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standard for predicting EE is indirect calorimetry, 1 a procedure that measures the consumption of O 2 and production of CO 2 in order to calculate resting EE (REE) and respiratory quotient (RQ). In order to accurately measure these gases, subjects must

Full access
in American Journal of Veterinary Research

SUMMARY

Although the cardiovascular and respiratory effects of halothane and isoflurane have been documented in a variety of common mammalian laboratory animals, they have not been investigated in birds. In this study, the effects of halothane and isoflurane anesthesia on respiratory rate, heart rate, heart rhythm, and mean arterial pressure in adult Pekin ducks were evaluated. Both anesthetics significantly increased heart rate and depressed blood pressure and respiration. Halothane induced a more profound alteration in heart rate and respiratory rate. With the ducks under halothane anesthesia, abnormal cardiac rhythms included ventricular fibrillation, ventricular bigeminy, and multifocal ventricular rhythms. Other than cardiac tachycardia, isoflurane induced no changes in cardiac rhythm.

Free access
in American Journal of Veterinary Research

Summary

Distribution of blood flow among various respiratory muscles was examined in 8 healthy ponies during submaximal exercise lasting 30 minutes, using radionuclide labeled 15-μm diameter microspheres injected into the left ventricle. From the resting values (40 ± 2 beats/min; 37.3 ± 0.2 C), heart rate and pulmonary arterial blood temperature increased significantly at 5 (152 ± 8 beats/min; 38.6 ± 0.2 C), 15 (169 ± 6 beats/min; 39.8 ± 0.2 C), and 26 (186 ± 8 beats/min; 40.8 ± 0.2 C) minutes of exertion, and the ponies sweated profusely. Mean aortic pressure also increased progressively as exercise duration increased. Blood flow increased significantly with exercise in all respiratory muscles. Among inspiratory muscles, perfusion was greatest in the diaphragm and ventral serratus, compared with external intercostal, dorsal serratas, and scalenus muscles. Among expiratory muscles, blood flow in the internal abdominal oblique muscle was greatest, followed by that in internal intercostal and transverse throacic muscles, in which the flow values remained similar. The remaining 3 abdominal muscles had similar blood flow, but these values were less than that in the internal intercostal, transverse thoracic, and internal abdominal oblique muscles. Blood flow values for all inspiratory and expiratory muscles remained similar for the 5 and 15 minutes of exertion. However, at 26 minutes, blood flow had increased further in the diaphragm, external intercostal, internal intercostal, transverse thoracic, and the external abdominal oblique muscle as vascular resistance decreased. On the basis of our findings, all respiratory muscles were activated during submaximal exercise and their perfusion had marked heterogeneity. Also, blood flow in respiratory muscles was well maintained as exercise duration progressed; in fact, several muscles had a further increase in perfusion late during exercise.

Free access
in American Journal of Veterinary Research

Summary

Respiratory syncytial virus (rsv) infection causes severe lower respiratory tract disease in infants and calves. Neonatal respiratory tract infection in children often produces persistent changes in lung function. The specific objective of this study was to determine whether neonatal calves have transient or persistent alterations in pulmonary function and airway reactivity following rsv infection. Six 2- to 3-day-old Holstein bull calves were inoculated with 10 ml of bovine respiratory syncytial virus (brsv) inoculum (102.7 to 103.8 cell culture infective doses/ml) intranasally and 10 ml of brsv inoculum (104.8 to 105.9 cell culture infective doses/ml) intratracheally for 4 consecutive days, and 5 other calves were sham-inoculated. Prior to inoculation (day 0) and on days 4, 14, and 30 after the last inoculation, body weight (kg), dynamic compliance (Cdyn), pulmonary resistance (RL), and 2 indices of airway reactivity (effective dose [ed] 65Cdyn and ed 200RL) were measured. Control calves gained weight progressively throughout the study, whereas rsv-inoculated calves failed to gain weight for 14 days, but equaled control calf weight by 30 days after inoculation. The Cdyn of control calves increased significantly by 30 days, but did not in the rsv-infected calves. Pulmonary resistance was increased significantly at 4, 14, and 30 days, but was unaffected by sham inoculation. The ed 65Cdyn and ed 200RL indicated an age-dependent increase in reactivity to histamine and an increase in responsiveness in the infected group beginning at 14 days and persisting until the end of the study. The data indicate that brsv causes airway obstruction and hyperreactivity in neonatal calves, which persists for at least 30 days following viral exposure.

Free access
in American Journal of Veterinary Research

SUMMARY

Anesthesia of equids is associated with pulmonary dysfunction. Cardiovascular and respiratory effects of inhalation anesthetic agents and duration of anesthesia have been studied, using oxygen as the carrier gas. To our knowledge, the effects of inspired oxygen have not been determined. We studied the cardiovascular and respiratory effects of 2 inspired oxygen fractions (0.30 and > 0.85) in 5 laterally recumbent, halothane-anesthetized horses. Mean systemic arterial blood pressure, cardiac output, central venous pressure, pulmonary arterial pressure, arterial pH, and arterial base excess were similar in horses of the 2 groups during 4 hours of anesthesia at constant end-tidal halothane concentration. End-tidal partial pressure of CO2, arterial partial pressure of CO2 and O2, and alveolar-to-arterial O2 tension difference were greater in horses exposed to the higher oxygen concentration. On the basis of the data obtained, we suggest that greater hypoventilation and ventilation/perfusion mismatch occur when horses are breathing high-oxygen fraction. Arterial partial pressure of O2 was not different between the 2 groups of horses after they were disconnected from the anesthesia circuit and allowed to breathe room air. Horses recovered from anesthesia without complications.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine the effects of endotracheal intubation on respiratory mechanics during xylazine sedation and xylazine-diazepam-ketamine anesthesia in adult horses.

Animals

5 healthy adult horses.

Procedure

Measurements were derived from recordings of respiratory gas flow, and transpulmonary and transtracheal pressures. Total pulmonary resistance (RT) was partitioned into upper airway resistance (extrathoracic portion of trachea, larynx, pharynx, nasal cavity, nares; RUA) and lower airway resistance (intrathoracic portion of trachea, bronchi, bronchioles). Baseline measurements were obtained in unsedated horses, after xylazine administration, and following nasotracheal intubation (ID, 18 mm). Measurements were obtained following induction of xylazine-diazepam-ketamine anesthesia and subsequent to endotracheal intubations (ID, 22, 20, and 16 mm). During recovery, horses were nasotracheally intubated (ID, 18 mm). Measurements were obtained upon standing, and repeated after extubation. Data were examined by use of ANOVA with repeated measures.

Results

Significant increases in mean work of breathing (W), RT, and RUA observed with xylazine sedation were variably attenuated by nasotracheal intubation. During xylazine-diazepam-ketamine anesthesia, the highest mean values for W, RT, RUA, transpulmonary and transtracheal pressures developed during nonintubation periods. The magnitudes of resistance and pressure values were inversely proportional to the internal diameter of the endotracheal tube. At recovery, values of the W and all measurements of resistances and pressures were significantly increased, compared with presedation values. Extubation resulted in further increases in these measurements.

Conclusions

Work of breathing in horses is substantially increased when RUA is increased during xylazine sedation and xylazine-diazepam-ketamine anesthesia. Endotracheal intubation reduces W by reducing RUA. (Am J Vet Res 1997;58:641–646)

Free access
in American Journal of Veterinary Research

Summary

The respiratory, renal, hematologic, and serum biochemical effects of hypertonic saline solution (hss) treatment were examined in 12 endotoxic, pentobarbitalanesthetized calves (8 to 20 days old). Escherichia coli endotoxin (055:B5) was infused iv at a rate of 0.1 μg/kg of body weight over 30 minutes. Endotoxin induced severe respiratory effects, with marked hypoxemia and increases in arterial-alveolar O2 gradient (P[A —a]O2), physiologic shunt fraction (Qs/Qt), and physiologic dead space to tidal volume ratio (Vd/Vt). Oxygen consumption was decreased, despite an increase in the systemic O2 extraction ratio. Peak effects were observed at the end of endotoxin infusion. The renal response to endotoxemia was characterized by a decrease in free-water reabsorption and osmotic clearance, as well as a decrease in sodium and phosphorus excretion. Endotoxemia induced leukopenia, thrombocytopenia, hyperphosphatemia, hypoglycemia, acidemia, and increased serum alkaline phosphatase concentrations.

Calves were treated with hss (2,400 mosm/L of NaCl, 4 ml/kg, n = 4) or an equivalent sodium load of isotonic saline solution (iss; 300 mosm/L of NaCl, 32 ml/kg, n = 4) 90 minutes after the end of endotoxin administration. Both solutions were infused over a 4- to 6-minute period. A control group (n = 4> was not treated. Infusion of hss or iss failed to induce a significant change in Pao2 , P(A-a)o2, (Qs/Qt), (Vd/Vt), or oxygen consumption. Both solutions increased systemic oxygen delivery to above preendotoxin values. Hypertonic saline infusion induced significant (P < 0.05) increases in serum Na and Cl concentrations and osmolality, whereas iss induced a significant increase in serum Cl concentration and a significant decrease in serum phosphorus concentration. Both hss and iss reversed the endotoxin-induced changes in renal function, with increases in free water reabsorption and osmotic clearance, as well as increases in sodium and phosphorus excretion. Sodium retention was greater following hss administration. On the basis of these findings, hypertonic saline solutions can be rapidly and safely administered to endotoxic calves.

Free access
in American Journal of Veterinary Research

SUMMARY

We examined the electromyographic activity of the costal portion of the diaphragm and the transverse abdominal and external oblique muscles in 6 chronically instrumented awake adult horses during eupneic breathing, during 2 levels of hypercapnia (fractional concentration of inspired CO2; FI CO2 = 0.4 and 0.6), and during 2 levels of hypocapnic hypoxia (FI CO2 = 0.15 and 0.12). Using the inert gas technique, we also measured the end-expiratory lung volumes of the 6 horses during eupnea, 6% CO2 challenge, and 12% O2 breathing. During eupneic breathing, phasic electrical activity of these 3 muscles was always present and was preceded by the onset of mechanical flow. At progressive levels of hypercapnia, the magnitude of inspiratory and expiratory electrical activity increased, and for the expiratory muscles, this recruitment coincided with significant (P < 0.05) increases in peak expiratory gastric pressure. However, during hypocapnic hypoxia, differential recruitment patterns of the respiratory muscles were found. The electrical activity of the diaphragm increased in magnitude and occurred sooner relative to the onset of mechanical flow. The magnitude and onset of abdominal expiratory activity failed to increase significantly during these episodes of hyperpnea and this pattern of activity coincided with decrements in peak expiratory gastric pressure. Despite alterations in muscle recruitment patterns during these hyperpneic episodes, end-expiratory lung volume remained unchanged. Thus, we conclude that adult horses respond similarly to awake dogs during peripheral and central chemoreceptor stimulation.

Free access
in American Journal of Veterinary Research

SUMMARY

Cardiovascular and respiratory responses to variable Pa o 2 were measured in 6 horses anesthetized only with halothane during spontaneous (sv) and controlled (cv) ventilation. The minimal alveolar concentration (mac) for halothane in oxygen was determined in each spontaneously breathing horse prior to establishing Pa o 2 study conditions—mean ± sem,0.95 ± 0.03 vol%. The Pa o 2 conditions conditions of > 250, 120, 80, and 50 mm of Hg were studied in each horse anesthetized at 1.2 mac of halothane and positioned in left lateral recumbency. In response to a decrease in Pa o 2 , total peripheral resistance and systolic and distolic arterial blood pressure decreased (P < 0.05) during sv. Cardiac output tended to increase because heart rate increased (P < 0.05) during these same conditions. During cv, cardiovascular function was usually less than it was at comparable Pa o 2 during sv (P < 0.05). Heart rate, cardiac output, and left ventricular work increased (P < 0.05) in response to a decrease in Pa o 2 , whereas total peripheral resistance decreased (P < 0.05). During sv, cardiac output and stroke volume increased and arterial blood pressure and total peripheral resistance decreased with duration of anesthesia at Pa o 2 > 250 mm of Hg. During sv, minute expired volume increased (P < 0.05) because respiratory frequency tended to increase as Pa o 2 decreased. Decrease in Pa co 2 (P < 0.05) also accompanied these respiratory changes. Although oxygen utilization was nearly constant over all treatment periods, oxygen delivery decreased (P < 0.05) with decrease in Pa o 2 , and was less (P < 0.05) during cv, compared with sv, for comparable Pa o 2 values. Muscle and hepatic-derived serum biochemical values were substantially increased and evidence of depressed renal function was observed in these horses immediately after anesthesia recovery. These serum biochemical changes exceeded values in horses previously studied during prolonged halothane anesthesia in the absence of low Pa o 2 .

Free access
in American Journal of Veterinary Research

SUMMARY

Objective

To compare the efficacy of positive pressure ventilation applied through a mask versus an endotracheal tube, using anesthetized/paralyzed foals as a model for foals with hypoventilation.

Animals

Six 1-month-old foals.

Procedure

A crossover design was used to compare the physiologic response of foals to 2 ventilatory techniques, noninvasive mask mechanical ventilation (NIMV) versus endotracheal mechanical ventilation (ETMV), during a single period of anesthesia and paralysis. Arterial pH, Pao2 , Paco2 , oxygen saturation, end-tidal CO2 tension, airway pressures, total respiratory system resistance, resistance across the upper airways (proximal to the midtracheal region), and pos-itive end-expiratory pressures (PEEP) were measured. Only tidal volume (VT; 10, 12.5, and 15 ml/kg of body weight) or PEEP (7 cm of H2O) varied.

Results

Compared with ETMV, use of NIMV at equivalent VT resulted in Paco2 and pH values that were significantly higher, but Pao2 was only slightly lower. Between the 2 methods, peak airway pressure was similar, but peak expiratory flow was significantly lower and total respiratory resistance higher at each VT for NIMV. Delivery of PEEP (7 cm of H2O) was slightly better for ETMV (7.1 ± 1.3 cm of H2O) than for NIMV (5.6 ± 0.6 cm of H2O).

Conclusion

These data suggest that use of NIMV induces similar physiologic effects as ETMV, but the nasal cavities and mask contribute greater dead space, manifesting in hypercapnia. Increasing the VT used on a per kilogram of body wieght basis, or the use of pressure-cycled ventilation might reduce hypercapnia during NIMV.

Clinical Relevance

Use of NIMV might be applicable in selected foals, such as those with hypoventilation and minimal changes in lung compliance, during weaning from endotracheal mechanical ventilation, or for short-term ventilation in weak foals. (Am J Vet Res 1997;58:1463–1467)

Free access
in American Journal of Veterinary Research