Mediana P10 Manual de Serviço descarregar pdf (Página 107)

101

-20

-15

-10

-5

200180160140120100

SYSTOLIC PRESSURE

Mean difference(MD): 0 mmHg

Standard deviation(SD): 6 mmHg

mean + 2 SD

mean

mean - 2 SD

Average of test and reference methods (mmHg)

Difference between test and reference methods (mmHg)

(EXAMPLE) Agreement between test and reference methods for systolic pressure. Hypothetical data

SpO

Processing

Pulse oximetry works by applying a sensor to a pulsating arteriolar vascular bed. The

sensor contains a dual light source and photodetector. Bone, tissue, pigmentation, and

venous vessels normally absorb a constant amount of light over time. The arteriolar bed

normally pulsates and absorbs variable amounts of light during systole and diastole, as

blood volume increases and decreases. The ratio of light absorbed at systole and diastole

is translated into an oxygen saturation measurement (SpO

). Because a measurement of

SpO

is dependent upon light from the sensor, excessive ambient light can interfere with

this measurement.

Pulse oximetry is based on two principles: that oxyhemoglobin and deoxyhemoglobin

differ in their absorption of red and infrared light (spectrophotometry), and that the volume

of arterial blood in tissue (and hence, light absorption by that blood) changes during the

pulse (plethysmography). The monitor determines SpO

by passing red and infrared light

into an arteriolar bed and measuring changes in light absorption during the pulsatile cycle.

Red and infrared low-voltage light-emitting diodes (LED) in the oximetry SpO

sensor

serve as light sources; a photo diode serves as the photo detector. Because

oxyhemoglobin and deoxyhemoglobin differ in light absorption, the amount of red and

infrared light absorbed by blood is related to hemoglobin oxygen saturation. To identify

the oxygen saturation of arterial hemoglobin, the monitor uses the pulsatile nature of

arterial flow. During systole, a new pulse of arterial blood enters the vascular bed, and

blood volume and light absorption increase. During diastole, blood volume and light

absorption reach their lowest point. The monitor bases its SpO

measurements on the

difference between maximum and minimum absorption (measurements at systole and

diastole). By doing so, it focuses on light absorption by pulsatile arterial blood, eliminating

the effects of nonpulsatile absorbers such as tissue, bone, and venous blood.

Automatic Calibration (Nellcor module)

Because light absorption by hemoglobin is wavelength dependent and because the mean

wavelength of LEDs varies, an oximeter must know the mean wavelength of the SpO

sensor’s red LED to accurately measure SpO

. During monitoring, the instrument’s

software selects coefficients that are appropriate for the wavelength of that individual

sensor’s red LED; these coefficients are then used to determine SpO

Additionally, to compensate for differences in tissue thickness, the light intensity of the

sensor’s LEDs is adjusted automatically.

1 2 ... 102 103 104 105 106 107 108 109 110

Comentários a estes Manuais

Sem comentários

Mediana P10 Manual de Serviço Página 107

Comentários a estes Manuais