Ultrasound measurements of the caudal vena cava before and after blood donation in 9 greyhound dogs.

This prospective study evaluated variation in the diameter of the caudal vena cava (DCdVC) as a marker of change in intravascular volume before and after blood donation in greyhound dogs. A preliminary study determined that the DCdVC increased with body weight. Nine greyhound blood donors had ultrasonographic images acquired of the maximum and minimum DCdVCs in transverse and sagittal orientations and sagittal aortic diameter (AoD) before and after blood donation. The collapsibility index = [(maximal mean transverse DCdVC - minimal mean transverse DCdVC)/maximal mean transverse DCdVC] and transverse DCdVC:AoD ratio were calculated for each dog. In the greyhounds, the changes in mean minimal and maximal transverse DCdVC (0.69 and 0.84 mm, respectively) and sagittal mean maximal DCdVC (0.9 mm) and collapsibility index (0.018) were significantly different (P < 0.05) before and after blood donation. While statistically significant, the magnitude of DCdVC change found in this limited number of greyhound dogs with 8% intravascular volume loss during blood donation was small. This magnitude of change is likely indistinguishable in clinical patients.

Mesures par ultrason de la veine cave caudale avant et après le don de sang chez 9 chiens Greyhound. Cette étude prospective a évalué la variation du diamètre de la veine cave caudale (DCdVC) comme marqueur du changement du volume intravasculaire avant et après le don de sang chez les chiens Greyhound. Une étude préliminaire a déterminé que le DCdVC a augmenté le poids corporel. Neuf Greyhound donneurs de sang avaient des images échographiques acquises pour les DCdVC maximum et minimum dans les orientations transversales et sagittales et le diamètre aortique sagittal (AoD) avant et après le don de sang. L'indice de collapsibilité = [(DCdVC maximal transversal moyen ­ DCdVC minimal transversal moyen)/DCdVC maximal transversal moyen] et le ratio transversal DCdVC:AoD ont été calculés pour chaque chien. Chez les Greyhounds, les changements des DCdVC minimaux et maximaux transversaux moyens (0,69 et 0,84 mm, respectivement) et le DCdVC maximal sagittal moyen (0,9 mm) et l'indice de collapsibilité (0,018) étaient significativement différents (P < 0,05) avant et après le don de sang. Même si ce changement est significatif sur le plan statistique, l'ampleur du changement DCdVC constatée dans ce nombre limité de chiens Greyhound ayant 8 % de perte de volume intravasculaire durant le don de sang était faible. Cette ampleur de changement est probablement impossible à distinguer chez les patients cliniques.(Traduit par Isabelle Vallières).

Sonographic assessment of volaemia: development and validation of a new method in dogs.

OBJECTIVES: The aims of this study were to describe a method for the sonographic assessment of volaemia, to determinate inter- and intra-operator variability and to assess the ability to detect blood loss after blood donation in healthy dogs. MATERIALS AND METHODS: The left kidney was identified in a spleno-renal view, and transverse views of the caudal vena cava and aorta were obtained in 12 dogs. Vessel diameters were measured in B-mode, in duplicate by two operators, and the caudal vena cava:aorta ratio was calculated. Intra- and inter-operator variabilities were assessed using a Bland-Altman method by plotting the differences between the repeated measurements obtained from the same subject by the same operator and by the two operators against their means. Before and after blood donation measurements were compared using paired t-tests or one-sample t-tests, if appropriate. RESULTS: Intra- and inter-operator variability was within the limit of agreement for the vast majority of measurements. After a blood donation of 9·8 ±2·2 mL/kg, the mean aorta measurements were not significantly different from those obtained before blood donation (1·11 versus 1·10, P=0·28), whereas the mean caudal vena cava measurements and caudal vena cava:aorta ratios were significantly lower (1·28 versus 1·01, P<0·0001; 1·17 versus 1·01, P=0·0001, respectively). CLINICAL SIGNIFICANCE: The low intra- and inter-operator variabilities in the caudal vena cava, aorta and caudal vena cava:aorta ratio measurements support their reliability and operator independency. The sonographic assessment of volaemia appears to be a promising non-invasive, repeatable point-of-care ultrasound protocol for assessment and monitoring of blood loss. Further studies are needed to assess the sonographic assessment of volaemia protocol in spontaneously bleeding dogs.

Contrast-enhanced ultrasonographic characteristics of the diseased canine prostate gland.

The work was carried out on a total of 26 male dogs that on the basis of clinical examination, prostate ultrasound and prostate biopsy, were divided prospectively into four groups: (1) normal dogs (control group; n = 8); (2) dogs with benign prostatic hyperplasia (group BPH; n = 8); (3) dogs suffering from prostatitis (group prostatitis; n = 4); (4) dogs with prostatic tumors (group tumors; n = 6). The examination of the prostate by means of contrast medium and dedicated ultrasound system allowed a detailed qualitative and quantitative analysis of prostatic vessels in normal and diseased conditions, enabling the detection and characterization of different disease states, and quantification of parameters such as peak intensity of perfusion (%), arrival time of the contrast medium to its maximum value of video intensity (time to peak [TTP; seconds]), regional blood volume, regional blood flow, and mean transit time (MTT [seconds]). The hemodynamic indices TTP (P < 0.01) and MTT (P < 0.001) of diseased prostate groups were significantly lower than those in the normal prostate group although there were no differences among diseases. Optimal cutoff values were 31 seconds (Sensitivity: 72%; Specificity: 88%) and 47 seconds (Sensitivity: 100%; Specificity: 88%) while area under receiver operating characteristic curves were 0.86 (P < 0.01) and 0.97 (P < 0.01) for TTP and MTT, respectively. The qualitative evaluation of vascular patterns showed differences between normal and diseased prostate glands. The latter were characterized by an alteration of the normal vascular appearance consisting of loss of the subcapsular arterioles and lack of a centripetal vascular pattern. The qualitative aspect of the study highlighted the different vascular architecture between BPH, prostatitis, adenocarcinoma, and lymphoma. This study shows how contrast-enhanced ultrasound represents a valid and noninvasive method for highlighting and characterizing prostatic vasculature. Furthermore, it allows the operator to obtain qualitative and quantitative data that are useful for the diagnosis of selected prostatic diseases. In conclusion, contrast-enhanced ultrasound can be a valuable noninvasive diagnostic tool to improve the diagnostic accuracy of prostate diseases in the dog.

Comparison of cardiac output determined by an ultrasound velocity dilution cardiac output method and by the lithium dilution cardiac output method in juvenile horses with experimentally induced hypovolemia.

OBJECTIVE: To assess the accuracy of an ultrasound velocity dilution cardiac output (UDCO) method, compared with that of the lithium dilution cardiac output (LiDCO) method, for determination of cardiac output (CO) in juvenile horses with experimentally induced hypovolemia. ANIMALS: 12 anesthetized 2- to 6-month-old horses. PROCEDURES: For each anesthetized horse, CO was determined by the LiDCO and UDCO methods prior to any intervention (baseline state), after withdrawal of approximately 40% of the horse's blood volume (low CO state), after maintenance of hypovolemia and infusion of norepinephrine until mean arterial blood pressure was equal to baseline value (high CO state), and after further infusion of norepinephrine and back-transfusion of withdrawn blood (posttransfusion state). For each of the 4 hemodynamic situations, CO and calculated cardiac index (CI) values were obtained by each method in duplicate (8 pairs of measurements/horse); mean values for each horse and overall mean values across all horses were calculated. Agreement between CI determined by each method (96 paired values) was assessed by Bland-Altman analysis. RESULTS: For the UDCO method-derived CI measurements among the 12 horses, mean ± SD bias was -4 ± 11.3 mL/kg/min (95% limits of agreement, -26.1 to 18.2 mL/kg/min) and mean relative bias was -10.4 ± 21.5% (95% limits of agreement, -52.6% to 31.8%). CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that, compared with the LiDCO method, the UDCO method has acceptable clinical usefulness for determination of CO in foals.

Challenges of cardiopulmonary bypass-a review of the veterinary literature.

Cardiopulmonary bypass (CPB) has been used in veterinary medicine in experimental surgery and to address congenital and acquired diseases. We review the veterinary literature and expose common challenges of CPB in dogs and cats. Specifically, we describe the most specific elements of this technique in veterinary patients. The variety in animal size has made it difficult to standardize cannulation techniques, oxygenators, and priming volumes and solutions. The fact that one of the most common cardiovascular disorders, mitral valve disease, occurs predominantly in small dogs has limited the use of bypass in these patients because of the need for small, low prime oxygenators and pumps that have been unavailable until recently. Coagulation, hemostasis, and blood product availability have also represented important factors in the way CPB has developed over the years. The cost and the challenges in operating the bypass machine have represented substantial limitations in its broader use.

Determination of cardiac output by ultrasound velocity dilution in normovolemia and hypovolemia in dogs.

OBJECTIVE: The purpose of this study was to compare CO measured by use of lithium dilution (LiDCO) and ultrasound velocity dilution (UDCO) in a canine model of acute hemorrhage. STUDY DESIGN: Prospective descriptive evaluation. ANIMALS: Twelve dogs (15-34 kg). METHODS: Dogs were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases and CO. The CO was measured by use of LiDCO and UDCO techniques. Measurements were obtained from each animal at baseline and during a low CO state (hemorrhagic state). Measurements were converted to cardiac index (CI = CO/BSA) values for statistical analysis. To measure CO using UDCO, a 20 mL bolus of 0.9% sodium chloride was administered and CO was calculated from the transient dilution of blood proteins created by the injection bolus. Hypovolemia was induced by withdrawing 40% of the blood volume until the mean arterial blood pressure (MAP) was stable at 40 mmHg for 10 minutes. Agreement was determined using Bland & Altman analysis and concordance correlation coefficients. RESULTS: Twenty-four comparisons were made. Lithium determinations of CI ranged between 7.5 and 1.3 L minute(-1) m(-2), and the mean overall difference between the two methods was -0.40 L minute(-1) m(-2). The mean relative bias was -17 ± 21% (limits of agreements: -59% to 25%). There was no significant effect of state of CI on bias or relative bias (p = 0.24 and p = 0.10, respectively). The concordance correlation coefficient between LiDCO and UDCO as 0.88 (p < 0.0001). CONCLUSIONS: When compared to lithium dilution, the UDCO technique is a viable method for measuring cardiac output in a model of normovolemia and hypovolemia in dogs.

Cardiovascular performance of adult breeding sows fails to obey allometric scaling laws.

In view of the remarkable decrease of the relative heart weight (HW) and the relative blood volume in growing pigs, we investigated whether HW, cardiac output (CO), and stroke volume (SV) of modern growing pigs are proportional to BW, as predicted by allometric scaling laws: HW (or CO or SV) = a·BW(b), in which a and b are constants, and constant b is a multiple of 0.25 (quarter-power scaling law). Specifically, we tested the hypothesis that both HW and CO scale with BW to the power of 0.75 (HW or CO = a·BW(0.75)) and SV scales with BW to the power of 1.00 (SV = a·BW(1.0)). For this purpose, 2 groups of pigs (group 1, consisting of 157 pigs of 50 ± 1 kg; group 2, consisting of 45 pigs of 268 ± 18 kg) were surgically instrumented with a flow probe or a thermodilution dilution catheter, under open-chest anesthetized conditions to measure CO and SV, after which HW was determined. The 95% confidence intervals of power-coefficient b for HW were 0.74 to 0.80, encompassing the predicted value of 0.75, suggesting that HW increased proportionally with BW, as predicted by the allometric scaling laws. In contrast, the 95% confidence intervals of power-coefficient b for CO and SV as measured with flow probes were 0.40 to 0.56 and 0.39 to 0.61, respectively, and values obtained with the thermodilution technique were 0.34 to 0.53 and 0.40 to 0.62, respectively. Thus, the 95% confidence limits failed to encompass the predicted values of b for CO and SV of 0.75 and 1.0, respectively. In conclusion, although adult breeding sows display normal heart growth, cardiac performance appears to be disproportionately low for BW. This raises concern regarding the health status of adult breeding sows.

Assessment of changes in vascularity and blood volume in canine sarcomas and squamous cell carcinomas during fractionated radiation therapy using quantified contrast-enhanced power Doppler ultrasonography: a preliminary study.

Radiation therapy does not only target tumour cells but also affects tumour vascularity. In the present study, changes in tumour vascularity and blood volume were investigated in five grade 1 oral fibrosarcomas, eight other sarcomas (non-oral soft tissue and bone sarcomas) and 12 squamous cell carcinomas in dogs during fractionated radiation therapy (total dose, 45-56 Gy). Contrast-enhanced power Doppler ultrasound was performed before fraction 1, 3, 6, 8, 10, 12, 14 and 15 or 16 (sarcomas) or 17 (squamous cell carcinomas). Prior to treatment, median vascularity and blood volume were significantly higher in squamous cell carcinomas (P=0.0005 and 0.001), whereas measurements did not differ between oral fibrosarcomas and other sarcomas (P=0.88 and 0.999). During the course of radiation therapy, only small, non-significant changes in vascularity and blood volume were observed in all three tumour histology groups (P=0.08 and P=0.213), whereas median tumour volume significantly decreased until the end of treatment (P=0.04 for fibrosarcomas and other sarcomas, P=0.008 for squamous cell carcinomas). It appeared that there was a proportional decrease in tumour volume, vascularity and blood volume. Doppler measurements did not predict progression free interval or survival in any of the three tumour groups (P=0.06-0.86). However, the number of tumours investigated was small and therefore, the results can only be considered preliminary.

Evaluation of three methods for measurement of hemoglobin and calculated hemoglobin variables with the ADVIA 120 and ADVIA 2120 systems in goats.

The present study investigated 3 methods of hemoglobin (Hb) determination in goats using the ADVIA 120 and ADVIA 2120 systems. Ethylenediaminetetraacetic acid anticoagulated caprine blood samples (n = 40 goats) were subjected to Hb determination via the cyanmethemoglobin methods in both instruments and a novel, cyanide-free, colorimetric method with the ADVIA 2120. Statistical analysis of the data included a linear regression, Passing-Bablok regression, and Bland-Altman diagram. Colorimetric Hb results determined with both analyzers had excellent correlation (r = 0.98); however, a mean proportional bias of -19.1% was present in comparison to the reference method. There also was excellent agreement between cellular Hb concentrations when measured with both analyzers (r = 0.96), and the constant bias was close to zero. However, imprecision was higher compared to colorimetric methods. Excellent to fair agreement was evident for all calculated erythrocyte and Hb variables. Because of the excellent correlation between the ADVIA 120 and ADVIA 2120, the cyanide-free method of Hb determination could be used with caprine blood specimens; however, the proportional bias must be considered.

Personal view: crystalloid transfusion in acute gastrointestinal haemorrhage: is it beneficial? An historical perspective.

The conventional management of acute gastrointestinal haemorrhage mandates early repletion of blood volume with crystalloids and blood, as part of the initial management, where there is evidence of hypovolaemia. Meanwhile there is a major trend towards a restrained use of fluid to raise blood pressure to near normal for the bleeding patient in trauma and similar emergencies. This divergence of view requires analysis. An Ovid/MEDLINE, Google and extensive literature search focused on the resuscitation and transfusion of bleeding trauma patients was performed. In addition to clear evidence from animal experiments that early restoration of blood volume perpetuates bleeding, there is considerable evidence in humans - both in war and civilian life - that rapid crystalloid infusion is harmful. I also report a personal series of benefit from restricted transfusion in acute upper gastrointestinal haemorrhage in humans. Given the lack of evidence of benefit for rapid blood volume repletion in acute gastrointestinal haemorrhage, there is need for controlled studies of the most appropriate approach to crystalloid transfusion in acute gastrointestinal bleeding.

Gender differences in the blood volume of conscious Sprague-Dawley rats.

Reference values of blood volume (BV) and plasma volume (PV) of animal species are given as functions of body weight and gender specification generally is not given. Considering the common observation of a decreased hematocrit (Hct) in the females of many species, the BV, the PV, or both must differ between genders. The present study was performed to determine the magnitude of those differences. We measured Hct and PV in 24 female and 23 male Sprague-Dawley rats in their 12th week of life. The rats were surgically prepared with indwelling femoral arterial catheters 4 d prior to the determination of BV. Evan's Blue dye dilution was used to determine PV in conscious, quietly resting animals. BV was calculated as PV/(1-Hct). Mean Hct was 2% lower in female rats than males, and PV (mean +/- 1 standard deviation) was 4.86 +/- 0.54 ml/100 g in females compared with 4.12 +/- 0.32 ml/100 g in males. Calculated BV in female rats was 7.84 +/- 0.70 ml/100 g compared with 6.86 +/- 0.53 ml/100 g in males. When precise estimates of BV or PV are needed for research or dosing purposes, gender differences of 18% for PV and 14% for BV must be considered. In addition, species other than the rat may have similar discrepancies between sexes, and the prudent investigator must determine individual volume assessments of both sexes before assumptions of BV and PV for a species can be made.

Pre-exercise hypervolaemia is not detrimental to arterial oxygenation of horses performing a prolonged exercise protocol simulating the second day of a 3-day equestrian event.

REASONS FOR PERFORMING STUDY: Hyperhydration, prior to prolonged moderate-intensity exercise simulating the 2nd day of a 3-day equestrian event (E3DEC), may induce arterial hypoxaemia detrimental to performance. OBJECTIVES: Because moderate-intensity exercise does not induce arterial hypoxaemia in healthy horses, the effects of pre-exercise hypervolaemia on arterial oxygenation were examined during a prolonged exercise protocol. METHODS: Blood-gas studies were carried out on 7 healthy, exercise-trained Thoroughbred horses in control and hyperhydration experiments. The study conformed to a randomised crossover design. The sequence of treatments was randomised for each horse and 7 days were allowed between studies. Hyperhydration was induced by administering 0.425 g/kg bwt NaCl via nasogastric tube followed by free access to water. The exercise protocol was carried out on a treadmill set at a 3% uphill grade and consisted of walking at 2 m/sec for 2 min, trotting for 10 min at 3.7 m/sec, galloping for 2 min at 14 m/sec (which elicited maximal heart rate), trotting for 20 min at 3.7 m/sec, walking for 10 min at 1.8 m/sec, cantering for 8 min at 9.2 m/sec, trotting for 1 min at 5 m/sec and walking for 5 min at 2 m/sec. RESULTS: NaCl administration induced a significant mean +/- s.e. 15.5 +/- 1.1% increase in plasma volume as indicated by a significant reduction in plasma protein concentration. In either treatment, whereas arterial hypoxaemia was not observed during periods of submaximal exercise, short-term maximal exertion caused significant arterial hypoxaemia, desaturation of haemoglobin, hypercapnoea, and acidosis in both treatments. However, the magnitude of exercise-induced arterial hypoxaemia, desaturation of haemoglobin, hypercapnoea, and acidosis in both treatments remained similar, and statistically significant differences between treatments could not be demonstrated. CONCLUSIONS: It was concluded that significant pre-exercise expansion of plasma volume by this method does not adversely affect the arterial oxygenation of horses performing a prolonged exercise protocol simulating the 2nd day of an E3DEC.

Effects of chronic acetazolamide administration on fluid flux from the pulmonary vasculature at rest and during exercise in horses.

REASONS FOR PERFORMING STUDY: Horses develop high pulmonary pressures during exercise, which force fluid out of pulmonary capillaries. Specific airway diseases in horses, especially those associated with hypoxaemia, hypercapnoea and acidosis may influence pulmonary haemodynamics and pulmonary interstitial fluid equilibrium. OBJECTIVES: This study was designed to determine fluid flux (J(V-A) l/min) across the lung in exercising horses treated chronically with acetazolamide. METHODS: Six horses were exercised on a treadmill until fatigue without (Con) and with chronic carbonic anhydrase (CA) inhibition (AczTr) and associated hypercapnoea and acidosis. Carbonic anhydrase inhibition was achieved with administration of acetazolamide (Acz). Arterial and mixed venous blood were sampled, and VCO2 and VO2 measured. Blood volume changes across the lung (deltaBV%) were calculated from changes in plasma protein, haemoglobin and packed cell volume (PCV). Cardiac output (Q) was calculated using Fick principle. J(V-A) across the alveolar-capillary barrier was then quantified based on Q and deltaBV. Variables were analysed using 2-way repeated-measures ANOVA (P<0.05). A significant F ratio was further analysed using Tukey post hoc analysis. RESULTS: Treatment had a significant effect on J(V-A) (P = 0.002). At rest there was no J(V-A) in Con (0.63 +/- 0.6 l/min) and AczTr (0.84 +/- 0.3 l/min). During exercise Con fluid moved from the pulmonary circulation into the pulmonary interstitium (mean +/- s.e. J(V-A) 9.4 +/- 2.4 l/min). This was different from AczTr (mean +/- s.e. J(V-A) 1.8 +/- 1.9 l/min), where no transvascular fluxes from pulmonary circulation were present during exercise (P = 0.008). CONCLUSIONS: Chronic Acz treatment with associated hypercapnoea and acidosis affects J(V-A) in lungs of exercising horses. Lung fluid dynamics adapted to hypercapnoea and acidosis with reduction of fluid flow from the pulmonary circulation. POTENTIAL RELEVANCE: The current data provide comprehensive evidence of in vivo fluid homeostasis in lungs of exercising horses without and with CA inhibition.

Comparison of lactated Ringer's solution and a physiologically balanced 6% hetastarch plasma expander for the treatment of hypotension induced via blood withdrawal in isoflurane-anesthetized dogs.

OBJECTIVE: To compare the effects of lactated Ringer's solution (LRS) with those of a physiologically balanced 6% hetastarch plasma expander administered to isoflurane-anesthetized dogs with hypotension induced by blood withdrawal. ANIMALS: 12 healthy Beagles. PROCEDURE: Blood was withdrawn from isoflurane-anesthetized dogs (volume withdrawn measured) to a systolic arterial blood pressure (SAP) of 80 mm Hg. Six dogs each received either LRS or hetastarch solution (90 mL/kg/h, i.v.). Hemodynamic variables, pH, blood gas concentrations, PCV, serum electrolyte and total protein concentrations, and colloid osmotic pressure (COP) were determined at baseline, while SAP was 80 mm Hg, and after fluid treatment. The volume of fluid administered and rate of return of SAP to within 10% of baseline values were recorded. RESULTS: Mean +/- SD volume of blood withdrawn to decrease SAP to 80 mm Hg was 173 +/- 38 mL. Hemodynamic variables decreased after blood withdrawal but returned to baseline values more rapidly after infusion of a smaller volume of hetastarch solution, compared with the response to LRS infusion. Whereas PCV and serum total protein concentration decreased after administration of either solution, COP decreased only after administration of LRS. The total volume of hetastarch solution and LRS required to restore and maintain SAP to within 10% of baseline values was 1.1 +/- 0.9 and 4.4 +/- 1.7 times greater than the volume of blood removed, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Compared with LRS infusion, smaller volumes of hetastarch solution normalized and maintained SAP without lowering COP in isoflurane-anesthetized dogs after blood withdrawal.

Effect of dietary restriction, pregnancy, and fetal type on intestinal cellularity and vascularity in Columbia and Romanov ewes.

The objectives of this study were to evaluate intestinal cellularity and vascularity in mature ewes in response to dietary restriction and pregnancy status and to quantify the response of these variables to increased nutrient demand of fetal growth. In Exp. 1, 28 mature Dorset x crossbred white-faced ewes (61.6+/-1.8 kg initial BW) were fed a pelleted, forage-based diet. Treatments were arranged in a 2 x 3 factorial, with dietary restriction (60% restriction vs. 100% maintenance for respective states of pregnancy) and pregnancy status (nonpregnant, NP; d 90 and 130) as main effects. Dietary treatments were initiated on d 50 of gestation and remained at 60 or 100% maintenance throughout the experiment. Nonpregnant ewes were fed dietary treatments for 40 d. In Exp. 2, four Romanov ewes were naturally serviced (Romanov fetus and Romanov dam; R/R); two Romanov embryos per recipient were transferred to four Columbia recipients (Romanov fetus and Columbia recipient; R/C), and three Columbia ewes were naturally serviced (Columbia fetus and Columbia dam; C/C). In Exp. 1, dietary restriction and pregnancy status interacted with regard to maternal jejunal DNA concentration (P < 0.01), with restricted ewes having a greater DNA concentration (mg/g; fresh basis) at d 130. Vascularity (percentage of total tissue area) in the jejunum was increased (P < 0.06) as a result of dietary restriction and pregnancy status. Total microvascular volume ofjejunal tissue was not altered by dietary restriction and increased (P < 0.01) at d 130 of pregnancy. In Exp. 2, R/R ewes had less (P < 0.09) DNA (g) in the jejunum compared with R/C and C/C ewes. Jejunal vascularity (%) was increased (P < 0.05) in R/R ewes compared with R/C or C/C ewes, whereas total jejunal microvascular volume remained unchanged. These data demonstrate intestinal vascular density responds to changes in diet and physiological state. In addition, pregnancy increased total jejunal microvascular volume.

Effect of blood withdrawal and angiotensin II on prolactin release in the tilapia, Oreochromis mossambicus.

Repeated blood withdrawal (5% of estimated blood volume at 0, 1, 4, 8, 24, 48 and 76 h) from tilapia acclimated to fresh water (FW) resulted in a marked increase in plasma levels of prolactin (PRL) during the first 8 h, reaching a peak above 300 ng/ml after 4 h. The increase in plasma PRL levels was significant except for the level after 72 h. A slight but significant decrease in plasma osmolality was observed at all time points after the blood withdrawal. Repeated blood withdrawal from fish acclimated to seawater (SW) resulted in a marked increase in plasma osmolality after 4 and 8 h. A significant increase was observed in plasma growth hormone (GH) in the fish in SW until the end of the experiment, but there was no change in plasma PRL. Plasma levels of cortisol were significantly higher in the fish in SW than in those in FW during the first 24 h. Blood withdrawal resulted in a significant reduction in hematocrit values in both FW- and SW-adapted fish, suggesting hemodilution. In a separate experiment, a single blood withdrawal (20% of total blood) stimulated drinking after 5 h, regardless of whether the fish were held in FW or SW. Plasma PRL level was also elevated following a single blood withdrawal in the fish acclimated to FW, but not in the fish in SW. Intraperitoneal injection of ANG II (1.0 microg/g) into the fish in FW significantly increased plasma PRL levels after 1 h. Activation of the renin-angiotensin system after blood withdrawal and the dipsogenic action of angiotensin II (ANG II) are well established in fish. The reduction in plasma osmolality after repeated blood withdrawal in FW and the increased osmolality in SW suggest that blood volume is restored, at least in part, by drinking environmental water. These results suggest that the marked increase in PRL concentration after blood withdrawal from the fish in FW is due, at least in part, to a facilitative effect between ANG II and reduced plasma osmolality.

Immunopathologic investigations with an attenuated chicken anemia virus in day-old chickens.

The immunopathologic effects induced by two attenuated chicken anemia virus (CAV) isolates, known as cloned isolate 34 (CI 34) and cloned revertant isolate 18 (CRI 18), that were derived from highly passaged pools of Cux-1 CAV isolate, were compared with those induced by a pathogenic, molecularly cloned, low-passage Cux-1 isolate (CI Cux). This comparison involved the intramuscular inoculation of 1-day-old specific-pathogen-free chicks with each of the viruses and investigation of birds at selected days postinoculation for gross pathology and depletions in the thymic T-cell populations as determined by flow cytometry. Whereas infection with the pathogenic CI Cux produced severe anemia and pronounced bone marrow and thymus lesions, infections with the attenuated CRI 18 and CI 34 isolates produced no anemia, no or mild lesions, respectively, and moderate T-cell depletion. The results suggest that, with CAV, reduced pathogenicity for 1-day-old chicks correlates with reduced depletion of T-cell populations in the thymus and with reduced severity of lesions in the thymus and bone marrow.

Hyperhydration prior to moderate-intensity exercise causes arterial hypoxaemia.

The second day of a 3-day event is the most physically demanding of the 3 days. If this is performed under hot and humid environmental conditions, detrimental effects on cardiovascular and thermoregulatory function and, therefore, on exercise capacity, may occur due to exercise-induced dehydration. We hypothesised that the administration of fluid equivalent to 6% of the horse's bodyweight prior to a simulated second day of a 3-day event would increase plasma volume and limit increases in core temperature. Seven Standardbred geldings underwent a training protocol prior to the study. A standardised exercise test was developed for each horse so that exercise intensity at each phase would be the same percentage of the maximal heart rate for all horses. The exercise test involved 4 phases: Phase A involved 30 min exercise at 3.7 m/s (approximately 25% VO2max); Phase B 4 min exercise at 8 m/s (approximately 60% VO2max); and Phase C 50 min at 3.7 m/s, after which there was a 10 min rest. Phase D involved 14 min at 7.3 m/s (55% VO2max). In a cross-over design, horses were grouped randomly and allocated to either exercise with no fluid (control) or approximately 26 l isotonic fluid by nasogastric tube, 120 min prior to exercise. Arterial and mixed venous blood samples were collected prior to exercise, towards the end of each of the phases and during the rest period. The administration of fluid prior to exercise resulted in a pre-exercise bodyweight gain of 21.3 +/- 1.2 kg. Hyperhydration resulted in a greater degree of arterial hypoxaemia than the control group in Phases B and D, but not in Phases A and C or at rest. During Phases B and D, mean PaO2 values in the horses that received fluid were about 15 torr lower than in the control group, but there were no differences in PaCO2 values between the 2 groups. In both arterial and mixed venous blood, pH and HCO3- were significantly lower in the group that were hyperhydrated. We concluded that the most likely cause of the more severe arterial hypoxaemia in the hyperhydrated group during the intense exercise phase was some degree of pulmonary oedema, from the extravasation of the administered fluid. Hyperhydration prior to exercise may be detrimental to respiratory function and therefore care must be taken in administration of large volumes of fluid prior to exercise.

Relationship between body composition, blood volume and maximal oxygen uptake.

It has long been known that body mass and, more specifically, lean body mass are strongly correlated with maximal oxygen uptake (VO2max) in man and animals. However, there are no data to date describing this phenomenon in the horse. The purpose of this paper is to examine the relationship between body composition and VO2max in the horse. Twenty-three healthy and unfit Standardbred mares performed an incremental exercise test (GXT) to measure VO2max. Rump fat thickness (RTH), a measure of fat covering, was measured using B-mode ultrasound. Plasma volume, total blood volume and red cell volume were determined, using the Evan's Blue dye dilution technique and packed cell volume. VO2max was correlated with body mass (r = 0.541; P<0.01) and exercise haematocrit (exHCT; r = 0.407; P<0.05) but not RTH or the other haematological variables. To eliminate the influence of body mass on the individual variables, a regression analysis was performed on the mass-residuals of VO2max, RTH, plasma volume and exHCT. The residuals of VO2max were correlated negatively with the residuals of RTH (r = -0.687; P = 0.0003) and positively with the residuals of exHCT (r = 0.422; P = 0.045) but not plasma volume. VO2max could be predicted from a linear combination of the residuals of RTH and exHCT (r = 0.767; P<0.0001). These data indicate that VO2max in the horse is significantly related to fat-free mass (FFM), independent of body mass. Red blood cells from the splenic reserve constitute an important factor in the horse's ability to achieve a high VO2max. Therefore, lean body mass may be a more appropriate basis for assessing metabolic function in the athletic horse.

Ureteral ligation prevents the haemodynamic effect of frusemide in pentobarbitol anaesthetised horses.

Frusemide reduces pulmonary vascular pressures in resting horses and attenuates exercise-induced increases in these pressures in exercising horses. The mechanism underlying these effects of frusemide is unclear. We tested the hypothesis that the haemodynamic effects of frusemide are dependent on diuresis by examining the effect of frusemide in anaesthetised horses in which diuresis was prevented by ligation of ureters. Twenty four horses were assigned randomly to one of 4 treatments: 1) frusemide (1 mg/kg bwt i.v.) and intact ureters; 2) frusemide and ligated ureters; 3) saline placebo and ligated ureters; and 4) frusemide and phenylbutazone (4.4 mg/kg bwt i.v. 12 h and 15 min before frusemide) and ligated ureters. Frusemide administration to anaesthetised horses with intact ureters increased plasma total protein concentration and reduced mean right atrial, pulmonary artery and aortic pressures. There was no significant effect of frusemide administration on haemodynamic variables or plasma total protein concentration in horses with ligated ureters. The combination of frusemide and phenylbutazone increased mean right atrial, pulmonary artery and aortic pressures in horses with ligated ureters. This study demonstrates that, in anaesthetised horses, the haemodynamic effect of frusemide is dependent upon diuresis. We interpret these results as providing further evidence that the haemodynamic effect of frusemide in horses is attributable to a reduction in plasma and blood volume.