Environmental and occupational exposure to metals (manganese, mercury, iron) and Parkinson's disease in low and middle-income countries: a narrative review.

OBJECTIVES: We designed and conducted a narrative review consistent with the PRISMA guidelines (PROSPERO registration number: CRD42018099498) to evaluate the association between environmental metals (manganese, mercury, iron) and Parkinson's Disease (PD) in low and middle-income countries (LMIC). METHODS: Data sources: A total of 19 databases were screened, and 2,048 references were gathered. Study selection: Randomized controlled trials, cluster trials, cohort studies, case-control studies, nested case-control studies, ecological studies, cross-sectional studies, case series, and case reports carried out in human adults of LMIC, in which the association between at least one of these three metals and the primary outcome were reported. Data extraction: We extracted qualitative and quantitative data. The primary outcome was PD cases, defined by clinical criteria. A qualitative analysis was conducted. RESULTS: Fourteen observational studies fulfilled the selection criteria. Considerable variation was observed between these studies' methodologies for the measurement of metal exposure and outcome assessment. A fraction of studies suggested an association between the exposure and primary outcome; nevertheless, these findings should be weighted and appraised on the studies' design and its implementation limitations, flaws, and implications. CONCLUSIONS: Further research is required to confirm a potential risk of metal exposure and its relationship to PD. To our awareness, this is the first attempt to evaluate the association between environmental and occupational exposure to metals and PD in LMIC settings using the social determinants of health as a framework.

[Effect of muscle contraction on heart rate and skin blood flow. Preliminary results]. / Efecto de la contracción muscular en la frecuencia cardiaca y en el flujo sanguíneo cutáneo. Resultados preliminares.

Evaluation of heart rate variability is an important tool to study several diseases. The most important tests include the variability of the heart rate as a function of time and as function of frequency, variability of blood pressure and pulsatile cutaneous blood flow (PCBF). We studied the effect of a sustained contraction of the quadriceps muscle on the instantaneous heart rate and pulsatile cutaneous blood flow in 10 healthy subjects. We measured the R-R interval and the instantaneous heart rate, in the time domain, 10 beats before the contraction, the R-R interval that coincided with the onset of the contraction, and the 30 R-R intervals after the beginning of the contraction. To measure the PCBF we used a photopletismograph designed for this purpose. We recorded the surface electromyographic activity (EMG) of the quadriceps muscle to determine the onset and end of the muscle contraction, and measured respiratory movements with a belt. We found an increase of the instantaneous heart rate at the first and second beats after the onset of the contraction. There was a decrease of the pulsatile cutaneous blood flow of the finger pad immediately after the contraction, which lasted for approximately eight beats. The findings support the idea of a central command and co-activation of the motor and sympathetic nervous systems. This efferent sympathetic activity seems to act not just on the contracting muscle but also on the heart and the cutaneous blood vessels of the extremities. These findings imply that it is quite likely that the sympathetic efferent effect has a supraspinal origin. This is a test that could be used to study cardiovascular control by the sympathetic nervous system.

Efecto de la contracción muscular en la frecuencia cardiaca y en el flujo sanguÝneo cutßneo / Resultados preliminares. Effect of muscle contraction on heart rate and skin blood flow. Preliminary results

Evaluation of heart rate variability is an important tool to study several diseases. The most important tests include the variability of the heart rate as a function of time and as function of frequency, variability of blood pressure and pulsatile cutaneous blood flow (PCBF). We studied the effect of a sustained contraction of the quadriceps muscle on the instantaneous heart rate and pulsatile cutaneous blood flow in 10 healthy subjects. We measured the R-R interval and the instantaneous heart rate, in the time domain, 10 beats before the contraction, the R-R interval that coincided with the onset of the contraction, and the 30 R-R intervals after the beginning of the contraction. To measure the PCBF we used a photopletismograph designed for this purpose. We recorded the surface electromyographic activity (EMG) of the quadriceps muscle to determine the onset and end of the muscle contraction, and measured respiratory movements with a belt. We found an increase of the instantaneous heart rate at the first and second beats after the onset of the contraction. There was a decrease of the pulsatile cutaneous blood flow of the finger pad immediately after the contraction, which lasted for approximately eight beats. The findings support the idea of a central command and co-activation of the motor and sympathetic nervous systems. This efferent sympathetic activity seems to act not just on the contracting muscle but also on the heart and the cutaneous blood vessels of the extremities. These findings imply that it is quite likely that the sympathetic efferent effect has a supraspinal origin. This is a test that could be used to study cardiovascular control by the sympathetic nervous system.