Features of the non-contact carotid pressure waveform: Cardiac and vascular dynamics during rebreathing.

This report amplifies and extends prior descriptions of the use of laser Doppler vibrometry (LDV) as a method for assessing cardiovascular activity, on a non-contact basis. A rebreathing task (n = 35 healthy individuals) was used to elicit multiple effects associated with changes in autonomic drive as well as blood gases including hypercapnia. The LDV pulse was obtained from two sites overlying the carotid artery, separated by 40 mm. A robust pulse signal was obtained from both sites, in accord with the well-described changes in carotid diameter over the blood pressure cycle. Emphasis was placed on extracting timing measures from the LDV pulse, which could serve as surrogate measures of pulse wave velocity (PWV) and the associated arterial stiffness. For validation purposes, a standard measure of pulse transit time (PTT) to the radial artery was obtained using a tonometric sensor. Two key measures of timing were extracted from the LDV pulse. One involved the transit time along the 40 mm distance separating the two LDV measurement sites. A second measure involved the timing of a late feature of the LDV pulse contour, which was interpreted as reflection wave latency and thus a measure of round-trip travel time. Both LDV measures agreed with the conventional PTT measure, in disclosing increased PWV during periods of active rebreathing. These results thus provide additional evidence that measures based on the non-contact LDV technique might provide surrogate measures for those obtained using conventional, more obtrusive assessment methods that require attached sensors.

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.

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.