Educational intervention among farmers in a community health care setting.

BACKGROUND: Farmers are at increased risk of developing work-related respiratory diseases including asthma, but little is known about their occupational health and safety (OHS) knowledge and exposure prevention practices. Educational interventions may improve knowledge and practice related to prevention. AIMS: To determine the feasibility of an educational intervention for farmers in a community health centre setting. METHODS: This was a pilot study. Farmers were recruited by the community health centre and completed a questionnaire on symptoms, OHS knowledge and exposure prevention practices. The intervention group received education on work-related asthma and exposure control strategies, and was offered spirometry and respirator fit testing. All subjects were asked to repeat the questionnaire 6 months later. RESULTS: There were 68 study participants of whom 38 formed the intervention group. At baseline, almost 60% of farmers reported having received OHS training and were familiar with material safety data sheets (MSDSs); fewer (approximately 40%) reported knowledge of OHS legislation and availability of MSDSs. Approximately, two-thirds of subjects reported using respiratory protection. The response rate for repeating the questionnaire was 76% in the intervention group and 77% in the controls. Among the intervention subjects, statistically significant increases were observed in reported safety training, familiarity and availability of MSDSs and knowledge of OHS legislation. CONCLUSIONS: Gaps in OHS knowledge were observed. The educational intervention on OHS knowledge and exposure prevention practices in the community health centre setting was feasible. Larger, more-controlled studies should be undertaken as this study suggests a positive effect on OHS knowledge and prevention practices.

Detection of excessive bronchoconstriction in asthma.

Airway hyperresponsiveness is easily assessed by measuring the concentration or dose of an inhaled agonist that produces a defined response, e.g., PC20 or PD20. However, this measure does not assess excessive bronchoconstriction. We report the results of analyzing bronchial dose-response curves by measuring percent fall in vital capacity (delta FVC%) as the response rather than the PC20. In our analysis, delta FVC% was measured at the PC20, and therefore it was the dependent variable, whereas the concentration of agonist was the independent variable, in contrast to the usual bronchoprovocation tests in which the response is the independent variable and the dose is the dependent variable. We reasoned that a dose-dependent increase in gas trapping with histamine would detect excessive bronchoconstriction as a decrease in FVC; in contrast, PC20 measures only the ease of bronchoconstriction. In 10 patients with mild asthma the reproducibility of delta FVC% when FEV1 fell by 20%, i.e., at the PC20 concentration of histamine, taken from a greater than 6-s FVC on an otherwise standard histamine challenge test was comparable to that of PC20. In 10 healthy asymptomatic subjects there were only trivial falls (0.3%) in FVC to as much as 16 mg/ml histamine. In a retrospective study of 146 patients with mild asthma, the delta FVC% was normally distributed (13.2 +/- 5.5 SD%) and did not correlate with the number of beta 2-agonist prescriptions or the PC20, but it did correlate with the number of prescriptions written per month for oral prednisone (r = 0.55, p < 0.02). We conclude that delta FVC% when FEV1 falls by 20% is a safe method of detecting excessive bronchoconstriction, and it reveals that different asthmatics react in fundamentally different ways to the same agonist. This may be useful in detecting the asthmatic at risk for serious disease.

Breathlessness during induced lung hyperinflation in asthma: the role of the inspiratory threshold load.

The effects of the inspiratory threshold load (ITL) on breathlessness and ventilatory mechanics during acute bronchoconstriction were studied by comparing responses to continuous positive airway pressure (CPAP) and inspiratory positive airway pressure (IPAP) in 12 asthmatic subjects after methacholine bronchoprovocation to a maximum change (delta) in FEV1 of 50%. At maximum response, "optimal CPAP" (CPAPOPT) was selected as the level of CPAP providing maximum subjective improvement in breathlessness. Spirometry, breathing pattern, esophageal pressure (Pes), and operational lung volumes were monitored. At maximum response, FEV1 decreased by 54 +/- 3% (mean +/- SEM) (p < 0.001), dynamic end-expiratory volume (EELVdyn) increased 66 +/- 8%, by 1.4 +/- 0.2 L (p < 0.001), and subjects reported severe breathlessness (Borg Scale = 5.6 +/- 0.8). CPAPOPT (5.3 +/- 0.6 cm H2O) significantly (p < 0.001) reduced breathlessness (delta Borg Scale = -3.0 +/- 0.5) and did not cause further dynamic hyperinflation. CPAPOPT reduced peak inspiratory Pes by 27% (p < 0.001), the tension-time index (TTI) for the inspiratory muscles by 27% (p < 0.01), and the inspiratory work rate per liter of ventilation by 14% (p < 0.05). During CPAPOPT, the delivered extrinsic positive end-expiratory pressure (PEEPe) (6.4 +/- 0.4 cm H2O) was strongly related (p < 0.001) to the measured ITL (6.9 +/- 1.0 cm H2O) at maximum response. Responses to IPAP of the same magnitude as CPAP OPT at maximum response were similar to those during CPAPOPT, except that IPAP did not counteract ITL or reduce breathlessness.(ABSTRACT TRUNCATED AT 250 WORDS)

Maximal airway narrowing in a general population.

To characterize airway responses in a population sample, respiratory symptoms, smoking habits, and changes in FEV1 (delta FEV1) to inhaled methacholine (maximal cumulative dose of 196 mumol or maximal decrease in FEV1 of 50%) were recorded in 201 subjects. From each dose-response curve the plateau (delta FEV1 less than or equal to 5% over two or more dose steps) response, the maximal response (average of responses on the plateau or maximal delta FEV1 when no plateau was present), slope, and PD20 (dose required to cause delta FEV1 greater than 20%) were derived. The pattern of dose-response curves was a continuous change from being flat (maximal delta FEV1 less than or equal to 5%), becoming steeper with a plateau that occurred at a greater change in FEV1 as the curves were shifted more to the left, to being the steepest without a plateau response. Maximal delta FEV1 was significantly related to the PD20 (r = -0.64, p less than 0.001) and the slope (r = 0.63, p less than 0.001). A history of doctor-diagnosed asthma or wheeze in the last 12 months was related to the level of the maximal delta FEV1 and to PD20. Likelihood ratios [LR = sensitivity/(1-specificity)] for asthma or wheeze were higher for a maximal delta FEV1 of 50% plus a PD20 of 4 mumol (LR = 6.5) or 1 mumol (LR = 7) than for either alone. Subjects without reported asthma or wheeze more often had a plateau on the dose-response curve (76%) than those with a positive history (49%, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)