Technical Supplement; S1 Introduction; Oximetry Overview - Nellcor NPB-190 Service Manual

TECHNICAL SUPPLEMENT

S1 INTRODUCTION
S2

OXIMETRY OVERVIEW

S1 Introduction

S2 Oximetry Overview
S3 Circuit Analysis
S4 Functional Overview
S5 AC Input
S6 Power Supply PCB
S7 Battery
S8 User Interface PCB
S9 Front Panel Display PCB and Controls
S10 Schematics
This Technical Supplement provides the reader with a discussion of oximetry
principles and a more in-depth discussion of NPB-190 circuits. A functional
overview and detailed circuit analysis is supported by block and schematic
diagrams. The schematic diagrams are located at the end of this supplement.
The NPB-190 is based on the principles of spectrophotometry and optical
plethysmography. Optical plethysmography uses light absorption technology to
reproduce waveforms produced by pulsatile blood. The changes that occur in the
absorption of light due to vascular bed changes are reproduced by the pulse
oximeter as plethysmographic waveforms.
Spectrophotometry uses various wavelengths of light to qualitatively measure
light absorption through given substances. Many times each second, the NPB-
190 passes red and infrared light into the sensor site and determines absorption.
The measurements that are taken during the arterial pulse reflect absorption by
arterial blood, nonpulsatile blood, and tissue. The measurements that are
obtained between arterial pulses reflect absorption by nonpulsatile blood and
tissue.
By correcting "during pulse" absorption for "between pulse" absorption, the
NPB-190 determines red and infrared absorption by pulsatile arterial blood.
Because oxyhemoglobin and deoxyhemoglobin differ in red and infrared
absorption, this corrected measurement can be used to determine the percent of
oxyhemoglobin in arterial blood: SpO2 is the ratio of corrected absorption at
each wavelength.
S-1