Physiological stimuli of thirst and drinking patterns in ponies

The stimuli that elicit thirst were studied in four ponies. Nineteen hours of water deprivation produced an increase in plasma protein from 67 +/- 0.1 g/litre to 72 +/- 2 g/litre, a mean (+/- se) increase in plasma sodium from 139 +/- 3 to 145 +/- 2 mmol/litre and an increase in plasma osmolality from 297 +/- 1 to 306 +/- 2 mosmol/litre. Undeprived ponies drank 1.5 +/- 0.9 kg/30 mins; 19 h deprived ponies drank 10.2 +/- 2.5 kg/30 mins and corrected the deficits in plasma protein, plasma sodium and plasma osmolality as well as compensating for the water they would have drunk during the deprivation period. In order to determine if an increase in plasma osmolality would stimulate thirst, 250 ml of 15 per cent sodium chloride was infused intravenously. The ponies drank when osmolality increased 3 per cent and when plasma sodium rose from 136 +/- 3 mmol/litre to 143 +/- 3 mmol/litre. Ponies infused with 15 per cent sodium chloride drank 2.9 +/- 0.7 kg; those infused with 0.9 per cent sodium chloride drank 0.7 +/- 0.5 kg. In order to determine if a decrease in plasma volume would stimulate thirst, ponies were injected with 1 or 2 mg/kg bodyweight (bwt) frusemide. Plasma protein rose from 68 +/- 2 g/litre pre-injection to 75 +/- 2 g/litre 1 h after 1 mg/kg bwt frusemide and to 81 +/- 1 g/litre 1 h after 2 mg/kg bwt frusemide.(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.     

Bronchial circulation during prolonged exercise in ponies.

Tracheal, bronchial, and renal flow were studied in 8 healthy ponies at rest and during exercise performed on a treadmill at a speed setting of 20.8 km/h and 7% grade (incline) for 30 minutes. Blood flow was determined with 15-microns-diameter radionuclide-labeled microspheres that were injected into the left ventricle when the ponies were at rest, and at 5, 15, and 26 minutes of exertion. Heart rate and mean aortic pressure increased from resting values (40 +/- 2 beats/min and 124 +/- 3 mm of Hg, respectively) to 152 +/- 8 beats/min and 133 +/- 4 mm of Hg at 5 minutes of exercise, to 169 +/- 6 beats/min and 143 +/- 5 mm of Hg at 15 minutes of exercise, and to 186 +/- 8 beats/min, and 150 +/- 5 mm of Hg at 26 minutes of exercise. Tracheal blood flow at rest and during exercise remained significantly (P less than 0.05) less than bronchial blood flow. Tracheal blood flow increased only slightly with exercise. Vasodilation caused bronchial blood flow to increase throughout exercise. Pulmonary arterial blood temperature of ponies also increased significantly (P less than 0.05) with exercise and a significant (P less than 0.005) correlation was found between bronchial blood flow and pulmonary arterial blood temperature during exertion. At 5 minutes of exercise, renal blood flow was unchanged from the resting value; however, renal vasoconstriction was observed at 15 and 26 minutes of exercise. We concluded that bronchial circulation of ponies increased with exercise in close association with a rise in pulmonary arterial blood temperature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of exercise on the partitioning of equine respiratory resistance

Pleural, tracheal, pharyngeal and mask pressures as well as airflow and tidal volume of five ponies on a treadmill (incline 8.3 degrees) were recorded simultaneously while resting, walking, trotting slowly, trotting fast, after standing for 30 secs and 5 mins after the end of the exercise. The curves obtained were used to calculate total pulmonary resistance (RL), lower airway resistance (RLA) and upper airway resistance (RUA). The latter was also divided into nasal resistance (Rnas) and laryngeal plus extrathoracic tracheal resistance (Retr + lar). Furthermore, the inspiratory and expiratory components of each of these R values were estimated. Levels of RL, RLA and RUA were increased significantly during exercise but, during the recovery period, the values were significantly lower than those pre-exercise. RUA represented 82 per cent of RL at rest and this percentage did not change significantly during and after exercise. The nasal resistance to RUA ratio was always higher than 0.5. The fact that RL increased with exercise intensity was due to the increase of RUA during inspiration, and mainly a result of the increase of RLA during expiration. At fast trot, RLA represented 5 and 50 per cent of RL during inspiration and expiration respectively. It was concluded that heavy exercise induces in ponies an increase of RL, one reason for which could be the partial collapse of the extrathoracic and intrathoracic airways during inspiration and expiration respectively.     

Pulmonary wedge pressure and heart frequency measurements during standardized treadmill exercise for extension of left atrial function diagnosis in warmblood horses

In 12 healthy warmblood horses (six trained and six untrained) the pulmonary wedge pressure and heart frequency was measured at rest and during a standardised exercise test on a treadmill. The mean pulmonary wedge pressure at rest was 14.53 +/- 2.36 mmHg. There was no significant difference in pulmonary wedge pressure either at rest or during exercise between trained and untrained horses. During walking (1.8 m/s) the mean pulmonary wedge pressure was 19.62 +/- 4.03 mmHg, during trotting (4 und 5 m/s) it was between 22.38 +/- 3.92 mmHg and 25.28 +/- 3.7 mmHg. During canter (6 m/s) and gallop (8 m/s) the mean pulmonary wedge pressure increased to a level of 25.54 +/- 4.3 mmHg and 31.86 +/- 4.29 mmHg. There was a significant increase in pulmonary wedge pressure with each incremental step of the standardised treadmill test. Concerning mean heart frequency a highly significant increase could be observed at the beginning and at the end (treadmill speed of 7 and 8 m/s) of the standardised exercise test. At higher intensity of the exercise test (7 m/s and 8 m/s) untrained horses showed a significantly increased heart rate compared to trained horses. Neither at rest nor during the different exercise levels a significant correlation factor greater 0.5 between heart frequency and pulmonary wedge pressure could be observed. The increase of heart frequency and pulmonary wedge pressure during exercise showed no correlation. Between left atrial size and pulmonary wedge pressure a statistical weak correlation could be observed up to a treadmill velocity of 6 and 7 m/s.     

Atropine reduces dobutamine-induced side effects in ponies undergoing a pharmacological stress protocol

REASONS FOR PERFORMING STUDY: High-dose dobutamine stress echocardiography has been shown to be cardiotoxic and arrhythmogenic in horses. However, the test may have benefit in practice as a pharmacological challenge of exercise without the treadmill being required. OBJECTIVES: To investigate the effect of low-dose dobutamine on cardiac performance in ponies previously treated with atropine, in order to develop a pharmacological protocol that allows examination of the equine heart under stimulation. METHODS: In 13 healthy Shetland ponies, heart rate (HR), stroke index (SI) and cardiac index (CI) were calculated from pulsed-wave Doppler ultrasound measurements performed at rest and during incremental steps of dobutamine infusion. Group 1 (n = 7) received dobutamine infusion at 2 microg/kg bwt/min for 5 mins followed by incremental rates of 5 microg/kg bwt/min every 5 mins, from 5 to 40 microg/kg bwt/min. Group 2 (n = 6) received dobutamine infusion in incremental rates of 1 microg/kg bwt/min, every 5 mins, from 2 microg/kg bwt/min to 5 microg/kg bwt/min, after premedication with 2 injections of 25 microg/kg bwt of atropine 5 mins apart. RESULTS: The increase in CI during the pharmacological challenge was higher in Group 2 and reached about 2.5 times the resting value. This increase in CI was mediated by a significant increase in HR in both groups, while SI significantly decreased in Group 1 and did not change significantly in Group 2. Ponies of Group 1, but not those of Group 2, showed excessive restlessness and cardiac arrhythmias during the pharmacological challenge and a high intragroup variability in cardiac response. CONCLUSIONS: The results of this study suggest that a low dose of dobutamine in ponies previously given atropine could be a helpful pharmacological protocol to perform stress echocardiography in equids. POTENTIAL RELEVANCE: Further studies should evaluate left ventricular wall motion in horses undergoing low-dose dobutamine protocol after pretreatment with atropine.     

Pulmonary artery wedge pressure and heart rate measurement during pharmacological stress induction for left cardial function diagnosis in horses with and without heart disease

In 18 horses, the pulmonary artery wedge pressure and the heart rate were measured during pharmacological stress load. 12 horses were healthy (4 trained, 8 untrained) and 6 horses had a heart disease (3 trained, 3 untrained). Pharmacological stress induction was carried out with the sympathomimetic drug dobutamine at a dosage rate of 7.5 microg/kg/min over 10 minutes of infusion. At the fourth minute, the parasympatholytic drug atropine was administered (5 microg/kg bw), and the heart rate and the pulmonary artery wedge pressure were continuously measured over 26 minutes. During sole dobutamine infusion, a significant decrease in heart rate and a significant increase in pulmonary artery wedge pressure were observed. After the application of atropine in the fourth minute, a significant increase in heart rate (from 35.7 +/- 6 up to 106 +/- 38/ min) and in pulmonary artery wedge pressure (from 15.7 +/- 3 up to 24 +/- 8.6 mmHg) were visible in the group of healthy horses. The horses with heart diseases had a significantly higher increase in both parameters (heart rate and pulmonary artery wedge pressure) with a significantly positive correlation (r = 0.7). The heart rate increased in the horses with heart diseases from 35.2 +/- 2,8 beats/min up to 132 +/- 45.7 beats/min and the pulmonary artery wedge pressure increased from 17.3 +/- 3,2 mmHg up to 32.7 +/- 13 mmHg. The cardiac status (healthy or heart disease) as well as the training level of the horses (untrained or trained) had a significant influence on the heart rate and the pulmonary artery wedge pressure. The untrained horses (healthy and heart disease) showed significantly higher values over a longer period of time than did the trained horses with the same cardiac status. Additionally the influence of pharmacological stress induction on echocardiographic parameters was investigated. The left atrial size (p = 0.015) and left ventricular diameter were significanly different in the systole (p = 0.008) and in the diastole (p = 0.001) between healthy horses and horses with heart diseases. All horses showed a positive correlation between the pulmonary artery wedge pressure and the left atrial size (r = 0.8), as well as between the left ventricular systolic (r = 0.6) and the diastolic diameter (r = 0.6). The correlation between the pulmonary artery wedge pressure and the left atrial size was nearly the same in the healthy horses (r = 0.74) and in the horses with heart diseases (r = 0.76). Regarding the training level, all untrained horses had a significantly higher correlation between the pulmonary artery wedge pressure and the left atrial size (r = 0.87) in comparison to the trained horses (r = 0.74). Particularly in the untrained horses with heart diseases, this correlation was remarcable (r = 0.99).     

Effect of atropine-dobutamine stress test on left ventricular echocardiographic parameters in untrained warmblood horses

The aim of this study was to investigate the effect of combined atropine low-dose dobutamine stress test on left ventricular parameters in adult warmblood horses, to establish a potential protocol for pharmacological stress echocardiography. Seven healthy untrained warmblood horses aged 9 to 22 years were used. Heart rate (HR) and left ventricular B- and M-mode dimensions were recorded at baseline and during stress testing with 35 microg/kg atropine IV followed by incremental dobutamine infusion of 2 to 6 microg/kg/min. HR increased significantly (P < .05) during the pharmacological challenge, and a maximal HR of 156.6 +/- 12.5 bpm was reached at maximal dobutamine infusion rate. Systolic and diastolic interventricular septum thickness, systolic and diastolic left ventricular free wall thickness, and fractional shortening increased significantly and reached a maximum at the highest infusion rate (mean +/- SD: 4.51 +/- 0.27 versus 5.65 +/- 0.31 cm, 2.89 +/- 0.19 versus 3.78 +/- 0.10 cm, 3.72 +/- 0.34 versus 4.77 +/- 0.18 cm, 2.44 +/- 0.28 versus 3.11 +/- 0.34 cm, 34.98 +/- 3.82 versus 50.56 +/- 3.42%, respectively). Systolic and diastolic left ventricular internal diameter decreased significantly during dobutamine infusion. Left ventricular external and internal area were significantly lower at a dobutamine infusion rate of 2 microg/kg/min but no further decrease was observed during the subsequent steps. Systolic and diastolic myocardial area was significantly lower after the administration of dobutamine but not significantly different during dobutamine infusion, when compared to baseline values. This pharmacological stress test induced significant changes in left ventricular echocardiographic parameters in adult warmblood horses. Additional research should evaluate the value of this stress test in horses suffering from cardiac disease.     

Comparison of yearling, two-year-old and adult Thoroughbreds using a standardised exercise test

The purpose of this study was to compare exercise measurements in yearling, two-year-old and adult Thoroughbreds using a standardised treadmill incremental exercise test. Peak oxygen consumption (VO2 peak: 128.0 +/- 2.1, 140.0 +/- 2.1, 163.7 +/- 3.4; ml/kg/min +/- se, P less than 0.05), peak packed cell volume (PCV peak: 0.50 +/- 0.01, 0.58 +/- 0.01, 0.64 +/- 0.01 litres/litre +/- se, P less than 0.05) and the maximum number of steps completed in the exercise test (STEPmax: 7.7 +/- 0.1, 8.1 +/- 0.1, 8.6 +/- 0.1; steps +/- se, P less than 0.05) increased with age and degree of physical activity. Peak venous lactate concentration (LACpeak: 21.3 +/- 1.5, 19.5 +/- 1.7, 14.4 +/- 1.7; mmol/litre +/- se, P less than 0.05) and peak respiratory exchange ratio (Rpeak) were significantly higher in both groups of younger horses compared to the adult racehorses. Peak heart rate (HRpeak: 230 +/- 2, 231 +/- 3, 229 +/- 3; beats/min +/- se) did not change with age or training. The rate of change of VO2 between steps in the exercise test (VO2trans) was significantly lower in the adult racehorses at the highest exercise intensities. The slopes of the linear approximation between R (LinR bx), the natural log transformation of venous lactate concentration (LogLAC bx), and heart rate (HR bx) with velocity were significantly lower in the trained adult racehorses. The slope of venous lactate concentration normalised to per cent VO2peak (LogLAC per cent bx) was significantly lower and R breakpoint (R brkpt) normalised to per cent VO2peak was significantly higher in the trained adult racehorses. There was a more rapid decrease in venous lactate and a more rapid return to initial R values in the adult horses relative to the younger, untrained horses. No significant age or training effects were found in the remainder of the post exercise measurements. These results indicate that aerobic power and exercise capacity increased with age and training. Anaerobic power was already well developed even at a young age.     

Long‐term assessment of horses and ponies post exposure to monensin sodium in commercial feed

Reasons for performing study: Acute monensin intoxication in equids is well described; however, the long‐term effects of sublethal intoxication and ability to return to previous use are less well understood. Long‐term observations may allow improved estimation of prognosis in cases of sublethal intoxication. Objectives: To assess horses and ponies exposed to sublethal amounts of monensin for evidence of chronic sequelae and ability to return to prior/intended use. Methods: Twenty‐nine horses and 8 ponies were assessed utilising serum biochemistry, treadmill exercise stress testing, electrocardiography, and pre‐ and post exercise echocardiography ≥6 weeks after ingestion of monensin‐contaminated feed. Animals with evidence of monensin‐induced cardiomyopathy were re‐examined after a period of rest of ≥11 months. Follow‐up information was obtained by owner telephone interview ≥52 months after exposure. Results: During resting echocardiography, 11 animals had reduced/low‐normal left ventricular fractional shortening (FS); an increase in FS in 8 of these animals was measured ≥11 months later. Six animals had reduced or low‐normal FS during post exercise echocardiography. Two horses had ventricular premature depolarisations during exercise. Follow‐up information was available for 35 animals: 21 returned to athletic/reproductive use, 13 were retired immediately and one died. Mean FS increased significantly (P<0.001) between initial and second examination in 15 animals that underwent resting echocardiography on 2 occasions. Conclusions: Some equids exposed to sublethal doses of monensin may not develop permanent myocardial disease and a return to athletic/reproductive use is possible. Potential relevance: Exercise stress testing, echocardiography and electrocardiography may be useful for detection and monitoring of cardiac dysfunction in equids exposed to monensin and determining whether a return to athletic/reproductive use is possible.     

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.     

Quantification, repeatability, and reproducibility of feline radial and longitudinal left ventricular velocities by tissue Doppler imaging

OBJECTIVE: To measure the radial and longitudinal velocities of several myocardial segments of the left ventricular wall by use of tissue Doppler imaging (TDI) in healthy cats and determine the repeatability and reproducibility of the technique. ANIMALS: 6 healthy cats. PROCEDURE: 72 TDI examinations were performed on 4 days by the same trained observer. Radial parameters included left endocardial and epicardial myocardial velocities. Longitudinal parameters included left basal, middle, and apical myocardial velocities. RESULTS: All velocity profiles had 1 positive systolic wave (S) and 2 negative diastolic waves (E and A). Myocardial velocities were higher in the endocardial than epicardial segments during the entire cardiac cycle (systolic wave S, 4.4 +/- 0.82 and 1.9 +/- 0.55; diastolic wave E, 9.7 +/- 1.70 and 2.2 +/- 0.74; and diastolic wave A, 5.1 +/- 1.56 and 1.4 +/- 0.76, respectively). Velocities were also higher in the basal than in the apical segments (systolic wave S, 4.7 +/- 0.76 and 0.2 +/- 0.11; diastolic wave E, 9.7 +/- 1.36 and 0.5 +/- 0.17; and diastolic wave A, 3.7 +/- 1.51 and 0.2 +/- 0.13, respectively). The lowest within-day and between-day coefficients of variation were observed in endocardial segments (8.2% and 6.5% for systolic wave S and diastolic wave E, respectively) and in the basal segment in protodiastole (5.5%). CONCLUSIONS AND CLINICAL RELEVANCE: Repeatability and reproducibility of TDI were adequate for measurement of longitudinal and radial left ventricular motion in healthy awake cats. Validation of TDI is a prerequisite before this new technique can be recommended for clinical use.     

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.     

Adverse haemodynamic effects of the rapid intravenous injection of hypotonic solutions in sheep

The rapid intravenous administration of 10 ml of sterile water or hypotonic saline to five conscious sheep induced substantial adverse haemodynamic effects lasting 10 to 20 seconds. They included reductions in cardiac output (to 44 per cent of the baseline value measured in the 30 seconds before the injection), arterial blood pressure (67 per cent of baseline), left ventricular systolic pressure (60 per cent of baseline), myocardial contractility (60 per cent of baseline), and left coronary arterial blood flow (39 per cent of baseline), and increases in heart rate to 137 per cent of the baseline. The intensities of these effects were related directly to the rates of injection and inversely to the osmolalities of the solutions injected. Intravascular haemolysis was associated with the effects. These data are of potential importance to anyone administering drugs intravenously to sheep.     

Use of quantitative two-dimensional color tissue Doppler imaging for assessment of left ventricular radial and longitudinal myocardial velocities in dogs

OBJECTIVE: To determine left ventricular free wall (LVFW) radial and longitudinal myocardial contraction velocities in healthy dogs via quantitative 2-dimensional color tissue Doppler imaging (TDI). ANIMALS: 100 dogs. PROCEDURE: TDI was used by a single trained observer to measure radial and longitudinal myocardial movement in the LVFW. Radial myocardial velocities were recorded in segments in the endocardial and epicardial layers of the LVFW, and longitudinal velocities were recorded in segments at 3 levels (basal, middle, apical) of the LVFW. RESULTS: LVFW velocities were higher in the endocardial layers than in the epicardial layers. Left ventricular free wall velocities were higher in the basal segments than in the middle and apical segments. Radial myocardial velocity gradients, defined as the difference between endocardial and epicardial velocities, were (mean +/- SD) 2.5 +/- 0.8 cm/s, 3.8 +/- 1.5 cm/s, and 2.3 +/- 0.9 cm/s in systole, early diastole, and late diastole, respectively. Longitudinal myocardial velocity gradients, defined as the difference between basal and apical velocities, were 5.9 +/- 2.2 cm/s, 6.9 +/- 2.5 cm/s, and 4.9 +/- 1.7 cm/s in systole, early diastole, and late diastole, respectively. A breed effect was detected for several systolic and diastolic TDI variables. In all segments, systolic velocities were independent of fractional shortening. CONCLUSIONS AND CLINICAL RELEVANCE: LVFW myocardial velocities decreased from the endocardium to the epicardium and from base to apex, thus revealing intramyocardial radial and longitudinal velocity gradients. These indices could enhance conventional echocardiographic analysis of left ventricular function in dogs. Breed-specific reference intervals should be defined.     

Longitudinal left ventricular myocardial dysfunction assessed by 2D colour tissue Doppler imaging in a dog with systemic hypertension and severe arteriosclerosis

A 12-year-old sexually intact male Vendee Griffon Basset was presented for acute pulmonary oedema. Severe systemic systolic arterial hypertension (SAH) was diagnosed (290 mmHg). Despite blood and abdominal ultrasound tests, the underlying cause of the systemic hypertension could not be determined, and primary SAH was therefore suspected. Conventional echocardiography showed eccentric left ventricular hypertrophy with normal fractional shortening. Despite this apparent normal systolic function, 2D colour tissue Doppler imaging (TDI) identified a marked longitudinal systolic left ventricular myocardial alteration, whereas radial function was still preserved. Three months later, the dog underwent euthanasia because of an acute episode of distal aortic thromboembolism. Necropsy revealed severe aortic and iliac arteriosclerosis. SAH related to arteriosclerosis is a common finding in humans, but has not been previously described in dogs. Moreover, its consequence on longitudinal myocardial function using TDI has never been documented before in this species.     

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)     

Decreased systolic function and inadequate hypertrophy in large and small breed dogs with chronic mitral valve insufficiency

BACKGROUND: Systolic dysfunction associated with chronic mitral valve insufficiency (CMVI) has been demonstrated in experimental animal models and large breed (LB) dogs but has been reported as an uncommon finding in small breed (SB) dogs with naturally occurring disease. It has been suggested the myocardial failure could be, in part, because of an insufficient increase in left ventricular mass. HYPOTHESIS: To test if SB and LB dogs with CMVI and moderate heart failure have systolic dysfunction and if they have adequate eccentric hypertrophy. ANIMALS: Data from 38 SB and 18 LB dogs affected with CMVI were compared retrospectively with results from 2 groups of normal dogs (17 SB and 32 LB). METHODS: Systolic function was investigated echocardiographically by using percentage fractional shortening (FS), the ratio between observed and expected end-systolic diameter (ESD/ESDe), and end-systolic volume index (ESVI). Left ventricular hypertrophy was estimated by using the ratio between the thickness of the left ventricular free wall and the radius in diastole (h/R). RESULTS: Both affected SB and LB dogs had a significantly increased FS and ESVI (FS% SB 45.6 + 8.04 versus 40.06 + 8.9, P < .05; FS% LB 33.64 + 8.61 versus 27.3 + 7.3 P < .05; ESVI SB 30.0 +/- 2.3 mL/m2 versus 21.18 +/- 13.9 mL/m2, P < .05; ESVI LB 83.22 +/- 43.84 mL/m2 versus 36.43 +/- 13.30 mL/m2 versus P < .001). The h/R in affected animals was decreased (0.53 +/- 0.11 versus 0.41 +/- 0.12, P < .05 SB; 0.47 +/- 0.11 versus 0.38 +/- 0.09, P < .05, LB). CONCLUSIONS AND CLINICAL IMPORTANCE: Data from this study indicate that dogs with moderate heart failure caused by CMVI have systolic dysfunction. Inadequate hypertrophy of the left ventricle may be, in part, responsible for this finding.     

Cardiovascular effects of 7.2% hypertonic saline solution in halothane anaesthetized ponies

The haemodynamic effects of intravenously (iv) administered hypertonic saline solution (7.2%, 4 ml/kg of body weight [bwt]) were investigated in normovolaemic ponies during halothane anaesthesia (dorsal recumbent position, intermittent pressure ventilation). Heart rate, arterial blood and pulmonary artery pressures, cardiac output, and arterial blood gases were measured throughout the experiment while related haemodynamic parameters (cardiac index, systemic and pulmonary vascular resistance, stroke volume, ventricular work) were calculated.
A transient decrease in arterial blood pressure occurred during the administration of the hypertonic solution. Significant increases in cardiac output and index, stroke work, and systolic arterial pressure were observed 5 min after the administration of the hypertonic infusion. A gradual normalization of the increased parameters occurred afterwards. Heart rate and arterial blood gases remained constant throughout the study. No clinical side-effects, except for an increase in urinary production in the recovery period, were seen during and after anaesthesia.     

Arterial oxygen and carbon dioxide tensions in conscious laterally recumbent ponies

Six adult ponies were trained calmly to assume and maintain left lateral recumbency without the use of sedative or immobilising agents. During a 30 min recumbent period, pHa, arterial oxygen and carbon dioxide tensions (PaO2 and PaCO2) and heart and respiratory rates were monitored at regular intervals to evaluate ventilatory response. Overall, there were no statistically significant differences found between mean control and recumbent or final standing values. When lightweight ponies were compared to heavyweight ponies, only mean PaO2 at 10 mins recumbency was different. This information supports the hypothesis that ventilation impairment during the first 30 mins of equine general anesthesia is primarily drug-mediated, rather than initiated by recumbency per se.