Thoracic geometry changes during equine locomotion

Classic descriptions of rib motion during ventilation include three-dimensional movements that are tied to the locomotor pattern. It is still not clear how chest wall and diaphragmatic movements contribute to ventilation. The purpose of this paper was to evaluate how gait affects local thoracic geometry in horses. Hemispherical markers were placed on the skin over the ribs and spine to calculate thoracic hemi-diameter. Ventilatory airflows were recorded using an ultrasonic flowmeter system. Airflow and kinematic data were collected synchronously at walk (1.8 m s-1), trot (4 m s-1), canter and gallop (6, 8 and 10 m s-1) on the treadmill. At walk and trot, the changes in right and left hemi-diameter were approximately symmetric. At walk, mean hemi-diameter changes were 40 mm (rib 10) and 47 mm (rib 16). At trot, they were 33 mm (rib 10) and 34 mm (rib 16). Across the three canter and gallop speeds, leading (right) side hemi-diameter change increased from 25 to 30 to 35 mm (rib 10) and from 23 to 37 to 46 mm (rib 16). The trailing (left) side hemi-diameter increased from 50 to 67 to 70 mm (rib 10) and from 36 to 48 to 54 mm (rib 16) (P≪0.01). At canter and gallop, the non-lead side of the thorax is subjected to larger amplitude changes in hemi-diameter than the lead side, which tends to be more compressed overall and demonstrates smaller amplitudes of change in diameter.

Lung volumes during sustained microgravity on Spacelab SLS-1

Gravity is known to influence the mechanical behavior of the lung and chest wall. However, the effect of sustained microgravity (mu G) on lung volumes has not been reported. Pulmonary function tests were performed by four subjects before, during, and after 9 days of mu G exposure. Ground measurements were made in standing and supine postures. Tests were performed using a bag-in-box-and-flowmeter system and a respiratory mass spectrometer. Measurements included functional residual capacity (FRC), expiratory reserve volume (ERV), residual volume (RV), inspiratory and expiratory vital capacities (IVC and EVC), and tidal volume (VT). Total lung capacity (TLC) was derived from the measured EVC and RV values. With preflight standing values as a comparison, FRC was significantly reduced by 15% (approximately 500 ml) in mu G and 32% in the supine posture. ERV was reduced by 10–20% in mu G and decreased by 64% in the supine posture. RV was significantly reduced by 18% (310 ml) in mu G but did not significantly change in the supine posture compared with standing. IVC and EVC were slightly reduced during the first 24 h of mu G but returned to 1-G standing values within 72 h of mu G exposure. IVC and EVC in the supine posture were significantly reduced by 12% compared with standing. During mu G, VT decreased by 15% (approximately 90 ml), but supine VT was unchanged compared with preflight standing values. TLC decreased by approximately 8% during mu G and in the supine posture compared with preflight standing. The reductions in FRC, ERV, and RV during mu G are probably due to the cranial shift of the diaphragm, an increase in intrathoracic blood volume, and more uniform alveolar expansion.

Identifying hydraulically conductive fractures with a slow-velocity borehole flowmeter

The U.S. Geological Survey used a recently developed heat-pulse flowmeter to measure very slow borehole axial water velocities in granitic rock at a site near Lac du Bonnet, Manitoba, Canada. The flowmeter was used with other geophysical measurements to locate and identify hydraulically conducting fractures contributing to the very slow vertical water flow in the two boreholes selected for study. The heat-pulse flowmeter has no moving parts and operates on the tag–trace principle. It is an improved version of the flowmeter developed by the Water Research Centre in England in 1975. The U.S. Geological Survey's heat-pulse flowmeter has a flow-measuring range in water of 0.06–6 m/min, and can resolve velocity differences as slow as 0.01 m/min. This is an order of magnitude slower than the stall speed of spinner flowmeters. The flowmeter is 1.16 m long and 44 mm in diameter. It was calibrated in columns of 76 and 152 mm diameter, to correspond to the boreholes studied. The heat-pulse flowmeter system is evaluated, and problems peculiar to the measurement of very slow axial water velocities in boreholes are discussed. Key words: flowmeter, borehole flow, low flow, borehole geophysics.

Regional blood flow measurement with pulsed Doppler flowmeter in conscious rat

Development of techniques for the continuous measurement of regional blood flow and vascular resistance in intact small animals has been impeded primarily by the bulkiness of flow probes. The availability of an ultrasonic pulsed Doppler flowmeter system enabled us to construct miniaturized probes using 1-mm-diameter piezoelectric crystals that emit a 20-mHz signal and receive the reflected sound waves from passing blood cells. The finished flow probe is approximately 2.5-4 mm long and 2 mm in cross-sectional diameter with lumen diameters appropriate for the rat, ranging from 0.7 to 1.2 mm. This report describes the materials and methods involved in constructing and implanting the probes in rats to monitor renal, mesenteric, and hindquarter blood flow velocity. The accuracy of the pulsed Doppler method in detecting changes in regional blood flow and vascular resistance was established by the demonstration of a highly significant correlation between velocity recorded from the Doppler unit and volume flow recorded simultaneously. These data indicate that the ultrasonic pulsed Doppler flowmeter provides the opportunity to measure changes in regional blood flow and vascular resistance in a conscious freely moving rat.