Assessing breathing effort by barometric whole‐body plethysmography and its relationship with prognosis in client‐owned cats with respiratory distress

Abstract

Background

Cats in respiratory distress have limited tolerance for manipulation, hindering clinical monitoring. Minute volume (MV) can be utilized to rate dyspnea in humans, but its relationship with respiratory distress in cats remains poorly investigated.

Hypothesis

Cats with respiratory distress will show higher MV per kg body weight (MV/BW) than normal cats, and the MV/BW increase will correlate with survival.

Animals

Fifty‐two cats with respiratory distress from lung parenchymal disease, pleural space disease, lower airway obstruction (LAO), or upper airway obstruction were recruited since 2014.

Methods

This is a prospective observational study. Study cats were placed in a transparent chamber, allowing clinicians to easily observe their breathing status and record ventilation using barometric whole‐body plethysmography (BWBP). Ventilatory variables of the 52 cats were compared with those of 14 historic control cats. Follow‐up data, including disease category, clinical outcomes, and survival, were prospectively collected.

Results

Cats in respiratory distress demonstrated significantly higher MV/BW (397 mL/kg; range, 158‐1240) than normal cats (269 mL/kg; range, 168‐389; P < .001). Among the etiologies, cats with LAO, parenchymal, and pleural space disease exhibited higher‐than‐normal MV/BW trends. A cutoff value of 373 mL/kg (1.4‐fold increase) indicated abnormally increased breathing efforts (sensitivity, 67%; specificity, 93%). MV/BW was independently associated with increased cardiorespiratory mortality in cats with respiratory distress (adjusted hazard ratio 1.17, 95% confidence interval [CI] 1.02‐1.35; P = .03).

Conclusions and Clinical Importance

Breathing efforts in cats can be noninvasively quantified using BWBP. Measurement of MV/BW could serve as a prognostic index for monitoring cats experiencing respiratory distress.

Abbreviations

BWBP

barometric whole‐body plethysmography

CI

confidence interval

HR

hazard ratio

LAO

lower airway obstruction

MV

minute volume

PEF

peak expiratory flow

Penh

enhanced pause

PIF

peak inspiratory flow

ROC

receiver operating characteristic

RR

respiratory rate

RT

relaxation time

Te

expiratory time

Ti

inspiratory time

TV

tidal volume

UAO

upper airway obstruction

1. INTRODUCTION

Respiratory distress can be a consequence of diverse etiologies such as airway obstruction, lung parenchymal problems, or pleural space disease. ¹ Cats presenting with respiratory distress are often potentially fragile and cannot tolerate extensive manipulation. Monitoring the progression or response to management in these cats is sometimes limited to counting respiratory rate (RR) and subjectively observing the breathing effort. ¹ , ² , ³

The aerodynamics of the respiratory system in conscious animals can be evaluated by measuring inhaled and exhaled airflow through a pneumotachograph with an associated differential pressure transducer. ⁴ , ⁵ The changes in pressure through the pneumotachograph are proportional to the flow rate of air, and the volumes inhaled and exhaled are measured by integrating the flow signals. ⁵ Among the available techniques, barometric whole‐body plethysmography (BWBP) is a nonrestrained system used to assess ventilation in various animal species. ⁴ , ⁵ , ⁶ , ⁷ It enables an animal to stay and move freely within a test chamber, minimizing stress during the evaluation. The animal's breathing in the chamber generates both airflow at nasal opening and thoracic expansion from warming and humidifying air during inhalation; hence, the resulting signal detected by the pneumotachograph is not solely airflow. ⁴ , ⁶ , ⁷ The signals from the BWBP system are conventionally termed pseudo‐flow, representing the net difference between nasal airflow and thoracic movement. The pseudo‐flow and pseudo‐volume differ from, but correspond to, the true flow and volume of the animal. ⁵ , ⁷ , ⁸ BWBP has been demonstrated to be applicable in client‐owned cats to noninvasively evaluate pulmonary function in recent years, and promising results have been obtained in a few clinical circumstances, such as feline lower airway disease, lungworm infection, heartworm‐associated respiratory disease, and obesity. ⁸ , ⁹ , ¹⁰ , ¹¹ , ¹² , ¹³ , ¹⁴ , ¹⁵ , ¹⁶

The minute volume (MV), which represents the total output of the respiratory system, has been used to validate clinical scores for rating the severity of dyspnea in human patients with lung disease. ¹⁷ Individuals with cardiorespiratory diseases are expected to have a higher MV at rest or during exertion, which results from a reduction in the pulmonary reserve or an impaired capacity for gas exchange. ¹⁸ To date, the relationship between MV and respiratory distress in cats has not been thoroughly investigated in clinical practice. Therefore, it is unclear whether MV measurement is clinically useful for quantifying breathing effort and adding value in predicting the prognosis of cats. We hypothesized that cats with respiratory distress would have higher MV values than normal cats. An additional aim of this study was to evaluate the prognostic value of assessing MV in clinical cats with respiratory distress by analyzing the survival and level of increase in MV.

2. MATERIALS AND METHODS

2.1. Animals and study design

Client‐owned cats presenting with respiratory distress due to various etiologies, including lung parenchymal disease, pleural space disease, lower airway obstruction (LAO), or upper airway obstruction (UAO), were included in this prospective observational study starting in 2014. Enrollment was restricted to cats with increased breathing effort, as identified by veterinary clinicians in the examination room. Cases were excluded if the cat had a history of respiratory distress but showed no signs at present, if the researchers failed to obtain consent from pet owners, or if immediate therapeutic intervention was required. Written informed consent was obtained from the cat owners, and the cats were placed in a transparent Plexiglas chamber (38 L) in a quiet and isolated room together with their owners. This setting allowed clinicians to easily observe the breathing status of the cat without causing disturbance or stress, and breathing signals were acquired during this observational period by the BWBP system connected to the animal chamber. The recordings of breathing signals were conducted with cats breathing room air; however, when an elevated inspired fraction of oxygen was required, supplementary oxygen could be immediately provided into the chamber. The diagnostics and therapeutics for each case were determined according to the individual's clinical condition and the owner's willingness. Subsequent clinical and follow‐up information were constantly collected during the study period, and telephone interviews were conducted to obtain prognostic information for cases that did not revisit the hospital. The conventionally used BWBP variables of the study cats were compared with those of a historic control group comprising student‐, staff‐, and client‐owned cats. This control group was previously recruited to establish reference intervals for the BWBP system within the same pulmonary function laboratory. It consisted of 14 cats without any respiratory signs, history of bronchopulmonary disease, or exposure to cigarette smoke. The disease category, clinical outcome, and survival of cats with respiratory distress were analyzed with regard to ventilatory data from the BWBP system. The events of interest associated with an unfavorable prognosis were defined as cardiorespiratory‐related death (including sudden death and euthanasia due to cardiorespiratory status) and all‐cause mortality. Sudden death was defined as either the owner witnessing the cat die suddenly or finding a deceased cat that had experienced no premonitory signs of illness within the past 24 hours. This study was approved by the Research Ethical Committee of National Taiwan University Veterinary Hospital (approval no: 000003) and the Institutional Animal Care and Use Committee of National Taiwan University (approval no: NTU104‐EL‐00010 and NTU107‐EL‐00163).

2.2. Assessment using BWBP

The BWBP system was calibrated before each use by injecting 50 mL of air into the chamber, according to the manufacturer's instructions (Buxco Electronics, Wilmington, NC). The cat was placed in the BWBP chamber (length: 51 cm, width: 30 cm, and height: 25 cm) without any restraint, and an acclimation period (until the cat sat or laid down in a comfortable position with stable breathing signals) based on each cat's status was allowed before recording the signals, as previously described. ¹⁴ , ¹⁹ A bias flow of 6 L per minute was provided throughout the assessment to prevent carbon dioxide accumulation in the chamber, with temperature and humidity monitoring. Analog breathing signals detected using a differential pressure transducer were amplified and digitalized. Breathing signals were recorded for a minimum of 5 minutes for each cat. Conventional BWBP variables were calculated from breath‐by‐breath analysis of box flow waveforms by the software (Biosystem XA 2.11.0 software; Buxco Electronics), including RR (breaths/min), tidal volume per kg body weight (TV/BW; mL/kg), MV per kg BW (MV/BW; mL/kg; calculated by multiplying TV/BW by RR), inspiratory and expiratory times (Ti and Te; s), peak inspiratory and expiratory flow per kg BW (PIF/BW and PEF/BW; mL/s/BW), relaxation time (RT; s; time point when 65% of TV is expired), pause (unitless; [Te‐ RT]/RT), and enhanced pause (Penh; unitless; [PEF/PIF] × pause). Artifactual signals from nonbreathing activities (eg, posture change or vocalization) were excluded by applying both the automatic rejection settings of the software (TV < 10 mL, Ti < 0.15 s, Te > 10 s, or a difference in inspiratory and expiratory volume > 20%) and manual methodology (manually deleting time periods that were not free of artifacts based on simultaneous inspection). ¹⁹ Considering that the nature of the pseudo‐volume differs from that of the true volume, the level of increase in MV was also expressed as a fold increase relative to the normal median value of the control group, with the aim of facilitating future applications in different systems.

2.3. Statistical analysis

Statistical analyses were conducted using SPSS version 26 (IBM Corp, Armonk, NY). The Shapiro‐Wilk test was used to determine the normal distribution of continuous variables. Data with normal distribution were presented as mean ± SD and compared with an independent t test, while nonnormal data were reported as median with range and compared with a Mann‐Whitney test. Baseline signalment between the respiratory distress and historic control group was compared utilizing Mann‐Whitney test and independent t test. Receiver operating characteristic (ROC) curve was applied to determine the optimal cutoff value of MV/BW for discriminating normal from increased breathing effort based on Youden index. Comparison of MV/BW among cats with different etiology subgroups was analyzed by Kruskal‐Wallis test. Survival time was measured from the date of BWBP assessment until death or last contact. Cats that remained alive or were lost to follow‐up at the end of the study were right‐censored. Cox regression was conducted to identify the risk factors associated with survival and to calculate the hazard ratios (HR) for MV/BW on cardiorespiratory mortality. In the Cox proportional hazards regression, only 1 of the variables with a high correlation based on Spearman's correlation analysis was included in the model to prevent multicollinearity. Univariable Cox proportional hazards regression was utilized to define the potential predictive variables. A multivariable Cox regression model was obtained including predictors with a P value <.2 in univariable analysis using the forward stepwise approach (with 0.2 of removal probability). The proportional hazard assumption was assessed using the interaction of time and covariates, and the overall model fit was assessed using the likelihood ratio test. Survival among different etiology subgroups was calculated by Kaplan‐Meier curves and compared by log‐rank tests. A P value of less than .05 was considered statistically significant.

3. RESULTS

3.1. Study cohort and overall survival

A total of 52 cats with respiratory distress were enrolled in the final study cohort. The median recording time of BWBP was 7 minutes, with a range of 5 to 13.5 minutes. The median age was 9.5 years (range, 1.0‐15.0), and 62% (32/52) of the cats were female. The BW and 9‐point body condition scores were 4.18 ± 1.19 kg and 5 (range, 2‐8), respectively. The breeds represented included domestic short hair (34), American short hair (6), Persian (4), crossbreeds (3), and 1 each of Siamese, Himalayan, British short hair, Munchkin, and Scottish fold. The study cats with respiratory distress were older compared with historic control group (median age: 9.5 years; range, 1.0‐15.0 versus 5.0 years; range, 1.0‐14.0, P = 0.01) with a similar BW (4.18 ± 1.19 kg versus 4.31 ± 0.95 kg, P = 0.75).

The etiologies associated with the presenting respiratory distress in these cats included lung parenchymal disease (n = 26; pneumonia/pneumonitis in 9/26, primary or metastatic lung cancer in 4/26, interstitial lung disease in 1/26, bullae/emphysema in 2/26, and undetermined in 10/26), LAO (n = 14; inflammatory lower airway disease in 7/14, bronchiolar disease in 3/14, lower respiratory tract infection in 2/14, gastroesophageal reflux‐related chronic cough in 1/14, and undetermined in 1/14), UAO (n = 5; nasopharyngeal stenosis or dynamic collapse in 3/5, mass at thoracic inlet in 1/5, and severely redundant dorsal membrane of trachea in 1/5), pleural space disease (n = 5; diaphragmatic or hiatal hernia in 2/5, chylothorax in 1/5, cat infectious peritonitis with concurrent congestive heart failure in 1/5, and immune‐mediated pleuritis in 1/5), and mixed etiologies (n = 2; atelectasis involving multiple lung lobes with bronchitis and mucus plugging in 1/2, chronic rhinitis with bronchitis/pneumonia in 1/2; Table S1). Twenty‐three of 52 cats required further cardiac evaluation and underwent echocardiography, revealing 16 cats without cardiomyopathy or other abnormalities, and 7 cats diagnosed with hypertrophic cardiomyopathy (5 with stage B1, 1 with stage B2) or nonspecific cardiomyopathy (1 with stage C). Follow‐up data after BWBP assessment were available for 51/52 of the cases, and mortality events occurred in 33 cats (64%). The median survival times for cardiorespiratory‐related death and all‐cause mortality were 506 days (95% confidence interval [CI], 0‐1059 days) and 474 days (95% CI, 22‐926 days), respectively (Figure 1).

FIGURE 1.

Kaplan‐Meier survival curve for all cats with respiratory distress in this study. The median survival time for cardiorespiratory death was 16.9 months. Nineteen of the 51 cats (37%) died within the first 3 months of presentation.

3.2. Minute ventilation and ventilatory variables

Cats that received oxygen in the BWBP chamber after turning off the breathing recording were not documented. In 2 cats that required oxygen supplementation during the recording of BWBP, only the time period when the cat was breathing room air was used for statistical analysis. Cats with respiratory distress demonstrated significantly higher MV/BW values (397 mL/kg; range, 158‐1240) than control cats (269 mL/kg; range, 168‐389; P < .001). Other ventilatory variables, including TV/BW, PEF/BW, PIF/BW, and Penh, were significantly higher in cats with respiratory distress than in the control cats (Table 1). There were no statistically significant differences in RR, Te, or Ti between the 2 groups.

TABLE 1.

Minute volume (MV) and other ventilatory variables measured by barometric whole‐body plethysmography (BWBP) in the study cats with respiratory distress (n = 52) and in a historic control group of cats (n = 14).

Variables	Respiratory distress (n = 52)	Control cats (n = 14)	P
RR (breaths/min)	50 (18‐110)	52 (36‐121)	.44
TV/BW (mL/kg)	8.8 (3.8‐27.2)	5.0 (2.5‐9.0)	<.001*
MV/BW (mL/kg)	397 (158–1240)	269 (168–389)	<.001*
PIF/BW (mL/s/kg)	24.5 (11.9‐79.9)	15.8 (9.1‐23.0)	<.001*
PEF/BW (mL/s/kg)	33.3 (13.3‐129.9)	13.7 (7.8‐18.2)	<.001*
Ti (s)	0.54 (0.26‐1.33)	0.48 (0.22‐0.67)	.29
Te (s)	0.68 (0.26‐2.18)	0.67 (0.27‐0.97)	.44
Penh	2.40 (0.53‐14.41)	0.75 (0.54‐1.50)	<.001*

Abbreviations: RR, respiratory rate; TV/BW, tidal volume per kg body weight; MV/BW, minute volume per kg body weight; PIF/BW, peak inspiratory flow per kg body weight; PEF/BW, peak expiratory flow per kg body weight; Ti, inspiratory time; Te, expiratory time; Penh, enhanced pause.

^*Significant differences (P < .05).

The ROC curve analysis demonstrated that MV/BW effectively identified cats with increased breathing effort, with an area under the curve of 0.85 (95% CI, 0.75‐0.94, P < .001). The sensitivity and specificity for identifying abnormally increased breathing effort were 67% and 93%, respectively, using MV/BW at a cutoff of 373 mL/kg (corresponding to a 1.39‐fold increase relative to the normal reference value).

3.3. Effect of different etiologies

The MV/BW values were significantly different among cats with 4 different etiologies and normal cats (P < .001; Figure 2). Cats with UAO exhibited MV/BW values (278 mL/kg; range, 183‐380) similar to those of normal cats (269 mL/kg; range, 168‐389; P = .99) and lower than those of cats with lung parenchymal disease (436 mL/kg; range, 277‐1240; P = .001), pleural space disease (385 mL/kg; range, 158‐832; P = .057), and LAO (387 mL/kg; range, 258‐1204; P = .007).

FIGURE 2.

Minute volume (MV) among cats with upper airway obstruction (UAO), lower airway obstruction (LAO), lung parenchymal disease, pleural space disease, and normal cats.

The overall survival was statistically different among cats with respiratory distress resulting from the above‐mentioned 4 etiologies (log‐rank test, 8.54; P = .04). Cats with lung parenchymal disease had significantly shorter survival times than those with LAO (log‐rank test, 5.99; P = .01).

3.4. Minute volume and survival

The influence of MV elevation on survival in cats with respiratory distress was evaluated using Cox regression analysis; cats with mixed etiologies were excluded from this analysis. Among the ventilatory variables, only MV/BW, RR, and Penh were included in the regression model to minimize the likelihood of multicollinearity from highly correlated variables. In univariable Cox proportional hazard analysis, MV/BW was not a potential predictor of all‐cause mortality (P = .26). For cardiorespiratory death, based on the univariable Cox proportional hazard analysis, MV/BW, disease etiology, and age (P < .2) were selected for the multivariable Cox proportional hazard analysis (Table 2). Only age (P = .004) and MV/BW (P = .03) were independently associated with survival time in the multivariable model. After adjusting for age, MV/BW was identified as an independent predictor of cardiorespiratory death, indicating that each 100 mL/kg increase corresponded to a 1.17‐fold increased risk of cardiorespiratory mortality (adjusted HR, 1.17; 95% CI, 1.02‐1.35; P = .03).

TABLE 2.

Univariable and multivariable Cox proportional hazard regression analysis of factors predictive for survival regarding cardiorespiratory death in cats with respiratory distress.

Variable	Univariable analysis		Multivariable analysis
	HR (95% CI)	P	Adjusted HR (95% CI)	P
Age (years)	1.15 (1.03‐1.29)	.01*	1.19 (1.06‐1.34)	.004*
BW (kg)	0.94 (0.68‐1.32)	.73
Disease category
LAO (n = 14)	1.00
UAO (n = 5)	1.22 (0.23‐6.32)	.82		.91
Parenchymal lung disease (n = 26)	3.57 (1.28‐9.94)	.02*		.07
Pleural space disease (n = 5)	1.29 (0.29‐5.71)	.74		.82
MV/BW (mL/kg, per 100 mL)	1.11 (0.97‐1.26)	.14	1.17 (1.02‐1.35)	.03*
RR (breaths/min)	1.01 (0.99‐1.02)	.28
Penh (unitless)	0.97 (0.86‐1.10)	.63

Abbreviations: BW, body weight; CI, confidence interval; HR, hazard ratio; LAO, lower airway obstruction; MV/BW, minute volume per kg body weight; RR, respiratory rate; Penh, enhanced pause; UAO, upper airway obstruction.

^*Significant differences (P < .05).

4. DISCUSSION

This study assessed minute ventilation by using the BWBP in cats with respiratory distress. Our results indicated that the MV was significantly higher in cats with respiratory distress than in control cats. Increased breathing effort can be quantified by measuring MV, with a cutoff of 373 mL/kg (1.4‐fold increase from normal), which helps to identify abnormal elevations of breathing effort. Each 100 mL/kg increase in MV corresponded to a 1.17‐fold increased risk of cardiorespiratory mortality in cats with respiratory distress. MV measurement is clinically applicable in cats with respiratory distress and adds value in predicting prognosis.

Minute ventilation refers to the volume of air inhaled/exhaled in 1 minute, influenced by the rate and depth of breaths. In normal resting individuals, MV generally remains constant despite dynamic changes in RR and TV. ⁶ , ²⁰ , ²¹ When severe pathologies compromise the gas exchange capacity, higher minute ventilation is required to remove the accumulated carbon dioxide. This increase in MV is a compensatory response of the respiratory system that aims to maintain sufficient oxygenation and ensure adequate removal of carbon dioxide, thus balancing the increased physiological dead space or impaired gas exchange. ¹⁷ , ¹⁸ , ²¹ , ²² , ²³ Elevation of MV has been observed in experimental rat models of ventilator‐induced lung injury, human patients with certain lung diseases, cats with heartworm‐associated respiratory disease, and individual cats with eosinophilic bronchitis or lungworm infection. ¹⁰ , ¹¹ , ¹⁵ , ¹⁷ , ¹⁸ , ²⁴ In our study, the estimated MV/BW from the BWBP could be used to quantify breathing effort and was clinically associated with cardiorespiratory death. MV measurement is helpful for objectively identifying increased breathing effort in clinical cats.

Monitoring cats with respiratory distress can be challenging. Cats presenting respiratory distress may exhibit an increase in breathing rate, effort, or both. While the RR can be visually measured in clinical cats, assessing the breathing effort primarily relies on the clinician's recognition of its presence or absence. ² , ²⁵ Hence, in various situations, the calculation of the RR remains the only available quantitative evaluation to assess the improvement or deterioration of the ventilatory status. Delayed detection of ventilatory compromise can lead to critically low respiratory reserves in cats. Although other monitoring methods, such as peripheral oxygen saturation from a pulse oximeter and arterial blood gas analysis, can be obtained in some cats, these measurements provide information about gas exchange rather than ventilation. ²⁵ Given the delicate nature of cats experiencing respiratory distress, it is crucial to strike a balance between diagnostic efforts and the cat's condition because additional stress can have devastating consequences. ²⁶ The nonrestrained feature and transparent chamber of the BWBP enable clinicians to easily observe cats, and their ventilatory status, including both rate and effort, could be objectively measured in the meanwhile. Our work revealed that BWBP assessment can serve as a cat‐friendly practice for cats with respiratory distress, providing valuable insights for predicting prognosis beyond relying solely on subjective observations.

Although tachypnea is commonly observed in cats with respiratory distress, RR should be interpreted with caution because some cats are easily irritated to exhibit emotional tachypnea, which is temporary during clinical visits. Notably, although healthy cats showed a median sleeping/resting RR of 19 to 27 breaths/min in the home environment (counted by cat owners), ²⁷ the average RR of healthy cats measured in a plethysmographic chamber in a hospital environment was consistently higher (51‐109 breaths/min) in all previous BWBP studies. ⁴ , ⁶ , ⁸ , ¹⁰ , ²⁸ In our study, the RR was not statistically different between cats with increased breathing effort and normal cats, and the RR was not associated with cardiorespiratory mortality in the study cats. This was not unexpected, as the breathing rate can vary significantly across different etiologies. Rapid and shallow breathing is related to restrictive lungs from parenchymal and pleural space diseases, whereas prolonged inspiration or expiration can lead to reduced RR in obstructive upper or lower airway diseases. ² , ²⁹ Therefore, the assessment of RR in cats with respiratory distress should take into account the emotional state, environmental factors, and disease categories.

Cats with persistent labored breathing are at higher risk of complications and rarely undergo further diagnostic procedures to identify the precise cause of respiratory distress. Therefore, the design of this study aimed to classify cases into several major categories that clinicians can distinguish using readily available information. Among the various etiologies in our study, cats with respiratory distress from LAO, parenchymal, and pleural space disease exhibited a higher‐than‐normal trend in minute ventilation. This phenomenon has also been observed in a few cats with lower airway and lung parenchymal problems from previous literature. ¹⁰ , ¹¹ , ¹⁵ On the contrary, minute ventilation in cats with UAO showed no difference from that in normal cats, revealing a distinct trend compared with other etiologies. It is likely that cats experiencing respiratory distress from UAO can be easily recognized by pet owners owing to the presence of loud breath noises, facilitating the prompt seeking of veterinary care at an earlier stage before further compromise occurs.

The variations in MV/BW in cats with LAO, parenchymal, and pleural space disease were much higher than those in the control group. This can be attributed to the varying levels of breathing effort among diseased cats. A similar phenomenon was observed in a previous study comparing cats with heartworm‐associated respiratory disease with control cats. ¹⁰ Although cats requiring immediate intubation or thoracentesis were not included in the current study, the study population included cats with a wide spectrum of conditions ranging from mildly to severely labored breathing. The diversity in the levels of breathing effort likely contributed to the greater variation in MV/BW in this group than in control cats without respiratory distress. This suggests that the MV/BW value serves as a potential surrogate index of disease severity rather than of disease etiology.

This study has several limitations. One unavoidable limitation is the target population of this study. Some cats presenting with extreme respiratory distress, which necessitated immediate therapeutic intervention (eg, intubation or thoracocentesis), were not included in the study. Cats with congestive heart failure were seldom recruited during the study period, as these cats were usually rapidly recognized and administered therapeutics before the enrollment process. Therefore, it is unknown whether the current findings can be applied to these cats without further investigation. As a result, selection bias might have been present, which could have affected the analyses of the prognosis and survival data. This also accounts for the relatively small number of cats with UAO and pleural space disease included in this study. Moreover, variability in the BWBP variables may be present for various reasons, including the time of day when the cats were enrolled for breathing signal recording. For instance, circadian changes in the RR and flow rates have been observed in experimental cats, ²⁸ though it is not clear whether a similar phenomenon is shown in clinical cats. Therefore, factors associated with technical aspects should be considered when interpreting BWBP data.

In conclusion, the ventilatory status of cats with respiratory distress can be assessed noninvasively using BWBP. Among the various etiologies, cats with respiratory distress because of LAO, parenchymal, and pleural space disease exhibited a higher‐than‐normal trend in MV/BW. Minute ventilation can be utilized to identify abnormal breathing effort, with a cutoff value for MV set at a 1.4‐fold increase from normal reference of the lab. An elevation in MV is associated with an increased risk of cardiorespiratory mortality in cats with abnormal breathing efforts.

CONFLICT OF INTEREST DECLARATION

The authors declare no conflict of interest.

INSTITUTIONAL ANIMAL CARE AND USE COMMITTEE (IACUC) APPROVAL DECLARATION

Approved by the Research Ethical Committee of National Taiwan University Veterinary Hospital (Approval No: 000003) and the IACUC of National Taiwan University (Approval No: NTU104‐EL‐00010 and NTU107‐EL‐00163) at the authors' institutions.

OFF‐LABEL ANTIMICROBIAL DECLARATION

The authors declare no off‐label use of antimicrobials.

HUMAN ETHICS APPROVAL DECLARATION

The authors declare human ethics approval was not needed for this study.

Supporting information

Table S1. Detail summary of data in 52 cats with respiratory distress resulting from various disease etiologies.

Chang W‐T, Lin C‐H, Chang C‐H, Lo P‐Y, Chen H‐W, Wu H‐D. Assessing breathing effort by barometric whole‐body plethysmography and its relationship with prognosis in client‐owned cats with respiratory distress. J Vet Intern Med. 2024;38(3):1718‐1724. doi: 10.1111/jvim.17069