Carbon dioxide accumulation during small animal, whole body plethysmography: effects on ventilation, indices of airway function, and aerosol deposition

Respiratory and antinociceptive effects of dexmedetomidine and doxapram in ball pythons (Python regius)

OBJECTIVE

To determine the effects of dexmedetomidine, doxapram, and dexmedetomidine plus doxapram on ventilation ([Formula: see text]e), breath frequency, and tidal volume (Vt) in ball pythons (Python regius) and of doxapram on the thermal antinociceptive efficacy of dexmedetomidine.

ANIMALS

14 ball pythons.

PROCEDURES

Respiratory effects of dexmedetomidine and doxapram were assessed with whole-body, closed-chamber plethysmography, which allowed for estimates of [Formula: see text]e and Vt. In the first experiment of this study with a complete crossover design, snakes were injected, SC, with saline (0.9% NaCl) solution, dexmedetomidine (0.1 mg/kg), doxapram (10 mg/kg), or dexmedetomidine and doxapram, and breath frequency, [Formula: see text]e, and Vt were measured before and every 30 minutes thereafter, through 240 minutes. In the second experiment, antinociceptive efficacy of saline solution, dexmedetomidine, and dexmedetomidine plus doxapram was assessed by measuring thermal withdrawal latencies before and 60 minutes after SC injection.

RESULTS

Dexmedetomidine significantly decreased breath frequency and increased Vt but did not affect [Formula: see text]e at all time points, compared with baseline. Doxapram significantly increased [Formula: see text]e, breath frequency, and Vt at 60 minutes after injection, compared with saline solution. The combination of dexmedetomidine and doxapram, compared with dexmedetomidine alone, significantly increased [Formula: see text]e at 30 and 60 minutes after injection and did not affect breath frequency and Vt at all time points. Thermal withdrawal latencies significantly increased when snakes received dexmedetomidine or dexmedetomidine plus doxapram, versus saline solution.

CONCLUSIONS AND CLINICAL RELEVANCE

Concurrent administration of doxapram may mitigate the dexmedetomidine-induced reduction of breathing frequency without disrupting thermal antinociceptive efficacy in ball pythons.

Comparative Analysis of Pulmonary Irritation by Measurements of Penh and Protein in Bronchoalveolar Lavage Fluid in Brown Norway Rats and Wistar Rats Exposed to Irritant Aerosols

The object of this study was to compare in two strain of rats (Brown Norway and Wistar) that were acutely exposed (1 x 6 hrs) to aerosols of polymeric methylenediphenyl-4,4'-diisocyanate (MDI), the relative sensitivity of the functional endpoint "enhanced pause (Penh)" with endpoints in bronchoalveolar lavage fluid (BALF) indicative of lower respiratory tract irritation. This approach included an analysis of both the concentration-response and the time-course of effects. Penh was measured repeatedly prior to (baseline) and during a stepped methacholine (MCh) bronchoprovocation challenge in barometric plethysmographic chambers on postexposure days 1, 3, and 7. Results show that total protein in BALF was a sensitive endpoint to probe early effects caused by exposure to irritant polyisocyanate aerosol. Baseline Penh increased in a concentration-dependent manner and paralleled closely the magnitude of increased BALF-protein on postexposure day 1. The time-course of changes in Penh complemented those of BALF-protein observed in previous studies. The incremental increase of Penh during a stepped MCh-challenge was attenuated with increasing baseline Penh values. In summary, these data show that the exposure to irritant concentrations of this aerosolized polyisocyanate caused a transient perturbation of the blood/air-barrier, which can suitably be probed by measurements of protein in BALF. Although Penh appears to parallel these changes, it displays substantially greater variability. The increase in Penh is apparently more related to changes in breathing patterns either caused by stimulation of receptors or changes in the mechanical properties of lung parenchyma. In regard to Penh and BALF-protein, both strains of rats were equally susceptible, although some endpoints displayed a higher variability in Brown Norway rats when compared to Wistar rats. This supports the conclusion that Wistar rats afford a higher diagnostic resolution than BN rats.

Brown Norway rat asthma model of diphenylmethane-4,4'-diisocyanate (MDI): analysis of the elicitation dose-response relationship

The known human asthmagen polymeric diphenylmethane-diisocyanate (MDI) was investigated in the Brown Norway rat skin asthma model. Two types of dose-response relationships are addressed with the following focus: (1) does sensitization dose and surface area influence the subsequent elicitation response and (2) is the elicitation response more dependent on previous elicitation doses or more on skin sensitizing dose? These two aims are investigated in two elaborated experiments, using inflammatory (bronchoalveolar lavage, BAL) and physiologic (Penh) endpoints to characterize asthma-like responses in rats. Postchallenge measurements of Penh focused on responses delayed in onset. Inflammatory endpoints in BAL were performed one day after the fourth challenge. Both protocols utilized a dermal sensitization phase with two administrations on days 0 and 7 followed by four inhalation challenges with approximately 38 mg MDI/m(3) in intervals of 2 weeks. In the first protocol three groups of rats were topically dosed with 40, 10, and 2.5 mul of MDI per rat. Each dose group consisted of three subgroups with dosed surface areas of 3.1-12.6 cm(2), 0.8-3.1 cm(2), and 0.4-0.8 cm(2), respectively. In the second protocol groups of rats were topically dosed with 40 microl of MDI per rat followed by three challenges with 37 mg MDI/m(3). At the fourth challenge subgroups of rats were either challenged with 8, 18, or 39 mg MDI/m(3). Independent of the protocol used, response was characterized by increased influx of neutrophilic granulocytes in BAL and delayed respiratory response. All groups from the first study sensitized to and challenged with MDI elicited a distinct response relative to similarly challenged naive rats. A sensitization dose dependence of the elicitation response was not found. The second protocol revealed that the elicitation dose correlates with increased neutrophils in BAL and delayed-onset respiratory responses. In summary, these data suggest that the vigor of asthma-like responses appear to be more dependent on the inhalation elicitation dose of previously challenged rats rather than the dermal induction dose.

Comparative assessment of early acute lung injury in mice and rats exposed to 1,6-hexamethylene diisocyanate-polyisocyanate aerosols

The aliphatic diisocyanate monomer 1,6-hexamethylene diisocyanate (HDI) is used as a building block for non-volatile polycondensation products, such as HDI-isocyanurate (HDI-IC) and HDI-biuret (HDI-BT). This paper describes the results from acute inhalation studies with these types of polyisocyanate aerosols in OF1 and C57BL/6J mice and in Wistar rats. The modifying role of different concentrations of residual HDI in HDI-BT on pulmonary irritation was also addressed. These data close data gaps for acute mouse inhalation studies in direct comparison with rats. The sensory irritant potency was examined in OF1 mice during a 3h nose-only exposure to the polyisocyanate aerosols. Concurrent with exposure, breathing patterns suitable to distinguish upper/lower respiratory tract irritation where examined. Functional measurements in barometric plethysmographs (Penh) addressed changes in respiratory function in C57BL/6J mice exposed for 6h up to 16h postexposure. These measurements revealed that these polyisocyanates elicit changes slow in onset suggestive of pulmonary irritation rather than upper airway irritation. This conclusion was supported by similarly exposed OF1 mice exposed to non-irritant, surface active respirable particles of amorphous silica. In C57BL/6J mice and Wistar rats, nose-only exposed for 6h to 10mg/m(3) of aerosolized HDI-BT HDI (0.1% or 2% residual HDI), the pulmonary irritation potency was comparatively assessed by bronchoalveolar lavage (BAL) on postexposure day 1. Similarly air-exposed animals served as concurrent controls. Most changes in BAL suggestive of acute pulmonary irritation were more pronounced in Wistar rats than in C57BL/6J mice. A conclusive dependence of BAL endpoints on the residual content of residual HDI monomer in the polyisocyanate was not found. The results of this study show that mice may be particularly suitable to functionally analyze at which location of the respiratory tract predominant irritation may occur. However, with regard to analysis of lower respiratory tract irritation, rats were demonstrated to be more susceptible than mice. In summary, this study supports the conclusion that data from rat inhalation studies with these types of isocyanates appear to be more conservative and less variable than the respective data from mice.

Acute effect of glucan-spiked office dust on nasal and pulmonary inflammation in guinea pigs

The acute effects of pure inhaled glucan on respiratory inflammation remain inconclusive and not sufficiently examined with regards to the simultaneous interaction of glucan, endotoxin (lipopolysaccharide, LPS), and house dust in airway inflammation. This study aims at determining effects of simultaneous exposure to office dust and glucan on nasal and pulmonary inflammation. This is relevant for humans with occupational exposure in waste handling and farming and buildings with mold problems. Office dust collected from Danish offices was spiked with 1% (1-3)-beta-glucan (curdlan). Guinea pig nasal cavity volume was measured by acoustic rhinometry (AR) and animals were exposed by inhalation for 4 h to curdlan-spiked dust, unspiked dust, purified air (negative controls), or LPS (positive controls). After exposure (+5 h) or the following day (+18 h), measurements were repeated by AR and followed by bronchoalveolar lavage (BAL). Total and differential cell counts, interleukin (IL)-8 in BAL fluid, and change in nasal volume were compared between groups. A 5-10% increase in nasal volume was seen for all groups including clean air except for a significant 5% decrease for spiked-dust inhalation (+18 h). No marked differences were observed in BAL cells or IL-8 except in LPS-exposed controls. The delayed decrease of nasal cavity volume after exposure to glucan spiked dust suggests a slow effect on the upper airways for curdlan and office dust together, though no pulmonary response or direct signs of inflammation were observed. Glucan-spiked office dust exposures produced a delayed nasal subacute congestion in guinea pigs compared to office dust alone, but extrapolated to nasal congestion in humans, paralleling the nasal congestion seen in human volunteers exposed to the same dust, this may not have clinical importance.

Experimental approaches to evaluate respiratory allergy in animal models

Asthma is defined as a chronic disease of the entire lung and asthma attacks may either be immediate, delayed or dual in onset. Allergic asthma is a complex chronic inflammatory disease of the airways and its etiology is multifactorial. It involves the recruitment and activation of many inflammatory and structural cells, all of which release mediators that result in typical pathological changes of asthma. A wealth of clinical and experimental data suggests that allergic asthma is due to an aberrant lung immune response mediated through T-helper type 2 (Th2) cells and associated cytokine-signaling pathways. The pathology of asthma is associated with reversible narrowing of airways, associated with prominent features that involve structural changes in the airway walls and extracellular matrix remodeling including abnormalities of bronchial smooth muscle, eosinophilic inflammation of the bronchial wall, hyperplasia and hypertrophy of mucous glands. The primary objective of respiratory allergy tests is to determine whether a low-molecular-weight chemical (hapten) or high-molecular-weight compound (antigen) exhibits sensitizing properties to the respiratory tract. This may range from reactions occurring in the nose (allergic rhinitis), in the bronchial airways (i.e., allergic bronchitis, asthma) or alveoli (e.g., hypersensitivity pneumonitis). Current assays utilize several phases, viz. an induction phase, which includes multiple exposures to the test compound (sensitization) via the respiratory tract (e.g., by intranasal or intratracheal instillations), by inhalation exposures or by dermal contact, and a single or multiple challenge or elicitation phase. The challenge can either be with the chemical (hapten), the homologous protein conjugate of the hapten or the antigen. The choice depends both on the irritant potency and the physical form (vapor, aerosol) of the hapten. The appropriate selection of concentrations (dosages) both for the induction and elicitation of respiratory allergy appears to be paramount for the outcome of test. Endpoints to characterize positive response range from the induction of immunoglobulins, cytokine or lymphokine patterns in serum (or the lung) to (patho-)physiological reactions typifying asthma. None of the currently applied animal models duplicate all features of human asthma. Accordingly, the specific pros and cons of the selected animal model, including protocol variables, animal species and strain selected, must be interpreted cautiously in order to arrive at a meaningful extrapolation for humans.

Airway responsiveness after acute exposure to urban particulate matter 1648 in a DO11.10 murine model

Enhanced airway responsiveness (AR) is a well-established characteristic of asthma that epidemiological evidence has linked with inhalation of ambient particulate matter (PM). To determine whether acute exposure to urban particulate matter PM1648 can exacerbate airway responsiveness and alter the early inflammatory state, a unique murine model was created using DO11.10 mice, transgenic for a T cell receptor recognizing ovalbumin(323-339). Because these mice are sensitive to ovalbumin, immunization procedures involving adjuvant or long aerosolization procedures are not necessary and, therefore, allow for the study of an acute AR response to particulate and antigen in young animals. AR was assessed by barometric whole body plethysmography and measured by enhanced pause (Penh). PM1648 and ovalbumin were administered intranasally 72 and 4 h before to AR assessment, respectively. A dose-response relationship between PM1648 and Penh was determined, and doses at or above 500 microg had Penh values significantly higher than saline controls. Penh values of control particle titanium dioxide (TiO(2)) were similar to saline controls demonstrating no nonspecific particulate effect on AR. Lung lavage at time of AR assessment showed no significant inflammation due to particulate exposure or ovalbumin alone; however, PM1648/ovalbumin and TiO(2)/ovalbumin combinations resulted in significant neutrophilia. In addition, treatment with polymyxin B to remove surface-bound endotoxin did not significantly affect Penh levels. These results indicate that PM1648 specifically increases AR in a dose-dependent manner and that this exacerbation is not a direct response to increased neutrophil concentration, particle-bound endotoxin or nonspecific particle effects.

A typical path model of tracheobronchial clearance of inhaled particles in rats

A mathematical description of particle clearance from the ciliated conducting airways (tracheobronchial region) of the lungs in rats was developed, assuming that particles on the mucus blanket behave as a fluid and adhere to principles of fluid flow described by the continuity equation. Effective particle transport velocities for given generations of airways were estimated from reported tracheal mucus velocities. Using typical rat airway geometry and estimated particle transport velocities, solutions of sets of rate equations for transport from each generation of airways were summed to estimate total particle clearance from the tracheobronchial region of the lung as a function of time. Aerosol particle size distribution (MMAD ranging from 0.1 to 4.2 microm, and sigma(g) from 1 to 2.7) and concentration data from several investigators were used to predict short-term, tracheobronchial clearance (retention) in rats up to 24 h following exposure. Comparisons between predicted and observed retention showed an average difference between model predictions, and observed fractional retention of initial lung or body burden was 4.9%, with a tendency toward underprediction of clearance of particles >3.0 microm.