Objective--To determine whether larkspur-derived N-(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids alter heart rate and electrically evoked electromyographic (eEMG) response of the external anal sphincter (EAS) in cattle and whether these effects can be reversed by acetylcholinesterase inhibitors. Animals--12 beef heifers and 4 cows. Procedures--3 or 4 heifers were used in 1 or 2 of 7 dose-response experiments; heart rate and EAS eEMG response were assessed before and 24 hours after oral treatment with larkspur (doses equivalent to 0.5 to 15 mg of MSAL-type alkaloids/kg). In 3 subsequent experiments, 3 heifers (1 of which was replaced with another heifer in the control experiment) each received 10 mg of MSAL-type alkaloids/kg and were injected IV with physostigmine (0.04 mg/kg), neostigmine (0.04 mg/kg), or saline (0.9% NaCl) solution 24 hours later, prior to assessment. Additionally, EAS eEMG response was measured in 4 cows before and after epidural administration of 2% lidocaine hydrochloride. Results--Larkspur-treated heifers developed dose-related increases in heart rate and decreases in EAS eEMG response. Twenty-four hours after administration of MSAL-type alkaloids, neostigmine decreased heart rate but did not affect eEMG response, whereas physostigmine did not affect heart rate but caused a 2-fold increase in eEMG response. In cows, epidural anesthesia did not alter eEMG response, suggesting that transdermal stimulation of the EAS pudendal innervation did not occur. Conclusions and Clinical Relevance--In cattle, cardiac effects and muscle weakness or loss of EAS eEMG response induced by larkspur-derived MSAL-type alkaloids were reversed by neostigmine or physostigmine, respectively. Treatment with anticholinesterase inhibitors may alter the clinical effects of larkspur poisoning in cattle.

Cardiopulmonary responses were evaluated in 12 dogs undergoing endoscopy (gastroscopy and enteroscopy). Constant endoscopic insufflation was used to distend the stomach and small intestine for 30 minutes in groups of small (< 10 kg n = 4), medium (10 to 20 kg n = 4), and large (> 20 kg n = 4) dogs. Cardiopulmonary measurements within groups prior to gastric distention (preendoscopy) were compared with postendoscopy measurements and with those made during endoscopy. After distending the stomach and small intestine, increased luminal pressure within the body of the stomach and in the descending duodenum (P < 0.05) and increased abdominal girth (P < 0.05) were observed, with the greatest changes in small dogs. Caudal vena cava pressures and mean arterial and pulmonary artery pressures increased (P < 0.05) during endoscopy. Cardiac index varied, with small dogs having greater cardiac index (P < 0.05) during endoscopy, compared with that in medium and large dogs. Minute volume remained unchanged during insufflation, despite a decrease in tidal volume (P < 0.05), because of an increase in respiratory rate (P < 0.05). Arterial blood gas analysis revealed a mild, mixed metabolic/respiratory acidosis in all groups. Although cardiopulmonary changes associated with gastrointestinal tract endoscopy were common, the changes were often small and of little clinical significance.

Eighteen dogs undergoing lateral thoracotomy at the left fifth intercostal space were randomly assigned to 1 of 3 postoperative analgesic treatment groups of 6 dogs each as follows: group A, morphine, 1.0 mg/kg of body weight, IM; group B, 0.5% bupivacaine, 1.5 mg/kg given interpleurally; and group C, morphine, 1.0 mg/kg given interpleurally. Heart rate, respiratory rate, arterial blood pressure, arterial blood gas tensions, alveolar-arterial oxygen differences, rectal temperature, pain score, and pulmonary mechanics were recorded hourly for the first 8 hours after surgery, and at postoperative hours 12, 24, and 48. These values were compared with preoperative (control) values for each dog. Serum morphine and cortisol concentrations were measured at 10, 20, and 30 minutes, hours 1 to 8, and 12 hours after treatment administration . All dogs had significant decreases in pHa, PaO2, and oxygen saturation of hemoglobin, and significant increases in PaCO2 and alveolar-arterial oxygen differences in the postoperative period, but these changes were less severe in group-B dogs. Decreases of 50% in lung compliance, and increases of 100 to 200% in work of breathing and of 185 to 383% in pulmonary resistance were observed in all dogs after surgery. Increases in work of breathing were lower, and returned to preoperative values earlier in group-B dogs. The inspiratory time-to-total respiratory time ratio was significantly higher in group-B dogs during postoperative hours 5 to 8, suggesting improved analgesia. Blood pressure was significantly lower in group-A dogs for the first postoperative hour. Significant decreases in rectal temperature were observed in all dogs after surgery, and hypothermia was prolonged in dogs of groups A and C. Significant differences in pain score were not observed between treatment groups. Cortisol concentration was high in all dogs after anesthesia and surgery, and was significantly increased in group-B dogs at hours 4 and 8. Significant differences in serum morphine concentration between groups A and C were only observed 10 minutes after treatment administration. In general, significant differences in physiologic variables between groups A and C were not observed. Results of the study indicate that anesthesia and thoracotomy are associated with significant alterations in pulmonary function and lung mechanics. Interpleurally administered bupivacaine appears to be associated with fewer blood gas alterations and earlier return to normal of certain pulmonary function values. Interpleural administration of morphine does not appear to provide any advantages, in terms of analgesia or pulmonary function, compared with its IM administration.

Cardiovascular effects of epidurally administered morphine, a morphine-xylazine combination, and saline solution (control) during isoflurane-maintained anesthesia were assessed in 6 healthy dogs. Anesthesia was induced with isoflurane in O2 and was maintained at 2.0% end-tidal isoflurane concentration. Ventilation was controlled to maintain PaCO2 at 35 to 45 mm of Hg. The dorsal pedal artery was cannulated for measurement of systolic, mean, and diastolic pressures, and for blood sample collection. Arterial blood pH and gas tensions were determined every 30 minutes. Cardiac output was determined by thermodilution. The ECG, heart rate, body temperature, central venous pressure, mean pulmonary artery pressure, pulmonary capillary wedge pressure, end-tidal isoflurane concentration, and CO2 tension were monitored. Systemic and pulmonary vascular resistance, arterial HCO3(-) concentration, base excess, and cardiac index were calculated. After baseline measurements were taken, morphine (0.1 mg/kg of body weight) in 5 ml of isotonic saline solution, morphine and xylazine (0.1 mg of morphine and 0.09 mg of xylazine/kg) in 5 ml of isotonic saline solution, or 5 ml of isotonic saline solution was injected into the lumbosacral epidural space. Data were recorded at 5, 15, 30, 45, 60, 75, 90, 105, and 120 minutes after epidural injection. Statistical analysis included ANOVA for repeated measures. Significance was set at P < 0.05. None of the measured variables was significantly different among the 3 treatments at any time. Results of the study indicated that epidural administration of morphine or morphine and xylazine is not associated with significant cardiovascular side effects during isoflurane-maintained anesthesia in dogs.

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 less than or equal to 0.05 to 0.001) lower but, in contrast, pulmonary and systemic vascular resistance indices were significantly (P less than or equal to 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.

Pharmacologically induced splenic contraction might be useful during certain medical or surgical procedures in horses. The effects of phenylephrine, an alpha 1-adrenergic receptor agonist, on hemodynamic function and splenic dimensions were examined in 6 healthy adult horses. Phenylephrine infusion (1, 3, or 6 microgram/kg of body weight/min for 15 minutes) resulted in a dose-related increase in mean pulmonary artery pressure; right atrial pressure; systolic, mean, and diastolic arterial pressures; and packed cell volume (P = 0.0001). Concurrent decreases in heart rate and specific cardiac output (P = 0.0001) were detected, but stroke volume did not vary significantly. The rate-pressure product was increased only at the highest phenylephrine dosage (P = 0.012). Bradycardia was observed at all dosages during drug infusion, and second-degree atrioventricular block was detected in 88% of horses during infusion. Phenylephrine administration caused dose-dependent splenic contraction, as detected by ultrasonographic measurements of splenic area and thickness (P = 0.0001). At the 3- and 6-microgram/kg/min infusion rates, splenic area was reduced to 28 and 17% of baseline measurement, respectively. Splenic dimensions had returned to baseline values by 35 minutes after the end of infusion. Infusion of phenylephrine at a dosage of 3 microgram/kg/min for 15 minutes can be used to induce splenic contraction in horses.

Cardiorespiratory effects of abdominal insufflation were evaluated in 8 dogs during isoflurane anesthesia. Each dog was studied 3 times, in 1 of the following orders of insufflation pressures: 10-20-30, 20-30-10, 30-20-10, 10-30-20, 20-10-30, and 30-10-20 mm of Hg. Anesthesia was induced by use of a mask, dogs were intubated, and anesthesia was maintained by isoflurane in 100% oxygen. After instrumentation, baseline values were recorded (time 0), and the abdomen was insufflated with nitrous oxide. Data were recorded at 5, 10, 15, 20, 25, and 30 minutes after insufflation. The abdomen was then desufflated, with recording of data continuing at 35 and 40 minutes. Mean arterial pressure increased at 5 minutes during 20 mm of Hg insufflation pressure, and from 20 to 30 minutes during 30 mm of Hg pressure. Tidal volume decreased from 5 to 30 minutes during 10 and 20 mm of Hg pressures, and from 5 to 40 minutes during 30 mm of Hg pressure. Minute ventilation decreased at 10 and 20 minutes during 20 mm of Hg pressure. End-tidal CO2 concentration increased from 5 to 30 minutes during 20 and 30 mm of Hg pressure. The PaCO2 decreased at 40 minutes during 10 mm of Hg pressure, at 30 minutes during 20 mm of Hg pressure, and from 10 to 40 minutes during 30 mm of Hg pressure. Values for pH decreased from 10 to 30 minutes during 20 and 30 mm of Hg pressures. The PaO2 decreased from 20 to 40 minutes during 10 mm of Hg pressure, at 30 minutes during 20 mm of Hg pressure, and from 10 to 40 minutes during 30 mm of Hg pressure. Percentage decrease in tidal volume was greater at 5 and 15 minutes with 30 mm of Hg pressure. Differences in percentage increase in end tidal CO2 concentration were observed among the 3 pressures from 5 to 30 minutes. Although significant, these changes do not preclude use of laparoscopy if insufflation pressure > 20 mm of Hg is avoided.

The cardiopulmonary effects of thiopental sodium were studied in hypovolemic dogs from completion of until 1 hour after administration of the drug. Hypovolemia was induced by withdrawal of blood from dogs until mean arterial pressure of 60 mm of Hg was achieved. After stabilization at this pressure for 1 hour, 8 mg of thiopental/kg of body weight was administered IV to 7 dogs, and cardiopulmonary effects were measured. After blood withdrawal and prior to thiopental administration, heart rate and oxygen utilization ratio increased, whereas mean arterial pressure, mean pulmonary arterial pressure, central venous pressure, pulmonary wedge pressure, cardiac index, oxygen delivery, mixed venous oxygen tension, and mixed venous oxygen content decreased from baseline. Three minutes after thiopental administration, heart rate, mean arterial pressure, mean pulmonary arterial pressure, pulmonary vascular resistance, and mixed venous oxygen tension increased, whereas oxygen utilization ratio and arterial and mixed venous pH decreased from values measured prior to thiopental administration. Fifteen minutes after thiopental administration, heart rate was still increased; however by 60 minutes after thiopental administration, all measurements had returned to values similar to those obtained prior to thiopental administration.

Central venous pressure (CVP), portal pressure (PP), and heart rate (HR) were monitored in 6 female, sexually intact, middle-age Beagles during temporary portal vein obstruction, anesthetic recovery, abdominal bandaging, and propranolol administration. Intraoperative baseline PP was 7.3 mm of Hg (+/- 1.7 SD). Portal pressure was significantly increased throughout portal vein occlusion, but returned to baseline values 2 minutes after release of the ligature. Central venous pressure was significantly decreased throughout portal vein occlusion, but did not differ significantly from baseline values 3 minutes after release of the portal vein ligature. Portal pressure increased significantly (8 +/- 3.3 mm of Hg) over baseline values after application of an abdominal bandage; however, CVP did not change significantly. During postoperative monitoring, CVP and PP did not change significantly from respective 18-hour mean postoperative values in resting dogs. At 60 and 75 minutes after surgery, heart rate was significantly increased over the 18-hour mean. Portal pressure and CVP, respectively, were significantly increased over intraoperative baseline values in the first hour and the first 8 hours after surgery. Postoperative CVP and HR were significantly correlated. Individual measurements of PP in dogs that were abdominal pressing during barking or defecation were significantly increased (9 +/- 3 mm of Hg) above measurements taken after cessation of abdominal press. Portal pressure measurements in standing dogs decreased 7.5 +/- 2 mm of Hg, compared with measurements of the same dog in lateral recumbency. Central venous pressure was inaccurate in dogs performing abdominal press. Portal pressure did not decrease significantly from baseline after injection of propranolol (2 mg/kg, IV). Central venous pressure was significantly decreased at 2.5 and 3.0 hours after propranolol injection, and HR was significantly decreased from 1 to 3.5 hours after injection. Heart rate quickly returned to normal values if the dogs became excited. After propranolol administration, significant correlations were found between PP and HR, and between CVP and HR.

To investigate the cardiopulmonary effects of positive end-expiratory pressure (PEEP), values of 10, 20, and 30 cm of H2O, were applied to anesthetized, dorsally recumbent, ventilated ponies. After IV induction of general anesthesia, PEEP was superimposed on controlled ventilation with 100% oxygen, and changes in gas exchange and cardiac function were measured. Increasing values of PEEP in these ponies caused a linear increase in the mean (+/- SEM) functional residual capacity, from a control value (zero end-expiratory pressure) of 1.7 +/- 0.24 L to 2.2 +/- 0.31, 2.9 +/- 0.32 and 3.4 +/- 0.3 L at PEEP of 10, 20, and 30 cm of H2O, respectively (P < 0.05). Paralleling these changes, intrapulmonary shunt fraction decreased significantly (P < 0.05) from a control value of 12.9 +/- 0.5%, to 7.5 +/- 1.1 and 2.1 +/- 0.6%, at PEEP of 20 and 30 cm of H2O, respectively. Cardiac output was decreased by increasing values of PEEP, from control value of 11.7 +/- 1.56 L/min to 9.9 +/- 1.51, 8.8 +/- 1.33 and 5.62 +/- 0.56 L/min at PEEP of 10, 20, and 30 cm of H2O, respectively. Related to decreasing cardiac output, tissue oxygen delivery also decreased as PEEP was increased, from control value of 2.0 +/- 0.09 L/min to 1.8 +/- 0.07, 1.6 +/- 0.06, and 1.03 +/- 0.04 L/min at PEEP of 10, 20, and 30 cm of H2O, respectively. Thus, the effects of increasing values of PEEP in these ponies included increased functional residual capacity and arterial oxygenation, but marked reduction in cardiac output, resulting in no improvement or decrease in total oxygen delivery. Although PEEP is useful for improving arterial oxygenation, the deleterious cardiovascular effects should be anticipated or ameliorated by use of volume loading and/or inotrope administration.