2005 Progress Report: Regional Cardiac Blood Flow with Air Particle Exposure

EPA Grant Number: R831917
Title: Regional Cardiac Blood Flow with Air Particle Exposure
Investigators: Godleski, John J. , Okabe, Kazunori , Verrier, Richard
Institution: Harvard University , Beth Israel Deaconess Medical Center
Current Institution: Beth Israel Deaconess Medical Center , Brigham and Women's Hospital, Inc.
EPA Project Officer: Chung, Serena
Project Period: August 1, 2004 through July 31, 2006
Project Period Covered by this Report: August 1, 2004 through July 31, 2005
Project Amount: $473,924
RFA: The Role of Air Pollutants in Cardiovascular Disease (2003) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Health Effects , Particulate Matter , Air

Objective:

The objectives of this research project are to: (1) assess the mechanisms by which exposure to ambient particles exacerbates myocardial ischemia during acute coronary occlusion through assessment of regional myocardial blood flow; and (2) evaluate the role of the autonomic nervous system in regulation of regional myocardial blood flow with coronary occlusion and exposure to ambient particles.

Progress Summary:

During Year 1 of the project, we made considerable progress in the development of techniques to carry out these studies. We purchased and tested new materials for use in these studies. These are Access Technology vascular access ports and balloon occluders that connect to subcutaneously implanted buttons for access. These optimize use of the occlusion model of the coronary arteries as well as provide for the needed access to the left atrium and the aorta in awake, alert animals undergoing studies. We also have optimized the surgical placement of these devices and have tested several sources of fluorescent beads to assess cardiac perfusion.

Figure 1 shows the placement of hardware devices in the animals at surgery. After recovery from surgery, a 3-4 week period is needed for the animals to completely heal, and then undergo training for use in the laboratory and in exposure situations so that the repeated exposure protocols can be used optimally.

Each dog undergoes thoracotomy and permanent tracheostomy. The thoracotomy allows placement of the permanently installed subcutaneously accessed hydraulic balloon occluder placed on the anterior descending coronary artery. A permanent subcutaneous vascular access catheter is implanted in the aorta for sampling arterial blood during the injection of fluorescent beads to assess perfusion, and another is installed into the left atrium as an injection port for the beads. A subcutaneous telemetry transmitter is installed that includes a femoral blood pressure (BP) catheter and two subcutaneous supracardiac electrocardiogram (ECG) leads.

Figure 1. Placement of Hardware Devices at Surgery

Operation Protocol

The dogs are pre-anesthetized using ketamine (10 mg/kg bolus), xylazine (1.5 mg/kg bolus), and atropine (0.04 mg/kg) bolus. An endotracheal tube is inserted to initiate mechanical ventilation with 1.5 percent isoflurane and pure oxygen. Tidal volume and respiratory rate are adjusted, maintaining oxygen tension at >100 mmHg, and arterial oxygen saturation at >93 percent. Anesthesia is maintained by continuous ventilation with 1.5 percent isoflurane and pure oxygen.

The dog is placed on the table in her right decubitus position. After an intercostals rib block, a 14 cm left chest incision is made above the fourth intercostal space. The latissimus muscle is dissected and spared. The scalenus muscle is transected. The serratus ventralis muscle is divided. The intercostal muscles are cut and the chest cavity is entered. The pericardium is opened and the left anterior descending coronary artery (LAD) is then dissected from surrounding myocardium and a balloon occluder is installed around the LAD. The left atrium is partially clamped and double purse string sutures are put in place. A stab incision is made in the center of the purse string and a 7-French silicone vascular access catheter is threaded into the left atrium, and secured in place with the purse string sutures. The pericardium is approximated but not fully closed. The aorta is exposed and dissected from surrounding tissue. The aorta is partially clamped, and a 7 French silicone vascular access catheter is implanted with the double purse string suture method. Three separate 3 mm incisions are made on the back. The balloon occluder tube, and vascular access catheter are tunneled out to theses incisions and secured in the subcutaneous tissue. A chest tube is placed. The ribs are approximated. The seratus ventralis muscle and the scalenus muscle are repaired. An incision is made in the left flank for placement of the telemetry unit. ECG leads are tunneled subcutaneously up to the thoracotomy incision and the leads are sutured in place in a lead II configuration diagonally across the heart from base to apex. The thoracotomy incision is then closed. The femoral artery is dissected free, and the blood pressure probe of the telemetry device is tunneled to that area and implanted in the femoral artery using the vascular surgical technique described above. All incisions are closed in multi-layers. An anterior neck incision is made above the trachea. The trachea is exposed. The anterior neck muscles are sutured to the lateral trachea. The trachea is opened from the second ring to the fourth ring. The skin is sutured to the trachea to make a permanent tracheostomy stoma. The dogs are managed post-operatively in a manner to speed recovery and limit any pain resulting from the surgery. The dogs recover quickly from this surgery, all incisions are usually healed with skin staples removed within 10 days to two weeks. The animals then undergo several weeks of training to be fully comfortable with the laboratory environment and comfortable with our exposure protocols.

Data Collection

In acclimatized dogs, continuous measurements of ECG and arterial BP data are collected using the implanted telemetry device (Data Sciences, Inc.). ECG is analyzed with respect to morphology of the waveforms and potential changes in the level of T-wave alternans, an indicator of cardiac electrical instability. Respiratory parameters are monitored continuously with a respiratory flow probe attached to the permanent tracheostomy. Blood assessments include complete blood counts including white blood count differential, hemoglobin, hematocrit, and red cell count. Subjects are exposed in pairs; one subject is randomly chosen to receive CAPs, and the other receives a sham exposure using filtered air (FA). After one week of rest, this procedure is repeated with each subject being exposed to the alternate inhalate.

For these studies, eight different colors of fluorescent beads are used to assess cardiac blood flow. The first color is given before any exposures are done and without any coronary occlusion. This color defines normal perfusion of the heart. The first exposure is a double sham, so that each dog gets FA for 5 hours, followed by a 5-minute preconditioning coronary occlusion, followed by 20 minutes of rest with ECG monitoring, followed by a second 5-minute occlusion. During this occlusion, fluorescent microspheres of the second color are injected into the left atrium in a 10 second time frame at the 3 minute time point into the occlusion. At this time blood is drawn at a constant rate from the aorta for 1 minute to define the flow rate of beads in the arterial system. This color defines the pattern of blood perfusion in the heart with the coronary occlusion. The next six colors are used to define perfusion with concentrated ambient particles (CAPs) or sham exposures. The schedule is defined based on a coin flip as to which dog of a pair will receive CAPs exposure first, and then on one day of the ensuing weeks the dogs will alternate between CAPs and sham exposures with one dog receiving CAPs and her chamber mate a sham exposure. After each exposure, the dogs undergo two coronary occlusions and a bead injection appropriate for the week. After all eight colors have been injected, the dogs are sacrificed, the heart removed, dissected into pieces each about 1 cm3, and then each piece is digested to recover the fluorescent beads contained in that piece. Four dogs completed this protocol, and two of these have had data analyzed. Two more have analyses in progress, and based on the initial findings that will be described below, two more dogs now are in the exposure protocol, and two more have their surgeries planned for next month. Although we have not yet collected sufficient data yet to draw specific conclusions, the following sections describe and illustrate the type of data that is being collected and provides examples of the data collected to date.

Respiratory. The flow patterns measured during breathing are analyzed by the BUXCO software package to derive the respiratory parameters. The parameters include breathing or respiratory frequency, tidal volume (TV), minute ventilation, time for inspiration (ti), time for expiration (te), peak inspiratory flow (PIF), peak expiratory flow (PEF), relaxation time (RT), end inspiratory pause, end expiratory pause, pause (PAU = [te-RT]/RT), enhanced pause (Penh = PAU PEF/PIF), index of ventilatory drive (IVD = TV/ti), inspiratory duty cycle (IDC = ti /[ti + te]), and a dimensionless parameter (Pbroncho = [te/ti][PIF/PEF]), which is a measure of bronchoconstriction. Figure 2 is an example of one parameter and the differences in magnitude and changes over a 6 hour exposure in the same dog with CAPs or sham exposure. In this example, Penh is higher with the CAPs compared to the sham exposure.

Figure 2. Penh Parameter of Dog 1 With CAPs or Sham Exposure During a 6 Hour Exposure

ECG/BP. In each animal, real-time ECG and pressure waveforms are transmitted from the Data Sciences International system and continuously displayed and recorded using a PC-based system. The resulting data are exported to analysis packages in our laboratory. Illustrated in Figures 3 and 4 are examples of the BP and ECG waveforms from a dog during exposure. These figures also provide examples of the trends of these parameters during exposures. In the tracing of the whole exposure period in comparing the same dog with a CAPs or a corresponding sham exposure, it is clear that BP is higher throughout in the CAPs-exposed dog. Heart rate starts out higher in the sham dog and falls, whereas the CAPs dog’s BP rises during the experiment.

Figure 3. A Dog’s Blood Pressure and ECG Waveforms During Exposure


Figure 4. Illustrations of Continuous Femoral Pressure and ECG Patterns in Two Different Leads Acquired During an Exposure

BP data have been analyzed for the completed exposures of this study. In four dogs each with multiple CAPs and FA sham exposures, exposure to CAPs raised systolic and diastolic BP as compared to FA exposure. Average systolic BP during CAPs exposure was 139.4 mmHg (which was 9.1 ± 1.8 [sem] mmHg greater than during exposure to FA and was statistically significant [p = 0.01] by paired t-test). Average diastolic BP during CAPs exposure was 89.0 mmHg (which was 3.9 ± 2.8 mmHg greater than during exposure to FA but was not statistically significant [p = 0.26]). Heart rate was not significantly different with CAPs or FA exposure. CAPs mass concentration ranged from 222.7 to 1,445.1 µg/m3 with a mean of 587.8 µg/m3. Diastolic BP robustly correlated with CAPs concentration (r = 0.88), whereas systolic BP did not (r = 0.12). Consistent with human observational studies, these results indicated that exposure to CAPs elevates systolic BP in canines. This experimental model provides an opportunity to elucidate the pathophysiological mechanisms responsible for particulate-pollution induced hypertensive response. These findings have been submitted in abstract for presentation at the 2006 American Thoracic Society Meeting.

Preliminary Findings of Perusionsion Studies. In the two dogs that have been analyzed completely, CAPs exposure globally reduced myocardial perfusion in both animals. When all data from all dogs and each color assessment were grouped as to whether they were baseline, sham, or CAPs exposures, it was clear that there was little overall difference between baseline and sham, but CAPs had a clear decreasing effect on myocardial perfusion. In comparing these data, the CAPs effect was highly statistically significant (p < .0001). Figures 5 and 6 map the perfusion in the locations of individual pieces of myocardium under baseline, sham, and CAPs exposure conditions. The anterior descending coronary artery distributional area has decreased perfusion with sham exposure because these were done with occlusion. With CAPs, however, the area of decreased perfusion was substantially larger.

Figure 5. Baseline, Sham Group, and CAPs Exposed Dog’s Myocardial Perfusion

Figure 6. Perfusion of Individual Pieces of Myocardium Under Baseline, Sham, and CAPs Exposure Conditions

Blood From Vascular Access Ports, Coronary Occlusion, Exposure Data. We have successfully collected from the vascular access port chronically implanted in the aorta. This site will be particularly important for the collection of mediators such as endothelins that can be generated in the lung and have profound effects on vasoconstriction of the coronary arteries. In addition, the coronary artery occluders that we now use have subcutaneous access ports. We have tested these successfully for the production of coronary occlusion. Exposure data also are collected during each exposure as detailed in our proposal.

No publications resulted from this work in its first year. A manuscript detailing the experience with implantation of this hardware has been submitted. Publication of the results of our initial studies are expected in Year 2.

Future Activities:

We expect to complete the full preparation of a total of eight dogs for the proposed studies in the coming year. We will continue to do repeated CAPs and sham exposures on each animal to determine the effect of various sources of pollution based on daily variations in exposure and effects found. As proposed, we intend to do at least 20 different CAPs exposures with these dogs to determine changes in coronary perfusion. These will be completed in the coming year. If the data continues to show consistent patterns as we have seen thus far, these studies will make a sizeable impact on our understanding of particulate effects on the coronary vascular system. We expect to make significant progress on these experiments in the coming year. If the dogs continue to tolerate the implanted devices as well as they have thus far, we will be able to complete that phase of the study and move on to our proposed autonomic nervous system manipulation studies as proposed.


Journal Articles on this Report : 5 Displayed | Download in RIS Format

Other project views: All 10 publications 10 publications in selected types All 10 journal articles
Type Citation Project Document Sources
Journal Article Bartoli CRG, Okabe K, Akiyama I, Verrier RL, Godleski JJ. Technique for implantation of chronic indwelling aortic access catheters. Journal of Investigative Surgery 2006;19(6):397-405. R831917 (2005)
R831917 (Final)
  • Abstract from PubMed
  • Abstract: Taylor & Francis-Abstract
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  • Other: ResearchGate-Abstract
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  • Journal Article Bartoli CRG, Akiyama I, Godleski JJ, Verrier RL. Long-term pericardial catheterization is associated with minimum foreign-body response. Catheterization and Cardiovascular Interventions 2007;70(2):221-227. R831917 (2005)
    R831917 (Final)
  • Abstract from PubMed
  • Abstract: Wiley-Abstract
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  • Other: ResearchGate-Abstract
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  • Journal Article Bartoli CRG, Akiyama I, Okabe K, Diaz EA, Godleski JJ. Permanent tracheostomy for long-term respiratory studies. Journal of Surgical Research 2008;145(1):124-129. R831917 (2005)
    R831917 (Final)
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  • Abstract from PubMed
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  • Abstract: ScienceDirect-Abstract
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  • Journal Article Bartoli CRG, Okabe K, Akiyama I, Coull B, Godleski JJ. Repeated microsphere delivery for serial measurement of regional blood perfusion in the chronically instrumented, conscious canine. Journal of Surgical Research 2008;145(1):135-141. R831917 (2005)
    R831917 (Final)
  • Full-text from PubMed
  • Abstract from PubMed
  • Associated PubMed link
  • Full-text: ResearchGate-Abstract & Full Text-PDF
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  • Abstract: JSR-Abstract
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  • Other: ScienceDirect-Abstract
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  • Journal Article Godleski JJ. Responses of the heart to ambient particle inhalation. Clinics in Occupational and Environmental Medicine 2006;5(4):849-864. R831917 (2005)
    R831917 (Final)
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  • Abstract: EM Consulte-Abstract
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  • Other: ResearchGate-Abstract
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  • Supplemental Keywords:

    concentrated air particulates, inhalation exposure, cardiovascular, ischemic heart disease, myocardial infarction, coronary artery perfusion, human health risk, cardiovascular vulnerability, particulate matter,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Air, particulate matter, Toxicology, Health Risk Assessment, Risk Assessments, Physical Processes, ambient aerosol, lung injury, morbidity, long term exposure, lung disease, acute cardiovascular effects, airway disease, cardiovascular vulnerability, exposure, airborne particulate matter, atherosclerosis, ambient particle health effects, blood viscosity, concentrated air particles, cardiovascular disease

    Progress and Final Reports:

    Original Abstract
  • Final Report