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- Author or Editor: Pierre M. Lekeux x
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Summary
Effects of iv and aerosol administration of 5-hydroxytryptamine (5-ht) on ventilation, pulmonary mechanics values, pulmonary arterial pressure, and heart rate were investigated in healthy unsedated Friesian calves.
Minute volume increased significantly, mainly because of an increase in respiratory rate. Except for total pulmonary resistance after bolus injection, continuous administration of 5-ht given by either route caused significant alterations of lung dynamic compliance and total pulmonary resistance, the former decreasing to one-fifth of its baseline value and the latter increasing twofold. Pulmonary arterial pressure increased significantly, whatever the speed or route of administration. Administration of a bolus did not affect heart rate, whereas continuous iv administration of 5-ht as well by perfusion or by aerosol resulted in sustained tachycardia.
It was concluded that 5-ht induces reversible bronchoconstriction and pulmonary vasoconstriction in healthy unsedated calves, 5-ht-induced functional alterations depend on the speed of administration, and excess of 5-ht production or depression in uptake by the lungs during bovine respiratory tract diseases could contribute to pulmonary dysfunction.
Abstract
Objective—To evaluate the hemodynamic effects of dobutamine hydrochloride (0.5 µg/kg of body weight/min) in halothane-anesthetized horses.
Animals—6 adult Thoroughbred horses.
Procedure—Anesthesia was induced by use of romifidine (100 µg/kg) and ketamine (2.2 mg/kg), IV. Anesthesia was maintained by halothane (end-tidal concentration 0.9 to 1.0%). Aortic, left ventricular, and right atrial pressures were measured, using cathetermounted strain gauge transducers. Cardiac output (CO), velocity time integral, maximal aortic blood flow velocity and acceleration, and left ventricular preejection period and ejection time were measured from aortic velocity waveforms obtained by transesophageal Doppler echocardiography. Velocity waveforms were recorded from the femoral vessels, using Doppler ultrasonography. The time-averaged mean velocity and early diastolic deceleration slope (EDDS) were measured. Pulsatility index (PI) and volumetric flow were calculated. Microvascular perfusion was measured in the semimembranosus muscles by laser Doppler flowmetry. Data were recorded 60 minutes after induction of anesthesia (control) and at 15 and 30 minutes after start of an infusion of dobutamine (0.5 µg/kg/min).
Results—Aortic pressures were significantly increased during the infusion of dobutamine. No change was observed in the indices of left ventricular systolic function including CO. Femoral arterial flow significantly increased, and the PI and EDDS decreased. No change was observed in the femoral venous flow or in microvascular perfusion.
Conclusions and Clinical Relevance—At this dosage, dobutamine did not alter left ventricular systolic function. Femoral blood flow was preferentially increased as the result of local vasodilatation. The lack of effect of dobutamine on microvascular perfusion suggests that increased femoral flow is not necessarily associated with improved perfusion of skeletal muscles. (Am J Vet Res 2000;61:1282–1288)
Abstract
Objective—To use Doppler ultrasonography and singlefiber laser Doppler flowmetry (LDF) to evaluate blood flow in the dependent and nondependent hind limbs of anesthetized horses and to evaluate changes in femoral arterial blood flow and microvascular skeletal muscle perfusion in response to administration of phenylephrine hydrochloride or dobutamine hydrochloride.
Animals—6 healthy adult horses.
Procedure—Horses were anesthetized and positioned in left lateral recumbency. Doppler ultrasonography was used to measure velocity and volumetric flow in the femoral vessels. Single-fiber LDF was used to measure relative microvascular perfusion at a single site in the semimembranosus muscles. Phenylephrine or dobutamine was then administered to decrease or increase femoral arterial blood flow, and changes in blood flow and microvascular perfusion were recorded.
Results—Administration of phenylephrine resulted in significant decreases in femoral arterial and venous blood flows and cardiac output and significant increases in mean aortic blood pressure, systemic vascular resistance, and PCV. Administration of dobutamine resulted in significant increases in femoral arterial blood flow, mean aortic blood pressure, and PCV. Significant changes in microvascular perfusion were not detected.
Conclusion and Clinical Relevance—Results suggest that Doppler ultrasonography and single-fiber LDF can be used to study blood flows in the hind limbs of anesthetized horses. However, further studies are required to determine why changes in femoral arterial blood flows were not associated with changes in microvascular perfusion. (Am J Vet Res 2000;61:286–290)
SUMMARY
The purpose of this study was to investigate the mechanism by which 5-hydroxytryptamine (5-ht) modifies respiratory function, specifically, hyperventilation, diffuse bronchoconstriction, and pulmonary arterial hypertension in cattle. We determined whether the IV response to 5-ht in calves was attributable to stimulation of 5-ht2 receptors.
Six healthy unsedated young bull calves of the Friesian (n = 4) and of the Belgian White and Blue (n = 2) breeds were used. A specific 5-ht2 antagonist (metrenperone, 0.05 mg/kg of body weight) was administered IM 30 minutes before the cattle were given a 5-minute IV 5-ht infusion. Pulmonary function values were registered before, during, and after the 5-ht challenge infusion. Minute volume increased significantly, because of an increase in respiratory rate. Conversely, lung dynamic compliance, total pulmonary resistance, and pulmonary arterial pressure were not changed.
We concluded that in cattle, 5-ht-induced ventilatory response is not mediated through activation of 5-ht2 receptors. However, the 5-ht2 receptors are involved in 5-ht-induced broncho- and pulmonary vasoconstriction.
Summary
During growth, central venous, right ventricular, pulmonary arterial, pulmonary capillary wedge, and systemic arterial pressures, heart rate, and cardiac output were repeatedly measured in 41 Friesian calves, considered as having conventional muscular conformation, and in 19 Belgian White and Blue double-muscled calves. A total of 123 and 70 recordings were collected in conventional and double-muscled calves, respectively. These circulatory indices were calculated: stroke volume, cardiac and stroke indices, pulmonary and systemic pulse pressures, pulmonary and systemic vascular resistance indices, and right and left ventricular work indices.
Results indicated that systemic arterial and pulse pressures, as well as cardiac output, stroke volume, cardiac and stroke indices, and right and left ventricular work indices were significantly (P ≤ 0.05 to 0.001) lower but, in contrast, pulmonary and systemic vascular resistance indices were significantly (P ≤ 0.001) higher in double-muscled than in conventional calves. Right-sided vascular pressures and heart rate were similar in the 2 groups. These results indicated that global cardiac performance may be considerably poorer in double-muscled calves. Diminished cardiac performance of double-muscled calves appears to be related neither to relative bradycardia nor to reduced ventricular preload. The potential role of increased ventricular afterload or of reduced myocardial contractility in double-muscled cattle should be determined by direct measurements.
