Sara Casaccia

Decoding carotid pressure waveforms recorded by laser Doppler vibrometry: Effects of rebreathing

The principal goal of this study was to assess the capability of the laser Doppler vibrometry (LDV) method for assessing cardiovascular activity. A rebreathing task was used to provoke changes within individuals in cardiac and vascular performance. The rebreathing task is known to produce multiple effects, associated with changes in autonomic drive as well as alterations in blood gases. The rise in CO2 (hypercapnia), in particular, produces changes in the cerebral and systemic circulation. The results from a rebreathing task (involving rebreathing the same air in a rubber bag) are presented for 35 individuals. The LDV pulse was measured from a site overlying the carotid artery. For comparison and validation purposes, several conventional measures of cardiovascular function were also obtained, with an emphasis on the electrocardiogram (ECG), continuous blood pressure (BP) from the radial artery, and measures of myocardial performance using impedance cardiography (ICG). During periods of active rebreathing,...

Laser doppler myography (LDMi): A novel non-contact measurement method for the muscle activity

BACKGROUND AND AIMS Electromyography (EMG) is considered the gold-standard for the evaluation of muscle activity. Transversal and dimensional changes of the muscle, during muscle activity, generate vibrational phenomena which can be measured by Laser Doppler Vibrometry (LDVi). There is a relationship between muscle contraction and vibrational activity, therefore, some information on fundamental muscle parameters can be assessed without contact with LDVi. In this paper, we explore the possibility to relate the EMG signal causing the muscle contraction and the vibrational activity also measureable on the muscle. A novel non-contact measurement method - Laser Doppler myography (LDMi) - aiming to measure the vibrational behavior of muscle during contraction, is presented herein. Correlations with some parameters normally measured with EMG are reported. MATERIALS AND METHODS The proposed method has been compared with standard superficial EMG (sEMG). Signals produced with sEMG and laser Doppler myography have been simultaneously acquired and processed to test correlations on a population of 20 healthy volunteers. Tests have been carried out on the flexor carpi ulnaris and the tibialis anterior muscles (left and right). RESULTS RESULTS show that it is possible to measure: The timing of muscle activation (max differences: 440 ms), the amplitude of the signals acquired during activation respect to the signals during rest (S/N), the correlation between the S/N of the sEMG and LDMi signals at different levels of force (P> 0.89), and to assess muscle fatigue. CONCLUSIONS LDMi is a valid measurement technique for the assessment of muscle activity and fatigue. It is a non-contact method and this characteristic could suggest its use together with low level laser therapy pre-, intra- and post-LLLT sessions to evaluate the efficacy and effects of the treatments without the need for invasive electrodes.

Muscle activity characterization by laser Doppler Myography

Electromiography (EMG) is the gold-standard technique used for the evaluation of muscle activity. This technique is used in biomechanics, sport medicine, neurology and rehabilitation therapy and it provides the electrical activity produced by skeletal muscles. Among the parameters measured with EMG, two very important quantities are: signal amplitude and duration of muscle contraction, muscle fatigue and maximum muscle power. Recently, a new measurement procedure, named Laser Doppler Myography (LDMi), for the non contact assessment of muscle activity has been proposed to measure the vibro-mechanical behaviour of the muscle. The aim of this study is to present the LDMi technique and to evaluate its capacity to measure some characteristic features proper of the muscle. In this paper LDMi is compared with standard superficial EMG (sEMG) requiring the application of sensors on the skin of each patient. sEMG and LDMi signals have been simultaneously acquired and processed to test correlations. Three parameters has been analyzed to compare these techniques: Muscle activation timing, signal amplitude and muscle fatigue. LDMi appears to be a reliable and promising measurement technique allowing the measurements without contact with the patient skin.

Implementation of an “at-home” e-Health system using heterogeneous devices

Systems enabling long-term monitoring of physiological data and everyday activities has been the subject of considerable research efforts in the last years, in order to improve the quality of life of patients, elderly people and common citizens at home, out of the hospitalization. With the availability of inexpensive, low power, wireless and integrated devices, current smart homes are typically equipped with a large amount of sensors, which collaboratively process and make deductions from the acquired data on the state of the home, as well as the activities and behaviors of its residents. According to the field of application and the end-users involved (healthy people, elderly, people with disabilities), the definition of the parameters (e.g. heart rate, blood pressure, activity, body mass, etc.) and the appropriate sensors (electrocardiogram, sphygmomanometer, glucometer, etc.) for their acquisition assume a fundamental role. One of the goals of the Italian project Health@Home is to create a network of health sensors and home automation devices to monitor the users status within the home environment. We present a candidate implementation of such a system, describing the software architecture and the selected components, and a testbed of the architecture, realized in a lab room and used for a preliminary experimental study involving seven users.

Indirect measurement of the carotid arterial pressure from vibrocardiographic signal: Calibration of the waveform and comparison with photoplethysmographic signal

The detection of arterial Blood Pressure waveform provides important information about the subject health status. Laser Doppler Vibrometry (LDV) is a non-contact technique with high sensitivity able to detect mechanical movements of the arterial wall; several previous studies have shown that LDV is able to characterize cardiac activity. Photoplethysmogram (PPG) quantifies the digital volume artery pulse, which has been demonstrated to be closely related to the pressure signal measured by an arterial tonometer. In this paper, an indirect measurement of carotid arterial pressure by means of LDV is presented. Moreover, a comparison between LDV and PPG is conducted in order to estimate the time interval between opening and closing of the aortic valve, that is the Left Ventricular Ejection Time (LVET). Results show an average reduction of around 20% of the systolic pressure derived from LDV signal measured over the carotid artery with respect to the systolic pressure measured at brachial level (i.e. peripheral pressure value). Finally, the comparison between LDV and PPG in the estimation of LVET shows a mean percentage deviation <;10%. So, in conclusion, it can be stated that LDV technique has the potential of providing a displacement waveform that, adequately calibrated, can furnish significant information about pressure waveform.The detection of arterial Blood Pressure waveform provides important information about the subject health status. Laser Doppler Vibrometry (LDV) is a non-contact technique with high sensitivity able to detect mechanical movements of the arterial wall; several previous studies have shown that LDV is able to characterize cardiac activity. Photoplethysmogram (PPG) quantifies the digital volume artery pulse, which has been demonstrated to be closely related to the pressure signal measured by an arterial tonometer. In this paper, an indirect measurement of carotid arterial pressure by means of LDV is presented. Moreover, a comparison between LDV and PPG is conducted in order to estimate the time interval between opening and closing of the aortic valve, that is the Left Ventricular Ejection Time (LVET). Results show an average reduction of around 20% of the systolic pressure derived from LDV signal measured over the carotid artery with respect to the systolic pressure measured at brachial level (i.e. peripheral pressure value). Finally, the comparison between LDV and PPG in the estimation of LVET shows a mean percentage deviation <;10%. So, in conclusion, it can be stated that LDV technique has the potential of providing a displacement waveform that, adequately calibrated, can furnish significant information about pressure waveform.

LDV arterial pulse signal: Evidence for local generation in the carotid

The external blood pressure pulse, recorded on a non-contact basis using the method of laser Doppler vibrometry (LDV), has been shown to be a rich source of information regarding cardiac and vascular dynamics. Considerable attention has been directed specifically to the pulse from the neck, overlying the carotid artery, which is of special interest because the carotid pulse is highly similar to the central aortic pressure pulse. The findings presented here are consistent with an interpretation of the signal at the neck as originating in the carotid artery. A detailed mapping study involving a 35 point matrix over the right neck disclosed a focal zone of maximal signal amplitude, with a course consistent with the tract of the underlying carotid. Appreciable individual differences in the 22 examinees were disclosed, particularly at lower sites. In addition to confirming a local source for the LDV carotid pulse, the data highlight the importance of accurate targeting considerations.

Non-contact assessment of muscle contraction: Laser Doppler Myography

Electromyography (EMG) is the gold-standard technique used for the evaluation of muscle activity and contraction. The EMG signal supports analysis of a number of important parameters including amplitude and duration, engagement of motor units, and functional characteristics associated with factors such a force production and fatigue. Recently, a novel measurement method (Laser Doppler Myography, LDM) for the non-contact assessment of muscle activity has been proposed to measure the vibro-mechanical behavior of the muscles that conventionally is referred to as the mechanomyogram (MMG). The fact that contracting skeletal muscles produce vibrations and sounds has been known for more than three centuries. The aim of this study is to report on the LDM technique and to evaluate its capacity to measure without contact some characteristics properties of skeletal muscle contractions. This is accomplished with the very high vibration sensitivity inherent in the Laser Doppler Vibrometry method (in comparison to commonly used devices such as microphones, piezo electric pressure sensors, and accelerometers). Data measured by LDM are compared with signals measured using standard surface EMG (sEMG) which requires the use of skin electrodes. sEMG and LDM signals are simultaneously acquired and processed. The LDM and sEMG signals are compared with respect to the critical features of muscle activation timing, signal amplitude and force production. LDM appears to be a reliable and promising technique that allows measurement without the need for contact with the patient skin. LDM has additional potential advantages in terms of sensor properties, insofar as there are no significant issues relating to bandwidth or sensor resonance, and no mass loading is applied to the skin.

A Smart Sensing Architecture for Domestic Monitoring: Methodological Approach and Experimental Validation

Smart homes play a strategic role for improving life quality of people, enabling to monitor people at home with numerous intelligent devices. Sensors can be installed to provide a continuous assistance without limiting the resident’s daily routine, giving her/him greater comfort, well-being and safety. This paper is based on the development of domestic technological solutions to improve the life quality of citizens and monitor the users and the domestic environment, based on features extracted from the collected data. The proposed smart sensing architecture is based on an integrated sensor network to monitor the user and the environment to derive information about the user’s behavior and her/his health status. The proposed platform includes biomedical, wearable, and unobtrusive sensors for monitoring user’s physiological parameters and home automation sensors to obtain information about her/his environment. The sensor network stores the heterogeneous data both locally and remotely in Cloud, where machine learning algorithms and data mining strategies are used for user behavior identification, classification of user health conditions, classification of the smart home profile, and data analytics to implement services for the community. The proposed solution has been experimentally tested in a pilot study based on the development of both sensors and services for elderly users at home.

The measurement of blood pressure without contact: An LDV-based technique

This work is aiming to demonstrate the possibility to assess arterial blood pressure without the need to put any element in physical contact with the subject (except for the signal calibration). The authors have developed a measurement technique for the non contact measurement of blood pressure (BP) as manifest in the carotid artery, based on the use of a laser Doppler vibrometer (LDV). The LDV produces a signal that can be related to the continuous pressure pulse waveform. As such, the signal supports the calculation of some physiologically important time intervals. In this paper, we provide a comparison with the pressure waveform recorded using conventional applanation tonometry: the waveform has an analogous shape and, overall, provides the same characteristics in the time axis. More in details, results show that the systolic blood pressure have a mean deviation of 8% with respect to the reference value (obtained from tonometric data). Fundamental aspects to be considered are the precise laser pointing perpendicularly to the measurement site (to optimize the signal-to-noise ratio), the measurement conditions (e.g. the subject has to remain as still as possible) and also the reflective properties of the subjects skin, which can be improved by applying a proper reflective lotion or tape. The major factors contributing to uncertainty of the LDV measures have been evaluated, in order to identify ways to enhance performance. The current uncertainty value of 15% is not negligible, but does not greatly exceed that of the standard BP measuring devices.

Derived Non-contact Continuous Recording of Blood Pressure Pulse Waveform by Means of Vibrocardiography

Blood Pressure (BP) is considered a significant indicator of cardiac risk. By providing information about the hemodynamic load on the heart, BP detected in a central site may have added value with respect to the more familiar peripheral arterial pressure (i.e. measured on the brachial artery). Laser Doppler Vibrometry (LDV) has been demonstrated to be a reliable non-contact technique to measure the cardiovascular signals and parameters. LDV has a high sensitivity of acquisition and it is able to measure the skin vibrations related to cardiac activity when the laser beam is pointed in correspondence of the carotid artery. The obtainable vibrational signal (i.e. a velocity signal), VibroCardioGram (VCG), can provide relevant physiological parameters, including Heart Rate (HR) as well as more advanced features encoded in the contour of the pulse waveform. In this work, the authors aim to discuss the possibility of deriving the blood pressure signal from the vibrations of the carotid artery detected by LDV. 6 healthy participants were tested; the VCG was calibrated by means of diastolic and mean arterial pressure values measured by means of an oscillometric cuff. An exponential model was applied to the VCG signal of each participant in order to derive the pressure waveform from the displacement of the investigated vessel. Results show an average difference of around 20% between systolic pressure measured at brachial level (i.e. peripheral pressure value) and systolic pressure derived from VCG signal measured over the carotid artery (i.e. central pressure). This is consistent with the literature describing the physiological increase of Systolic Blood Pressure (SBP) and Pressure Pulse (PP) at increased distances from the heart (because of the presence of reflected waves). Moreover, the average measured displacements of the carotid artery are physiologically reliable (i.e. hundreds of micrometers). LDV seems to have the potential of correctly detecting the pressure waveform without contact. However, a comparison with a reference method is required to validate the proposed measurement technique.