Tonometry

Overview:

Blood pressure is a widely used parameter in cardiovascular assessment. Therefore, non-invasive blood pressure recording methods are important when invasive techniques are not possible. Auscultatory, oscillometric and volume-clamp measurements are common non-invasive blood pressure recording methods, which do not require complicated setup, and are relatively comfortable for the subject or animal.

Non-invasive blood pressure recording requires particular care to ensure reproducible and accurate recordings. These methods are often inaccurate due to difficulties in calibration. Continuous recordings are often impractical as the technique requires partial or total occlusion of blood flow. If occlusion techniques are applied, it is important to ensure that the ischemic period is limited.


 

Method:

Non-Invasive Techniques for Humans

Peripheral Blood Flow Occlusion
Systolic blood pressure may be determined by the return of peripheral blood flow following arterial occlusion. The brachial arterial may be occluded using a Sphygmomanometer and peripheral blood flow in the finger measured using a:

• Piezo Electric Pulse Transducer to convert force applied to the active surface of the transducer from the finger blood pressure pulse into an electrical signal.
• Infrared Plethysmograph (finger clip) photoelectric sensor to record changes in blood volume as the arterial pulse expands and contracts the microvasculature

The Finometer MIDI is a non-invasive continuous blood pressure measuring system used to monitor the brachial arterial pressure via a finger arterial pressure measurement. Beat-to-beat values of systolic, diastolic and mean pressure can be recorded. The Finometer MIDI features hydrostatic height correction, remote and automatic control. Optional hardware may be ordered separately for recording ECG, viewing the finger pressure waveforms, and calculating cardiac output using Beatscope software.

Note: Other third-party products that operate according to tonometry or volume-clamp techniques may connect to PowerLab data acquisition systems provided they have a suitable analog output (±10V).

Oscillometry
Peripheral blood flow to the arm or wrist is occluded using an inflatable cuff such as a Sphygmomanometer. A calibrated Pressure Transducer is then used to record the pressure oscillations within the cuff following the return of blood flow.

The sphygmomanometer cuff is inflated to a pressure greater than the systolic arterial pressure and then reduced to below diastolic pressure. When the cuff pressure exceeds the systolic pressure, blood flow is non-existent and the cuff pressure is essentially constant. When cuff pressure is below diastolic pressure, blood flow is unimpeded and the cuff pressure is essentially constant. When blood flow is present, but restricted, (i.e. between systolic and diastolic occlusion pressures), the cuff pressure (monitored by the pressure transducer) will vary periodically in synchrony with the cyclic expansion and contraction of the brachial artery. Therefore, the pressure signal oscillates corresponding to systolic and diastolic arterial pressure.

Auscultatory
The auscultatory technique also involves occlusion of arterial blood flow using an inflatable cuff such as a Sphygmomanometer. However, rather than using cuff oscillations to determine the systolic and diastolic blood pressures, an Electronic Stethoscope is applied to the brachial artery to detect Korotkoff sounds following the return of blood flow.

The sphygmomanometer cuff is inflated manually by repeatedly squeezing the rubber bulb until the artery is completely occluded. The stethoscope is used to listen to the brachial artery at the elbow as the pressure in the cuff is slowly released. The first Korotkoff sound can be heard (usually a loud whoosh) when blood just starts to flow through the artery. This corresponds to the systolic arterial pressure. As the cuff pressure is further released, no sound can be heard and this corresponds to the diastolic arterial pressure.

Non-Invasive Techniques for Animals

Tail Blood Flow Occlusion
ADInstruments supply non-invasive blood pressure or NIBP Systems, used in conjunction with a PowerLab system, to obtain non-invasive blood pressure measurements from tails of rats and mice using methods similar to the peripheral blood flow occlusion technique as discussed previously.

Small animal NIBP systems operate by occluding blood flow to the tail using a specialized tail cuff and pulse transducer to intermittently measure blood pressure based on the periodic occlusion of tail blood flow.

Software:

The LabChart Advantage:

(may require additional Modules and Extensions)

• LabChart data files can be marked with events using the Comments feature
• Maximum (systolic), minimum (diastolic) and average (mean arterial) signal amplitudes can be calculated using the Data Pad
• The Units Conversion feature can be used to convert signals into relevant units e.g. mmHg
• Macros can automate many tedious and repetitive analysis tasks
• Data smoothing and arithmetic calculations required to correctly identify pressure oscillations and can be performed using LabChart’s Smoothing (Savitzky-Golay) and Arithmetic functions
• The Blood Pressure Module can automatically detect and analyse arterial pressure waveforms recorded by the Finometer MIDI

LabChart

LabChart software (for Windows and Macintosh) together with a PowerLab data acquisition system offers up to 32 channels of real-time data acquisition, data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Additional acquisition and analysis functionality is provided with the use of specialized LabChart Extensions and LabChart Modules. Modules are available as part of LabChart Pro while Extensions are free for download from the website for existing LabChart users.

Rodent Non-Invasive BP (using NIBP System)

Blood Pressure Module

The Blood Pressure Module (Windows) provides easy data extraction and analysis of cardiovascular parameters from arterial or ventricular pressure signals.

It provides:

• Real-time analysis and data extraction of pressure parameters
  • Max and min pressures
  • Max and min dP/dt
• Analysis of blood and cardiac pressure in real-time or offline
• Automated detection of pressure cycles
• Automated tabulation and data extraction of pressure parameters
• Analysis View
  • Averaging of pressure waveforms
  • Automated pressure parameter labeling

BeatScope® Software

In addition to using LabChart software with the Blood Pressure Module, ADInstruments also provide the BeatScope® Easy (Windows) software. The BeatScope® Easy software (purchased separately) in conjunction with the Finometer MIDI provides insight in blood pressure waveforms (i.e. systolic, diastolic and mean arterial pressure) and beat-to-beat trending of blood pressure and heart rate parameters including cardiac output. It features online monitoring, control, storage and offline review of pressure data and heart rate parameters. Additionally, the BeatScope® 1.1a (Windows) offers an extended range of hemodynamic parameters (e.g. Pulse Rate Variability) and additional statistical analyses capabilities, including the offline analysis of stored blood pressure waveform data.

Human Non-Invasive BP (using Finometer MIDI)

GLP and 21 CFR Part 11

For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance, the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

Hardware:

PowerLab Data Acquisition Systems

The PowerLab is a high-performance data acquisition unit capable of recording at speeds of up to 400,000 samples per second continuously to disk (aggregate). PowerLab units are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other third-party companies. In addition to standard single-ended BNC inputs, 4 differential Pod ports are also available for direct connection of Pod signal conditioners and appropriate transducers. Research PowerLab units include:

• PL3504 PowerLab 4/35 - 4 Channels
• PL3508 PowerLab 8/35 – 8 Channels
• PL3516 PowerLab 16/35 – 16 Channels

Instruments

The MLE1054-V Finometer MIDI in conjunction with a PowerLab is a non-invasive stationary blood pressure measurement and beat-to-beat hemodynamic monitoring system for human subjects. The Finometer MIDI captures the continuous blood pressure waveform, which can be recorded and analysed with the PowerLab data acquisition system.

The ML125/R NIBP System in conjunction with a PowerLab is used to obtain non-invasive blood pressure measurements from rats (tail diameters ≤ 10 mm). Includes;

• ML125 NIBP Controller
• MLT125/R Pulse Transducer and Tail Cuff (suitable for rats)

The ML125/M NIBP System is used in conjunction with a PowerLab system to obtain non-invasive blood pressure measurements from mice (tail diameters ≤ 6 mm). Includes;

• ML125 NIBP Controller
• MLT125/M Pulse Transducer and Tail Cuff (suitable for mice)

Signal Conditioners

• FE221 Bridge Amp
• FE224 Quad Bridge Amp
• FE228 Octal Bridge Amp
• ML142 GP (General Purpose) Amp
• ML305 Pod Expander
• ML301 Bridge Pod

Transducers and Accessories

• MLT1100/D Sphygmomanometer (DIN) Connects to any PowerLab Pod port or Pod expander, as well as any Bridge Amp and is supplied with both an adult and child-sized cuff
• MLT1100/A Sphygmomanometer Connects to the Bridge Pod
• MLT206 Electronic Stethoscope Connects directly to the BNC input of a PowerLab using the supplied MLAC08 BNC to 2.5mm plug
• MLT1010 Piezo Electric Pulse Transducer Connects directly to the BNC input of a PowerLab
• MLT1010/D Piezo Electric Pulse Transducer Connects directly to the DIN input of a PowerLab
• SPT-301 Non-Invasive Pulse Tonometer is a hand-held wand probe equipped with a Mikro-Tip pressure sensor at the tip, designed for non-invasive recording of pulse pressure wave contours and requires an AEC-10C Catheter Interface Cable for connection to any Bridge Amp.
• MLT1020FC IR Plethysmograph (Finger Clip) Connects directly to a PowerLab Pod port or can be used with a GP Amp or Bridge Amp

Rat Restrainers

• MLA5020 Rodent Restrainer (80 to 200 g)
• MLA5022 Rodent Restrainer (180 to 320 g)
• MLA5024 Rodent Restrainer (300 to 440 g)
• MLA5025 Rodent Restrainer (440 to 550 g)

Mouse Restrainers

• MLA5016 Rodent Restrainer (up to 35 g)
• MLA5018 Rodent Restrainer (up to 50 g)

MLA5030 Rodent Tail Cuff Holder allows the user to secure the rat or mouse tail transducer and cuff (MLT125/M or MLT125/R) when attached to a mouse or rat tail.

Note: A selection of spare parts are also available for the rodent NIBP systems.

Sex differences in limb vasoconstriction responses to increases in transmural pressures
Lott M E, Hogeman C, Herr M, Bhagat M, Sinoway L I, American Journal of Physiology: Heart and Circulatory Physiology, H186–H194, 2009

Proteinuria in mice expressing PKB/SGK-resistant GSK3
Boini K M, Amann K, Kempe D, Alessi D R, Lang F, American Journal of Physiology: Renal Physiology, F153–F159, 2009

Cardioprotective effects of nitric oxide-aspirin in myocardial ischemia-reperfused rats
Fu Y, Wang Z, Chen WL, Moore PK, Zhu YZ, American Journal of Physiology: Heart and Circulatory Physiology, H1545–H1552, 2007