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Biomedical subjects

L Tripp

Publications and source records attributed to L Tripp.

15 recordsLinked to original sources
PubMed2000

Pharmacokinetics and safety of single intravenous infusions of the adenosine agonist, AMP 579, in patients with end-stage renal insufficiency.

The pharmacokinetics of an adenosine agonist (AMP 579) were characterized in patients with end-stage renal disease compared to sex- and age-matched healthy volunteers. All study participants were administered single AMP 579 doses of 50 micrograms/kg as a 6-hour, constant-rate intravenous infusion. Serial blood samples were obtained for measurement of plasma AMP 579 concentration, and predose samples were collected for determination of AMP 579 plasma protein binding. The safety of AMP 579 administration in renally impaired patients also was evaluated. AMP 579 was rapidly cleared from the systemic circulation in all subjects as plasma concentrations were below the limit of detection by 2 to 4 hours after terminating the infusion. Noncompartmental analysis yielded mean values for the plasma AMP 579 concentration at the end of the 6-hour infusion (C6 h) of 9.6 and 10.5 ng/mL and for systemic clearances (Cl) of 0.91 and 0.72 L/h/kg in renally impaired patients and healthy volunteers, respectively. Mean volumes of distribution (Vss) in the renally impaired and healthy volunteers were 0.92 and 0.84 L/kg, and terminal elimination half-life values (t1/2) were 1.61 and 1.33 hours, respectively. The extent to which AMP 579 is bound to plasma protein was not altered in renally impaired patients since the free fractions were 4.0% and 3.4% for renally impaired and healthy volunteers, respectively. It was concluded that the pharmacokinetic parameters of AMP 579 were similar in both groups. The 6-hour AMP 579 infusion was generally well tolerated by both renal patients and healthy volunteers. There were no serious adverse events, and there were only two mild adverse events in 1 renally impaired patient judged possibly related to the study drug that quickly resolved. There were no clinically significant changes in laboratory values or clinical evaluations during the study. There was a slight increase in heart rate during the infusion of similar magnitude for both the renal patients and healthy volunteers. These data suggest that AMP 579 may be administered to renally impaired patients with minimal cardiovascular effects and adverse events. These results in end-stage renal patients (worst-case scenario) indicate that dose adjustment in patients with renal insufficiency of any degree is not indicated in future studies of AMP 579.

Adult↗
PubMed1999

Polychromatic percepts during hypergravity.

Future helmet mounted systems and cockpit displays will rely on color graphics and information that high performance aircraft pilots will need to discern and understand. Color in displays may help reduce pilot workload. The effect of high G and reduced eye level blood pressure on field-of-view has been study extensively. The effect of high sustained acceleration on color vision, however, is unknown. Research on visual contrast sensitivity, night vision, and visual acuity under acceleration in a human centrifuge has demonstrated changes in vision. We began by having normal color vision subjects view a magnified color aerial map and describe what they saw as we slowly ramped up the G profile from baseline (1.4 G) at 0.1G/sec until they experienced almost complete blackout. At that point subjects began straining and the centrifuge was rapidly decelerated. Several subjects described the river fading away before much else happened. Then the yellow and green features of the terrain faded together. Reds and dark blues appeared to change to black but remained legible until the entire image also faded to black. Computer types call the color of a river on a map cyan. So a display was created that resembled a device know as a "light bar" that is routinely used in centrifuge research. It consisted of a 45 degree wide square projection of green dots in the periphery and a red dot in the center on a white background. Due to our new curiosity about cyan we added dots halfway between the green and red that were cyan. We then ran several people through the same slow onset ramp until near blackout. Several reported that the cyan disappeared completely, significantly before the green. Then the green disappeared, and finally the central red dot. For those who experience it, it is a very useful and repeatable early end point where vision is affected but still available. Next we borrowed a color wheel from the hypobaric chamber and taped it to the wall of the cab. Several subjects reported discomforting angular optical vection due to torsional nystagmus. Thus, a vertical bar arrangement of colors was selected that minimized disruption from involuntary eye movements.

Aerospace Medicine↗
PubMed1994

The effect of head and body position on +Gz acceleration tolerance.

It has been suggested there is a relationship between acceleration-induced loss of consciousness (G-LOC) and head/body position. A two-part investigation was conducted to determine whether head and body position affects acceleration tolerance. A retrospective analysis of high-G training data (N = 1,914) compared G-LOC occurrence during straight-ahead exposure to a "check-6" exposure [10 s at +9 Gz; 6 G/s onset rate; G-suit inflated; anti-G straining maneuver (AGSM) performed]. A prospective study (N = 12) was conducted with acceleration exposures using light loss criteria with subjects in straight-ahead, above, over-the-right shoulder, or over-the-left shoulder positions. Profiles consisted of 0.1 G/s onset-rate runs (no G-suit inflation; relaxed) to a maximum of +9 Gz and 0.5 G/s onset-rate runs (G-suit inflated; AGSM performed) to +9 Gz for up to 26 s. In the retrospective study, no significant difference existed between G-LOC occurrence during straight-ahead (22/1914) and check-6 (32/1914) positions. During the prospective study with AGSM runs, there was no significant difference in the time at maximum G among any of the positions. During the relaxed runs, several comparisons yielded significant differences in peak G attained. These results indicate there may be an underlying physiologic effect of head and body position on acceleration tolerance; however, the AGSM and the G-suit overcame this effect. Although task saturation and distraction may compromise performance of the AGSM and subsequently predispose acceleration-related hazards, a proper AGSM, combined with effective protective systems, remains essential components of a protection strategy.

Acceleration↗
PubMed1986

Effect of inspiratory volume on intrathoracic pressure generated by an L-1 maneuver.

Since each muscle has an optimal length at which it can generate the maximum tension, an optimal inspiratory volume may exist for producing the maximum intrathoracic pressure during the L-1 maneuver. Intrathoracic pressures were measured in eight healthy men after they inspired various volumes of air and performed the L-1 straining maneuver in a 1-G environment. Both the peak and mean intrathoracic pressures increased at greater inspiratory volumes, except for the mean intrathoracic pressure at the highest volumes. The ability to increase intrathoracic pressure with larger inspiratory volumes may improve +Gz tolerance.

Adult↗
PubMed1985

Effect of body inversion on hemodynamics determined by two-dimensional echocardiography.

The purpose of this study was to determine if head-down inversion of normal men from a supine position would increase blood return to the heart. Eight healthy, normovolemic men were placed into 10 degrees, 30 degrees, 60 degrees, and 90 degrees head-down tilt positions. BP and two-dimensional echocardiograms were recorded at the supine baseline and immediately after inversion. There was no significant change in left ventricular end-diastolic volume, stroke volume, cardiac output, or BP with inversion, except for a significant increase in diastolic pressure at the 60 degree position. The efficacy of placing hypotensive shock patients in the head-down tilt position is discussed.

Adult↗
PubMed1976

Hydrodynamics of shunt valves.

A study of differential pressure valves (DPV) used in the treatment of hydrocephalus was undertaken to determine their pressure-flow characteristics and compatability with the antisiphon valve (ASV). DPV could be classified into two groups: low resistance valves (LRV) and high resistance valves (HRV). The LRV maintains intraventricular pressure (IVP) near the closing pressure (CP) of the valve by permitting a high flow whenever CP is exceeded. The HRV regulates IVP by attempting to match inflow with some point on the pressure-flow curve of the valve. These characteristics were lost unless valve outlet pressure was maintained at atmospheric pressure. This could be accomplished by using a proximal DPV with an ASV at the DPV outlet, thus converting the DPV into a gauge pressure valve and preventing the 'siphon effect' seen with the use of a DPV alone.

Cerebrospinal Fluid Shunts↗