 18.1%) and THA patients (77.4%), a longer mean surgical duration (174.3 vs. 143.5 mins), and a higher average BT (36.4°C vs. 36.2°C) than the no-SSI group. The SSI patients had a higher intraoperative BT. A multivariable analysis revealed that SSI was associated with male sex (OR 2.3, 95%CI: 1.031-4.921, p=0.042), longer surgery (OR, 1.01, 95%CI: 1.003-1.017, p=0.004), THA (OR 3.6, 95%CI: 1.258-10.085, p=0.017), and intraoperative BT >36.0°C (OR 3.6, 95%CI: 1.367-9.475, p=0.009). Intraoperative hypothermia was not associated with SSI in adults who underwent THA or TKA. These results suggest that hypothermia might not be the problem for SSI.

Comparison of forehead and finger oximetry sensors during the six minute walk test.

BackgroundMeasurement of oxygen saturation (SpO2) during the 6 minute walk test (6MWT) could be impacted by the measurement site.AimsTo compare SpO2 and heart rate (HR) between forehead and finger sensors during the 6MWT. Sensor readings were also to be compared for signal quality and with capillary blood gas (CBG) pre and post 6MWT.Method80 subjects with pulmonary vascular disease (PVD) and/or interstitial lung disease (ILD) performed the 6MWT. Pulse oximetry was recorded at 30 s intervals. CBG was taken pre and post 6MWT to determine capillary oxygen saturation (SCO2).ResultsThe forehead sensor recorded higher values for SpO2 (p < 0.001) and HR (p < 0.01) compared with the finger sensor during the 6MWT. For both sensors, the demonstrated bias compared to CBG post 6MWT was higher and more variable in subjects who desaturated. During the 6MWT there was a higher occurrence (p < 0.001) of poor signal quality in the finger sensor compared with the forehead sensor.ConclusionThis study suggests that the sensor site can impact pulse oximetry readings. The variance in bias suggests pulse oximetry may not accurately reflect SCO2 measurements particularly in subjects who desaturate during 6MWT.

Comparison of Nasal and Frontal BIS Monitoring in Neurosurgery: Does the Site of Sensor Placement Affect the BIS Values?

Background and Goal of Study: Intraoperative awareness is a serious but preventable complication of general anaesthesia. Bispectral index (BIS) is the most widely used method monitoring anaesthesia depth. BIS monitoring requires attachment of forehead sensors, which poses a challenge when the surgical field involves the forehead. We aimed to compare the gold standard forehead position of BIS sensors with an alternative position across the nasal dorsum for neurosurgical procedures. Materials and Methods: After ethical committee approval and informed consent were obtained, 62 patients were enrolled in this prospective observational study. Frontal and nasal BIS values were compared in all patients. Results and Discussion: The mean BIS value from frontal versus nasal sensors was 49 ± 22 and 49 ± 21 respectively (n: 62). These values were statistically correlated (ICC 0.78, p < 0.001) indicating that nasal BIS measurement does not present a disadvantage for routine use when needed. Conclusion: Our data reveal that for measuring anesthesia depth, BIS sensor placement on the nasal dorsum shows comparable efficiency in comparison to standard frontal measurements

Role of TFA-1 adhesive forehead sensors in predicting fluid responsiveness in anaesthetised children: A prospective cohort study.

The TFA-1 adhesive forehead sensor is a newly developed pulse oximeter for the measurement of the plethysmographic variability index (PVI) at the forehead, and for the rapid detection of changes in oxygen saturation during low perfusion. We evaluated the ability of the TFA-1 sensor to predict fluid responsiveness in children under general anaesthesia. Prospective cohort study. Single tertiary care children's hospital. Thirty-seven children aged 1 to 5 years under general anaesthesia and requiring invasive arterial pressure monitoring. The baseline PVI of TFA-1 and finger sensors, respiratory variation of aorta blood flow peak velocity (ΔVpeak) and stroke volume index (SVI) obtained using transthoracic echocardiography were assessed. After fluid loading of 10 ml kg crystalloids over 10 min, SVI was reassessed. Responders were defined as those with an increase in SVI greater than 15% from the baseline. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the predictive ability of the PVI of TFA-1 and finger sensors and ΔVpeak for fluid responsiveness. Seventeen (56.6%) patients responded to volume expansion. Before fluid loading, the PVI of TFA-1 and finger sensors and ΔVpeak (mean ± SD) of the responders were 11.2 ± 4.4, 11.4 ± 5.1 and 14.8 ± 3.9%, respectively, and those of the nonresponders were 7.4 ± 3.9, 8.1 ± 3.6 and 11.0 ± 3.3%, respectively. ROC curve analysis indicated that the PVI of TFA-1 and finger sensors and ΔVpeak could predict fluid responsiveness. The areas under the curve were 0.8 [P = 0.00; 95% confidence interval (CI) 0.60 to 0.91], 0.7 (P = 0.02; 95% CI 0.53 to 0.87) and 0.8 (P = 0.00; 95% CI 0.59 to 0.91), respectively. The cut-off values for the PVI of TFA-1 and finger sensors and ΔVpeak were 6.0, 9.0 and 10.6%, respectively. The PVI of TFA-1 forehead sensor is a good alternative, but is not superior to the finger sensor and ΔVpeak in evaluating fluid responsiveness in mechanically ventilated children under general anaesthesia. www.clinicaltrials.gov, NCT03132480.

Augmented Wire-Embedded Silicon-Based Dry-Contact Sensors for Electroencephalography Signal Measurements

The aim of this study was to develop a novel dry electroencephalography (EEG) sensor with a soft, pliable pad that conforms to the contours of the skin and skull, providing a suitable surface contact area for collecting electrical potential signals and ensuring a reliable connection. In this study, based on our experience in developing flexible silver/silicon-based dry-contact sensors (SBDSs) for biosignal measurements, we proposed a new, augmented wire-embedded silicon-based dry-contact sensor (WSBDS) with a long lifespan and better performance in EEG measurements. The following two augmentation concepts were proposed in this design and implemented in fabrication: 1) the addition of a metal stud and 2) the embedding of copper wires into the fingers of an acicular SBDS. The forehead sensor is suitable for forehead EEG measurements, and the acicular sensor is designed for application to hair-covered sites, where it can overcome hair interference to achieve satisfactory scalp contact while maintaining low impedance at the skin-electrode interface. Finally, this augmented WSBDS performed well in human EEG recording in a designed brain-computer interface (BCI) experiment and is feasible for practical applications.

Pulse oximeter to detect peripheral oxygen saturation in underwater rebreather ECCR diver: a preliminary study

Hypoxia is one of the main problems an underwater diver may have to face. The probability of experiencing hypoxia is related to the type of dive and the equipment used. Hypoxia in diving is a potentially fatal event for the diver, as it can lead to the loss of brain functions and consequently to the loss of breathing control, all in the absence of specific premonitory symptoms. It is a risk that may be encountered more frequently by divers who use a closed-circuit rebreather (CCR). For those who use this type of equipment, hypoxia is usually the most frequent cause of death [1]. Our study was aimed at the detection of peripheral oxygen saturation in order to identify, in the future, a preclinical hypoxic condition. We combined the use of pulse oximetry with two forehead sensors on an underwater diver subject who was using an electronic closed-circuit rebreather (ECCR). Despite the known limits of this method and the preliminary status of these findings [2], the recorded data show a clear validity in the use of pulse oximetry in immersion for the detection of peripheral oxygen saturation. In the future, the pulse oximeter could become part of the instrumentation of the diver who uses CCR gear. The device could easily be implemented in these rebreathers. The possibility of being able to perform a basic instrumental analysis means that the diver can become more quickly aware of imminent hypoxia, characterized by the absence of clearly identifiable warning symptoms, and can put in place all the correct procedures for an emergency ascent, avoiding serious consequences.

Comparison of nasal and forehead oximetry accuracy and pressure injury in critically ill patients

BackgroundIn critically ill patients, clinicians can have difficulty obtaining accurate oximetry measurements. ObjectiveTo compare the accuracy of nasal alar and forehead sensor measurements and incidence of pressure injury. Methods43 patients had forehead and nasal alar sensors applied. Arterial samples were obtained at 0, 24, and 120 hours. Oxygen saturations measured by co-oximetry were compared to sensor values. Skin was assessed every 8 hours. ResultsOxygen saturations ranged from 69.8%-97.8%, with 18% of measures < 90%. Measurements were within 3% of co-oximetry values for 54% of nasal alar compared to 35% of forehead measurements. Measurement failures occurred in 6% for nasal alar and 22% for forehead. Three patients developed a pressure injury with the nasal alar sensor and 13 patients developed a pressure injury with the forehead sensor (χ2 = 7.68; p = .006). ConclusionsIn this group of patients with decreased perfusion, nasal alar sensors provided a potential alternative for continuous monitoring of oxygen saturation.

Abstract 21060: The Association Between Post-Resusciation Cerebral Oxygenation and Survival With Favorable Neurological Outcomes: A Multicenter Study

Background: Cerebral ischemia/reperfusion injury in the post-resuscitation period contributes to morbidity and mortality following cardiac arrest (CA). Cerebral oximetry is a non-invasive system that uses near infrared spectroscopy to measure regional cerebral oxygenation level (rSO2) in the frontal lobe of the brain. Studies have shown that post-resuscitation rSO2 may be associated with survival and neurological outcomes in out-of-hospital cardiac arrest patients, however no studies have examined this in in-hospital cardiac arrest (IHCA) patients. Hypothesis: rSO2 changes following return of spontaneous circulation (ROSC) after IHCA are associated with survival with favorable neurological outcomes. Methods: A multi-site prospective study of consecutive day-time IHCA patients admitted to the ICU after ROSC at 7 sites. Continuous rSO2 monitoring (Equanox 7600, Nonin Medical, MN, USA) was applied for 48 hours after ROSC using a forehead sensor. Mean rSO2 was calculated hourly between 1-6 hrs. and at 6, 12, 18, 24, 48 hr. intervals. Demographic and data pertaining to possible confounding variables for rSO2 and survival with favorable neurological outcomes (cerebral performance scale [CPC] 1-2) vs death or severe neurological injury (CPC 3-5) at hospital discharge were collected. Results: Among 87 studied patients, 26 (29.9%) achieved CPC1-2. There were no differences in age, Charlson comorbidity index, APACHE II scores, and resuscitation duration, however, CPC 1-2 was higher in men vs. women (36.5% vs. 12.5%, p = 0.036). A significant difference in mean rSO2 was observed during hours 1-2 after ROSC in CPC 1-2 vs CPC3-5 (73.08 vs. 66.59, p = 0.031) but not at other time points. There were no differences in mean arterial pressure, PaO2, PaCO2, and hemoglobin levels, however subjects with CPC 1-2 had lower glucose (154.4mg/dL vs. 202.8mg/dL, p = 0.0054), lactate level (4.11 mmol/dL vs. 6.39 mmol/dL, p = 0.030), and higher Glasgow coma scale (9.42 vs. 5.96, p = 0.0026) within the first 24 hours. Conclusions: Changes in rSO2 as measured by cerebral oximetry in the first two hours after ROSC may predict survival with neurological outcomes after resuscitation following IHCA.

Determination of saturation, heart rate, and respiratory rate at forearm using a Nellcor™ forehead SpO2-saturation sensor.

Alterations in arterial blood oxygen saturation, heart rate (HR), and respiratory rate (RR) are strongly associated with intra-hospital cardiac arrests and resuscitations. A wireless, easy-to-use, and comfortable method for monitoring these important clinical signs would be highly useful. We investigated whether the Nellcor™ OxiMask MAX-FAST forehead sensor could provide data for vital sign measurements when located at the distal forearm instead of its intended location at the forehead to provide improved comfortability and easy placement. In a prospective setting, we recruited 30 patients undergoing surgery requiring postoperative care. At the postoperative care unit, patients were monitored for two hours using a standard patient monitor and with a study device equipped with a Nellcor™ Forehead SpO2 sensor. The readings were electronically recorded and compared in post hoc analysis using Bland-Altman plots, Spearman's correlation, and root-mean-square error (RMSE). Bland-Altman plot showed that saturation (SpO2) differed by a mean of -0.2% points (SD, 4.6), with a patient-weighted Spearman's correlation (r) of 0.142, and an RMSE of 4.2 points. For HR measurements, the mean difference was 0.6bpm (SD, 2.5), r=0.997, and RMSE=1.8. For RR, the mean difference was -0.5 1/min (4.1), r=0.586, and RMSE=4.0. The SpO2 readings showed a low mean difference, but also a low correlation and high RMSE, indicating that the Nellcor™ saturation sensor cannot reliably assess oxygen saturation at the forearm when compared to finger PPG measurements.

Accelerometer Measurement of Head Movement During Laparoscopic Surgery as a Tool to Evaluate Skill Development of Surgeons

To detect and measure surgeons' head movement during laparoscopic simulator performance to determine whether expert surgeons have economy of motion in their head movement, including change of direction, compared with intermediate and novice surgeons. We investigated head movement as an objective tool for assessment of laparoscopic surgical skill and its potential use for assessing novice surgeons' progress on the learning curve. After obtaining institutional review board approval, medical students, urology residents, and attending staff surgeons from an academic institution were recruited. Participants were grouped by level of experience and performed tasks on the Electronic Data Generation for Evaluation laparoscopic simulator. Surgeons wore a commercially available wireless electroencephalogram monitor as a flexible, adjustable, and lightweight headband with 7 sensors-2 forehead sensors, 2 ear sensors, and 3 reference sensors. The headband incorporates a 3-axis accelerometer enabling head movement quantification. A variance analysis was used to compare the average head movement acceleration data between each group. Tulane University Medical Center, New Orleans, LA, an academic medical center and the principal teaching hospital for Tulane University School of Medicine. A total of following 19 participants were recruited for the study and stratified by surgical experience into novice (n = 6), intermediate (n = 9), and expert (n = 4) laparoscopy groups: 6 medical students, 9 urology residents (postgraduate years 1 to5), and 4 attending urologists, respectively. Analysis of the average acceleration rate of head movement showed statistically significant differences among groups on both the vertical axis (p = 0.006) and horizontal axis (p = 0.018) in the laparoscopic suturing task. This demonstrated the ability to distinguish between experts and novice laparoscopic surgeons. The average acceleration among groups did not demonstrate statistical significance on the vertical axis (p = 0.078) and horizontal axis (p = 0.077) in the peg transfer task. This may be in response to the ease of the task. The analysis of the forward-backward axis or depth perception also showed no significant differences between groups. Accelerometer-based motion analysis of head movement appears to be a useful tool to evaluate laparoscopic skill development of surgeons in terms of their economy of motion, and it could potentially be used for ergonomic assessment of training in the future, and progression on the learning curve.

Intraoperative auditory evoked potential recordings are more reliable at signal detection from different sensor sites on the forehead compared to bispectral index.

Bispectral index (BIS) and auditory evoked potential (AEP) monitoring require the attachment of forehead sensors, posing difficulties when the surgical field involves the forehead. This study analyzed the relationship between BIS values and AEP indices from different sites on the head to establish alternative sensor locations for AEP recording. Thirty patients scheduled for elective surgery under sevoflurane anesthesia were randomly assigned to the forehead, nose or mandible groups (n=10 patients per group). AEP sensors were placed at the assigned position for each group and BIS sensors were placed on the forehead. BIS value and AEP index were simultaneously recorded from induction until emergence from general anesthesia. Relationships between BIS values and AEP indices were analyzed using a regression method and compared between groups using Pearson's correlation coefficients. Square regression models better expressed the relationships than linear models in all groups. The z-transformed coefficient in the forehead group was the same as the nose group (p=0.24) and significantly different in the mandible group (p=0.0046). These findings suggest that AEPs can be accurately recorded from sensors placed on the nose. Nasal AEP might be useful for monitoring electrical activity in the brain during surgeries involving the forehead.

Influence of neuromuscular block and reversal on bispectral index and NeuroSense values

Influence of neuromuscular block and reversal on bispectral index and NeuroSense values

Forehead pulse oximeter-associated pressure injury.

Peripherally placed transmittance pulse oximeter sensors have been associated with patient injury including burns, gangrene, and necrosis. There are 2 reports of burn injuries associated with the use of forehead reflectance sensors, but there is no report of a pressure injury associated with the use of an OxiMax™ MAX-FAST™ forehead sensor and headband. We report the case of a patient who developed tissue necrosis associated with prolonged application of a forehead pulse oximeter sensor under a headband and displacement of the sensor cable.

Comparing finger and forehead sensors to measure oxygen saturation in people with chronic obstructive pulmonary disease

Oxyhaemoglobin saturation of arterial blood is commonly measured using a finger sensor attached to a pulse oximeter (SpO(2)). We sought to compare SpO(2) measured using finger and forehead sensors with oxyhaemoglobin saturation in arterialized capillary samples (ACS) in people with chronic obstructive pulmonary disease (COPD) during exercise. During aerobic exercise, SpO(2) was measured continuously by two pulse oximeters: one connected to a finger sensor and to a forehead sensor. Before and after the task, ACS were collected to provide a minimally invasive reference measure of oxyhaemoglobin saturation. Patients with COPD were eligible for inclusion if they desaturated when walking by >4% from resting levels to <90%. Current smokers and those prescribed supplemental oxygen were excluded. Fourteen participants completed the study (forced expiratory volume in 1 s = 35 ± 10% predicted). Compared with ACS, SpO(2) measured via the finger sensor was 2% lower (limit of agreement 3%), and SpO(2) measured via the forehead sensor was 2% higher (limit of agreement 4%). Differences were not systematic. The change in oxygen saturation during exercise was similar among the finger sensor (-7; 95% confidence interval (CI): -4 to -10%), forehead sensor (-7; 95% CI: -3 to -10%) and ACS (-6; 95% CI: -3 to -9%). Oxygen saturation measured using the forehead sensor was higher than that measured in ACS. Assuming that oxygen saturation in ACS is slightly less than arterial blood, forehead sensors may yield measures more concordant with arterial blood. Both sensors detected exercise-induced desaturation.

Swimmers can train in hypoxia at sea level through voluntary hypoventilation

This study used an innovative technique of pulse oximetry to investigate whether swimmers can train under hypoxic conditions through voluntary hypoventilation (VH). Ten trained subjects performed a front crawl swimming series with normal breathing (NB), VH at high (VHhigh) and low pulmonary volume (VHlow). Arterial oxygen saturation was continuously measured via pulse oximetry (SpO2) with a waterproofed forehead sensor. Gas exchanges were recorded continuously and lactate concentration ([La]) was assessed at the end of each test. In VHlow, SpO2 fell down to 87% at the end of the series whereas it remained above 94% in VHhigh during most part of the series. Ventilation, oxygen uptake and end-tidal O2 pressure were lower in both VHhigh and VHlow than in NB. Compared to NB, [La] significantly increased in VHlow and decreased in VHhigh. This study demonstrated that swimmers can train under hypoxic conditions at sea level and can accentuate the glycolytic stimulus of their training if they perform VH at low but not high pulmonary volume.

In vivo measurement of the 3D kinematics of the temporomandibular joint using miniaturized electromagnetic trackers: technical report

The aim of this study was to evaluate the use of miniaturized electromagnetic trackers (1 × 0.5 × 0.5 cm) fixed on teeth of the maxilla and mandible to analyse in vivo the 3D kinematics of the temporomandibular joint (TMJ). A third sensor was fixed to the forehead, and a fourth sensor was used as a stylus pointer to detect several anatomical landmarks in order to embed a local frame on the cranium. Temporomandibular opening/closing, chewing, laterotrusion and protrusion were examined. The prime objective within this study was to rigidly attach electromagnetic minisensors on teeth. The key for a successful affixation was the kevlar interface. The distances between the two mandibular affixed sensors and between the two maxillar affixed sensors were overall smaller than 0.033 cm for position and 0.2° for attitude throughout the temporomandibular motions. The relative motions between a forehead sensor and the maxilla affixed sensor are too big to suggest a forehead sensor as an alternative for a maxilla affixed sensor. The technique using miniaturized electromagnetic trackers furthers on the methods using electromagnetic trackers on external appliances. The method allows full range of motion of the TMJ and does not disturb normal TMJ function.