Evaluation of the Surgical Pleth Index (SPI) for the monitoring of the nociception-antinociception balance in dogs undergoing castration: A prospective clinical trial.

The aim of this prospective clinical study was to evaluate the efficacy of the Surgical Pleth Index (SPI), a validated nociception monitor in human anaesthesia, in dogs. The technology uses a plethysmographic signal from a specific pulse oximetry probe to analyse pulse wave amplitudes and heartbeat intervals. Twenty-six healthy dogs anaesthetised for castration were included. SPI, invasive mean arterial pressure (MAP) and heart rate (HR) were continuously monitored. The occurrence or resolution of a haemodynamic reaction (HDR), defined as a > 20% increase in HR and/or MAP, was assessed at predefined times: cutaneous incision, testicles' exteriorization, cutaneous suture, and fentanyl administration. Following nociceptive events, the dogs presenting a HDR showed a significant 8% and 10% increase in SPI at 3 and 5 min respectively, whereas after fentanyl administration, a 13% and 16% significant decrease in SPI were noted. Receiver operating characteristic curves analysis indicated a moderate performance for the dynamic variations of SPI over 1 min to predict a HDR (AUC: 0.68, threshold value: +15%) or its resolution after fentanyl administration (AUC of 0.72, threshold value: -15%) within 3 min. The SPI varied according to perioperative nociceptive events and analgesic treatment; however, its performance to anticipate a HDR was limited with high specificity but low sensivity. Refinement of the algorithm to specifically accommodate for the canine species may be warranted. Further studies are required to evaluate the influence of other factors on the performance of this index.

Doppler ultrasound is more accurate than pulse oximeter plethysmography in the measurement of systolic arterial pressure from the median caudal artery in anesthetized dogs.

OBJECTIVE: To compare the accuracy of doppler ultrasound (DOP) and pulse oximeter plethysmography (POP) in the measurement of systolic arterial pressure (SAP) to invasive blood pressure (IBP) in anesthetized dogs. ANIMALS: 40 client-owned healthy dogs > 10 kg. METHODS: Dogs were anesthetized for surgical procedures in dorsal recumbency. Invasive blood pressure was measured from a dorsal pedal artery. DOP and POP device probes were placed over the median caudal artery with a flow-occluding cuff for noninvasive blood pressure measurement. Systolic arterial pressure measured by DOP, loss of pulse oximeter plethysmograph (POPL), and return of pulse oximeter plethysmograph (POPR) were compared to SAP measured by IBP. A linear mixed model was used to determine correlation. Bland-Altman analyses were performed to determine bias, SD, and limits of agreement. The accuracy of DOP and POP was compared to IBP across different tensive states. RESULTS: Conditional R2 values for DOP, POPL, and POPR versus IBP were 0.92, 0.85, and 0.87, respectively (all P < .001). The biases for DOP, POPL, and POPR compared to IBP were +7.6 ± 13.1, +3.9 ± 14.4, and +8.6 ± 15.2 mm Hg (bias ± SD), respectively. Limits of agreement (lower, upper) were (-18.1, +33.3), (-24.3, +32.1), and (-21.2, +38.4) mm Hg for DOP, POPL, and POPR, respectively. DOP and POP overestimated SAP during hypotension (SAP < 90 mm Hg), DOP to a lesser magnitude. CLINICAL RELEVANCE: DOP measured from the median caudal artery may be acceptable for SAP measurement in dorsally recumbent, healthy anesthetized dogs > 10 kg. POP was determined an unacceptable method.

Evaluation of pulse pressure variation and pleth variability index to predict fluid responsiveness in mechanically ventilated isoflurane-anesthetized dogs.

OBJECTIVE: To evaluate whether pulse pressure variation (PPV) and pleth variability index (PVI) are more accurate than central venous pressure (CVP) for predicting fluid responsiveness in mechanically ventilated isoflurane-anesthetized dogs after premedication with acepromazine. DESIGN: Prospective experimental trial. SETTING: University teaching hospital. ANIMALS: Twelve Harrier hound dogs. INTERVENTIONS: Each dog was anesthetized and had a fluid challenge performed. This was repeated 4 weeks later for a total of 24 fluid challenges. After premedication with intramuscular acepromazine, anesthesia was induced with propofol and maintained with isoflurane. The dogs were mechanically ventilated with constant settings. The fluid challenge consisted of 10 mL/kg of 6% hydroxyethyl starch intravenously over 13 minutes. MEASUREMENTS AND MAIN RESULTS: Before and after the fluid challenge, PPV, PVI, CVP, and other hemodynamics were recorded. Change in velocity time integral of pulmonary arterial blood flow by echocardiography was calculated as an indication of change in stroke volume. A fluid responder was defined as an increase in velocity time integral ≥ 15%. Receiver operator characteristic (ROC) curves were used to determine cutoff values. Areas under ROC curve were calculated and compared. Dogs responded on 14 fluid challenges and did not on 10. Cutoff values for PPV and PVI were 11% (sensitivity 79%; specificity 80%) and 9.3% (sensitivity 86%; specificity 70%), respectively. The areas under the ROC curve of PPV [0.85, 95% confidence interval (CI): 0.70-1.00, P = 0.038] and PVI (0.84, 95% CI: 0.68-1.00, P = 0.043) were significantly higher than CVP (0.56, 95% CI: 0.32-0.81). CONCLUSIONS: PPV and PVI predicted fluid responsiveness more accurately than CVP and may be useful to guide fluid administration in mechanically ventilated isoflurane-anesthetized dogs after premedication with acepromazine.

Evaluation of the dynamic predictors of fluid responsiveness in dogs receiving goal-directed fluid therapy.

OBJECTIVES: Goal-directed fluid therapy (GDFT) based on pulse pressure variation (PPV) was used in anaesthetized dogs undergoing abdominal surgeries. The aims were 1) to evaluate the success rate of the PPV ≥13% in detecting fluid responsiveness [delta stroke volume (ΔSV) ≥10%]; 2) to assess the correlation between PPV, systolic pressure variation (SPV), Plethysmograph Variability Index (PVI) and central venous pressure (CVP) and 3) to establish the threshold value for the PVI that would predict a PPV value of ≥13% and indirectly discriminate responders from nonresponders to fluid therapy. STUDY DESIGN: Clinical, prospective, interventional study. ANIMALS: A total of 63 client-owned dogs scheduled for abdominal procedures. METHODS: PPV and SPV were calculated manually from the invasive blood pressure trace on the Datex monitor. PVI was recorded from the Masimo pulse oximeter. Fluid challenge (10 mL kg-1 Compound Sodium Lactate) was performed when PPV was ≥13% and/or mean arterial pressure (MAP) < 60 mmHg. Fluid responsiveness was assessed by the transoesophageal Doppler probe. Cardiovascular parameters (heart rate, MAP, PPV, SPV, PVI, SV and if available, CVP) were measured before and after each fluid intervention. RESULTS: PPV ≥ 13% reliably predicted fluid responsiveness in 82.9% of cases. There was positive correlation between PPV and SPV (r = 0.84%), PPV and logPVI (r = 0.46) as well as SPV and logPVI (r = 0.45). Noninvasive PVI value ≥13% should predict PPV threshold value (13%) with 97% sensitivity and 68% specificity. There was no statistically significant correlation between PPV and CVP. CONCLUSIONS: PPV is a useful clinical tool to detect occult hypovolaemia and predict cardiovascular response to fluid challenge. Use of PPV is recommended as a part of GDFT in dogs undergoing abdominal procedures.

Plethysmography variability index for prediction of fluid responsiveness during graded haemorrhage and transfusion in sevoflurane-anaesthetized mechanically ventilated dogs.

OBJECTIVE: To examine the accuracy of plethysmography variability index (PVI) as a noninvasive indicator of fluid responsiveness in hypovolaemic dogs. STUDY DESIGN: Prospective experimental study. ANIMALS: Six adult healthy sevoflurane-anaesthetized Beagle dogs. METHODS: Dogs were anaesthetized with 1.3-fold their individual minimum alveolar concentration of sevoflurane. The lungs were mechanically ventilated after neuromuscular blockade with vecuronium bromide. Cardiopulmonary variables including mean arterial blood pressure (MAP), central venous pressure (CVP), transpulmonary thermodilution cardiac output (TPTDCO), stroke volume (SV), perfusion index (PI), pulse pressure variation (PPV), stroke volume variation (SVV) and PVI were determined during six stages of graded venous blood withdrawal (5 mL kg-1 increments) and six stages of graded blood infusion (5 mL kg-1 increments). The cardiopulmonary variables were analysed using paired t test or Wilcoxon signed rank test. Correlations between PPV and SVV or PVI were analysed by linear regression. The accuracy of PPV, SVV and PVI for predicting fluid responsiveness was examined by using receiver operating characteristic curve analysis. A value of p < 0.05 was considered statistically significant. RESULTS: Blood withdrawal resulted in significant increases in PPV and PVI and decreases in MAP, CVP, TPTDCO, SV and PI. Blood infusion resulted in significant increases in MAP, CVP, TPTDCO, SV and PI and decreases in PPV and PVI. PPV and PVI showed a relevant correlation (p < 0.001, r2 = 0.62) and threshold values of PPV ≥ 16% (sensitivity 71%, specificity 82%) and PVI ≥ 12% (sensitivity 78%, specificity 72%) for identifying fluid responsiveness. SVV did not change. CONCLUSIONS AND CLINICAL RELEVANCE: Noninvasive measurement of PVI predicted fluid responsiveness with moderate accuracy equal to PPV in sevoflurane-anaesthetized mechanically ventilated dogs. Provisional threshold values for identification of fluid responsiveness were PPV ≥ 16% and PVI ≥ 12%. Clinical trials are needed to confirm these threshold values in dogs.

Insect Bite Hypersensitivity in Horses is Associated with Airway Hyperreactivity.

BACKGROUND: Genetic and epidemiologic evidence suggests that in horses, as in other species, different manifestations of hypersensitivity may occur together. HYPOTHESIS: Horses affected with insect bite hypersensitivity (IBH) show airway hyperreactivity (AH) to inhaled histamine, even in the absence of overt clinical signs of equine asthma (EA). ANIMALS: Twenty-two healthy controls (group C), 24 horses suffering from IBH alone (group IBH), and 23 horses suffering from IBH and EA (group IBH/EA). METHODS: The clinical histories were assessed using 2 standardized questionnaires, the Horse Owner Assessed Respiratory Signs Index (HOARSI), and IBH scoring. Horses were classified as EA-affected if their HOARSI was >1 and as IBH-affected if IBH score was >0. Confounding disorders were excluded by clinical examination. The arterial partial pressure of oxygen (PaO2 ) was measured and flowmetric plethysmography used to assess airway reactivity to increasing doses of inhaled histamine. RESULTS: The median histamine provocation concentration (PC) when ∆flow values increased by 35% (PC35) was significantly higher in group C (5.94 [1.11-26.33] mg/mL) compared to group IBH (2.95 [0.23-10.13] mg/mL) and group IBH/EA (2.03 [0.43-10.94] mg/mL; P < 0.01). The PC50 and PC75 showed very similar differences between groups. Furthermore, PaO2 was significantly lower in group IBH (84 ± 8 mmHg) and group IBH/EA (78 ± 11 mmHg) compared to group C (89 ± 6 mmHg; P < 0.01). CONCLUSIONS AND CLINICAL IMPORTANCE: IBH is associated with AH and decreased PaO2 , even in the absence of overt respiratory clinical signs.

Relationships between equine airway reactivity measured by flowmetric plethysmography and specific indicators of airway inflammation in horses with suspected inflammatory airway disease.

REASONS FOR PERFORMING STUDY: Agreement between airway reactivity measured by flowmetric plethysmography and histamine bronchoprovocation, and lower airway inflammation measured by bronchoalveolar lavage (BAL) cytology, has not been studied in horses with suspected inflammatory airway disease (IAD). OBJECTIVES: We tested the hypothesis that airway reactivity is associated with BAL cytology in horses presenting for unexplained poor performance and/or chronic cough. STUDY DESIGN: Prospective clinical study. METHODS: Forty-five horses, predominantly young Standardbred racehorses, presenting for unexplained poor performance or chronic cough, underwent endoscopic evaluation, tracheal wash, flowmetric plethysmography with histamine bronchoprovocation and BAL. Histamine response was measured by calculating PC35, the concentration of nebulised histamine eliciting an increase in Δflow of 35%. RESULTS: In this population, there was no significant correlation between histamine response and cell populations in BAL cytology. When airway hyperreactivity (AHR) was defined as ≥35% increase in Δflow at a histamine concentration of <6 mg/ml, 24 of the 45 horses (53%) were determined to have AHR. Thirty-three (73%) had either abnormal BAL cytology or AHR, and were diagnosed with IAD on this basis. Of horses diagnosed with IAD, 9 (27%) had an abnormal BAL, 11 (33%) had AHR and 13 (39%) had both. CONCLUSIONS: Airway reactivity and BAL cytology did not show concordance in this population of horses presenting for unexplained poor performance and/or chronic cough. Failure to include tests of airway reactivity may lead to underdiagnosis of IAD in young Standardbred racehorses that present with clinical signs suggestive of IAD.

Comparative assessment of effectiveness of ketoprofen and ketoprofen/beta-cyclodextrin complex in two experimental models of inflammation in rats.

Oral administration of non-steroidal anti-inflammatory drugs (NSAIDs) can lead to adverse effects such as gastrointestinal distress. The complexation of different groups of active substances with ß-cyclodextrin (ß-CD) has drawn considerable interest over recent years. The purpose of this study was to analyze the ketoprofen/ß-cyclodextrin (K/ß-CD) conjugate complex as well as to assess its anti-inflammatory effect after oral administration (doses of 30 mg/m(2) and 15 mg/m(2) of body surface), compared with ketoprofen. The studies were done on two models of experimentally-induced acute inflammation in rats (n = 48, 6/group), by means of intraplantar administration of a 10% aqueous kaolin suspension and intraperitoneal administration of a 1% sodium thioglycolate solution. The dynamics of the acute inflammatory process and the anti-inflammatory effects were monitored using plethysmometric determinations after 3, 6, 9, 12, 24 and 48 h (plantar inflammation), and the absorbance of the exudates (spectrophotometrically read) and nucleated cell counts after 24 h (peritoneal inflammation). The coupling of ketoprofen with ß-CD resulted in increased solubility (100% in 60 min) of the newly-formed product, which further resulted in a higher bioavailability compared with ketoprofen (<40% in 120 min). In both models of experimentally-induced inflammation, the K/ß-CD complex had a higher anti-inflammatory activity than ketoprofen.

Measurement of tidal volume using respiratory ultrasonic plethysmography in anaesthetized, mechanically ventilated horses.

OBJECTIVE: To compare tidal volume estimations obtained from Respiratory Ultrasonic Plethysmography (RUP) with simultaneous spirometric measurements in anaesthetized, mechanically ventilated horses. STUDY DESIGN: Prospective randomized experimental study. ANIMALS: Five experimental horses. METHODS: Five horses were anaesthetized twice (1 week apart) in random order in lateral and in dorsal recumbency. Nine ventilation modes (treatments) were scheduled in random order (each lasting 4 minutes) applying combinations of different tidal volumes (8, 10, 12 mL kg(-1)) and positive end-expiratory pressures (PEEP) (0, 10, 20 cm H(2)O). Baseline ventilation mode (tidal volume=15 mL kg(-1), PEEP=0 cm H(2)O) was applied for 4 minutes between all treatments. Spirometry and RUP data were downloaded to personal computers. Linear regression analyses (RUP versus spirometric tidal volume) were performed using different subsets of data. Additonally RUP was calibrated against spirometry using a regression equation for all RUP signal values (thoracic, abdominal and combined) with all data collectively and also by an individually determined best regression equation (highest R(2)) for each experiment (horse versus recumbency) separately. Agreement between methods was assessed with Bland-Altman analyses. RESULTS: The highest correlation of RUP and spirometric tidal volume (R(2)=0.81) was found with the combined RUP signal in horses in lateral recumbency and ventilated without PEEP. The bias ±2 SD was 0±2.66 L when RUP was calibrated for collective data, but decreased to 0±0.87 L when RUP was calibrated with individual data. CONCLUSIONS AND CLINICAL RELEVANCE: A possible use of RUP for tidal volume measurement during IPPV needs individual calibration to obtain limits of agreement within ±20%.

In vitro validation of a new respiratory ultrasonic plethysmograph.

OBJECTIVE: The in-vitro validation of a novel Respiratory Ultrasonic Plethysmography (RUP) system designed to detect circumference changes of rib cage and abdominal compartments in large and small animals. STUDY DESIGN: Experimental in vitro study. METHODS: The experimental system includes two compliant fluid-filled rubber tubes functioning as ultrasonic waveguides. Each has an ultrasonic transmitter and a detector at the opposing ends. Sensor length can be individually adapted in the range of 0.15-2 m. Data are downloaded to a computer at a sampling rate of 10 or 100 Hz. Measurements have a resolution of 0.3 mm. Baseline stability, linearity and repeatability were investigated with dedicated experiments. The base line drift was tested measuring a fixed distance for 2 hours continuously and then 18 hours later. A hand-operated horse thorax dummy (elliptically shaped, circumference 1.73 m) was used to compare waveforms of RUP with a respiratory inductive plethysmograph (RIP). The electromagnetic interference was tested by approaching metallic objects. RESULTS: Baseline drift and repeatability (10 repeated steps of 1.6% and 6.6% elongations and contractions) were within ± 0.3 mm. The response of the system for tube stretching up to 11% of total length was linear with a coefficient of determination for linearity of 0.998. In contrast to RIP, electromagnetic interference could not be observed with RUP. CONCLUSIONS AND CLINICAL RELEVANCE: The low baseline drift and the lack of electromagnetic interference favours the use of RUP compared to an RIP device when studying the breathing pattern and end expiratory lung volume changes in conscious and anaesthetized animals.

Evaluation of pulmonary function variables by using plethysmography in cats with respiratory disease associated to Dirofilaria immitis.

Heartworm Associated Respiratory Disease (HARD) is a pulmonary syndrome that results from the vascular and parenchymal inflammatory response associated with the arrival and death of Dirofilaria immitis in the distal pulmonary arteries. Barometric whole-body plethysmography (BWBP) is a non-invasive pulmonary function test (PFT) that allows a dynamic study of breathing patterns and is useful to study airway disease and the response to different treatments. The aim of this prospective non-blinded study was to compare respiratory function variables between healthy cats and HARD cats (seropositive to D. immitis) by use of BWBP. Twenty-five healthy cats and six HARD cats were put into the plethysmograph chamber and different respiratory variables were measured. The results were analyzed and compared between the two groups of animals. There were significant differences for bronchoconstriction index variables Pause (P-value<0.001) and enhanced pause (P-value<0.001), minute volume (P-value<0.05) and tidal volume (P-value<0.05) between healthy and HARD cats. There were no significant differences in respiratory rate and inspiratory and expiratory times between both groups of animals. The results obtained in our study support that HARD cats show significant differences in pulmonary function variables obtained by BWBP due to an acute inflammatory response at bronchial, vascular and parenchymal level. This PFT could be a useful method to facilitate the diagnosis of pathological states of bronchoconstriction in HARD cats.

Effect of prolonged administration of clenbuterol on airway reactivity and sweating in horses with inflammatory airway disease.

OBJECTIVE: To determine whether prolonged administration of clenbuterol results in tachyphylaxis, specifically regarding its bronchoprotective properties and effect on sweating in horses. ANIMALS: 8 Thoroughbreds with inflammatory airway disease. PROCEDURES: In a crossover design, horses received clenbuterol (0.8 µg/kg, p.o., q 12 h) or placebo for 21 days, with a washout period of ≥ 30 days between the 2 treatments. Airway reactivity was evaluated by use of flowmetric plethysmography and histamine broncho-provocation before (day 0; baseline) and every 7 days after the start of treatment. Sweat function was evaluated via response to epinephrine administered ID before and every 10 days after the start of treatment. RESULTS: The concentration of histamine required to increase total airway obstruction by 35% (PC35) was significantly reduced during treatment with clenbuterol (mean change, 11.5 mg/mL), compared with during administration of the placebo (mean change, -1.56 mg/mL), with a peak effect at 14 days. Tachyphylaxis was evident by day 21, with 7 of 8 horses having a PC35 below the baseline value (mean change, -0.48 mg/mL), which returned to baseline values during the washout period. No effect of clenbuterol was seen in sweat response to epinephrine administration. CONCLUSIONS AND CLINICAL RELEVANCE: Clenbuterol initially reduced airway sensitivity to inhaled histamine, but tachyphylaxis that resulted in increased airway reactivity was evident by day 21. Although no effects on sweating were detected, the technique may not have been sensitive enough to identify subtle changes. Prolonged administration of clenbuterol likely results in a clinically important reduction in its bronchodilatory effects.

Evaluation of respiratory function in freely moving Beagle dogs using implanted impedance technology.

INTRODUCTION: The Safety Pharmacology ICH S7A guidelines mandate the preclinical evaluation of drug effects on respiratory function. Chronic measurements of potential drug effects are commonly performed in rodents due to lack of a viable alternative in large animals. Presently, although the value and validity of these standard methods cannot be refuted, each method presents inherent limitations; such as the introduction of restraint stress (e.g. head-out rodent plethysmography and the pneumotachograph-equipped dog face mask), or sensitivity issues (e.g. whole body plethysmography). Since these approaches may limit the number of time points tested or affect respiratory parameters, new and accurate methods are needed for assessing respiratory function in conscious, freely moving animals. METHODS: We evaluated a new surgically implanted telemetry device, which adds an impedance sensor for the chronic measurement of respiratory parameters to the standard device used for safety pharmacology cardiovascular studies. The feasibility of the implantable device was assessed based on concordance of respiratory data with pneumotachograph-recorded parameters in conscious Beagle dogs following intravenous administration of a positive control (4 mg/kg doxapram). RESULTS: Linear regression analysis of data collected under restrained conditions showed a high correlation (R(2) 0.95) between impedance-derived respiratory parameters (tidal volume and respiratory frequency) and direct measurements of respiration via pneumotachograph. The correlation was reproduced when animals were challenged under the same dosing regimen. Volume changes similar to those obtained during the restrained collection were observed during the ambulatory collection following doxapram administration. Calibration of impedance-based values was adequate using both individual and population-based baseline conversion factors, both approximating actual mean respiratory variables collected with the pneumotachograph. DISCUSSION: The benefit of this model is the accurate, continuous measurement of respiratory endpoints in restrained, as well as ambulatory settings. Assessment of multiple physiological parameters collected concurrently and the use of population-based calibrations may enable the maximization of resources and shortened timelines in drug development.

Airway responsiveness measured by barometric plethysmography in guinea pigs.

Barometric plethysmography has become an increasingly used method to indirectly measure respiratory function in unrestrained freely-moving animals. This technique has been criticized because of physiological uncertainty of its major index, the enhanced pause (Penh). Moreover, a recent study raises concerns that during histamine challenges part of the Penh response could be produced by upper airways (nasal) responses. In this study we compared airway responsiveness measured by barometric plethysmography and total lung resistance (RL: ) in guinea pigs, and evaluated the role of upper airways during Penh measurement. Our results showed that intravenous acetylcholine or histamine caused a dose-dependent increase of the Penh values in non-anesthetized guinea pigs, which were correlated with RL: values obtained in separate groups of anesthetized animals. In anesthetized but spontaneously breathing guinea pigs intravenous acetylcholine or histamine also produced a dose-dependent increment of Penh, which was similar regardless if guinea pigs breathed through the nose or through a tracheal tube. Our results suggest that, independently of the physiological meaning of Penh, this index seems to be a useful indirect measurement for evaluating airway responsiveness to intravenous agonists in guinea pigs, and that nasal passage seems not to be involved in this measurement.

Reproducibility of airway responsiveness in horses using flowmetric plethysmography and histamine bronchoprovocation.

BACKGROUND: Inflammatory airway disease has a high prevalence in horses, but is often a diagnostic challenge. Flowmetric plethysmography and histamine bronchoprovocation (FP/HBP) is a simple and effective tool for diagnosis, but reproducibility of these measurements made over time has not been established. HYPOTHESIS: We hypothesize that the measurement of airway responsiveness in horses using FP/HBP is consistent over both short and long periods of time. ANIMALS: Twenty-nine healthy adult horses from 2 university herds. METHODS: In this prospective experimental study, airway responsiveness was determined in each horse at day 0 (baseline [BL]) with FP/ HBP, using PC35 (provocative concentration of histamine needed to increase Delta(flow) by 35%) as a measure of airway responsiveness. Each horse was re-tested 1-4 weeks after BL (short-term [ST]) and again at 3-12 months after BL (long-term [LT]). RESULTS: In the ST period, 23/27 (85%) of the horses had a PC35 that was within 1 doubling concentration of histamine of their BL value, with a mean change of 0.52 doubling concentrations (95% CI 0.26-0.79, range 0-2.06). For the LT data, 19/26 (73%) of horses were within 1 doubling concentration of their BL value, with a mean change of 0.81 doubling concentrations (95% CI 0.45-1.17, range 0.14-3.10). There was no significant difference in reproducibility between the 2 groups of subjects. CONCLUSIONS AND CLINICAL IMPORTANCE: Repeated measurements of airway responsiveness obtained with FP/HBP show acceptable reproducibility over time periods up to a year. However, caution must be used when testing horses when ambient air temperature is low.

Plethysmographic comparison of breathing pattern in heaves (recurrent airway obstruction) versus experimental bronchoconstriction or hyperpnea in horses.

BACKGROUND: Horses with recurrent airway obstruction (heaves) are described as exhibiting "increased abdominal effort," but it is unknown whether this translates to an effective contribution to ventilation. HYPOTHESIS: We hypothesized that heaves is characterized by asynchrony between rib cage and abdominal motions, and that the abdominal component is the major contributor to ventilation. ANIMALS: The rib cage versus abdominal motion in naturally occurring heaves (n = 15) was compared to controls at rest (n = 7) and during hyperpnea because of lobeline treatment, and the effects of histamine-induced bronchoconstriction in controls (n = 10). METHODS: Flow patterns, phase angle (theta) between the rib and abdominal compartments, abdominal (Vabd) contribution to tidal volume (VT), and lung mechanics were measured. RESULTS: Findings unique to the heaves group included the loss of biphasic expiratory flow, severely increased theta with the abdomen consistently lagging behind the rib cage, and a reduced contribution of the abdomen to ventilation. A subgroup of heaves (n = 5) with abdominal paradox showed a significant (P < .05) reduction in tidal volume, and increased respiratory rate. Bronchodilation reduced theta in heaves (P = .06), but theta remained significantly higher after bronchodilation than found in controls. CONCLUSIONS AND CLINICAL IMPORTANCE: We conclude that breathing pattern in horses with heaves is characterized by severe rib cage/abdominal asynchrony, with the rib cage motion in synchrony with flow, therefore dominating ventilation. In a subset of heaves, the abdominal compartment (diaphragm, abdominal muscles) was completely out of synchrony with flow ("abdominal paradox") despite the clinical appearance of "increased abdominal effort."

Inhaled fluticasone reduces bronchial responsiveness and airway inflammation in cats with mild chronic bronchitis.

This study investigated the effect of inhaled fluticasone on lower airway inflammation and bronchial responsiveness (BR) to inhaled carbachol in cats with very mild, chronic bronchitis (n = 5) that were compared with healthy cats serving as controls (n = 6). Chest radiographs, BR tests performed non-invasively by barometric whole body plethysmography (BWBP) and bronchoalveolar lavage (BAL) were performed before and after treatment. BR was quantified by calculating the concentration of carbachol inducing bronchoconstriction (C-Penh300%), defined as a 300% increase of baseline Penh, an index of bronchoconstriction obtained by BWBP. BAL fluid was analyzed cytologically and the oxidant marker 8-iso-PGF2alpha was determined. At test 1, healthy cats and cats with bronchitis were untreated, whereas for test 2 inhalant fluticasone (250 microg once daily) was administrated for 2 consecutive weeks to cats with bronchitis. Control cats remained untreated. Inhaled fluticasone induced a significant increase in C-Penh300% and a significant decrease of BAL fluid total cells, macrophages, neutrophils and 8-iso-PGF2alpha in cats with bronchitis, whilst untreated control cats did not show significant changes over time. This study shows that a 2-week fluticasone treatment significantly reduced lower airway inflammation in very mild bronchitis. BR could be successfully monitored in cats using BWPB and decreased significantly in response to inhaled fluticasone. 8-Iso-PGF2alpha in BAL fluid was responsive to treatment and appeared as a sensitive biomarker of lower airway inflammation in cats.

Comparison of the depressive effects of four anesthetic regimens on ventilatory and cardiovascular variables in the guinea pig.

BACKGROUND AND PURPOSE: Guinea pigs are one of the most difficult rodents to anesthetize safely, and as a consequence, there is a paucity of reports regarding the effects of anesthesia on their cardiorespiratory variables. We used long-term indwelling cannulas for studying the guinea pig in the conscious state, and subsequently investigated the effects of four types of injectable anesthetic regimens on cardiorespiratory variables. METHODS: Using barometric plethysmography (conscious: long-term cannulated, n = 11; no cannulation, n = 28) or trachea-out plethysmography (anesthetized: n = 7 for each of the four groups), we recorded ventilatory, cardiovascular, metabolic, and arterial gas variables during air breathing and in response to 10 min of hypoxia (8% O2) and 10 min of hypercapnia (8% CO2). The four anesthetic regimens tested were: Saffan (infused at 9.75 mg/kg of body weight/h, i.v.); ketamine/xylazine (14.6/3.7 mg/kg/h, i.v.); pentobarbitone (8.3 mg/kg/h, i.v.) plus Innovar Vet (0.15 mg/kg every 1 to 1.5 h, s.c.); or pentobarbitone alone (22 mg/kg/h, i.v.). RESULTS: The least depressive anesthetic with regard to ventilation (VE) was ketamine/xylazine. Air breathing was depressed by only 17% (cf approx 50 to 60% for all other regimes), and the VE responses to hypoxia and hypercapnia were attenuated the least. All anesthetics equally depressed mean arterial blood pressure (from 70 mmHg to 56 mmHg) and ketamine/xylazine was the only anesthetic to reduce heart rate (from 260 beats/min to 198 beats/min). CONCLUSION: Although all anesthetics induce cardiorespiratory depression to some extent, the use of ketamine/ xylazine is recommended for future use in respiratory studies of the guinea pig where anesthesia cannot be avoided.

Movements of thoracic and abdominal compartments during ventilation at rest and during exercise.

The present investigation utilised simultaneous measurements of chest (Ch) and abdominal (Ab) circumferences and respiratory airflow to test the hypothesis that Ch circumferential expansion contributes proportionally little to tidal volume in the running Thoroughbred. During exercise, there were only small changes in Ch and Ab circumference and no increase with increasing tidal volume. At rest, walk and trot, the flow, Ch and Ab signals were in phase. However, during canter and gallop, the Ch and Ab changes were 180 degrees out of phase with each other and both were out of phase with airflow. In contrast to exercise, increase in ventilation at rest achieved by administration of lobeline resulted in a 4-6-fold increase in tidal volume; large excursions of the chest were always in phase with airflow. Furthermore, 3 horses showed an increase in chest circumference, demonstrating that chest stiffness per se does not preclude chest circumferential expansion. In conclusion, in the absence of significant increases in either Ch or Ab expansion during running, elongation of the thoracoabdominal segment may be the main determinant of tidal volume.