Response of soil respiration to changes in soil temperature and water table level in drained and restored peatlands of the southeastern United States.

BACKGROUND: Extensive drainage of peatlands in the southeastern United States coastal plain for the purposes of agriculture and timber harvesting has led to large releases of soil carbon as carbon dioxide (CO2) due to enhanced peat decomposition. Growth in mechanisms that provide financial incentives for reducing emissions from land use and land-use change could increase funding for hydrological restoration that reduces peat CO2 emissions from these ecosystems. Measuring soil respiration and physical drivers across a range of site characteristics and land use histories is valuable for understanding how CO2 emissions from peat decomposition may respond to raising water table levels. We combined measurements of total soil respiration, depth to water table from soil surface, and soil temperature from drained and restored peatlands at three locations in eastern North Carolina and one location in southeastern Virginia to investigate relationships among total soil respiration and physical drivers, and to develop models relating total soil respiration to parameters that can be easily measured and monitored in the field. RESULTS: Total soil respiration increased with deeper water tables and warmer soil temperatures in both drained and hydrologically restored peatlands. Variation in soil respiration was more strongly linked to soil temperature at drained (R2 = 0.57, p < 0.0001) than restored sites (R2 = 0.28, p < 0.0001). CONCLUSIONS: The results suggest that drainage amplifies the impact of warming temperatures on peat decomposition. Proxy measurements for estimation of CO2 emissions from peat decomposition represent a considerable cost reduction compared to direct soil flux measurements for land managers contemplating the potential climate impact of restoring drained peatland sites. Research can help to increase understanding of factors influencing variation in soil respiration in addition to physical variables such as depth to water table and soil temperature.

Plant nitrogen concentration and isotopic composition in residential lawns across seven US cities.

Human drivers are often proposed to be stronger than biophysical drivers in influencing ecosystem structure and function in highly urbanized areas. In residential land cover, private yards are influenced by individual homeowner preferences and actions while also experiencing large-scale human and biophysical drivers. We studied plant nitrogen (%N) and N stable isotopic composition (δ(15)N) in residential yards and paired native ecosystems in seven cities across the US that span major ecological biomes and climatic regions: Baltimore, Boston, Los Angeles, Miami, Minneapolis-St. Paul, Phoenix, and Salt Lake City. We found that residential lawns in three cities had enriched plant δ(15)N (P < 0.03) and in six cities higher plant N (%) relative to the associated native ecosystems (P < 0.05). Plant δ(15)N was progressively depleted across a gradient of urban density classes in Baltimore and Boston (P < 0.05). Lawn fertilization was associated with depleted plant δ(15)N in Boston and Los Angeles (P < 0.05), and organic fertilizer additions were associated with enriched plant δ(15)N in Los Angeles and Salt Lake City (P < 0.04). Plant δ(15)N was significantly enriched as a function of housing age in Baltimore (r (2) = 0.27, P < 0.02), Boston (r (2) = 0.27, P < 0.01), and Los Angeles (r (2) = 0.34, P < 0.01). These patterns in plant δ(15)N and plant N (%) across these cities suggests that N sources to lawns, as well as greater rates of N cycling combined with subsequent N losses, may be important drivers of plant N dynamics in lawn ecosystems at the national scale.

Recommendations for the management of irritable bowel syndrome in family practice. IBS Consensus Conference Participants.

To help family physicians manage patients with irritable bowel syndrome (IBS), a consensus conference was convened in June 1997 at which 5 internationally recognized experts in IBS presented position papers on selected topics previously circulated to the conference participants. Five working groups comprising family physicians, gastroenterologists and allied health care professionals from across Canada were then charged with developing recommendations for the diagnosis, patient education, psychosocial management, dietary advice and pharmacotherapy, respectively. An evidence-based approach was used where possible; otherwise, recommendations were made by consensus. The participants concluded that family physicians can make a positive diagnosis of IBS using symptom criteria. The pathophysiology is poorly understood, but motility and sensory disturbances appear to play a role. Neither psychological nor specific dietary factors cause IBS, but both can trigger symptoms. Drug therapy is not recommended for the routine treatment of IBS, but short-term trials of drug therapy may be targeted to predominant symptoms in selected patients. A step-wise, patient-centred approach to management is outlined.

Metabolism and excretion of zafirlukast in dogs, rats, and mice.

The in vivo metabolism and excretion of zafirlukast [Accolate; 4, 5-cyclopentoxycarbonylamino-3-[(2-methoxy-4,2- methylphenylsulfonylaminocarbonyl)phenylmethyl]-1-methylindole], a selective peptide leukotriene receptor agonist, were investigated in mice, rats, and dogs. Leukotrienes are a class of compounds that have been identified as being responsible for the contraction of human airway and lung vascular smooth muscle. A chemical agent that is effective in blocking the induced constricting actions of leukotrienes could be used to treat inflammatory processes in the pulmonary system. Zafirlukast has been shown to be clinically efficacious and has been approved for the treatment of asthma in humans. To determine the metabolic fate of zafirlukast, the radiolabeled compound was administered orally to mice, rats, and dogs and iv to rats and dogs. Plasma, urine, and feces samples were collected, assayed for radioactivity, and profiled for metabolites. Nearly all of the [14C]zafirlukast-derived radioactivity was excreted in the feces of the test species, indicating biliary clearance as the major route of elimination from the systemic circulation. The primary routes of metabolism in all species studied involved hydrolysis of the amide linkage at the 5-aminoindole position and hydroxylation at one or more sites. Additional metabolites were formed by N-acetylation (not in dogs), demethylation of the indole nitrogen, and N-desmethylation. Accolate is a registered trademark, property of Zeneca Ltd.

Asthma induced by cold air and its relation to nonspecific bronchial responsiveness to methacholine.

We compared bronchial responsiveness to isocapnic hyperventilation of cold dry air at -18 degrees C and 0% humidity with bronchial responsiveness to inhaled methacholine in 24 subjects with current or previous asthma and 2 nonasthmatics. Two inhalation tests with each agent were carried out in random order on 4 consecutive days. The response to cold air was expressed as the respiratory heat exchange required to reduce the FEV1 by 10% (PD10 RHE) and the response to methacholine as the provocation concentration required to reduce the FEV1 by 20% (PC20 methacholine). There was a close positive linear correlation between PD10 RHE and PC20 (r = 0.86, p less than 0.001). The responsiveness to each agent was highly reproducible. The PD10 RHE could be measured in all 21 subjects with current symptoms of asthma and it could be obtained by extrapolation in 2 normal subjects, but it could not be measured in 3 subjects with a past history of asthma. The PC20 in the current asthmatics was 6.3 mg/ml or less, in the 2 nonasthmatic subjects, it was 14 and 16 mg/ml, and in the previous asthmatics it was between 26 and 54 mg/ml. The results indicate that nonspecific bronchial responsiveness is an important factor influencing the bronchial response to cold air, that either cold air or methacholine are suitable stimuli to measure nonspecific bronchial responsiveness, and that the differences in bronchial responsiveness observed between asthmatics and nonasthmatic subjects are in keeping with a quantitative rather than a qualitative difference in responsiveness.

Pulmonary mechanics during exercise in normal males.

A body plethysmograph adapted to contain the pedals of an electrically braked cycle ergometer was used to measure pulmonary mechanics during steady-state exercise in 12 normal male subjects aged 22-65 yr. During exercise there was a progressive increase in residual volume to 119% of the value at rest (P less than 0.01), but functional residual capacity and total lung capacity did not change. The maximum expiratory flow-volume (MEFV) curves did not change and flow rates during tidal breathing did not exceed the MEFV curve. Dynamic pulmonary compliance fell to 91.3% of the control value and static expiratory pulmonary compliance fell to 76.9% of the control value (P less than 0.05). Pulmonary resistance did not change during exercise. Transpulmonary pressure during tidal breathing was negative even at the highest power outputs. The fall in compliance may be due to an increase in pulmonary capillary blood volume. These results demonstrate the importance of measuring absolute thoracic gas volume and the elastic properties of the lung when comparing pulmonary mechanics at rest and during exercise.

Pulmonary mechanics during exercise in subjects with chronic airflow obstruction.

A body plethysmograph was used to measure pulmonary mechanics in six subjects with chronic airflow obstruction during steady states at rest and during exercise at 200 and 400 kpm . min-1. The mean forced expired volume in 1 s was 1.32 liters (39.2% predicted). The flow rates during tidal breathing reached the maximum expiratory flow-volume (MEFV) curve in all but one subject, and on exercise they all reached the MEFV curve. Total lung capacity did not change significantly, but functional residual capacity increased to 104% of the control value (P less than 0.05) and residual volume increased to 113.3% of the control value (P less than 0.02). The MEFV curves did not change and tidal flow rates in excess of th MEFV curve were not seen. Dynamic compliance fell with increasing exercise to 52.8% (P less than 0.01) and static expiratory pulmonary compliance to 90.2% of the control value. Transpulmonary pressures during tidal breathing when expiratory flow reached the MEFV curve increased to progressively higher values as the work load increased. At low work loads there were several subjects with negative transpulmonary pressure when maximum flow rates were present. In patients with chronic airflow obstruction, little change occurs during exercise in pulmonary mechanics; the tidal flow patterns are dominated by the expired flow-volume curve, which is not changed by exercise; maximum flow occurs in some patients when transpulmonary pressure is still negative.

Interpretation of blood gas analysis by physicians in a community teaching hospital.

Forty-two interns and residents on the staff of a community teaching hospital were questioned to assess their understanding of blood gas abnormalities. Misunderstandings were such that 24% of the residents and interns might have given inadequate care had their interpretations dictated practice. Few therapeutic misadventures in fact occurred, largely because of supervision. Even without supervision, it is unlikely that much harm would have come about, partly because pattern recognition and rules of thumb provided adequate guidance and partly because no notice was taken of the results of the blood gas analysis anyway. Those who wish to promote rational practice should direct their educational efforts to improved understanding of the mechanisms of hypoxaemia and of the chemical, physiological and pathophysiological interactions of PCO2, bicarbonate and pH in the various acid-base disorders.

Bronchial responsiveness to inhaled histamine and exercise.

Bronchial responsiveness to inhaled histamine and exercise was measured in 19 asthmatics. Histamine aerosol was inhaled to determine the provocative concentration producing a 20% fall in forced expired volume in one second (FEV1) (PC20). Exercise was performed on a treadmill and a cycle ergometer; following each procedure the percent fall in the FEV1 (delta FEV1) and the exercise lability (percent rise in FEV1 plus percent fall in FEV1) were calculated. Delta FEV1 and exercise lability after both forms of exercise were similar. PC20 correlated with delta FEV1 and exercise lability in both forms of exercise; however, the correlation with exercise lability was better. PC20 was more sensitive in demonstrating bronchial hyperresponsiveness. The close correlation between the level of bronchial responsiveness to histamine and exercise supports the view that release of endogenous chemical mediators is an important determinant of exercise-induced asthma. The treadmill exercise and cycle ergometry protocols were equally effective in producing exercise-induced asthma.

A comparison of exercise responses in stairclimbing and cycling.

A free-paced 14.8-m stairclimb was compared to cycle ergometry at equivalent power outputs in six normal subjects. Heart rate (HR), inspiratory flow (VI) andd oxygen saturation in arterial blood (Sao2) were analyzed continuously, carbon dioxide output (Vco2) and oxygen consumption (Vo2) for the duration of exercise, and rebreathing mixed venous carbon dioxide pressure (Pvco2), capillary blood gases, and lactates at the completion of exercise. The average power output was 1,394 kpm/min sustained for 54.8 s. The HR and Vo2 responses were not significantly different between the two forms of exercise. VI was 20.3% less stairclimbing (P smaller than 0.005). A fall in Sao2 of 31.1% +/- 2.7) occurred in stairclimbing compared to 1.2% (+/- 2.1) in cycle ergometry. Differences in Sao2 between stairclimbing and cycling correlated with differences in VI (r = 0.80); falls in Sao2 could be prevented by overbreathing during stairclimbing or induced by controlled underbreathing during cycling. Vco2 and postexercise lactate levels were less stairclimbing (P smaller than 0.005 and P smaller than 0.01), as were Pvco2 measurements. The findings are consistent with a lower CO2 flow to the lung during stairclimbing than in cycling, which results in a lower alveolar ventilation and a consequent fall in Sao2.

Pragmatics of pulmonary function testing.

At present, there are a multitude of tests to assess respiratory function. The most reliable test of resting pulmonary function is simple spirometry. Using this, along with measurements of lung volume, one is able to make a useful assessment of a respiratory patient's pathophysiology. The where and how of these measurements, together with a discussion of other testing methods are described.

The effect of terbutaline in exercise-induced asthma.

A double blind study of 5 asthmatic subjects in remission demonstrated that the severity of bronchoconstriction after exercise was decreased by a single oral dose of 5 mg of terbutaline. The effect lasted for at least 6 hours and was significantly better than the protection afforded by 20 mg of metaproterenol, which was itself more effective than a placebo. In these doses, neither terbutaline nor metaproterenol affected heart rate or blood pressure at rest or in exercise, and no drug-induced side effects were found.