Influence of expiratory flow on closing capacity at low expiratory flow rates.

Single-breath oxygen (SBO2) tests at expiratory flow rates of 0.2, 0.5, and 1.01/s were performed by 10 normal subjects in a body plethysmograph. Closing capacity (CC)--the absolute lung volume at which phase IV began--increased significantly with increases in flow. Five subjects were restudied with a 200-ml bolus of 100% N2 inspired from residual volume after N2 washout by breathing 100% O2 and similar results were obtained. An additional five subjects performed SBO2 tests in the standing, supine, and prone positions; closing volume (CV)--the lung volume above residual volume at which phase IV began--also increased with increases of expiratory flow. The observed increase in CC with increasing flow did not appear to result from dependent lung regions reaching some critical "closing volume" at a higher overall lung volume. In normal subjects, the phase IV increase in NI concentration may be caused by the asynchronous onset of flow limitation occurring initially in dependent regions.     

Control of tissue blood flow at very low temperatures

Maximum levels of sustainable swimming activity rely on aerobic metabolism, and hence are limited by the cardiovascular supply capacity which is impaired at low temperatures. It is unclear to what extent species adapted to a continuous cold environment retain control of regional blood flow. Muscle blood flow (MBF) was therefore measured using the radiolabelled microsphere method in the Antarctic teleost Notothenia coriiceps and compared with data for trout at their preferred (optimal) temperatures of 0°C and 11°C, respectively. In resting fish, blood flow distribution to skeletal muscle was similar (around 8 ml/min/100 g), despite a lower cardiac output in Notothenia (7 vs. 27 ml/min). Following maximal exercise there was a significant increase in specific blood flow to slow, but not fast, muscle in both species. However, the relative hyperaemia was greater in trout (6.6- vs. 9.3-fold, respectively), with a similar relative increase in cardiac output (2.3- vs. 3.4-fold, respectively). The increase in blood flow to slow muscle, and decrease in peripheral resistance, during maximal exercise in trout (and hence regional O₂ delivery by convective transport) appears to be determined centrally. In contrast, reduced active redistribution from the viscera in Notothenia is presumably responsible for the attenuated increase in MBF on exercise. However, regional hyper- and hypoperfusion can occur within a single locomotory muscle, suggesting control of vascular tone is maintained.     

A theory of blood flow in skeletal muscle

A theoretical analysis of blood flow in the microcirculation of skeletal muscle is provided. The flow in the microvessels of this organ is quasi steady and has a very low Reynolds number. The blood is non-Newtonian and the blood vessels are distensible with viscoelastic properties. A formulation of the problem is provided using a viscoelastic model for the vessel wall which was recently derived from measurements in the rat spinotrapezius muscle (Skalak and Schmid-Sch?nbein, 1986b). Closed form solutions are derived for several physiologically important cases, such as perfusion at steady state, transient and oscillatory flows. The results show that resting skeletal muscle has, over a wide range of perfusion pressures an almost linear pressure-flow curve. At low flow it exhibits nonlinearities. Vessel distensibility and the non-Newtonian properties of blood both have a strong influence on the shape of the pressure-flow curve. During oscillatory flow the muscle exhibits hysteresis. The theoretical results are in qualitative agreement with experimental observations.     

A theory for the estimation of DNA synthesis rates by flow cytometry

A method is presented for estimating the rate of DNA synthesis of a cell population by examining the DNA histogram generated by flow cytometry (FCM). The model is based on the use renewal equations to estimate the steady-state fraction of cells in each DNA compartment. The fraction of cells in each compartment is shown to be related to the Laplace transform of the transit time through that compartment. Two methods are introduced for estimating the rate of DNA synthesis utilizing different transit time distributions. One method is shown to be a simplification of the method of Dean and Anderson. The other method allows for variability in the DNA synthesis rate. The effects of quiescent cells are considered and attention is paid to the various assumptions underlying the estimation.     

Vortex flow filtration of mammalian and insect cells

The use of vortex flow filtration for harvesting cells or conditioned medium from large scale bioreactors has proven to be an efficient, low shear method of cell concentration and conditioned medium clarification. Several 8–10 L batches of the human histiocytic lymphoma U-937 cell line (ATCC CRL 1593) were concentrated to less than 1 L by vortex flow filtration through a 3.0 m membrane. An aggressive filtration regimen caused a 17% loss of cell viability and a 32% loss of IL-4 receptor binding capacity when compared to a batch centrifuged control. A reduction of the rotor speed from 1500 to 500 RPM and reduction of system back pressure from 10 to 0 PSIG resulted in cell viability and IL-4 binding capacity comparable to the control. Several 10 L batches of baculovirus infected Sf-9 cells were also concentrated to less than 1 L by vortex flow filtration through a 3.0 m membrane. SDS-PAGE analysis of filtrate samples showed that aggressive filtration caused cell damage which led to contamination of the process stream by cellular lysate. When rotor speed was reduced to 500 RPM and system back pressure was reduced to 0 PSIG, the amount of contaminating lysate proteins in filtrate samples was comparable to a batch centrifuged control.     

Biotrickling air filtration of 2-chlorophenol at high loading rates

The degradation of 2-chlorophenol vapours in air was performed in a trickling biofilter packed with ceramic material seeded with the bacterium Pseudomonas pickettii, strain LD1. The system performance was evaluated under varying operating conditions (inlet 2-chlorophenol air concentrations from 0.10 to 3.50 g m^?3, and superficial air velocities of 30.0, 60.0, and 120.0 m h^?1). For all air velocity the maximum degradation rate was obtained for loading rates of 40 g m^?2 h^?1. Higher loading conditions resulted in strong inhibition of microbial activity, particularly severe at high air velocity. Process analysis, performed using data on pollutant concentration profiles along the filter packing obtained under different conditions of inlet concentration and air velocity, proves that best performance (i.e. maximum degradation efficiency and capacity) can be obtained for a narrow range of operating conditions, which can be ensured by proper design of biofilter size (i.e. diameter and height). Kinetic analysis of experimental data confirms that 2-CP inhibits microbial activity in the biofilter bed. Experimental data are satisfactorily fitted by the Haldane kinetic equation up to a critical value of loading rate, beyond which the experimental degradation rate is overestimated by the kinetic model. The inhibition appears to be affected by the loading rate, and the estimated inhibition constant linearly increases with increasing empty bed residence time.     

Modeling of intraorgan arterial vasculatures. I. A stationary blood flow at low Reynolds numbers

Based on the statistical relationships between the lengths and diameters of vessels in the arterial beds, obtained by measurements on plastic casts, a method for the generation of models of intraorgan arterial vasculatures was proposed. The dependence of the total hydraulic conductivity of the system on the model parameters was computed. The problem of selecting the adequate models by a comparison of the corresponding biophysical characteristics of vasculatures is discussed.     

Time-dependent rheological behaviour of blood flow at low shear in narrow horizontal tubes

Magnitude and time-dependence of the effects of red cell aggregation and sedimentation on the rheology of human blood were studied during low shear (tau W 2.5 to 92 mPa) flow through horizontal tubes (ID 25 to 105 microns). Immediately following reduction of perfusion pressure to a low value the red cell concentration near the tube walls decreases as a result of red cell aggregation. This is associated with a transient increase of centerline velocity. Simultaneously, sedimentation begins to occur and eventually leads to the formation of a cell-free supernatant plasma layer. Time-course and extent of this sedimentation process are strongly affected by wall shear stress variation, particularly in the larger tubes. At the lower shear stresses, centerline velocity decreases (flow resistance increases) with time following the initial acceleration period, due to sedimentation of red cells. This is followed by a further increase of resistance caused by the elevation of hematocrit occurring because of the reduction of cell/plasma velocity ratio. The time dependence of blood rheological behaviour under these flow conditions is interpreted to reflect the net effect of the partially counteracting phenomena of sedimentation and red cell aggregation.     

A method for analyzing non-Newtonian blood viscosity data in low shear rates

Viscosity measurements were made using a coaxial rotating cylinder viscometer for blood having various volume fractions of red cells. A method is described for analyzing non-Newtonian blood viscosity in low shear rates by taking account of an increase or a decrease in size of red cell aggregates induced by shear. Our results are compared with empirical formulae presented by Scott Blair, Weaver-Evans-Walder and Thurston.