CHRONIC otitis externa.

OBJECTIVES: Occupational exposure to dusts may result in chronic respiratory symptoms. METHODS: To investigate the utility of obtaining a history of occupational exposure to dust in US veterans, a respiratory health survey was conducted between 1988 and 1992 in a community-based cohort of US veterans in southeastern Massachusetts that were eligible for Veterans' Affairs (VA) healthcare benefits but were not regular users. A mail questionnaire was used to obtain a history of cough, phlegm, and wheeze, work in a dusty job, and duration, type, and intensity of dust exposure. Information on cigarette use and other possible confounders was obtained. RESULTS: In 2,617 white men, after the data had been adjusted for cigarette smoking, age, distance to the nearest major roadway, and chronic respiratory disease, the relative odds of chronic cough, chronic phlegm, and persistent wheeze attributable to occupational dust exposure was increased twofold. Risk also increased, based on exposure intensity. For heavy dust exposure the OR was 1.98 (95% CI 1.39-2.81) for chronic cough, 2.82 (95% CI 2.03-3.93) for chronic phlegm, and 2.70 (95% CI 1.95-3.75) for persistent wheeze. CONCLUSIONS: After active cigarette smoking and other possible confounders had been considered, it was found that dust exposure was related to respiratory symptoms in US veterans and that the greatest risk was attributable to heavy intensity exposure.

Chronic Disease↗

PubMed2004

Role of motoneurons in the generation of muscle spasms after spinal cord injury.

Motoneurons in the spinal cord have intrinsic voltage-dependent persistent inward currents (PICs; e.g. persistent calcium currents) that amplify synaptic inputs by three- to five-fold in addition to providing a sustained excitatory drive that allows motoneurons to fire repetitively following a brief synaptic excitation. In this study, we examined whether prolonged involuntary muscle spasms in subjects with long-term injury to the spinal cord are mediated by the activation of PICs in the motoneuron. To examine this in the human, we used a paired motor unit analysis technique where the firing frequency of one motor unit of the pair (control unit) was used to estimate the synaptic drive to the motoneuron pool, including the drive to a second higher-threshold motor unit of the pair (test unit). The degree to which a motoneuron PIC helped to sustain the discharge of a test motor unit (self-sustained firing) was determined from the reduction in control unit firing at de-recruitment (DeltaF) compared with recruitment of the test unit. This DeltaF value corresponds to the reduction in synaptic drive needed to counteract the intrinsic PIC and, thus, was used an indirect measure of this current. In the nine motor unit pairs studied, the average estimated synaptic drive, or control unit firing rate, required to recruit a test motor unit at the onset of a muscle spasm was significantly higher (by 43%) than the estimated synaptic drive during de-recruitment at the end of a muscle spasm. This indicated that a motoneuron PIC, and associated self-sustained firing, facilitated the firing of the test units during the prolonged muscle spasms. In addition, in all subjects tested (seven out of seven), we observed that following a muscle spasm or voluntary contraction, spontaneous and self-sustained firing of motor units could continue for many seconds, even minutes, at very low discharge rates (average 5.2 +/- 1.6 Hz) with extremely low spike-to-spike variability (coefficient of variation = 5.4 +/- 1.6%). Moreover, increases in synaptic drive (noise) to the spontaneously firing units with voluntary muscle contractions or muscle spasms increased both the mean firing rate of the motor units in addition to their firing variability. This suggests that the slow spontaneous firing commonly observed in chronic spinal injury likely occurs without appreciable synaptic noise and is likely driven to a substantial degree by PICs intrinsic to the motoneuron because it is self-sustained and very regular.

Chronic Disease↗