Biomedical subjects

B W Nelson

Publications and source records attributed to B W Nelson.

10 recordsLinked to original sources

PubMed2005

Tree allometry and improved estimation of carbon stocks and balance in tropical forests.

Tropical forests hold large stores of carbon, yet uncertainty remains regarding their quantitative contribution to the global carbon cycle. One approach to quantifying carbon biomass stores consists in inferring changes from long-term forest inventory plots. Regression models are used to convert inventory data into an estimate of aboveground biomass (AGB). We provide a critical reassessment of the quality and the robustness of these models across tropical forest types, using a large dataset of 2,410 trees >or= 5 cm diameter, directly harvested in 27 study sites across the tropics. Proportional relationships between aboveground biomass and the product of wood density, trunk cross-sectional area, and total height are constructed. We also develop a regression model involving wood density and stem diameter only. Our models were tested for secondary and old-growth forests, for dry, moist and wet forests, for lowland and montane forests, and for mangrove forests. The most important predictors of AGB of a tree were, in decreasing order of importance, its trunk diameter, wood specific gravity, total height, and forest type (dry, moist, or wet). Overestimates prevailed, giving a bias of 0.5-6.5% when errors were averaged across all stands. Our regression models can be used reliably to predict aboveground tree biomass across a broad range of tropical forests. Because they are based on an unprecedented dataset, these models should improve the quality of tropical biomass estimates, and bring consensus about the contribution of the tropical forest biome and tropical deforestation to the global carbon cycle.

Biomass↗

PubMed2001

Sediment dynamics in Rangoon river, Myanmar.

The behavior of fine-grained sediment in Rangoon River depends on seasonal variations in freshwater discharge and tidal amplitudes that range from 2 to 5 m. During the monsoon, freshwater with sediment concentrations of 1 g/l, or less, causes unidirectional, seaward flow. In the dry season, salinities reach 20% and sediment concentrations rise to 6 g/l. The saline intrusion advects large quantities of sediment landward from seaward sources. Near-surface sediment concentrations are very low during neap tides, while a layer of 'fluid mud' rests on the bottom. Current speeds greater than 0.2 m/s are needed to entrain sediment into the upper layer. Layered suspensions occur most commonly during decelerating phases of tidal flow and are dispersed by rapidly accelerating flow. When current speeds exceed 0.6 m/s, no 'fluid mud' forms, and sediment concentrations as great as 6-8 g/l extend through the water column.

Journal Article↗

PubMed1999

Can spinal surgery be prevented by aggressive strengthening exercises? A prospective study of cervical and lumbar patients.

OBJECTIVE: To determine if patients recommended for spinal surgery can avoid the surgery through an aggressive strengthening program. SETTING: A privately owned clinic, staffed by physicians and physical therapists, that provides treatment for patients with neck and/or back pain. METHODS: Over a period of 2 1/2 years, consecutive patients referred to the clinic for evaluation and treatment were enrolled in the study if they (1) had a physician's recommendation for lumbar or cervical surgery, (2) had no medical condition preventing exercise, and (3) were willing to participate in the approximately 10-week outpatient program. Treatment consisted mainly of intensive, progressive resistance exercise of the isolated lumbar or cervical spine. Exercise was continued to failure, and patients were encouraged to work through their pain. Third-party payors in Minneapolis were surveyed for average costs. Average follow-up occurred 16 months after discharge. RESULTS: Forty-six of the 60 participants completed the program; 38 were available for follow-up and three required surgery after completing the program. DISCUSSION/CONCLUSIONS: Despite methodologic limitations, the results are intriguing. A large number of patients who had been told they needed surgery were able to avoid surgery in the short term by aggressive strengthening exercise. This study suggests the need to define precisely what constitutes "adequate conservative care."

Adult↗

PubMed1999

Low back strengthening for the prevention and treatment of low back pain.

PURPOSE: Chronic low back pain (CLBP) remains one of the most difficult and costly medical problems in the industrialized world. A review of nineteenth and early twentieth century spine rehabilitation shows that back disorders were commonly treated with aggressive and specific progressive resistance exercise (PRE). Despite a lack of scientific evidence to support their efficacy, therapeutic approaches to back rehabilitation over the past 30 yr have focused primarily upon passive care for symptom relief. Recent spine rehabilitation programs have returned to active reconditioning PRE centered around low back strengthening to restore normal musculoskeletal function. Research has shown that lumbar extension exercise using PRE significantly increases strength and decreases pain in CLBP patients. It appears that isolated lumbar extension exercise with the pelvis stabilized using specialized equipment elicits the most favorable improvements in low back strength, muscle cross-sectional area, and vertebral bone mineral density (BMD). These improvements occur with a low training volume of 1 set of 8 to 15 repetitions performed to volitional fatigue one time per week. CLBP patients participating in isolated lumbar extension PRE programs demonstrate significant reductions in pain and symptoms associated with improved muscle strength, endurance, and joint mobility. Improvements occur independent of diagnosis, are long-lasting, and appear to result in less re-utilization of the health care system than other more passive treatments. Low back strengthening shows promise for the reduction of industrial back injuries and associated costs.

Back Injuries↗

PubMed1995

The clinical effects of intensive, specific exercise on chronic low back pain: a controlled study of 895 consecutive patients with 1-year follow up.

Eight hundred ninety-five consecutive chronic low back pain patients were evaluated. Six hundred twenty-seven completed the program. One hundred sixty-one began, but dropped out, and 107 were recommended for treatment but did not undergo treatment for various reasons. Average duration of symptoms prior to evaluation was 26 months. Forty-seven percent of patients were workers' compensation patients. The primary treatment was intensive, specific exercise using firm pelvic stabilization to isolate and rehabilitate the lumbar spine musculature. Patients were encouraged to work hard to achieve specific goals. Seventy-six percent of patients completing the program had excellent or good results. At 1-year follow up 94% of patients with good or excellent results reported maintaining their improvement. Results in the control group were significantly poorer in all areas surveyed except employment.

Adolescent↗

PubMed1981