ABSTRACT. We studied the feeding behavior of the surface-deposit feeder Saccoglossus kowalevsbl under oscillatory flows in the laboratory. Low oscillatory flow (peak speed = 10 cm S-') without assoclated sediment transport had no effect on egestion rates in comparison to no-flow conditions. Moderate flows (peak speed = 15 and 17.5 cm S-') with incipient sediment trdnsport caused an increase in egestion rates of 35 to 100% relative to low-flow rates. High flow (peak speed = 25 cm S-') with bulk sediment transport caused a decrease in egestion rates to one-third the low-flow rates. When compared to a functional response curve previously determined for S. kou-dl~vskii, our data show that under high flow S. kowalevskii does not feed at rates predicted by the availdble food resources (as measured by chlorophyll a concentration). Under moderate flow, S. kowalevskii is stimulated to feed at higher rates than predicted by the available food resources. And under low flow. S. kowalevskii appears to be unaffected by flow and continues feeding at rates predicted by the available food resources. Flow and the associated sediment flux thus lead to an envelope of egestiun rates about the no-flow functional response, indicating that the feed~ng behavior of S. kowalevskll 1s a function both of available food resources and flow regime. Laboratory still-water functional responses and simple ttreding models are thus inadequate. Accurate extrapolation and prediction require that flow and sediment flux parameters be incorporated in feeding models.
Renewed interest in the use of “fresh” and cryopreserved allograft valves for aortic valve replacement (AVR) prompted an updated analysis of the long‐term results of our old experience (1964–1971) with free‐hand AVR. Eighty‐three patients received “fresh” (antibiotic stored at 4°C for intervals between 24 hrs and 18 days), free‐hand allograft valves. Current (1986) follow‐up was 96% complete; cumulative follow‐up included 773 patient‐years (pt‐yr) and averaged 9 yrs. Importantly, 37 patients were still at risk with their original allograft valve at ten yrs, and 12 patients at 17 yrs. Standard conservative criteria were used to assess valve‐related complications. Thromboembolism (TE) occurred at a linearized incidence of 1.0 %/pt‐yr, anticoagulation‐related hemorrhage (ACH) at 0.2 %/pt‐yr), and fatal prosthetic valve endocarditis (PVE) at 0.5 %/pt‐yr. In actuarial terms, the incidence of degenerative valve failure was 30 ± 6% (± SEM) at ten yrs and 40 ± 7% at 15 yrs. Valve failure due to all causes (including sudden, unexplained deaths and PVE) occurred in 38 ‐± 6% of patients at ten yrs and 57 ±: 7% after 15 yrs. The incidence of fatal valve failure was 11 ± 4% at six yrs (the time of the last event). The rate of reoperation was 33 ± 6% at ten yrs and 52 ± 7% at 15 yrs. Given the relatively crude methods of allograft valve preparation and storage during this remote era, we believe that these long‐term results with free‐hand allograft AVR are satisfactory, albeit far from optimal. Theoretically, more refined procurement and preservation methods used today for “fresh” and cryopreserved allograft valves, more strict patient selection criteria, and ABO donor‐host matching will translate into long‐term durability superior to that reported herein. Hence, we continue to use both “fresh” and cryopreserved free‐hand allograft valves in carefully selected patients, including children and young adults, certain patients with PVE, and infants and children with complex, multilevel left ventricular out‐flow tract obstruction.
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