Barometric whole body plethysmography and enhanced pause (PENH): How relevant are they?

Influence of acclimatization time on parameters of barometric whole-body plethysmography in healthy adult cats

BACKGROUND

Pulmonary function testing by barometric whole-body plethysmography (BWBP) is a long-established and well-accepted, non-invasive investigative procedure in cats.

HYPOTHESIS/OBJECTIVES

To evaluate, if different acclimatization times influence the measurement parameters of BWBP in healthy adult cats.

ANIMALS

48 healthy adult cats.

METHODS

In the prospective observational study, healthy cats were placed in a measuring chamber and BWBP was performed over 30 minutes. Parameters obtained during the three measurement units of 10 minutes each (T1, T2 and T3) were compared.

RESULTS

All measurement parameters except for tidal volume per body weight changed significantly (p<0.05) over the three time periods. From T1-T2, the parameters minute volume per body weight (p<0.001), peak inspiratory flow per body weight (p<0.001), peak expiratory flow per body weight (p = 0.002), pause (p = 0.03), enhanced pause (p = 0.03) and quotient of peak expiratory flow divided by expiratory flow at end expiratory volume plus 50% tidal volume (p = 0.03) changed significantly. From the time interval T2-T3, only respiratory rate (p = 0.02), inspiratory time (p = 0.02), expiratory time (p = 0.04), and relaxation time (p = 0.01) changed significantly. All measurement parameters except for tidal volume per body weight changed significantly (p<0.05) between T1 and T3. Age had a significant influence on all parameters except for peak expiratory flow per body weight and peak inspiratory flow per body weight. The parameters were not influenced by sex.

CONCLUSION AND CLINICAL IMPORTANCE

All measurement parameters except tidal volume per body weight were significantly affected by acclimatization time. Controlling for age and sex, there was still a significant influence of acclimatization time on all parameters except for tidal volume per body weight. Standardization of the acclimatization time for future studies would be appropriate in order to maintain comparability.

Evaluation of barometric whole-body plethysmography for therapy monitoring in cats with feline lower airway disease

OBJECTIVES

Feline lower airway disease (FLAD) is a common respiratory condition in cats. Traditionally, response to therapy is monitored only by evaluation of clinical signs and radiographic examination of the lungs. Barometric whole-body plethysmography (BWBP) is considered a non-invasive, well-tolerated form of measuring airway reactivity in cats. The aim of the study was to assess pulmonary function testing by BWBP for non-invasive evaluation of response to therapy in cats with FLAD and to investigate whether BWBP parameters correlate with clinical severity.

MATERIAL AND METHODS

The prospective study included 25 client-owned cats, diagnosed with FLAD on the basis of their medical history, clinical signs, radiographic findings, and bronchoalveolar lavage fluid (BALF) examination. At three time points (day 0, 14, and 60), a standardised owner questionnaire, a clinical examination and BWBP measurements were carried out. Results of the questionnaire and the clinical examination were evaluated using a clinical 12-point score. Individual therapy was administered to all patients after diagnosis, based on the severity of disease and compliance of the cat.

RESULTS

The total clinical score significantly improved over the entire study period (p<0.001). Significant improvement was detected for the frequency of coughing (p = 0.009), respiratory distress (p = 0.001), lung auscultation findings (p = 0.002), and general condition and appetite (p = 0.045). The BWBP parameter Penh, an indicator of bronchoconstriction, improved significantly under initial therapy between day 0 and 14 (p = 0.009). A significant correlation between Penh and the severity of auscultation findings was seen on day 0 (r = 0.40; p = 0.013).

CONCLUSION

The study supports the role of Penh as a non-invasive parameter for monitoring initial treatment response in cats with FLAD. Further studies are needed to address whether other BWBP parameters might be suitable for non-invasive therapy monitoring of FLAD. Clinical evaluation is always essential in cats with FLAD to evaluate treatment response.

[Pulmonary function testing in the cat - an overview]

This article provides an overview of currently available pulmonary function tests in cats, divided into invasive and non-invasive methods. Invasive techniques comprise arterial blood gas analysis and measurement of pulmonary mechanics. Non-invasive techniques include pulse oximetry and capnography, as well as methods not yet integrated into everyday practice such as tidal breathing airflow-volume loops, whole-body barometric plethysmography and thorax compression. In this article, the background, execution, interpretation, and limitations of each test are discussed. Proper performance and assessment of pulmonary function measurements may aid in understanding the pathophysiology of feline respiratory disease and in increasing objectivity when assessing the existing disease and treatment efficacy.

Enhanced pause correlates with airway neutrophils and airway-epithelial injury in asthmatic mice treated with dexamethasone

OBJECTIVE

To investigate the correlations among airway inflammation, airway epithelial injury and airway hyperresponsiveness (AHR) in asthmatic mice treated with dexamethasone.

METHODS

Female BALB/c mice were sensitized with intraperitoneal and hypodermic injections of ovalbumin (OVA) and aluminum on days 0, 7 and 14, challenged with OVA starting on day 21 for 10 days, and treated with dexamethasone via intraperitoneal injection starting on day 28 for 3 days. Female C57BL/6 mice were treated intranasally with house dust mite (HDM) on days 1 and 14, challenged intranasally with HDM on days 21, 23, 25, 27 and 29, and treated with sivelestat (a selective neutrophil elastase inhibitor) via intraperitoneal injection after each challenge. Following the final challenge, enhanced pause (Penh) and differential cell counts in the broncho-alveolar lavage fluid were measured and the correlations were analyzed.

RESULTS

Compared with OVA-challenged BALB/c mice, the counterpart mice treated with dexamethasone showed reduced Penh and shedding of airway epithelial cells. In addition, we found that Penh 50 (an indicator of AHR) had positive correlations with airway neutrophils and shedding of airway epithelial cells, but no correlation with eosinophils, lymphocytes or macrophages. Moreover, shedding of airway epithelial cells had positive correlations with airway neutrophils, but no correlation with eosinophils, lymphocytes or macrophages. Further, sivelestat decreased Penh 50 and shed airway-epithelial cells in HDM-challenged C57BL/6 mice.

CONCLUSIONS

Collectively, our findings suggest that airway neutrophils and excessive shedding of airway epithelial cells, but not eosinophils, lymphocytes or macrophages, may be involved in AHR in asthmatic mice treated with dexamethasone.

Simultaneous visual inspection for barometric whole-body plethysmography waveforms during pulmonary function testing in client-owned cats

OBJECTIVES

For the purpose of applying a barometric whole-body plethysmography (BWBP) device as a routine clinical tool in client-owned cats, the objective of this study was to evaluate the methodological importance of simultaneous visual inspection (SVI) of graphic tracing.

METHODS

To investigate the effect of SVI on the results obtained, 50 client-owned cats were included. Breath-by-breath analysis was conducted with BWBP software, and a commonly used rejection setting was chosen for automatic elimination (AE) of non-breath artefactual waveforms, according to tidal volume (TV), inspiratory and expiratory time, and the difference between inspiratory and expiratory volumes. During 10 mins of data recording, SVI for BWBP waveforms was performed to record manually time periods that were free of any artefacts. The two datasets derived from AE alone (AEA method) and AE plus SVI (SVI-AE method) were compared. The inter-observer effect on the process of SVI was evaluated on six cats.

RESULTS

There were statistically significant differences (P <0.001) between the AEA and SVI-AE datasets for most BWBP parameters. Bland-Altman analysis of the parameter-enhanced pause (Penh) showed heterogeneous variances, indicating less agreement when the Penh values were large. Intra-individual coefficients of variation of Penh were significantly higher with the AEA method than with the SVI-AE method (61.1% vs 34.7%, respectively; P <0.001). Inter-observer agreement on the SVI process was excellent, and no statistically significant differences between the two observers were found for any BWBP parameters obtained by the SVI-AE method (P >0.05).

CONCLUSIONS AND RELEVANCE

Visual inspection for BWBP waveforms in real time can reliably identify stable breathing signals in client-owned cats. The obtained results were significantly different when the SVI method was used in addition to AE. In the interpretation of BWBP parameters or comparison of measurements among studies, whether an SVI methodology was applied should be considered.

Functional phenotype and its correlation with therapeutic response and inflammatory type of bronchoalveolar lavage fluid in feline lower airway disease

Background

Currently, functional assessment to monitor therapeutic response in feline lower airway disease (FLAD) has limited application.

Objectives

To evaluate if expiratory indices derived from pseudo‐tidal breathing flow‐volume loop (pTBFVL) representing lower airway obstruction would decrease after clinical improvement and to investigate the correlation between functional phenotype and inflammatory cell type in bronchoalveolar lavage (BAL) fluid.

Animals

Nineteen client‐owned cats with FLAD.

Methods

Prospective observational study. Functional assessment with pTBFVL indices (eg, peak to mid‐expiratory flow; PEF/EF50) and conventional barometric whole body plethysmography (BWBP) parameters (eg, enhanced pause) was carried out before receiving treatment. BAL was performed to analyze inflammatory cell types. Signs were assessed by scoring. The cats were treated with glucocorticoids daily and functional testing was repeated.

Results

Loop indices PEF/EF50 and PEF/EF25 were significantly decreased after treatment (P < .001). Conventional BWBP parameters were not significantly different before and after treatment. Cats with PEF/EF50 > 1.51 before treatment had a significantly higher granulocyte (eosinophil plus neutrophil) percentage in BAL fluid (P = .014). Granulocyte percentage in BAL fluid was strongly correlated with PEF/EF25 (P = .001, r_s = 0.74) and moderately correlated with PEF/EF50 (P = .022, r_s = 0.57), whereas eosinophil or neutrophil percentage alone had no significant correlation with functional parameters.

Conclusions and Clinical Importance

Functional parameters including PEF/EF50 and PEF/EF25 can be used for monitoring therapeutic response. The presence of airflow limitation during mid‐ to late expiration is affected by the overall extent of granulocyte infiltration.

Functional assessment of expiratory flow pattern in feline lower airway disease

Feline lower airway disease (FLAD) is a chronic respiratory disease of which there is a lack of information on functional assessment in current veterinary medicine. The purposes of this study were to investigate expiratory pattern and evaluate the diagnostic utility of functional parameters in cats with FLAD. Thirty-three client-owned cats (23 FLAD cats and 10 control cats) were studied. Under quiet tidal breathing, pseudo-tidal breathing flow-volume loop (pTBFVL) was obtained from a barometric whole body plethysmography (BWBP) device. There were significant differences in the shapes of expiratory, but not inspiratory, curves between FLAD and control cats. The incidence of the presence of concave expiratory curve indicating lower airway obstruction was 74% in FLAD cats. To assess the diagnostic utility of pTBFVL indices in cats with FLAD, area under the receiver-operator curve was 0.86 for PEF/EF50 (peak expiratory flow divided by expiratory flow at end expiratory volume plus 50% tidal volume); a cuff-off value of PEF/EF50 >1.51 distinguished normal from FLAD (73.9% sensitivity, 100% specificity). There were no significant differences in traditionally measured BWBP parameters (ie, enhanced pause) between cats with and without FLAD in the present study. In conclusion, underlying change on expiratory flow pattern during natural tidal breathing existed in FLAD cats, and selected pTBFVL indices were useful in discriminating FLAD from normal cats. Tidal breathing pattern depicted by pseudoflow-pseudovolume loops from a BWBP system could be a non-invasive tool for functional assessment in client-owned cats.

Comparison of direct and indirect bronchoprovocation testing using ventilator-acquired pulmonary mechanics in healthy cats and cats with experimental allergic asthma

Airway hyperresponsiveness (AHR) is a key feature of asthma and can be measured using bronchoprovocation. Direct (methacholine, MCh) or indirect (adenosine-5-monophosphate, AMP; or mannitol) bronchoprovocants are used in human patients, the latter inducing AHR only with pre-existing airway inflammation. The present study compared the responses to direct (MCh) and indirect (mannitol, AMP) bronchoprovocation in healthy and asthmatic cats (n=6/group). The order of bronchoprovocant was randomized using a published table of random numbers and there was a 1-month washout before crossover to the next treatment. Pulmonary mechanics were measured in anesthetized and mechanically ventilated cats using a critical care ventilator. Saline at baseline and increasing doses of each bronchoprovocant were aerosolized for 30 s, followed by 4 min of data collection between doses. The endpoint for each bronchoprovocant was reached when airway resistance exceeded 200% of baseline values (EC200Raw). There was a significant difference (P<0.001) in the airway response of asthmatic vs. healthy cats over the range of MCh concentrations, despite there being no significant difference in the EC200Raw between the groups. Response to MCh was significantly greater (P<0.05) in asthmatic than in healthy cats at MCh concentrations as low as 0.0625 mg/mL. For AMP, a small subset of asthmatics (n=2/6) responded at low concentrations; four asthmatic cats and all healthy cats failed to respond even to the highest concentrations of AMP. One asthmatic cat but no healthy cats responded to mannitol. In conclusion, MCh discriminated asthmatic from healthy cats but neither AMP nor mannitol was an effective bronchoprovocant in this model.

Endotracheal nebulization of N-acetylcysteine increases airway resistance in cats with experimental asthma

N-acetylcysteine (NAC), a mucolytic and antioxidant, is speculated to cause bronchoconstriction in cats when delivered via aerosol. We hypothesized that in cats with experimental asthma, aerosol delivery of NAC (400mg cumulative dose) via an endotracheal tube would increase airflow limitation as measured by ventilator-acquired mechanics. After endotracheal drug delivery, airway resistance and inspiratory plateau pressure (Pplat) measurements were obtained in six mechanically ventilated asthmatic cats. Results demonstrated significantly increased airway resistance (P=0.0007) compared with aerosolized saline control; Pplats were not significantly different (P=0.059). All cats exhibited at least one adverse effect: excessive airway secretions (n=3), spontaneous cough (n=2), unilateral strabismus (n=1) and post-anesthetic death (n=1). No adverse reactions were noted with saline aerosol; cough was noted in one cat with methacholine challenge. In conclusion, airway resistance and adverse reactions were documented in all cats after NAC aerosol delivery. Further studies must be performed to evaluate if it is an effective mucolytic and/or antioxidant in cats and to determine if bronchodilator pre-treatment will negate NAC-induced bronchoconstriction.

Advances in the understanding of pathogenesis, and diagnostics and therapeutics for feline allergic asthma

Asthma is a common inflammatory disease of the lower airways and is believed to be of allergic etiology in cats. As little progress has been made in establishing rigorous criteria to differentiate it from other inflammatory lower airway diseases such as chronic bronchitis, descriptions of 'asthma' in the literature have often been inaccurate, grouping this syndrome with other feline airway diseases. With the development of more sensitive and specific diagnostics, it will become easier to distinguish asthma as a disease entity. Pulmonary function testing with bronchoprovocation/bronchodilator responsiveness trials and biomarkers hold particular promise. Discrimination is of critical importance as targeted therapies for the allergic inflammatory cascade are developed and become available for therapeutic trials in pet cats.