Letter to the Editor Arterial pulse pressure waveform monitoring by novel optical probe ☆ , ☆☆ Tânia Pereira a, ⁎, Telmo Santos Pereira b , Helder Santos b , Carlos Correia a , João Cardoso a a Instrumentation Center, Physics Department, University of Coimbra, Portugal b Coimbra College of Health Technology, Coimbra, Portugal article info Article history: Received 5 October 2014 Accepted 18 October 2014 Available online 22 October 2014 Keywords: Hemodynamic monitoring Arterial pulse waveform Carotid stenosis Collateral circulation Novel cardiovascular instrumentation Non-invasive optical probe Blood pressure indices can be considered as main risk factors of car- diovascular disease (CVD). This fact highlights the growing awareness that there are more vascular health parameters to assess rather than the maximum and minimum pressures, measured as brachial blood pressure with a sphygmomanometer in the traditional clinical assess- ment [1]. Information about the interaction between the left ventricle ejection and the physical properties of the arterial circulation can be determined by the descriptive and quantitative analysis of the arterial pulse wave- form (APW), providing indirect but global markers of arterial stiffness. It is that morphologic features of individual arterial pressure waveforms provide diagnostic clues to various pathologic conditions [2]. Emerging innovations in cardiovascular monitoring are moving away from more invasive technologies to portable and non-invasive solutions [3], partic- ularly those able to perform multi-parameter assessment from the APW analysis. However, all of them establish direct contact with the patient's tissues at the artery site. The clinical application of a non-contact method can overcome practical and technical limitations inherent to the currently used methods, such as arterial applanation tonometry, ultrasound and plethysmography, that require physical contact of the probe with the pa- tient, compress the artery and distort the shape of the pulse curve [4,5]. The non-contact nature of optical technology allows a measurement without distortions in the shape of the arterial pulse. The optical probe used in this work is enclosed in a plastic box that ensures a non-contact signal acquisition, by keeping a small distance be- tween the sensors and skin, 3 mm. This optical system proved to be re- liable in detecting the arterial distension waveform. A comparative test between the distension waveform measuring with optical probe at the carotid artery and the invasive profile of the pulse pressure acquired by an intra-arterial catheter showed a strong correlation between the waves, and validates the capability to estimate the APW with a non- invasive way by the contactless optical probe [6]. For these reasons the concept of pulse pressure waveform and distension waveform is used based on their correspondence. In this work, the study protocol was approved by the ethical commit- tee of the Centro Hospitalar e Universitário de Coimbra, Portugal. The pa- tient volunteered and gave a written informed consent. The tests were performed in a patient who had undergone a carotid angiography, and the assessment trials were made before and after the endovascular angio- plasty proceeding. The subject under study is a 76-year-old woman with a diagnosis of 90% left internal carotid artery stenosis. Measurements were performed after a rest period (15 min) in a temperature-controlled environment (21 °C). Each exam procedure consisted in the acquisition of a set of cardiac cycles at the carotid artery with the optical probe and the patient laid in supine position for 2 min. The carotid artery is the natural probing site for APW measurement due to the heart proximity and because it is easily accessible (i.e. it is close to the skin surface). The operator positioned the probe in the proximal common carotid artery, about 1 cm from the bifurcation site (estimated by the trained operator) and the same procedure was followed pre- and post-surgery. The detected waveform before the surgery revealed a modified pro- file when compared to the normal range, with a large increase of pres- sure at the end of the diastole period (Fig. 1a). In Fig. 1a, the APWs show the presence of a reflected wave, marked in blue for the reflection point (RP), prior to the systolic point (SP), which is caused by the reflec- tion of the APW in the atherosclerotic plaque of the internal carotid ar- tery wall. At the end of the diastole period an increase of pressure is noticed, marked with red circle, that is not common in normal pulse waveforms that will be analyzed below. International Journal of Cardiology 179 (2015) 95–96 ☆ This author takes responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation. ☆☆ The authors acknowledge the support from Fundação para a Ciência e Tecnologia (FCT) for funding PhD grant (SFRH/BD/79334/2011). ⁎ Corresponding author at: Physics Department, University of Coimbra, Rua Larga, 3004-516 Coimbra, Portugal. E-mail address: taniapereira@lei.fis.uc.pt (T. Pereira). http://dx.doi.org/10.1016/j.ijcard.2014.10.050 0167-5273/© 2014 Elsevier Ireland Ltd. All rights reserved. Contents lists available at ScienceDirect International Journal of Cardiology journal homepage: www.elsevier.com/locate/ijcard