Age effects on blood gas, spirometry, airway reactivity, and bronchoalveolar lavage fluid cytology in clinically healthy horses.

BACKGROUND: Despite the increasing number of geriatric horses attended by veterinarians, there is a lack of understanding of aging-related changes on the respiratory system of horses. OBJECTIVE: To identify aging-related changes on the respiratory function and bronchoalveolar lavage fluid (BALF) cytology of horses. ANIMALS: Fifteen healthy young adult (2-11 years) and 16 healthy aged (≥20 years) horses. METHODS: The respiratory system was examined by measurement of arterial blood gases (ABG), use of respiratory inductive plethysmography (RIP) for assessment of breathing pattern and ventilatory parameters, histamine bronchoprovocation, and BALF cytology. RESULTS: No significant differences were detected with regard to values obtained by ABG or bronchoprovocation of young adult and aged healthy horses. In aged horses, there were significant differences in mean ± SD of the following parameters when compared to young horses: prolonged expiratory time (Te) measured by RIP (3.9 ± 1.5 s versus 3.0 ± 0.6 s), decreased percentage of alveolar macrophages (40.6 ± 11.3% versus 53.5 ± 9.6%), and increased percentage of lymphocytes (53.4 ± 9.5% versus 43.9 ± 11.0%). No correlations between airway reactivity and ventilatory parameters, ABG, or BALF cytology were found in this asymptomatic population. CONCLUSIONS: These results suggest that aging does not cause changes in the results obtained by ABG, most RIP-derived variables, and bronchoprovocation in the horse. A decreased percentage of macrophage and an increased percentage of lymphocytes in the BALF cytology may be expected in the asymptomatic geriatric horse and may be a result of aging.

Matrix modulation of compensatory lung regrowth and progenitor cell proliferation in mice.

Mechanical stress is an important modulator of lung morphogenesis, postnatal lung development, and compensatory lung regrowth. The effect of mechanical stress on stem or progenitor cells is unclear. We examined whether proliferative responses of epithelial progenitor cells, including dually immunoreactive (CCSP and proSP-C) progenitor cells (CCSP+/SP-C+) and type II alveolar epithelial cells (ATII), are affected by physical factors found in the lung of emphysematics, including loss of elastic recoil, reduced elastin content, and alveolar destruction. Mice underwent single lung pneumonectomy (PNY) to modulate transpulmonary pressure (mechanical stress) and to stimulate lung regeneration. Control mice underwent sham thoracotomy. Plombage of different levels was employed to partially or completely abolish this mechanical stress. Responses to graded changes in transpulmonary pressure were assessed in elastin-insufficient mice (elastin +/-, ELN+/-) and elastase-treated mice with elastase-induced emphysema. Physiological regrowth, morphometry (linear mean intercept; Lmi), and the proliferative responses of CCSP+/SP-C+, Clara cells, and ATII were evaluated. Plombage following PNY significantly reduced transpulmonary pressure, regrowth, and CCSP+/SP-C+, Clara cell, and ATII proliferation following PNY. In the ELN+/- group, CCSP+/SP-C+ and ATII proliferation responses were completely abolished, although compensatory lung regrowth was not significantly altered. In contrast, in elastase-injured mice, compensatory lung regrowth was significantly reduced, and ATII but not CCSP+/SP-C+ proliferation responses were impaired. Elastase injury also reduced the baseline abundance of CCSP+/SP-C+, and CCSP+/SP-C+ were found to be displaced from the bronchioalveolar duct junction. These data suggest that qualities of the extracellular matrix including elastin content, mechanical stress, and alveolar integrity strongly influence the regenerative capacity of the lung, and the patterns of cell proliferation in the lungs of adult mice.

Reproducibility of airway responsiveness in horses using flowmetric plethysmography and histamine bronchoprovocation.

BACKGROUND: Inflammatory airway disease has a high prevalence in horses, but is often a diagnostic challenge. Flowmetric plethysmography and histamine bronchoprovocation (FP/HBP) is a simple and effective tool for diagnosis, but reproducibility of these measurements made over time has not been established. HYPOTHESIS: We hypothesize that the measurement of airway responsiveness in horses using FP/HBP is consistent over both short and long periods of time. ANIMALS: Twenty-nine healthy adult horses from 2 university herds. METHODS: In this prospective experimental study, airway responsiveness was determined in each horse at day 0 (baseline [BL]) with FP/ HBP, using PC35 (provocative concentration of histamine needed to increase Delta(flow) by 35%) as a measure of airway responsiveness. Each horse was re-tested 1-4 weeks after BL (short-term [ST]) and again at 3-12 months after BL (long-term [LT]). RESULTS: In the ST period, 23/27 (85%) of the horses had a PC35 that was within 1 doubling concentration of histamine of their BL value, with a mean change of 0.52 doubling concentrations (95% CI 0.26-0.79, range 0-2.06). For the LT data, 19/26 (73%) of horses were within 1 doubling concentration of their BL value, with a mean change of 0.81 doubling concentrations (95% CI 0.45-1.17, range 0.14-3.10). There was no significant difference in reproducibility between the 2 groups of subjects. CONCLUSIONS AND CLINICAL IMPORTANCE: Repeated measurements of airway responsiveness obtained with FP/HBP show acceptable reproducibility over time periods up to a year. However, caution must be used when testing horses when ambient air temperature is low.

Association between cough and cytology of bronchoalveolar lavage fluid and pulmonary function in horses diagnosed with inflammatory airway disease.

BACKGROUND: The objective of this study was to examine the relationship between chronic cough, pulmonary mechanical function, bronchial hyper-responsiveness, and peripheral airway inflammation in adult performance horses with nonseptic inflammatory airway disease (IAD). HYPOTHESIS: We hypothesized that horses with a presenting complaint of cough have a higher percentage of inflammatory cells on bronchoalveolar lavage (BAL), greater airway obstruction, and airway hyper-responsiveness (AHR) than do horses without cough. ANIMALS/SAMPLE POPULATION: Adult performance horses (n = 137) referred for evaluation of signs of IAD including cough or exercise intolerance (university hospital patients) and BAL samples (n = 142) taken in first opinion practice. METHODS: A descriptive, retrospective cohort analysis was performed to evaluate the association between chronic cough and pulmonary mechanical function, AHR, BAL cytology, patient signalment, and comorbid features (multivariable logistic regression). RESULTS: Cough was significantly more prevalent in horses >7 years, and best characterized by a high BAL neutrophil count (>5%) and nasal discharge. Lung function mechanics, abnormal thoracic auscultation, and exercise intolerance did not retain statistical significance in the logistical regression analysis of cough. Although AHR was not related to neutrophilic airway inflammation (BAL neutrophils >5%), it was significantly associated with BAL mast cells >2%. CONCLUSIONS AND CLINICAL IMPORTANCE: Our data support that neutrophilic airway inflammation may potentiate cough without further changing respiratory mechanical function in IAD. In contrast, mast cell release increased AHR without affecting the incidence of cough. Cough may be used as an indicator of neutrophilic airway inflammation in the presence of low-grade nonseptic respiratory disease.

Cellular kinetics and modeling of bronchioalveolar stem cell response during lung regeneration.

Organ regeneration in mammals is hypothesized to require a functional pool of stem or progenitor cells, but the role of these cells in lung regeneration is unknown. Whereas postnatal regeneration of alveolar tissue has been attributed to type II alveolar epithelial cells (AECII), we reasoned that bronchioalveolar stem cells (BASCs) have the potential to contribute substantially to this process. To test this hypothesis, unilateral pneumonectomy (PNX) was performed on adult female C57/BL6 mice to stimulate compensatory lung regrowth. The density of BASCs and AECII, and morphometric and physiological measurements, were recorded on days 1, 3, 7, 14, 28, and 45 after surgery. Vital capacity was restored by day 7 after PNX. BASC numbers increased by day 3, peaked to 220% of controls (P<0.05) by day 14, and then returned to baseline after active lung regrowth was complete, whereas AECII cell densities increased to 124% of baseline (N/S). Proliferation studies revealed significant BrdU uptake in BASCs and AECII within the first 7 days after PNX. Quantitative analysis using a systems biology model was used to evaluate the potential contribution of BASCs and AECII. The model demonstrated that BASC proliferation and differentiation contributes between 0 and 25% of compensatory alveolar epithelial (type I and II cell) regrowth, demonstrating that regeneration requires a substantial contribution from AECII. The observed cell kinetic profiles can be reconciled using a dual-compartment (BASC and AECII) proliferation model assuming a linear hierarchy of BASCs, AECII, and AECI cells to achieve lung regrowth.

Radiographic scoring lacks predictive value in inflammatory airway disease.

REASONS FOR PERFORMING STUDY: Diagnosis of inflammatory airway disease (IAD) currently rests upon the results of bronchoalveolar lavage (BAL) cytology, lung function testing and histamine bronchoprovocation (HBP), none of which provides direct information about structural change in the lung. HYPOTHESIS: That thoracic radiography might better portray structural change in the lungs and therefore offer a good clinical assessment of IAD. METHODS: A radiographic scoring system was developed to assess the extent of bronchial and interstitial pattern on thoracic radiographs in the dorsocaudal, dorsocranial and caudoventral regions in 16 control horses and 33 horses with IAD. Mean scores were compared to ascertain whether thoracic radiographs could distinguish between the 2 groups. In order to determine whether independent observers reliably scored radiographs similarly, an inter-rater reliability score was employed for each radiographic observation. Correlations between radiographic scores, BAL cytology, lung function testing using the forced oscillatory technique and HBP were examined. RESULTS: Inter-rater reliability was only moderate. Radiographic scoring demonstrated no differences between the 2 groups. There were no correlations among BAL cytology, lung function testing, HBP and radiographic scores. CONCLUSIONS AND POTENTIAL RELEVANCE: Thoracic radiographs are a low-yield diagnostic modality in horses with a clinical history compatible with IAD. In the absence of clinical evidence of more extensive, infectious disease, thoracic radiographs neither refine nor improve diagnosis of IAD, but increase diagnostic costs.

Effects of aerosolized albuterol on physiologic responses to exercise in standardbreds.

OBJECTIVE: To examine the effects of an aerosolized beta2-adrenoreceptor agonist, albuterol, on performance during a standardized incremental exercise test in clinically normal horses. ANIMALS: 8 Standardbred pacing mares. PROCEDURE: Clinically normal horses, as judged by use of physical examination, hematologic findings, serum biochemical analysis, and airway endoscopy, were randomly assigned to 2 groups and were given 900 microg of albuterol via a metered-dose inhaler 30 minutes before beginning a standardized incremental exercise test in a crossover design with a 7-day minimum washout. Further examination included measurement of baseline lung mechanics, response to histamine bronchoprovocation, and bronchoalveolar lavage. RESULTS: No significant differences (albuterol vs placebo) were seen for any incremental exercise test variables (ie, maximum oxygen consumption, maximum carbon dioxide consumption, respiratory quotient, treadmill speed at heart rate of 200 beats/min, or number of steps completed during an incremental exercise protocol). Mast cell percentage was significantly (r = -0.84) associated with the concentration of aerosolized histamine that evoked a 100% increase in total respiratory system resistance. No other direct correlations between bronchoalveolar lavage fluid cell types and any indices of exercise capacity or airway reactivity were found. CONCLUSIONS AND CLINICAL RELEVANCE: Although no horse had exercise intolerance, 4 horses had airway hyperreactivity with bronchoalveolar lavage fluid mastocytosis; these horses may have been subclinically affected with inflammatory airway disease. In our study, albuterol did not enhance performance in 8 clinically normal racing-fit Standardbreds.

Comparison of forced oscillation with the conventional method for histamine bronchoprovocation testing in horses.

OBJECTIVE: To compare response of horses to histamine bronchoprovocation (HBP), using total respiratory resistance (Rrs) measured by forced oscillatory mechanics (FOM) with dynamic compliance (Cdyn) and pulmonary resistance (RL) measured by the esophageal balloon method. ANIMALS: 10 horses with various degrees of airway reactivity. PROCEDURE: The 2 methods for measuring airway responses to HBP were performed on separate days. Endpoints compared were increase of 150 or 200% of baseline Rrs (PC150Rrs, PC200Rrs) and to 150% of baseline RL (PC150RL) or decrease to 65% of baseline Cdyn (PC65Cdyn). Frequency dependence of respiratory mechanics, using FOM, was evaluated, using the slope of Rrs over 1 to 3 Hz and the ratios of Rrs at 1 Hz to Rrs at 2 and 3 Hz (Rrs1Hz/Rrs2Hz, Rrs1Hz/Rrs3Hz) and of Rrs at 2 Hz to Rrs at 3 Hz (Rrs2Hz/Rrs3Hz). Effect of histamine on frequency dependence was assessed. RESULTS: Correlation with PC65Cdyn was high for PC150Rrs (rs = 0.93) and PC200Rrs (rs = 0.96). Correlation between PC65Cdyn and PC150RL was weakly positive (rs = 0.61). The slope of Rrs over 1 to 3 Hz changed significantly between baseline (-0.07+/-0.09 cm H2O/L/s/Hz) and final histamine dose (-0.28+/-0.10 cm H2O/L/s/Hz). The Rrs1Hz/Rrs3Hz and Rrs2Hz/Rrs3Hz differed significantly (P < 0.05 between baseline [1.27+/-0.36 and 0.96+/-0.11, respectively] and final histamine dose [1.62+/-0.37 and 1.09+/-0.14, respectively]). CONCLUSIONS: Correlation between histamine-induced changes in respiratory mechanics, as measured by FOM and the pneumotachograph-esophageal balloon method, was good. The FOM results indicated frequency dependence of respiratory mechanics during HBP. CLINICAL RELEVANCE: A noninvasive method of measuring airway reactivity will facilitate routine evaluation of horses with suspected small airway disease and may be suitable for field studies.

Association between bronchoalveolar lavage cytologic features and airway reactivity in horses with a history of exercise intolerance.

OBJECTIVE: To correlate indices of airway reactivity to bronchoalveolar lavage (BAL) fluid cytologic features in horses with a recent decline in exercise tolerance. ANIMALS: 20 actively working horses from 2 to 24 years old. PROCEDURE: Bronchoalveolar lavage fluid samples were obtained and analyzed. Forced oscillatory mechanics (1-7 Hz) technique was used for measurements of total respiratory system resistance (RRS), compliance (CRS), and resonant frequency (fres). Changes in RRS (1 Hz) during histamine challenge were used to generate histamine dose-response curves, from which the provocative concentrations that evoked a 75 or 100% increase in baseline RRS (PCRRS75 and PCRRS 100, respectively) were determined. Age, sex, baseline lung mechanics, and BAL cytologic findings were correlated with PCRRS75 and PCRRS100. RESULTS: No horse of the study had clinical signs or history of obstructive pulmonary disease or increased percentage (> 7%) of neutrophils in bronchoalveolar lavage fluid samples. Mean (+/- SEM) RRS, CRS, and fres were 0.67 +/- 0.06 cm of H2O/L/s, 0.52 +/- 0.04 L/cm H2O, and 2.46 +/- 0.02 Hz, respectively. There was no correlation between age or sex, and RRS, CRS, fres, PCRRS75, or PCRRS100. There was a significant correlation (rs = -0.78, P < 0.001) between percentage of BAL fluid mast cells and PCRRS75 or PCRRS100, but correlation with other cell types and indices of airway reactivity were not observed. CONCLUSION: The strong association between mast cell percentage in BAL fluid and airway reactivity in this group suggests that mast cell products may contribute to bronchospasm, airway wall thickening, and/or loss of elastic recoil, which underlie airway hyperreactivity. Alternatively, mast cells may contribute to nonspecific airway reactivity in horses through unknown mechanisms.

Medical management of a full-thickness tear of the retroperitoneal portion of the rectum in a horse with hyperadrenocorticism.

A 30-year-old Morgan-Quarter Horse gelding with hyperadrenocorticism was referred for treatment of a full-thickness tear of the retroperitoneal portion of the rectum. In older horses, the caudal end of the peritoneal space may be farther cranial than is commonly thought. Thus, there is a greater chance that full-thickness rectal tears will involve the retroperitoneal, rather than the peritoneal, portion of the rectum. This horse had a quick recovery and good outcome, despite underlying hyperadrenocorticism that would be expected to impair healing. Although relatively little is known about management and prognosis of full-thickness tears of the retroperitoneal portion of the rectum, results in this horse suggest that medical management may be appropriate.