Cardiovascular and respiratory effects of propofol administration in hypovolemic dogs.

Cardiopulmonary effects of propofol were studied in hypovolemic dogs from completion of, until 1 hour after administration. 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, 6 mg of propofol/kg of body weight was administered IV to 7 dogs, and cardiopulmonary effects were measured. After blood withdrawal and prior to propofol administration, oxygen utilization ratio increased, whereas mean arterial pressure, mean pulmonary arterial pressure, central venous pressure, pulmonary capillary wedge pressure, cardiac index, oxygen delivery, mixed venous oxygen tension, and mixed venous oxygen content decreased from baseline. Three minutes after propofol administration, mean pulmonary arterial pressure, pulmonary vascular resistance, oxygen utilization ratio, venous admixture, and arterial and mixed venous carbon dioxide tensions increased, whereas mean arterial pressure, arterial oxygen tension, mixed venous oxygen content, arterial and mixed venous pH decreased from values measured prior to propofol administration. Fifteen minutes after propofol administration, mixed venous carbon dioxide tension was still increased; however by 30 minutes after propofol administration, all measurements had returned to values similar to those measured prior to propofol administration.     

Cardiopulmonary effects of etomidate in hypovolemic dogs.

Cardiopulmonary effects of etomidate administration were studied in hypovolemic dogs. Baseline cardiopulmonary data were recorded from conscious dogs after instrumentation. Hypovolemia was induced by withdrawal of blood from dogs until mean arterial pressure of 60 mm of Hg was achieved. Blood pressure was maintained at 60 mm of Hg for 1 hour, by further removal or replacement of blood. One milligram of etomidate/kg of body weight was then administered IV to 7 dogs, and the cardiopulmonary effects were measured 3, 15, 30, and 60 minutes later. After blood withdrawal and prior to etomidate administration, heart rate, arterial oxygen tension, and oxygen utilization ratio increased. Compared with baseline values, the following variables were decreased: mean arterial pressure, mean pulmonary arterial pressure, central venous pressure, pulmonary wedge pressure, cardiac index, oxygen delivery, mixed venous oxygen tension, mixed venous oxygen content, and arterial carbon dioxide tension. Three minutes after etomidate administration, central venous pressure, mixed venous and arterial carbon dioxide tension, and venous admixture increased, and heart rate, arterial and venous pH, and arterial oxygen tension decreased, compared with values measured immediately prior to etomidate administration. Fifteen minutes after etomidate injection, arterial pH and heart rate remained decreased. At 30 minutes, only heart rate was decreased, and at 60 minutes, mean arterial pressure was increased, compared with values measured before etomidate administration. Results of this study indicate that etomidate induces minimal changes in cardiopulmonary function when administered to hypovolemic dogs.     

Cardiovascular and respiratory effects of thiopental administration in hypovolemic dogs

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.     

Responses to sprint exercise in the greyhound: effects on haematology, serum biochemistry and muscle metabolites

To investigate the haematological, biochemical and metabolic response of greyhounds to sprint exercise, five greyhound dogs with previously placed carotid arterial catheters were sprinted over a distance of 400 m, chasing a lure. The time to complete the 400 m ranged from 25 to 27 seconds. Before exercise and at intervals for up to one hour after exercise, arterial blood samples were collected for haematology, serum biochemistry, plasma lactate and arterial blood gas measurements. Muscle samples for metabolite measurements were collected by needle biopsy of the vastus lateralis muscle. Red cell indices were increased for up to 20 minutes after exercise and there was a transient leucocytosis and neutrophilia. Serum biochemical changes reflected some fluid movement from the vascular compartment, there being increases in osmolality and total protein. Other changes included significant increases over resting control values for serum glucose, creatinine and potassium. The tension of oxygen in arterial blood was increased after exercise, while that of carbon dioxide fell, and there was a decrease in arterial pH. These changes were no longer significant by 30 minutes after exercise. The mean rectal temperature increased to 41 degrees C after exercise and remained elevated up to and including the 30 minutes after exercise measurement. No changes were found in muscle ATP or glycogen from before to after exercise. However, concentrations of muscle glucose and glucose-6-phosphate were increased immediately after exercise. Muscle and plasma lactate concentrations showed a similar time course for disappearance and after peaking at 27 mmol litre-1, five minutes after exercise, the plasma lactate returned towards pre-exercise values by 30 minutes after exercise.     

Influence of the neuroleptanalgesic combination of etorphine and acepromazine on the horse: blood gases and acid-base balance.

Respiratory function and acid-base variables were studied in Welsh Mountain ponies before and at predetermined times after the intravenous injection of Immobilon and Revivon.A marked depression of respiratory rate was accompanied by large reductions in arterial blood oxygen tension and saturation and the development of a mild respiratory acidosis following the injection of Immobilon. It was concluded that at least three factors contributed to the hypoxic hypoxia produced by Immobilon; the posture of lateral recumbency, the decrease in respiratory rate and the laboured character of the respiration. Arterial oxygen and carbon dioxide tensions returned towards control levels soon after administering Revivon. Mixed venous oxygen tensions were little affected by either Immobilon or Revivon, and mixed venous carbon dioxide tensions were increased to smaller degrees that those of arterial blood. Haemoglobin was increased initially by Immobilon, had returned to the control level by 30 min and fell below the control following the administration of Revivon.     

Effects of detomidine in young water buffalo

Following preliminary studies with detomidine hydrochloride in 10 young buffaloes (Bubalus bubalis), the effects of an intramuscular injection of 40 /ixg.kg-¹ were studied in 6 healthy buffaloes of VA to 2 years of age, weighing between 85 and 140 kg. Arterial blood pressure, central venous pressure, heart rate, electrocardiogram, electroencephalogram, respiratory rate, arterial pH, arterial and venous blood gases and rectal temperature were monitored before, and for an hour after, intramuscular injection of detomidine. Marked ataxia and sternal recumbency occurred within 10 minutes of injection, and an apparent complete recovery occurred in about 90 minutes. The electroencephalograms never demonstrated the high-voltage-low-frequency wave forms normally associated with sedation, but the animals appeared well sedated.
After injection there was marked decrease in heart rate which then tended to increase but it remained significantly (P < 0.05) below pre-injection values at 60 minutes. The mean arterial pressure increased initially, especially when electrocardiogram showed AV block, but after 15 minutes it had declined to below pre-injection values. These changes in the arterial blood pressure were, however, not statistically significant. Central venous pressure tended to increase during sedation but except at 30 minutes this increase was not statistically significant.
Rectal temperature, arterial pH, arterial carbon dioxide tension, standard bicarbonate and cranial vena caval oxygen tension did not show any significant variation. Respiratory rate and arterial oxygen tension decreased significantly.     

Hemodynamic response of calves to tiletamine-zolazepam-xylazine anesthesia.

Six healthy Holstein calves were anesthesized with isoflurane in O2 and instrumented for hemodynamic studies. A saphenous artery was catheterized for measurement of blood pressure and withdrawal of blood for determination of the partial pressure of carbon dioxide (PaCO2), oxygen (PaO2), and arterial pH (pHa). Respiration was controlled throughout the study. The ECG and EEG were monitored continuously. A thermodilution catheter was passed via the right jugular vein into the pulmonary artery for determination of cardiac output and measurement of central venous pressure, pulmonary arterial pressure, and pulmonary capillary wedge pressure. Baseline values (time 0) were recorded following recovery from isoflurane. Tiletamine-zolazepam (4 mg/kg)-xylazine (0.1 mg/kg) were administered IV immediately after recording baseline values. Values were again recorded at 5, 10, 20, 30, 40, 50, and 60 minutes after injection. Changes in left ventricular stroke work index, PaCO2, and pHa were insignificant. Arterial blood pressure and systemic vascular resistance increased above baseline at 5 minutes and then gradually decreased below baseline at 40 minutes, demonstrating a biphasic response. Values for pulmonary capillary wedge pressure, pulmonary arterial pressure, central venous pressure, and PaO2 were increased above baseline from 5 to 60 minutes. Stroke volume, stroke index, and right ventricular stroke work index were increased from 20 or 30 minutes to 60 minutes. Pulmonary vascular resistance increased at 10 minutes, returned to baseline at 20 minutes, and was increased again at 60 minutes. Heart rate, cardiac output, cardiac index, and rate pressure product were decreased at 5 minutes, and with the exception of cardiac output, remained so for 60 minutes. Cardiac output returned to the baseline value at 30 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

The anti-nociceptive and cardiopulmonary effects of extradural fentanyl–xylazine in sheep

Objective To compare the anti‐nociceptive effects of extradural xylazine, fentanyl and a xylazine–fentanyl combination in sheep, and to measure the cardiopulmonary effects of the xylazine–fentanyl combination. Study design Prospective, randomized study. Animals Twenty‐five half‐merino ewes 2–4 years of age and body mass 54.2 ± 1.1 kg. Methods Six sheep in group 1 received 0.2 mg kg^?1 xylazine by extradural injection, six in group 2 received fentanyl 1.5 µg kg^?1 and 13 in group 3 received the combination of both treatments. In all groups, drugs were mixed with saline (0.15 mL kg^?1 before injection). Pulmonary and carotid arterial catheters were placed in seven sheep of group 3 which were used to evaluate cardiopulmonary effects. Anti‐nociception was determined by the response to electrical stimulation (40 V for 1.5 milliseconds) of the left flank and by superficial and deep muscular ‘pinpricking’ stimulation of the pelvic and thoracic limbs and thoracolumbar region. Results Lack of response to electrical stimulation at the left flank was present in 10 ± 1.1 minutes (mean ± SEM) (group 1) and in 4.5 ± 0.5 minutes in group 3. The duration of lack of response to electrical stimulation at the left flank was 96 ± 6 minutes in group 1 and 315 ± 6 minutes in group 3. Responses persisted in group 3. Significant decreases (p < 0.05) in cardiac output 30, 45, 60 and 90 minutes after injection, and in cardiac work at 30 and 45 minutes were observed in the seven animals of group 3. Arterial blood pH was lowest at 90 minutes, arterial bicarbonate was lowest at 60 minutes and values for both arterial and mixed venous base excess increased significantly at 60 and 90 minutes. There was no significant change from baseline values in heart rate, mean arterial blood pressure, respiratory rate, body temperature, systemic vascular resistance, arterial and mixed venous PO₂, PCO₂, oxygen saturation, blood oxygen content, haemoglobin concentration, mixed venous blood bicarbonate and pH. Conclusions Fentanyl decreases the onset time and prolongs the duration of anti‐nociception produced by xylazine. The combination decreases cardiac output but is without significant respiratory effects. Clinical relevance Further studies are required to show that surgery is possible in sheep after extradural xylazine–fentanyl injection.     

The Effects of Equivalent Doses of Tromethamine or Sodium Bicarbonate in Healthy Horses

Objective—To describe the effects of tromethamine, a putative treatment for metabolic acidosis, and to compare its biochemical effects with those of sodium bicarbonate.
Design—Randomized intervention study with repeated measures.
Animals—16 healthy horses, 3 to 17 years old, weighing 391 to 684 kg.
Methods—Ten horses received 3 mEq/kg tromethamine and six received 3 mEq/kg sodium bicarbonate. Samples of venous blood and cerebrospinal fluid (CSF) were collected at intervals before and after drug administration. Heart rate and breathing rate were also recorded at intervals. Results—Median standard base excess increased significantly ( P < .05) from baseline immediately after both bicarbonate and tromethamine. These increases were not significantly different between treatments. Standard base excess returned toward baseline but remained significantly increased 3 hours after infusion of either treatment. After tromethamine, there was a significant decrease in plasma sodium concentration that lasted for at least 90 minutes. After sodium bicarbonate, no change in plasma sodium concentration was detected. Both sodium bicarbonate and tromethamine increased carbon dioxide tension in venous blood and CSF. Despite venous alkalemia, the pH of CSF decreased after both treatments.
Conclusions—Tromethamine and sodium bicarbonate have similar alkalinizing ability. Tromethamine causes hyponatremia, whereas both tromethamine and sodium bicarbonate increase carbon dioxide tension in venous blood and CSF.
Clinical Relevance—If hyponatremia, hypercarbia, and acidosis of the CSF occur after tromethamine is given to horses with existing metabolic acidosis, some of the potential advantages of tromethamine may prove theoretical rather than practical.     

Cardiopulmonary effects of a two hour medetomidine infusion and its antagonism by atipamezole in horses and ponies

The cardiopulmonary effects of an intravenous (iv) medetomidine injection (5 μg/kg) followed 5 min later by its infusion at 3.5 μg/kg/h for 115 rnin were studied in 9 horses and ponies. Five minutes after the end of infusion 60 μg/kg atipamezole were given. Physiological data during infusion were compared with pre-sedation values. Stroke volume was reduced significantly 5 min after initial medetomidine injection. Cardiac index was reduced significantly and systemic vascular resistance increased significantly for the first 20 min, but returned towards pre-sedation values after this time. Arterial blood pressures were reduced significantly from 30 min until the end of the procedure (minimum MAP was 102.4 ± 9.61 mmHg). Mixed venous oxygen tension was reduced significantly during the infusion. Respiratory rate fell and PaCO₂- rose significantly from 40 min onward. Other variables showed no significant changes. The horses recovered rapidly after atipamezole was injected. Arterial blood pressures remained significantly lowered, but other cardiovascular variables returned towards pre-sedation values. It is concluded that the infusion of medetomidine at 3.5 μg/kg/h causes minimum cardiopulmonary depression once the effects of an initial 5 μg/kg injection have waned, and so could prove suitable as part of an anaesthetic technique in equidae.     

Effects of training on biochemical values in standardbred horses.

Effects of training at a regular, fixed, standard exercise load on venous lactic acid, mixed venous and arterial blood gases and pH, and serum muscle enzymes were determined on previously unconditioned, healthy, adult, Standardbred horses. Arterial and mixed venous blood gases, pH, and serum muscle enzymes did not change in a consistent manner during training. Venous lactic acid concentrations did increase significantly with training and may be of value for the biochemical evaluation of fitness in horses.     

Effects of 2 different infusion rates of medetomidine on sedation score,cardiopulmonary parameters,and serum levels of medetomidine in healthy dogs

The effects of 2 different continuous rate infusions (CRIs) of medetomidine over an 8-hour period on sedation score, selected cardiopulmonary parameters, and serum levels of medetomidine were evaluated in 6 healthy, conscious dogs using a crossover study design. The treatment groups were: CONTROL = saline bolus followed by saline CRI; MED1 = 2 μg/kg body weight (BW) medetomidine loading dose followed by 1 μg/kg BW per hour CRI; and MED2 = 4 μg/kg BW medetomidine loading dose followed by 2 μg/kg BW per hour CRI. Sedation score (SS), heart rate (HR), respiratory rate (RR), temperature (TEMP), systolic arterial pressure (SAP), mean arterial pressure (MAP), and diastolic arterial pressure (DAP), arterial and mixed venous blood gas analyses, lactate, and plasma levels of medetomidine were evaluated at baseline, at various intervals during the infusion, and 2 h after terminating the infusion. Statistical analysis involved a repeated measures linear model. Both infusion rates of medetomidine-induced dose-dependent increases in SS and dose-dependent decreases in HR, SAP, MAP, and DAP were measured. Respiratory rate (RR), TEMP, central venous pH, central venous oxygen tension, and oxygen extraction ratio also decreased significantly in the MED2 group at certain time points. Arterial oxygen and carbon dioxide tensions were not significantly affected by either infusion rate. In healthy dogs, both infusion rates of medetomidine-induced clinically relevant sedative effects, accompanied by typical alpha₂ agonist-induced hemodynamic effects, which plateaued during the infusion and subsequently returned to baseline. While additional studies in unhealthy animals are required, the results presented here suggest that medetomidine infusions at the doses studied may be useful in canine patients requiring sedation for extended periods.     

The Influence of Body Position on the Blood Gas and Acid-base Status of Halothane-anesithetized Sheep

Eleven adult sheep were divided into three groups. Baseline arterial blood samples were taken with the sheep standing and breathing room air. They were then anesthetized and placed in right (group one), left (group two), or dorsal (group three) recumbency. Arterial blood samples were taken at 30, 60, 90, and 120 minute intervals during anesthesia, and 15 minutes after the discontinuation of halothane in oxygen.
Anesthetic induction resulted in an increase in arterial oxygen (Pao₂) and carbon dioxide (Paco₂) tensions and a decrease in arterial pH (pHa) and base excess (BE). During anesthetic maintenance, no positional effects were noted, and pHa and BE increased in all groups. With the termination of anesthesia and the animals breathing room air, pHa increased, and Pao₂ and Paco, decreased; BE was elevated in group two when compared to group three. Only BE had returned to control values 15 minutes after halothane was discontinued.     

Blood gas and acid-base analysis of arterial blood in 57 newborn calves

The pH, partial pressure of oxygen (pO(2)), partial pressure of carbon dioxide (pCO(2)), concentration of bicarbonate (HCO(3)(-)), base excess and oxygen saturation (SO(2)) were measured in venous and arterial blood from 57 newborn calves from 55 dams. Blood samples were collected immediately after birth and 30 minutes, four, 12 and 24 hours later from a jugular vein and a caudal auricular artery. The mean (sd) pO(2) and SO(2) of arterial blood increased from 45.31 (16.02) mmHg and 64.16 (20.82) per cent at birth to a maximum of 71.89 (8.32) mmHg and 92.81 (2.32) per cent 12 hours after birth, respectively. During the same period, the arterial pCO(2) decreased from 57.31 (4.98) mmHg to 43.74 (4.75) mmHg. The correlation coefficients for arterial and venous blood were r=0.86 for pH, r=0.85 for base excess and r=0.76 for HCO(3)(-). The calves with a venous blood pH of less than 7.2 immediately after birth had significantly lower base excess and HCO(3)(-) concentrations for 30 minutes after birth than the calves with a venous blood pH of 7.2 or higher. In contrast, the arterial pO(2) was higher in the calves with a blood pH of less than 7.2 than in those with a higher pH for 30 minutes after birth.     

Cardio-pulmonary function values in double-muscled cattle during muscular exercise

Eleven double-muscled calves of the Belgian White and Blue breed and eleven Friesian calves have been investigated at rest, during exercise on a treadmill (11% incline; speed 1.3 m.sec^-1) and 10 and 30 minutes after the end of this exercise. Blood gases and acid-base status were determined in mixed venous and arterial blood sampled from the pulmonary and the carotid artery respectively. Expired gases were collected in a balloon. The time of collection, volume of expired gases and fractional O₂ and CO₂ concentrations in expired gases were measured.In double-muscled calves, inadequate oxygen intake and carbon dioxide elimination were demonstrated by the increase in the carbon dioxide tension (PaCO₂) and in the hydrogen ion concentration [H⁺]_a and the decrease in the oxygen tension (PaO₂) in arterial blood during exercise. In Friesian calves, an adequate increase in oxygen intake occurred and no acidosis was recorded. A metabolic acidosis explained by only a 1.5-fold increase in the cardiac output and by the small increase in haemoglobin concentration was recorded in double-muscled calves.It was concluded that some aspects of the cardio-pulmonary and metabolic responses to exercise in double-muscled calves can be related to their inability to greatly increase their O₂ consumption.     

Anesthesia of horses with a combination of detomidine, zolazepam, tiletamine, and isoflurane immediately after strenuous treadmill exercise.

OBJECTIVES: To evaluate effects of strenuous exercise in adult horses immediately before anesthesia and to determine whether prior exercise affects anesthesia induction, recovery, or both. ANIMALS: 6 healthy Thoroughbreds in good condition and trained to run on a treadmill, each horse serving as its own control. PROCEDURE: Horses ran on a treadmill until fatigued, then were sedated immediately with detomidine hydrochloride and anesthetized with a zolazepam hydrochloride-tiletamine combination. Anesthesia was maintained with isoflurane in oxygen for another 90 minutes. Blood samples were taken before, during, and after exercise and during anesthesia. RESULTS: During exercise, changes in heart rate, core body temperature, plasma lactate concentration, arterial pH, and PaCO2 were significant. Plasma ionized calcium concentration was lower after exercise, compared with baseline values, and remained lower at 30 minutes of isoflurane anesthesia. Compared with baseline values, plasma chloride concentration decreased significantly during anesthesia after exercise. Cardiac output during anesthesia was significantly lower than that during preexercise, but significant differences between experimental and control periods were not observed. Arterial blood pressure during anesthesia was significantly lower than that during preexercise and initially was maintained better during isoflurane anesthesia after exercise. Cardiac output and blood pressure values were clinically acceptable throughout anesthesia. CONCLUSION: Administration of detomidine hydrochloride followed by zolazepam hydrochloride-tiletamine appeared to be safe and effective for sedation and anesthesia of horses that had just completed strenuous exercise. CLINICAL RELEVANCE: Anesthetic given in accordance with this protocol can be used to anesthetize horses that are injured during athletic competition to assess injuries, facilitate first aid, and possibly allow salvage of injured horses.     

Assessment of acid-base status and plasma lactate concentrations in arterial,mixed venous,and portal blood from dogs during experimental hepatic blood inflow occlusion

OBJECTIVE: To determine the effects of extended experimental hepatic blood flow occlusion (ie, portal triad clamping [PTC]) in dogs by measuring acid-base status and plasma lactate concentrations in arterial, mixed venous, and portal blood and evaluating the relationship between metabolic and concurrent hemodynamic changes. ANIMALS: 6 healthy Beagles. PROCEDURE: During anesthesia with isoflurane, cardiac output and arterial blood pressure were measured. Arterial, mixed venous, and portal blood samples were collected simultaneously for blood gas analyses and plasma lactate measurements before PTC and at 8-minute intervals thereafter. RESULTS: PTC resulted in severe hemodynamic and metabolic alterations. Eight minutes after PTC, significant decreases in cardiac index from a baseline value of 3.40 +/- 0.27 to 1.54 +/- 0.26 L/min/m2 and in mean arterial blood pressure from a baseline value of 74 +/- 6 to 43 +/- 6 mm Hg were recorded. After PTC, results indicative of lactic acidosis were found in portal blood at 16 minutes, in mixed venous at 32 minutes, and in arterial blood at 48 minutes. Significant differences in measured variables were also found between arterial and portal blood samples, between mixed venous and portal blood samples, and between arterial and mixed venous blood samples after PTC, compared with differences at baseline. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of mixed venous blood is preferable to analysis of arterial blood in the assessment of metabolic derangement. In a clinical setting, occluded portal blood is released to the systemic circulation, and the degree of reperfusion injury may depend on the metabolic status of pooled portal blood.     

Responses to submaximal treadmill exercise and training in the horse: changes in haematology, arterial blood gas and acid base measurements, plasma biochemical values and heart rate

Four standardbred horses with subcutaneously relocated carotid arteries were given a seven week training programme of treadmill exercise at a gradient of 19 per cent in order to assess if there were any effects of exercise and training on haematology, arterial blood gas and acid base measurements, plasma biochemistry and heart rate. The exercise consisted of one minute walking at 110 metres/minute followed by five minutes trotting at 200 metres/minute, twice daily in the first week. The period of trotting exercise was increased by one minute per week so that by the seventh week the horses were being given 12 minutes trotting twice daily. Before training commenced venous blood samples, for complete blood counts and plasma biochemistry, and arterial samples, for blood gas, acid base and lactate measurements, were taken at rest, after five minutes and 15 minutes of treadmill exercise (200 metres/minute) and 30 minutes and 60 minutes after completing the exercise. Heart rate was measured by telemetric electrocardiogram at similar intervals. This exercise test and blood collection were repeated after one, three, five and seven weeks of training. The only significant changes were a decrease in exercise lactate with training, increases in exercise and recovery total protein. The haematological response to treadmill exercise included an increase in certain red cell parametes and a leucocytosis which was caused by both a neutrophilia and a lymphocytosis. These effects had largely disappeared by 30 minutes after exercise and all values had returned to resting values by one hour after exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Determinants of oxygen delivery and hemoglobin saturation during incremental exercise in horses

OBJECTIVE: To determine components of the increase in oxygen consumption (VO2) and evaluate determinants of hemoglobin saturation (SO2) during incremental treadmill exercise in unfit horses. ANIMALS: 7 unfit adult mares. PROCEDURES: Horses performed 1 preliminary exercise test (EXT) and 2 experimental EXT. Arterial and mixed venous blood samples and hemodynamic measurements were taken during the last 30 seconds of each step of the GXT to measure PO2, hemoglobin concentration ([Hb]), SO2, and determinants of acid-base state (protein, electrolytes, and PCO2). RESULTS: Increased VO2 during exercise was facilitated by significant increases in cardiac output (CO), [Hb], and widening of the arteriovenous difference in O2. Arterial and venous pH, PaO2, and PvO2 decreased during exercise. Arterial PCO2, bicarbonate ([HCO3-])a, and [HCO3-] decreased significantly, whereas PVCO2 and increased. Arterial and venous sodium concentration, potassium concentration, strong ion difference, and venous lactate concentration all increased significantly during exercise. CONCLUSIONS AND CLINICAL RELEVANCE: Increases in CO, [Hb], and O2 extraction contributed equally to increased VO2 during exercise. Higher PCO2 did not provide an independent contribution to shift in the oxyhemoglobin dissociation curve (OCD) in venous blood. However, lower PaCO2 shifted the curve leftward, facilitating O2 loading. The shift of ODC resulted in minimal effect on O2 extraction because of convergence of the ODC at lower values of PO2. Decreased pH appeared responsible for the rightward shift of the ODC, which may be necessary to allow maximal O2 extraction at high blood flows achieved during exercise.