Subjective self-assessment of physical activity is negatively affected by monitoring awareness in subjects with mild cognitive impairment: a crossover randomised controlled trial.

OBJECTIVE: Physical activity plays an important role in maintaining mental and physical health. This study assessed the effect of physical activity monitoring awareness on the physical activity level and subjective self-assessment of physical activity in middle-aged subjects with normal cognitive function (NCF) and mild cognitive impairment (MCI). PATIENTS AND METHODS: Thirty-five subjects aged 50-65 years with NCF and MCI were randomised into two experimental groups, each taking part in two one-week intervention periods. Subjects in group A were not aware that their physical activity was monitored in the first week (phase I) and were aware of the monitoring in the second week (phase II), whereas it was the opposite order for group B. Physical activity was assessed using the ActiGraph GT9X accelerometer and International Physical Activity Questionnaire (IPAQ). RESULTS: A total of 32 subjects (MCI: n = 12, NCF: n = 20) completed both intervention periods, with MCI subjects having significantly lower objectively assessed physical activity than NCF participants. Moreover, subjectively assessed physical activity in the MCI group was significantly higher when the participants were unaware of physical activity monitoring. A significant phase-group interaction was found in total (MET-min/d: p = 0.0072; min/d: p = 0.0194) and moderate (MET-min/d: p = 0.0015; min/d: p = 0.0020) physical activity as well as energy expenditure (p = 0.0366) assessed by the IPAQ and in the percentage of sedentary behaviour (p = 0.0330) and the average number of steps (p = 0.0342) assessed by ActiGraph. CONCLUSIONS: The awareness of physical activity assessment might decrease the ability to subjectively assess physical activity in subjects with MCI.

New design for a pumping artificial lung.

A new prototype of a pumping artificial lung (PAL) has been designed and tested. The device performs the functions of both the pump and oxygenator components of an extracorporeal perfusion circuit. Previous prototypes that the authors developed (Type A) had gas exchanging microporous fibers formed into propeller-like vanes that, upon rotation, pump the blood. The design of the new PAL prototypes (Type B) uses the rotation of an annular bank of fibers to drive flow. The fiber bank, including sealed gas manifolds, lies within the housing of a modified Bio-Medicus BMP-50 pump head (Bio-Medicus, Eden Prairie, MN). Rotation of the fiber bank is driven through a magnetic coupling. Inlet and outlet gas lines enter the pump head through a sealed bearing. The Type A PAL suffered from insufficient pumping rates and gas exchange, necessitating redesign. The authors have constructed two PAL-B prototypes with a priming volume of only 140 ml and gas exchange surface areas of 0.16 and 0.60 m2. During in vitro saline testing, these prototypes showed significant pump performance, pumping 7.0 L/min against zero head at 3,500 rpm. The larger prototype had exchange rates in saline of up to 71 ml O2/min and 75 ml CO2/min. Gas exchange fluxes (O2 = 119 ml/[min.m2] and CO2 = 125 ml/[min.m2]) for the PAL-B are significantly higher than that of commercially available oxygenators in saline. Future prototypes will have increased surface area and fibers smaller than the 0.038 cm outside diameter fibers used in the present prototypes. A primary concern in using microporous fibers to push the blood was the durability of the fibers at high pump speeds. High speeds exhibited no negative effects on gas exchange abilities or fiber durability.

A pumping intravascular artificial lung with active mixing.

Intravascular, as well as extracorporeal, artificial lungs need to be effective and efficient in transferring both oxygen and carbon dioxide. This paper describes the preliminary development of a device that not only is efficient in gas transfer, but also can reduce any pressure loss by providing its own pumping action. The exchange surfaces of the device consist of many short, microporous, hollow fibers arranged in layers like the threads of a screw and placed in a cross-flow configuration. Rotation of the device greatly increases gas transfer efficiency, by increasing the relative velocity between the blood and the fiber surfaces, and pushes the blood along a path similar to that of an Archime-dean screw. In vitro water tests of prototype devices indicate that the rotation can enhance the gas transfer rates by as much as a factor of six. In vitro blood studies indicate moderate blood pumping against zero pressure head, a simulation of veno-venous bypass.

A pumping artificial lung.

The authors have developed a single device that performs the functions of a centrifugal pump and a membrane artificial lung. Unlike other systems that combine pre-existing components, our device is constructed so that the vanes of an impeller pump are made up of gas exchanging microporous fibers. The device has a variety of applications: in an easily primed emergency cardiopulmonary bypass circuit, as a low surface area component of extracorporeal life support (ECLS) circuits, and as a low volume, high perfusion rate bridge to transplant. Five prototype devices, with gas exchange surface areas ranging from 0.09 to 0.35 m2, have been tested in vitro to characterize the gas exchange and pumping capabilities of the device. These small devices pump fluid effectively. The larger device could pump 2.7 l/min with 91 mmHg pressure difference from inlet to outlet. These preliminary devices transferred to only 33 ml/min of oxygen (O2) and 35 ml/min of carbon dioxide (CO2), however. The combination of pumping ability and gas exchange is encouraging, but it is apparent that larger surface areas and less blood shunting around the gas exchanging impellers are needed for sufficient gas exchange. Somewhat higher surface areas are feasible within the pump-head casing used for these preliminary prototypes; larger casings could be used for still higher surface areas.

A dynamic intravascular artificial lung.

Intravascular lung assist devices (ILADs) must transfer sufficient amounts of oxygen and carbon dioxide to and from limited surface areas. It has become apparent that passive devices, i.e., those without an active means for enhancing transfer, cannot achieve sufficient transfer within the space available. High speed rotation or oscillation of fiber sheets can increase transfer rates up to 800% over the rates achieved by a stationary device, judiciously configured fiber sheets cause an additional benefit when rotated: reduced resistance to blood flow across the device. The authors have developed a series of device prototypes based on these principles of transfer augmentation and minimization of flow resistance. The prototypes are small enough to fit inside the vena cava, with transfer surface areas ranging from 0.1 m2 to 0.5 m2. Transfer rates of O2 up to 53 ml/min and CO2 up to 51 ml/min and fluxes of 208 ml (min/m2) for O2 and 310 ml (min/m2) for CO2 have been achieved.

Testing of an intrathoracic artificial lung in a pig model.

A low input impedance, intrathoracic artificial lung is being developed for use in acute respiratory failure or as a bridge to transplantation. The device uses microporous, hollow fibers in a 0.74 void fraction, 1.83 m2 surface area bundle. The bundle is placed within a thermoformed polyethylene terephthalate glucose modified housing with a gross volume of 800 cm3. The blood inlet and outlet are 18 mm inner diameter vascular grafts. Between the inlet graft and the device is a 1 inch inner diameter, thin-walled, latex tubing compliance chamber. These devices were implanted in Yorkshire pigs via median sternotomy with an end to side anastomosis to the pulmonary artery and left atrium. The distal pulmonary artery was occluded to divert the right ventricular output to the device. Pigs 1 and 2 were supported fully for 24 hrs and then killed. Pig 3 was supported partially for 20 hrs and died from bleeding complications. The first implant, in a 55 kg male pig, transferred an average of 176 ml/min +/- 42.4 of O2 and 190 ml/min +/- 39.7 of CO2 with an average blood flow rate of 2.71/min +/- 0.46. The normalized average right ventricular output power, Pn, was 0.062 W/(L/min) +/- 0.0082, and the average device resistance, R, was 3.5 mmHg/(L/min) +/- 0.62. The second implant, in a 60 kg male pig, transferred an average of 204 ml/min +/- 22.5 of O2 and 242 ml/min +/- 17.2 of CO2 with an average blood flow rate of 3.7 L/min +/- 0.45, Pn of 0.064 W/(L/min) +/- 0.0067, and R of 4.3 mmHg/(L/min) +/- 0.89. The third implant, in an 89 kg male pig, transferred an average of 156 ml/min +/- 39.6 of O2 and 187 ml/min +/- 21.4 of CO2 with an average blood flow rate of 2.5 L/min +/- 0.49, Pn of 0.052 W/(l/min) +/- 0.0067, and R of 3.4 mmHg/(L/min) +/- 0.74. These experiments suggest that such an artificial lung can temporarily support the gas transfer requirements of adult humans without over-loading the right ventricle.