Enhancement of ozone-induced lung injury by exercise.

Rats were exposed for up to 3.75 h to 0.20-0.80 ppm O3 under conditions of rest and treadmill exercise up to 30 m/min, 20% grade, to assess the importance of exposure duration, O3 concentration, and exercise on lung tissue injury. Focal lung parenchymal lesions increased in abundance and severity in response to the three variables; however, exercise was the most important. Lesion response to exercise was greater than that predicted by a simple proportion to estimated effective dose of O3. The results emphasize the importance of including exercise in assessment of possible adverse health effects of exposure to airborne pollutants.

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.

Occupation related fire fighter hearing loss.

A noise exposure survey and audiometric assessment of 750 Los Angeles City fire fighters carried out to study the impact of fire service noise exposure on fire fighter hearing loss revealed evidence of excess hearing loss at the 3000Hz, 4000Hz, and 6000Hz test frequencies. Fire fighter medical history and life-style data did not point to a significant impact of hobbies and diseases on hearing threshold changes. The hearing loss observed at the test frequencies was, in relation to age, in excess of a general national population. This increased hearing loss with age for fire fighters suggests occupational overexposure to noise. A hearing conservation program for the fire service is therefore recommended.

Dynamics of ventilatory response to exercise in humans.

The dynamics of the ventilatory response to moderate exercise on a bicycle ergometer have been studied in humans. The work load was varied between 25 and 100 W as a pseudorandom binary sequence (PRBS) that enabled the impulse responses to be calculated by cross-correlation techniques. The response of all five subjects exhibited a bimodal response, i.e., a fast component that was followed after a delay by a slow component. The fast component accounted for a relatively small proportion of the total response. Also, it was demonstrated that to identify the rapid component it was necessary to excite the respiratory system with an input containing highfrequency components; this result was used to reconcile the findings from this study with those of previous investigation.

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.

Arterial PCO2 response to intravenous CO2 in awake dogs unencumbered by external breathing apparatus.

The steady-state arterial CO2 tension (PaCO2) was examined during control and intravenous CO2 loading in awake dogs unencumbered by any breathing apparatus. The dogs inhaled air while undergoing intravenous CO2 loading, and we estimated the gain, delta VA/delta PACO2. CO2 was introduced into the systemic venous blood via a membrane gas exchanger in a femoral arteriovenous shunt circuit, and the extracorporeal blood flow was maintained constant at 0.5 l/min. A total of 11 experiments were performed in 3 dogs comprising 93 control observations and 83 CO2 loading observations. Intravenous CO2 produced a significant increase in the steady state PaCO2, a finding consistent with our previous study in tracheostomized awake dogs. We conclude that intravenous CO2 produces hypercapnia in the awake dog with an intact airway unencumbered by external respiratory apparatus.

Fire fighter noise exposure.

Occupational noise exposure was evaluated for eight fire fighter positions on board three types of emergency vehicles. One hundred seventy code-3responses were monitored and sound pressure levels in excess of 115 dBA found. Futhermore, sound pressures exceeding the OSHA allowable level of 90 dBA for eight hours exposure were determined. Octave band analyses were performed for overall code-3 noise and for specific noise sources on each vehicle. An evaluation of eighty-nine audiograms of fire fighters was also carried out. The findings of this study suggest that under present operational conditions fire fighters experience excessive short-duration, high intensity noise exposure and a hearing conservation program for the fire service is therefore recommended.

Safety limits for a firefighter proximity suit.

A standard one-piece firefighter proximity suit (jumpsuit style) was tested for heat accumulation and hood compartment ventilation. Large increases in temperature of the skin and hood compartmental air were recorded. Oxygen and carbon dioxide were monitored and hypoxic conditions found. Using the O2 and CO2 data, mathematical regression analyses were performed to predict the time exposures allowed for firemen entering various ambient atmospheric conditions. The short permissible exposure periods predicted for the proximity suit suggests limited usefulness and the need for immediate improvements in the design of the suit.

Respiratory responses to intravenous and intrapulmonary CO2 in awake dogs.

Ventilatory responses to CO2 inhalation and CO2 infusion were compared in the awake dog. The CO2 was introduced directly into the systemic venous blood via a membrane gas exchanger in a femoral arteriovenous shunt circuit, and the extracorporeal blood flow, QX, was maintained constant at one of two rates: low, 0.5 l/min; or high, 2.0 l/min. A total of 13 experiments was performed in four dogs comprising 50 control and 25 inhalation and infusion observations at each of the two flow rates. Comparison of CO2-response curve slopes, S = delta V E/delta PaCO2, between CO2 inhalation and infusion showed no significant difference either within or between flow rates. The mean value of S for all conditions was 1.88 l/min per Torr with a 95% confidence interval of 1.66 -2.14. An independent additive ventilatory drive amounting to 28% of low-flow control VE was found at the highflow rate. We conclude that at constant blood flow the responses to both CO2 inhalation and infusion are hypercapnic and not significantly different.

Radiotelemetry-based study of occupational heat stress in a steel factory.

Heat stress conditions prevailing in a steel factory were evaluated using a newly developed radiotelemetry system. This system was used as a station monitor for determining environmental temperature conditions and as a personal monitor to obtain data of worker physiological responses. Environmental information was used in calculating wet-bulb globe temperature heat stress index values. Physiological data were used in confirming safety limits. The study demonstrated the effectiveness of radiotelemetry in assessing occupational exposures to heat stress.

Pulse width to analog converter for a portable radio telemetry receiver.

A pulse width tracking system is described which converts a pulse width modulated telemetry signal into an analog signal. The converter, which is based on an integrated circuit chip design, contains a feedback feature that makes it ideal for high stability servo applications. The converter was designed as an integral part of a long-range radiotelemetry system used in occupational health field research.