Influence of Contact Forces on Wrist Photo plethysmography – Prestudy for a Wearable Patient Monitor / Einfluß von Kontaktkräften auf die photoplethysmografische Pulsmessung am Handgelenk – Vorstudie zu einem tragbaren Patientenmonitor
Abstract
The practical setting shows that gentle manual pressure on a photosensor suffices to improve the detectability of arterial pulses, but changes in the pressure applied may also produce signal artefacts. To study these effects, stepwise increasing contact forces (0.5 to 4 N) were applied to a photosensor placed over the radial artery. Additionally, the influence of optical coupling between sensor and skin surface was examined by introducing an elastic distance ring. The AC and DC components from the recorded photoplethysmogram were analysed. The AC component (absorption due to arterial pulsation) increased with the pressure applied; at lower forces (0.5 to 3 N) an introduction of the ring enhanced this effect. The characteristic of the DC component (backscattering from non-pulsating tissues) depends on optical coupling: without the ring the DC component increased stepwise with force (slope 0.035 V/N), but with the ring in place this component decreased (slope −0.075 V/N). Since the sensitivity of the pulse signal to artifacts is related to the slope of the DC component, such artefacts can be minimized by making the slope small. The utilization of these results to improve pulse detection and reduce motion artefacts in a wearable wrist device is discussed. Oft genügt schon ein geringer manueller Andruck auf einen Photosensor, um eine arterielle Pulswelle besser zu detektieren, bei Änderung des Andrucks kommt es dabei aber auch zu Artefakten im Pulssignal. Um hier den Einfluß auf photoplethysmografische Signale zu quantifizieren, wurden mit einem Galvanometer schrittweise zunehmende Andruckkräfte (0.5 bis 4 N) auf das Sensorgehäuse appliziert. Um dabei auch den Einfluß des optischen Übergangs zwischen Haut und Sensor zu studieren, wurde dieser Andrucktest zuerst ohne und dann mit einem elastischen Distanzring durchgeführt. Zur Analyse wurden die aufgezeichneten photoplethysmografischen Signale in ihre AC (0.1 bis 20 Hz) und DC-Komponenten zerlegt. Bei der AC-Komponente (Absorption infolge arterieller Pulsation) zeigte sich eine Zunahme mit der Andruckkraft, wobei diese Charakteristik durch den Ring noch verstärkt wurde. Die Kraftcharakeristik der DC-Komponente (nichtpulsierendes reflektiertes Licht) hingegen war unterschiedlich: Ohne Ring kam es, ausgehend von niedrigen Werten, zu einer stufenweisen Zunahme (Steigung 0.035 N/V) und mit Ring zu einer Abnahme (Steigung −0.075 V/N) der Reflektanz. Da die Artefaktempfindlichkeit des Pulssignals von der Steigung der DC-Charakteristik abhängt, ergibt sich durch die Gestaltung des optischen Übergangs hier eine Möglichkeit zur Artefaktunterdrükkung. Der Transfer dieser Ergebnisse zur Verbesserung der Pulsdetektion und der Artefaktunterdrückung bei einem Handgelenkmonitor wurde diskutiert.
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PPG sensors used to measure HR are liable to poor accuracy during activities with increased physical exertion or activities involving repetitive contractions of forearm skeletal muscles.
“Prior research has suggested that PPG sensors used to measure the HR are liable to poor accuracy during activities with increased physical exertion or activities involving repetitive contractions of forearm skeletal muscles [36-38].”
From Accuracy of Wrist-Worn Activity Monitors During Common Daily Physical Activities and Types of Structured Exercise: Evaluation Study (2018) · cites this paper as [36]
During activities involving sustained muscle contractions or higher intensity exercises, the contact between the device's PPG sensor and skin is decreased, leading to a disruption in the signal quality and causing poor quality data.
“It has been suggested that during activities involving sustained muscle contractions or higher intensity exercises, the contact between the device’s PPG sensor and skin is decreased, leading to a disruption in the signal quality and causing poor quality data [36,37].”
From Accuracy of Wrist-Worn Activity Monitors During Common Daily Physical Activities and Types of Structured Exercise: Evaluation Study (2018) · cites this paper as [36]
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- Authors
- Rafolt, D., & Gallasch, E.
- Affiliations
- Vienna General Hospital (AT)
- Corresponding author
- Rafolt, D
- ORCID
- Rafolt, D
- Venue
- Biomedizinische Technik/Biomedical Engineering
- Publisher
- Walter de Gruyter GmbH
- Published
- 2004-01-01
- Volume
- 49
- Issue
- 1-2
- Pages
- 22-26
- ISSN
- 0013-5585 (ISSN-L)
- 1862-278X
- OpenAlex
- W2017198338
- Cited by
- 19
- References
- 9
- Citations by year
- 2025: 2 · 2024: 4 · 2023: 3 · 2022: 2 · 2021: 2 · 2018: 2 · 2017: 3 · 2016: 1
- FWCI
- 0.00
- Type
- journal article
- Language
- de
- Open access
- closed
- Locations
- Biomedizinische Technik/Biomedical Engineering (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Physical Sciences › Engineering › Biomedical Engineering › Non-Invasive Vital Sign Monitoring
- Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Cardiovascular Health and Disease Prevention
- Physical Sciences › Engineering › Biomedical Engineering › Advanced Sensor and Energy Harvesting Materials
- Keywords
- photoplethysmography, contact force, radial artery, optical coupling, DC component, pulse detection, motion artifacts, pulse wave amplitude, pulse wave reflection
- MeSH terms
- Equipment Design, Heart Rate, Humans, Monitoring, Physiologic, Motor Activity, Paraplegia, Pulse, Signal Processing, Computer-Assisted, Wrist, Photoplethysmography, Radial Artery
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