Errors in healthcare provision often stem from the absence of timely and comprehensive information, resulting in incorrect clinical diagnoses. To ensure safety and avert potential fatalities, healthcare providers should have seamless access to precise and reliable patient data. Thus, physiological parameters play an important role in clinical decision-making. 3 Nowadays, a wide variety of wearables and automatic devices that are capable of monitoring and tracking different physiological parameters have been widely available for healthcare and medical purposes. 5 Technological advances have allowed users to effortlessly collect their information, such as time of sleep, heartbeat, number of daily steps, number of movements, etc. 4 Patients, whether located in urban or rural areas, can utilize such devices with or without the internet. This not only alleviates stress and reduces the workload of healthcare providers but also minimizes errors through continuous monitoring, lowers healthcare service costs, and enhances patient comfort. 3 With these benefits as well as their potential benefits, the market for wearable devices has been steadily expanding. Although these devices can offer quicker and more convenient vital sign measurements, concerns about their accuracy persist. 1 Only a limited number of studies have addressed the validity and reliability of wearable devices such as smartwatches. 6
Wearable devices like ASWs8 provide precise heart rate measurements by capturing blood flow in the wrist and calculating it as heartbeats per minute. For many years, determining heart rate has remained a crucial parameter for both medical diagnoses and daily health monitoring. 11 Alongside blood pressure and electrocardiography (ECG), heart rate serves as a potential predictor of a heart attack. 12 In a prior study, researchers developed an application wherein patients with cardiac diseases were monitored using various sensors. This research combined a universal computation with the aid of digital health advancements, enabling the continuous monitoring of high-risk cardiac patients through sensors and smartphones. The analyses generated by smartphones served as real-time ECG, offering critical insights into whether the patient required external support and assistance. Depending on the assessed risk, the smartphone would automatically send alerts to the designated healthcare provider and/or ambulance. Additionally, patients received personalized exercise recommendations based on environmental information. In conclusion, the authors effectively processed sensor data using smartphones, enabling uninterrupted monitoring without the need for hospitalization. 13 Previously, the U.S. FDA approved ECG features in Apple smartwatches, starting with series 4. Such features allow safe tracking of heart rhythm, offering advantages in managing patients with a variety of conditions, including COVID-19. 14
This study revealed that the reliability of ASWs8 in determining heart rate has similar results to that obtained with the CMD without any statistically significant differences. Moreover, the mean differences almost fell within the zero axis, which implies that these differences might not be significant enough to show reliability differences. The results of the current study agreed with some prior studies conducted to compare the reliability of smartwatches with standard vital signs recording methods. Spaccorotella et al. (2022) verified the accuracy of the Apple smartwatch Series 6 against a standard pulse oximeter using data obtained from 257 adult patients, with a mean age of 64 years old. Results revealed that the two devices have good concordance with a bias of -0.11 only, and a range of -5.84 and 5.63%. Thus, the reliability of the two methods was found to be clinically insignificant. 15 Meanwhile, Pipek et al (2021) conducted a study comparing heart rate measurements obtained from an Apple smartwatch series 6 and a conventional oximeter in a sample of 100 patients. Their findings indicated no significant differences between the two devices in determining these parameters, with a mean difference of 0% and limits of agreement ranging from − 8 to 8%. 4 Similarly, Seshadri et al. (2020) assessed the reliability of the Apple smartwatch series 4 in measuring heart rate by comparing its readings to telemetry in a controlled setting. They included fifty post-operative patients with atrial fibrillation in their study. The results revealed that the mean heart rate readings obtained from the Apple smartwatch were 88 ± 14, ranging from 57 to 125 BPM, while telemetry recorded rates of 86 ± 15, ranging from 54 to 137 BPM. Concordance was employed to evaluate the agreement between the two devices, revealing less-than-optimal agreement for patients with atrial fibrillation. As a result, further evaluation was deemed necessary. 16
Hernando et al. (2018) validated the reliability of the Apple smartwatch in determining heart rate variability among twenty healthy individuals during their relaxation and mental stress. They employed a validated heart rate monitor, specifically the Polar H7 chest band, as a reference. Their findings revealed strong reliability between the two devices, with a correlation coefficient exceeding 0.90. 17 On the contrary, Khushhal et al. (2017) evaluated the reliability and validity of the Apple smartwatch in determining heart rate during and after various physical activities, including walking, jogging, and running. Their study involved twenty-nine healthy males with a mean age of 31.4 ± 7.4. The criteria for evaluation were set using a Polar S810i monitor. The results revealed a trend where device reliability decreased with increasing physical activity intensity, displaying a stronger correlation during milder activities such as walking and a varying, though generally less reliable, correlation during higher-intensity activities like jogging and running. A similar trend was observed in terms of device validity with accuracy decreasing as exercise intensity increased. 18 In addition, Hahnen et al. (2020) conducted a related study in which they compared heart rate readings from a smartwatch (brand: Everlast) to a standard device. Their findings indicated an average absolute difference of 6.5 ± 9.2 BPM, demonstrating that the Everlast smartwatch met accuracy standards for heart rate measurements. 5 On a different note, Scherbina et al. (2017) assessed the accuracy of seven commercially available wearable devices, including the Apple smartwatch, in determining heart rate. The results revealed that the Apple Watch achieved the lowest overall error, with an accuracy rate of 2.0%. The minimum and maximum error values were found to be 1.2 and 2.8%, respectively. 6
When comparing the reliability of heart rate measurement with wearable devices, it’s important to note that the assessment of oxygen saturation is a relatively newer and less explored field. Oxygen saturation, like any other vital sign, serves as an indicator of a patient’s respiratory adequacy, making it a critical parameter for continuous monitored, especially for those with respiratory issues. Traditionally, pulse oximeters have been the go-to method for measuring oxygen saturation. These devices employ a probe that is typically placed on either the finger or ear. They utilize light-emitting diodes (LEDs) to gauge oxygen saturation in the blood by shining infrared light through the tissue, measuring the absorbed light’s corresponding saturation value. 11,15
More recently, wearable devices with sensors and applications capable of continuous oxygen saturation measurement have emerged. 19 According to Barros et al. (2021), the Oxitone 100 M 8 is the first FDA-approved wearable health monitor, that features a pulse sensor positioned on the upper part of the ulnar wrist bone. However, measuring oxygen saturation on the wrist imposes certain challenges. Data collection on the wrist is area-specific, akin to the radial artery, and even slight variations in measurement placement can significantly impact results. 14 Even with these possible drawbacks, the availability and accessibility of wearable devices, such as the Apple smartwatch, can still allow monitoring oxygen saturation at home. During the COVID-19 pandemic, there has been a surge in the popularity of home-based vital signs monitoring, particularly for oxygen saturation. This is due to the presentation of hypoxia, panting with difficulty in breathing, and the potential need for intubation among COVID-19 patients. In times when healthcare facilities are overwhelmed, wearable devices have played a pivotal role in monitoring oxygen saturation, serving as an indicator for hospitalization or early intubation. Home-based healthcare monitoring has also contributed to reducing the spread of COVID-19 contagion brought by suspected or infected individuals. 14
In this study, the reliability of ASWs8 in measuring oxygen saturation was also validated. The mean oxygen saturation obtained with ASWs8 was 97.10 ± 1.6, while with CMD, it was 98.23 ± 1.0. This resulted in a mean difference of 0.74%, with a range of -1.50 and 2.50%. The results revealed no significant difference between the measurements obtained from ASWs8 and CMD. These findings aligned with those of Spaccarotella et al. (2022), who found a strong correlation between Apple Watch Series 6 and conventional devices in determining oxygen saturation among 257 adult patients, with a bias of -0.23% and limits of -3.49 and 3.04%. The authors concluded that the Apple smartwatch can provide accurate results for oxygen saturation in both healthy and cardiovascular patients. 15
Similarly, Littell et al. (2022) assessed the accuracy of Apple Watch Series 6 against a conventional pulse oximeter in 84 pediatric cardiology patients, averaging 7.2 years old. Using the traditional oximeter as the reference, the median oxygen saturation was obtained at 98%, ranging from 78 to 100%. Comparing the two devices, the average absolute difference was only 2%m with a correlation coefficient of 0.76 and limits of agreement between − 7% and 5%. The study concluded that the Apple smartwatch series 6 is accurate enough for measuring oxygen saturation in the pediatric population. 20 In the same year, Rafl et al. (2022) compared the reliability of Apple smartwatch series 6 against a conventional pulse oximeter (Masimo Radical − 7) in detecting hypoxemia among twenty-four healthy participants. Their oxygen saturation measurements were taken at 30-second intervals. After obtaining 642 individual data points, the bias or mean difference was computed to be 0% (95% CI: -0.2 to 0.3) for the entire range, 1.2% (95% CI: 0.7 to 1.7) for the < 90% oxygen saturation range, and − 0.3% (95% CI: -0.6 to 0.1) for the 90–100% oxygen saturation range. These relatively low biases suggested that the Apple smartwatch 6 can reliably and accurately detect hypoxemia or any reduction in blood oxygen saturation. 21
Pipek et al. (2021) assessed the oxygen saturation of sixty-one patients, including those with interstitial lung disease. The average readings were 94.4% with a conventional oximeter and 95.9% with an Apple watch. The study found a correlation coefficient of 0.81 and limits of agreement between − 2.7% and 4.1%, concluding that the Apple Watch Series 6 is reliable for measuring oxygen saturation in patients with lung diseases. 5 Moreover, Hearn et al. (2021) compared arterial oxygen saturation measurements using four different wearable devices, including the Apple smartwatch Series 6 and the FDA-approved Oxitone 100M, 8 against a traditional pulse oximeter as the reference. The study involved ten healthy volunteers (6 male, 4 female) with a mean age of 27 ± 6 years. The oxygen saturation was measured at different activity intensities, such as stationary, slight body motion, and moderate body motion. The results showed no significant differences between the readings from the Apple smartwatch and Oxitone 100M 8 compared to the reference pulse oximeter. suggests that the Apple smartwatch has high validity after passing reliability tests against both a traditional reference and an FDA-approved device. 22
In summary, validating the reliability and accuracy of ASWs8 offers substantial benefits, including its non-invasive nature, user-friendly interface, and widespread availability. For these reasons, this device serves as an excellent alternative that facilitates reliable, frequent, and uninterrupted health monitoring, potentially leading to enhanced healthcare outcomes and cost reduction. 23 In addition, individuals generally favor smartwatches due to their comfortable and sleek design, offering prolonged usability. 14
Although ASWs8 presents promising features and this study provides novel and valuable insights and directions, it’s crucial to acknowledge certain potential. First, Apple smartwatches are often considered expensive compared to other digital devices. Previous research has highlighted that the general population’s familiarity with using such devices is limited, with more substantial knowledge primarily confined to healthcare professionals. Consequently, it becomes imperative for users of wearables to receive adequate training in terms of both device operation and data analysis. 24 This knowledge, especially as it pertains to data analysis is important to prevent unnecessary anxiety and apprehension. Moreover, it’s worth noting that most of the studies conducted so far have taken place in a controlled environment with stable temperatures. This implies that the applicability of ASWs8 might not be consistent under varying temperature conditions. 15 Additionally, wearable devices may exhibit variability in performance under conditions involving minimal body movement and variation in data collection sites. We only included healthy patients, but we needed someone who is not healthy like CVS or resp. diseases when determining these levels. Are they functional? That is a limitation because we excluded them.