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Summary The effects of an acute non-isocapnic hypoxia on ventilation and pulmonary mechanics were investigated in 6 healthy unsedated Holstein-Friesian (HF) calves and in 7 double-muscled calves of the Belgian White and Blue (BWB) breed known to develop more severe hypoxemia during exercise and respiratory diseases. Data were collected at 1 min intervals throughout the following protocol: breathing air (FIO2 = 21%), then breathing hypoxic gas mixture (FIO2 = 10%) for 5 min, and, finally, breathing air again for 5 min of recovery. Arterial blood was sampled at rest and at the 4th min of hypoxia for blood gas analysis. In HF and BWB calves, hypoxia induced a significant increase in tidal and minute volume, but did not change respiratory rate, dynamic lung compliance and total pulmonary resistance. However, with regard to their ventilation during normoxia at rest, BWB calves showed a comparatively greater rise in ventilation than HF calves during the first 4 min of hypoxia. On the contrary, by the 5th minute of hypoxia, ventilation of BWB calves declined to the normoxic level while HF calves largely sustained hyperventilation. This hypoxic ventilatory depression in BWB calves could be explained by the proportionately greater initial increase in ventilation. It was concluded that BWB calves supported this hypoxic challenge less easily than HF calves.

Summary The purpose of this study was to establish a standardized protocol in order to obtain accurate and reproducible cardiac output (CO) measurements by the thermodilution technique in the unsedated calf. In 5 healthy calves, the effect of various temperatures, volumes, rates, means and sites of injection of the thermal indicator were tested for their effect on accuracy and reproducibility of CO measurement by the thermodilution technique, the Fick method being used as the standard technique. Five milliliters of an iced 5% dextrose solution per 100 kg body weight constituted the correct amount of thermal indicator. Manual injection of the indicator bolus and/or injection of this bolus through the proximal lumen of a thermodilution Swan-Ganz catheter gave poor results of CO measurements by the thermodilution technique. On the other hand, results of CO measurements were highly reliable when the bolus injection was performed by an ECG-synchronized injection pump and/or through a right atrial catheter with a larger diameter and a shorter length than the classical Swan-Ganz catheter. It was concluded that an iced 5% solution of dextrose (5 ml/100 kg body weight) injectated through a right atrial catheter by an ECG-synchronized pump gives the most accurate and reproducible CO measurements by the thermodilution technique in unsedated calves.

Summary The mechanics of breathing was investigated in six healthy calves breathing either air or a mixture of 79% helium and 21% oxygen (He-O2). Intrapleural pressure (Ppl) was measured with an esophageal balloon catheter and transpulmonary pressure was obtained by subtracting the mouth pressure (Pm) from Ppl. Respiratory airflow (V) was measured using a Fleisch pneumotachograph N°3 and tidal volume (Vt) was electronically derived by integrating V with respect to time. Respiratory airflow, Vt, Ppl and Pm were simultaneously recorded while the calves breathed first air (1 min), secondly He-O2 (1 min) and finally air again (1 min). The pulmonary function values were calculated on the tracings and the He-O2 values were compared to the corresponding “air” values. The ventilatory response to resistance unloading was characterized by a significant increase in minute volume exclusively due to an increase in respiratory frequency, while Vt remained unchanged. A decrease of 32% in the total pulmonary resistance (RL) and 16% in the work per litre of ventilation (Wrm/1) were observed when calves breathed He-O2. The effect of the He-O2 on RL and on Wrm/1 suggests that, in the bovine species, airflow turbulences in the upper part of the respiratory tract play a significant role in the total airways resistance.

Seven sport horses were investigated to compare physiological and pharmacological stresses on the plasma glucocorticosteroid levels. Venous blood was sampled and analysed for cortisol concentrations before and after each type of stress. The physiological stress was induced by the completion of a cross-country and the pharmacological one, by an intravenous ACTH administration (200 micrograms) in the same horses, one week after the course. Both exercise and ACTH injection induced a highly significant cortisol increase of 79 +/- 0.10% and 160 +/- 0.18%, respectively. The relative plasma cortisol increases due to exercise on the one hand, and due to ACTH administration on the other hand, were correlated with a coefficient of 0.82. It was concluded that the plasma cortisol increase induced by a standardised pharmacological stress could be used in order to predict the exercise-induced stress response.

ummary The aim of the present experiment was to investigate the hypothesis that there is a respiration-locomotion coupling in trotting equids. Therefore the respiratory airflow (V), the gastric pressure (Pga) and pleural pressure (Ppl) changes and the step frequency (SF) were simultaneously recorded in 5 trotting ponies (body weight: 255±15 kg; age: 3. 5±0. 4 years). Airflow was measured using a Fleisch pneumotachograph fixed on a face mask. Esophageal and gastric balloon catheters coupled to pressure transducers allowed the recording of Ppl and Pga. The exercise was performed on a treadmill and consisted of 1 min walking (1. 5m · s−1), 1 min slow trotting (3. 0m · s−1) (Trot 1) and 3 min fast trotting (3. 5m · s−1) (Trot 2). Data were continuously recorded before and during exercise. At walk and Trot 1, none of the ponies displayed a coupling between SF and the respiratory frequency (RF). In one pony, SF and RF were coupled at a constant ratio of 2:1 during Trot 2 while two other ponies displayed the same coupling only up to the second minute of Trot 2. In the two last ponies, a coupling occurred at the third minute of Trot 2. In all ponies, the peaks in Pga occurring during expiration occurred always simultaneously with the first and/or the second peak V, whether or not there was a relationship between SF and RF. On the other hand, when SF and RF were coupled, the first part of inspiration was always simultaneous to a decrease in Pga. It was concluded that in trotting ponies respiration and locomotion are not always independent and that the abdominal piston may act in synergy with the respiratory pump in some phases of the breathing cycle. Zusammenfassung Synchronisation von Lokomotion und Atmung bei trabenden Ponies Ziel der Untersuchung war es, die Hypothese einer Koppelung zwischen Atmung und Lokomotion bei trabenden Equiden zu prufen. Bei 5 trabenden Ponies (Korpergewicht: 255±15 kg, Alter: 3,5±0,4 Jahre) wurde daher das Atemzeitvolumen (V), die Veranderungen des intragastralen Drucks (Pga) und des pleuralen Drucks (Ppl) sowie die Schnittfrequenz (SF) gleichzeitig registriert. Das Atemzeitvolumen wurde mit einem an einer Gesichtsmaske fixierten Pneumotochographen nach Fleisch gemessen. Jeweils an einen Druckwandler angeschlossene Osophagus- bzw. Magen-Ballon-katheter ermoglichten die Aufzeichnung des Ppl und des Pga. Die Bewegung der Tiere erfolgte auf einem Laufband und umfaste einminutiges Gehen (1,5m · s−1), einminiitiges langsames Traben (3,0m · s−1) (Trab 1) und dreiminiitiges schnelles Traben (3,5m · s−1) (Trab 2). Die Daten wurden vor und wahrend der Bewegung kontinuierlich registriert. Beim Gehen und beim Trab 1 ergab sich bei keinem der Ponies eine Koppelung zwischen SF und Respirationsfrequenz (RF). Wahrend des Trabes 1 waren SF und RF bei einem Pony konstant im Verhaltnis 2:1 gekoppelt, wahrend zwei weitere Ponies diese Koppelung nur bis zur zweiten Minute des Trabes 2 aufwiesen. Bei den anderen zwei Ponies ergab sich eine entsprechende Koppelung in der dritten Minute des Trabes 2. Bei alien Ponies trat der wahrend der Exspiration zu verzeichnende Peak des Pga unabhangig von der Beziehung zwischen SF und RF immer gleichzeitig mit dem ersten und/oder zweiten Peak von V auf. Bei einer Koppelung von SF und RF fiel andererseits der erste Abschnitt der Inspiration immer mit einer Verringerung des Pga zusammen. Es wird geschlossen, das beim trabenden Pony Atmung und Lokomotion nicht immer unabhangig voneinander sind und das wahrend einiger Phasen des Atmungszyklus die sich wie ein Kolben verhaltenden abdominalen Eingeweide synergistisch zur respiratorischen “Pumpe” verhalten.