• View in gallery
    Figure 1—

    Mean ± SD values of CO for healthy Beagles measured with 2 methods (thermodilution [criterion-referenced standard; squares] and CT coronary angiography [diamonds]) at each of 3 CO values. Normal represents unmanipulated CO; moderate and high CO values were obtained by constant rate infusion of dobutamine. Results represent data for 5 dogs for normal CO and 4 dogs for moderate and high CO.

  • View in gallery
    Figure 2—

    Bland-Altman plot for CO measured in healthy Beagles by use of thermodilution (TD) and CT. Each symbol represents results for 1 comparison. The mean difference between the 2 methods (solid line) is 0.09 L•min−1, and the 95% CI (dashed lines) is 0.52 to −0.34 L•min−1.

  • View in gallery
    Figure 3—

    Bland-Altman plot of CO measured in healthy Beagles by use of thermodilution (TD) and CT. Each symbol represents results for 1 comparison. The line of best fit for the data is plotted.

  • 1. Beaulieu KE, Kerr CL, McDonell WN. Evaluation of transpulmonary thermodilution as a method to measure cardiac output in anesthetized cats. Can J Vet Res 2009; 73:16.

    • Search Google Scholar
    • Export Citation
  • 2. Hug CJ. Monitoramento. In: Miller RD, ed. Tratado de anesthesia. 2nd ed. São Paulo, Brazil: Manole, 1989; 419471.

  • 3. Garrett JS, Lanzer P, Jaschke W, et al. Measurement of cardiac output by cine computed tomography. Am J Cardiol 1985; 56:657661.

  • 4. Nishikawa T, Dohi S. Errors in the measurement of cardiac output by thermodilution. Can J Anaesth 1993; 40:142153.

  • 5. Kienle RD. Cardiac catheterization. In: Kittleson MD, Kienle RD, eds. Small animal cardiovascular medicine. St Louis: CV Mosby, 1998:118132.

    • Search Google Scholar
    • Export Citation
  • 6. Lopes PC, Sousa MG, Camacho AA, et al. Comparison between two methods for cardiac output measurement in propofol-anesthetized dogs: thermodilution and Doppler. Vet Anaesth Analg 2010; 37:401408.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7. Haskins SC. Monitoring the anesthetized patient. In: Tranquilli WJ, Thurmon JC, Grimm KA, eds. Lumb & Jones' veterinary anesthesia. Oxford: Blackwell Publishing, 2007; 4:533558.

    • Search Google Scholar
    • Export Citation
  • 8. Mehta HH, Choi BG, Sanai R, et al. Validation of a novel method for cardiac output estimation by CT coronary angiography. Adv Computed Tomog 2012; 1:1116.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9. Chang SM, Bhatti S, Nabi F. Coronary computed tomography angiography. Curr Opin Cardiol 2011; 26:392402.

  • 10. Daniel GB, Kerstetter KK, Sackman JE, et al. Quantitative assessment of surgically induced mitral regurgitation using radionuclide ventriculography and first pass radionuclide angiography. Vet Radiol Ultrasound 1998; 39:459469.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11. Mehta Y, Arora D. Newer methods of cardiac output monitoring. World J Cardiol 2014; 6:10221029.

  • 12. Ganz W, Donoso R, Marcus HS, et al. A new technique for measurement of cardiac output by thermodilution in man. Am J Cardiol 1971; 27:392396.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13. Runciman WB, Ilsley AH, Roberts JG. Thermodilution cardiac output—a system error. Anaesth Intensive Care 1981; 9:135139.

  • 14. Meisner H, Glanert S, Steckmeier B, et al. Indicator loss during injection in the thermodilution system. Res Exp Med (Berl) 1973; 159:183196.

  • 15. Kim ME, Lin YC. Determination of catheter wall heat transfer in cardiac output measurement by thermodilution. Clin Exp Pharmacol Physiol 1980; 7:383389.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16. Hosie KF. Thermal-dilution technics. Circ Res 1962; 10:491504.

  • 17. Levett JM, Replogle RL. Thermodilution cardiac output: a critical analysis and review of the literature. J Surg Res 1979; 27:392404.

  • 18. Bland JM, Altman DG. Agreement between methods of measurement with multiple observations per individual. J Biopharm Stat 2007; 17:571582.

    • Crossref
    • Search Google Scholar
    • Export Citation

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Comparison of cardiac output measured by use of computed tomography and thermodilution in dogs

Sharon TenenbaumDepartment of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32608.

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Fernando L. Garcia-PereiraDepartment of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32608.

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Clifford R. BerryDepartment of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32608.

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Tori ObertDepartment of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32608.

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Abstract

OBJECTIVE To compare cardiac output (CO) measured by use of CT coronary angiography and thermodilution (criterion-referenced standard) at various CO values, record adverse effects, and determine the time needed to measure CO.

ANIMALS 5 healthy purpose-bred Beagles (2 males and 3 females).

PROCEDURES A prospective nonrandomized crossover study was conducted. Dogs were premedicated with butorphanol tartrate (0.2 mg•kg−1, IM). Anesthesia was induced by IV administration of etomidate (1 to 2 mg•kg−1) and midazolam (0.25 mg•kg−1). Orotracheal intubation was performed, and anesthesia was maintained by administration of isoflurane. The CO was determined by use of thermodilution and by use of CT at 3 CO values. Dobutamine was infused at various rates to obtain the 3 CO values.

RESULTS 13 values were obtained and analyzed. The mean ± SD difference between methods was 0.09 ± 0.71 L•min−1 (95% confidence interval [CI], 0.52 to −0.34 L•min−1). Only 1 of 13 values was located on the 100% agreement line (ie, 0 line), 7 of 13 values were located within the 95% CI, and 5 of 13 values were outside the 95% CI.

CONCLUSIONS AND CLINICAL RELEVANCE For this study, there was poor agreement between the 2 methods. The 95% CI interval was 0.52 to −0.34 L•min−1, and 5 of 13 values were outside the 95% CI. Therefore, results for the CT method appeared to be inappropriate for use in making clinical decisions.

Abstract

OBJECTIVE To compare cardiac output (CO) measured by use of CT coronary angiography and thermodilution (criterion-referenced standard) at various CO values, record adverse effects, and determine the time needed to measure CO.

ANIMALS 5 healthy purpose-bred Beagles (2 males and 3 females).

PROCEDURES A prospective nonrandomized crossover study was conducted. Dogs were premedicated with butorphanol tartrate (0.2 mg•kg−1, IM). Anesthesia was induced by IV administration of etomidate (1 to 2 mg•kg−1) and midazolam (0.25 mg•kg−1). Orotracheal intubation was performed, and anesthesia was maintained by administration of isoflurane. The CO was determined by use of thermodilution and by use of CT at 3 CO values. Dobutamine was infused at various rates to obtain the 3 CO values.

RESULTS 13 values were obtained and analyzed. The mean ± SD difference between methods was 0.09 ± 0.71 L•min−1 (95% confidence interval [CI], 0.52 to −0.34 L•min−1). Only 1 of 13 values was located on the 100% agreement line (ie, 0 line), 7 of 13 values were located within the 95% CI, and 5 of 13 values were outside the 95% CI.

CONCLUSIONS AND CLINICAL RELEVANCE For this study, there was poor agreement between the 2 methods. The 95% CI interval was 0.52 to −0.34 L•min−1, and 5 of 13 values were outside the 95% CI. Therefore, results for the CT method appeared to be inappropriate for use in making clinical decisions.

The cardiovascular system plays a pivotal role in homeostasis. Information on the cardiac performance of patients can be of vital importance to clinicians, especially when treating critically ill patients, such as those with heart failure, trauma, or sepsis. These patients can have an abnormal blood volume and cardiovascular dysfunction; therefore, additional information on their cardiovascular status could influence the course of treatment selected by a clinician. Common variables used to assess cardiovascular status include heart rate, arterial blood pressure, capillary refill time, pulse rate, and pulse quality.1 However, these variables may not provide sufficient hemodynamic information about critically ill patients to improve decision making with regard to the course of treatment.

Cardiac performance can be defined as the blood volume per unit of time supplied to the body and organs.2 Cardiac output is the most precise variable for evaluating overall cardiac function.3 In both human and veterinary medicine, thermodilution is considered the criterion-referenced standard for CO measurement.1 This method is widely accepted in human and veterinary medicine because it is easy to perform, many measurements can be accurately obtained in a short period, and it does not require collection of blood samples for subsequent analysis.4 However, disadvantages exist for use of this technique. One disadvantage is that thermodilution is an invasive technique that involves placement of a catheter in a pulmonary artery, which can cause arrhythmias, thrombi, and infections, among other complications.5 Therefore, there is a need for less invasive techniques that can yield similar results. Unfortunately, most of the techniques described for use in dogs lack accuracy or are also invasive, requiring central venous and arterial catheters. Furthermore, they may require expensive specialized equipment.1 In response to these issues, newer and less invasive methods have been introduced as an alternative to thermodilution. These methods include lithium dilution, thoracic electrical impedance, pulse analysis, Doppler echocardiography,6,7 MRI, and CT.8

Computed tomography coronary angiography has been used to evaluate CO. This method involves administration of contrast medium followed by the use of ECG-gated images to evaluate cardiac performance. The test yields a high-resolution 3-D image that can be used to visually examine cardiac structures and major vessels as well as for calculation of cardiac performance indices, cardiac blood volume, and CO.9,10

Even though CT is a minimally invasive technique, in most circumstances it requires the use of expensive equipment and that patients be anesthetized for examination. However, many referral animal hospitals already have CT equipment, so additional expenditures are not required, which makes this method an extremely attractive alternative. Also, determination of CO by use of a noninvasive method that can be used in place of thermodilution may decrease the probability for adverse effects of the procedure. Cardiac output could be used to guide treatments to ameliorate cardiovascular and hemodynamic abnormalities in critically ill patients. Determination of CO by use of CT is easier to perform and has fewer adverse effects and risks, including the absence of arrhythmias, thromboemboli, and infections, compared with adverse effects and risks associated with the use of thermodilution.11

The specific objectives of the study reported here were to compare CO measured by use of CT coronary angiography with CO obtained with thermodilution (criterion-referenced standard method) for various CO values. Also, adverse effects for CT coronary angiography and the amount of time needed to perform CO measurements with this method were recorded.

Materials and Methods

Animals

Five sexually intact (2 males and 3 females) purpose-bred Beagles were enrolled in the study. Mean ± SD age of the dogs was 15.6 ± 2.2 months, and mean body weight was 9.2 ± 2.6 kg. Dogs were deemed healthy on the basis of results of a physical examination, CBC, and serum biochemical analysis. The study was approved by the Institutional Animal Care and Use Committee at the University of Florida.

Procedures

Food was withheld from dogs for 12 hours prior to premedication; dogs had access to water until the time of administration of the premedicant. All dogs received butorphanol tartratea (0.2 mg•kg−1, IM). Twenty minutes after butorphanol was administered, a catheter was placed in a cephalic vein. Anesthesia was induced by IV administration of etomidateb (1 to 2 mg•kg−1) and midazolamc (0.25 mg•kg−1). The trachea was intubated with an appropriately sized endotracheal tube, and anesthesia was maintained with isofluraned and oxygen (flow rate, 10 to 20 mL•kg−1•min−1) administered through a semiclosed breathing system. Mechanical ventilation was instituted to maintain end-tidal partial pressure of CO2 at 35 to 45 mm Hg. Mechanical ventilation was discontinued during CO measurements. Body temperature was maintained within reference limits by the use of a forced-air heating device.e Dogs were instrumented with a multiparameter monitor,f and a catheter was placed in a dorsal pedal artery and connected to a calibrated pressure transducer for continuous monitoring of blood pressure throughout the procedure. Heart rate, respiratory rate, ECG, oxygen saturation as measured via pulse oximetry, esophageal body temperature, arterial blood pressure, and capnography were monitored. Physiologic variables were recorded every 5 minutes throughout the duration of anesthesia. Lactated Ringer solutiong was administered IV (rate, 3 mL•kg−1•h−1) throughout anesthesia.

The end-tidal isoflurane concentration was titrated to maintain an adequate plane of anesthesia to allow placement of a Swan-Ganz catheter12,h in the right jugular vein. The catheter was advanced into the pulmonary artery, as determined by evaluation of the blood pressure waveform. Dogs then were moved to the CT facility. Dogs were positioned in sternal recumbency, and ECG leads from the CT equipmenti were connected. A bolus (3 mL of 5% dextrose solutionj) was injected into the proximal port of the catheter for the thermodilution calculation of CO by use of a CO modulek attached to the multiparameter monitor.12–17 Three consecutive measurements were recorded, and the mean value for those 3 measurements was calculated. Values of the 3 measurements were within 20% of each other or they were discarded and another 3 measurements were obtained.10 Measurements of CO were obtained for each of 3 CO values: normal (ie, unmanipulated), moderate, and high. Moderate and high CO values were obtained by constant rate infusion of dobutamineb; moderate CO was obtained by infusion at a rate of 5 μg•kg−1•min−1, and high CO was obtained by infusion at a rate of 7.5 μg•kg−1•min−1.

Thermodilution and CT measurement of CO were performed concurrently at all points. Immediately after CO was measured by use of thermodilution, and in synchronization with a dog's heartbeat, iohexoll (20 mg•kg−1, IV) was administered with an electronic injectorm while CT scanning was performed simultaneously to provide a 3-D image of the heart. The CO values obtained by use of CT were then compared with values calculated for thermodilution to determine accuracy of the CO measurements obtained by use of CT.

After the procedures were completed, dogs were allowed to recover from anesthesia. Heart rate, blood pressure, rectal temperature, and pulse oximetry were monitored by one of the authors (ST) until the dogs were conscious. Adverse effects were recorded until the dogs were conscious and in sternal position.

Statistical analysis

Bland-Altman plots with multiple measurements per subject were used to estimate agreement between the 2 methods. The Bland-Altman method consists of plotting differences of the paired measurements against the mean of the paired measurements.18,n

Results

The mean CO for each of the 3 CO values measured by use of each method was calculated. Mean ± SD for CT was 1.35 ± 0.4 L•min−1, 1.38 ± 0.6 L•min−1, and 2.0 ± 0.58 L•min−1 for the normal, moderate, and high CO values, respectively. Mean for thermodilution was 1.25 ± 0.3 L•min−1, 1.28 ± 0.1 L•min−1, and 2.17 ± 0.1 L•min−1 for the normal, moderate, and high CO values, respectively (Figure 1).

Figure 1—
Figure 1—

Mean ± SD values of CO for healthy Beagles measured with 2 methods (thermodilution [criterion-referenced standard; squares] and CT coronary angiography [diamonds]) at each of 3 CO values. Normal represents unmanipulated CO; moderate and high CO values were obtained by constant rate infusion of dobutamine. Results represent data for 5 dogs for normal CO and 4 dogs for moderate and high CO.

Citation: American Journal of Veterinary Research 78, 8; 10.2460/ajvr.78.8.906

For each of 4 dogs, 3 thermodilution CO measurements were obtained (and the mean calculated) for each of 3 CO values immediately prior to administration of contrast medium for CT measurement of the CO and comparison by use of a Bland-Altman plot (Figure 2). One dog had an extremely high heart rate; therefore, the contrast medium was cleared too rapidly and images could not be obtained for this dog at moderate and high CO. Thus, 13 values were obtained for analysis. Mean ± SD difference between methods was 0.09 ± 0.71 L•min−1 (95% CI, 0.52 to −0.34 L•min−1). Of the 13 values, 1 was located on the 100% agreement line (ie, 0 line), 7 were located within the 95% CI, and 5 were located outside of the 95% CI. A linear regression line was plotted for visual evaluation of the agreement between the methods (Figure 3).

Figure 2—
Figure 2—

Bland-Altman plot for CO measured in healthy Beagles by use of thermodilution (TD) and CT. Each symbol represents results for 1 comparison. The mean difference between the 2 methods (solid line) is 0.09 L•min−1, and the 95% CI (dashed lines) is 0.52 to −0.34 L•min−1.

Citation: American Journal of Veterinary Research 78, 8; 10.2460/ajvr.78.8.906

Figure 3—
Figure 3—

Bland-Altman plot of CO measured in healthy Beagles by use of thermodilution (TD) and CT. Each symbol represents results for 1 comparison. The line of best fit for the data is plotted.

Citation: American Journal of Veterinary Research 78, 8; 10.2460/ajvr.78.8.906

Discussion

Measurement of CO can be a useful tool to assess cardiovascular status of animals with trauma or cardiac disease or to monitor treatments. This variable is often underutilized by general practitioners because it requires special equipment and skill. Thermodilution is an invasive method and considered the criterion-referenced standard, but use of this method might add complications such as arrhythmias, infections, and emboli. Computer tomography is an imaging modality that is commonly available in most academic institutions and specialty practice hospitals. It is easy to use and can be performed quickly; however, anesthesia or heavy sedation of patients is often required. In the study reported here, 5 Beagles were anesthetized and their CO measured after manipulation with various doses of dobutamine. Because of the necessity for injection of contrast medium for CT angiography to enable us to obtain measurements for all 3 CO values, no low CO values were induced because the maximum amount of contrast medium was already being administered. There also was difficulty obtaining images at higher heart rates, which may pose a problem in tachycardic patients.

Agreement between the 2 methods was poor; therefore, use of the CT method for obtaining CO on which to base decisions regarding a patient's hemodynamic status may not be appropriate. The 95% CI was 0.52 to −0.34 L•min−1, with a mean of 0.09 L•min−1, for the mean difference between methods which covers a large portion of the CO of healthy dogs. More concerning was the fact that 5 of 13 values were outside the 95% CI. The disparity between these 2 methods indicated that the use of CT was clinically inappropriate for obtaining CO of the dogs in the present study. Therefore, we concluded that use of the CT method to make treatment decisions would be unacceptable. However, CT certainly could be used to monitor trends in CO because CO for both methods moved in the same direction for the various CO values obtained after dobutamine infusion.

Full agreement for the Bland-Altman method indicates that the difference between the 2 methods is 0. Any departure from 0 indicates a reduction in agreement. In addition, a regression line for the difference between values can be generated. Analysis of the Bland-Altman plot of the data for the present study revealed that the 2 methods had poor agreement because only 1 of 13 values was located on the 0 line. The small sample size for this study also may have influenced the poor agreement for these 2 methods. A larger sample size would have provided more meaningful information on the usefulness of the CT method for clinical patients. Nevertheless, the difference between the 2 methods was considered clinically relevant, and we concluded that no clinical decisions for the dogs of the present study should have been made with CO values obtained by use of CT angiography.

No adverse effects, including allergic reactions to the contrast agent, were detected during the study. One dog had an extremely high CO; therefore, the contrast medium was cleared too rapidly and CT images could not be obtained. Analysis of results for this study indicated a poor correlation for CO obtained by use of CT. However, studies with a larger sample size and extremes of CO values may yield an improvement in the agreement between the 2 methods.

Acknowledgments

This manuscript represents the resident research project submitted by Dr. Tenenbaum to the Department of Large Animal Clinical Sciences at the University of Florida as partial fulfillment of the requirements for the residency training program.

ABBREVIATIONS

CI

Confidence interval

CO

Cardiac output

Footnotes

a.

Fort Dodge Animal Health, New York, NY.

b.

Hospira Inc, Lake Forest, Ill.

c.

West Ward, Eatontown, NJ.

d.

Piramal Enterprises Ltd, Anhdra Pradesh, India.

e.

Bair hugger, 3M Animal Care, Saint Paul, Minn.

f.

IntelliVue MP50, Philips, Norwell, Mass.

g.

Abbott Laboratories Inc, North Chicago, Ill.

h.

Edwards Lifesciences LLC, Irvine, Calif.

i.

CT equipment Aquilion Prime, Toshiba Medical Systems Corp, Otawara, Japan.

j.

Baxter Healthcare Corp, Deerfield, Ill.

k.

Philips, Norwell, Mass.

l.

GE Healthcare, Shanghai, People's Republic of China.

m.

Medrad, Indianola, Pa.

n.

JMP Pro, version 12, SAS, SAS Institute Inc, Cary, NC.

References

  • 1. Beaulieu KE, Kerr CL, McDonell WN. Evaluation of transpulmonary thermodilution as a method to measure cardiac output in anesthetized cats. Can J Vet Res 2009; 73:16.

    • Search Google Scholar
    • Export Citation
  • 2. Hug CJ. Monitoramento. In: Miller RD, ed. Tratado de anesthesia. 2nd ed. São Paulo, Brazil: Manole, 1989; 419471.

  • 3. Garrett JS, Lanzer P, Jaschke W, et al. Measurement of cardiac output by cine computed tomography. Am J Cardiol 1985; 56:657661.

  • 4. Nishikawa T, Dohi S. Errors in the measurement of cardiac output by thermodilution. Can J Anaesth 1993; 40:142153.

  • 5. Kienle RD. Cardiac catheterization. In: Kittleson MD, Kienle RD, eds. Small animal cardiovascular medicine. St Louis: CV Mosby, 1998:118132.

    • Search Google Scholar
    • Export Citation
  • 6. Lopes PC, Sousa MG, Camacho AA, et al. Comparison between two methods for cardiac output measurement in propofol-anesthetized dogs: thermodilution and Doppler. Vet Anaesth Analg 2010; 37:401408.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7. Haskins SC. Monitoring the anesthetized patient. In: Tranquilli WJ, Thurmon JC, Grimm KA, eds. Lumb & Jones' veterinary anesthesia. Oxford: Blackwell Publishing, 2007; 4:533558.

    • Search Google Scholar
    • Export Citation
  • 8. Mehta HH, Choi BG, Sanai R, et al. Validation of a novel method for cardiac output estimation by CT coronary angiography. Adv Computed Tomog 2012; 1:1116.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9. Chang SM, Bhatti S, Nabi F. Coronary computed tomography angiography. Curr Opin Cardiol 2011; 26:392402.

  • 10. Daniel GB, Kerstetter KK, Sackman JE, et al. Quantitative assessment of surgically induced mitral regurgitation using radionuclide ventriculography and first pass radionuclide angiography. Vet Radiol Ultrasound 1998; 39:459469.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11. Mehta Y, Arora D. Newer methods of cardiac output monitoring. World J Cardiol 2014; 6:10221029.

  • 12. Ganz W, Donoso R, Marcus HS, et al. A new technique for measurement of cardiac output by thermodilution in man. Am J Cardiol 1971; 27:392396.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13. Runciman WB, Ilsley AH, Roberts JG. Thermodilution cardiac output—a system error. Anaesth Intensive Care 1981; 9:135139.

  • 14. Meisner H, Glanert S, Steckmeier B, et al. Indicator loss during injection in the thermodilution system. Res Exp Med (Berl) 1973; 159:183196.

  • 15. Kim ME, Lin YC. Determination of catheter wall heat transfer in cardiac output measurement by thermodilution. Clin Exp Pharmacol Physiol 1980; 7:383389.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16. Hosie KF. Thermal-dilution technics. Circ Res 1962; 10:491504.

  • 17. Levett JM, Replogle RL. Thermodilution cardiac output: a critical analysis and review of the literature. J Surg Res 1979; 27:392404.

  • 18. Bland JM, Altman DG. Agreement between methods of measurement with multiple observations per individual. J Biopharm Stat 2007; 17:571582.

    • Crossref
    • Search Google Scholar
    • Export Citation

Contributor Notes

Address correspondence to Dr. Garcia-Pereira (garciaf@ufl.edu).