Biomedical subjects

W N McDonell

Publications and source records attributed to W N McDonell.

At least 19 recordsLinked to original sources

PubMed1991

Pulmonary structure and function in adult dairy cows with an expanded lung field.

Pulmonary function tests were performed on seven adult dairy cows with an expanded lung field (ExLF) and the results were compared to the values from seven cows with normal lung fields. The cows with ExLF had an increased functional residual capacity (FRC) and end-tidal N2 concentration of the final breath of the multiple-breath N2 washout (FETN2,fb), and an abnormal distribution of ventilation. The measurements of ventilation and gas exchange and pulmonary mechanics did not differ between the two groups. Postmortem examination of the lungs of five of the cows in each group indicated the cows with ExLF had a bronchiolitis with varying degrees of goblet cell hyperplasia, epithelial cell hyperplasia and metaplasia, smooth muscle hypertrophy, inflammatory cell infiltrate, vascular thickening, peribronchiolar fibrosis, and a mild overinflation of the lung. A histopathological score, based on the preceding indices and bronchus-associated lymphoid tissue, was correlated with FRC, FETN2,fb, the lung clearance index and pulmonary resistance. There were no correlations between the histopathological score and any of the measures of ventilation and gas exchange.

Animals↗

PubMed1991

Comparative hemodynamic effects of halothane and halothane-acepromazine at equipotent doses in dogs.

The purpose of this study was to compare the cardiovascular effects of halothane when used alone at increasing doses (1.2, 1.45 and 1.7 minimum alveolar concentration, MAC) to those produced with equipotent doses of halothane after potentiation of the anesthetic effect with acepromazine (ACP) sedation (45% reduction of halothane MAC). Six healthy mature dogs were used on three occasions. The treatments were halothane and intramuscular (IM) saline (1.0 mL), halothane and ACP (0.04 mg/kg IM), or halothane and ACP (0.2 mg/kg IM). Anesthesia was induced and maintained with halothane in oxygen and the dogs were prepared for the collection of arterial and mixed venous blood and for the determination of heart rate, systolic, diastolic and mean arterial pressure, mean pulmonary arterial pressure (PAP), central venous pressure and cardiac output. Following animal preparation the saline or ACP was administered and positive pressure ventilation instituted. Twenty-five minutes later the dogs were exposed to the first of three anesthetic levels, with random assignment of the sequence of administration. At each anesthetic level, measurements were obtained at 20 and 35 min. Calculated values included cardiac index, stroke index, left ventricular work, systemic vascular resistance, arterial oxygen content, mixed venous oxygen content, oxygen delivery and oxygen consumption. Heart rate was significantly higher with halothane alone than with both halothane-ACP combinations and was significantly higher with high dose ACP compared to low dose ACP. Systolic and mean blood pressures were lowest with halothane alone and highest with 0.2 mg/kg ACP, the differences being significant for each treatment. Oxygen uptake and PAP were significantly lower in dogs treated with ACP. It was concluded that ACP does not potentiate the cardiovascular depression that accompanies halothane anesthesia when the resultant lower dose requirements of halothane are taken into consideration.

Acepromazine↗

PubMed1991

Comparison of the hemodynamic effects of halothane alone and halothane combined with epidurally administered morphine for anesthesia in ventilated dogs.

The hemodynamic effects of 1.5 minimal alveolar concentration of halothane alone (1.6% end-tidal) and 1.5 minimal alveolar concentration of halothane (1.1% end-tidal concentration) combined with epidurally administered morphine were compared during controlled ventilation in 10 dogs used on 2 occasions and randomly allocated to 2 groups. Arterial blood pressure, cardiac index, stroke volume, left ventricular work, and pulmonary arterial pressure were significantly (P less than 0.05) higher in dogs of the morphine-treated group before administration of morphine. After epidural administration of morphine (0.1 mg/kg of body weight diluted in 0.26 ml of saline solution/kg), hemodynamic changes were not observed, and the aforementioned variables remained significantly (P less than 0.05) higher than values in dogs of the halothane only group. Compared with halothane (1.6%) alone, the reduction in halothane end-tidal concentration (1.1%) associated with epidurally administered morphine is beneficial in maintaining hemodynamic function.

Anesthesia↗

PubMed1990

Use of laser Doppler flowmetry to determine blood flow in and viability of island axial pattern skin flaps in rabbits.

Perfusion and viability of island axial pattern skin flaps were tested in 37 healthy New Zealand white rabbits, using laser Doppler monitoring of blood flow in the capillary loops and the subpapillary plexus of the dermis. Skin flaps, selected on the basis of the caudal superficial epigastric vein and artery, were lifted and replaced in their original locus after selective occlusion of their vascular pedicles. Subjects were allotted into groups: control group (n = 10); arterial occlusion (n = 7); venous occlusion (n = 10); and arterial and venous occlusion (n = 10). The rabbits were monitored from 48 hours before surgery until euthanasia 48 to 72 hours after replacement of the flap. Flap viability was assessed on a clinical basis, using a comparative scoring method based on a numeric scale. The degree of necrosis in histologic sections was evaluated, using a scoring system. Laser Doppler measurements were obtained on 3 consecutive days before surgery, to establish the normal basal blood flow in the skin. Postsurgical measurements were obtained at 2-hour intervals for the first 8 hours and at 24, 48, and 72 hours after surgery. Measurements of basal blood flow varied significantly (P less than 0.05) from site to site on the surface of individual flaps and over time. When laser Doppler flowmetric (LDF) measurements from 6 sites on a flap were used as a measure of laser Doppler flow for the total flap, there was no significant difference between contralateral flap areas outlined on the abdomen of the rabbits. Temporal variations over 3 days for each rabbit or among rabbits were not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

An evaluation of the multiple-breath nitrogen washout as a pulmonary function test in horses.

Multiple-breath nitrogen washouts (MBNW) were performed with 29 light horses. Seven normal horses were used to examine the reproducibility, and 22, ranging from normal to severely diseased, were used to examine the changes in chronic obstructive pulmonary disease (COPD) and the effect of a bronchodilator, salbutamol, on the distribution of ventilation. The MBNW were analyzed using the functional residual capacity (FRC), end-tidal N2 concentration of the final breath of the MBNW (FETN2,fb), end-tidal N2 concentration when the cumulative expired volume was equal to body weight (FETN2,bw), lung clearance index (LCI), Becklake index (BI), mixing ratio (MR), index of distribution of inspiration (IDI), pulmonary N2 clearance delay (PCD) and ventilatory efficiency (EFF). The LCI, MR, IDI, PCD and EFF were calculated at end-tidal N2 concentrations (FETN2), equal to 3%, 2% and FETN2,fb. The EFF was also calculated at FETN2 = 8%, as was BI. The within day coefficient of variation for most indices of the MBNW was 10-15%. None of the indices varied significantly from day-to-day. The FETN2,fb, FETN2,bw, MR, IDI, PCD, and EFFfb, EFF3% and EFF2% differed between the horses with COPD and the normal horses, and all of the indices, except FRC, were correlated with a histopathological score of the small airways. The FETN2,bw appeared to be the most sensitive index in detecting the horses with COPD. In the horses with COPD, salbutamol caused a decrease in FRC and FETN2,fb indicating increased ventilation of the lung. However, LCI increased suggesting a less efficient distribution of ventilation.

Animals↗

PubMed1989

Epidural morphine reduces halothane MAC in the dog.

Morphine, 0.1 mg.kg-1 was administered epidurally on two different occasions to ten dogs to determine the effect of two different volumes of saline dilution, 0.13 and 0.26 ml.kg-1, on the minimum alveolar concentration (MAC) of halothane as determined by subcutaneous electrical current applied to the fore and hind limbs in a random order. Following MAC determination with halothane alone, epidural morphine was administered and MAC was redetermined. Epidural morphine significantly reduced, P less than 0.001, the MAC of halothane for fore and hind legs in both volume groups; from 1.04 +/- 0.038 to 0.68 +/- 0.034 and 0.60 +/- 0.017 for for and hind limbs, respectively, in the large volume group, and from 0.96 +/- 0.038 to 0.66 +/- 0.088 and 0.60 +/- 0.030 for fore and hind limbs, respectively, in the small volume group. The reduction in MAC was significantly greater, P less than 0.025, in the hind limb. This study indicates that epidural morphine reduces the halothane requirements in the dog in a segmental manner. The volume of administration was not shown to be critical. Epidural morphine, 0.1 mg.kg-1, diluted in 0.13 to 0.26 ml.kg-1 saline produces significant analgesia in the dog as far forward as the fore limb and will reduce the halothane requirement to permit surgery.

Analgesia, Epidural↗

PubMed1989

An evaluation of the multiple-breath nitrogen washout as a pulmonary function test in dairy cattle.

Multiple-breath nitrogen washouts (MBNW) were performed with 21 adult dairy cows (seven normal cows tested on two days each, four clinically normal cows tested on six days, and ten cows with respiratory disease tested on one day each). The functional residual capacity (FRC), lung clearance index (LCI), Becklake index (BI), mixing ratio (MR), pulmonary N2 clearance delay (PCD), index of distribution of inspiration (IDI) and ventilatory efficiency (EFF) were calculated for each MBNW. The LCI, MR, PCD, IDI and EFF were calculated at an end-tidal N2 concentration of 3% (FETN2,3%) and the end-tidal N2 concentration of the final breath of the MBNW (FETN2,fb), while BI was calculated and EFF was also calculated at FETN2 = 8% (i.e. after washout of 90% of the N2 in the lung). All of the MBNW were irregular due to breath-to-breath variability in the breathing pattern of cows and variability in FRC. The within day coefficients of variation for FRC, LCI, MR, IDI, EFF3% and EFFfb were less than 10%, but in the four cows tested on six days there was significant day-to-day variability for individuals for FRC, LCI, BI, MR, PCD and IDI. The shape of the MBNW curves differed between the normal cows and those with respiratory disease. The FRC, EFF3% and EFFfb were the most sensitive indices in detecting the cows with respiratory disease, and when EFF3%, EFFfb or FETN2fb, was used in conjunction with FRC it was possible to detect all of the cows with respiratory disease.

Animals↗

PubMed1989

Simple nonrebreathing valves for use with large mammals.

Two simple nonrebreathing valves suitable for use with large mammals are described. These valves can be constructed in a reasonably well equipped workshop using materials that are readily available. The resistive pressure of both valves is less than 0.1 kPa at flow rates up to 15 L.s-1. Their main limitation is a relatively large dead space, although the dead space of valve B (290 mL) is less than the dead space of some commercially available valves. Healthy adult horses and cows compensate for the increased dead space by an increase in tidal volume.

Animals↗

PubMed1989

Comparative pulmonary mechanics in the horse and the cow.

Pulmonary mechanics and lung volumes were measured in horses and cows to determine if differences in breathing pattern between the two species were due to differences in the mechanical properties of the lungs. Tidal volume (VT) was larger in the horses, while the respiratory rate (fR) and minute ventilation (VE) were higher in the cows. The horses often had a double peak in airflow during inspiration and, or, expiration, while the cows had a single peak during expiration. Measured lung volumes were larger in the horses and they had a higher dynamic lung compliance (Cdyn,L), although the static compliance of the lung, chest wall and respiratory system (Cst,L,Cst,w and Cst,rs respectively) did not appear to differ between the two species. The cows had a greater change in maximum transpulmonary pressure (delta PLmax) and an increased nonelastic work of breathing (Wb). However, the pulmonary resistance (RL) did not differ between the two species, thus the higher delta PLmax and Wb in the cows were most likely a function of their higher flow rates. Calculations of the rate of work of breathing (W) indicate that both species breathed at an fR above the minimum W. The fR in the horses was close to the fR predicted for the average minimum muscle force, but the fR in the cows was higher. As the differences in the mechanical properties of the lung do not explain the differences in flow pattern, nor adequately account for the higher fR in the cows, it is suggested that the differences in breathing pattern between the two species is due to differences in the chest wall, particularly the size and shape of the abdomen.

Animals↗

PubMed1989

Comparative ventilation and gas exchange in the horse and the cow.

Ventilation and gas exchange were studied in healthy, adult horses and cows, two large species with different lung structures and different breathing patterns. The oxygen uptake (VO2), carbon dioxide output (VCO2), respiratory rate (fR), minute ventilation (VE), alveolar ventilation (VA), alveolar oxygen pressure (PAO2), and VE/VO2 ratio were higher in the cows, while the tidal volume (VT) and physiological dead space (VD) were larger in the horses. The arterial blood gases, alveolar-arterial oxygen pressure difference (PAO2-PaO2) and VD/VT ratio did not differ between the two species. The higher VO2 in the cows was most likely due to the energy cost of standing, and possibly to a higher cost of digestion. The higher VE, VA, VE/VO2 and PAO2 were most likely secondary to the increased VO2 and the slightly higher respiratory exchange ratio (R) in the cows. In contrast to hypotheses based on allometric equations, the PAO2 of horses and cows did not appear to differ from that of smaller mammals. The VD was larger than that predicted from allometric equations, and even though the VD/VT ratio (0.50) was lower than the previously reported values for horses and cows, it was significantly larger than the predicted weight-independent value of 0.36. Re-examination of the data used to derive the equation for VD raised questions as to the validity of this equation, and it is suggested that caution be exercised in the use of allometric equations for prediction.

Animals↗

PubMed1988

Reproducibility of pulmonary mechanics measurements in dairy cattle.

The reproducibility of pulmonary mechanics measurements in dairy cattle was examined using two study designs. In design A measurements were made with six cows on two days, and in design B measurements were made with four cows on six days. The mean coefficients of variation for within-day measurements for individuals ranged from 9.2 to 25.9% indicating considerable within-day variability. In design A there were no significant differences between days (P less than 0.05) for any measured variable for the group, but there were often significant differences between the two days for individuals. In design B there were significant cow-day interactions for all variables, again indicating significant differences between days for individuals. There were significant differences between days for the group for respiratory rate, and duration of inspiration and expiration. Both the interactions and differences between days appeared to be random. The high variability and limited reproducibility of pulmonary mechanics measurements, particularly in individual animals, indicate the need for caution in the interpretation of pulmonary mechanics measurements in dairy cattle.

Analysis of Variance↗

PubMed1988

Open canalicular system of platelets in porcine stress syndrome.

A study was undertaken to test whether a previously reported alteration in platelet morphology could be of predictive value for the detection of stress-susceptibility in pigs. Platelets from 20 normal pigs, nine pigs classified as stress-susceptible on the basis of their response to halothane challenge, and 11 siblings of halothane reactors belonging to two different breeds were subjected to electron microscopic examination. A quantitative analysis of electron micrographs, based on the extent of dilatation of the open canalicular system in platelets and the percentage of affected platelets, revealed that halothane reactor pigs could be distinguished from normal animals on the basis of their open canalicular system score. The discrete nature of the score categories in siblings indicates that platelet alteration may be an inherent component of the porcine stress syndrome and suggests that some of the false negatives in the halothane test may be identified as stress-susceptible on this criterion. Further studies involving a larger number of halothane reactors and siblings are needed to ascertain the consistency of the open canalicular system features and eventually, to develop a simple test system based on platelet alterations for the detection of stress-susceptibility in pigs.

Animals↗

PubMed1987

Platelet alterations in porcine stress syndrome.

Platelets in blood collected from pigs identified as normal (21) or stress susceptible (25) on the basis of their response to halothane challenge, were subjected to electron microscopic examination in order to test whether the ultrastructural features of stress susceptible pigs exhibit any deviation from those of normal. The most striking feature of the platelets from stress susceptible pigs was the extent of dilatation of the open canalicular system (OCS). The difference in platelet morphology between normal and stress susceptible pigs was consistent regardless of the anticoagulants used for blood collection indicating that the platelet alteration may be an inherent component of the porcine stress syndrome.

Animals↗

PubMed1987

Antagonism of xylazine induced sedation by idazoxan in calves.

Idazoxan was studied at three dose rates to assess its potential as an antagonist to xylazine. Calves in the study group were initially given xylazine at a dose rate of 0.2 mg/kg intravenously followed 12 minutes later by idazoxan at a dose rate of either 0.05, 0.075 or 0.10 mg/kg intravenously. A control group received a saline injection instead of idazoxan. All three dose levels of idazoxan successfully reversed the xylazine induced central nervous depression and all animals stood within two minutes of injection. No residual signs of sedation were noticed and relapse did not occur. In addition idazoxan was successful in reversing respiratory and cardiovascular depression produced by xylazine. The results indicated that idazoxan may be used for rapid reversal of xylazine induced sedation in calves.

Adrenergic alpha-Antagonists↗

PubMed1986

The noxious effects of electroimmobilization in adult Holstein cows: a pilot study.

Ten adult Holstein cows were used in an experiment to determine whether the induction of electroimmobilization was a noxious event. The cows were halter trained and accustomed to being led into a set of stocks. The time taken for the cattle to walk the last ten metres into the stocks was recorded. The heart rate of the cow was recorded for a three minute period prior to a ten second exposure to a high pitched sound (the conditioning stimulus). Measurements were collected for three repetitions and then the cows were assigned to two groups of five. One group was immobilized for 30 seconds using a commercial electroimmobilizer, the other group was not treated. This procedure was repeated ten times over a period of eight days. The cows were then exposed to the conditioning stimulus and their response observed. The treated group took significantly (P less than 0.05) longer to get into the stocks and the regression slopes for heart rate were significantly different from the control group. The treated cows responded to the conditioning stimulus at five and nine months after the end of the conditioning period. Adult Holstein cows regarded electroimmobilization as a noxious event and were very strongly conditioned to this stimulus.

Animals↗

PubMed1986

Evaluation of a commercial creatine kinase screening test for malignant hyperthermia (porcine stress syndrome).

Two hundred and seven boars entering a Record of Performance Test Station at New Hamburg, Ontario were screened for susceptibility to malignant hyperthermia or the porcine stress syndrome. Screening tests included the determination of whole blood creatine kinase levels by a commercially available test using the method of bioluminescence and a halothane challenge. The validity of the bioluminescent or whole blood creatine kinase test as a screening mechanism for malignant hyperthermia was evaluated in boars in a field trial. The susceptibility of these animals to malignant hyperthermia or the porcine stress syndrome was unknown at the time of the study. It was determined in the initial field trial that 76.3% or 158 of the 207 boars tested by the bioluminescent creatine kinase screening test were stress susceptible. In contrast, only one boar (0.5%) reacted to a standard five minute halothane challenge. After further examination of the commercial screening test, little correlation was found to exist between the bioluminescent and Rosalki methods of creatine kinase determination. The coefficient of analytical variation for the bioluminescent method of creatine kinase determination ranged from 17.6% at a mean of 359 LU to 21.9% at a mean of 318 LU. Similarly, the coefficient for the Rosalki technique ranged from 7.1% at a mean of 324 U/L to 14.0% at a mean of 64 U/L. In addition, little correlation was found to exist between creatine kinase levels as determined by the bioluminescent method and outcome to the halothane or halothane/succinylcholine challenge, age of boars in weeks or percentage gain in weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1986

Cardiopulmonary effects of xylazine and yohimbine in laterally recumbent sheep.

The effects of yohimbine (0.125 mg/kg) on cardiopulmonary parameters in six adult, xylazine treated (0.15 mg/kg), laterally recumbent sheep were studied. Following collection of baseline data, xylazine was administered intravenously and data were collected five and fifteen minutes later. At twenty minutes post-xylazine either yohimbine (0.125 mg/kg) or saline was given and further collection of data occurred at 25, 30, 40 and 50 minutes. Xylazine administration resulted in significant (P less than 0.05) respiratory depression, as reflected by a decrease in arterial oxygen partial pressure (PaO2). No significant changes in haemodynamic variables were observed. Yohimbine produced a significant improvement in PaO2 at the 50 minute period and abolished the paradoxical respiratory pattern when present. The results indicated that yohimbine can be used as an antagonist to control the duration of xylazine induced respiratory depression, although the degree of reversal was less than is clinically desirable.

Animals↗

PubMed1985

Evaluation of the wick catheter as used to measure intracompartmental muscle pressure in equine muscle.

The use of the wick catheter to measure intracompartmental muscle pressure in equine muscle was documented. The presence of muscle compartments involving the extensor carpi radialis muscle and the long head of the triceps brachii was demonstrated by anatomic dissection and radiographic technique. The wick catheter was capable of accurately measuring pressures within both of these compartments. Furthermore, the wick catheter was sensitive to pressure changes resulting from external compression of muscle compartments. Manipulation of systemic blood pressure and PaCO2 in 1 anesthetized horse did not affect intracompartmental muscle pressure.

Anesthesia, General↗