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Ann Thorac Surg 2004;78:167-172
© 2004 The Society of Thoracic Surgeons

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Original article: cardiovascular

Instant myocardial blood flow monitor: its calibration and assessment of flow capacity of the intracoronary shunt tube

^a Department of General and Cardiothoracic Surgery, Kanazawa University School of Medicine, Kanazawa, Japan

Accepted for publication December 10, 2003.

^* Address reprint requests to Dr Kamiya, Department of General and Cardiothoracic Surgery, Kanazawa University School of Medicine, Takaramachi 13-1, Kanazawa 920-8641, Japan
e-mail: h.kamiya{at}triton.ocn.ne.jp

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
BACKGROUND: We developed a new instant regional myocardial blood flow (RMBF) monitor utilizing the thermal diffusion method in which the RMBF value is presented as the value inversely proportional to the thermocouple voltage output (1/V). The purposes of this study were (1) to validate the accuracy of RMBF measurement by the instant RMBF monitor in comparison with the colored microsphere method for calibration; (2) to investigate influences of it on the RMBF; and (3) to assess changes in RMBF caused by the shunt tube insertion.

METHODS: Twenty pigs were used for this study: 4 for comparison between the instant RMBF meter and the colored microsphere method, 4 for validation of reproducibility, and 6 for measurement of RMBF during shunt tube.

RESULTS: The relation between RMBF values obtained by the colored microsphere method and 1/V values by instant RMBF monitor was colored microsphere = 140,992 (1/V) – 231 in epicardial layer (R² = 0.819) and colored microsphere = 111,381 (1/V) – 165 in endocardial layer (R² = 0.693). The correlation coefficient and R² values between RMBF values measured by both methods were 0.985 and 0.839 in epicardial layer, and 0.963 and 0.679 in endocardial layer, respectively. The RMBF at each layer did not change after the attachment of the monitor. Fifteen minutes after shunt tube insertion, RMBF measured by the colored microsphere method decreased to 31.1% (p = 0.0001) and 33.7% (p = 0.0001) in epicardium and endocardium, respectively, and no difference was observed from the value measured by the instant RMBF monitor.

CONCLUSIONS: This instant RMBF monitor can provide instantaneous and continuous information of RMBF without requiring tissue examination.

	Introduction

Top Abstract Introduction Material and methods Results Comment References

 
Until recently, there had been no method that could measure regional myocardial blood flow (RMBF) instantly and continuously. In our previous study, we employed a thermal diffusion method to assess RMBF, and demonstrated that RMBF could be measured instantly and continuously. In this study, the measurement using the thermal diffusion method significantly correlated with RMBF measured by an electrolytic hydrogen clearance method [1]. However, the thermal diffusion probe that we used in the previous study was sutured directly on the heart surface, and concern remained that it might adversely affect the myocardium.

We devised a new instant RMBF monitor using a thermal diffusion probe that is attached to the heart surface with a suction system. Suction systems including a stabilizer and a heart positioner have been applied widely in off-pump coronary artery bypass graft (OPCABG) surgery as a safe and effective method. There was the possibility that the suction system applied for the new thermal diffusion probe may influence the RMBF itself, however, and the problem had to be investigated in experiments. Moreover, the new thermal diffusion probe required a calibration study comparing it with another established method.

The purposes of this study were (1) to validate the accuracy of RMBF measurement by the instant RMBF monitor in comparison with the colored microsphere method for calibration; (2) to investigate influences of the new thermal diffusion probe on the RMBF; and (3) to assess changes in RMBF caused by the shunt tube insertion.

	Material and methods

Top Abstract Introduction Material and methods Results Comment References

 
Thermal diffusion method and instant RMBF monitor
The thermal diffusion method is based on the linear relationship between blood flow and the heat conductivity change in tissue [1–4]. The instant RMBF monitor (BTG-221; Biomedical Science, Kanazawa, Japan) consists of a body part that receives thermal diffusion signals and a vacuumed cuff that enables close attachment between the heart surface and the body part (Fig 1). The body part covered regional myocardium 12 mm in diameter. The body part consists of a Peltier stack with gold plates arranged so that the voltage output is proportional to the temperature difference between the plates. Activation of the stack creates a temperature gradient between the plates that brackets the ambient heart temperature. Blood flow changes temperature gradients cool the heated plate and warm the cold plate, causing a decrease in the thermocouple voltage output. Thus, theoretically the tissue blood flow is inversely proportional to the thermocouple voltage output, and these two variables should be presented in a simple linear regression [1, 4].

View larger version (116K): [in this window] [in a new window]   Fig 1. The new thermal diffusion probe. (A) A downward view of the probe. (B) The probe attached to the heart surface. The body part of the probe was closely attached against heart beat motion.

where C_T and C_R are the absorbances from dispersed microspheres in the tissue and reference blood sample, respectively; F_R is the reference rate; and W_T is the total weight of the tissue sample in grams. Results are expressed as milliliters per minute per 100 g of tissue.

Animal preparation
All animals received human care in compliance with the "Principles of Laboratory Animals Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the Institute of Laboratory Animal Resources and published by the National Institute of Health (NIH Publication No. 86-23, revised 1985).

Twelve healthy pigs weighing between 25.0 and 35.0 kg (average weight 29.5 ± 3.4 kg) were used. Anesthesia was induced with an intramuscular administration of ketamine hydrochloride (20 mg/kg). After trachiotomy, a cuffed endotracheal tube was inserted, and ventilation was performed with a volume-regulated ventilator (KMA-1300IIS, Acoma, Tokyo, Japan). Then, muscle relaxation was achieved with pancuronium 0.1 mg/kg through peripheral intravenous access. Anesthesia was maintained with 1% halothene. A 5F catheter was inserted into the ascending aorta through the right carotid artery to achieve continuous aortic pressure. A Swan-Ganz catheter (746HF8; Edwards Lifesciences, Irvine, CA) was inserted in the pulmonary artery through the right internal jugular vein for pressure monitoring and continuous cardiac output measurements (VGSVSVS; Edwards Lifesciences). A polyethylene catheter was inserted into the left atrium for injection of the colored microspheres. Another solid catheter was inserted into the left ventricular cavity through an apical stab wound to measure left ventricular pressure. A 5F catheter was inserted into the right femoral artery to obtain reference samples. After median sternotomy, the heart was elevated in a pericardial sling.

Experimental protocol I
For experimental protocol I (n = 4) using the thermal diffusion method, the RMBF value should be calculated as follows [3]:

where is a coefficient value, and I is an intercept value; V is the voltage difference of the thermocouples. The purpose of this protocol was to compare the V value obtained by the thermal diffusion probe with the RMBF value obtained by the colored microsphere method, and to determine and I values.

Five instant RMBF monitors were attached to the heart surface at the left ventricular free wall. Then, colored microspheres were injected into left atrium and reference blood sample was obtained from the femoral artery. The V values obtained by the instant RMBF monitor were simultaneously recorded while the measurements of RMBF by colored microsphere method were performed. The RMBFs were measured under the following conditions: (1) baseline; (2) stress induced by administration of the dopamine concentration of 5 µg · min^–1 · kg^–1; (3) further stress induced by administration of the dopamine concentration of 10 µg · min^–1 · kg^–1; (4) systemic hypotension induced by increasing concentration of halothene up to 1.5%; and (5) further systemic hypotension induced by increasing concentration of halothene up to 2.0%. Then pigs were sacrificed by administration of a fatal dose of halothene and potassium chloride injection through the left atrial catheter. Myocardial tissue just under the instant RMBF monitor was excised and the sample was separated to the subepicardial block and the subendocardial block. The RMBF was calculated separately for epicardium and endocardium.

The and I values were calculated separately each for epicardial RMBF (epi and Iepi) and endocardial RMBF (endo and Iendo) using a linear regression analysis.

Experimental protocol II
The purpose of this protocol (n = 4) was to confirm the reproducibility of the instant RMBF monitor compared with the colored microsphere method. Five instant RMBF monitors were attached to the heart surface as in the experimental protocol I. The RMBFs were measured by the thermal diffusion method with and I values calculated in the protocol I, and by the colored microsphere method. This protocol was underwent with the heart condition identical to protocol I. Then, correlations between RMBF values of the instant RMBF monitor and the colored microsphere method were analyzed using the linear regression analysis.

Experimental protocol III
The purposes of this protocol (n = 6) were to investigate influences of the instant RMBF monitor on the RMBF and to assess RMBF during the shunt tube insertion. At first, colored microspheres were injected into left atrium, and reference blood sample was obtained from the femoral artery for baseline RMBF measurement. Then, the instant RMBF monitor was attached, and the same manipulation for RMBF measurement by colored microsphere method was repeated. Simultaneously, epicardial and endocardial RMBFs were recorded using the instant RMBF monitor. After reversible ligation of the left anterior descending coronary artery, an arteriotomy was performed at a point just proximal to the first diagonal branch through which a 2.0 mm intracoronary shunt tube (AnastaFLO; Baxter Healthcare, Edwards Division, Santa Ana, CA) was inserted. The outer diameter of the shunt was 90% of the left anterior descending artery diameter at the point of insertion. The RMBF was measured 5, 10, and 15 minutes after shunt tube insertion using both methods. At the end of experiments, myocardial samples were prepared by the same procedures taken in the other protocols.

Statistical analysis
Results are presented as the mean ± standard deviation. Simple linear regression was used to analyze the relationship between the RMBF measured by the colored microsphere method and the 1/V value in protocol I, and the relationship between the RMBFs measured by the colored microsphere method and those by the instant RMBF monitor in protocol II. Hemodynamic data and the RMBF measured in protocol III were analyzed by means of one-way analysis of variance for repeated measures to identify intervention interactions. If significant interactions were found, then further pairwise analysis was performed by using Bonferronivalues measured analysis to locate the source of the difference. An unpaired Student's t test was used for comparison of RMBF values measured by colored microsphere method before and after the instant RMBF monitor attachment in protocol III. A p value of less than 0.05 was considered significant. In this study, SPSS 10.0 software (SPSS Japan, Tokyo, Japan) was used for statistical analysis.

	Results

Top Abstract Introduction Material and methods Results Comment References

 
Experimental protocol I
One hundred myocardial samples in each layer were analyzed for RMBF measurement. The epicardial and endocardial RMBF values obtained by the colored microsphere method and 1/V value were plotted for linear regression analysis (Fig 2). Significant correlations were found between 1/V value and RMBF in each layer. The calculated epi, Iepi, endo, and Iendo values were 140,992 (p = 0.0001); 231 (p = 0.0001), 111,381 (p = 0.0001); and 165 (p = 0.0001), respectively. The r values in the epicardial layer and the endocardial layer were 0.905 (p = 0.0001) and 0.832 (p = 0.0001), respectively.

View larger version (19K): [in this window] [in a new window]   Fig 2. Correlation between regional myocardial blood flow (RMBF) measured by the colored microspheres method and 1/V value obtained from the thermal diffusion probe. (A) Epicardial (epi) RMBF and 1/V. (B) Endocardial (endo) RMBF and 1/V.

View larger version (19K): [in this window] [in a new window]   Fig 3. Correlation between regional myocardial blood flow (RMBF) measured by both the thermal diffusion (TD) method and the colored microsphere (MS) method. (A) Epicardial (epi) RMBF. (B) Endocardial (endo) RMBF.

View larger version (20K): [in this window] [in a new window]   Fig 4. Regional myocardial blood flow (RMBF) measured by colored microsphere method in protocol III. (TD = thermal diffusion.)

View larger version (12K): [in this window] [in a new window]   Fig 5. An example of demonstration of regional myocardial blood flow (RMBF) measured by thermal diffusion (TD) method.

	Comment

Top Abstract Introduction Material and methods Results Comment References

The thermal diffusion method is not novel. In 1968, Brawly [6] reported that the Peltier stack commonly used in electrical refrigerators could be used in the thermal diffusion method, and marked improvements in the stability of recordings using this method were thereby obtained. However, the thermal diffusion method had not been applied for RMBF measurement for a long time. In our previous study, we applied the thermal diffusion method for RMBF measurement for the first time [1]. The previous study demonstrated measurement of RMBF by the thermal diffusion method, with simultaneous measurement by the electrolytic hydrogen clearance method for calibration. The study had some problems, however. First, the thermal diffusion probe that we used in the previous study was sutured directly on the heart surface, and concerns remained that it may affect adversely to the myocardium. Second, the electrolytic hydrogen clearance method used for the calibration study is not one of the gold standard methods for RMBF measurement. Third, the previous study did not clarify whether the thermal diffusion probe had measured epicardial or endocardial RMBF, or both.

To solve these problems, we devised the new thermal diffusion probe that attaches to the heart surface with a suction system in order to avoid direct suturing, and in this study, performed its calibration in comparison with the colored microsphere method separately in each myocardial layer. For the measurement of RMBF in experimental cardiology, the radioactive microsphere method has been considered to be the standard method. However, there are disadvantages such as the high cost of the multichannel gamma analyzer required by the technique, and the expense and inconveniency of the disposal of radioactive carcasses. Hale and coworkers [7] demonstrated that the colored microsphere method correlated with the radioactive technique. The colored microsphere method is safe and convenient, requiring no special disposal of carcasses and expensive instrument; and recently this method has become widely applied as one of the gold standard methods for RMBF measurement.

In the present study, calibration of the new instant RMBF monitor was performed separately for epicardial and endocardial RMBFs. The 1/V value obtained by the new probe closely correlated with epicardial and endocardial RMBFs measured by the colored microsphere method. The attachment of the probe did not affect RMBF or any other hemodynamic value. After calibration, RMBF measured by the thermal diffusion probe also closely correlated with that measured by the colored microsphere method in each myocardial layer. That meant that the thermal diffusion method had satisfactory reproducibility to be applied as a method for RMBF measurement.

In addition to examining reproducibility, the intracoronary shunt model was used as one of the models to see RMBF changes caused by shunt insertion. Although off-pump coronary artery bypass is becoming popular with several advantages over conventional coronary artery bypass grafting with cardiopulmonary bypass, concerns still exist regarding myocardial ischemia in the area supplied by the target vessel. Several methods have been devised to avoid or reduce myocardial ischemia during anastomoses, and at present, the most popular method for such purpose with acceptable clinical and experimental results is the one using the intracoronary shunt tube [7–9]. However, Muraki and colleagues [10] demonstrated that RMBF decreased to approximately 30% of the baseline value under normotension, and that it decreased to approximately 10% of the baseline value under hypotension in an intracoronary shunt perfusion model.

In a previous study, we investigated the efficacy of the intracoronary shunt tube in a theoretical model on basis of fluid dynamics [11]. In the report, the coronary flow under intracoronary shunt perfusion was estimated as less than 14% of the preattachment flow. In the present study, however, RMBF under shunt tube perfusion decreased to approximately 30% of the baseline value, similar to results reported by Muraki and associates [10]. The difference between the results in our previous theoretical study and that in the present study may have been caused by the fact that RMBF under the shunt was dominantly supplied by collateral arteries that were immediately induced by acute coronary flow decrease [12].

We demonstrated that RMBF could be adequately measured using the new instant RMBF monitor, but we do not consider that this method is an alternative that will take the place of one of the current gold standard methods of RMBF measurement such as the radioactive or colored microsphere method. However, the instant RMBF monitor has some advantages over these microsphere methods. First, instantaneous and continuous RMBF can be measured, as shown in Figure 3. Second, the thermal diffusion method does not require tissue examination. In an experimental study, the use of the instant RMBF monitor together with the microsphere method may provide accurate and continuous information of RMBF, and it may be useful for investigations of beating heart surgery. Moreover, the thermal diffusion method can be performed with almost no invasion to the myocardium, and it can also be used for further clinical investigations.

In conclusion, RMBF could be measured using the instant RMBF monitor with results closely correlating to those of the colored microsphere method with reproducibility. The attachment of the new probe had no influence on RMBF or any other hemodynamic value. The intracoronary shunt tube had very limited capacity regarding RMBF. This instant RMBF monitor can provide instantaneous and continuous information of RMBF, and it has a potential to contribute to investigations for beating-heart surgery.

	References

Top Abstract Introduction Material and methods Results Comment References

 

1. Kamiya H., Watanabe G., Saito T., et al. Real-time and continuous monitoring of myocardial blood flow using a thermal diffusion method. Eur J Cardiothorac Surg 2002;21:748-752.[Abstract/Free Full Text]
2. Lauritzen M., Fabricius M. Real time laser-Doppler perfusion imaging of cortical spreading depression in rat neocortex. Neuroreport 1995;19:1271-1273.
3. Carter L.P., Erspamer R., Bro W.J. Cortical blood flow: thermal diffusion versus isotope clearance. Stroke 1981;12:513-518.[Abstract/Free Full Text]
4. Koshu K., Hirota S., Sonobe M., et al. Continuous recording of cerebral blood flow by means of a thermal diffusion method using a Peltier stack. Neurosurgery 1987;21:693-698.[Medline]
5. Hale S.L., Alker K.J., Kloner R.A. Evaluation of nonradioactive, colored microspheres for measurement of regional myocardial blood flow in dogs. Circulation 1988;78:428-434.[Abstract/Free Full Text]
6. Brawley BW. The pathophysiology of intracerebral steal following carbon dioxide inhalation, an experimental study. Scand J Clin Lab Invest 1968;102(Suppl):XIII:B
7. Revetti L.A., Gandra S.M. Initial experience using an intraluminal shunt during revascularization of the beating heart. Ann Thorac Surg 1997;63:1742-1747.[Abstract/Free Full Text]
8. Dapunt O.E., Raji M.R., Jeschkeit S., et al. Intracoronary shunt insertion prevents myocardial shunting in a juvenile porcine MIDCAB model absent of coronary artery disease. Eur J Cardiothorac Surg 1999;15:173-178.[Abstract/Free Full Text]
9. Luccheeti V., Capasso F., Caputo M., et al. Intracoronary shunt prevents left ventricular function impairment during beating heart coronary revascularization. Eur J Cardiothorac Surg 1999;15:255-259.[Abstract/Free Full Text]
10. Muraki S., Morris C.D., Budde J.M., et al. Preserved myocardial blood flow and oxygen supply-demand balance with active coronary perfusion simulated off-pump coronary artery bypass grafting. J Thorac Cardiovasc Surg 2002;123:53-62.[Abstract/Free Full Text]
11. Kamiya H., Watanabe G., Kanamori T. Flow simulation of the intracoronary shunt tube for off-pump coronary artery bypass. Eur J Cardiothorac Surg 2003;23:665-669.[Abstract/Free Full Text]
12. Rentrop K.P., Cohen M., Blanke H., et al. Changes in collateral channel filling immediately after controlled coronary artery occlusion by an angioplasty balloon in human subjects. J Am Coll Cardiol 1988;5:587-592.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Hiroyuki Kamiya Go Watanabe Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kamiya, H. Articles by Kawakami, K. Search for Related Content PubMed PubMed Citation Articles by Kamiya, H. Articles by Kawakami, K. Related Collections Cardiac - physiology