- 00:07Overview
- 01:26Principles of Blood Pressure
- 03:10Wireless Blood Pressure Measurement Technique for Humans
- 04:09Noninvasive Blood Pressure Measurement Technique for Rodents
- 06:49Results
- 08:14Applications
- 09:08Summary
非侵襲的な血圧測定技術
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Overview
ソース:ハムナ・J・クレシとクレイグ・J・ガーゲン,インディアナ州パデュー大学,パデュー大学,ウェルドン・スクール・オブ・バイオメディカル・エンジニアリング
ここでは、ヒトとげっ歯類の非侵襲的な血圧測定技術の主な類似点と相違点を取り上げ、血圧を支配する工学原理を検討する。収縮期および拡張期圧を獲得するために現在のカフ技術を支配する原則についても議論する。
モバイルデバイスと接続する市販のカフスは、一般的にコンパクトでポータブルなので、ほぼすべての場所で測定を行うことができる。非侵襲的な、携帯用血圧カフは、高血圧および血圧の変化の注意深い監視および早期発見を必要とする他の心血管の問題を有する患者にとって特に有用である。
同様に、非侵襲的な血圧測定システムはげっ歯類のためにまた利用できる。この技術は実験室の設定で使用され、研究全体を通して動物の健康を監視するために有用である。放射線テレメトリはげっ歯類の血圧測定のゴールドスタンダードですが、この技術は侵襲的であり、誤って行われると動物の死亡率につながる可能性があります。従って非侵襲的な方法は装置の注入を必要とせずに貴重なデータを提供できるので動物の測定のためによい。市販のシステムは、臨床環境外のヒトで血圧を測定する方法を実証するために使用されます。この技術は、患者がこれらの測定を行うたびに診療所を訪問することなく、定期的に自分の血圧を監視することができます。
ここで説明する方法は、圧力センサと閉塞カフを使用してげっ歯類の尾部を通る血流を利用する。ヒト用の移動式血圧カフとげっ歯類用の非侵襲的な尾カフ法の両方が、同様の血行力学的原理を利用して、臨床医、研究者、および患者。
Principles
Procedure
Results
A typical graph obtained from taking rodent blood pressure using a noninvasive blood pressure system is shown in Figure 1. There are two curves on the graph: one for the VPR sensor and one for the occlusion cuff. The inflection points of the VPR sensor curve are where systolic and diastolic blood pressures are determined, as depicted in Figure 1. A status is indicated at the bottom of the figure that communicates whether this measurement is deemed acceptable by the system. In order to obtain acceptable readings, blood pressures are taken multiple times per trial.
Figure 1. Systolic and diastolic blood pressures obtained by a noninvasive measurement system.
Figure 2. Screenshot of systolic and diastolic blood pressure.
For a commercially available cuff for humans, the results of the blood pressure measurement are outputted on a screen as shown in Figure 2. Users can see their systolic and diastolic blood pressure measurements using this technology. Blood pressure can be taken multiple times so that the results output an average of the data that was collected.
Applications and Summary
Both commercial cuffs available for at-home use and noninvasive methods for animal research studies take advantage of automated technologies. By tracking changes in blood flow with sensors, algorithms detect the systolic and diastolic pressures and then communicate these results to users. While technologically similar, there are some key differences between the two measurement techniques that should be noted. When taking blood pressures in human subjects, the environment is typically relaxed as the subject is unrestrained and fairly comfortable. Conversely, animals must be restrained or anesthetized. Restraining can make the animal anxious and therefore skew blood pressure measurements to be higher, whereas anesthesia can lead to hypothermia and vasoconstriction, making reliable measurements even harder to acquire. This is why it is preferable to obtain rodent blood pressures in conscious animals that are in a calm, dimly lit environment where they can be kept warm with no startling noises. Vasodilation through heating is also used when rodents are having their blood pressure measured to promote blood flow through their tail. Acclimating animals to the holder and cuffs before acquiring data can help reduce discomfort and allow collection of more accurate results. Also, if a user is collecting measurements from the same animal on multiple days, the results will be more meaningful if acquired at roughly the same time each day.
Being able to take blood pressure measurements with a user-friendly, compact cuff is an extremely useful tool for patients as it allows patients to monitor their blood pressures at their own convenience. Commercially available blood pressure cuffs, however, are not meant to replace clinically obtained measurements; rather these cuffs are meant to help patients monitor their systemic blood pressure between visits. Commercial cuffs are also subject to noise and do not always collect accurate results. Similarly, noninvasive measurements of rodent blood pressure are also noisy, especially when the animal moves. As such, it is important to be judicious when looking at data from these systems.
Portable noninvasive blood pressure measurement methods are useful for a variety of applications. Commercial cuffs allow hypertensive patients to monitor their health between visits to the clinic. This method can help patients become more conscious of their dietary and exercise decisions, as they can see the direct impact that their lifestyle has on their blood pressure. Commercial cuffs can also help pregnant women track their blood pressures in the final months of their pregnancies. Pregnant women are at risk for developing preeclampsia. Therefore, it is important for these women to know if they are at risk for this condition during the latter half of gestation. Using a portable cuff helps these women track their blood pressure in the critical months before the baby is born.
For animal use, noninvasive blood pressure measurements are valuable for research purposes, especially those regarding cardiovascular health. Taking blood pressures of animals after procedures and studies, such as those inducing hypertension in rodents, can show the effects of these actions on an animal's health. While other invasive techniques can provide more consistent data, the noninvasive nature of tail-cuff systems make them an attractive method for those using animal models of cardiovascular disease.
Transcript
Blood pressure measurements are often used to monitor cardiovascular health. Blood pressure is the lateral pressure produced by circulating blood on vessel walls. Close monitoring is important to detect and treat hypotension, low blood pressure, and hypertension, high blood pressure, both of which can impair the function of vital organs, such as the heart, kidneys, and brain.
Blood pressure is measured manually by auscultation, where the clinician occludes the artery using an inflatable cuff and then listens for the sound of blood flow through the brachial artery as it deflates. Blood pressure can also be measured automatically by oscillometry, which allows patients to measure their blood pressure at home. The inflatable cuff contains a pressure transducer that converts the arterial vibrations to systolic and diastolic pressures based on hemodynamic principles.
This video will illustrate the principles of blood pressure, demonstrate the current methods to measure the systolic and diastolic blood pressures of humans and small animals, and discuss some applications.
Blood pressure measurements consist of systolic and diastolic components, both of which are important indicators of cardiovascular health.
The systolic blood pressure is a measure of the maximum intraluminal pressure exerted against the artery during heart contraction when your heart beats, and the diastolic pressure is a measure of the minimum intraluminal pressure, or the pressure in between beats when the heart relaxes and the aortic valve is closed. To measure blood pressure, a cuff is placed on the patient’s upper arm and then inflated to the point where blood flow is completely occluded. As the cuff deflates, the clinician auscultates while observing the manometer readings.
The first audible Korotkoff sound corresponds to the systolic pressure, the pressure at which blood begins to flow again through the open vessel. As the cuff continues to deflate, blood flows more freely as the vessel remains open. Diastolic pressure is recorded at the point when the clinician no longer hears the beating sound or the self-monitoring device detects a leveling-off of oscillations.
A similar method can be used to monitor rodent blood pressure. A cuff is inflated and deflated around the tail artery, while a pressure transducer detects systolic and diastolic pressure. Now that you understand the difference between systolic and diastolic pressure, let’s demonstrate how to measure blood pressure using a wireless cuff for humans and a noninvasive technique for rodents.
Turn on the wireless cuff and the mobile device and open the cuff application. Then, pair the devices via Bluetooth and open the cuff application on the mobile device. Then, strap the cuff onto your upper arm. Make sure that the blood pressure monitor is placed against your inner bicep. The strap should be secured tightly on your arm. Sit in a position so that the cuff is at the same level as your heart. Make sure you are calm and relaxed before starting.
Now, begin the blood pressure measurement by pressing start. Each measurement takes about one to three minutes. Repeat the measurement several times to obtain an average value in the results. The result will be displayed on the screen of the mobile device. After saving the results, unstrap the cuff from your arm and shut off the device.
To measure the blood pressure of a rodent, first turn on the desktop computer, blood pressure system, and heated stage. Then, attach the VPR cuff and occlusion cuff to the blood pressure system. Use software to confirm that the cuffs are properly calibrated and working as expected. Choose the appropriate parameters for data acquisition. Parameters include deflation time, the number of sets per cycle, occlusion pressure, and the delay between sets. Occlusion pressure is typically set to 250 millimeters of mercury, and there are usually 20 sets per cycle. Other parameters can be specified based on user needs.
Calm the animal to prevent it from experiencing unnecessary stress. The environment should be quiet, with minimal noise. Then, place the animal in an appropriately sized holder. Make sure the animal’s paws do not get stuck in the attachments of the holder and that the tail is outside of the restrainer. Now, place the holder on the heated stage. Slide the occlusion cuff, followed by the VPR cuff onto the base of the tail, approximately one to two millimeters apart. Once the cuffs are in place, tape them to the stage. This will restrict tail movement.
Then, heat the tail to 32 to 34 degrees Celsius to promote vasodilation and blood flow through the tail. As the stage is warming, choose the type of animal on the computer whose blood pressure you will be acquiring and then enter its animal ID into the system so you can access its data later. Once the stage is sufficiently heated, start acquiring blood pressure data by pressing start. Try to maintain a calm environment. Keep the position of the cuff constant and make a note if the animal moves substantially. If the cuffs slide down the tail, or if the animal moves inside the restrainer, press the pause button, then make adjustments after the current measurement is completed, and resume testing.
Check to make sure the blood pressure data are being acquired as expected. Collect 20 to 40 measurements. Once all data has been collected, remove the animal from the holder and place it back into a cage. Then turn off the equipment and clean the surfaces that were in contact with the animal.
The results using the blood pressure monitor for humans are outputted on a screen as shown. Using this technology, systolic and diastolic blood pressure measurements are displayed and multiple readings are averaged.
Healthy blood pressures in humans are typically below 120 millimeters of mercury for the systolic pressure and below 80 millimeters of mercury for the diastolic pressure. Blood pressures above these values could indicate that a patient is starting to develop high blood pressure, which can lead to further health complications.
Here is a typical graph that is obtained when taking rodent blood pressure. The two curves on the graph represent data collected from the VPR sensor, the blue line, and the occlusion cuff, the red line. The inflection points of the blue curve are used to calculate the systolic and diastolic pressure. The measurements are listed at the bottom of the graph along with the OK status, which indicates that this measurement is deemed acceptable by the system.
Typical blood pressure measurements for mice are around 120 over 70 millimeters of mercury, whereas rats have slightly higher blood pressures at around 130 over 90 millimeters of mercury.
Now, let’s take a look at how blood pressure is noninvasively measured in the public and scientific community.
Portable noninvasive blood pressure cuffs allow hypertensive patients to monitor their health between visits to the clinic. Pregnant women at risk for developing pre-eclampsia can monitor their risk for this condition in the critical months before the baby is born.
Research on the development of new therapeutic agents requires frequent blood pressure assessment. While invasive techniques such as subcutaneous telemetry and carotid artery cannulation in mice provide long-term blood pressure data, noninvasive tail-cuff systems are an attractive method to monitor the blood pressure in animal models of cardiovascular disease.
You’ve just watched JoVE’s introduction to blood pressure measurement techniques. You should now understand how noninvasive measurement methods are used for both humans and rodents and how the technology is applied to improve health monitoring for the community. Thanks for watching!