Exercise potentiation of lung injury following inhalation of a pneumoedematogenic gas: perfluoroisobutylene.

Exercise performed after exposure to various pneumoedematogenic gases can increase the severity of pulmonary edema beyond that which occurs when exposure is followed by rest. The present study was performed to investigate the potential relationship between a preexisting breach in the lung's permeability status following exposure to an edematogenic gas (perfluoroisobutylene, PFIB) and the potentiating effects of postexposure exercise. Rats were exposed to a concentration of PFIB (100 mg/M3 for 10 min) that results in a unique postexposure latency period (approximately 8 h) prior to the occurrence of overt pulmonary edema. The study examined how exercise performed during and after the latency period affects the severity of the injurious response to this toxic gas. The initial results indicated that exercise performed during the post-PFIB exposure latency period does not potentiate the injurious response, as judged by conventional lung gravimetric and histopathological criteria, but when overt pulmonary edema was preexistent, exercise had a potentiating effect. Changes in lavageable protein were assessed as a more sensitive indicator of permeability changes that may occur during the latency period following PFIB exposure, and the study examined how exercise performed early during the latency period affects this index of pulmonary edema. The study also assessed whether PFIB-induced damage to lung cells is enhanced by exercise during the latency period by measuring lavageable lactate dehydrogenase activity. The results from these latter experiments suggest that a preexisting enhancement in lung permeability is not an absolute requirement for exercise to potentiate the pulmonary edematous response in lungs that are undergoing insidious injury, and that postexposure exercise does not enhance the cell-killing effects of PFIB as a mechanism underlying the exercise potentiating response. Conceivably, the ability of exercise to increase lavageable protein in the absence of a preexisting increase in lung permeability may be due to hyperventilation- and/or pulmonary hypertension-associated intercellular junctional changes that may occur during exercise. Additionally, it remains possible that exercise during PFIB-induced insideous lung injury results in an enhancement in the rate of transcellular transport of blood proteins onto the alveolar surface.

Lung injury following exposure of rats to relatively high mass concentrations of nitrogen dioxide.

Human inhalation exposures to relatively high mass concentrations of the oxidant gas nitrogen dioxide (NO2) can result in a variety of pulmonary disorders, including life-threatening pulmonary edema, pneumonia, and bronchiolitis obliterans. Inasmuch as most experimental studies to date have examined NO2-induced lung injury following exposures to near ambient or supra-ambient concentrations of NO2, e.g., < or = 50 ppm, little detailed information about the pulmonary injurious responses following the acute inhalation of higher NO2 concentrations that are more commensurate with some actual human exposure conditions is currently available. Described in this report are the results from a series of investigations in which various aspects of the inhalation toxicity of high concentrations of NO2 have been examined in laboratory rats. In the first component of our study, we characterized the kinetic course of development of lung injury following acute exposures to high concentrations of NO2 delivered over varying durations, and we assessed the relative importance of NO2 exposure concentration versus exposure time in producing lung injury. For a given exposure duration, the resulting severity of lung injury was found to generally scale proportionately with inhaled mass concentration, whereas for a given concentration of inhaled NO2, the magnitude of resulting injury was not directly proportional to exposure duration. Moreover, evidence was obtained that indicated exposure concentration is more important than exposure time when high concentrations of NO2 are inhaled. In a second component of our investigation, we assessed the pulmonary injurious response that occurs when NO2 is inhaled during very brief, 'high burst' exposures to very high concentrations of NO2. Such exposures resulted in significant lung injury, with the magnitude of such injury being directly proportional to exposure concentration. Comparisons of results obtained from this and the first component studies additionally revealed that brief exposures to the very high concentrations of NO2 are more hazardous than longer duration exposures to lower concentrations. In a third study series, we examined pre-exposure, exposure, and post-exposure modifiers of NO2-induced lung injury, including dietary taurine, minute ventilation, and post-exposure exercise. Results from these studies indicated: (i) dietary taurine does not protect the rat lung against high concentration NO2 exposure, (ii) the severity of acute lung injury in response to NO2 inhalation is increased by an increase in minute ventilation during exposure, and (iii) the performance of exercise after NO2 exposure can significantly enhance the injurious response to NO2.(ABSTRACT TRUNCATED AT 400 WORDS)

High-performance capillary electrophoresis of proteins from the fluid lining of the lungs of rats exposed to perfluoroisobutylene.

Measurements of the biochemical constituents in the fluid lining of the lung can be used for diagnosing and assessing lung disorders. To facilitate such measurements, a high-performance capillary electrophoresis (HPCE) method has been developed by which the proteins in lung fluid can be analyzed. The lung fluid was obtained by a bronchoalveolar lavage procedure using 48 ml of physiological saline to wash out the lung fluid of rats. The proteins were precipitated from the fluid with 10 volumes of acetone and concentrated by dissolution in 2 ml of water containing 0.2% of trifluoroacetic acid. Aliquots of these samples (5 microliters) were then injected into a Bio-Rad HPE-100 capillary electrophoresis instrument fitted with a 50 cm x 50 microns I.D. coated capillary filled with 0.1 M phosphate buffer (pH 2.5). With phosphate buffer in the outlet electrode chamber (cathode) and water in the inlet electrode chamber (anode), the proteins were loaded into the capillary electrophoretically for 10 s at 10 kV constant voltage. The inlet electrode chamber was then filled with phosphate buffer and HPCE was performed at 8 kV constant voltage. Six major protein fractions were resolved in 35 min, and were detected by UV absorption at 200 nm. The procedure was used to compare the lung fluid proteins of normal untreated rats with those of rats exposed by inhalation to perfluoroisobutylene (PFIB) at a concentration of 100 mg/m3. It was found that PFIB induced pulmonary edema involving a translocation of blood compartment proteins into the lung's alveolar compartment. Comparison of the HPCE fractions with similar fractions obtained by high-performance liquid chromatography confirmed albumin, transferrin and IgG as three major proteins translocated into the alveolar space after PFIB exposure.

Relative acute toxicities of hydrogen fluoride, hydrogen chloride, and hydrogen bromide in nose- and pseudo-mouth-breathing rats.

Hydrogen fluoride (HF), hydrogen bromide (HBr), and hydrogen chloride (HCl) gases can be generated during the pyrolysis of a variety of materials and they may be encountered in numerous industrial settings. Although injury to the respiratory tract has been characterized following the inhalation of halide gases via the nasal route, essentially no experimental information is currently available about their injurious effects when they are inhaled during mouth breathing. In this study, we simulated mouth breathing by using a pseudo-mouth-breathing (MB) rat model in order to: (1) characterize the profiles and magnitudes of respiratory tract injury that result from the acute inhalation of relatively high mass concentrations of the above halides when the upper airway is bypassed, and (2) assess the relative toxicities of HF, HBr, and HCl when inhaled by way of either the nasal or the oral pathways. Tracheal tubes connected to mouthpieces were inserted into temporarily anesthetized rats, i.e., mouth breathers. Awake rats were placed into whole body flow plethysmographs for pulmonary ventilation studies while they were exposed either to air or to 1300 ppm of HF, HBr, or HCl for 30 min. Similarly pretreated rats were also exposed but without the mouthpiece, i.e., nose breathers (NB). The animals were euthanized 24 hr after exposure for histopathologic analyses of their upper and lower respiratory tracts and for lung gravimetric measurements. Tissue injury following NB exposure to the halides was confined to the nasal region, e.g., epithelial and submucosal necrosis, accumulations of inflammatory cells, exudates, and the extravasation of erythrocytes. MB exposure caused higher mortality rates and major tissue disruption in the trachea, including epithelial, submucosal, glandular, and cartilage necrosis, and accumulations of inflammatory cells and exudates. More peripheral lung damage was manifested by lung gravimetric increases and histopathologic changes primarily in the larger conducting airways. The results of this study demonstrate that the injurious response profiles to HF, HBr, and HCl markedly differ as a function of the route by which they are inhaled. Furthermore, examinations of the magnitudes of injury caused by exposure to the halides during nose or mouth breathing in conjunction with animal ventilatory data obtained during exposure to the halides suggest that HF, HBr, and HCl are quantitatively similar in their toxic effects in the respiratory tract.

Potentiation of the expression of nitrogen dioxide-induced lung injury by postexposure exercise.

Previous investigations have indicated that postexposure exercise (E) can can potentiate nitrogen dioxide (NO2)-induced lung injury. In this report, we (1) further characterize the potentiation of expression of NO2-induced lung injury in the rat by E; (2) characterize the postexposure period during which such potentiation by E can occur, i.e., "window of susceptibility"; (3) assess whether two E bouts performed during the "window of susceptibility" have even greater potentiating effects; and (4) determine if early postexposure E can extend the window of susceptibility. Groups of Fischer-344 rats were exposed to 100 ppm NO2 for 15 min, exercised at times ranging from 30 min to 24 hr thereafter, and sacrificed during a 24-hr postexposure period. Other exposed rats were exercised 30 min to 24 hr thereafter and sacrificed for lung studies 30 min following the E runs. Still other exposed animals were exercised immediately and at 8 or 24 hr postexposure and sacrificed 30 min after the last E run. NO2-exposed but rested rats, and sham-air-exposed and rested or exercised rats served as controls. E immediately or at 8 hr post-NO2 exposure caused marked increases in lung wet weight (LWW) and right cranial lobe dry weights (RCLDW) and more pronounced histopathologic disturbances beyond those following NO2 exposure and rest only. Potentiation of injury was not observed in rats exercised 24 hr after exposure. The pattern of subsidence of the LWW and RCLDW increases after immediate or 8 hr E differed with the increases in the former being more persistent. Two E bouts (30 min and 8 hr postexposure) caused lung changes consistent with an additive effect. E performed immediately after NO2 exposure extended the window of susceptibility to E beyond 24 hr.

Nitrogen dioxide exposure and development of pulmonary emphysema.

This study assessed the relationship between nitrogen dioxide inhalation and the development of pulmonary emphysema and investigated how the severity of preexisting emphysema brought about by protease (elastase) instillation into the lung may be augmented by a subchronic exposure to a relatively high concentration of nitrogen dioxide. Lungs of adult Fischer-344 rats were evaluated for emphysematous changes after (1) a single intratracheal instillation of elastase (E), (2) a 25-d exposure to 35 ppm nitrogen dioxide (NO2), and (3) elastase instillation followed by 25-d exposure to 35 ppm NO2 (E + NO2). Rats instilled with sterile normal saline and subsequently exposed to filtered air served as a control group (NS). Residual volumes (RV) of the NO2 and NS groups were virtually identical, whereas the RV of the E and E + NO2 lungs (2.3 and 2.3 ml, respectively) were significantly greater than those of the NS and NO2 lungs (1.3 and 1.4 ml, respectively). Directionally similar changes in the excised lung volumes and total lung capacities were obtained with the E and E + NO2 groups; NO2 alone, however, did not alter these volumetric parameters. No differences in arterial blood gases and pH values, minute ventilation, or breathing frequencies were found among the experimental groups. The mean linear intercept values (MLI) obtained with the NS and NO2 exposed lungs were essentially identical with average values of approximately 62 micron. This morphometric parameter was substantially increased in the E- and E + NO2-exposed lungs; no significant differences, however, were found between the MLI values obtained with the E and E + NO2 lungs (approximately 95 and approximately 97 micron, respectively). From these data, as well as histologic examinations of lung sections for evidence of emphysema, we conclude that (1) a subchronic, moderately high level of NO2 exposure does not produce an irreversible emphysematous lesion in the rat model and (2) exposure of rats to 35 ppm for 25 d after elastase instillation into the lungs does not potentiate protease-induced emphysema or bring about a progression in preexisting emphysema.

Arterial CO2 response to low levels of inspired CO2 in awake beagle dogs.

We have previously shown, using a repeated-measures experimental design, that 1% inspired CO2 with a partial pressure of 7 Torr at sea level results in an increased end-tidal CO2 pressure (PETCO2) in awake beagle dogs (22), suggesting hypercapnia rather than the isocapnia found by some investigators in human and nonhuman subjects. Because PETCO2 may, not equal arterial PCO2 (PaCO2), we examined the steady-state PaCO2 during air and 1% CO2 inhalation periods in three awake beagle dogs having exteriorized carotid arterial loops and an intact airway, and breathing through a low dead-space respiratory mask. Six low-level CO2 inhalation experiments were performed in three dogs with two experimental sequences in each dog on separate days. An experimental session consisted of alternating control and CO2 inhalation states for up to 10 low-CO2 and 11 control conditions, resulting in a total of 75 control and 57 low-level CO2 inhalation observations. Ten minutes were allowed to reach steady state in each condition. Blood samples (1.5 ml) drawn anaerobically over a 0.5-min time period from an indwelling arterial catheter were immediately analyzed with a radiometer blood gas system. The 1% inhaled CO2 produced a significant increase of 0.88 Torr in the steady-state PaCO2, compared with bracketing controls (t = 5.82, P less than 0.05, df = 2). We conclude that 1% inhaled CO2 results in hypercapnia detectable by a repeated-measures experimental design.

A refrigerated treadmill apparatus for exercising dogs.

To prevent overheating and panting in exercising dogs, a refrigerated enclosure was constructed on a standard laboratory treadmill to regulate skin and body temperature of exercising beagles. The enclosure temperature is controlled by a computer software algorithm that analyzes the exercising dog's skin and rectal temperatures and stabilizes rectal temperature to within +/- 0.1 degree C of a preselected resting level. Refrigeration is activated depending on the skin and rectal temperature dynamics lowering enclosure temperature as skin temperature and rectal temperature increase. The system has been used extensively to inhibit panting in exercising beagles, maintaining a mean and standard deviation respiratory frequency of 32 +/- 5 breaths/min during exercise at 5 km/h, 0% grade. These respiratory rates can be compared with reported respiratory frequencies of 95 +/- 57 breaths/min for beagles exercising at the same work load but at room temperature (Mauderly and Pickrell, Research Animals in Medicine, DHEW Publ. 72-333, 1973). This reduction in respiratory frequency is also accompanied by a reduced and repeatable expired minute ventilation and O2 consumption of 9.40 +/- 1.0 1/min (BTPS) and 0.331 +/- 0.031 1/min (STPD), respectively, and can be compared with 24.84 +/- 6.44 1/min (BTPS) and 0.440 +/- 0.0831 1/min (STPD) reported for beagles exercising at room temperature.

A respiratory mask for resting and exercising dogs.

A respiratory face mask has been developed for use with unsedated beagles trained to run on a treadmill. The latex rubber mask, shaped to fit the animal's muzzle, incorporates two modified, commercially available, pulmonary valves for separating inspiratory and expiratory flows. The mask has a dead space of 30 cm3 and a flow resistance below 1 cmH2O . 1(-1) . s. The flexible mask is used to measure breath-by-breath respiratory variables over extended periods of time during rest and exercise.

End-tidal CO2 response to low levels of inspired CO2 in awake beagle dogs.

The steady-state end-tidal CO2 tension (PCO2) was examined during control and 1% CO2 inhalation periods in awake beagle dogs with an intact airway breathing through a low dead-space respiratory mask. A total of eight experiments were performed in four dogs, comprising 31 control observations and 23 CO2 inhalation observations. The 1% inhaled CO2 produced a significant increase in the steady-state end-tidal PCO2 comparable to the expected 1 Torr predicted from conventional CO2 control of ventilation. We conclude that 1% inhaled CO2 results in a hypercapnia. Any protocol that is to resolve the question of whether mechanisms are acting during low levels of inhaled CO2 such that ventilation increases without any change in arterial PCO2 must have sufficient resolving power to discriminate changes in gas tension in magnitude predicted from conventional (i.e., arterial PCO2) control of ventilation.