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Biomedical subjects

W H Paloski

Publications and source records attributed to W H Paloski.

16 recordsLinked to original sources
PubMed1995

Vestibular plasticity following orbital spaceflight: recovery from postflight postural instability.

Results of previous studies suggested that the vestibular mediated postural instability observed in astronauts upon return to earth from orbital spaceflight may be exacerbated by an increased weighting of visual inputs for spatial orientation and control of movement. This study was performed to better understand the roles of visual and somatosensory contributions to recovery of normal sensori-motor postural control in returning astronauts. Preflight and postflight, 23 astronaut volunteers were presented randomly with three trials of six sensory organization test (SOT) conditions in the EquiTest system test battery. Sagittal plane center-of-gravity (COG) excursions computed from ground reaction forces were significantly higher on landing day than preflight for those test conditions presenting sway-referenced visual and/or somatosensory orientation cues. The ratio of summed peak-to-peak COG sway amplitudes on the two sway-referenced vision tests (SOTs 3 + 6) compared to the two eyes closed tests (SOTs 2 + 5) was increased on landing day, indicating an increased reliance on visual orientation cues for postural control. The ratio of peak-to-peak COG excursions on sway-referenced surfaces (SOTs 4, 5 & 6) to an earth fixed support surfaces (SOTs 1, 2 & 3) increased even more after landing suggesting primary reliance on somatosensory orientation cues for recovery of postflight postural stability. Readaptation to sway-referenced support surfaces took longer than readaptation to sway-referenced vision. The increased reliance on visual and somatosensory inputs disappeared in all astronauts 4-8 days following return to earth.

Astronauts↗
PubMed1994

Space flight and neurovestibular adaptation.

Space flight represents a form of sensory stimulus rearrangement requiring modification of established terrestrial response patterns through central reinterpretation. Evidence of sensory reinterpretation is manifested as postflight modifications of eye/head coordination, locomotor patterns, postural control strategies, and illusory perceptions of self or surround motion in conjunction with head movements. Under normal preflight conditions, the head is stabilized during locomotion, but immediately postflight reduced head stability, coupled with inappropriate eye/head coordination, results in modifications of gait. Postflight postural control exhibits increased dependence on vision which compensates for inappropriate interpretation of otolith and proprioceptive inputs. Eye movements compensatory for perceived self motion, rather than actual head movements have been observed postflight. Overall, the in-flight adaptive modification of head stabilization strategies, changes in head/eye coordination, illusionary motion, and postural control are maladaptive for a return to the terrestrial environment.

Adaptation, Physiological↗
PubMed1993

Vestibular ataxia following shuttle flights: effects of microgravity on otolith-mediated sensorimotor control of posture.

Orbital spaceflight exposes astronauts to an environment in which gravity is reduced to negligible magnitudes of 10(-3) to 10(-6) G. Upon insertion into earth orbit, the abrupt loss of the constant linear acceleration provided by gravity removes the otolith stimulus for vestibular sensation of vertical orientation constantly present on Earth. Since the central nervous system (CNS) assesses spatial orientation by simultaneously interpreting sensory inputs from the vestibular, visual, and proprioceptive systems, loss of the otolith-mediated vertical reference input results in an incorrect estimation of spatial orientation, which, in turn, causes a degradation in movement control. Over time, however, the CNS adapts to the loss of gravitational signals. Upon return to Earth, the vertical reference provided by gravitational stimulation of the otolith organ reappears. As a result, a period of CNS readaptation must occur upon return to terrestrial environment. Among the physiological changes observed during the postflight CNS readaptation period is a disruption of postural equilibrium control. Using a dynamic posturography system (modified NeuroCom EquiTest), 16 astronauts were tested at 60, 30, and 10 days preflight and retested at 1 to 5 hours, and 8 days postflight. All astronauts tested demonstrated decreased postural stability immediately upon return to Earth. The most dramatic increases in postural sway occurred during those sensory conditions in which both the visual and proprioceptive feedback information used for postural control were altered by the dynamic posturography system, requiring reliance primarily upon vestibular function for control of upright stance. Less marked but statistically significant increases in sway were observed under those conditions in which visual and foot support surface inputs alone were altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Recovery of postural equilibrium control following spaceflight.

Decreased postural stability is observed in most astronauts immediately following spaceflight. Because ataxia may present postflight operational hazards, it is important to determine the incidence of postural instability immediately following landing and the dynamics of recovery of normal postural equilibrium control. It is postulated that postflight postural instability results from in-flight adaptive changes in central nervous system (CNS) processing of sensory information from the visual, vestibular, and proprioceptive systems. The purpose of the present investigation was to determine the magnitude and time course of postflight recovery of postural equilibrium control and, hence, readaptation of CNS processing of sensory information. Thirteen crew members from six spaceflight missions were studied pre- and postflight using a modified commercial posturography system. Postural equilibrium control was found to be seriously disrupted immediately following spaceflight in all subjects. Readaptation to the terrestrial environment began immediately upon landing, proceeded rapidly for the first 10-12 hours, and then proceeded much more slowly for the subsequent 2-4 days until preflight stability levels were reachieved. It is concluded that the overall postflight recovery of postural stability follows a predictable time course.

Adult↗
PubMed1987

Effects of gas properties and waveform asymmetry on gas transport in a branching tube network.

Local gas transport coefficients, quantifying longitudinal dispersion through a symmetrical constant-diameter tube network, have been measured during oscillation with both symmetrical and nonsymmetrical waveforms. Experiments were carried out over a range of conditions that would prevail in the central to lower airways during high-frequency ventilation at moderate frequency (5 Hz) and tidal volume (15-80 ml). Gas transport coefficients resulting from oscillation of three different resident-trace gas pairs were measured using a new analytic technique. This technique allowed rapid determination of the transport coefficient distribution along the entire network. Results demonstrate a small but significant influence attributable to changes in gas properties that is similar to that found in a straight tube and indicate that augmented dispersion is an important mechanism of axial transport. Gas transport coefficients were found to be unaffected by changes in flow waveform symmetry, suggesting that previously reported improvements in gas exchange associated with decreasing inspiratory to expiratory time ratios are not due to a change in local conditions such as asymmetry in the velocity profile.

Air↗
PubMed1985

Effects of changing inspiratory to expiratory time ratio on carbon dioxide elimination during high-frequency jet ventilation.

Clinical observations indicate that gas exchange during high-frequency ventilation can be improved by decreasing the inspiratory to expiratory time ratio (I/E). Decreasing I/E at a fixed frequency may therefore allow a reduction of tidal volume (VT) without affecting gas exchange. This decreased VT may result in lower airway pressures, and thereby reduce the incidence of barotrauma. In order to quantify the effects of I/E on gas exchange, the relationship between carbon dioxide elimination and VT was studied in 6 mongrel dogs at I/E of 1/2, 1/1, and 2/1. Ventilation was provided by a jet-type high-frequency ventilator using a frequency of 5 Hz and VT of 17 to 100% of the anatomic dead space. Carbon dioxide elimination was found to vary inversely with (I/E)0.9, corroborating the clinical observations. These data add further evidence that I/E may be a useful parameter in optimizing high-frequency ventilation and provide a quantitative relationship that can be used to predict the effect that altering I/E will have on gas exchange.

Animals↗
PubMed1982

Failure of red blood cell transfusion to increase oxygen transport or mixed venous PO2 in injured patients.

Post-trauma patients have an oxygen consumption which is proportional to oxygen delivery, suggesting that tissue oxygen consumption is limited by diffusion. Transfusion of packed red blood cells (RBC), which increases the oxygen-carrying capacity of blood, would be expected to increase mixed venous PO2, thereby improving tissue oxygenation. However, the low P50 of stored blood may increase the affinity of hemoglobin for oxygen and reduce oxygen consumption. To evaluate the net effect of these mechanisms, we studied hemodynamic and oxygen transport parameters before and after RBC transfusion in eight critically ill patients. Mixed venous O2 content was measured directly by fuel cell O2 analyzer, and standard P50 was calculated. Following transfusion of one unit of packed RBC which increased mean hemoglobin from 9.2 +/- 0.3 gm/dl to 10.1 +/- 0.3 gm/dl (p less than 0.01), there were no changes in oxygen delivery (490 +/- 80 ml/min/m2), oxygen consumption (210 +/- 30 ml/min/m2), or mixed venous PO/ (37 +/- 2 Torr). Cardiac index (4.1 +/- 0.71 L/min) decreased by 0.4 L/min/m2 (p less than 0.05). Standard P50 decreased by 4.2 +/- 2.4 Torr following transfusion of two units of RBC (p less than 0.05). Red blood cell transfusion thus failed to increase oxygen consumption in these patients, despite an increase in oxygen content. Thus, RBC transfusion may not improve tissue oxygenation.

Adult↗
PubMed1982

Delayed pulmonary dysfunction in head-injured patients.

Intracranial pressure (ICP), cardiopulmonary function, and the degree of neurological dysfunction were measured in 13 patients with serious head injury to determine the relationship of these indices to the development of delayed pulmonary dysfunction. All patients had serious isolated head injury with Glasgow Coma Scale scores of 7 or less 6 hours after injury and elevated ICP at the time of admission to the protocol. Three patients developed arterial pO2 of less than or equal to 80 torr despite the initiation of elevated inspired oxygen fraction (FIO2 greater than or equal to 0.5) and positive end expiratory pressure (greater than or equal to 5 cm H2O. One of these three patients had a decline in neurological function, quantified by the Albany Head-Injury Watch Sheet, associated with hypoxemia. The only patients who developed intrapulmonary shunt fractions of more than 15% were five patients who had increased pulmonary vascular resistance (PVR) and elevated or increasing cardiac index, suggesting persistent perfusion to areas of the lung which normally are hypoperfused due to hypoxic pulmonary vasoconstriction. This mismatching of the distribution of ventilation and perfusion was confirmed using the multiple inert gas elimination technique in two patients with an increased shunt fraction. Unperfused gas exchange units were also found to be present, as confirmed by an abnormal multiple inert gas elimination techniques, high PVR and dead space/tidal volume ratio (VD/VT), and low extravascular lung water. Abnormalities of ICP and cerebral perfusion pressure could not be correlated with changes in any of the cardiopulmonary functions studied.

Adolescent↗
PubMed1981

A system to measure functional residual capacity in critically ill patients.

The use of continuous positive airway pressure (CPAP) and intermittent mandatory ventilation (IMV) in spontaneously breathing, intubated patients has prompted the development of new procedures for measuring functional residual capacity (FRC). The authors have developed a system for measuring FRC by the multiple breath nitrogen washout technique, which is suitable for use on intubated patients breathing with CPAP, IMV, or intermittent positive pressure ventilation (CONTROL) and on nonintubated patients. This system uses a pair of synchronized volume ventilators to permit a step change in inspired N2 fraction while providing therapeutic ventilatory support. A rapid-response nitrogen analyzer and a modified bellows spirometer are used for continuous measurement of airway nitrogen concentration and expired gas flow rate. FRC is calculated on-line by a digital computer. The system accuracy was tested on a mechanical lung simulator in the CPAP and CONTROL modes. The measured volume was found to agree within 58 +/- 52 ml of the actual volume in the CONTROL mode and within 104 +/- 22 ml in the CPAP mode. The system was also tested for repeatability by making duplicate FRC determinations in patients with respiratory insufficiency. In the 18 patients studied, the correlation coefficient of these duplicate measurements was r = 0.987 and the mean difference between measurements was 49 +/- 24 ml. This noninvasive system also provides data used to calculate anatomical deadspace by Fowler's method (VSDS) and uniformity of ventilation (V/V) for multicompartment lung models.

Functional Residual Capacity↗
PubMed1981

Nitroprusside and nitroglycerine in patients with posttraumatic pulmonary failure.

Pulmonary artery pressure is frequently elevated in patients with post-traumatic pulmonary dysfunction. To ascertain whether or not this increase is reversible and what effects such reversal would have on gas exchange, the vasodilators nitroprusside and nitroglycerine were administered to 11 such patients. Pulmonary hemodynamics an gas exchange were observed. Mean pulmonary artery pressure and pulmonary vascular resistance decreased and pulmonary shunt increased. Cardiac output did not change. These results imply that much of the increase in pulmonary artery pressure is due to a reversible restriction of blood flow past unventilated alveoli. Hypoxic vasoconstriction is postulated to be a major cause of the increase in pulmonary artery pressure.

Blood Pressure↗
PubMed1980

Detrimental effects of removing end-expiratory pressure prior to endotracheal extubation.

Patients recovering from acute respiratory insufficiency are usually not extubated until they can ventilate adequately while breathing spontaneously at ambient end-expiratory pressure (T-tube). It is hypothesized that this period of T-tube breathing might be detrimental to gas exchange since the endotracheal tube abolishes the expiratory retard produced by the glottis and thereby inhibits the patient's ability to maintain adequate functional residual capacity (FRC). To test this hypothesis, pulmonary function of 17 patients was compared during T-tube breathing and Continuous Positive Airway Pressure (CPAP) and after extubation. Intrapulmonary shunt was higher (p less than 0.05) and arterial PO2 and FRC were lower (p less than 0.05) during T-tube breathing than during CPAP or after extubation. In contrast, shunt, PaO2 and FRC were similar during CPAP and after extubation. Furthermore, after extubation there was an increase (p less than 0.05) in mean expiratory airway pressure as compared to T-tube breathing. A comparison of patients extubated from T-tube with patients extubated from CPAP showed no difference in postextubation shunt, PaO2 or FRC. These data suggest that endotracheal intubation should be accompanied by low levels of CPAP and that patients should be extubated directly from CPAP. The practice of placing patients in T-tube prior to extubation should be abandoned as unnecessary and potentially harmful.

Adult↗
PubMed1980

Increased creatinine clearance following cryoprecipitate infusion in trauma and surgical patients with decreased renal function.

Deficiency of opsonic alpha 2 surface binding (SB) glycoprotein (cold-insoluble globulin, plasma fibrinectin) is related to depressed reticulendothelial function as well as to multiple organ failure after tissue injury and sepsis. Cryoprecipitate (250 ml), extracted from 10 units of human plasma, was infused over 60 minutes into 11 hypo-opsonemic patients with decreased renal function. Cardiac output, mean arterial pressure, creatinine clearance, and limb blood flow were measured before and at intervals of 14 to 20, 35 to 44, and 60 to 66 hours following cryoprecipitate infusion. Before infusion, the mean creatinine clearance was 30 +/- 4 ml/min/M2 body surface area (BSA) and increased to 40 +/- 6 ml/min/M2 BSA at 14 to 20 hrs (p < 0.05); to 40 +/- 4 ml/min/M2 BSA at 35 to 44 hrs (p < 0.05); and to 40 +/- 5 ml/min/M2 BSA at 60 to 66 hrs (p < 0.05). In contrast, mean arterial pressure and cardiac index at each time interval showed no significant changes from the pretreatment values of 81 +/- 6 mm Hg and 3.4 +/- .2 L/min/M2 BSA, respectively. Limb blood flow increased significantly at 4 hours and returned to control values by 35 to 44 hours. Thus cryoprecipitate infusion to critically ill trauma and surgical patients with depressed renal function may improve glomerular filtration rate independently of mean arterial pressure or cardiac output. This improved renal function may be related to increased reticuloendothelial clearance of blood-borne particulates and/or improved microcirculatory function and lends support to the concept that RES failure may be involved in the etiology of multiple organ failure secondary to combined tissue injury and sepsis.

Adolescent↗
PubMedDate not supplied

Geometric adjustments to account for eye eccentricity in processing horizontal and vertical eye and head movement data.

Neglecting the eccentric position of the eyes in the head can lead to erroneous interpretation of ocular motor data, particularly for near targets. We discuss the geometric effects that eye eccentricity has on the processing of target-directed eye and head movement data, and we highlight two approaches to processing and interpreting such data. The first approach involves determining the true position of the target with respect to the location of the eyes in space for evaluating the efficacy of gaze, and it allows calculation of retinal error directly from measured eye, head, and target data. The second approach effectively eliminates eye eccentricity effects by adjusting measured eye movement data to yield equivalent responses relative to a specified reference location (such as the center of head rotation). This latter technique can be used to standardize measured eye movement signals, enabling waveforms collected under different experimental conditions to be directly compared, both with the measured target signals and with each other. Mathematical relationships describing these approaches are presented for horizontal and vertical rotations, for both tangential and circumferential display screens, and efforts are made to describe the sensitivity of parameter variations on the calculated results.

Eye Movements↗