Limb Occlusion Pressure (LOP) by The LOP Device
LOP Device (V1.1)
- Quick Guide for The LOP Device & App ⇩
- Guide For Assessment of Lower Body LOP ⇩
- Limb Occlusion Pressure (LOP) – The Minimum Pressure To Stop Blood Flow ⇩
- How the Device Works – Nerd Alert ⇩
- Charging – Use the micro USB cable (lithium-polymer battery), it takes approximately 2 hours to fully charge and recharge the LOP Device. It will turn off automatically after 2 minutes of inactivity.
- Optional – Download the corresponding 3. party app to your phone (IOS and Android) – You will receive information concerning the app in the email sent from email@example.com also containing the tracking number of Your parcel. ⇩
- Optional – Connect Your phone with the LOP Device via the app interface (4.0 BLE). Do not pair in your phone settings. ⇩
- Attach the Cuff to the corresponding limb. – Remember, to have a tight fit for the lower body. ⇩
- Connect the LOP Device with the Fit Manometer (Pressure Gauge) & Cuff. ⇩
- Sit still and relax your muscles then start inflation (pumping) the Cuff. Remember, the LOP Device will automatically deflate (release air) the cuff. ⇩
- After successful measurements, LOP will be displayed on the LED display to the left, on the App interface as SYS (LOP) at the top-left. ⇩
- Detach the LOP Device from the Cuff and Pressure Gauge. ⇩
- Set the pressure relative to the measured LOP (40-80%), but always without the LOP Device attached. To help with the % calculation of LOP please use the “LOP Module” at training.fitcuffs.com.
- Before exercising please remember to read and follow the guide at fitcuffs.com/how-to-use.
❔If you’re experiencing problems during lower body measurements, please see the “Troubleshooting” section.
- Make sure the cuff is completely deflated (no air pressure within the cuff) – please follow these links to see how: “Complete Deflation”, or if your product includes the Deflation Plugs remember to use these ⇩
- Wear the Leg Cuff tight before inflation (pumping), and please remember not to place any weight on the Cuff like sitting on it. ⇩
- Position yourself or your client as displayed, resting the foot on the floor with a straight or slight bend knee. ⇩
- Sit still – minuscule movement or subtle muscle contraction/twitch can interfere with the pressure sensor and make it impossible for the device to detect LOP. ⇩
- For larger thighs (>70cm) Inflate to about 280 mmHg before you let the LOP Device deflate the Cuff. ⇩
- If you receive the message “Air is blocked” as displayed below in the 2. app interface, you should manually increase the rate of deflation. Successful measurements look similar to the 4. app interface. Only the very peak of the green pulse waves is accepted outside the app display. You can see how to adjust the deflation speed accordingly in the videos above. ⇩ ⇩
6A – As displayed in the 1. video just above. Adjust the pressure gauge before inflating the cuff, to accelerate the rate at which air is released.
6B – As displayed in the 2. video just above. Before the cuff has been deflated below 230 mmHg, turn the valve anticlockwise on the pressure gauge to slightly increase the rate of deflation. Please consider that only minor fine-tuning is needed. Be patient, as it can take some time to get it just right as practice makes perfect.
1. App interface displaying delayed deflation speed with the pulse wave out of bounds
2. Unsuccessful measurement because of delayed deflation
3. Inflation to near 280 mmHg to allow for an increased deflation rate by turning the valve on the pressure gauge before the pressure is below 230 mmHg
4. Displaying a correct pulse wave after the rate of deflation has been increased just slightly. For the lower body aim for a deflation time of 20-50 seconds from the moment you stop pumping
Disclaimer: 230 mmHg is the maximum measurable pressure the device can assess, so if you have excessively large thighs (>75 cm), it might not be possible to detect LOP. As an alternative method to determine the pressure, check the convenient “Calculate Pressure” module at training.fitcuffs.com read more about the module at fitcuffs.com/web-app-explained.
Limb Occlusion Pressure (LOP) can be applied by various methods or devices. Using LOP is regarded as the most favorable way of personalizing pressure applications to ensure a sub occlusive and effective stimulus.
“Systolic Blood Pressure”, in the app interface shown as “SYS”, is 100% Limb Occlusion Pressure (LOP) for that limb in that particular position with the particular cuff used for the assessment. On the other hand, conventional blood pressure measurement should always be conducted with a calibrated cuff, not Fit Cuffs, but more about this below.
The Bluetooth Device measures the least amount of pressure that is needed to block blood flow completely. This is fundamentally the same physiological assessment as the common but prolonged method with handheld Dopplers or the less valid method of Pulse oximetry.
LOP and Arterial Occlusion Pressure (AOP) can for practical application and explanation be used interchangeably. Both terms means the lowest tourniquet pressure required to cease the arterial blood flow into the extremity distal to the cuff.
Please mind the physiological property of LOP which is inherently dynamic. Because of this, LOP will fluctuate if you do consecutive measurements because of the hemodynamic (the study of blood flow) response to exercise and external pressure stimulus.
See the explanation of Total Occlusion Pressure (TOP) in the “How the Device Works” Section.
Minimum Recommended % LOP for Effective & Safe BFR Pressure Stimuli
LOP is defined as the minimum pressure required to stop arterial and venous blood flow to the corresponding limb, at a specific time, in a specific position with a specific cuff being applied.
Noordinn et al. (2009). So, always consider the variance of 5-15% of SYS/LOP relative to body positioning, e.g. standing vs. seated vs. lying.
We recommend measuring LOP with the Bluetooth Device in a seated or lying position. Following a seated assessment of LOP, please follow these recommendations for setting the pressure during lower body BFR Training.
- Lying exercise: 40-70% of LOP
- Seated exercise: 40-80% of LOP
- Standing exercise: 50-90% of LOP
Example of LOP = 160 mmHg:
- Lying exercise, about: 70-110 mmHg
- Seated exercise, about: 70-130 mmHg
- Standing exercise, about: 80-140 mmHg
The LOP Device works by oscillometric i.e., analyzing arterial pulse waves and the absence of arterial pulse waves (CE 0197). When blood passes through the artery between systolic and diastolic pressure it causes vibrations. These vibrations travel through the air inside the cuff and are transduced into electrical signals via The LOP Device pressure sensor, which ultimately produces a digital readout on the LED & app interface. This is fundamentally the same physiological phenomenon measured by Handheld Doppler Ultrasound, which detects the absence of blood flow by auscultation (Korotkoff sounds).
Independent comparative product testing at 3 separate research institutions around the globe are all showing very good validity, i.e., Inter-Rater Reliability (Correlations) and Test-Retest Reliability (Intra-Class Correlation Coefficient) – (ICC). The data shows a variance of only 1-5% by comparing the LOP Device vs. LOP assessment by Handheld Doppler Ultrasound and the second “golden standard” Doppler Pulse Wave Ultrasound.
In conclusion, the research shows a clinically acceptable agreement between the different methods of LOP measurement.
Nice to know – The actual “golden standard” for the study of blood flow is “direct intra-arterial recordings”.
The following universities have participated in the study of the Bluetooth Device (v1.0) vs. doppler ultrasound: Lebanese University Faculty of Public Health & Gazi University Faculty of Sports Sciences Turkey & Institute of Physiotherapy ZHAW School of Health Professions Switzerland.
“Based on the results of our study, we recommend using the Fit Cuffs® portable Bluetooth Device for objective and personalized BFR practice. This device is a valid, reliable, and low-cost replacement for other measurement devices, which are substantially more expensive and require considerable usage skills. Thus, using the Bluetooth Device would offer BFR practitioners the ability to provide high-quality services for their clients or patients, ensuring minimal risks and optimal results regardless of location.” El-Zein (2020).
“The inexpensive oscillatory device is a valid and reliable measurement device for determining the AOP in the lower extremity in healthy adults. For the upper extremity it can be concluded that the oscillatory device is a valid method to measure the AOP when compared to the HH Doppler. When both methods are compared to the Doppler US, they seem to be less accurate and overestimate the AOP in the upper extremity. It is recommended to take at least two measurements to determine the AOP with the oscillatory device.” Schmidt (2021)
“Our findings suggest that changes in limb occlusion pressure measured by hand-held Doppler track similarly to traditional measurements of brachial systolic blood pressure following isometric knee extension exercise.” – “In conclusion, this study supports the use of limb occlusion pressure measurements as a potential alternative measure of systolic blood pressure (when both cuffs are of similar widths).” Bell et al. (2020)
“The fact that brachial Systolic Blood Pressure explains a significant amount of the variance with arterial occlusion is logical given that they are essentially measures of the same thing, except that brachial SBP was measured with a different sized cuff.” Loenneke et al. (2014).
“When the cuff is fully inflated to this pressure, no blood flow occurs through the artery. As the cuff is deflated below the systolic pressure, the reducing pressure exerted on the artery allows blood to flow through it and sets up a detectable vibration in the arterial wall.” Berger et al. (2001)
Interestingly, oscillometry is currently being utilized by the manufactures of autoregulated systems to determine LOP developed for bloodless surgery and also for Blood Flow Restriction (BFR) Training. That is autoregulated tourniquet instruments containing pressure sensors and software to calculate LOP such as Delfi Medical Innovation Inc.:
“The instrument connected to the tourniquet cuff increases the cuff pressure in 10-mmHg stepwise increments, analyzes the pneumatic pressure pulsations induced in the cuff bladder by the arterial pressure pulsations at each cuff pressure increment, and uses these characteristics to determine LOP.” Masri et al. (2016)
“The first method, the ‘embedded LOP method’ , measures LOP by employing a dual-purpose tourniquet cuff to monitor arterial pulsations in an underlying limb by sensing pneumatic pressure pulsations in the cuff associated with volume changes in the limb as the cuff pressure is gradually increased.” Hughes & McEwen (2021)
Arterial Occlusion Pressure (AOP) and LOP can for practical applications be used interchangeably. Though, Total Limb Occlusion (TOP) is yet another terminology used in BFR research to describe the absence of pulsation. This method considers the hemodynamic (blood flow) response to restrictions as the pressure variability in relation to external or internal stimuli. So please mind, when doing repeated measurements on the same limb, LOP will vary significantly because of the hemodynamic response to blood flow restriction and/or exercise.
The discrepancy of LOP/AOP vs. TOP does not affect the prescription of pressures in the clinical application of LOP, as the common recommendation of 40-80% of LOP measured by the LOP Device, Handheld Dopplers or Pulse Oximetry.
“The results support that Doppler Ultrasound has a good reproducibility for the measurement of total obstruction pressure in the brachial artery. Furthermore, systolic and diastolic blood pressures should be considered as the major predictive variables for determining the upper limb total obstruction pressure.” Morais et al. (2016).
If you would like more about the LOP Device (v1.1), vascular doppler and oscillatory blood pressure measurements, please see our Blog page (December 10, + February 4, 2020) & the video from YouTube channel: @BPM biosignals
Disclaimer: When assessing conventional blood pressure, you should always use a calibrated cuff in terms of the bladder width at least (0.4) and bladder length (0.8) relative to the limb circumference you’re assessing. (Pickering et al. (2005)
That is why you cannot use Fit Cuffs product selection to measure conventional blood pressure. Please also mind, when doing repeated and continuous measurements of LOP, SYS will vary because of the hemodynamic response as described above.
- Noordinn et al. (2009) Surgical Tourniquets in Orthopaedics.
- Babbs (2012) Oscillometric measurement of systolic and diastolic blood pressures validated in a physiologic mathematical model.
- Berger et al. (2001) How Does It Work? – Oscillatory blood pressure monitoring devices.
- Bell et al. (2020) Limb Occlusion Pressure: A Method to Assess Changes in Systolic Blood Pressure.
- Beevers et al. (2001) ABC of hypertension Blood pressure measurement Part I -Sphygmomanometry: factors common to all techniques. Clinical review.
- Croft & Cruickshank (1990) Blood pressure measurement in adults: large cuffs for all?
- Jordanow et al. (2018) Comparison of oscillometric, Doppler and invasive blood pressure measurement in anesthetized goat.
- Morais et al. (2016) – Upper limbs total occlusion pressure assessment- Doppler ultrasound reproducibility and determination of predictive variables.
- Zachary et al. (2020) Limb Occlusion Pressure: A Method to Assess Changes in Systolic Blood Pressure.
- Evin et al. (2020) Limb occlusion pressure for blood flow restricted exercise- variability and relations with participant characteristics.
- Loenneke et al. (2014) Blood flow restriction in the upper and lower limbs is predicted by limb circumference and systolic blood pressure.
- Masri et al. (2016) Technique for Measuring Limb Occlusion Pressure that Facilitates Personalized Tourniquet Systems: A Randomized Trial.
- Hughes et al. (2017) Influence and reliability of lower-limb arterial occlusion pressure at different body positions.
- Hughes & McEwen (2021) Investigation of clinically acceptable agreement between two methods of automatic measurement of limb occlusion pressure- a randomised trial
- El-Zein (2020) (Thesis) the use of a portable Bluetooth Device to measure blood flow restriction training pressure requirements: a validation study.
- Schmidt (2021) (Thesis) Validity and reliability of an oscillatory blood pressure measurement device to determine the arterial occlusion pressure in healthy adults for blood flow restriction training exercise protocols: a cross-sectional study.
- Pickering et al. (2005) Recommendations for blood pressure measurement in humans and experimental animals: Part 1: blood pressure measurement in humans: a statement for professionals from the Subcommittee of Professional and Public Education of the American Heart Association Council on High Blood Pressure Research