Forced oscillation measurements do not affect upper airway muscle tone or sleep in clinical studies.

Upper airway obstruction in the sleep apnoea/hypopnoea syndrome (SAHS) can be easily assessed by measuring respiratory impedance with the forced oscillation technique (FOT). This methodology has been proposed as a useful clinical tool both for the diagnosis of sleep breathing disorders and for continuous positive airway pressure (CPAP) titration. However, previous studies suggest that the application of high-frequency pressure oscillation to the upper airway may induce changes in the electroencephalogram (EEG) or upper airway muscle function. The effect of FOT measurements on upper airway muscle tone and EEG in clinical sleep studies was examined. Seven patients with moderate SAHS were included (age: 54+/-11 yrs; apnoea/hypopnoea index: 43+/-21 events x h(-1); body mass index: 30+/-2 kg x m(-2)). Genioglossus surface electromyogram activity (EMGgg) and EEG signal were analysed with and without FOT application (frequency: 5 Hz and 30 Hz; peak-to-peak pressure oscillation: 1 cmH2O) during stable sleep. Measurements were carried out in two different situations. Step 1: applying FOT during episodes of obstructive events or flow limitation; and step 2: during prolonged periods of normal breathing at optimal CPAP. The root mean square of EMGgg activity and fast Fourier analysis (alpha and delta bands) of the EEG signal were performed. The application of FOT did not increase EMGgg activity in any of the situations studied. In addition, no evidence of the effects on EEG was found: alpha/delta relationship: awake:0.70, baseline sleep:0.13, FOT(5 Hz):0.18, FOT(30 Hz):0.11. The presented results suggest that the use of forced oscillation technique over the ranges of frequency and amplitude proposed for clinical sleep studies does not induce changes in upper airway muscle activity and neurological variables in patients with sleep apnoea/hypopnoea syndrome.

[Correlation of protoporphyrin zinc with lead in blood in workers of the car batteries industry in Bogota, Colombia]. / Correlación de protoporfirina zinc y plomo en sangre en trabajadores de fábricas de baterías, de Bogotá, Colombia.

OBJECTIVE: To determine the usefulness of zinc protoporphyrin in blood (PPz) as an indicator of lead exposure in workers of the homemade car battery industry. MATERIAL AND METHODS: A cross-sectional study was performed in 116 workers of the car battery industry in Bogotá, Colombia. Data on general, occupational, and health variables were collected by interview. Two categories of PPz values were established: Those below the cutoff value (70 micrograms/dL) and those above it. A linear regression analysis was performed to measure the correlation between logarithm values of PPz (> 70 micrograms/dL) and lead in blood (PbB) (> 38 micrograms/dL). RESULTS: A semi-logarithmic correlation coefficient of r = 0.54 was found, and statistically significant associations between high levels of PPz and direct exposure to lead were observed (OR: 3.35, 95% IC 1.02-11.91; p: 0.02); for workers who often use lead as a raw material (OR: 7.80, 95% IC 2.96-21.03; p < 0.01), as well as for workers who do not change work clothes often (OR: 3.55, 95% IC 1.17-11.01; p < 0.01). CONCLUSIONS: PPz may be a useful diagnostic indicator for lead poisoning; it may also be used as a screening test for surveillance programs in the biological monitoring of workers exposed to lead.