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How Does A Pulse Oximeter Measure Heart Rate

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Why Would I Need This Test

Fingertip Pulse Oximeter | Measure your blood oxygen and heart rate by Zacurate

Your doctor will use pulse oximetry whenever they think that your blood-oxygen levels could be too low. The device can help:

  • Diagnose symptoms like shortness of breath
  • Track your blood oxygen level during surgery
  • Test oxygen levels when you use supplemental oxygen
  • Show if you need extra oxygen when you exercise

You might need pulse oximetry if you have:

  • A heart attack

How To Measure Blood Oxygen Level And Heart Rate Using Iphone

Follow these step-by-step instructions to measure blood oxygen level and heart rate using your iPhone:

Step 1:;Open the CarePlix Vital app on your iPhone and sign up for the free service.

CarePlix Vitals

Step 2: On the main page, tap on Scan Vitals.

Step 3: A calibration window will pop up. Place your index finger on the camera in a way that your finger covers both the camera sensor and the flash.

Itll show the signal strength underneath the small camera window. Make sure youre covering the whole part for accurate results.

Step 4:;Wait for the scan to start. Once the scan starts, itll show the real-time blood oxygen level, heart rate, and respiration rate. Do not remove your finger in between the process.

Step 5: Once the scan is complete, a window with your measurements will pop up. You can save the result on this screen or start a new scan.

You can also check out our step-by-step video tutorial to learn how to measure blood oxygen and heart rate using your iPhone:

Can Pulse Oximeter Givefalse Reading

Pulse oximeter reading maynot be accurate or may show errors in certain conditions such as…

If the device isimproperly placed.

If there is thick nailpolish, tattoos, or henna dye on the finger or on placed part.

During measurement, thereis much movement of the finger or much trembling of hands. So keep your fingersteady while using the device.

In heavy cold, there maybe wrinkling of finger skin or if your fingers are wet, there may not beaccurate results. So dry and warm up your hand before taking a reading.

Before using the deviceconfirm that it is in working condition and the battery is not drained.

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Patients Who Have Been Given A Pulse Oximeter For Heart Rate And Blood Oxygen Level

If you have COVID-19 symptoms your ;GP may have;given you or your carer a pulse oximeter and asked you to fill in a diary.

A pulse oximeter helps you to monitor how fast your heart is beating and the level of oxygen in your blood.; Blood oxygen level is the most accurate way of keeping an eye on your progress with COVID-19,; An ideal heart rate is between 50 and 90 beats per minute

What Is The Accuracy Of Pulse Oximeters

Easy@Home Fingertip Pulse Oximeter SpO2 Blood Oxygen ...

Quality pulse oximeters have a 95% confidence rate with an accuracy of ±4%. Thus, oximeters give reliable readings if the readings are between 70% and 100% SpO2.

Most devices provide readings within a 2% difference. Thus, if your reading is 95%, your true blood oxygen saturation level may be anywhere between 93% and 97%.

The following factors can affect the accuracy of the reading:

  • Improper placement of the probe
  • Cold fingers or fever

(Ensure the finger or the body part in question is sweat-free.

  • Edema
  • Movement
  • Carbon monoxide waveform
  • High-intensity lighting like fluorescent lights
  • Nail polish or artificial fingernails

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Alternatives May Be Less Accurate

A number of wearable wellness devices have built-in pulse oximeters, but they are likely to be even less accurate than home pulse oximeters.

For example, a Fitbit spokesperson told CR that over-the-counter pulse oximeters measure estimated oxygen levels at the finger, where blood supply is rich and near the surface of the skin. But Fitbits measure oxygen levels at the wrist, where there is less blood supply near the surface. In addition, devices worn on your wrist are more likely to move during measurement than are those on your finger, making the results less reliable.

For those reasons, Fitbit says its devices are not intended to track the kind of changes in blood oxygen levels that might occur with acute or chronic respiratory problems. Rather, the pulse oximeter function in Fitbits is primarily intended to monitor interruptions in breathing, particularly during sleep, to help users who may be dealing with sleep apnea.

Garmin, another maker of fitness trackers, said its wearables have pulse oximeter sensors that can gauge a persons blood oxygen saturation during the day and night, but that theyre not designed or intended to diagnose or treat any disease or condition. Like the Fitbits, the Garmin trackers use light beams to measure oxygen saturation in the blood, through sensors on the wrist, rather than the finger.

Apple Watch does not currently have a feature that measures oxygen saturation.

Pulse Oximeters: Vital Signs At Your Fingertips

A pulse oximeter is a small medical device that measures heart rate and blood oxygen saturation. It’s usually clipped to your finger, but it can also attach to your ear, nose, toe or forehead. On Apple Watches, it’s the sensor on the underside of the watch, the part that goes against the top of your wrist, that takes the measurement.

Some pulse oximeters are battery powered and provide real-time results on a small LED display on the device itself. Others connect with a wire to a separate vital sign monitor that records even more precise information about your heart rhythm, body temperature and blood pressure using other sensors connected to your body.

A pulse oximeter attaches to a finger and uses light to detect the level of oxygen in your blood.

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System Description And Diagram

A modern pulse oximeter uses Aoyagis approximation of the ratio ) and Wilbers calibration curve. It may incorporate adaptive noise canceling for minimizing the effects of patient motion and low perfusion.

A disposable or reusable probe is typically positioned on a patients digit. The clinician powers on the unit, which may run on lead acid batteries or be connected to AC power. An LED driver powers on and off two LEDs at a modulation rate, such as 625;Hz. Typical red and infrared wavelengths used are 660 and 940;nm, respectively. During each modulation cycle, the red LED is powered on, both LEDs are powered off, the infrared LED is powered on, and both LEDs are powered off in sequence. LED light is naturally isolated from the patient.

Light transmitted from an LED and through the finger is received by a photodiode . The photodiode current is amplified and undergoes data acquisition. Within the processor module, the digitized data are demodulated to isolate the photoplethysmogram waveform at each wavelength. Plethysmography is the measurement of volume. The so-called pleth waveform is misnamed because it is not directly proportional to pulse volume.

Figure 11.13. Pulse oximeter system diagram.

Sandeep Kumar Vashist, John H.T. Luong, in, 2018

Accounting For Ambient Light

How to Use a Pulse Oximeter

The pulse oximeter probe, as shown below, has a red LED and one infrared LED. On the other side, is a light detector. However, you will note that, though there are only two LEDs, the light detector is exposed to three sources of light. In addition to the red and infra red LED light sources, there is also light in the room that the pulse oximeter is working in. Some of this room light can also reach the detector. The pulse oximeter has to work with these three sources of light. It wants the red and infra red light to calculate oxygen saturation. On the other hand, the room light is unwanted noise, and needs to be taken account of. The way it does this will be explained.

The above diagram shows both LEDs lit to make the explanation easier. In reality, both LEDs are never lit together. Instead, the pulse oximeter rapidly switches the LEDs on and off in a particular sequence. First, the pulse oximeter activates the red LED light. The red light goes through the finger and reaches the detector. Stray room light also reaches the detector. The detector therefore records red light and room light that falls on it.

Next, the pulse oximeter switches off the red LED light and switches on the infrared LED light. The infrared light goes through the finger and reaches the detector. Stray room light also reaches the detector. The detector therefore records infrared light and room light that falls on it.

So here is the sequence:

Only red LED is on. Sensor measures red plus room light.

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Normal Pulse Rate In Oximeter

The medical device measure SpO2 in the range of 70%99% with the accuracy of ±2%. The normal resting pulse rate in humans is between 60 and 100 beats per minute , but it is also dependent on the fitness level, body weight, emotional state, medication, body position, and involvement in physical activities.


  • 3 Normal oxygen saturation by age
  • Which Pulse Oximeter Tobuy

    Only buy pulse oximeter ofreliable manufacturers. You can take advice from your doctor for this. Here aresome pulse oximeters on with good ratings and good customer reviews.

    Note: If you buy productsfrom the links given in this article, we may have little commission. Pleaseensure product reliability and all details before purchasing it.

    This article is forinformation purposes only. Please take the advice of health care experts beforetaking any action.

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    Anatomy Of An Oximeter

    Typical pulse oximeters monitor the SpO2 of a persons blood based on the red light and infrared light absorption characteristics of HbO2 and Hb. This type of pulse oximeter flashes the red and infrared lights alternately through a body part, such as a finger, to a photodiode sensor.

    The photodiode is normally utilized to receive the non-absorbed light from each LED. This signal is then inverted using an inverting operational amplifier, or op amp. The resulting signal represents the light that has been absorbed by the finger .

    Figure 2:


    The pulse amplitudes of the red and infrared signals are measured and converted to Vrms, in order to produce a ratio value: Ratio = / .

    The SpO2 can be determined using the ratio value and a look-up table that is made up of empirical formulas. The pulse rate can be calculated based on the pulse oximeters Analog-to-Digital Converter sample number and sampling rate.

    A look-up table is an important part of a pulse oximeter. Look-up tables are specific to a particular oximeter design and are usually based on calibration curves derived from, among other things, a high number of measurements from subjects with various SpO2 levels. Figure 3 shows an example of a calibration curve.

    Types Of Pulse Oximeter

    How Does A Pulse Oximeter Measure Heart Rate

    Ear probes are lightweight and are useful in children or if the patient is very vasoconstricted. Small probes have been designed for children but an adult hinged probe may be used on the thumb or big toe of a child. For finger or toe probes, the manufacturer marks the correct orientation of the nail bed on the probe.

    The oximeter probe is the most delicate part of a pulse oximeter and is easily damaged. Handle the probe carefully and never leave it in a place where it could be dropped on the floor.

    The probe connects to the oximeter using a connector with a series of very fine pins that can be easily damaged-see diagram. Always align the connector correctly before attempting to insert it into the monitor.

    Never pull the probe from the machine by pulling on the cable; always grasp the connector firmly between finger and thumb.

    When not in use, the oximeter probe cable may be loosely coiled for storage or carrying, but should not be coiled too tightly as this will damage the wires inside the cable. The lens and detector should be kept clean. Use soapy water or an alcohol soaked swab to gently clean dust, dirt or blood from the probe.

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    Need And Applications Of A Pulse Oximeter

    High blood pressure or Hypertension causes up to 1,100 deaths each day in the USA alone. Hence, we feel it is very crucial to monitor all people at risk frequently. Such conditions can easily result in reduced blood flow, heart disease, and even strokes.

    Hypoxia the lack of availability of oxygen to the tissues is a giant danger to patients as well. Tissue hypoxia is a significant reason for morbidity and, ultimately, a large cause of death for humans. Pulse oximeters usually help provide accurate data within a 2% error range, aiming for a 70% to 100% hemoglobin saturation when the sensors receive a satisfactory signal.

    Can A Pulse Oximeter Detect Covid

    Not exactly. Although many doctors report that patients with COVID-19 are presenting with dangerously low blood oxygen levels, COVID-19 isn’t the only disease that can cause such a problem. Chronic lung diseases, like COPD, asthma and other non-COVID-19 lung infections can also result in a low oxygen count.

    A low oxygen reading by itself is not enough to diagnose COVID-19, but your doctor would want to know about it, especially if you notice the level decreasing over time. And if you’ve been diagnosed with COVID-19, your doctor may want you to monitor your oxygen level to determine whether your condition is worsening or improving.

    Although medical professionals continue to rely on temperature checks as an indication of a coronavirus infection, many patients with COVID-19 do not have fevers.

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    Why Should I Have A Pulse Oximeter At Home

    A pulse oximeter helps determine how well your heart is pumping oxygen through the body. You can; thus, use it to track health conditions that can affect heart rates and blood oxygen levels.

    Such conditions include:

    • Chronic obstructive pulmonary disease
    • Heart failure
    • COVID-19

    Having a pulse oximeter at home is particularly helpful amid the pandemic.

    In her 18-minute video Guide to Managing Mild Cases of Covid-19 Dr. Sandhya Ramanathan, an Auckland-based GP encourages people to invest in a pulse oximeter, and for reasons.

    She says, People with respiratory illnesses including Covid-19 are at risk of low oxygen saturation levels in the blood.

    She continues, It became clear in the early stages of the crisis that many people were unaware their oxygen levels were dipping until it was almost too late.

    Ramanathan suggests that people should track their oxygen concentration levels daily. Especially for the first 14 days after diagnosis with COVID-19.

    She notes the normal rate ranges between 95% and 100%. She encourages medical intervention if the SpO2 levels dip below 93%. Or when theres shortness of breath.

    Prof Sam McConkey, an expert in infectious diseases at the Royal College of Surgeons in Ireland, backs her views.

    He notes that Some patients with Covid-19 dont develop symptoms of hypoxia such as shortness of breath or even coughing, and report as being merely tired.

    What Is A Pulse Oximeter

    How to Use a Pulse Oximeter Nonin GO2 Brand Home Pulse Oximeter

    COPD Homecare Pulse Oximetry

    A pulse oximeter is a small, lightweight device used to monitor the amount of oxygen carried in the body. This noninvasive tool attaches painlessly to your fingertip, sending two wavelengths of light through the finger to measure your pulse rate and how much oxygen is in your system. Once the oximeter finishes its assessment, its screen will display the percent of oxygen in your blood coming from your heartas well as your current pulse rate. This article will explain the significance of the measurements provided by a pulse oximeter and how they affect you.

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    Factors Which Affect Accuracy Of Readings

    Patient condition -;To calculate the difference between full and empty capillaries, oximetry measures light absorption over a number of pulses, usually five . In order for a pulsatile flow to be detected, there must be sufficient perfusion in the monitored area. If the patient has a weak or absent peripheral pulse, pulse oximeter readings will not be precise. Patients most at risk of low perfusional states are those with hypotension, hypovolaemia and hypothermia and those in cardiac arrest. Patients who are cold but not hypothermic may have vasoconstriction in their fingers and toes that may also compromise arterial flow .

    Non-arterial pulses may be detected if the probe is secured too tightly, creating venous pulsations in the finger. Venous pulsations are also caused by right-sided heart failure, tricuspid regurgitation , and the tourniquet effect of a blood pressure cuff above the probe.

    Cardiac arrhythmias may cause very inaccurate measurements, especially if there are significant apex/radial deficits .

    Intravenous dyes used in diagnostic and haemodynamic testing may cause inaccurate, usually lower, estimates of oxygen saturations . The effects of deeply pigmented skin, jaundice or bilirubin levels should also be considered.

    Optical shunting affects accuracy and occurs when the sensor is improperly positioned so that light goes directly from the LED to the photodetector without passing through the vascular bed.

    How To Take A Reading:

    • Follow your health care providers recommendations about when and how often to check your oxygen levels.
    • Be aware that multiple factors can affect the accuracy of a pulse oximeter reading, such as poor circulation, skin pigmentation, skin thickness, skin temperature, current tobacco use, and use of fingernail polish. To get the best reading from a pulse oximeter:
    • Follow the manufacturers instructions for use.
    • When placing the oximeter on your finger, make sure your hand is warm, relaxed, and held below the level of the heart. Remove any fingernail polish on that finger.
    • Sit still and do not move the part of your body where the pulse oximeter is located.
    • Wait a few seconds until the reading stops changing and displays one steady number.
  • Write down your oxygen levels with the date and time of the reading so you can easily track changes and report these to your health care provider.
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