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2010 3rd International Conference on Biomedical Engineering and Informatics (BMEI 2010)

In Vivo Animal Experimental Research of Magnetic Nanoparticles Influence on Pulse Wave

Yupeng Yao, Shouliang Qi, Jingshu Zhang, Bo Song, Cong Feng, Lisheng Xu Sino-Dutch Biomedical and Information Engineering School

Northeastern University Shenyang, China

Abstract—In vivo animal experimental research is performed to study the influence of magnetic nanoparticles on the pulse wave. An interventional pulse wave transducer is connected to the rabbit’s blood circulation through the ingenious two-end carotid intubations, so that the pulse wave with low noise could be acquired. The data obtained before and after the injection of the magnetic nanoparticles, which have the diameter of 20 nm, is processed and compared in both time and frequency domain. It is found that after injection, pulse wave height is about 10 mmHg higher, and its interval is about 4.55% longer. While the fluctuation of respiration is much more gently, the acuity of pulse wave fluctuation increases. It is likely to say that injection has elevated the blood pressure and brought down the excitation of the rabbits. According to the relationship between the blood pressure and the blood viscosity of human body, the injection of nanoparticles has increased the blood viscosity of the rabbit. The results are very instructive for the study of in vivo transport of magnetic nanoparticles, which is the base of targeted drug delivery, hyperthermia and embolism therapy using nanoparticles.

Keywords-nanoparticles; pulse wave; viscocity; in vivo

I. INTRODUCTION Magnetic nanoparticles (MNPs) have wide potential

application in biomedical fields for their many unique features. Small size makes them easily escape the recognition and clearness of the reticuloendothelial system (RES) of liver and spleen [1]. With surface coating, the perfect biocompatibility helps nanoparticles evade the body's defense system and protect the drug from premature degradation. Multifunctional properties let it possible to realize targeted diagnosis (multimodalities imaging) and integrated treatment (thermotherapy, chemotherapy, radiotherapy and genotherapy) [2, 3]. MNPs can be manipulated by external magnetic field and used to MR imaging and theromtherapy [4, 5]. It is reported the targeted drug delivery system using MNPs have entered the mainstream [6].

However, nanoparticles medial applications face up the complex realities as well. It is because to explain the behaivour of living system is necessary for these applications, which is not a facile matter [7, 8]. The influence of nanopartices on the blood flow is not investigated in depth. The experimental study of nanoparticles flowing in vivo proves to be difficult because mixing the nanoparticles into the blood will change its viscosity, the direction of which is difficult to estimate.

Meanwhile the viscosity may affect on the blood pressure. Wang et al. [9] had compared blood rheology indexes between blood from hypertensive patients and healthy persons, they found out that blood viscosity of the former one is much higher than that of the latter one, especially at the low share rate. Artery blood pressure varies when cardiac output and peripheral resistance change. The peripheral resistance is the product of vascular impedance and whole blood viscosity. Thus, rise of blood pressure is related to cardiac output, vascular impedance, especially the whole blood viscosity. Wang et al. [10] also found that many indexes of whole blood viscosity of hypertensive patients are higher than that of healthy persons.

The present works aim to study the influence of nanoparticles on the wave pulse through the in vivo animal model experiments.

II. MATERIAL AND METHOD

A. Materials Six health rabbits with weights ranging in 3.1 ± 0.4 Kg are

provided by China Medical University while only one experiment is successful. Normal saline, heparin and urethane (20% solution of urethane) are from Sinopharm Chemical Reagent Co., LtdS. Nano-particles of 20 nm diameter is from Nanjing Emperor Nano Material Co., Ltd., and have the purity of 99%. Setting the ammonium citrate as the dispersant agent and the distilled water as the dilution agent, the nanoparticles suspension with the mass concentration of 1.0% can be prepared after half an hour’ mechanical agitation and ultrasound dispersion. The pressure transducer is from Chengdu Taimeng Co., Ltd.

B. Animal Methods Rabbits are chosen as the animal model for the rabbit has

the similar physiological parameters of wave pulse with human being. And Rabbit’s auricular vein is a good site for drug injection due to its well superficial exposure. In order to get the pulse wave with low noise, an interventional pulse wave transducer is connected to the rabbit’s blood circulation through the ingenious two-end carotid intubations. The brief diagram of the in vivo experiment system is shown in Figure. 1(a). There is the small operation space to finish the two-end carotid intubations for the rabbit carotid is very short, which

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increases the experiment difficulties. Hence the detailed animal experiment methods are described as following.

• Full calibrated pressure sensor (pressure transducer) and arterial cannula with heparin by syringe and three-port valve to prevent blood coagulation on the pipeline.

• Anesthetize the rabbit through auricular vein injection of urethane with 1 g/kg according to the body weight.

• After the rabbit’s corneal reflex disappearance, fix it on the dissecting table.

• Use a scalpel to incise down to the sternum level from the thyroid cartilage for about 5 cm. Use the surgical scissors to cut the skin, stretch out the skin and muscle tissue with a hemostat to expose jugular blood vessels, nerves and trachea. Separate the jugular blood vessels and nerves to find the common carotid artery.

• Systemic heparin is realized through auricular vein injection. Clamp the left/right common carotid artery (LCCA / RCCA) with two arterial clips on proximal part and distal end respectively.

• Cut two 30 degree oblique incision on the vessel wall (VW) respectively beside the two arterial clips, and intubate LCCA / RCCA to proximal part and distal end with the prepared arterial cannula.

• Tie and fix the blood vessel with saline soaked sutures at the intubations site.

The pressure transducer is connected with the four-channel physiometry, and sampling frequency is set to be 800 Hz. After that, we remove the artery clips, the blood pulse signals under normal conditions before injection of nano-particle solution are then measured and recorded. The final version in the experiments is shown in Figure. 1(b).

C. Analysis on Achieved Data After pulse wave data of the whole process was acquired,

analysis was implemented in both time and frequency domains. The whole data contain two parts: pre-injection and post-injection. Each part is of three different statuses: normal, distal-end-shut and proximal-end-shut status. Time-domain analysis is achieved by finding out peaks and valleys of the pulse waves and calculating differences and variances of peak-valley heights.

Frequency domain analysis is implemented utilizing Fast Fourier Transform (FFT) method. After acquired the FFT of a segment of time-domain data, each line from the former one indicates a periodic variation of the latter one, and its height refers to the acuity of the fluctuation amplitude.

(a)

(b)

Figure 1. In vivo experiment system: (a) a brief diagram of the system; (b) a real picture during the experiment.

III. RESULTS

A. Comparison between blood pressure performance in normal status and when distal end is shut before injection in the time domain One hundred periods of pulse wave interval data in normal

and distal-end-shut status is sampled and processed. The average of all values, peak values, valley values and peak-value heights is calculated respectively, shown in Figure. 2.

Figure 2. Average Data of Normal and Distal-End-Shut Status without Injection

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It is obvious that before injection, the blood pressure of distal-end-shut status is 30 mmHg higher than that of the normal status, and the peak-value height is 7 mmHg higher, which indicates that pulse beats stronger after injection.

B. Comparison between pre-injection and post-injection performances in normal status in time domain One hundred periods of pre-injection and post-injection

data in normal status is sampled and processed in the time domain, the average and variance of all values, peak values, valley values and peak-valley heights are calculated, and shown in Figure. 3.

(a)

(b)

Figure 3. (a) Average data of pre-injection and post-injection of normal status; (b) Variance data of pre-injection and post-injection of normal status

It can be seen that average blood pressure after injection is about 10 mmHg higher than that of before, but the peak-valley height is 2 mm lower in normal status. While variances all decrease, and pulse wave interval increases about 4.55%, from 0.22 s to 0.23 s. These results indicate that pulse fluctuation becomes slower, steadier and more gently after injection.

C. Comparison between pre-injection and post-injection performances at distal-end-shut status in time domain Using the same way, the pre-injection and post-injection

data in distal-end-shut status is processed in the time domain. The average and variance of all values, peak values, valley values and peak-valley heights are calculated, as shown in Figure. 4.

The results are generally similar to the case of normal status, but the peak-valley doesn’t decrease much.

(a)

(b)

Figure 4. (a) Average data of pre-injection and post-injection of distal-end-shut status; (b) Variance data of pre-injection and post-injection of distal-end-

shut status

Based on the above analysis the average pulse pressure is about 10 mmHg higher after injection. So if one knows the blood pressure at distal-end-shut status, the value of normal status can be deduced. For the works conducted by Wang et al. [9] in human body, the rise of pulse pressure may indicate the increase of blood viscosity in rabbit model.

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D. Comparison of blood pressure in frequency domain

(a)

(b)

Figure 5. Frequency domain analysis of pre-injection and post injection: (a) in normal status; (b) distal-end-shut status.

TABLE I. SPECIFIC VALUES OF FIGURE.5

Status Respiration Pulse Wave

Freq. (Hz) Energy Freq. (Hz) Energy

Normal

Pre-Injection 0.80 4.641 4.55 4.455

Post-Injection 0.70 2.527 4.30 5.652

Distal-End-Shut

Pre-Injection 0.85 6.392 4.55 8.067

Pose-Injection 0.75 5.585 4.35 9.165

The data of pre-injection and post-injection in normal and

distal-end-shut statuses is analyzed in frequency domain, and the results are shown in Figure. 5(a) and 5(b), respectively. There is a feature line at about 0.8 Hz, which is considered to be the respiration frequency. Another one at 4.5 Hz around denotes the frequency of pulse wave of the rabbit. The quantified data is listed in Table 1. It shows some similarity in features of the data, i.e., the respiration amplitude is much more

gently while pulse wave fluctuation is acuter after injection. Meanwhile the frequencies of both situations decrease, which means respirations and pulse waves become slower.

IV. CONCLUSION

Two-end carotid intubations can be used to investigate the pulse wave and the related hemodynamic parameters in vivo. Injection of nanoparticles leads to the pulse wave alternations, and these alternations can be quantified by the pulse wave analyzing approaches. It is found that, pulse wave height increases 10 mmHg after injection of nanoparticles, and the interval grows about 4.55%. While the fluctuation of respiration is much more gently, the acuity of pulse wave fluctuation increases. According to the relationship between the blood pressure and the blood viscosity of human body, it is deduced the injection of nanoparticles has increased the blood viscosity of the rabbit. Nanoparticles’ behaviors in vivo are complicated, but critical for biomedical application and can be widely researched further.

ACKNOWLEDGMENT

The authors would like to thank the help provided by Danqi Chen, Yuan Lv and Yan Zhao from Department of Medical Genetics, China Medical University during the in vivo animal experiments.

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