Effects of clenbuterol hydrochloride on pulmonary gas exchange and hemodynamics in anesthetized horses

John R. Dodam From the Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606 (Dodam, Olson, Swanson); the Department of Anesthesiology, Duke University Medical Center, Box 3094, Duke University, Durham, NC 27710 (Moon, Exposito, Fawcett, Huang, Theil); and the Department of Anesthesiology, State University of New York Health Sciences Center, 750 East Adams St, Syracuse 13210 (Camporesi).

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Richard E. Moon From the Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606 (Dodam, Olson, Swanson); the Department of Anesthesiology, Duke University Medical Center, Box 3094, Duke University, Durham, NC 27710 (Moon, Exposito, Fawcett, Huang, Theil); and the Department of Anesthesiology, State University of New York Health Sciences Center, 750 East Adams St, Syracuse 13210 (Camporesi).

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Neil C. Olson From the Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606 (Dodam, Olson, Swanson); the Department of Anesthesiology, Duke University Medical Center, Box 3094, Duke University, Durham, NC 27710 (Moon, Exposito, Fawcett, Huang, Theil); and the Department of Anesthesiology, State University of New York Health Sciences Center, 750 East Adams St, Syracuse 13210 (Camporesi).

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Andres J. Exposito From the Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606 (Dodam, Olson, Swanson); the Department of Anesthesiology, Duke University Medical Center, Box 3094, Duke University, Durham, NC 27710 (Moon, Exposito, Fawcett, Huang, Theil); and the Department of Anesthesiology, State University of New York Health Sciences Center, 750 East Adams St, Syracuse 13210 (Camporesi).

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Thomas A. Fawcett From the Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606 (Dodam, Olson, Swanson); the Department of Anesthesiology, Duke University Medical Center, Box 3094, Duke University, Durham, NC 27710 (Moon, Exposito, Fawcett, Huang, Theil); and the Department of Anesthesiology, State University of New York Health Sciences Center, 750 East Adams St, Syracuse 13210 (Camporesi).

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Y. C. Huang From the Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606 (Dodam, Olson, Swanson); the Department of Anesthesiology, Duke University Medical Center, Box 3094, Duke University, Durham, NC 27710 (Moon, Exposito, Fawcett, Huang, Theil); and the Department of Anesthesiology, State University of New York Health Sciences Center, 750 East Adams St, Syracuse 13210 (Camporesi).

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David R. Theil From the Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606 (Dodam, Olson, Swanson); the Department of Anesthesiology, Duke University Medical Center, Box 3094, Duke University, Durham, NC 27710 (Moon, Exposito, Fawcett, Huang, Theil); and the Department of Anesthesiology, State University of New York Health Sciences Center, 750 East Adams St, Syracuse 13210 (Camporesi).

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Enrico Camporesi From the Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606 (Dodam, Olson, Swanson); the Department of Anesthesiology, Duke University Medical Center, Box 3094, Duke University, Durham, NC 27710 (Moon, Exposito, Fawcett, Huang, Theil); and the Department of Anesthesiology, State University of New York Health Sciences Center, 750 East Adams St, Syracuse 13210 (Camporesi).

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Clifford R. Swanson From the Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606 (Dodam, Olson, Swanson); the Department of Anesthesiology, Duke University Medical Center, Box 3094, Duke University, Durham, NC 27710 (Moon, Exposito, Fawcett, Huang, Theil); and the Department of Anesthesiology, State University of New York Health Sciences Center, 750 East Adams St, Syracuse 13210 (Camporesi).

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Summary

We evaluated the effects of clenbuterol HCl (0.8 μg/kg, of body weight, iv), a β2, agonist, on ventilation-perfusion matching and hemodynamic variables in anesthetized (by iv route), laterally recumbent horses. The multiple inert gas elimination technique was used to assess pulmonary gas exchange. Clenbuterol HCl induced a decrease in arterial oxygen tension (from 57.0 ± 1.8 to 49.3 ± 1.2 mm of Hg; mean ± sem) as a result of increased shunt fraction (from 6.6 ± 2.1 to 14.4 ± 3.1%) and ventilation to regions with high ventilation-perfusion ratios. In contrast, no changes in these variables were found in horses given sterile water. In horses given clenbuterol HCl, O2 consumption increased from 2.23 ± 0.18 to 2.70 ± 0.14 ml · min-1 · kg-1, and respiratory exchange ratio decreased from 0.80 ± 0.02 to 0.72 ± 0.01. Respiratory exchange ratio and O, consumption were not significantly modified in sterile water-treated (control) horses. Clenbuterol HCl administration was associated with increased cardiac index (from 57.4 ± 4.0 to 84.2 ± 6.3 ml. min-1 · kg-1), decreased total peripheral vascular resistance (from 108.3 ± 9.3 to 47.6 ± 2.8 mm of Hg · s · kg · ml-1), and decreased pulmonary vascular resistance (from 31.3 ± 3.8 to 13.6 ± 0.7 mm of Hg · s · kg · ml-1). Our findings indicated that clenbuterol HCl may potentiate hypoxemia as a result of increased shunt fraction in horses anesthetized by the iv route, and caused changes in hemodynamic variables that were consistent with its ability to stimulate β2-adrenergic receptors.

Summary

We evaluated the effects of clenbuterol HCl (0.8 μg/kg, of body weight, iv), a β2, agonist, on ventilation-perfusion matching and hemodynamic variables in anesthetized (by iv route), laterally recumbent horses. The multiple inert gas elimination technique was used to assess pulmonary gas exchange. Clenbuterol HCl induced a decrease in arterial oxygen tension (from 57.0 ± 1.8 to 49.3 ± 1.2 mm of Hg; mean ± sem) as a result of increased shunt fraction (from 6.6 ± 2.1 to 14.4 ± 3.1%) and ventilation to regions with high ventilation-perfusion ratios. In contrast, no changes in these variables were found in horses given sterile water. In horses given clenbuterol HCl, O2 consumption increased from 2.23 ± 0.18 to 2.70 ± 0.14 ml · min-1 · kg-1, and respiratory exchange ratio decreased from 0.80 ± 0.02 to 0.72 ± 0.01. Respiratory exchange ratio and O, consumption were not significantly modified in sterile water-treated (control) horses. Clenbuterol HCl administration was associated with increased cardiac index (from 57.4 ± 4.0 to 84.2 ± 6.3 ml. min-1 · kg-1), decreased total peripheral vascular resistance (from 108.3 ± 9.3 to 47.6 ± 2.8 mm of Hg · s · kg · ml-1), and decreased pulmonary vascular resistance (from 31.3 ± 3.8 to 13.6 ± 0.7 mm of Hg · s · kg · ml-1). Our findings indicated that clenbuterol HCl may potentiate hypoxemia as a result of increased shunt fraction in horses anesthetized by the iv route, and caused changes in hemodynamic variables that were consistent with its ability to stimulate β2-adrenergic receptors.

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