Use of the impulse oscillometry system for testing pulmonary function during methacholine bronchoprovocation in horses

OBJECTIVE: To compare sensitivity of the impulse oscillometry system (IOS) with that of the conventional reference technique (CRT; ie, esophageal balloon method) for pulmonary function testing in horses. ANIMALS: 10 horses (4 healthy; 6 with recurrent airway obstruction [heaves] in remission). PROCEDURE: Healthy horses (group-A horses) and heaves-affected horses (group-B horses) were housed in a controlled environment. At each step of a methacholine bronchoprovocation test, threshold concentration (TC(2SD); results in a 2-fold increase in SD of a value) and sensitivity index (SI) were determined for respiratory tract system resistance (R(rs)) and respiratory tract system reactance (X(rs)) at 5 to 20 Hz by use of IOS and for total pulmonary resistance (RL) and dynamic lung compliance (C(dyn)), by use of CRT. RESULTS: Bronchoconstriction resulted in an increase in R(rs) at 5 Hz (R(5Hz)) and a decrease in X(rs) at all frequencies. Most sensitive parameters were X(rs) at 5 Hz (X(5Hz)), R(5Hz), and R(5Hz):R(10Hz) ratio; RL and the provocation concentration of methacholine resulting in a 35% decrease in dynamic compliance (PC(35)C(dyn)) were significantly less sensitive than these IOS parameters. The TC(2SD) for X(rs) at 5 and 10 Hz was significantly lower in group-B horses, compared with group-A horses. The lowest TC(2SD) was obtained for X(5Hz) in group-B horses and R(5Hz) in group-A horses. CONCLUSIONS AND CLINICAL RELEVANCE: In contrast to CRT parameters, IOS parameters were significantly more sensitive for testing pulmonary function.The IOS provides a practical and noninvasive pulmonary function test that may be useful in assessing subclinical changes in horses.     

Qualitative and quantitative evaluation of equine respiratory mechanics by impulse oscillometry

REASONS FOR PERFORMING STUDY: The long-established conventional reference technique (CRT) for measuring respiratory mechanics in horses lacks sensitivity and there is a need for further refinement in new technology, such as the impulse oscillometry system (IOS). OBJECTIVES: To evaluate the potential use of the IOS as a clinical respiratory function test and compare it to the current CRT in horses suffering from common upper and lower airway dysfunctions. METHODS: Six healthy horses were tested before and after induction of a unilateral nasal obstruction (UNO) or transient left laryngeal hemiplegia (LLH). Six heaves-affected horses were tested in clinical remission and during a heaves crisis, before and after nebulisation of cumulative doses of a bronchodilator therapy (ipratropium bromide; IPB). RESULTS: As opposed to the CRT, the IOS was able to detect partial upper airway obstruction (UAO) caused by UNO or LLH in resting horses, without differentiating both conditions. Upper airway obstruction caused an upward shift of resistance (R(rs)) from 5 to 35 Hz without altering reactance (X(rs)). As for the CRT, IOS respiratory parameters measured in heaves-affected horses in crisis differed significantly from values measured during remission. The difference in frequency-dependent behaviour of R(rs) and X(rs) allowed discrimination between upper and lower airway obstructions. Bronchodilator treatment induced significant dose-dependent changes in X(rs) at 5 and 10 Hz, from the first dose. Total pulmonary resistance (RL) and R(rs) at 5 Hz were affected from the second dose and displayed similar sensitivity. Although post treatment RL values were comparable to remission, R(rs) and X(rs) remained significantly different, characterising persistent peripheral obstruction. CONCLUSIONS: The IOS was more sensitive than the CRT in detecting partial UAO in resting horses and persistent post treatment peripheral dysfunction in heaves-affected horses. The IOS is a sensitive test that provides graded quantitative and qualitative information on disease-induced respiratory dysfunctions as well as on treatment efficiency in horses. POTENTIAL RELEVANCE: The IOS could represent a practical and sensitive alternative respiratory function test for routine clinical investigations of common airway obstructive diseases and therapy in horses.     

Measurement of respiratory function by impulse oscillometry in horses

REASONS FOR PERFORMING STUDY: Due to technical implementations and lack of sensitivity, pulmonary function tests are seldom used in clinical practice. Impulse oscillometry (IOS) could represent an alternative method. OBJECTIVES: To define feasibility, methodology and repeatability of IOS, a forced oscillation technique that measures respiratory resistance (Rrs) and reactance (Xrs) from 5 to 35 Hz during spontaneous breathing, in horses. METHODS: Using 38 healthy horses, Rrs and Xrs reference values were defined and influence of individual biometrical parameters was investigated. In addition, IOS measurements of 6 horses showing clinical signs of heaves were compared to those of 6 healthy horses. RESULTS: Airtightness and minimal dead space in the facemask were prerequisites to IOS testing and standardisation of head position was necessary to avoid variations in Rrs due to modified upper airway geometry. In both healthy and diseased animals, measurements were repeatable. In standard-type breeds, the influence of the horse's size on IOS parameters was negligible. An increase in R5Hz greater than 0.10 kPa/l/sec and R5Hz>R10Hz, combined with negative values of Xrs between 5 and 20 Hz, was indicative of heaves crisis. CONCLUSIONS: IOS is a quick, minimally invasive and informative method for pulmonary function testing in healthy and diseased horses. POTENTIAL RELEVANCE: IOS is a promising method for routine and/or field respiratory clinical testing in the equine species.     

The use of impulse oscillometry for separate analysis of inspiratory and expiratory impedance parameters in horses: effects of sedation with xylazine

AIM: To improve the outcome of parameters measured by the impulse oscillometry system (IOS) in horses by separate assessment of inspiratory and expiratory impedance spectra in the frequency range between 1 and 10 Hz. As basis for further studies, the influence of sedation with xylazine on respiratory impedance was also investigated. METHODS: (i) The respiratory impedance of 11 horses was measured using IOS before and 6 min after sedation (xylazine; 0.6 mg/kg b.w.). (ii) The time course of impedance parameters in a period of 24 min after administration of xylazine was evaluated in 12 horses at regular intervals of 3 min. Resistance (R(rs)), reactance (X(rs)), and coherence (Co) were calculated as mean spectra (R(rs),X(rs),Co) of the entire measurement as well as separated into inspiration (Ri(rs),Xi(rs),Coi) and expiration (Re(rs),Xe(rs),Coe) at frequencies of 1, 5, and 10 Hz. RESULTS: (i) R(rs), X(rs) as well as Re(rs) and Xe(rs) revealed no significant influence of sedation. However, separate analysis of inspiration and expiration revealed a significant influence of sedation on all inspiratory impedance parameters. (ii) During the 24 min period after sedation, almost all inspiratory parameters were found significantly dependent on the time course of sedation whereas expiratory parameters Re10, Xe1, and Xe5 were not influenced. These results indicate that confounding factors due to sedation act mainly during inspiration. Muscle relaxation in upper airways due to xylazine is suspected to be the main cause of these phenomena.     

Whole body barometric plethysmography: a screening method to investigate airway reactivity and acute lung injuries in freely moving pigs

The aim of this work was to investigate whether the Penh index, measured using whole body barometric plethysmography, can be used as a screening parameter to evaluate the airway reactivity and the intensity of the pulmonary response to endotoxins. Penh was firstly recorded in non-sedated freely moving piglets exposed (1) to a nebulized acetylcholine (Ach) pre-treated or not with clenbuterol, or (2) to endotoxin challenge. To measure Penh simultaneously with total pulmonary resistance (R(L)), dynamic compliance (C(dyn)) and intrapleural pressure changes (Max Delta Ppl), an oesophageal balloon catheter technique was used and the piglets were anaesthetised. The recordings were performed during (1) an intravenous metacholine (Mch) challenge and (2) in endotoxin-exposed animals. In freely moving animals, Ach induced a significant dose-dependent increase in Penh, which was significantly blocked by clenbuterol. Endotoxin instillation also resulted in a significant rise in Penh while the corresponding response measured under anaesthesia was significantly and positively correlated with R(L) and Max Delta Ppl. Similar results were obtained during Mch challenge but the Penh was negatively correlated with C(dyn). We conclude that Penh could be used in freely moving piglets as a screening index for airway reactivity and pulmonary functional changes in cholinergic and endotoxin challenges.     

Influence of subclinical inflammatory airway disease on equine respiratory function evaluated by impulse oscillometry

Reasons for performing study: Inflammatory airway disease (IAD) is a nonseptic condition of the lower respiratory tract. Its negative impact on respiratory function has previously been described using either forced expiration or forced oscillations techniques. However, sedation or drug‐induced bronchoconstriction were usually required. The impulse oscillometry system (IOS) is a noninvasive and sensitive respiratory function test validated in horses, which could be useful to evaluate IAD‐affected horses without further procedures. Objectives: To determine the sensitivity of IOS in detecting alterations of the respiratory function in subclinically IAD‐affected horses without inducing bronchoprovocation and to characterise their respiratory impedance according to frequency for each respiratory phase. Methods: Pulmonary function was evaluated at rest by IOS in 34 Standardbred trotters. According to the cytology of bronchoalveolar lavage fluid (BALF), 19 horses were defined as IAD‐affected and 15 horses were used as control (CTL). Total respiratory resistance (Rrs) and reactance (Xrs) from 1–20 Hz as well as their inspiratory and expiratory components were compared between groups. Results: A significant increase of Rrs at the lower frequencies (R_{1–10 Hz}) as well as a significant decrease of Xrs beyond 5 Hz (X_{5–20 Hz}) was observed in IAD compared to CTL horses. IOS‐data was also significantly different between inspiration and expiration in IAD‐affected horses. In the whole population, both BALF eosinophil and mast cell counts were significantly correlated with IOS measurements. Conclusions: Functional respiratory impairment may be measured, even in the absence of clinical signs of disease. In IAD‐affected horses, the different parameters of respiratory function (Rrs or Xrs) may vary depending on the inflammatory cell profiles represented in BALF. Potential relevance: Impulse oscillometry could be used in a routine clinical setting as a noninvasive method for early detection of subclinical respiratory disease and of the results of treatment in horses.     

Growth-related changes in the pulmonary function of goats

Growth-related changes in pulmonary function values were investigated in 20 healthy French Alpine goats, aged between 20 and 550 days, weighing 7–55 kg. Pulmonary ventilation, mechanics of breathing and arterial oxyten tension were measured using standardized techniques and methods adapted for goats of different body sizes. The Ppl values and the tI/tTOT ratio showed no significant changes with age and body size. The ventilation values (Vt, Ve, mVI and mVE) increased linearly with growth. There was a significant correlation of age and body weight with dynamic lung compliance (Cdyn), total pulmonary resistance (RL), viscous work of breathing (Wvis tot) and minute viscous work (Wvis min) throughout the age range studied. Cdyn, Wvis tot and Wvis min increased and RL decreased with age and body weight. Arterial blood gases (PaO₂ and PaCO₂) did not show significant changes over the age range studied. Regression equations for each pulmonary function parameter are given with body weight as the independent variable. Data for the mechanics of breathing were compared with those elsewhere for cattle, horses, man and dogs.     

Comparison of the performance of linear resistance and ultrasonic pneumotachometers at rest and during lobeline-induced hyperpnoea

The performance of a Fleisch No. 5 pneumotachometer (F), and two commercial ultrasonic pneumotachometers, the BRDL (B) and the Spiroson (S) systems were compared in respect to their use for determination of ventilatory parameters at rest and during lobeline-induced hyperpnoea. Five clinically healthy Thoroughbred horses were tested with the three pneumotachometers in random order. Respiratory airflow, respired gas concentrations, oesophageal pressures, pressures within the mask systems and arterial blood gases were determined before and during lobeline-induced hyperpnoea. Because measured peak expiratory airflow rates exceeded the stated linear range of the Fleisch pneumotachometer ( approximately +/- 25 l s(-1)) differential pressure-flow curves were determined in vitro over the range of flows recorded in vivo. Expired flows greater than the linear range were corrected according to the derived regression equation. No differences in any of the measured variables among the three systems were present at rest. At peak ventilation of lobeline-induced hyperpnoea mask pressures [Delta P(mask)(mean (SEM)): F: 9.6 (2.8) cm H(2)O, B: 0.8 (0.4) cm H(2)O, S: 1.4 (0.8) cm H(2)O] and end tidal carbon dioxide [ ET CO(2)(mean (SEM)): F: 2. 6 (0.1)%, B: 2.1 (0.2)%, S: 2.1 (0.1)%] were significantly higher in system F. Despite a tendency for respiratory frequency and peak inspired and expired flows, to be lower with system F, no significant differences in the measurements of ventilatory mechanics were detected. In conclusion, the ultrasonic flowmeters pose significantly lower resistive loads onto the respiratory system during ventilation above resting levels than Fleisch No 5 pneumotachometers. However, at the flowrates achieved during lobeline-induced hyperpnoea an in vitro calibration of the differential pressure-flow relationship allows correction for expiratory alinearity in system F. In addition, the performance of the Spiroson flowmeter is accurate in determining ventilatory mechanics at rest and during lobeline-induced hyperpnoea.     

Histamine inhalation challenge in normal horses and in horses with small airway disease

A histamine inhalation challenge (HIC) procedure was developed to assess hyperreactive states in horses. Following clinical evaluation, percutaneous lung biopsies were performed on nine light breed mares aged 6 to 15 years. Five horses, with normal small airways, were classified as group A and four subjects with small airway disease (SAD) lesions formed group B. Pulmonary mechanics parameters were monitored following an aerosol of 0.9% saline and every 5 min for up to 30 min after HIC with 0.5% w/v of histamine diphosphate, administered through a face mask for 2.5 min. Tidal volume (VT) and airflow (V) values were obtained with a pneumotachograph. Transpulmonary pressure (delta Ppl) was measured by the esophageal balloon catheter method. Dynamic compliance (Cdyn), total pulmonary resistance (RL), end expiratory work of breathing (EEW) and respiratory rate (f) were calculated by a pulmonary mechanics computer. Group A horses had increases in RL, and decreases in Cdyn whereas horses in group B were hyperreactive and showed greater changes in EEW, Cdyn, and delta Ppl but with a relatively lower variation of RL. One horse in clinical remission from SAD, but with a high biopsy score (group B), and one clinically normal horse belonging to group A showed marked hyperreactivity as shown by increases in EEW, maximum change in delta Ppl and RL and decreases in Cdyn. These results suggest that the HIC described can be used as a method to investigate airway hyperreactivity and SAD in horses.     

Influence of modified open lung concept ventilation on the cardiovascular and pulmonary function of horses during total intravenous anaesthesia

The influence of a modified open lung concept (mOLC) on pulmonary and cardiovascular function during total intravenous anaesthesia (TIVA) in horses was evaluated. Forty-two warmblood horses (American Society of Anesthesiologists class 1 to 2), scheduled for elective surgery (mean [sd] weight 526 [65] kg, age 6.4 [5.4] years) were randomly divided into three groups: ventilation with mOLC, intermittent positive-pressure ventilation (IPPV), and spontaneous breathing. Premedication (0.8 mg/kg xylazine), induction (2.2 mg/kg ketamine and 0.05 mg/kg diazepam) and maintenance of anaesthesia with TIVA (1.4 mg/kg/hour xylazine, 5.6 mg/kg/hour ketamine and 131.1 mg/kg/hour guaifenesin), with inhalation of 35 per cent oxygen in air, were identical in all horses. Heart rate, respiratory rate, mean arterial blood pressure (MAP), pH, and arterial partial pressure of oxygen (p(a)O(2)) and carbon dioxide (p(a)CO(2)) were evaluated. Data were collected every 10 minutes from 20 to 90 minutes anaesthesia time. Factorial analysis of variance and Tukey's post hoc test were used for statistical analysis (a=5 per cent). Horses in the mOLC-ventilated group had an overall significantly higher p(a)O(2) (16.9 [1.0] v 11.7 [1.34] v 10.5 [0.57] kPa) and lower MAP (93.1 [5.47] v 107.1 [6.99] v 101.2 [5.45] mmHg) than the IPPV and spontaneously breathing groups, respectively.     

A critical assessment of pulmonary function testing in exercising ponies

Pulmonary function measurements during exercise were tested for accuracy and reproducibility in 5 saddle ponies weighing 267±9 Kg. Airflow (V) and tidal volume (VT) were measured with a Fleisch pneumotachograph mounted on a face mask. The linearity of the response and the symmetry of this device were carefully checked. Pleural pressure changes were measured by pleural puncture (Ppl) and with an esophageal balloon catheter (Pes). The elastance of the esophageal wall and the effect of the position of the esophageal catheter tip on Pes were also investigated. Airflow, VT, Ppl, Pes, mask pressure, an electrocardiogram and limb movements were simultaneously recorded before, during and after exercise. These recordings were used to assess the validity of some pulmonary function measurements and to evaluate the influence of the breathing apparatus on the respiratory pattern. Maximal intrathoracic pressure changes and total pulmonary resistance values did not differ significantly when calculated on the basis of the Ppl and the Pes curves respectively. Although the absolute Ppl values were significantly different from the absolute Pes values, both pressures recorded at different workloads were closely correlated (R=0.99). The mean specific elastance of the esophagus was 1.56±0.24 kPa.cm.ml.^-1. Changes in the position of the esophageal catheter tip induced significant differences in the recorded Pes values. The pressure/flow relationship of the pneumotachograph pressure transducer system was linear within the range of the V measured during exercise. The mask had a significant influence on respiratory frequency and maximum difference in Pes, but did not not modify the exerciseinduced changes in these parameters. It was concluded that the technique and methods used in this study can allow accurate pulmonary function measurements in exercising ponies.     

Respiratory mechanics in Standardbred horses with sub-clinical inflammatory airway disease and poor athletic performance

The aim of this study was to investigate and quantify respiratory mechanical dysfunctions in Standardbred horses with both poor performance and bronchoalveolar lavage fluid cytology characteristic of inflammatory airway disease (IAD). A control group of healthy Standardbred horses was compared. Respiratory mechanics and breathing pattern were examined at rest and during hyperventilation induced using a rebreathing method. At rest, respiratory mechanics and breathing pattern were superimposable in both groups. In IAD horses, rebreathing increased ventilation, with larger tidal volumes and lower respiratory frequencies. During hyperventilation, IAD animals showed frequency-dependent dynamic lung compliance, and had greater viscous lung resistance and rate of dynamic work of breathing. As IAD alters pulmonary mechanics, the ventilatory load increases and horses requiring significantly higher energy for breathing may suffer restrictions in their athletic performance. This rebreathing method permits early evaluation of respiratory mechanical dysfunction in poorly performing horses with sub-clinical IAD.     

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.     

Respiratory-induced variability of pulmonary arterial pressure measurements in cattle

The purpose of this study was to investigate the variability of the peak systolic (PAPs) and the end diastolic (PAPd) pulmonary arterial pressures induced by intrapleural pressure changes in cattle.The pleural pressure (Ppl), the electrocardiogram and the pulmonary arterial pressure (PAP) were simultaneously recorded in five healthy calves under three different conditions, i.e. normoxia (N), normoxia with an added airflow resistance (R) and hypoxia (H). PAPs, PAPd and their corresponding transmural pressures were measured and averaged over 10 successive regular cardiac cycles. The maximum Ppl changes (maxPpl) were measured on the same tracings. The variance and coefficients of variation were calculated for each set of vascular measurements.MaxPpl was significantly increased with regard to N values during R and H conditions. This increase in maxPpl induced a simultaneous rise in the variability of PAP measurements, while in each condition, this variability was greatly lowered by use of the corresponding transmural pressure.It was concluded that, in calves with high maxPpl, the influence of respiration on PAP becomes considerable. In such cases, the use of transmural pressures rather than luminal pressures can greatly reduce the variability of these pulmonary pressure measurements and therefore increase their sensitivity.     

The effects of spontaneous and mechanical ventilation on central cardiovascular function and peripheral perfusion during isoflurane anaesthesia in horses

OBJECTIVE: To compare the effects of spontaneous breathing and mechanical ventilation on haemodynamic variables, including muscle and skin perfusion measured with laser Doppler flowmetery, in horses anaesthetized with isoflurane. STUDY DESIGN: Prospective controlled study. ANIMALS: Ten warm-blood trotter horses (five males, five females). Mean mass was 492 kg (range 420-584 kg) and mean age was 5 years (range 4-8 years). MATERIALS AND METHODS: After pre-anaesthetic medication with detomidine (10 microg kg(-1)) anaesthesia was induced with intravenous (IV) guaifenesin and thiopental (4-5 mg kg(-1) IV) and maintained using isoflurane in oxygen. The horses were positioned in dorsal recumbency. In five animals breathing was initially spontaneous (SB) while the lungs of the other five were ventilated mechanically using intermittent positive pressure ventilation (IPPV). Total anaesthesia time was 4 hours with the ventilatory mode changed after 2 hours. During anaesthesia, heart rate (HR) cardiac output (Qt) stroke volume (SV) systemic arterial blood pressures (sAP), and pulmonary arterial pressure (pAP) were recorded. Peripheral perfusion was measured in the semimembranosus and gluteal muscles and on the tail skin using laser Doppler flowmetry. Arterial (a) and mixed venous (v) blood gases, pH, haemoglobin concentration [Hb], haematocrit (Hct), plasma lactate concentration and muscle temperature were measured. Oxygen content, venous admixture (s/Qt) oxygen delivery (DO(2)) and oxygen consumption (VO(2)) were calculated. RESULTS: During mechanical ventilation, HR, sAP, pAP, Qt, SV, Qs/Qt and PaCO(2) were lower and PaO(2) was higher compared with spontaneous breathing. There were no differences between the modes of ventilation in the level of perfusion, DO(2), VO(2), [Hb], (Hct), or plasma lactate concentration. After the change from IPPV to SB, left semimembranosus muscle and skin perfusion improved, while muscle perfusion tended to decrease when SB was changed to IPPV. Low-frequency flow motion was seen twice as frequently during IPPV compared with SB. CONCLUSIONS: Mechanical ventilation impaired cardiovascular function compared with SB in horses during isoflurane anaesthesia. Muscle and skin perfusion changes occurred with ventilation, although further studies are needed to elucidate the underlying mechanisms.     

Respiratory mechanics in conscious swine: effects of face mask,head position and bronchoconstriction evaluated by impulse oscillometry

Airway obstruction in pigs (sedated or non-sedated) fixed in a sling was studied using impulse oscillometry (IOS). (i) Vertical flexion of the pig's head was used to simulate an artificial obstruction of the upper airways. (ii) Bronchial obstruction was induced by inhaling differing quantities of an aerosol produced from 0.33% carbachol solution. The ventilatory pattern was examined by measuring respiratory rate (RR) and tidal volume (V(t)). To evaluate respiratory mechanics, impedance parameters resistance (R) and reactance (X) as well as coherence (Co) were examined, each at frequencies of 5, 10, 15, 20, 25 and 35 Hz. Using a simple 7-element-model introduced by J. Mead [Physiological Review 41 (1961) 281], distal respiratory resistance (R(dist)), proximal airway resistance (R(prox)), and additional shunt compliance (C(a)) of the animal's snout and the air inside the facemask were evaluated. By fitting this model to the primary measured impedance spectra, the influence of the face mask could be eliminated in the model calculation to allow assessment of the real respiratory impedance. This recalculation made clear that the facemask had an influence on the spectral course of R and X, depending on the clinical situation, and the upper frequency range was altered the most. Under conditions of (i) upper airway obstruction, especially the X values were distorted by facemask almost over the whole frequency range. Once the data were corrected for the mask, resistance was increased across all frequencies by a fixed amount while reactance was not affected. Under (ii) bronchial airway obstruction (bronchospasm) caused the resistance spectrum to be increased mainly in the lower frequency range. This became visible in both, originally measured impedance spectra and spectra after correction of the mask influence. The reactance course (originally measured and recalculated) decreased at all frequencies during bronchospasm. Coherence over the whole frequency range was lowered at both bronchial and upper airway obstruction.     

Monthly, daily, and circadian variations of measurements of pulmonary mechanics in horses with chronic obstructive pulmonary disease

OBJECTIVES: To determine temporal variations of pulmonary function in horses without respiratory tract disease (controls) and horses with chronic obstructive pulmonary disease (COPD) and determine whether reversibility of airway obstruction after environmental control can be predicted by response to atropine administration. ANIMALS: 7 COPD-affected and 5 control horses. PROCEDURES: Pulmonary function testing was performed monthly during 3 consecutive months, daily for 5 consecutive days, and at 6-hour intervals for 24 hours before and after administration of atropine (0.02 mg/kg of body weight, i.v.) and after 5 consecutive months at pasture. Respiratory rate, tidal volume (VT), minute ventilation (VE), maximal change in transpulmonary pressure (deltaP(L)), pulmonary resistance (R(L)), and pulmonary elastance (E(L)) were calculated. RESULTS: COPD-affected horses had a significantly higher expiratory to inspiratory time ratio (T(E)/T(I)) and deltaP(L), E(L), and R(L) than horses without respiratory tract diseases during all periods and higher V(E) during monthly and daily evaluations. Daily variation in VT and monthly and circadian variation in E(L) were significant in COPD-affected horses. In control horses, significant changes were apparent only in T(E)/T(I) during daily recordings. In COPD-affected horses, reduction in deltaP(L), R(L), and E(L) was significant after atropine administration and after maintenance on pasture. CONCLUSIONS AND CLINICAL RELEVANCE: Despite variations in measurements of respiratory mechanics in both groups of horses, values remained significantly different between groups over time. Despite individual variation, measurements were repeatable during short and long periods. Response to administration of atropine to COPD-affected horses underestimated improvement in respiratory tract function that resulted from maintenance on pasture.     

Effects of a demand valve on pulmonary ventilation in spontaneously breathing, anaesthetised horses

The pressure flow characteristics of a demand valve which has been suggested to be suitable for use in anaesthetised horses were determined at a range of flow rates commonly encountered in equine anaesthesia. The resistance of the valve was found to be very much greater than the resistance of normal large animal anaesthetic apparatus or the equine lower respiratory tract. The effects of the valve on pulmonary ventilation were investigated in seven anaesthetised, intubated horses. Respiratory rate and dynamic compliance were unaffected by connection of the valve but mean tidal and minute volumes and peak flow rates were substantially reduced. The change in transpulmonary pressure over the respiratory cycle was doubled and indices of work of breathing increased by a factor of three. It was concluded that the resistance offered by the valve was too great for its use in spontaneously breathing horses to be recommended.     

Effects of aerosolized histamine and carbachol in the conscious horse.

Pulmonary function tests were performed in seven conscious, standing horses. Changes in pulmonary mechanics and ventilation volumes were measured after inhalation challenge with saline (baseline), histamine (1% w/v solution for 5 min) and carbachol (0.5% w/v solution for 3 min). Comparisons between baseline and posthistamine values revealed a significant (P less than 0.05) increase in nonelastic work of breathing (Wb), maximum change in transpulmonary pressure (max delta Ppl), and pulmonary resistance (RL), while dynamic compliance (Cdyn) decreased (P less than 0.05). Tripelennamine completely abolished these histamine induced changes suggesting the involvement of H1 receptors. A nonsignificant increase occurred in functional residual capacity. However, the amount of nitrogen retained in the lung at the end of a nitrogen washout test was significantly (P less than 0.05) greater after histamine when compared to baseline values. The effect of carbachol was qualitatively similar to that of histamine, Wb and max delta Ppl increased while Cdyn decreased (P less than 0.05). The increase in lower RL reached statistical significance (P less than 0.05) only at the beginning of expiration (/ 25% VT). The present investigation demonstrates that the physiological measurements of lung function could be carried out in conscious, unsedated horses and that the pulmonary function test methods could be used as a tool for study of drug induced changes in pulmonary mechanics.     

Effects of acetylpromazine on ventilatory variables in the horse.

The influence of breathing various concentrations of carbon dioxide and oxygen upon minute volume, tidal volume, and respiratory rate were examined in acetylpromazine-tranquilized horses. Responses in the horses before (control period) and after tranquilization were qualitatively similar to increases in carbon dioxide and to alterations in oxygen. The quantitative responses to these changes were less in tranquilized horses than in the same horses studied in the untranquilized state. Tranquilization had its most prominent effect upon respiratory rate in horses breathing room air.