Section 11: Technical Supplement; Introduction; Oximetry Overview - Mallinckrodt NELLCOR NPB-195 Service Manual

SECTION 11: TECHNICAL SUPPLEMENT

11.1 INTRODUCTION

11.2 OXIMETRY OVERVIEW

11.2.1 Functional Versus Fractional Saturation
11-1 Introduction
11-2 Oximetry Overview
11-3 Circuit Analysis
11-4 Functional Overview
11-5 AC Input
11-6 Power Supply Theory of Operation
11-7 Battery
11-8 User Interface PCB (UIF)
11-9 Front Panel Display PCB and Controls
11-10 Schematic Diagrams
This Technical Supplement provides the reader with a discussion of oximetry
principles and a more in-depth discussion of NPB-195 circuits. Block and
schematic diagrams support a functional overview and detailed circuit analysis.
The schematic diagrams are located at the end of this supplement.
The NPB-195 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 wave forms.
Spectrophotometry uses various wavelengths of light to qualitatively measure
light absorption through given substances. Many times each second, the NPB-
195 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-195 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: SpO
each wavelength.
The NPB-195 measures functional saturation, that is, oxygenated hemoglobin
expressed as a percentage of the hemoglobin that is capable of transporting
oxygen. It does not detect significant levels of dyshemoglobins. In contrast,
some instruments such as the IL282 Co-oximeter measure fractional saturation,
that is, oxygenated hemoglobin expressed as a percentage of all measured
hemoglobin, including dyshemoglobins.
is the ratio of corrected absorption at
2
11-1