Plethysmographic Comparison of Breathing Pattern in Heaves (Recurrent Airway Obstruction) Versus Experimental Bronchoconstriction or Hyperpnea in Horses

Abstract

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 5 15) was compared to controls at rest (n 5 7) and during hyperpnea because of lobeline treatment, and the effects of histamine-induced bronchoconstriction in controls (n 5 10).Methods: Flow patterns, phase angle (h) between the rib and abdominal compartments, abdominal (V abd ) contribution to tidal volume (V T ), and lung mechanics were measured.Results: Findings unique to the heaves group included the loss of biphasic expiratory flow, severely increased h with the abdomen consistently lagging behind the rib cage, and a reduced contribution of the abdomen to ventilation. A subgroup of heaves (n 5 5) with abdominal paradox showed a significant (P , .05) reduction in tidal volume, and increased respiratory rate. Bronchodilation reduced h in heaves (P 5 .06), but h 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.''

Reliability of breath by breath spirometry and relative flow-time indices for pulmonary function testing in horses

“…In the current study, horses averaged a tidal volume of 7.89 ± 1.43 L (mean ± stdev) and respiratory frequency of 12 bpm during eupnoeic respiration, which is similar to previous studies using ultrasound or Fleisch-type pneumotachometers [32–35], and slightly greater than values determined by respiratory inductance plethysmography and pneumotachography [25, 36]. In addition to differences due to technique, it is possible that equipment differences, such as mask volume and airflow resistance, or physiological differences between horses, such as age [36], use [35] or sub-clinical airway disease [34, 35], may influence values determined during pulmonary function testing.…”

“…Study horses exhibited PIF and PEF variably in early, middle and late phases of respiration in apparent random distribution. Although such variability is well documented [17] and previous studies have differed in their conclusions regarding normal resting respiratory patterns in horses [20, 32, 38], it has been suggested that normal horses typically have PEF early in expiration and PIF late in inspiration [25, 32, 33]. Expiratory flows have greater sensitivity and accuracy for the diagnosis of obstructive airway disease in human patients and horses [4], and both human and equine studies have demonstrated that PEF occurs earlier in expiration in individuals with airway obstruction [22, 39, 40].…”

“…The ratio of time to reach peak expiratory flow to expiratory time (Tpef/Te) has been used to differentiate and characterise airflow obstruction in children and infants during forced expiratory breaths [21, 22] and tidal breathing [23]. As biphasic respiration, characteristic of healthy horses, is lost with obstructive conditions [24, 25], characterisation of relative flow values may prove helpful in equine patients. It has been proposed that relative flow-time relationships can indicate lower airway disease and negate the need to use maximal forced inspirations and expirations in horses [18], and the assessment of relative flow-time relationships has been used to demonstrate potential airflow limitations in horses with increased tracheal wash neutrophil percentages [26].…”

Respiratory dysfunction in unsedated dogs with golden retriever muscular dystrophy

“…However, increased tidal breathing peak expiratory flow has been reported in horses with recurrent airway obstruction (heaves). [37,38] Horses in the study by Petsche, et al also showed increased ratios of expiratory flows compared with expiratory flows later in expiration, as found in GRMD dogs. [37] Dogs with chronic bronchitis were reported to have greater PTEF:EF25 compared with control dogs, also consistent with our findings.…”

“…[33-38] For each dog, 8-10 tidal breaths representative of the predominant pattern were selected. Criteria for selection of breaths included: lack of artifacts, such as resulting from panting, sniffing, cough, or movement, on visual examination of the flow-time tracings; a difference of ≤5% between inspiratory and expiratory volumes, to exclude breaths with evidence of leaking of air from the mask; and, a respiratory frequency of ≤60 breaths per minute, to exclude panting.…”