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Biomedical subjects

M Verrier

Publications and source records attributed to M Verrier.

At least 19 recordsLinked to original sources
PubMed2005

Traffic related pollution and heart rate variability in a panel of elderly subjects.

BACKGROUND: Particulate air pollution has been associated with increased cardiovascular deaths and hospital admissions. To help understand the mechanisms, the types of particles most involved, and the types of persons most susceptible, the association between exposure to summertime air pollution and heart rate variability (HRV) was examined in a panel study of 28 elderly subjects. METHODS: Subjects were seen once a week for up to 12 weeks and HRV (SDNN, r-MSSD, PNN50, low frequency/high frequency ratio (LFHFR)) was measured for approximately 30 minutes at each session using a defined protocol. Temperature, day of the week, and hour of the day were controlled, and dummy variables for each subject were controlled for subject specific risk factors. RESULTS: PM2.5 was associated with r-MSSD (-10.1% change for an interquartile range (IQR) increase in exposure (95% CI -2.8 to -16.9)) and PNN50, but stronger associations were seen with black carbon, an indicator of traffic particles, which was also associated with SDNN (-4.6% per IQR (95% CI -2.0 to -7.2)) and LFHFR. Secondary particles were more weakly associated with r-MSSD, as was ozone. No associations were seen with SO2 or NO2. CO had similar patterns of association to black carbon, which disappeared after controlling for black carbon. Black carbon had a substantially higher effect on SDNN in subjects who had had a previous myocardial infarction (-12.7%, 95% CI -5.7 to -19.25). CONCLUSIONS: Particles, especially from traffic, are associated with disturbances of autonomic control of the heart.

Aged↗
PubMed2000

Ambient pollution and heart rate variability.

BACKGROUND: We investigated associations between ambient pollution levels and cardiovascular function in a repeated measures study including 163 observations on twenty-one 53- to 87-year-old active Boston residents observed up to 12 times from June to September 1997. Particles with aerodynamic diameter </=2.5 microm (PM(2.5)) were measured continuously using a tapered element oscillating microbalance. METHODS AND RESULTS: The protocol involved 25 minutes per week of continuous Holter ECG monitoring, including 5 minutes of rest, 5 minutes of standing, 5 minutes of exercise outdoors, 5 minutes of recovery, and 20 cycles of slow breathing. Heart rate variability (HRV) was assessed through time domain variables: the standard deviation of normal RR intervals (SDNN) and the square root of the mean of the squared differences between adjacent normal RR intervals (r-MSSD). Mean 4-hour PM(2.5) levels ranged from 3 to 49 microg/m(3); 1-hour ozone levels ranged from 1 to 77 ppb. In multivariate analyses, significantly less HRV (SDNN and r-MSSD) was associated with elevated PM(2.5). During slow breathing, a reduction in r-MSSD of 6.1 ms was associated with an interquartile (14.3 microg/m(3)) increase in PM(2.5) during the hour of and the 3 hours previous to the Holter session (P=0.006). During slow breathing, a multiple pollution model was associated with a reduction in r-MSSD of 5.4 ms (P=0.02) and 5.5 ms (P=0.03) for interquartile changes in PM(2.5) and ozone, respectively, resulting in a combined effect equivalent to a 33% reduction in the mean r-MSSD. CONCLUSIONS: Particle and ozone exposure may decrease vagal tone, resulting in reduced HRV.

Aged↗
PubMed1995

Proportional differences in births and infant mortality rates among the triethnic population in Texas from 1984 through 1986.

Birth at preterm gestation and/or with low birth weight is a major predictor of the infant mortality rate, which is twice as high in African-American as in Anglo and Hispanic infants in Texas. This study examined the relative proportions of Anglo, African-American, and Hispanic births that occurred in Texas at specific gestational ages and birth weights, and the neonatal, postneonatal, and infant mortality rates associated with those births. African-American infants showed a systematic tendency to be born at earlier gestational ages and with lower birth weights than did Anglo infants, while Hispanic-Anglo differences were limited to a small excess of preterm but not low weight Hispanic births. Preterm and low-birth-weight African-American infants had neonatal and infant mortality rates that were lower than those of Anglo infants, but that benefit was inadequate to compensate for the greater proportion of African-American births that were at risk. No consistent difference could be identified between Hispanic and Anglo infant mortality rates. We conclude that the birth weight and gestational age predictors of infant mortality reflect the combined effects of two ethnic-specific factors: the mortality rates at specific birth weights and gestational ages, and the proportions of births that are at risk. The biological and/or sociological causes for these ethnic differences in pregnancy outcomes and mortality risk need to be identified if the mortality rate of African-American infants in Texas is to be reduced.

Black or African American↗
PubMed1994

Patterns of infant mortality in relation to birth weight, gestational and maternal age, parity, and prenatal care in Texas' triethnic population, 1984 through 1986.

Neonatal, postneonatal, and infant mortality rates were determined in Texas' triethnic populations from 1984 through 1986 with relation to gestational age, birth weight, maternal age, parity, and prenatal care. All mortality rates were increased in the black population. Preterm birth and low birth weight were both strong predictors of mortality. The neonatal mortality rate of preterm black infants was actually lower than those of the other ethnic groups, but the increased proportion of black pregnancies that resulted in preterm and low-birth-weight births, together with their elevated postneonatal mortality rates, produced an infant mortality rate that was twice as high in black as in Anglo and Hispanic infants. The infant mortality rate was highest in infants born to mothers younger than 18 years, of high multiparity, and with inadequate or no prenatal care. Recognition of these associations should enable improved planning of care for all Texas women and their infants.

Adolescent↗
PubMed1993

Patterns of birth weight in relation to gestational age, maternal age, parity, and prenatal care in Texas' triethnic population, 1984 through 1986.

This study investigated the distribution of birth weights in Texas' triethnic populations for the years 1984 through 1986 (more than 900,000 births) with regard to gestational age, maternal age, parity, and visits for prenatal care. African-American infants had a systematic tendency to be born earlier and smaller than Anglo and Hispanic infants. Among the maternal age categories, mothers younger than 18 years had the highest rates of preterm birth (less than 37 completed weeks), very low birth weight (less than 1500 g), and low birth weight (less than 2500 g). High multiparity and inadequate visits for prenatal care were associated with increased rates for the same adverse pregnancy outcomes, and the risks were always much higher in African-American than in Anglo and Hispanic women of the same age, parity, and prenatal care categories. The predictive values of these associations for individual pregnancies were limited, but their recognition may improve the planning of prenatal care for Texas women and of the anticipatory care for their infants.

Adolescent↗
PubMed1984

Neurophysiological changes following traumatic spinal lesions in man.

Neurophysiological observations were made on normal subjects and on 57 patients who had had injuries to the spinal cord. The amplitude of the muscle compound action potential (M response) recorded from triceps surae in response to supramaximal stimulation of the tibial nerve was reduced in the patients indicating that there are changes in motor units below the level of a spinal lesion in man. In the patients who were clinically spastic it was found that: (1) The proportion of the triceps surae motoneuron pool reflexly activated either by tapping the Achilles tendon or by stimulating the tibial nerve just below the threshold of the alpha motoneuron axons (H reflex) was greater than in normal subjects. This can be explained by an increase in the excitability of central reflex pathways. (2) Vibration of the tendo Achilles depressed the H reflex less effectively than in normal subjects. This may indicate altered transmission in the premotoneuronal portion of the H reflex pathway. (3) The H reflex elicited 50 and 100 ms after a standardised conditioning stimulus to the tibial nerve and expressed as percentage of the unconditioned reflex was greater than in normal subjects. This could reflect a change in the excitability of motoneurons or of interneurons.

Adolescent↗
PubMed1983

Monoclonal antibodies against Met-enkephalin as probe in the central nervous system.

Peptides with transmitter-like properties have been found in many brain areas. Immunochemical techniques have contributed most to clarification of the function and the pathway of these substances in neuronal systems. In this paper we report the production of 4 monoclonal antibodies against Met-enkephalin and their use in studying this peptide in rat cervical cord. Two of the antibodies recognize the COOH-terminus part of the Met-enkephalin, and do not cross-react with other known peptides. The other two antibodies are mainly directed against the NH2-terminus part of the peptide. Specific interactions of these monoclonal antibodies with regions of rat cervical cord were shown by immunochemistry techniques.

Animals↗
PubMed1977

Diazepam effect on reflex activity in patients with complete spinal lesions and in those with other causes of spasticity.

The effects of diazepam on reflex pathways in patients having complete spinal lesions and in patients having incomplete lesions of the spinal cord or multiple sclerosis are compared to determine whether diazepam has an action at spinal level. The drug produced no significant alteration in the excitability of the monosynaptic arc in the patients with complete spinal lesions. In contrast, in the group with incomplete spinal lesions or multiple sclerosis, diazepam reduced the excitability of the monosynaptic arc. This action did not appear to result from a reduction in fusimotor drive. Diazepam also reduced the tonic vibration reflex in this group. It is postulated that these effects may be due to a supraspinal action of the drug.

Achilles Tendon↗
PubMed1976

Spinal reflexes and the concentrations of 5-HIAA, MHPG, and HVA in lumbar cereborspinal fluid after spinal lesions in man.

Descending bulbospinal pathways that employ specific neurotransmitter substances are known to be capable of modulating segmental reflex activity in the experimental animal. To determine whether this might also occur in man correlations have been sought between the activity in spinal reflex pathways and the lumbar cerebrospinal fluid (CSF) concentrations of 5-hydroxyindolacetic acid (5-HIAA), 3 methoxy-4-hydroxyphenylglycol (MHPG), and homovanillic acid (HVA) in 12 patients with complete or virtually complete spinal lesions. The concentrations of 5-HIAA and MHPG in lumbar CSF ARE REDUCED AFTER COMPLETE OR VIRTUALLY COMPLETE SPINAL LESIONS IN MAN. This may occur within 18 days of the lesion. MHPG concentrations appear to be inversely related to the level of the lesion. The HVA concentration in lumbar CSF is reduced when there is obstruction of the CSF pathways. No relationship could be demonstrated between the concentrations of 5-HIAA or MHPG in lumbar CSF and the activity in the spinal monosynaptic pathway (estimated from the proportion of the motoneurone pool activated by the Achilles tendon reflex or H reflex) or the activity of a spinal inhibitory mechanism (estimated by the degree of vibratory inhibition of the monosynaptic reflex). Patients with a tonic vibration reflex (TVR) tended to have higher MHPG levels. There appeared to be an association between low CSF HVA and enhanced vibratory inhibition of the monosynaptic reflex in the nine patients whose spinal lesions were complete.

Adolescent↗
PubMed1976

Neurophysiologic changes in hemiplegia. Possible explanation for the initial disparity between muscle tone and tendon reflexes.

In an attempt to clarify the neurophysiologic changes that may follow a cerebral lesion in man, we have studied patients with recent and with long-standing hemiplegia from cerebral infarction. In patients with recent cerebral lesions, inhibition of the monosynaptic reflex by vibration is enhanced. In patients with long-standing cerebral lesions, this inhibitory mechanism is less effective and a comparison of the electrically and mechanically induced monosynaptic reflexes suggests that fusimotor drive may be increased. Related clinical findings are reduced muscle "tone" immediately after the lesion and increased muscle "tone" and exaggerated tendon jerks in patients with long-standing hemiplegia.

Adult↗
PubMed1976

Effect of diazepam on muscle contraction in spasticity.

The direct effect of diazepam on skeletal muscle has been examined in 15 patients with neurological lesions resulting in spasticity. Diazepam 15-30 mg. IV reduced the amplitude of the compound action potential of the direct muscle response (M response) and the isometric twitch tension. It is postulated that diazepam may affect the contractile properties of muscle and, possibly, the electrical properties of the muscle membrane. These peripheral effects may contribute to the reported clinical benefits of the drug in patients with spasticity including those patients with complete spinal lesions.

Action Potentials↗