Respiratory Physiology & Neurobiology 216 (2015) 23–27 Contents lists available at ScienceDirect Respiratory Physiology & Neurobiology jou rn al h om epa ge: www.elsevier.com/locate/resphysiol Noninvasive monitoring of peripheral microcirculatory hemodynamics under varying degrees of hypoxia Zehava Ovadia-Blechman a,* , Aviram Meilin a , Neta Rabin b , Michael Eldar c , David Castel c a Department of Medical Engineering, Afeka Tel Aviv Academic College of Engineering, Tel Aviv, Israel b Department of Exact Sciences, Afeka Tel Aviv Academic College of Engineering, Tel Aviv, Israel c Neufeld Cardiac Research Institute, Tel Aviv University, Sheba Medical Center, Tel-Hashomer, Israel a r t i c l e i n f o Article history: Received 28 January 2015 Received in revised form 21 April 2015 Accepted 18 May 2015 Available online 22 May 2015 Keywords: Hypoxia Peripheral microcirculation Laser Doppler flowmetry Photoplatysmograph Transcutaneous oxygen tension Noninvasive monitoring a b s t r a c t The effect of hypoxia on skin blood flow was examined in anesthetized rabbits during induction of various levels of hypoxia. Peripheral perfusion and oxygenation were monitoring using a combined system (LPT) composed of a laser Doppler flowmeter (LDF), a photoplatysmograph (PPG), and a transcutaneous oxygen tension monitor (tc-PO 2 ). Central blood parameters (PaO 2 , HCO - 3 , SaO 2 , pH, and lactate) were measured concomitantly throughout the experiment. A continuous decline was found in both peripheral and central values, depending on the severity of the hypoxia. The results clearly indicate that monitoring peripheral indices with the LPT system enables monitoring changes of vital blood parameters during hypoxia. The system has clinical potential for sensitive and noninvasive monitoring of vital variables during medical procedures in clinics, as well as for homecare for patients with respiratory diseases. Minimizing the system may be useful in various conditions of exposure to low oxygen levels, such as during mountain climbing. © 2015 Elsevier B.V. All rights reserved. 1. Introduction One of the main goals of hemodynamic support is preservation of tissue perfusion. Monitoring the microcirculation has long been difficult. Recent technological advances have made monitoring of the microcirculation at the bedside of critically ill patients feasible (Allen, 2007; Backer et al., 2012; Wright et al., 2006). Since hypoxia is a clinical condition that may lead to life-threatening complica- tions, early diagnosis as well as monitoring of clinical measures at different levels of hypoxia are therefore essential. Noninva- sive monitoring of blood oxygen levels is currently carried out by pulse-oximetry, which monitors oxygen saturation in the periph- ery. However, the great success of pulse oximetry masks the fact that it still carries an inherent potential error of 3–4% in measure- ments carried out on critically ill patients and preterm newborns (Nitzan et al., 2014). In addition, the method was found reliable only up to a level of 80% oxygen saturation (Jubran, 1999; Jubran and Tobin, 2013). Hence, there is still a need for a noninvasive device to monitor oxygen levels during severe hypoxia. Noninvasive methods for measuring cutaneous perfusion have been based on optical sensors (Boggett et al., 1985; Nilsson et al., * Corresponding author. Tel.: +972 3 7688696; fax: +972 3 7688692. E-mail address: zehava@afeka.ac.il (Z. Ovadia-Blechman). 1980; Tenland et al., 1983; Weinman, 1978; Nitzan et al., 2006), as well as devices to measure tissue oxygen pressure (Fagrell, 1995; Franzeck et al., 1984; Pittman, 2013). At the Neufeld Cardiac Research Institute, our group has designed a noninvasive system that combines LDF, PPG and tc-PO 2 devices (hence the name LPT) that measure the flux of RBC, the amount of RBC, and oxygen ten- sion, respectively. Each one of them is in clinical use (Ovadia et al., 1995). The LPT system was found in our previous studies to be a reliable noninvasive monitor of microcirculatory hemodynamic variables under different clinical conditions. The system was sensitive to changes in peripheral microcirculation variables, which it detected earlier than central measures under various clinical conditions such as hemorrhage and resuscitation fluid infusions. The set of devices was reported to assist the physician in diagnosis and medical man- agement (Ovadia et al., 1995; Ovadia et al., 1997). The microcirculation of the skin and its regulation have been investigated under normal and pathological conditions, including various respiratory states (Babchenko et al., 1999; Levy et al., 2015), diabetes (Arora et al., 2002; Golster et al., 2005; Hosking et al., 2013; Kasalova et al., 2006; Marik, 2006; Shah et al., 2014; Urbancic-Rovan et al., 2006), vascular diseases (De Graaff et al., 2003; Morales et al., 2005; Otah et al., 2005; Przywara et al., 2004; Salminen et al., 2014), and smoking (Arora et al., 2002; Dalla et al., 2004; Rossi et al., 2014). Our aim here was to test the ability of http://dx.doi.org/10.1016/j.resp.2015.05.011 1569-9048/© 2015 Elsevier B.V. All rights reserved.