Positioning device for magnetically sensitive environments.

Presented in this short communication are design principles for the construction of a positioning apparatus for biological specimens in magnetically sensitive environments. An apparatus with 3 degrees of freedom was built and found to provide position accuracy to within +/- 0.25 mm throughout a cubic volume measuring 9 cm on each side.

A three-year cohort study of the role of environmental factors in the respiratory health of children in Hamilton, Ontario. Epidemiologic survey design, methods, and description of cohort.

The relative importance of the effect of outdoor environmental factors (suspended particulates, sulphur dioxide) and indoor environmental factors (parental smoking, gas cooking), on the respiratory health of children is still unclear. To answer these questions, a 3-yr cohort analytic study has been conducted in Hamilton, Ontario between 1978 and 1981. The prevalence of respiratory symptoms and indoor environmental factors was determined by an interviewer-administered questionnaire. Pulmonary function measures included both the forced expiratory maneuver and the single- and multiple-breath nitrogen washouts. Outdoor air quality was measured by a comprehensive network of suspended particulate and sulphur dioxide monitors. There were 3,345 children 7 to 10 yr of age studied in the first year, a response rate of 95.4%, 3,727 in the second year, and 3,168 in the third year; 75.6% of the initial cohort were studied in both Year 2 and Year 3. Comprehensive quality control in the study included measurement of the repeatability of both the questionnaire and pulmonary function data. Repeatability was acceptable except for variables derived from the single-breath nitrogen washout (correlation between initial and repeat closing volume vital capacity was 0.14). Cigarette smoking in Year 3 was reported in 4.8% of the children. The distribution of other covariables was not uniform, and the prevalence of parental smoking and gas cooking was greatest in the industrial area with the highest particulate pollution. Future analysis of these data will require the effect of these covariables to be distinguished from that caused by outdoor air pollution.

Respiratory function of children in homes insulated with urea formaldehyde foam insulation.

A study was carried out to assess the respiratory function of children living in homes insulated with urea formaldehyde foam insulation (UFFI). A large data base on the effect of environmental variables on the respiratory function of 3500 children in the Hamilton, Ont., area had been collected from 1978 to 1980. From this data base 29 children who lived in UFFI-insulated homes were identified, and each was matched with 2 controls according to nine variables that had been shown to be strongly predictive of respiratory function. Reported respiratory symptoms and results of pulmonary function testing in the year immediately following installation of UFFI were examined. No significant differences in any variable were found between the subjects and controls. A power calculation indicated that the study had adequate power to detect clinically important changes. The authors conclude that there was no evidence of respiratory problems resulting from UFFI in the sample studied.

Decay of inspiratory muscle pressure during expiration in anesthetized cats.

In six spontaneously breathing anesthetized cats (pentobarbital sodium, 35 mg/kg) we studied the antagonistic pressure developed by the inspiratory muscles during expiration (PmusI). This was accomplished in two ways: 1) with our previously reported method (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 52: 1266-1271, 1982) based on the measurement of changes in lung volume and airflow during spontaneous expiration, together with determination of the total passive respiratory system elastance and resistance; and 2) measurement of the time course of changes in tracheal/pressure after airway occlusion at end inspiration, up to the moment when the inspiratory muscles become completely relaxed. The agreement between the two methods is generally good, both in the amplitude of PmusI and in its time course. We also applied the first method to spontaneous expirations through added linear resistive loads. These did not alter the relative decay of PmusI. Thus in anesthetized cats the braking action of the inspiratory muscles does not decrease when expiratory resistive loads are added, i.e., when such braking is clearly not required.

Active impedance of respiratory system in anesthetized cats.

We have assessed the validity of the method of Siafakas et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 51: 109-121, 1981) for determining active elastance (E'rs) and flow resistance (R'rs) of the respiratory system. In six cats anesthetized with pentobarbital sodium we have measured flow, volume, and tracheal occlusion pressure during spontaneous breathing. This allowed us to compute E'rs and R'rs. From these data and the occlusion pressure wave we predicted the time course of volume during inspirations with added linear flow resistances (delta R). These were compared to the actual loaded inspirograms. The agreement was generally good, except for small predictable discrepancies with the highest delta R values, which could be attributed to decompression of thoracic gas. These results indicate that the approach of Siakafas et al. to determine E'rs and R'rs is valid. In addition, we have quantified the "terminal inhibition" of inspiratory activity, which occurs toward the end of unoccluded breaths (both loaded and unloaded).

Single-breath method for measurement of respiratory mechanics in anesthetized animals.

In six spontaneously breathing anesthetized cats (pentobarbital sodium, 35 mg/kg ip) airflow, changes in lung volume and tracheal pressure were measured. The airways were occluded at end inspiration (VT). During the ensuing period of apnea (Breuer-Hering inflation reflex), the animal relaxed the respiratory muscles and the passive compliance of the respiratory system (Crs) was computed by dividing VT by the tracheal pressure. While the animal was still relaxed, the airways were reopened, and during the ensuing relaxed expiration the volume-flow relationship was linear, the slope representing the time constant of the respiratory system: tau rs = Crs . Rrs, where Rrs is the flow resistance of the passive respiratory system. From the measured values of tau rs and Crs, Rrs was computed. With this information it was also possible to quantitate the antagonistic pressure developed by the inspiratory muscles during spontaneous expiration.

Exposure estimates in assessing helath effects of air pollution.

Air pollution has been associated with adverse health effects. Difficulties in interpreting studies of health effects of exposure to air pollution arise in estimating exposure. Until recently, studies of effects of air pollution have relied on pollution exposure measurements obtained from fixed location air pollution stations monitoring outside air (to evaluate compliance with air quality standards, rather than to examine population exposure). However, recent evidence suggests that there are substantial differences between air pollution levels measured at such sites and levels to which people are actually exposed, i.e. 'personal exposure'. The present study examines effects of ambient urban air pollution on persons suffering from asthma, healthy non-asthmatic subjects and school children (in 2 Canadian cities, Toronto and Hamilton). Air pollution exposure is being assessed by data obtained from: (1) conventional 'abatement' oriented fixed location air pollution monitoring stations, (2) an extensive 'population' oriented network, (3) inside and (4) outside structures (homes and schools) as well as (5) 'personal' air pollution samplers. The data indicate variability in these different estimates of exposure which have implications on health effects assessment.

Pulmonary mechanics during exercise in normal males.

A body plethysmograph adapted to contain the pedals of an electrically braked cycle ergometer was used to measure pulmonary mechanics during steady-state exercise in 12 normal male subjects aged 22-65 yr. During exercise there was a progressive increase in residual volume to 119% of the value at rest (P less than 0.01), but functional residual capacity and total lung capacity did not change. The maximum expiratory flow-volume (MEFV) curves did not change and flow rates during tidal breathing did not exceed the MEFV curve. Dynamic pulmonary compliance fell to 91.3% of the control value and static expiratory pulmonary compliance fell to 76.9% of the control value (P less than 0.05). Pulmonary resistance did not change during exercise. Transpulmonary pressure during tidal breathing was negative even at the highest power outputs. The fall in compliance may be due to an increase in pulmonary capillary blood volume. These results demonstrate the importance of measuring absolute thoracic gas volume and the elastic properties of the lung when comparing pulmonary mechanics at rest and during exercise.

Pulmonary mechanics during exercise in subjects with chronic airflow obstruction.

A body plethysmograph was used to measure pulmonary mechanics in six subjects with chronic airflow obstruction during steady states at rest and during exercise at 200 and 400 kpm . min-1. The mean forced expired volume in 1 s was 1.32 liters (39.2% predicted). The flow rates during tidal breathing reached the maximum expiratory flow-volume (MEFV) curve in all but one subject, and on exercise they all reached the MEFV curve. Total lung capacity did not change significantly, but functional residual capacity increased to 104% of the control value (P less than 0.05) and residual volume increased to 113.3% of the control value (P less than 0.02). The MEFV curves did not change and tidal flow rates in excess of th MEFV curve were not seen. Dynamic compliance fell with increasing exercise to 52.8% (P less than 0.01) and static expiratory pulmonary compliance to 90.2% of the control value. Transpulmonary pressures during tidal breathing when expiratory flow reached the MEFV curve increased to progressively higher values as the work load increased. At low work loads there were several subjects with negative transpulmonary pressure when maximum flow rates were present. In patients with chronic airflow obstruction, little change occurs during exercise in pulmonary mechanics; the tidal flow patterns are dominated by the expired flow-volume curve, which is not changed by exercise; maximum flow occurs in some patients when transpulmonary pressure is still negative.

The effect of helium on nasal resistance and nasal flows.

Nasal inspiratory resistance and maximal inspiratory nasal flow were measured in 10 normal subjects while they breathed air and while they breathed a mixture of 80% helium and 20% O2. After the less dense helium-O2 mixture, there was a nonsignificant increase in K1 (15 +/- 93%), a 56 +/- 20% decrease in K2 (P less than 0.001), and a 48 +/- 20% increase in maximal inspiratory nasal flow (P less than 0.001). This is consistent with the accepted concept that K1 represents resistance to laminar flow and K2, resistance to nonlaminar flow (turbulent flow and/or flow due to convective acceleration), and that nonlaminar air flow predominates in the nose.

Nasal airway inspiratory resistance.

The relationship between transnasal pressure and nasal flow is markedly curvilinear during tidal breathing in man, and there is poor agreement among the results of various methods used to define this characteristic with a single number. We used Rohrer's equation (P = K1 V + K2 V2), where P = pressure and V = flow, and calculated values for K1 and K2 from 474 nasal inspiratory pressure/flow curves obtained from 34 human subjects by a standard method of posterior rhinometry. Nasal airway inspiratory resistance at an air flow of 0.4 liter per sec (NAIR0.4) was also calculated. Rohrer's equation was found by regression analysis to fit each curve well (0.86 less than r less than 0.9999; mean, 0.983). There was a strong correlation between NAIR0.4 and K2: NAIR 0.4 = 0.91 K2 + 0.39 (r = 0.97). Nasal congestion induced in 7 normal subjects with histamine resulted in larger changes in K2 and NAIR0.4 than K1. Patients given an intranasal corticosteroid aerosol (beclomethasone dipropionate) in a double blind crossover trial showed symptomatic improvement in nasal congestion (P less than 0.01) and significant decreases in K2 (P less than 0.02) and NAIR 0.4 (P less than 0.05), but no change in K1 (P greater than 0.2).

Contribution of rib cage and abdomen-diaphragm to tidal volume during CO2 rebreathing.

In man, there is wide interindividual range in the tidal volume response to CO2. To determine which (rib cage or abdomen-diaphragm) compartment had a greater influence on this range, ventilatory response to CO2 was measured, using Read's method, in eight men and two women seated in a constant-pressure body plethysmograph. Rib cage and abdominal tidal volume was simultaneously measured using magnetometers. Correcting for body size, the tidal volume response of the abdominal compartment was similar in all subjects, whereas that of the rib cage was larger in subjects with high tidal volume response to CO2; a significant correlation was found (P less than 0.01). Rib cage volume displacement lagged behind abdominal in all subjects; phase lag was greatest in the subject with the lowest ventilatory response to CO2. These results suggest that, at high levels of ventilation, a larger volume displacement of the rib cage may reflect a more effective coupling of the diaphragm pressure generator to it or alternatively a reduction in its impedance relative to the abdominal compartment.

Effect of curare on maximum static PV relationships of the respiratory system.

The effect of respiratory muscle weakness on the maximum static pressure-volume (PV) characteristics of the respiratory system was studied in four healthy males infused slowly with d-tubocurarine (dtc). Inspiratory capacity (IC), expiratory reserve volume (ERV), maximum static inspiratory and expiratory mouth pressures at four lung volumes, and handgrip were measured during induction of, and recovery from muscle weakness. The maximum effect of dtc varied among the muscle groups tested; peripheral muscles were most severely affected, expiratory muscles moderately, and inspiratory muscles least affected. At each level of weakness studied, decreases of IC and ERV were proportional to decreases of maximum static mouth pressures. Vital capacity, measured at each level of weakness was much less than values predicted from the static mechanical properties of the respiratory system. Our findings suggest that the marked change in the extremes of lung volume during submaximal neuromuscular blockade (SMNB) is due, in part, to unequal distribution of muscle weakness, reflected by decreased ability to change ribcage dimensions even at modest levels of SMNB.

Effects of ozone exposure in Canadians and Southern Californians. Evidence for adaptation?

Comparison of published reports on physiological effects of exposure to ozone (O3) suggests that Canadians are more reactive than southern Californians. Responses of subjects and experimental methods were compared in a cooperative investigation of this apparent difference in reactivity. Four Canadians and four Californians were exposed to 0.37 ppm O3 in purified air at 21 degrees C and 50% relative humidity for 2 hours with intermittent light exercise. Exposures to purified air alone served as controls. Responses of subjects were similar to those observed previously: Canadians on the average showed greater clinical and physiological reactivity to exposure than did Californians, who were no more than minimally reactive. Canadians also showed larger increases in erythrocyte fragility following exposure. No methodological differences sufficient to explain different results of previous studies were found. Although other possible explanations have not been ruled out entirely, adaptation of southern Californians to chronic ambient O3 exposure is a rational hypothesis to explain these results.

Changes in lung mechanics induced by acute isocapnic hypoxia.

We measured lung mechanics in seven healthy males during acute isocapnic hypoxia (PAO2 = 40-50 Torr; PACO2 = 38-42 Torr). Hypoxia was accompanied by increases in total lung capacity (mean increase +/- SD; 0.40 +/- 0.24 liters; P less than 0.005) functional residual capacity (0.34 +/- 0.25 liters; P less than 0.01) and residual volume (0.56 +/- 0.44 liters; P less than 0.02) in all subjects. Specific conductance of the lung decreased during hypoxia (P less than 0.02). The static deflation pressure-volume curve of the lung was shifted upward during hypoxia in all subjects. Resting end-expiratory recoil pressure of the lung was slightly, but not significantly lower during hypoxtic expiratory lung compliance was greater during hypoxia (0.39 +/- 0.04 l/cmH2O) than control measurements (0.31 +/- 0.05 l/cmH2O; P less than 0.005). No change was noted in dynamic lung compliance. All changes in lung mechanics were reversed within three minutes of reoxygenation. We conclude that acute isocapnic hypoxia increases total lung capacity in man and suggest that this may be due to the effect of hypoxia on the airways and pulmonary circulation.