Ds 033 no4.indd
Product No. 3147
Range: 0 to 200 bpm
Resolution: 1 bpm
Range: -2000 to 2000 mV
Resolution: 1 mV
Data Harvest Group Ltd
1 Eden Court, Leighton Buzzard,
Beds, LU7 4FY
Tel: 01525 373666
Fax: 01525 851638
DS 033 No 4
Data Harvest. Freely photocopiable for use within the purchasers establishment.
Heart Rate Sensors
The Smart Q
Heart Rate Sensor monitors the light level transmitted through the
vascular tissue of the fi ngertip or the ear lobe and the corresponding variations in
light intensities that occurs as the blood volume changes in the tissue.
SENSE unit can detect that the Smart Q Heart Rate Sensor is connected
and the range it is set to.
Insert jack plug of Pleth into jack socket
Sensor cable with locating arrow facing upwards
Hold the Heart Rate Sensor housing with the Smart Q label showing on the top.
Push one end of the sensor cable (supplied with the EASY
SENSE unit) into the
shaped socket at the end of the Sensor housing with the locating arrow on the
Connect the other end of the sensor cable to the Input socket on the
SENSE unit (with the locating arrow facing upwards).
Insert the jack plug from the fi nger/ear lobe clip into the jack socket at the end of
SENSE unit will detect that the Heart Rate Sensor is connected. If
the currently selected range is not suitable for your investigation, set to the
To set the range
The Heart Rate Sensor can record either Heart rate, in beats per minute (bpm) or
Heart waveform, in mV.
Connect the Heart Rate Sensor to the EASY
SENSE program and select one of the
logging modes from the Home page. Select Sensor
from the Settings
Select the Heart Rate Sensor from the list (it will be listed
using its current range) and click on the Change Range
The current range will be highlighted. Select the required
the change in range to be detected by the logging mode.
Heart Rate Sensors
The range setting will be retained until changed by the user. With some EASY
SENSE units it is possible to change the range from the unit. Please refer to
SENSE unit’s user manual.
Note: Avoid applying pressure to the clip as this could affect
2. Stay reasonably still as any muscle movements will
infl uence the signal. The red LED on the
Sensor housing will start to fl ash in time with the
heartbeat - wait for the signal to stabilise. If the clip is attached to the fi nger you
Note: If the red LED doesn’t fl ash, and the LCD display on the EASYSENSE logger is blank, press any
button on the panel of the EASYSENSE unit to wake it up.
3. Once a regular heart rate is detected, begin recording data.
The Smart Q
Heart Rate Sensor is used to measure the cardiovascular pulse wave
that is found throughout the human body. This pulse wave will result in a change in
the volume of arterial blood with each pulse beat. This change in blood volume can
be detected in peripheral parts of the body such as the fi ngertip or ear lobe using a
technique called Photoplethysmography. The device that detects the signal is called
a plethysmograph (or ‘Pleth’ for short).
An infrared LED which illuminates the tissue.
A light sensitive detector (LSD), which has been tuned to the same colour
frequency as the LED, and detects the amount of light transmitted from the
The Pleth supplied with this Sensor is a transmission mode plethysmographic signal (PPG) device, which uses transmitted light to estimate absorption. The infrared LED and the light sensitive detector (LSD) are mounted in a spring-loaded device that can be clipped onto the fi ngertip or ear lobe.
The infrared light emitted by the LED is diffusely scattered through the fi ngertip or ear lobe tissue. A light sensitive detector positioned on the surface of the skin on the
Heart Rate Sensors
opposite side can measure light transmitted through at a range of depths. Infrared light is absorbed well in blood and weakly absorbed in tissue. Any changes in blood volume will be registered since increasing (or decreasing) volume will cause more or less absorption. Assuming the subject does not move the level of absorption of the tissue and non-pulsating fl uids will remain the same.
Absorption due to changes in arterial blood volume
The amount of light that can be detected by the Light Sensitive Detector (LSD) will
vary with each test subject and as to whether the clip is attached to a fi ngertip or
fi nger clip so that the Light Sensitive
Detector is on the fl eshy side of the fi nger.
Fingers should be clean. Nail varnish may cause falsely low readings. Values should not be affected by skin colouring.
circulation (the extent to which the blood vessels in the fi ngertip are fi lled with
blood), in which case another subject should be selected.
If the heart rate does not seem to settle, try warming the hands by rubbing to
If readings are lower than expected, try repositioning the clip to make sure fi rm
Remove any earrings before attaching the fi nger/ear lobe clip to the ear lobe.
The clip can be made more secure by hooking the wire round the back of the
ear or by using the slide on the lead to attaching it to the subject’s clothing.
If the heart rate does not settle or if readings are lower than expected, try
repositioning the clip to make sure a fi rm contact is obtained.
Each time the fi nger/ear lobe clip is attached to a fi ngertip or ear lobe, wait until the signal stabilises before starting to record data - the initial unstable signal will be due to compression from the clip being attached.
Heart Rate Sensors
Stay reasonably still while recording data. Movement e.g. raising and lowering a hand, will alter the pressure the fi nger exerts on the clip whilst simultaneously causing a change in venous blood that will affect light transmission through the tissue.
It is possible to alter heart rate by simply decreasing respiratory rate. Encourage the test subject to breath normally.
The number of beats per minute is calculated by the Heart Rate Sensor by timing the width of a pulse and ‘scaling up’ to a rate of beats per minute. For example, a recorded wave form of a 0.7 second duration would become (1 ÷ 0.7) x 60 = 85.7 beats per minute. Sporadic short or longer beats will produce artifi cially high or low readings. This should not present a problem as trends in heart rate are studied, not absolute values or rapid changes.
The heart rate is averaged over every fi ve beats to achieve a smoother reading.
If the fi nger/ear lobe clip ‘loses contact’ with the
pulse, the Sensor will attempt to re-establish
communication. This may result in the reading
This Sensor is not
intended for medical
diagnosis. Do not be alarmed if results do not
correspond to quoted numbers. These numbers
represent typical averages and many healthy
hearts have data that falls outside these
parameters. It is quite normal for the heart to occasionally miss a beat.
It is possible for the dicrotic notch to be
Heart wave (mV) Heart waveform of a subject with a signifi cant dicrotic notch2000
effects are more noticeable if the clip is
attached to the fi nger; try using with the
This Sensor is not waterproof. Clean the clip by wiping with a cloth that has been
The light sensitive detector (LSD) in the clip can be sensitive to high levels of ambient infrared light e.g. strong sunlight. If this maybe the case try excluding the light by covering the clip with some dark fabric e.g. by placing your hand inside a cloth bag.
Heart Rate Sensors
The fastest speed
that the Heart Rate Sensor can be used with to capture data is
50Hz (20ms). If an intersample time of less than 20 milliseconds is selected, then
the values obtained will default to zero.
Blood passes through the heart in two phases that alternate continuously.
Diastole (heart expanding)
Systole (heart contracting)
Blood fl ows from the ventricles into arteries
The blood forced into the aorta during systole moves the blood in the vessels forwards and sets up a pressure wave that travels along the arteries. This pressure wave expands the arterial walls as it travels and is felt as the pulse.
The pulse may be felt at points where arteries pass over bones, known as pressure points e.g. in the wrist and neck. Pulse rate is a direct measure of the number of heart cycles in a minute (heart rate).
Heart rate can vary with age as shown below:
Average heart rate
(beats per minute)
In normal healthy individuals the heart rate, and thus the pulse rate, varies with the phases of respiration. Irregular changes in heart rate occur in all people. Heart rate may be increased by exercise, nervous excitement, stress due to mental effort, by adrenaline entering the bloodstream or with increase in temperature caused by fever. The heart rate decreases when asleep and some medical conditions may also cause a drop.
Following exercise it takes a while for the heart rate to return to resting level. This is the recovery time and gives an indication of the fi tness of the individual. Recovery time may vary from less than fi ve minute in very fi t individuals to around 15 minutes.
Heart Rate Sensors
Safe Pulse rates
During experiments the safe heart rate should not be exceeded. The safe level is
given as the maximum heart rate for age, minus 20 beats per minute.
Maximum heart rate = 210 – (0.65 x age)
Maximum heart rate
Safe heart rate
It is important that investigations do not become a competition. Consider any possible health problems before selecting the subject.
The heartbeat recorded by the Smart Q Heart Rate Sensor is smoothed by the
passage of blood through the capillaries and the pressure signal does not resemble
the pulse seen in an electrocardiogram (which is used to record the hearts
electrical activity). However, the periodicity of the signal is unchanged and the Heart
Rate Sensor can be effectively used to detect changes in heart rate.
The upstroke, called the anacrotic limb, 2000is abrupt and is due to contraction of
is more gradual and corresponds to the 500elastic recoil of the arterial walls. The
fl uctuation known as the dicrotic notch.
the aortic valve snaps shut – it has no
major signifi cance as an indicator of health. For a healthy person at rest, the heart beats on average at about 60 beats per minute or one a second i.e. around 1Hz. This frequency is not constant (even in a healthy individual at rest).
It takes approximately one second to record a complete wave, so it is usually best to select a short recording time.
Heart Rate Sensors
Monitoring fi tness - after exercise pulse is timed until it gets back to the normal
standing heart rate (this can be achieved by remaining in a sitting position and
Changes with mild stimulants (cups of coffee or cola – might show less effect on
people who are accustomed to large amounts of caffeine).
Variation in blood fl ow i.e. people who suffer with cold fi ngers will show a very
fl ow in their veins – try warming their hands.
Investigating pulse rate with different body positions (sitting, crouching,
The effect of music on pulse rate.
The effect of the strictest teacher entering the room!
All Data Harvest Sensors are warranted to be free from defects in materials and
workmanship for a period of 12 months from the date of purchase provided they
have been used in accordance with any instructions, under normal laboratory
conditions. This warranty does not apply if the Sensor has been damaged by
accident or misuse.
In the event of a fault developing within the 12-month period, the Sensor must be returned to Data Harvest for repair or replacement at no expense to the user other than postal charges.
Data Harvest products are designed for educational
use and are not intended for use
in industrial, medical or commercial applications.
lectrical and E
Data Harvest Group Ltd are fully compliant with WEEE legislation and are pleased to provide
a disposal service for any of our products when their life expires. Simply return them to us
identifi ed as ‘life expired’ and we will dispose of them for you.
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