Cardiopulmonary function of dogs with plutonium-induced chronic lung injury

Beagle dogs had signs of restrictive lung disease 1 to 5 years after exposure by inhalation to 239PuO2 aerosols. The 239PuO2 aerosols were monodisperse with activity median aerodynamic diameters of 0.75, 1.5, or 3.0 microns. The plutonium particles produced protracted alpha irradiation of the lungs. Ten dogs had specific initial pulmonary burdens (IPB) of 330 to 4,100 kBq of 239PuO2/kg of body mass. The average onset time of clinical signs of lung injury was 3 years after exposure; the average time from the onset of signs until cardiorespiratory function evaluation was 5.5 years. A second group of 10 dogs had IPB of 110 to 2000 kBq of 239Pu/kg of body mass but no signs of lung injury. A third group of 10 dogs, not exposed to 239Pu, were matched for age and sex. Cardiopulmonary function tests were performed. Only the dogs in group I with signs of lung injury had a mild respiratory function disorder consisting of smaller lung volumes, reduced compliance, increased respiratory frequency and minute volume, and reduced carbon monoxide diffusing capacity. Cardiac function of all three groups was similar. These findings indicate that alpha irradiation of the lungs of man could produce restrictive lung disease at long times after initial exposure.

Late effects of fractionated pi-mesons compared to X rays on mouse lung

Early and late delayed effects of up to 20 fractions of pions and X rays were investigated in the mouse lung. The whole thorax of female CD-1 mice was irradiated under Ethrane/O2 anesthesia. Respiration rate was measured by whole body plethysmography at biweekly to monthly intervals. With signs of irreversible respiratory distress, animals were sacrificed and their lungs evaluated histologically. In addition to the effect of fractionation, the influence of dose-rate and anesthesia was studied as well. The degree of injury for the most predominant lesions (macrophage accumulation, fibrosis, vascular congestion) was scored, and the correlation with the relative change in respiratory rate and survival was analyzed. This analysis showed the primary lesion to be radiation pneumonitis at a median survival time of approximately 100 days. Focal fibrosis was observed to occur soon thereafter, and no evidence was obtained for an independent second wave of fibrotic injury. Fibrosis seemed primarily the result of pathological organization in areas with heavy concentration of macrophages. It was observed that the mice were unusually sensitive, with a single dose X ray ED50/180 of 8.8 Gy. A similar value was found for unanesthetized mice. This might have been the result of performing these studies at an altitude of 2100 m. The fractionation effect also seemed more pronounced, with alpha/beta values of 0.6 Gy for X rays and 4 Gy for pions, which is significantly lower compared to reported values. At the pion dose-rate of 0.25 Gy.min-1, RBE values for single doses were 0.9 when compared to high dose-rate X rays, and 1.36 at equivalent dose rates. This clearly shows that significant repair occurs during the relatively low dose-rate pion irradiations. With smaller doses per fraction, the dose-rate effect became less dominant, and for 20 fractions of pions the RBE was 1.4 compared to fractionated high dose-rate X rays. These RBE's are similar to values reported for acute effects in skin.

An animal model of pulmonary radiation fibrosis with biochemical, physiologic, immunologic, and morphologic observations

An animal model of pulmonary radiation fibrosis was established, using male CBA/j mice. Both lungs of each mouse in one group (DL) were irradiated with two doses of 8.5 Gy each, separated by 30 days. A control group (CG) was sham-irradiated. There was a small but significant difference (P less than 0.03) in average breathing rate between DL and CG 27 weeks after the second irradiation which increased until the 34th week followed by a plateau. The accumulated hydroxyproline content of the irradiated mouse lung was 40% greater (P less than 0.02) than that of the sham-irradiated lung at 42 weeks and thereafter. Anticollagen antibodies assayed 52 weeks after irradiation by enzyme-linked immunosorbent assay were elevated by 49% in sera from the irradiated mice compared to sera from sham-irradiated mice. Mortality during the 52-week period following the second irradiation was low (13%) for both groups. Histological comparison of irradiated and control mouse lungs fixed under uniform inflation pressure indicated no significant differences. The model has unique features including an increase in collagen deposition, no acute changes attributable to radiation, a small but statistically significant abnormality in pulmonary function, an immunologic response to collagen, and low mortality.

Replicative activity of lung type 2 cells following lung X irradiation

We investigated the replicative activity of type 2 cells in the lungs of mice at various times from 3 to 22 weeks after 18 Gy of X rays to the thorax. No significant changes were found until 11 weeks after thoracic X irradiation. Thereafter the replicative index of type 2 cells was significantly elevated, rising four to sixfold above that of control, sham-irradiated mice. During the period when the replicative activity of type 2 cells was elevated, the breathing frequency increased and there was histologic evidence of the presence of radiation pneumonitis. The magnitude of each of these indices of pneumonitis correlated significantly with the type 2 cell replicative index, suggesting that type 2 cell replication is related to pneumonitis in extent as well as in chronology. How these changes relate to the pathogenesis of radiation pneumonitis is unclear.

Actinomycin D and radiation: effects on mouse lung

The effect of actinomycin D (0.4 mg/kg) on radiation-induced lung damage in the mouse was investigated. The drug was administered either 4 weeks before, immediately after, or 16 weeks after single doses of 240 kV X-rays applied to the thorax of CBA mice. Lung damage was assessed by measuring respiration rate, with a whole body plethysmograph. Dose-response curves were obtained at 2-week intervals from 12 to 40 weeks after irradiation. Actinomycin D had no significant effect on respiration rate in this study. A summary of other experimental studies is included which shows conflicting results.

Repair in mouse lung of multifraction X rays and neutrons: extension to 40 fractions

We have extended our previous multiple irradiations of mouse lung from 20 to 40 fractions of both X-ray and neutron radiation in order to test whether the repair parameters previously derived will hold for lower doses per fraction, down to 1.1 Gy of X rays and 0.18 Gy of 3 MeV neutrons per fraction. Repair parameters were calculated from measurements of breathing rate and lethality at monthly intervals up to 17 months after irradiation with 1, 10, 20 or 40 equal fractions. Sparing of neutron damage was negligible when the neutron dose was divided into multiple fractions, but progressively greater repair of lung damage was seen after increasing numbers of X-ray fractions. A significant increase in the iso-effect dose for 40 fractions of X rays was found compared with 20 fractions, even when two fractions per day were given at intervals of about 6 hours, as was the case in the 40 fraction experiment. The data were well fitted by the linear quadratic formula for response vs. dose per fraction and the ratio alpha/beta yielded values of approximately 3 Gy after X rays and 30 to 40 Gy after neutron irradiation; these values are not different from alpha/beta ratios found for up to 20 fractions. The single dose RBE was less than 2, increasing to about 6 at the lowest dose per fraction measured, in agreement with previous results. The ratio of the alpha component for neutrons to that for X rays was about 8, which is therefore the limiting RBE predicted for infinitely small doses per fraction.

The assessment of early and late radiation injury to the mouse lung using X-ray computerised tomography

X-ray computerised tomography (CT) was performed on the lungs of CBA and C57Bl mice at varying time intervals after 13 and 16 Gy irradiation to the whole thorax. With careful consideration of artefacts associated with lung cross-sectional area and breathing rate, the mean density of the lung was evaluated in Hounsfield units (CT number). In CBA mice, this parameter showed a biphasic increase in lung density with time from irradiation, corresponding to an early phase of radiation pneumonitis and a late phase dominated by pleural effusions. Reduced lung volumes were also seen during the late response and lung compression due to accumulations of pleural fluid is considered a major factor in these observations. C57Bl mice did not develop radiation pneumonitis but appeared to be equally responsive to later radiation-induced increases in lung density. The results obtained from CT-derived densitometry compared well with measurements gained from functional and survival endpoints. X-ray CT provides a sensitive and informative technique for assessing the extent of radiation injury to the mouse lung and is potentially useful for quantifying the counterpart in patients.

[Indices of external respiration in patients with Hodgkin's disease long after irradiation of the mediastinum]

The function of the respiratory organs using the results of ventilation, gas exchange and roentgenopneumopolygraphy, was analysed in 98 Hodgkin's disease patients in a state of a prolonged remission (5-12 yrs.) after radiation therapy of the mediastinum. Pulmonary ventilation disorders were revealed in 43.9% of the patients. The degree of ventilation disorders depended on the degree of expression of radiation fibrosis in the paramediastinal regions of the lungs. Usually there were no clinical signs of the revealed changes.

Effects of doxapram on body temperature of the rat during radiofrequency irradiation

Central nervous system stimulants can cause changes in body temperature and changes in susceptibility to high levels of radiofrequency radiation (RFR). In the present study, the effects of the central nervous system stimulant, doxapram, on thermal responses to 2.8 GHz pulsed RFR were examined in anaesthetized rats. During intermittent exposure to an average power density of 60 mW/cm2, doxapram significantly increased the time required for temperature to return to the pre-exposure level when irradiation was discontinued. When exposure was continued until lethal temperatures resulted, doxapram administration caused no significant change in survival time when compared to saline controls. Thus, although the drug decreased thermoregulatory efficiency during intermittent exposure to RFR, no change in susceptibility to terminal RFR exposure was observed.

The effect of sudden solar exposure on thermophysiological parameters and on plasma prolactin and cortisol concentrations in male Creole goats

Rectal temperature (RT), respiratory rhythm (RR), plasma cortisol and prolactin (PRL) levels and haematocrit were measured at noon in male Creole goats during their habituation to shade, during sudden exposure to sunlight and then while they were kept outdoors. Data on the microclimatic environment, especially black-globe temperature (Tg), were recorded. On the day (DO) the bucks were put in the sun, the increase of RT and RR, characteristic of circadian rhythm, was amplified (RT: 40.84 +/- 0,23 degrees C vs 39.48 +/- 0.19 degrees C P less than 0.001; RR: 98 +/- 22 vs 35 +/- 3 respirations/min; P less than 0.01). Plasma cortisol also increased (17.7 +/- 8.6 vs 5.57 +/- 1.7 ng/ml; P less than 0.05). After 24 h (D1), plasma prolactin concentration increased dramatically (923 +/- 653 vs 90 +/- 22 ng/ml; P less than 0.05) and haematocrit decreased (28.6 +/- 2.3 vs 33 +/- 2.3%; P less than 0.05). To clarify the simultaneous effects of time (t) and Tg, we developed a model Log-normal on t and linear on Tg for RR and PRL. A model decreasing exponentially with t and linear with Tg was developed for RT; the determination coefficients were R2 = 0.96, 0.75 and 0.59, respectively. About 3 weeks later, after the adaptation period, RT, RR and plasma PRL stabilized; RT and RR returned to shade values while the PRL level remained higher than the shade PRL level (248 +/- 109 vs 130 +/- 50 ng/ml; P less than 0.05). The 24-hour time-lag in prolactin hypersecretion and the role of prolactin in thermoregulation are discussed.

Heart rate changes due to 5.6-GHz radiofrequency radiation: relation to average power density

Effects of intermittent exposure to 5.6-GHz radiofrequency radiation (RFR) on heart rate, blood pressure, and respiratory rate were examined in anesthetized rats. During exposure to 60 mW/cm2 which resulted in a 1 degree C change in colonic temperature, heart rate increased; the values returned to control levels after exposure was discontinued. No changes in mean arterial blood pressure or in respiratory rate were observed. Exposure to 30 mW/cm2 caused no significant changes in heart rate, blood pressure, or respiratory rate. The data indicate that heart rate changes during exposure to 5.6-GHz RFR are related to the average power density applied, and thus to the rate of change in temperature, and not simply to the absolute change in temperature.

Effect of ionizing radiation on physiological function in the anesthetized rat

Exposure of pentobarbital-anesthetized rats to 14.5-MeV electrons results in radiation-induced physiological dysfunction. Responses include transient hypotension, a transient decrease in heart rate, respiratory dysrhythmias, and a prolonged increase in pulse pressure. Magnitudes of these responses are dose related, and maximal responses can be elicited by either whole- or partial-body (head or abdominal) exposure to 10,000 rad. These responses were associated with a fivefold increase in arterial plasma concentration of epinephrine, whereas histamine, norepinephrine, and beta-endorphin did not change during the first minute after the onset of exposure. Administration of diphenhydramine, a histamine receptor antagonist, resulted in a significant decline of baseline cardiovascular function and inhibited radiation-induced cardiovascular dysfunction. The diphenhydramine-induced decrease in preexposure blood pressure was reversed by angiotensin infusion, but this procedure failed to restore the mechanism(s) responsible for the cardiovascular responses to radiation. Results of these experiments and information available in the literature support the hypothesis that these responses are due to an interference in the autonomic pathways that modulate cardiovascular function.

Ventilatory frequency of mouse and hamster during microwave-induced heat exposure

Ventilatory frequency was recorded in unrestrained mice and hamsters using microwave radiation. The microwave exposure system was also used to impact varying heat loads to the rodents at ambient temperatures of 10, 20 and 30 degrees C. The absorbed heat load accrued from microwave exposure was measured as the time-averaged rate of energy absorption per unit body weight or specific absorption rate (SAR, W/kg). In both species there was an inverse relationship between ambient temperature (Ta) and threshold SAR to invoke an increase in ventilatory frequency. However, the threshold SAR's for mice were 270 to 450% higher than for hamsters depending on Ta. Above threshold SAR the increase in ventilatory frequency per unit elevation in SAR increased directly with Ta in mice but not with hamsters. On the basis of rate of absorbed energy normalized to body weight (i.e., W/kg), mice can tolerate much more heat from microwave exposure than hamsters. The differences in sensitivity to microwave exposure in the mouse and hamster are probably attributable to species-specific characteristics, and especially differences in body mass and, consequently, passive heat loss.

Identification of medullary loci critical for neurogenesis of gasping

We hypothesized that a discrete medullary locus, critical for gasping neurogenesis, could be identified. In decerebrate, cerebellectomized, vagotomized, paralyzed, and ventilated cats, activities of phrenic, hypoglossal, and recurrent laryngeal nerves were monitored. Gasping was induced by freezing the brain stem, via a fork thermode, at the pontomedullary junction. By reversible cooling of the medulla, chemical lesions with kainic acid, and radio-frequency lesions, a critical area for gasping neurogenesis was localized bilaterally 2-3 mm rostral to obex, 2.0-2.5 mm lateral to midline, and 3-4 mm ventral to medullary surface. Electrical stimulation in this area elicited premature gasps, whereas unilateral lesions or lidocaine injections eliminated gasping activities in all nerves. These procedures did not cause similar changes during eupnea. In apneusis, however, lidocaine injections markedly altered the pattern or caused apnea. We conclude that discharge of neurons in a discrete portion of the lateral tegmental field of medulla is required for gasping neurogenesis. Our results are consistent with these neurons comprising the central pattern generator for gasping.

The expression of early and late damage after thoracic irradiation: a comparison between CBA and C57B1 mice

Lung injury after localized irradiation of the thorax was quantified and compared in CBA and C57B1 mice. Using lethality and breathing rate as end points, two phases of damage separated in time were distinguished in CBA mice as an early pneumonitic phase and a later phase associated with pleural effusions. C57B1 mice failed to show the pneumonitic response over a large dose range extending beyond 20 Gy. In this respect they differ from most other mouse strains so far studied. At the lower doses the extent of the late phase was similar between these two strains. The interstrain comparison presented suggests that damage to separate tissue compartments was responsible for the acute and chronic responses.

Recommendations for using the standardized terminology of respiratory physiology in radiation research

A succinct review of the terminology and of correlations between basic quantities in respiration physiology is given with special regard to oxygen as the gas of topical interest in radiation research and tumor pathophysiology. The role of the oxygen partial pressure gradient as the driving force of O2 diffusion is emphasized. It is generally recommended that the O2 partial pressure be considered when investigating oxygen diffusion and distribution problems. During those studies the physical boundary conditions, in particular the temperature, the barometric pressure, and the water vapor saturation, have to be considered and should be indicated. During equilibration of suspensions containing oxygen-consuming sites the impact of geometry and fluid agitation on the efficiency of gas exchange has to be taken into account. Reviews on solutions of diffusion equations, on numerical data for relevant constants to be considered, and on terminology and units in respiration physiology are included.

Behavioral and autonomic thermoregulation in mice exposed to microwave radiation

Preferred ambient temperature (Ta) and breathing rate were measured in free-moving mice exposed to 2,450-MHz microwaves. A waveguide-exposure system was imposed with a longitudinal temperature gradient that permitted mice to select their preferred Ta. Breathing rate was determined by analyzing the rhythmic shifts in microwave energy not absorbed by the animal. Without microwave exposure mice selected an average Ta of 31 degrees C. This preferred Ta did not change until the specific absorption rate (SAR) at 2,450 MHz exceeded approximately 7.0 W X kg-1. Mice maintained their breathing rate near baseline levels by selecting a cooler Ta during microwave exposure. In contrast, mice maintained at 31 degrees C underwent a sharp increase in breathing rate when SAR exceeded approximately 7.0 W X kg-1. Mice exposed to microwaves in a waveguide with a temperature gradient increased breathing rate 0.6 breaths/min per unit increase in SAR, whereas without the temperature gradient breathing rate increased by 9.6 breaths/min per unit increase in SAR. Data from this study support previous studies that have shown behavioral thermoregulation is more effective (or efficient) in minimizing a thermal load than autonomic thermoregulation.

[Effects of mantle-field irradiation and chemotherapy on respiratory function (author's transl)]

In 15 patients with mediastinal Hodgkin's disease treated with chemotherapy followed by mantle-field irradiation respiratory function tests performed before and after irradiation showed a decrease in vital capacity and FEV1 as compared with pretreatment values. The decrease was maximum at 4 months and regressed over one year. No significant changes were observed in blood gas measurements. Respiratory symptoms, which were frequent after irradiation, almost completely disappeared within one year. The therapeutic combination had no cumulative adverse effect on respiratory function.