Selective ingestion of pelagic versus benthic algae by the cockle Cerastoderma edule (Linne, 1758)

The pre-ingestive selection of microphytobenthic algae by the cockle Cerastoderma edule was studied in comparison with diets containing the pelagic diatom Phaeodactylum tricomutum. Treatments with the different diets covered a range of seston concentrations and organic content similar to field conditions. Rejection rates of C. edule exposed to the different treatments were significantly correlated with the concentration of total particulate matter. No significant differences in total rejection rates were found between pelagic and benthic diets. Organic rejection rate was significantly correlated with particulate organic matter of the treatments and no significant differences were found between both diets. Selection efficiency was significantly correlated with particulate organic matter concentration in both diets and no significant differences were found between the diets. Analysis of the pseudofeces composition by flow cytometry from cockles exposed to a mixed diet of microphytobenthic algae and P. tricornutum, showed a preferential ingestion of the pelagic diatom. Benthic species, such as small pennates and Navicula sp., were preferentially ingested in comparison to larger microphytobenthic species. The largest microphytobenthic species, Cylindrotheca sp., was significantly rejected. In general, C. edule is an opportunistic filter feeder that takes advantage of both pelagic and benthic algal cells.

Measurement of muscle contraction with ultrasound imaging

To investigate the ability of ultrasonography to estimate musactivity, we measured architectural parameters (pennation angles, fascicle lengths, and muscle thickness) of several human muscles (tibialis anterior, biceps brachii, brachialis, transversus abdominis, obliquus internus abdominis, and obliquus externus abdominis) during isometric contractions of from 0 to 100% maximal voluntary contraction (MVC). Concurrently, electromyographic (EMG) activity was measured with surface (tibialis anterior only) or fine-wire electrodes. Most architectural parameters changed markedly with contractions up to 30% MVC but changed little at higher levels of contraction. Thus, ultrasound imaging can be used to detect low levels of muscle activity but cannot discriminate between moderate and strong contractions. Ultrasound measures could reliably detect changes in EMG of as little as 4% MVC (biceps muscle thickness), 5% MVC (brachialis muscle thickness), or 9% MVC (tibialis anterior pennation angle). They were generally less sensitive to changes in abdominal muscle activity, but it was possible to reliably detect contractions of 12% MVC in transversus abdominis (muscle length) and 22% MVC in obliquus internus (muscle thickness). Obliquus externus abdominis thickness did not change consistently with muscle contraction, so ultrasound measures of thickness cannot be used to detect activity of this muscle. Ultrasound imaging can thus provide a non-invasive method of detecting isometric muscle contractions of certain individual muscles.

High rate of detection of primary aldosteronism, including surgically treatable forms, after 'non-selective' screening of hypertensive patients

Background Wide testing of the aldosterone: renin ratio among hypertensive individuals has revealed primary aldosteronism to be common, with most patients normokalaemic. Some investigators, however, have reported aldosterone-producing adenoma to be rare among patients so detected. Objective To test the hypothesis that differences among reported studies in the rate of detection of aldosterone-producing adenoma (as opposed to bilateral adrenal hyperplasia) reflect differences in the procedures used for diagnosis of primary aldosteronism, and the methods used to identify aldosterone-producing adenomas. Methods In the newly established Princess Alexandra Hospital Hypertension Unit (PAHHU), we used procedures developed by Greenslopes Hospital Hypertension Unit (which reports that more than 30% of patients with primary aldosteronism have aldosterone-producing adenomas) to diagnose primary aldosteronism and determine the subtype. All patients with an increased aldosterone: renin ratio (measured after correction for hypokalaemia and while the patient was not receiving interfering medications) underwent fludrocortisone suppression testing to confirm or exclude primary aldosteronism; if they were positive, they underwent genetic testing to exclude glucocorticoid-remediable aldosteronism before adrenal venous sampling was used to differentiate lateralizing from bilateral primary aldosteronism. Results This approach allowed PAHHU to diagnose, within 2 years, 54 patients [only seven (13%) hypokalaemic] with primary aldosteronism. All tested negative for glucocorticoid-remediable aldosteronism. Aldosterone production was lateralized to one adrenal in 15 patients (31%; only six hypokalaemic) and was bilateral in 34 (69%; all normokalaemic) of 49 patients who underwent adrenal venous sampling. Among patients with lateralizing adrenal hyperplasia, computed tomography revealed an ipsilateral mass in only six and a contralateral lesion in one. Fourteen patients underwent unilateral adrenalectomy, which cured the hypertension in seven and improved it in the remainder. In patients with bilateral primary aldlosteronism, hypertension responded to spironolactone (112.5-50 mg/ day) or amiloride (2.5-10 mg/day). Conclusion When performed with careful regard to confounding factors, measurement of the aldosterone: renin ratio in all hypertensive individuals, followed by fludrocortisone suppression testing to confirm or exclude primary aldosteronism and adrenal venous sampling to determine the subtype, can result in the detection of significant numbers of patients with specifically treatable or potentially curable hypertension. (C) 2003 Lippincott Williams Wilkins.

Selective entrainment of sediment graded by size and density under waves

The influence of near-bed sorting processes on heavy mineral content in suspension is discussed. Sediment concentrations above a rippled bed of mixed quartz and heavy mineral sand were measured under regular nonbreaking waves in the laboratory. Using the traditional gradient diffusion process, settling velocity would be expected to strongly affect sediment distribution. This was not observed during present trials. In fact, the vertical gradients of time-averaged suspension concentrations were found to be similar for the light and heavy minerals, despite their different settling velocities. This behavior implies a convective rather than diffusive distribution mechanism. Between the nonmoving bed and the lowest suspension sampling point, fight and heavy mineral concentration differs by two orders of magnitude. This discrimination against the heavy minerals in the pickup process is due largely to selective entrainment at the ripple face. Bed-form dynamics and the nature of quartz suspension profiles are found to be little affected by the trialed proportion of overall heavy minerals in the bed (3.8-22.1%).