Influence of Fluid Compressibility and Movements of the Swash Plate Axis of Rotation on the Volumetric Efficiency of Axial Piston Pumps

This paper describes the design of a swash plate axial piston pump and the theoretical models describing the bulk modulus of aerated and non-aerated fluids. The dead space volume is defined and the influence of this volume and the fluid compressibility on the volumetric efficiency of the pump is considered. A displacement of the swash plate rotation axis is proposed to reduce the dead space volume for small swash plate swing angles. A prototype design of a pump with a displaced axis of rotation of a swash plate with two directions of delivery is presented, in which the capacity is changed by means of a valve follow-up mechanism. Comparative results for a pump with a displaced and a non-displaced swash plate rotation axis are presented, which confirm that displacement of the swash plate rotation axis causes an increase in volumetric efficiency that is apparent for high pressure discharge and small swash plate angles. The determined characteristics were compared with a mathematical model taking into account the compressibility of the fluid in the dead space volume and a satisfactory consistency was obtained.

Presample Volume Necessary to Obtain Accurate Laboratory Parameters from Central Venous Catheters in Dogs

ABSTRACT We compared laboratory parameters from central venous catheters using multiple presample volumes (PSVs) to venipuncture values. Blood was obtained from dogs for a venous blood gas, packed red blood cell volume (PCV), total solids (TS), and a coagulation panel. Blood was drawn both by venipuncture and from the catheter (using PSVs 300%, 600%, and 1200% of the dead space volume). Twenty dogs were enrolled. Venipuncture values were significantly higher than those obtained from the catheter for PCV (300% [P = .007], 600% [P = .005], and 1200% [P = .02]), TS (300% [P = .006] and 600% [P = .04]), and lactate (600% [P = .04] and 1200% [P = .01]). Venipuncture values were significantly lower than those obtained from a catheter for pH (1200% [P = .008]) and chloride (300% [P = .04], 600% [P = .003], and 1200% [P = .03]). An increase was found in prothrombin time in samples drawn with 600% PSV compared with 1200% (P = .008). The PCV and TS are diluted when smaller PSVs are used. A 1200% PSV best approximated the PCV and TS obtained by venipuncture. A 300% PSV may be adequate to evaluate coagulation and venous blood gas values.

Computations of State Ventilation and Respiratory Parameters

Background: In mechanical ventilation, there are still some challenges to turn a modern ventilator into a fully reactive device, such as lack of a comprehensive target variable and the unbridged gap between input parameters and output results. This paper aims to present a state ventilation which can provide a measure of two primary, but heterogenous, ventilation support goals. The paper also tries to develop a method to compute, rather than estimate, respiratory parameters to obtain the underlying causal information. Methods: This paper presents a state ventilation, which is calculated based on minute ventilation and blood gas partial pressures, to evaluate the efficacy of ventilation support and indicate disease progression. Through mathematical analysis, formulae are derived to compute dead space volume/ventilation, alveolar ventilation, and CO2 production. Results: Measurements from a reported clinical study are used to verify the analysis and demonstrate the application of derived formulae. The state ventilation gives the expected trend to show patient status, and the calculated mean values of dead space volume, alveolar ventilation, and CO2 production are 158mL, 8.8L/m, and 0.45L/m respectively for a group of patients. Discussions and Conclusions: State ventilation can be used as a target variable since it reflects patient respiratory effort and gas exchange. The derived formulas provide a means to accurately and continuously compute respiratory parameters using routinely available measurements to characterize the impact of different contributing factors.

Respiration

This chapter discusses the respiratory system of giraffes. The respiratory system supplies oxygen, removes of carbon dioxide and produces the airflow needed to make sounds. Giraffes do not have the velocity of airflow through the airways to vibrate vocal cords sufficiently to generate sounds able to be heard by humans but can produce sounds able to be heard by giraffes. Air reaches alveoli for gas exchange through a long trachea, which is relatively narrow (~4 cm in diameter). Dead space volume is large. A short trunk and rigid chest wall reduce the capacity of the thorax and consequently lung volume is small. Respiratory rate is low (~10 min-1), but tidal volume is relatively big, and alveolar ventilation rate (VA; ~60 L min-1) delivers sufficient air despite the large dead space volume. Laryngeal muscles act to prevent food from entering the trachea a process controlled by the (short) superior and (long) inferior (recurrent) laryngeal nerves. Air that has been delivered to alveoli comes into contact with pulmonary artery blood (=cardiac output, Q; ~40 L min-1). The VA: Q ratio is ~1.5 (cf 0.8 in humans). Gas exchange occurs by diffusion. The surface area for diffusion is related to the number of alveoli which increase in number during growth from ~1 billion in a newborn giraffe to 11 billion in an adult. Gas carriage of oxygen and carbon dioxide is a function of erythrocytes which are small (MCV = 12 fL) but numerous (12 × 1012 L-1) and each liter of blood contains ~150 g of hemoglobin.

Study of Respiratory System Response During Decompression of a Pressurized Compartment.

The paper presents a solution for modeling the dynamics of human gas ex-change indicators in space flight based on a static model of the respiratory sys-tem, taking into account the peculiarities of gas exchange process. The paper also describes a computational experiment which was carried out to simulate indicators during ascent, demonstrating the capabilities of the model to predict the state of the respiratory system. The simulation results show that a decrease in the total barometric pressure leads to the respiratory capacity changes: the volume of the alveolar space decreases and the tidal dead space volume in-creases in the ratio from 4.7 to 0.7. A noncompensated respiratory alkalosis leading to the acid-base disorders develops as well. The computational experi-ment applied under the considered methodological approach allows studying the problems related to the flight safety and risk management under various operating modes of life support systems.

Acute Effects of Using Added Respiratory Dead Space Volume in a Cycling Sprint Interval Exercise Protocol: A Cross-Over Study

Background: The aim of the study was to compare acute physiological, biochemical, and perceptual responses during sprint interval exercise (SIE) with breathing through a device increasing added respiratory dead space volume (ARDSV) and without the device. Methods: The study involved 11 healthy, physically active men (mean maximal oxygen uptake: 52.6 ± 8.2 mL∙kg1∙min−1). During four visits to a laboratory with a minimum interval of 72 h, they participated in (1) an incremental test on a cycle ergometer; (2) a familiarization session; (3) and (4) cross-over SIE sessions. SIE consisted of 6 × 10-s all-out bouts with 4-min active recovery. During one of the sessions the participants breathed through a 1200-mL ARDSv (SIEARDS). Results: The work performed was significantly higher by 4.4% during SIEARDS, with no differences in the fatigue index. The mean respiratory ventilation was significantly higher by 13.2%, and the mean oxygen uptake was higher by 31.3% during SIEARDS. Respiratory muscle strength did not change after the two SIE sessions. In SIEARDS, the mean pH turned out significantly lower (7.26 vs. 7.29), and the mean HCO3– concentration was higher by 7.6%. Average La− and rating of perceived exertion (RPE) did not differ between the sessions. Conclusions: Using ARDSV during SIE provokes respiratory acidosis, causes stronger acute physiological responses, and does not increase RPE.

Assessment of efficacy of postinfusion tubing flushing in reducing risk of cytotoxic contamination

Purpose Infusion of cytotoxic drugs carries the risk of occupational exposure of healthcare workers. Since disconnecting an infusion line is a source of contamination, flushing of tubing after infusion of cytotoxic agents is recommended, but the optimal volume of rinsing solution is unknown. The objective of this study was to assess whether postinfusion line flushing completely eliminates cytotoxics. Methods Infusions were simulated with 3 cytotoxics (gemcitabine, cytarabine, and paclitaxel) diluted in 5% dextrose injection or 0.9% sodium chloride injection in 250-mL infusion bags. Infusion lines were flushed using 5% dextrose injection or 0.9% sodium chloride solution at 2 different flow rates. The remaining concentration of cytotoxics in the infusion line was measured by a validated high-performance liquid chromatography (HPLC) method after passage of every 10 mL of flushing volume until a total of 100 mL had been flushed through. Results All cytotoxics remained detectable even after line flushing with 80 mL of flushing solution (a volume 3-fold greater than the dead space volume within the infusion set). Gemcitabine and cytarabine were still quantifiable via HPLC even after flushing with 100 mL of solution. Efficacy of flushing was influenced by the lipophilicity of drugs but not by either the flushing solvent used or the flushing flow rate. After 2-fold dead space volume flushing, the estimated amount of drug remaining in the infusion set was within 0.19% to 0.56% of the prescribed dose for all 3 cytotoxics evaluated. Conclusion Complete elimination of cytotoxics from an infusion line is an unrealistic objective. Two-fold dead space volume flushing could be considered optimal in terms of administered dose but not from an environmental contamination point of view. Even when flushed, the infusion set should still be considered a source of cytotoxic contamination.