García-Guasch L, Caro-Vadillo A, et al. Pulmonary function in obese vs non-obese cats. J Feline Med Surg 2015 Jun;17(6):494-9.
In humans and dogs, obesity is known to have an adverse impact on lung function and also is associated with increased resistance to airflow in the airways (bronchoconstriction). In obese individuals, pulmonary and total chest compliance is reduced. Moreover, excess intra-abdominal and intra-thoracic fat increase intra-abdominal pressure, which in turn impairs respiratory function. Respiratory system compliance, maximal inspiratory and expiratory pressures, maximum voluntary ventilation and lung volumes, and muscle strength are all reduced in obesity, which results in increased respiratory effort and oxygen cost of breathing.
In this study, the first of its kind performed in this area on the feline species, pulmonary function variables of obese and non-obese cats were compared. Six obese (body condition scores 8/9 or 9/9) and nine normal-weight cats (body condition scores 4/9 or 5/9) were evaluated using barometric whole-body plethysmography (BWBP), a non-invasive pulmonary function testing modality in which the cat is placed in a transparent Plexiglass chamber and a dynamic study of breathing is performed. The cats were all client-owned, and all had a normal cardiorespiratory and general physical examination and no history of upper airway, cardiac, or endocrine diseases. All subjects had normal thoracic radiographs, negative retrovirus and heartworm test results, had recently been dewormed, and had no history of secondhand smoke inhalation. This study was performed in Europe; all subjects were sexually intact and lived indoors only.
A number of pulmonary function variables were measured on all subjects using BWBP: respiratory rate, tidal volume, minute volume, inspiratory and expiratory intervals, bronchoconstriction index enhanced pause (Penh), and peak inspiratory and expiratory flows. Four of the variables: tidal volume, minute volume, and peak inspiratory and expiratory flows, were standardized according to body weight by dividing these values by subjects' body weight. Statistically significant differences in these latter four variables indexed to body weight were found between the obese and non-obese groups. Obese cats, compared to cats of normal body condition, have decreased tidal volume, minute volume, and peak inspiratory and expiratory air flows, which in turn suggests impairment of lung function in the obese feline. No statistically significant differences in any of the respiratory function variables were found to be associated with the sex or age of the subjects in either group or between groups.
Variables that did not demonstrate statistically significant differences between the obese and non-obese groups were respiratory rate, inspiratory and expiratory intervals and the inspiratory/expiratory interval ratio, and the bronchoconstriction index enhanced pause (Penh). Therefore, unlike in studies of respiratory function in humans and dogs, an obese body condition, at least in the cats of this study, was not associated with increased bronchoconstriction. Additional studies involving a larger number of animals would be valuable in confirming that bronchoconstriction is not potentiated by obesity in the feline species, as adipose tissue in general produces a wide variety of inflammatory mediators that could promote airway hyperresponsiveness. The cats utilized in this study were all healthy. Obese cats with intercurrent respiratory or cardiac disease, or those undergoing general anesthesia, may experience signficantly higher risk of morbidity or mortality in these situations than their non-obese counterparts due to overweight-related respiratory impairment. [PJS]
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