Photoplethysmography (PPG) is a simple and low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue. It is often used non-invasively to make measurements at the skin surface. The PPG waveform comprises a pulsatile ('AC') physiological waveform attributed to cardiac synchronous changes in the blood volume with each heart beat, and is superimposed on a slowly varying ('DC') baseline with various lower frequency components attributed to respiration, sympathetic nervous system activity and thermoregulation. Although the origins of the components of the PPG signal are not fully understood, it is generally accepted that they can provide valuable information about the cardiovascular system. There has been a resurgence of interest in the technique in recent years, driven by the demand for low cost, simple and portable technology for the primary care and community based clinical settings, the wide availability of low cost and small semiconductor components, and the advancement of computer-based pulse wave analysis techniques. The PPG technology has been used in a wide range of commercially available medical devices for measuring oxygen saturation, blood pressure and cardiac output, assessing autonomic function and also detecting peripheral vascular disease. The introductory sections of the topical review describe the basic principle of operation and interaction of light with tissue, early and recent history of PPG, instrumentation, measurement protocol, and pulse wave analysis. The review then focuses on the applications of PPG in clinical physiological measurements, including clinical physiological monitoring, vascular assessment and autonomic function.

https://iopscience.iop.org/article/10.1088/0967-3334/28/3/R01/pdf

Photoplethysmography and its application in clinical physiological measurement.

The present invention involves method and apparatus for analyzing two measured signals that are modeled as containing primary and secondary portions. Coefficients relate the two signals according to a model defined in accordance with the present invention. In one embodiment, the present invention involves utilizing a transformation which evaluates a plurality of possible signal coefficients in order to find appropriate coefficients. Alternatively, the present invention involves using statistical functions or Fourier transform and windowing techniques to determine the coefficients relating to two measured signals. Use of this invention is described in particular detail with respect to blood oximetry measurements.

Signal processing apparatus.

A method and an apparatus to analyze two measured signals that are modeled as containing desired and undesired portions such as noise, FM and AM modulation. Coefficients relate the two signals according to a model defined in accordance with the present invention. In one embodiment, a transformation is used to evaluate a ratio of the two measured signals in order to find appropriate coefficients. The measured signals are then fed into a signal scrubber which uses the coefficients to remove the unwanted portions. The signal scrubbing is performed in either the time domain or in the frequency domain. The method and apparatus are particularly advantageous to blood oximetry and pulserate measurements. In another embodiment, an estimate of the pulserate is obtained by applying a set of rules to a spectral transform of the scrubbed signal. In another embodiment, an estimate of the pulserate is obtained by transforming the scrubbed signal from a first spectral domain into a second spectral domain. The pulserate is found by identifying the largest spectral peak in the second spectral domain.

Signal processing apparatus and method

alpha(2)-adrenergic agonists for regional anesthesia - A clinical review of clonidine (1984-1995)

THE concept of preemptive analgesia to reduce the magnitude and duration of postoperative pain was paved in 1983 by Woolf, who showed evidence for a central component of postinjury pain hypersensitivity in experimental studies. Subsequently, an overwhelming amount of experimental data demonstrated that various antinociceptive techniques applied before injury were more effective in reducing the postinjury central sensitization phenomena as compared with administration after injury. Finally, these promising experimental findings were taken into clinical testing of the hypothesis. Although early reviews of clinical findings were mostly negative, there is still a widespread belief of the efficacy of preemptive analgesia among clinicians. The definition of preemptive analgesia has varied, thereby causing confusion and misunderstanding of the concept. Because the original observations in experimental studies suggested that timing of analgesic treatment was important to obtain efficient reduction of postinjury pain hypersensitivity phenomena, we performed an updated review of studies to compare the role of timing of analgesia i.e., preoperative versus intraoperative or postoperative initiation of analgesia. In this review we are not considering studies designed to compare preemptive analgesia versus no treatment. We have only included double-blind, randomized, controlled trials of identical or very similar analgesic regimens, where the only difference between study groups was timing of analgesia.

A qualitative and quantitative systematic review of preemptive analgesia for postoperative pain relief: the role of timing of analgesia

A diagnostic instrument for determining a cardiovascular system parameter. In one embodiment, the instrument takes the form of a portable pulse oximeter comprising a light to frequency converter (LFC) as a sensor. Also provided is a light to frequency converter comprising a photoresistor and capacitor in circuit communication with an inverting Schmitt trigger and configured such that the inverter generates a periodic electrical signal corresponding to the amount of electromagnetic radiation illuminating the photoresistor.

Portable pulse oximeter

The aim of this study was to determine if preemptive administration of systemic ketamine decreases postoperative pain when compared with postwound closure administration of ketamine.Patients undergoing abdominal procedures were randomized into a preemptive or postwound closure ketamine administration group. Before surgical incision, patients in the preemptive group (n = 20) were given 0.5 mg/kg ketamine followed by a ketamine infusion of 10 micro g [centered dot] kg-1 [centered dot] min-1, which was discontinued at abdominal closure. The patients in the postwound closure (n = 20) group were given 0.5 mg/kg of ketamine immediately after abdominal closure. Postoperatively, all patients received intravenous (IV) morphine in the postanesthesia care unit (PACU) and were started on IV morphine patient-controlled analgesia after discharge from the PACU. Postoperative pain was assessed by measuring morphine consumption and visual analog scale (0-100 mm) pain scores at rest. Patients in the preemptive group had significantly lower morphine consumption on postoperative Days 1 and 2. No significant intergroup differences were seen in the pain scores throughout the study period. Preemptive ketamine decreased postoperative opioid requirements, which was observed long after the normal expected duration of ketamine. (Anesth Analg 1997;84:1086-90)

Preemptive Ketamine Decreases Postoperative Narcotic Requirements in Patients Undergoing Abdominal Surgery

A reflectance pulse oximeter that determines oxygen saturation of hemoglobin using two sources of electromagnetic radiation in the green optical region, which provides the maximum reflectance pulsation spectrum. The use of green light allows placement of an oximetry probe at central body sites (e.g., wrist, thigh, abdomen, forehead, scalp, and back). Preferably, the two green light sources alternately emit light at 560 nm and 577 nm, respectively, which gives the biggest difference in hemoglobin extinction coefficients between deoxyhemoglobin, RHb, and oxyhemoglobin, HbO 2 .

Green light pulse oximeter

A reflectance pulse oximeter that determines oxygen saturation of hemoglobin using two sources of electromagnetic radiation in the green optical region, which provides the maximum reflectance pulsation spectrum. The use of green light allows placement of an oximetry probe at central body sites (e.g., wrist, thigh, abdomen, forehead, scalp, and back). Preferably, the two green light sources alternately emit light at 560 nm and 577 nm, respectively, which gives the biggest difference in hemoglobin extinction coefficients between deoxyhemoglobin, RHb, and oxyhemoglobin, HbO2.

/pdf/system-using-green-light-to-determine-parmeters-of-a-1dvzv5l90p.pdf

John E. Scharf

Papers

Portable pulse oximeter

Preemptive Ketamine Decreases Postoperative Narcotic Requirements in Patients Undergoing Abdominal Surgery

Green light pulse oximeter

System using green light to determine parmeters of a cardiovascular system

Pulse oximeter probe