Phoenix Ambulatory Blood Pressure Monitor
Inventory of Indirect Blood Pressure Analysis Techniques
This analysis is starting with the Ng article, which includes a succinct summary of measurement methods. As the author is still in a learning phase, much of the meterial here is taken wholesale from Ng.
DO NOT CITE THIS PAGE!
requires patient-specific calibration
[Ng] the radial artery is applanated by a tonometric sensor in such a way that the arterial wall tension around the sensor is parallel to the surface and the sensor detects only forces that are perpendicular to the surface. In this state, changes in the detected forces are proportional to changes in arterial pressure, enabling the arterial pulse waveform to be recorded. This waveform is then calibrated against the patient's oscillometric BP at the upper arm to establish a waveform amplitude-BP calibration curve, which is then used to derive BP from waveforms captured after the calibration, giving real-time, continuous beat-to-beat measurement. This calibration must be repeated periodically during monitoring because motion artefacts and changes to the mechanical (viscoelastic) properties of the compressed artery can alter the sensor-artery contact configuration and in turn alter the calibration relationship even when there is no change in arterial pressure. A recalibration is also necessary to correct for changes in hydrostatic pressure between the wrist and the heart if the wrist level changes from the level at which the last calibration was performed.
The concept of auscultation encompasses any technique of listening to the internal sounds of the body. When applied to blood pressure, the sounds listened for are the Korotkoff sounds, which are generated by pulse waves propagating through the arterial system.
Auscultatory methods of blood pressure measure a sphygmomanometer to occlude a blood vessel and measure pressure on the occluded vessel, and a stethoscope to listen for the Korotkoff sounds. The stethoscope can be replaced with an electronic stethoscope and computer-aided auscultation software, which would provide automatic detection of the Korotkoff sounds.
See alsohttp://en.wikipedia.org/wiki/Blood_pressure#Auscultatory.
See pulse wave velocity method.
does NOT require patient-specific calibration
see Medwave, Inc. (unsure if enterprise is still active)
does NOT require patient-specific calibration
[Ng] a wrist sensor is placed over the radial artery and a series of compression and decompression is applied to the artery for 12-15 heartbeats for each measurement. From the sensor signal, the monitor:
might be usable with either PTT or pulse wave analysis
Oscillometric methods of blood pressure measure usually employ an occluding cuff placed over a blood vessel, like the auscultatory method, but with an electronic pressure sensor (transducer) to observe cuff pressure oscillations, electronics to automatically interpret them, and automatic inflation and deflation of the cuff. The technique is dependent on the transmission of intra-arterial pulsation to the occluding cuff surrounding the limb.
See alsohttp://en.wikipedia.org/wiki/Blood_pressure#Oscillometric.
with sphygmomanometer
requires patient-specific calibration
[Ng] based on correlation between blood volume and BP. In one implementation, the blood volume pulse waveform is captured at an ear lobe, a finger, or a superficial artery, and calibrated against upper arm oscillometric BP to establish a correlation between components of the waveform integral and the oscillometric BP. This correlation is then used to derive BP from waveforms captured after the calibration, giving beat-to-beat measurement. Changes in hydrostatic pressure between the measurement site and the heart can be corrected by a recalibration or by using a hydrostatic pressure correction sensor.
The amount of pressure required to create the feeling of a pulse.
the time of a pulse wave traveling from the heart to an aterial site
requires patient-specific calibration
[Ng] changes in BP are derived from changes in the morphology of the arterial pulse waveform. In one implementation, the radial pulse waveform is captured by using a hemispherical pulse sensor and calibrated against upper arm oscillometric BP, and the device is then used for 24-h ambulatory BP monitoring (ABPM) at 15-min intervals without any further calibration.
requires patient-specific calibration
[Ng] based on correlation between PWV and BP; PWV increases with BP. One way to implement this method is to use the pulse transit time, the time it takes for a pulse wave to travel between two sites on the same artery at different distances from the heart. Another way is to use the pulse arrival time (PAT) between the peak of the R or Q wave of an electrocardiogram and the onset or another characteristic point of a pulse wave at a peripheral site, during the same cardiac cycle. This PAT, however, comprises not only the true pulse transit time between the heart and the peripheral site, but also a significant portion of the cardiac pre-ejection period. Yet another way is to use the difference between the PATs at two sites on the same artery or on different arteries. This method, called the differential PAT method, eliminates the pre-ejection period. The PWV method can be used to provide beat-to-beat measurement. It generally requires patient-specific calibration against a secondary method or device. Some monitors provide for only one calibration at rest, some provide for one at rest and one after exercise, and some require the calibration to be repeated periodically. In some monitors, the PAT is used to detect sudden changes in BP and trigger an oscillometric measurement between periodic measurements.
A proprietary technique of Tensys Medical, Inc.
[Ng] similar to the arterial tonometry method except that it uses a tonometric sensor with a built-in capability to calibrate the pulse waveform. During use, the monitor performs an initial calibration to determine the patient's MAP (at the applanation depth of maximum energy transfer) and then uses the patient's BMI to scale the pulsatile component of the waveform. After the calibration, the monitor tracks the MAP and scales the pulsatile component continuously, giving real-time, continuous beat-to-beat measurement. This calibration must be repeated after periods of excessive motion artefacts. The measured BP must be corrected for hydrostatic pressure if the wrist is not at the heart level.
Features: Dynamic Radial Artery Location; Applanation Sweep to Find MAP; Adjustment for Tissue Transfer of Pressure
requires patient-specific calibration
[Ng] usually implemented by applying an air-filled or fluid-filled cuff to the middle or basal phalanx of a finger and controlling the cuff pressure in such a way as to keep the finger arteries in an unloaded or unstretched state. In this way, the cuff pressure is always equal to the finger arterial pressure, giving real-time, continuous beat-to-beat measurement. This method requires an initial calibration to determine the unloaded arterial size and its corresponding time-weighted mean arterial pressure (MAP), and subsequent periodic calibrations to correct for changes in the unloaded arterial size; the determination of the unloaded arterial size and MAP is based on the oscillometric principle of maximum transfer of pulsatile energy from an artery to a cuff or sensor when the transmural pressure across the arterial wall is zero or the arterial wall is maximally compliant over a cardiac cycle. In one implementation, the finger arteries are kept continuously in the unloaded state during monitoring and the finger BP is calibrated periodically against upper-arm oscillometric BP; a recalibration is necessary to correct for changes in hydrostatic pressure between the finger and the heart. In a second implementation, the finger BP waveform is transformed into an equivalent brachial BP waveform by using a generalized transfer function and, in a third, further calibrated against return-to-flow brachial systolic pressure. Some monitors use two cuffs on adjacent fingers alternately for preset periods to give time for one finger to return to normal while the other is being used, and some come with an automatic height (hydrostatic pressure) correction unit. The vascular unloading method can also be implemented by keeping only part of the circumference of the arterial wall in an unloaded state, to reduce venous congestion.
Kim-Gau Ng. Review of measurement methods and clinical validation studies of noninvasive blood pressure monitors: accuracy requirements and protocol considerations for devices that require patient-specific calibration by a secondary method or device before use. Blood Pressure Monitoring 2011, Vol 16 No 6, pp 291-303.
This page is maintained by Christopher J. Adams.
It was last updated 14 October 2012.Copyright (c) 2012 Christopher J. Adams
This work is licensed under a Creative Commons Attribution 3.0 Unported License
