Limb Occlusion Pressure (LOP) by Bluetooth

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Limb Occlusion Pressure (LOP) is the minimum pressure needed to fully occlude both arterial & venous blood flow

SYS is 100% LOP for that limb in that particular position with this particular cuff, just as the standard but prolonged method with Handheld dopplers. When preparing for exercise just set the pressure relative to SYS (40-80%) but without the Bluetooth Device attached!

“LOP is defined as the minimum pressure required, at a specific time in a specific type of tourniquet cuff applied to a specific patient’s limb at a specific location, to stop the flow of arterial blood into the limb distal to the cuff.” Noordinn et al. (2009) Surgical Tourniquets in Orthopaedics.

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Minimum Recommended % LOP for Effective & Safe BFR Pressure Stimuli



We recommend to measure LOP in seated position as displayed above. – Follow these recommendations for setting the pressure during lower body exercise:

  • Lying exercise: 40-70% of LOP
  • Seated exercise: 40-80% of LOP
  • Standing exercise: 50-90% of LOP

Example of LOP at 160 mmHg measured in the recommended seated position:

  • Lying exercise, about: 70-110 mmHg
  • Seated exercise, about: 70-130 mmHg
  • Standing exercise, about: 80-140 mmHg

Troubleshooting – Relevant for Assessment of Lower Body LOP

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If you have any sort of problem using this device please try the following:


  • Completely deflate the cuff – please follow this link for a guidance on “Complete Deflation”.
  • Make sure you have a very tight fit of the Cuff before inflation (pumping up) and please remember to not sit directly on the Cuff.
  • Make sure you’re positioning your self or your client as displayed above resting the foot on the floor with a slight bend in the knee.
  • Even the slightest movement interferes with the measurement and can make it impossible to measure LOP.
  • Try Inflating up to about 280 mmHg before you let the Bluetooth Device deflate (release pressure) the Cuff. 230 mmHg SYS(LOP) is the maximum measurable pressure, so if you have excessively large thighs it might not be possible to measure.
  • SYS/LOP will drop slightly if you do consecutive measurements.
  • There may be a variance of 5-15% of SYS/LOP relative to body positioning, e.g. seated vs. lying.




  • If you receive the message displayed on the 1. picture, then you should manually control the deflation speed as shown on the 3. picture. The green graph should look like this on your phone, only the very peak is allowed outside the white window..
  • Turn the wheel on the Fit Manometer to slightly speed up deflation as shown below. Please be patient, as it can take some time to get it just right – practice makes perfect! – as an alternative, please use the convenient “Calculate Pressure” module at training.fitcuffs.com.
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How the Device works – Nerd Alert

Independent research is showing a very good inter-rater reliability, by comparing LOP by this Bluetooth Device vs. LOP assessment by Handheld doppler ultrasound, as a variance of only 1-3%!

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“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 Bluetooth Device works by oscillometrics i.e, analyzing pulse waves and the absence of pulse waves. This is fundamentally the same physiological phenomena measured by handheld doppler ultrasound which detects the absence of blood flow by auscultation. Interestingly enough, this method of oscillometry is currently being utilized by the manufactures of autoregulated devices developed for surgery and also for Blood Flow Restriction (BFR(Training).

“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) in the explanation of how modern autoregulated tourniquet devices works, i.e. tourniquet instrument containing LOP calculation sensors and software such as Delfi Medical Innovation Inc.

“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).

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Figure 1 – Berger et al. (2001) How Does It Work? – Oscillatory blood pressure monitoring devices. “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).” Zachary 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).

The correct terminology is probably “Arterial Occlusion Pressure” (AOP), but LOP and AOP can for practical applications and explanations be used interchangeably. Total Limb Occlusion (TOP) is another term used in BFR research, this method resolves the problem with hemodynamics i.e., blood pressure variability in relation to external stimuli. So please mind, when doing repeated and continues measurements of LOP on the same limb, readings will vary because of the hemodynamic response to blood flow restriction.

Nevertheless, this small variance of LOP vs. TOP, is not effecting the prescription of pressure in BFR for clinical applications of LOP. We recommend the prescription of relative pressure i.e. 40-80% of LOP measured by the Bluetooth Device or Handheld dopplers.

“The results support that Doppler Ultrasound has a good reproducibility for the measurement of total obstruction pressure in 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).



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Figure 1 – Total occlusion pressure (TOP) determination description scheme with Doppler ultrasound.

From Morais et al. (2016) Upper limbs total occlusion pressure assessment- Doppler ultrasound reproducibility and determination of predictive variables

 

If you would like to know more about the Bluetooth Device and oscillatory blood pressure measurement, please see our Blog page (December 10, + February 4, 2020)

Disclaimer: When assessing conventional blood pressure, you should always use a calibrated cuff in terms of the bladder width (0.4) and bladder length (0.8) relative to the limb circumference you’re assessing. That is why you can not use Fit Cuffs product selection to measure conventional blood pressure and this combined unit is only valid for assessment of LOP. Please also mind, when doing repeated and continues measurements of LOP on the same limb, the readings will vary because of the hemodynamic response to external pressure and deflation of the cuff as described above.

Source:

  1. Noordinn et al. (2009) Surgical Tourniquets in Orthopaedics.
  2. Babbs (2012) Oscillometric measurement of systolic and diastolic blood pressures validated in a physiologic mathematical model.
  3. Berger et al. (2001) How Does It Work? – Oscillatory blood pressure monitoring devices.
  4. Beevers et al. (2001) ABC of hypertension Blood pressure measurement Part I -Sphygmomanometry: factors common to all techniques. Clinical review.
  5. Croft & Cruickshank (1990) Blood pressure measurement in adults: large cuffs for all?
  6. Jordanow et al. (2018) Comparison of oscillometric, Doppler and invasive blood pressure measurement in anesthetized goat.
  7. Morais et al. (2016) – Upper limbs total occlusion pressure assessment- Doppler ultrasound reproducibility and determination of predictive variables.
  8. Zachary et al. (2020) Limb Occlusion Pressure: A Method to Assess Changes in Systolic Blood Pressure.
  9. Evin et al. (2020) Limb occlusion pressure for blood flow restricted exercise- variability and relations with participant characteristics.
  10. Loenneke et al. (2014) Blood flow restriction in the upper and lower limbs is predicted by limb circumference and systolic blood pressure.
  11. Masri et al. (2016) Technique for Measuring Limb Occlusion Pressure that Facilitates Personalized Tourniquet Systems- A Randomized Trial.
  12. El-Zein (2020) (Thesis) the use of a portable Bluetooth Device to measure blood flow restriction training pressure requirements: a validation study.
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