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Photoplethysmography in multiparameter monitoring of cardiorespiratory function
Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
2000 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Photoplethysmography (PPG) is an optical, non-invasive method to assess tissue blood volume/perfusion. When measured on human skin, the PPG signal includes both cardiac synchronous variations (AC) and respiratory induced intensity variations (RIIV). This makes the PPG signal appropriate for cardiorespiratory monitoring, as a single non-invasive sensor extracts both cardiac and respiratory information.

In this thesis, the origin of the RIIV signal is discussed, and invasive measurements of pressures in the circulatory system support the hypothesis of a venous origin. Important factors are intrathoracic and intra-abdominal pressure fluctuations, affecting venous return from the extrathoracic veins and the peripheral venous bed.

Previous reports have demonstrated a possibility to extract the RIIV signal for assessing respiratory rates. A more effective and reliable monitoring would be achieved if tidal volumes could be estimated from the PPG signal in addition to respiratory rates. This would provide a possibility to calculate and detect ventilatory trends. A relationship between the RIIV amplitude and the tidal volume was hypothesised, demonstrated in healthy subjects and verified in a theoretical (Windkessel) model of the circulatory system. Other factors than tidal volume influence intrathoracic and intra-abdominal pressures. Effects of thoraco-abdominal separation, posture and respiratory rate were observed, and their influence in tidal volume/ventilation monitoring was discussed.

Monitoring the cardiorespiratory function is essential in the postoperative and neonatal care environments. Studies have been performed in clinical settings including comparisons between the PPG method and more established monitoring systems. PPG was found to be suitable for monitoring heart and respiratory rates in these environments.

The arterial blood pressure contains respiratory related information, including heart rate fluctuations (respiratory sinus arrhythmia, RSA) and respiratory variations in cardiac stroke volume. These phenomena are seen in the PPG signal as frequency and amplitude modulation of the AC signal. An algorithm based on pattern recognition (neural networking) is presented, in which these respiratory components are extracted and combined with the RIIV signal. As the respiratory components are of different origins, the neural network algorithm is robust and more accurate for breath detection than algorithms utilising the components separately.

The main purposes of cardiorespiratory monitoring are to detect pathologic minute ventilation, apnoea, hypoxaemia, cardiac arrest, arrhythmia, and trends in heart rate. By using PPG, simultaneous information about heart rate, respiratory rate and tidal volume is obtained. Furthermore, as the measurement of arterial oxygen saturation by PPG is well established, a good coverage of the cardiorespiratory function can be obtained from a single non-invasive sensor.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2000. , 63 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 629
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-29446Local ID: 14793ISBN: 91-7219-715-3 (print)OAI: oai:DiVA.org:liu-29446DiVA: diva2:250261
Public defence
2000-04-28, Elsa Brändströms sal, Universitetssjukhuset, Linköping, 13:15 (Swedish)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-02-19
List of papers
1. Estimation of respiratory volumes from the photoplethysmographic signal. Part 1: experimental results
Open this publication in new window or tab >>Estimation of respiratory volumes from the photoplethysmographic signal. Part 1: experimental results
1999 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 37, no 1, 42-47 p.Article in journal (Refereed) Published
Abstract [en]

To evaluate the possibility of respiratory-volume measurement using photoplethysmography (PPG), PPG signals from 16 normal volunteers are collected, and the respiratory-induced intensity variations (RIIV) are digitally extracted. The RIIV signals are studied while reepiratory volume is varied. Furthermore, respiratory rate, body posture and type of respiration are varied. A Fleisch pneumotachograph is used as the inspired volume reference. The RIIV and pneumotachography signals are compared, and a statisical analysis is performed (linear regression and t-tests). The key idea is that the amplitude of the RIIV signal is related to the respiratory volume. The conclusion from the measurements is that there exists a relationship between the amplitude of the RIIV signal and the respiratory volume (R=0.842, s=0.428, p<0.005). Absolute measurements of the respiratory volume are not possible from the RIIV signal with the present set-up. The RIIV signal also seems to be affected by respiratory rate and type. More knowledge about respiratory parameters and improved sensor and filter design are required to make absolute measurements of volumes possible.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-32556 (URN)10.1007/BF02513264 (DOI)18469 (Local ID)18469 (Archive number)18469 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
2. Estimation of respiratory volumes from the photoplethysmographic signal. Part 2: a model study
Open this publication in new window or tab >>Estimation of respiratory volumes from the photoplethysmographic signal. Part 2: a model study
1999 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 37, no 1, 48-53 p.Article in journal (Refereed) Published
Abstract [en]

A Windkessel model has been constructed with the aim of investigating the respiratory-volume dependence of the photoplethysmographic (PPG) signal. Experimental studies show a correlation between respiratory volume and the peak-to-peak value of the respiratory-induced intensity variations (RIIV) in the PPG signal. The model compartments are organised in two closed chambers, representing the thorax and the abdomen, and in a peripheral part not directly influenced by respiration. Cardiac pulse and respiration are created by continuous adjustment of the pressures in the affected compartments. Together with the criteria for heart and venous valves, the model is based on a set of 17 differential equations. These equations are solved for varying thoracic and abdominal pressures corresponding to different respiratory volumes. Furthermore, a sensitivity analysis is performed to evaluate the properties of the model. The PPG signals are created as a combination of peripheral blood flow and pressure. From these signals, the respiratory synchronous parts are extracted and analysed. To study some important limitations of the model, respiratory type and rate are varied. From the simulations, it is possible to verify our earlier experimental results concerning the relationship between respiratory volume and the peak-to-peak value of the RIIV signal. An expected decrease in the amplitude of the respiratory signal with increased respiratory rate is also found, which is due to the lowpass characteristics of the vessel system. Variations in the relationship between thoracic and abdominal respiration also affect the RIIV signal. The simulations explain and verify what has been found previously in experimental studies.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-32557 (URN)10.1007/BF02513265 (DOI)18470 (Local ID)18470 (Archive number)18470 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
3. Monitoring of heart and respiratory rates in newborn infants using a new photoplethysmographic technique
Open this publication in new window or tab >>Monitoring of heart and respiratory rates in newborn infants using a new photoplethysmographic technique
1999 (English)In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 15, no 7-8, 461-467 p.Article in journal (Refereed) Published
Abstract [en]

Objective.A new photoplethysmographic (PPG) device for respiratoryand heart rate monitoring has been evaluated in the neonatal care units at theUniversity Children's Hospital of Uppsala, Sweden. The purpose of thisstudy was to compare this new device with more established techniques, i.e.,transthoracic impedance plethysmography (TTI) for monitoring of respiratoryrate and ECG for heart rate monitoring.

Methods.Data were acquiredcontinuously for 8-hours in each of 6 neonates. The signals were analysed forperiods of 30 seconds, in which the heart and respiratory signals from the PPGdevice were compared with the ECG and the impedance plethysmogram.

Results.The ECG recordings were of high quality in 77% of the analysed periods.In these periods, excluding periods (6%) disturbed by offset-adjustement ofthe PPG signal, the PPG heart signal included 1.1% (±0.7% SD) falsenegative beats and 0.9% (±0.6%) false positive beats. In periods withan impedance signal of high quality (29% of total time), the part of the PPGsignal synchronous with respiration included 2.7% (±1.1%) falsenegative breaths and 1.5% (±0.4%) false positive breaths. Here, 2% ofthe periods were discarded because of offset-adjustment. From the periods oflow signal quality, two other conclusions were drawn: 1) The impedance signalcontains more power in the respiratory range than the corresponding PPGrespiratory signal. 2) The breaths are easier to identify in the PPGrespiratory signal than in the impedance signal (subjective measure).

Conclusions.Electrode and motion artefacts seem to disturb the ECGsignals and, particularly, the impedance signals. During periods of highquality ECG and impedance signals, the new optical device produces signals ofequal quality to these traditional methods, and is in some cases even better.The new device is non-invasive and has a small optical probe. These factors indicate further advantages of the photoplethysmographic method.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-32558 (URN)10.1023/A:1009912831366 (DOI)18471 (Local ID)18471 (Archive number)18471 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
4. The influence of breathing pattern in ventilation monitoring using photoplethysmography
Open this publication in new window or tab >>The influence of breathing pattern in ventilation monitoring using photoplethysmography
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Objective. The present study aimed at determining the relative influences of tidal volume and thoraco-abdominal separation (relative thoracic and abdominal contribution to the tidal volume) on the respiratory induced intensity variations (RIIV) of the photoplethysmographic (PPG) signal. The effects were studied in two body positions.

Methods. Respiratory inductive plethysmography (RIP) was used for quantifying thoracoabdominal separation and for assessing tidal volumes. 10 subjects were trained to perform widely varying degrees of thoraco-abdominal separations at different tidal volumes. The relationship between the RIIV signal peak-to-peak value (measured at the forearm), and the tidal volume and separation was investigated in two body positions with the use of multiple linear regression.

Results. Larger tidal volume and more thoracic contribution to respiration were found to increase the RIIV peak-to-peak value (p<0.0005). In the supine position, tidal volume had a stronger influence than separation, and in the sitting position, the opposite was seen.

Conclusions. The effects on the RIIV signal from changes in thoraco abdominal separation and tidal volume are of similar magnitude. In the supine position, the influence of separation is less than in the sitting position, but the regression model fit is reduced. PPG is a promising technique for monitoring tidal volumes. However, in situations where the relative thoracic and abdominal contributions are likely to vary, the tidal volume information is less reliable.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88950 (URN)
Available from: 2013-02-19 Created: 2013-02-19 Last updated: 2013-02-19
5. Neural network for photoplethysmographic respiratory rate monitoring
Open this publication in new window or tab >>Neural network for photoplethysmographic respiratory rate monitoring
2003 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 41, no 3, 242-248 p.Article in journal (Refereed) Published
Abstract [en]

The reflection mode photoplethysmographic (PPG) signal was studied with the aim of determining respiratory rate. The PPG signal includes respiratory synchronous components, seen as frequency modulation of the heart rate (respiratory sinus arrhythmia), amplitude modulation of the cardiac pulse and respiratory-induced intensity variations (RIIVs) in the PPG baseline. PPG signals were recorded from the foreheads of 15 healthy subjects. From these signals, the systolic wavefrm diastolic waveform, respiratory sinus arrhythmia, pulse amplitude and RIIVs were extracted. Using basic algorithms, the rates of false positive and false negative detection of breaths were calculated separately for each of the five components. Furthermore, a neural network was assessed in a combined pattern recognition approach. The error rates (sum of false positive and false negative breath detections) for the basic algorithms ranged from 9.7% (pulse amplitude) to 14.5% (systolic waveform). The corresponding values for the neural network analysis were 9.5–9.6%. These results suggest the use of a combined PPG system for simultaneous monitoring of respiratory rate and arterial oxygen saturation (pulse oximetry).

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-24477 (URN)10.1007/BF02348427 (DOI)6593 (Local ID)6593 (Archive number)6593 (OAI)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-02-19

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