Studies on the changes in myocardial oxygen tension

An arterial oxygen tension (PO2) sensor was used to measure the myocardial PO2 at three sites in the left ventricle supplied by the paraconal interventricular branch of the left coronary artery, cranial descending coronary artery (CDCA): a subendocardial site, a subepicardial site and an intermediate point in the left ventricular wall. At first, the PO2 sensor had been compared with the values from a blood gas analyzer. The regression equation Y = 1.4X-4.9 with a correlation coefficient of 0.993 indicated a high correlation between these two measurements. The PO2 of the arterial blood in the left ventricular cavity was assigned an index value of 100%. The PO2 was about 70% in the subendocardial myocardium, about 15% in the mid-ventricular wall myocardium and 9% in the subepicardial myocardium, demonstrating a decreasing PO2 gradient from the endocardial to the epicardial surface. A transient occlusion of the CDCA confirmed the pathway of myocardial oxygen supply. In the mid-ventricular and subepicardial myocardium, marked hypoxia occurred after occlusion of the CDCA. Release of the occlusion resulted in a rapid return to the normal PO2 level. The oxygen supply to these sites is strongly influenced by coronary artery blood flow. The PO2 in the subendocardial myocardium was not dependent on the cranial descending coronary artery. Oxygen appears to be probably supplied through arterial blood in the left ventricle via the endocardium.     

Urine-blood carbon dioxide tension gradient in healthy dogs

The urine-blood carbon dioxide tension (PCO2) gradient was measured in 10 healthy mature Beagles after alkalinization of the urine by administration of sodium bicarbonate. The mean (+/- SD) urine-blood PCO2 gradient was 65.92 +/- 14.42 mm of Hg, with range of 38.2 to 82.2 mm of Hg. Mean urine PCO2 was 110.21 +/- 14.19 mm of Hg, with range of 84.1 to 127.3 mm of Hg. Because urine-blood PCO 2 gradient less than 30.0 mm of Hg or urine PCO2 less than 55 mm of Hg in people is diagnostic for a defect in distal nephron acidification, similar values might be applicable to diseases in dogs.     

Congenital lobar emphysema and tension pneumothorax in a dog.

Congenital lobar emphysema (CLE) and tension pneumothorax (TPT) are rarely reported in dogs. A case of CLE of the right middle lung lobe predisposing to air trapping, alveolar hyperinflation, and pleural rupture resulting in fatal spontaneous TPT in a 6-month-old mixed breed dog is described. The unique alteration of "bloat line" was observed in this case in addition to compressive atelectasis of all other lung lobes and lack of negative pressure within the thoracic cavity, signifying markedly elevated intrathoracic pressure. Bronchial cartilage hypoplasia and bronchiectasis were confirmed microscopically, which likely led to abnormal dynamic collapse of bronchi during expiration, consequentially leading to increased intrapulmonary pressure, bullous emphysema, and pleural rupture resulting in TPT. TPT consequent to CLE may therefore be considered one of the potential causes of sudden death in young dogs without overt clinical illness.     

Electrophysiological characteristics of tension receptors in the abomasal antrum of sheep

Unitary impulse activity from tension receptors in the abomasal antrum in sheep anaesthetized with chloralose was studied with concurrent measurements of isometric tension in the antral wall, intraluminal pressures and electromyography (EMG). Rhythmical background activity had a close correlation with intraluminal pressure changes and usually a close correlation with local increases in EMG activity and isometric tension. Impulse frequencies increased, but were not sustained, following changes from isotonic to isometric conditions. Tension receptors were excited by transmural compression, by antral distension and by local intra-arterial injections of acetylcholine (2.5–25 µg), pentagastrin (10–20 µg), 5-hydroxytryptamine (1–20 µg), adrenaline (10 µg) cholecystokinin-8 (1–5 µg) or bradykinin (0.5–20 µg), and by systemic injections of bethanecol (5–1000 µg). Local intra-arterial perfusions of atropine (50 µg) and hexamethonium (100 µg) did not abolish spontaneous antral movements or affect the enhanced impulse activity evoked by acetylcholine or 5-hydroxytryptamine. Most antral tension receptors were excited by increases in antral tension or passive distension; they therefore functioned in series with the muscularis externa. The discharges of three tension receptors were off-loaded early during the contraction evoked by local injections of pentagastrin (10–20 µg).Abbreviations b-t balloon-tipped - EMG electromyography - IMP impulse - TTL transistor-transistor logic On study leave from University of Massey, Palmerston North, New Zealand     

Rein tension acceptance in young horses in a voluntary test situation

Reasons for performing the study: During riding, horses are frequently exposed to pressure from the rider, e.g. through the bit and reins, but few studies have investigated at which point rein tension becomes uncomfortable for the horse. Objectives: To investigate how much rein tension young inexperienced horses are willing to accept in order to obtain a food reward; whether the tension acceptance changes during 3 consecutive test days; and whether rein tension correlates with the expression of conflict behaviour and heart rate. Hypotheses: Pressure‐naïve horses will apply only little rein tension in the first voluntary trial, but their acceptance will gradually increase. High levels of rein tension will lead to expression of conflict behaviour and increases in heart rate. Methods: Fifteen 2‐year‐old, bridle‐naïve mares were encouraged to stretch their head forward (across a 0.95 m high metal bar) to obtain a food reward in a voluntary test situation. On each test day, each horse was exposed to 2 control sessions (loose reins), an intermediate and a short rein session (1 min/session). Rein tension, heart rate and behaviour were recorded. Results: The horses applied significantly more tension on the first day (mean rein tension: 10.2 N), compared to the second and third test day (Day 2: 6.0 and Day 3: 5.7 N). The horses showed significantly more conflict behaviour in the short rein treatment. There was no treatment effect on heart rate. Conclusions and potential relevance: The horses applied the highest rein tension on the first day, and apparently learned to avoid the tension, rather than habituate to it. Rein tension correlated with expression of conflict behaviour, indicating that the horses found the tension aversive. Further studies should focus on the correlation between rein tension and conflict behaviour in ridden horses.     

Effect of pre-operative starvation on intra-operative arterial oxygen tension in horses

This study assessed the effect of pre-operative starvation on intramperative arteriaI oxygen tension (PaO₂) by examination of anaesthetic records from starved and non-starved horses undergoing general anaesthesia. PaO₂ data from 69 horses were included, 33 of which were starved pre-operatively and 36 were not. Thirty minutes after induction of anaesthesia the mean PaO₂ in the non-starved group was higher than in the starved group (non-starved 40 [2649] kPa vs starved 30 [15–46] kPa. median and 25–75 percentile) but at 60 and 90 min the values for PaO₂ for the non-starvcd group were lower than those for the starved group (60 min: starved 31 [15–49] kPa vs non-starved 27 [11–38] kPa; 90 min: starved 31 [1244] kPa vs non-starved 22 [12–38] kPa) None of the differences between these values was statistically significant. Pre-operative starvation did not significantly increase intra-operativc PaO₂ under the conditions of this study.     

A tension band technique for stabilisation of sacroiliac separations in cats

A tension band technique was used in conjunction with a transarticular pin to stabilise 24 sacroiliac separations in 19 cats. The authors suggest that this technique is simpler and safer than the transarticular screw technique, and as effective.     

Biomechanical comparison of dual interlocking single loop and double loop tension band techniques to the classic AO tension band technique for repair of olecranon osteotomies in dogs

OBJECTIVE: To compare olecranon fragment stability between the classic tension band wire (TBW) technique with the wire placed either in contact with (Arbeitsgemeinschaft für Osteosynthesefragen [AO]), or not in contact with, a Kirschner (K)-wire (AOW) to 2 novel wire patterns: a dual interlocking single loop (DISL) and a double loop (DL). STUDY DESIGN: Ex vivo mechanical evaluation on cadaveric bones. SAMPLE POPULATION: Canine ulnae (n=40) with olecranon osteotomies repaired with 2 K-wires and 1 of 4 TBW constructs. METHODS: Single load to failure applied through the triceps tendon. Displacement was measured from images captured from digital video. Techniques were compared based on the load resisted when the olecranon fragment was displaced 0.5, 1, and 2 mm. RESULTS: At 0.5 mm of displacement, the DISL construct resisted more load than the AOW construct (505 versus 350 N; P=.05). AO and DL constructs resisted an intermediate load (345 and 330 N, respectively). There was no significant difference between groups at 1 mm of displacement. At 2 mm of displacement, DL (785 N) resisted more load than AO (522 N, P=.01) and AOW (492 N, P=.03) groups. CONCLUSIONS: DISL constructs provided similar stability to classic TBW constructs whereas DL constructs were more stable at higher loads. CLINICAL RELEVANCE: The DL construct is easy to perform, less bulky, and provides comparable fragment stability to standard TBW techniques at functional loads. Surgical method is important for optimal performance of all TBW constructs.     

Riders' application of rein tension for walk-to-halt transitions on a model horse

Rein cues have been used for millennia when controlling horses. Recent research has quantified the range of tensions exerted on the horse's mouth by bit and rein apparatus under a variety of conditions and investigating the tension horses will freely tolerate. Given the importance of rein tension in terms of controlling horses and the potential for welfare issues arising from use of apparatus in the horse's mouth, this study the tensions created by riders (n = 12) performing walk to halt gait transitions on a model horse. The mean tension when applying the deceleration cue of the left rein (mean tension, 8.58 N; standard deviation = 5.15; range = 3.14-28.92 N) was greater than the right rein (mean tension, 6.24 N; standard deviation = 4.1; range = 2.27-16.17 N). Little correlation was found between rider morphometry and rein tension. Although the deceleration cue was significantly higher than the resting tension by 51% for the right rein (P < 0.001) and by 59% for the left rein (P < 0.001), there was large variation between and within riders. These findings suggest the need for greater awareness of the potential for rein tensions to vary from principles of good horse welfare and training principles.     

Improvement in arterial oxygen tension with change in posture in anaesthetised horses

Observations were made on horses spontaneously breathing oxygen, with halothane at a constant end tidal concentration. The horses were positioned in dorsal recumbency for the first 45 minutes of each anaesthetic episode during which the arterial oxygen tension (PaO2) was found to peak and then decline. The remaining 60 minutes of each anaesthesia was used to test the effect of various manoeuvres on PaO2. The PaO2 of horses decreased further both when remaining in dorsal recumbency and when repositioned in right or left recumbency. In contrast, placing the horses in sternal recumbency for these remaining 60 minutes caused the PaO2 to rise rapidly providing evidence for redistribution of ventilation. Replacing some inspired oxygen with less absorbable nitrogen did not improve PaO2 in dorsal recumbency. Thus there was no evidence that the low PaO2 of dorsal recumbency was associated with alveoli that had collapsed because of gas absorption.     

Preliminary studies on the measurement of conjunctival oxygen tension in the foal

The capability of a transconjunctival oxygen monitoring system to provide an accurate and reliable means of observing arterial oxygenation trends was evaluated in 12 horse and pony foals between 5 and 20 days of age. Ten of the foals were anesthetized with isoflurane in oxygen and nitrous oxide, and 2 foals were conscious. Inspired oxygen concentration was manipulated by differing proportions of oxygen and nitrous oxide in the fresh gas supplied to the breathing circuit. With arterial oxygen tension values ranging from less than 20 to greater than 400 mm of Hg, all foals had significant positive correlations between arterial and conjunctival oxygen tensions (P less than 0.001). Although the system seemed accurate and reliable, monitoring oxygenation in awake and mobile foals may require a ring conformer made to fit the foal's eye.     

Rate of rise of arterial carbon dioxide tension in the halothane-anesthetized horse

The rate of rise of arterial partial pressure of carbon dioxide (PaCO2) was determined in 49 apneic halothane-anesthetized horses following controlled ventilation. Drugs given for induction of anesthesia did not affect the rapid rate of rise of PaCO2 during the first minute after controlled ventilation, the PaCO2 at 1 minute after controlled ventilation, or the PaCO2 at which spontaneous ventilation began. Horses given xylazine-ketamine for induction of anesthesia had a significantly (P less than 0.05) faster rate of rise of PaCO2 after 1 minute following controlled ventilation than did horses receiving xylazine-thiamylal for induction.     

黄连水煎剂对家兔离体小肠张力的影响

据《全国中成药品种目录》统计，以黄连作为中成药的品种有108种，近年来，黄连及其复方的药理和临床研究又有了新的发现。在中兽医临床上黄连及其制品主要用于抗菌、抗病毒、解热、消炎、止泻、健胃、利胆等作用。秦彩玲等指出黄连提取液能轻度提高胃液、胰液、胆汁的分泌，促进胃的运动。但黄连水煎剂对家兔离体小肠张力的影响，尚未见报道。为探索黄连水煎剂对家兔离体小肠运动性能的影响，探讨其作用机理，设计并进行了本试验。