Respiratory muscle perfusion in ponies during prolonged submaximal exercise in thermoneutral environment.

Distribution of blood flow among various respiratory muscles was examined in 8 healthy ponies during submaximal exercise lasting 30 minutes, using radionuclide labeled 15-microns 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 serratus, and scalenus muscles. Among expiratory muscles, blood flow in the internal abdominal oblique muscle was greatest, followed by that in internal intercostal and transverse thoracic 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.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional brain blood flow during prolonged submaximal exercise in ponies.

Experiments were carried out on 8 healthy ponies to examine the effects of prolonged submaximal exercise on regional distribution of brain blood flow. Brain blood flow was ascertained by use of 15-microns-diameter radionuclide-labeled microspheres injected into the left ventricle. The reference blood was withdrawn from the thoracic aorta at a constant rate of 21.0 ml/min. Hemodynamic data were obtained with the ponies at rest (control), and at 5, 15, and 26 minutes of exercise performed at a speed setting of 13 mph on a treadmill with a fixed incline of 7%. Exercise lasted for 30 minutes and was carried out at an ambient temperature of 20 C. Heart rate, mean arterial pressure, and core temperature increased significantly with exercise. With the ponies at rest, a marked heterogeneity of perfusion was observed within the brain; the cerebral, as well as cerebellar gray matter, had greater blood flow than in the respective white matter, and a gradually decreasing gradient of blood flow existed from thalamus-hypothalamus to medulla. This pattern of perfusion heterogeneity was preserved during exercise. Regional brain blood flow at 5 and 15 minutes of exercise remained similar to resting values. However, at 26 minutes of exercise, vasoconstriction resulted in a significant reduction in blood flow to all cerebral and brain-stem regions. In the cerebellum, the gray matter blood flow and vascular resistance remained near control values even at 26 minutes of exercise. Vasoconstriction in various regions of the cerebrum and brainstem at 26 minutes of exertion may have occurred in response to exercise-induced hypocapnia, arterial hypertension, and/or sympathetic neural activation.     

Effect of furosemide administration on systemic circulation of ponies during severe exercise

Systemic distribution of blood flow was studied in 11 healthy adult grade ponies, using radionuclide-labeled microspheres (15 micron diameter) that were injected into the left ventricle. Measurements were made at rest, during severe exercise (SE) without furosemide, as well as during SE at 10 minutes and 120 minutes after furosemide administration (1.0 mg/kg, IV). During SE, heart rate, cardiac output, mean aortic pressure, and whole body O2 consumption were 220 +/- 4 beats/min, 720 +/- 44 ml/min/kg, 169 +/- 4 mm of Hg, and 126 +/- 9 ml of O2/min/kg, respectively. With SE performed after furosemide administration, mean aortic pressure decreased from prefurosemide SE value (P less than 0.05), but heart rate, cardiac output, and whole body O2 consumption remained similar to values during SE without furosemide. During SE, blood flow to cerebellar gray matter, pons, and medulla oblongata increased despite marked hypocapnia, but in other regions of the brain, blood flow was unchanged. As arterial O2 content increased by 58% with SE, O2 delivery to all brain regions increased. With SE, adrenal gland blood flow increased, but intense vasoconstriction in the kidneys, spleen, pancreas, small intestine, and colon caused blood flow to plummet. During SE, blood flow in the diaphragm, gluteus medius, biceps femoris (muscles of propulsion), and triceps brachii muscles increased to a similar level, indicating that metabolic requirements of the diaphragm during exercise may not be less than those of other vigorously contracting muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional blood flow changes in response to near maximal exercise in ponies: a review

In recent years, increasing attention has been focused on the physiological responses of the horse to maximal exercise. Cardiovascular response in near maximally exercised galloping ponies (heart rate 225 +/- 7 beats/min; whole body oxygen consumption 122 +/- 12 ml/min/kg) comprised a marked increase in blood flow to the cerebellum, myocardium, diaphragm and the working muscles, while renal blood flow decreased precipitously. Cerebral and brainstem perfusion did not vary from resting values. Transmural homogeneity of myocardial blood flow persisted during near maximal exercise. It was reported that tachycardia of exercise contributed about one-third of the total increment in left ventricular coronary blood flow. Considerable unutilised coronary vasodilator capacity was also demonstrated in near maximally exercised ponies and it was suggested that maximally exercising ponies were not limited from further exertion because of the coronary circulation.     

Distribution of blood flow during moderate and strenuous exercise in ponies (Equus caballus)

Blood flow to the brain, heart, kidneys, diaphragm, and skeletal muscles was studied at rest and during graded treadmill exercise, using radionuclide-labeled microspheres (15 microns diameter), in 11 healthy adult ponies. Hemodynamic changes brought about by exercise included marked increases in cardiac output, mean aortic pressure, left ventricular end-diastolic pressure, and right ventricular systolic and end-diastolic pressures. Blood flow to the brain stem and cerebral hemispheres was unchanged during both moderate exercise (heart rate = 154 +/- 3 beats/min) and severe exercise (heart rate = 225 +/- 7 beats/min). Despite marked hypocapnia during severe exercise, cerebellar blood flow increased by 32% above control value (94 +/- 7 ml/min/100 g). Myocardial blood flow increased transmurally with both levels of exercise. The endo:epi (inner:outer) perfusion ratio for the left ventricle and the interventricular septum decreased during exercise. It was, however, not different from unity. During severe exercise, renal blood flow decreased to 19% of its control value. Blood flow to the diaphragm exceeded that to the skeletal muscles during both intensities of exercise. Blood flow to the exercising muscles of the brachium and thigh increased by 31- to 38-fold during moderate exercise and by 70- to 76-fold during severe exercise. It is concluded that the cardiovascular response to strenuous exercise in the pony included an increase in blood flow to the cerebellum, myocardium, diaphragm, and exercising skeletal muscles, while blood flow was diverted away from the kidneys. It would appear that the pony's cardiovascular response to severe exercise is similar to that of persons.     

Pressures in the right side of the heart and esophagus (pleura) in ponies during exercise before and after furosemide administration

Pressures in the right side of the heart and esophagus (pleural) have not been determined in the exercising equine subjects. In the present study, 8 healthy ponies were examined to determine the changes in these variables caused by 2 degrees of exercise done on a treadmill (heart rate:183 +/- 5 beats/min [trot] and 220 +/- 6 beats/min [canter]). Measurements were also made during both degrees of exertion 10 minutes and 120 minutes after furosemide (1.0 mg/kg) administration. It was observed that both gaits resulted in significant increases in pulmonary artery, right ventricular, and right atrial pressures. The pulmonary artery systolic, mean, and diastolic pressures during strenuous exertion were 306%, 252%, and 242% of the respective resting values. At canter, when respiratory frequency (138 +/- 4 breaths/min) is synchronized with stride frequency, the delta esophageal pressure approached 30.4 +/- 2.86 cm of water. During exercise 10 minutes after furosemide administration, the increment in right atrial pressure was markedly attenuated. During strenuous exertion 120 minutes after furosemide administration, the right atrial and pulmonary arterial pressures increased, but to a significantly lower level than did the prefurosemide values. However, the mean pulmonary artery pressure was still 240% of the resting value. It is concluded that marked pulmonary hypertension is a consistent feature of moderate, as well as strenuous, exertion in the pony. Although furosemide administration attenuated the pulmonary hypertension somewhat, the significance remains unclear.     

Cardiopulmonary effects of butorphanol tartrate intravenously administered for placement of duodenal cannulae in isoflurane-anesthetized yearling steers

Cardiopulmonary effects of IV administered butorphanol tartrate (BUT) were assessed in 7 yearling steers medicated with atropine and anesthetized with guaifenesin, thiamylal sodium, and isoflurane in O2 for surgical placement of duodenal cannulae. Heart rate, respiratory rate, arterial blood pressures, pHa, PaCO2, PaO2, arterial [HCO3-], esophageal temperature, and end-tidal isoflurane concentrations were measured before and after IV administration of BUT (10 mg). Mean respiratory rate increased significantly (P less than 0.05) only at 45 and 60 minutes after BUT administration. Mean respiratory rate was 26 +/- 6.3 breaths/min before BUT administration and 46 +/- 12.1 breaths/min 60 minutes after BUT administration. Arterial blood pressures were increased significantly (P less than 0.05) at all times, except 5 minutes after BUT administration. The mean value for mean arterial pressure was 76 +/- 9.6 mm of Hg before BUT injection and 117 +/- 12.6 mm of Hg 60 minutes after BUT injection. Mean values for pHa and arterial [HCO3-] were significantly (P less than 0.05) higher at 60 minutes after BUT administration (baseline, pH = 7.25 +/- 0.04 and [HCO3-] = 29.9 +/- 3.5 mEq/L; 60 minutes after BUT, pH = 7.28 +/- 0.03 and [HCO3-] = 33.0 +/- 1.8 mEq/L). Although some statistically significant changes were recorded, IV administration of BUT to these steers did not have a marked effect on the cardiopulmonary variables measured.     

Infusion of a combination of propofol and medetomidine for long-term anesthesia in ponies

OBJECTIVE: To determine the minimal infusion rate of propofol in combination with medetomidine for long-term anesthesia in ponies and the effects of atipamezole on recovery. ANIMALS: 12 ponies. PROCEDURE: Ponies were sedated with medetomidine (7 microg/kg of body weight, IV). Ten minutes later, anesthesia was induced with propofol (2 mg/kg, IV). Anesthesia was maintained for 4 hours, using an infusion of medetomidine (3.5 microg/kg per hour, IV) and propofol at a rate sufficient to prevent ponies from moving after electrical stimulation. Arterial blood pressures and blood gas analysis, heart rates, and respiratory rates were monitored. For recovery, 6 ponies were given atipamezole (60 microg/kg, IV). Induction and recovery were scored. RESULTS: Minimal propofol infusion rates ranged from 0.06 to 0.1 mg/kg per min. Mean arterial blood pressure was stable (range, 74 to 86 mm Hg), and heart rate (34 to 51 beats/min) had minimal variations. Variable breathing patterns were observed. Mean PaO2 (range, 116 to 146 mm Hg) and mean PaCO2 (range, 48 to 51 mm Hg) did not change significantly with time, but hypoxemia was evident in some ponies (minimal PaO2, 47 mm Hg). Recovery was fast and uneventful with and without atipamezole (completed in 20.2 and 20.9 minutes, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: Infusion of a combination of medetomidine and propofol was suitable for prolonged anesthesia in ponies. Recovery was rapid and uneventful. A combination of propofol and medetomidine may prove suitable for long-term anesthesia in horses. Monitoring of blood gases is essential because of potential hypoxemia.     

Neuromuscular and cardiovascular effects of atracurium in ponies anesthetized with halothane

Atracurium besylate, a recently developed, intermediate-duration acting, neuromuscular-blocking agent, was given to 15 halothane-anesthetized ponies to produce surgical relaxation (95% to 99% reduction of hoof twitch). All 15 ponies were given 3 injections; 8 of the 15 ponies were given 2 additional injections. Initial dosage of 0.11 +/- 0.01 mg/kg (mean +/- SD) and all subsequent injections of 0.052 mg/kg produced desired relaxation. Paralysis phase (maximum twitch reduction to 10% twitch recovery) lasted 24 +/- 5 minutes for the initial injection. Paralysis from subsequent injections lasted for a slightly shorter time. Recovery phase (10% to 75% twitch recovery) was similar for all injections (initial and repeated) and lasted approximately 11 minutes. Cardiovascular side effects were not seen. Reversal of effects of atracurium with administration of 0.5 mg of edrophonium/kg was achieved when the evoked digital extensor tension (twitch height) had returned to 95% of base line after the last atracurium injection. Edrophonium caused systolic blood pressure to increase 121% +/- 7% of base-line pressure, which was 133 +/- 18 mm of Hg. Heart rate changed to 93% +/- 9% of base line after edrophonium was given, which was 49 +/- 7 beat/min, but this change did not occur until after the blood pressure increased. Recovery to standing was smooth and strong. Five ponies stood on their first attempt to rise, 5 on the 2nd attempt, 2 on the 3rd, and 1 on the 4th. Seven ponies stood within 30 minutes after transportation to the recovery stall, 7 within an hour.(ABSTRACT TRUNCATED AT 250 WORDS)     

The hemodynamic effects of intrathecal oxytocin in normal dogs

OBJECTIVE: To evaluate the hemodynamic effects produced by intrathecal administration of oxytocin in healthy isoflurane-anesthetized dogs. STUDY DESIGN: Prospective single-dose trial. ANIMAL POPULATION: Six healthy purpose-bred adult dogs weighing between 7.3 and 14.5 kg. METHODS: Dogs were anesthetized with isoflurane and instrumented. Oxytocin at a dosage of 1.6 microg/kg was administered intrathecally at the cisternal space at time 0. Hemodynamic data were recorded immediately before and at 1, 5, 15, 30, and 60 minutes after oxytocin administration. Statistical analysis included an analysis of variance (ANOVA) for repeated measures over time. A P < .05 was considered significant. RESULTS: Baseline values +/- standard error of the mean for heart rate, mean arterial pressure, central venous pressure, cardiac output, systemic vascular resistance, mean pulmonary arterial pressure, pulmonary arterial occlusion pressure, and pulmonary vascular resistance were 101 +/- 11 beats/minute, 76 +/- 7 mm Hg, 4 +/- 4 mm Hg, 1.9 +/- 0.7 L/min, 3834 +/- 2556 dynes x sec/cm5, 14 +/- 3 mm Hg, 4 +/- 2 mm Hg, and 430 +/- 201 dynes x sec/cm5, respectively. Variations from the baseline values were seen in all parameters after intrathecal oxytocin administration, but no statistically significant differences were found. CONCLUSION: The intrathecal injection of 1.6 microg/kg of oxytocin is associated with minimal hemodynamic effects during isoflurane anesthesia. CLINICAL RELEVANCE: This study revealed no clinically significant deleterious effects from the intrathecal administration of oxytocin, and investigations into its use as a perioperative analgesic are therefore warranted.     

Influence of gastrointestinal tract disease on pharmacokinetics of lidocaine after intravenous infusion in anesthetized horses

OBJECTIVE: To determine the disposition of lidocaine after IV infusion in anesthetized horses undergoing exploratory laparotomy because of gastrointestinal tract disease. ANIMALS: 11 horses (mean +/- SD, 10.3 +/- 7.4 years; 526 +/- 40 kg). PROCEDURE: Lidocaine hydrochloride (loading infusion, 1.3 mg/kg during a 15-minute period [87.5 microg/kg/min]; maintenance infusion, 50 microg/kg/min for 60 to 90 minutes) was administered IV to dorsally recumbent anesthetized horses. Blood samples were collected before and at fixed time points during and after lidocaine infusion for analysis of serum drug concentrations by use of liquid chromatography-mass spectrometry. Serum lidocaine concentrations were evaluated by use of standard noncompartmental analysis. Selected cardiopulmonary variables, including heart rate (HR), mean arterial pressure (MAP), arterial pH, PaCO2, and PaO2, were recorded. Recovery quality was assessed and recorded. RESULTS: Serum lidocaine concentrations paralleled administration, increasing rapidly with the initiation of the loading infusion and decreasing rapidly following discontinuation of the maintenance infusion. Mean +/- SD volume of distribution at steady state, total body clearance, and terminal half-life were 0.70 +/- 0.39 L/kg, 25 +/- 3 mL/kg/min, and 65 +/- 33 minutes, respectively. Cardiopulmonary variables were within reference ranges for horses anesthetized with inhalation anesthetics. Mean HR ranged from 36 +/- 1 beats/min to 43 +/- 9 beats/min, and mean MAP ranged from 74 +/- 18 mm Hg to 89 +/- 10 mm Hg. Recovery quality ranged from poor to excellent. CONCLUSIONS AND CLINICAL RELEVANCE: Availability of pharmacokinetic data for horses with gastrointestinal tract disease will facilitate appropriate clinical dosing of lidocaine.     

Effects of hypertension and sympathetic denervation on cerebral blood flow in newborn pigs

To investigate the potential role of sympathetic nerves in preventing pronounced increases in cerebral blood flow, we evaluated the effects of abrupt hypertension on the cerebral circulation of newborn pigs with intact cerebral sympathetic innervation and after cerebral sympathetic denervation. Epinephrine infusion was used to induce abrupt increases in mean (+/- SEM) arterial pressure (innervated pigs, 62 +/- 3 mm of Hg to 115 +/- 3 mm of Hg; denervated pigs, 71 +/- 4 mm of Hg to 132 +/- 4 mm of Hg) that remained increased for the 3 minutes of the study. Abrupt hypertension increased blood flow to all brain regions. In denervated pigs, the increased flow to the cerebrum was prolonged, compared with that in pigs with intact sympathetic innervation. Differences between pigs of the innervated and denervated groups were not apparent, with respect to blood flow to any other region (caudate region, brain stem, cerebellum). In newborn pigs, sympathetic nerves may attenuate hypertension-induced increases in blood flow to the cerebrum, but do not appear to affect flow to the rest of the brain.     

Effects of acepromazine on renal function in anesthetized dogs

OBJECTIVE: To investigate the effects of IM administration of acepromazine on indices of relative renal blood flow and glomerular filtration rate (GFR) by means of scintigraphy, as well as the effects on physiologic, hematologic, and serum biochemical variables in anesthetized dogs, compared with effects of administration of saline. ANIMAL: 6 healthy Beagles. PROCEDURE: Acepromazine (0.1 mg/kg) or physiologic saline (0.9 NaCI) solution was administered IM 30 minutes prior to induction of anesthesia with thiopentone; anesthesia was maintained with inspired isoflurane for 2.25 hours. Blood gases and circulatory and ventilatory variables were monitored. Renal function was evaluated by scintigraphic measurements of GFR and relative renal blood flow and analyses of serum and urine. Statistical analyses used ANOVA or Friedman ANOVA. RESULTS: Values of relative renal blood flow and GFR remained high despite low blood pressures. After administration of acepromazine, mean +/- SD arterial blood pressure was 66 +/- 8 mm Hg during anesthesia; this value was below the threshold (80 mm Hg) for renal autoregulation of GFR. In comparison, mean arterial blood pressure after administration of saline was significantly higher (87 +/- 13 mm Hg). However, between treatments, there were no significant differences in GFR, relative renal blood flow, or other indices of renal function. CONCLUSIONS AND CLINICAL RELEVANCE: Measurements of renal function and blood flow in dogs during anesthesia with thiopentone and isoflurane did not differ significantly between treatments, which suggested that acepromazine protects renal function despite inducing reduction in blood pressure, compared with effects of administration of saline.     

Arterial-venous difference in atrial natriuretic peptide concentration during exercise in horses.

Six nontrained mares were subjected to steady-state, submaximal treadmill exercise to examine the effect of exercise on the plasma concentration of atrial natriuretic peptide (ANP) in arterial, compared with mixed venous, blood. Horses ran on a treadmill up a 6 degree grade for 20 minutes at a speed calculated to require a power equivalent to 80% of maximal oxygen uptake (VO2MAX). Arterial and mixed venous blood samples were collected simultaneously from the carotid and pulmonary arteries of horses at rest and at 10 and 20 minutes of exercise. Plasma was stored at -80 C and was later thawed; ANP was extracted, and its concentration was determined by radioimmunoassay. Exercise caused significant (P < 0.05) increases in arterial and venous plasma ANP concentrations. Mean +/- SEM arterial ANP concentration increased from 25.2 +/- 4.4 pg/ml at rest to 52.7 +/- 5.2 pg/ml at 10 minutes of exercise and 62.5 +/- 5.2 pg/ml at 20 minutes of exercise. Mean venous ANP concentration increased from 24.8 +/- 4.3 pg/ml at rest to 67.2 +/- 14.5 pg/ml at 10 minutes of exercise and 65.3 +/- 13.5 pg/ml at 20 minutes of exercise. Significant differences were not evident between arterial or mixed venous ANP concentration at rest or during exercise, indicating that ANP either is not metabolized in the lungs or is released from the left atrium at a rate matching that of pulmonary metabolism.     

Reference cardiopulmonary physiologic parameters for standing, unrestrained white rhinoceroses (Ceratotherium simum).

Chemical restraint is an important tool for the management and medical care of both captive and free-ranging rhinoceroses. Current anesthetic protocols for the white rhinoceros (Ceratotherium simum) are reported to cause varying degrees of hypertension, tachycardia, muscular stiffness and fasciculation, acidosis, and, most importantly, respiratory depression with resulting hypoventilation, hypoxia, and hypercapnea. To assist in the assessment and development of new and improved anesthetic techniques for the white rhinoceros, the following cardiopulmonary reference parameters for standing, unrestrained white rhinoceroses were generated (mean +/- standard error [minimum maximum]): heart rate = 39 +/- 0.8 beats/min (32-42), respiratory rate = 19 +/- 0.6 breaths/min (16-23), corrected indirect systolic blood pressure = 160 +/- 2.9 mm Hg (146-183), corrected indirect diastolic blood pressure = 104 +/- 2.3 mm Hg (88-117), corrected indirect mean blood pressure = 124 +/- 2.2 mm Hg (108-135), end tidal CO2 = 45.1 +/- 0.7 mm Hg (41.7-48.0), rectal temperature = 36.8 +/- 0.1 degrees C (36.6-37.2), arterial blood pH = 7.391 +/- 0.007 (7.346-7.431), arterial partial pressure of oxygen = 98.2 +/- 1.4 mm Hg (90.2-108.6), arterial partial pressure of CO2 = 49.0 +/- 0.9 mm Hg (44.4-53.7), base excess = 3.5 +/- 0.4 mmol/L (1.9-5.9), bicarbonate = 29.3 +/- 0.4 mmol/L (27.3-32.2), and arterial hemoglobin oxygen saturation (SaO2) = 97.2 +/- 0.1% (96.6-98.0).     

Effects of propranolol on cardiopulmonary function in the pony during submaximal exercise

Cardiopulmonary responses of four ponies were monitored during standard exercise tests (SET), before and after beta-adrenergic receptor blockade with propranolol. The SET consisted of four 5 min increments of increasing speed from 1.0 to 2.8 m/sec on a treadmill at a 7 degrees incline. Data were collected at rest, throughout the SET and recovery. Administration of propranolol to ponies at rest had no effect on cardiopulmonary function. During the SET, increases in heart rate, mean pulmonary artery flow velocity (an index of cardiac output) and right ventricular dP/dt (an index of myocardial contractility) were progressively attenuated as running speed increased. Body temperature and mean pulmonary artery and right ventricular pressures were significantly elevated over normal. Propranolol treatment had no effect on the responses of mean arterial pressure, haematocrit, haemoglobin, blood lactate and arterial blood gases and pH to the SET. These results suggest that in the pony there is no sympathetic activity to the heart at rest and that during exercise there is pulmonary vasodilation mediated by beta-adrenergic receptors.     

Detomidine-Propofol Anesthesia for Abdominal Surgery in Horses

OBJECTIVE: To evaluate propofol for induction and maintenance of anesthesia, after detomidine premedication, in horses undergoing abdominal surgery for creation of an experimental intestinal adhesion model. STUDY DESIGN: Prospective study. ANIMALS: Twelve horses (424 +/- 81 kg) from 1 to 20 years of age (5 females, 7 males). METHODS: Horses were premedicated with detomidine (0.015 mg/kg i.v.) 20 to 25 minutes before induction, and a propofol bolus (2 mg/kg i.v.) was administered for induction. Propofol infusion (0.2 mg/kg/min i.v.) was used to maintain anesthesia. The infusion rate was adjusted to maintain an acceptable anesthetic plane as determined by muscle relaxation, occular signs, response to surgery, and cardiopulmonary responses. Oxygen (15 L/min) was insufflated through an endotracheal tube as necessary to maintain the SpO2 greater than 90%. Systolic (SAP), mean (MAP), and diastolic (DAP) arterial pressures, heart rate (HR), electrocardiogram (ECG), respiratory rate (RR), SpO2 (via pulse oximetry), and nasal temperature were recorded at 15 minute intervals, before premedication and after induction of anesthesia. Arterial blood gas samples were collected at the same times. Objective data are reported as mean (+/-SD); subjective data are reported as medians (range). RESULTS: Propofol (2.0 mg/kg i.v.) induced anesthesia (mean bolus time, 85 sec) within 24 sec (+/-22 sec) after the bolus was completed. Induction was good in 10 horses; 2 horses showed signs of excitement and these two inductions were not smooth. Propofol infusion (0.18 mg/kg/min +/- 0.04) was used to maintain anesthesia for 61 +/- 19 minutes with the horses in dorsal recumbency. Mean SAP, DAP, and MAP increased significantly over time from 131 to 148, 89 to 101, and 105 to 121 mm Hg, respectively. Mean HR varied over time from 43 to 45 beats/min, whereas mean RR increased significantly over anesthesia time from 4 to 6 breaths/min. Mean arterial pH decreased from a baseline of 7.41 +/- 0.07 to 7.30 +/- 0.05 at 15 minutes of anesthesia, then increased towards baseline values. Mean PaCO2 values increased during anesthesia, ranging from 47 to 61 mm Hg whereas PaO2 values decreased from baseline (97 +/- 20 mm Hg), ranging from 42 to 57 mm Hg. Muscle relaxation was good and no horses moved during surgery: Recovery was good in 9 horses and acceptable in 3; mean recovery time was 67 +/- 29 minutes with 2.4 +/- 2.4 attempts necessary for the horses to stand. CONCLUSIONS: Detomidine-propofol anesthesia in horses in dorsal recumbency was associated with little cardiovascular depression, but hypoxemia and respiratory depression occurred and some excitement was seen on induction. CLINICAL RELEVANCE: Detomidine-propofol anesthesia is not recommended for surgical procedures in horses if dorsal recumbency is necessary and supplemental oxygen is not available (eg, field anesthesia).     

Influence of subclinical pulmonary findings on cardiac parameters in Icelandic horses

In the present study we examined, if in Icelandic horses an increase in heart and/ or breathing rate is physiological and breed dependend or a sign of a pulmonary or cardiac disease. Therefore we examined 37 Icelandic horses with the prereport of being healthy. During clinical lung examination four horses showed symptoms of a pulmonary disease like increased breathing rate and enforced breathing at rest. These horses were excluded from the study. The other 33 horses were clinically normal. 17 of these horses were unridden (untrained) and 16 horses were regularly worked (trained). After clinical examination in all horses analysis of arterial blood gas, endoscopy with tracheo- bronchial secret analysis and radiographic examination of the lung were carried out. Additionally electro- and echocardiographic examinations and standardised exercise tests with determination of heart and breathing rate as well as plasma lactate values were performed in all horses. During electro- and echocardiographic examination no pathological findings were observed. In total 22 of the 33 horses showed abnormal lung findings. Seven horses had mild signs of RAO and 15 horses had mild signs of interstitial bronchitis. Three horses had additional pulmonary haemorrhage. Eleven out of the 33 horses showed no abnormal lung findings. The breathing rate at rest differed not significantly between horses with (21 +/- 1/min) or without (23 +/- 2/min) pulmonary findings. The heart rate also did not differ significantly between horses with (39 +/- 1/min) or without (42 +/- 1/min) pulmonary findings. In contrast to this the trained Icelandic horses with abnormal pulmonary findings had significantly higher heart rates (p = 0.01) and significantly lower breathing rates (p = 0.009) compared to those without abnormal pulmonary findings. During echocardiography Icelandic horses with abnormal pulmonary findings had significantly larger left atrial diameter (without abnormal pulmonary findings: 82 +/- 7 mm, with abnormal pulmonary findings: 90 +/- 8 mm, p = 0.02). Compared to the untrained Icelandic horses (5.4 +/- 2 mmol/l) the trained horses showed significantly lower plasma lactate values (3.1 +/- 2 mmol/l, p = 0.001) immediately after exercise. After exercise the icelandic horses with abnormal pulmonary findings had significantly higher breathing rates (p < 0.05) and longer recovery periods (30 minutes) than horses without abnormal respiratory findings (15 minutes). Recovery of heart rate after exercise showed no differences between groups.     

Effect of splenectomy on exercise-induced pulmonary and systemic hypertension in ponies

Large increases in systemic and pulmonary arterial pressures of exercising healthy ponies have been observed. Because exercise causes a considerable increase in PCV of ponies, we examined the effect of splenectomy on exercise-induced changes in systemic and pulmonary pressures. These pressures (taken with catheter-tip micromanometers) and indicator dilution cardiac output were determined on 9 healthy ponies that had undergone splenectomy 4 to 9 weeks before the study. Data obtained at rest and during submaximal (10.5 to 11.0 mph) and maximal (14 to 15 mph) exercise from these ponies were compared with similar data from clinically normal ponies. Following splenectomy, PCV increased by only 4 vol% during maximal exercise, but cardiac output of splenectomized ponies reached values similar to those of clinically normal ponies. Despite this similarity in cardiac output, the systemic and pulmonary arterial pressures of exercising splenectomized ponies increased to significantly lower levels than those in clinically normal ponies (P less than 0.01); total pulmonary vascular resistance and total peripheral resistance decreased to values significantly less than those in clinically normal ponies (P less than 0.01). Thus, it appears that increases in blood viscosity induced by increases in PCV may contribute substantially to the pulmonary and systemic hypertension of exercise in clinically normal ponies.