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PubMed2002

Gravity dependence of ocular drift in patients with cerebellar downbeat nystagmus.

Downbeat nystagmus is a frequent ocular motor sign in patients with lesions of the vestibulocerebellum. The upward drift in downbeat nystagmus is a combination of a gaze-evoked drift, due to an impaired vertical neural integrator, and a velocity bias. Using a three-dimensional turntable, we analyzed the influence of gravity on these two mechanisms. Patients with cerebellar downbeat nystagmus (n = 6) and healthy subjects (n = 12) were placed in various whole-body positions along the roll, pitch, and oblique vertical planes of the head. Ocular drift was monitored with scleral search coils. Although there was no gravity dependence of the vertical gaze-evoked drift, the vertical velocity bias consisted of two components: a gravity-dependent component that sinusoidally modulated as a function of body position along the pitch plane, and a gravity-independent component that was directed upward. The combination of the two components led to an overall drift that was minimal in supine and maximal in prone position. In healthy subjects, only the gravity-dependent component was present, but in a scaled-down manner. Our results suggest that the intact vestibulocerebellum minimizes an overacting otolith-ocular reflex elicited by pitch tilt and cancels an inherent upward ocular drift that is independent of gravity-modulated otolith signals.

Adult↗

PubMedDate not supplied

[Standardized sonographic investigation of the lumbar spine in 247 newborns].

Open dysraphism is generally known before birth due to prenatal screening but occult spinal malformation often remains unrecognized. Nevertheless, newborns with occult dysraphism could be easily diagnosed by ultrasound, which might be performed additionally to the neonatal screening of the hips. Early surgical treatment or close neuropediatric follow-ups could be administered as a consequence. As part of a prospective study-design, we screened the spinal cord of 247 newborns by ultrasound. Parents were interviewed about a positive family history, a folate intake during pregnancy, amniocentesis or chorionbiopsy. Clinically, cutaneous stigmata usually associated with occult spinal dysraphism were evaluated. An orthopedic and pediatric examination followed. The sonographic investigation was done in prone position using a newly designed positioning device. The sonographic examination was performed within 5 minutes and longitudinal and transversal pictures were taken for documentation. In all of the 247 examined newborns we were able to visualize the cartilageous structures of the spinal cord and the dural sack detailly. Dependent on the position of the newborn, variations of the width of the dural sack could be noted. Thus a newly designed positioning device helped to standardize the examination situation. We did not find any pathological changes of the spinal cord. Nevertheless ultrasonography provides a useful diagnostic tool in investigating the newborn where occult spinal dysraphism is expected.

Female↗

PubMed2005

Real-time sonographic imaging for periradicular injections in the lumbar spine: a sonographic anatomic study of a new technique.

OBJECTIVE: We conducted this study to develop a sonographically guided approach to the spinal nerve of the lumbar spine and to assess its feasibility and accuracy by means of computed tomography (CT). METHODS: Fifty sonographically guided approaches at 5 levels (L1-S1) were performed on 5 embalmed cadavers, which were positioned prone. The spinal nerves of the lumbar spine were shown under sonographic guidance. In 1 cadaver, the most lateral aspect of the roof of the intervertebral foramen was defined as a reference point. Its position was computed as a distance from the tip of the spinal process (A), the midline (B), and the intervertebral disk (C). Subsequently, axial transverse CT scans were made to verify these distances. In a second part of the experiment, a spinal needle was advanced under sonographic guidance to the spinal nerves for each lumbar spinal level on 1 embalmed cadaver. The exact placement of the needle tips was checked with the help of CT. RESULTS: This technique for a sonographically guided approach to the periradicular area proved to be feasible and accurate. Sonography and CT provided the same mean measurements of 4.0, 2.5, and 1.4 cm for distances A, B, and C, respectively. The Pearson correlation coefficient was 0.99 (P < .001) between sonography and CT. In the experimental study, all 10 needle tips were placed periradicular to the spinal nerves. CONCLUSIONS: Sonographic guidance is a useful adjunct to increase the safety and efficacy of periradicular injections in the lumbar spine.

Humans↗

PubMed1987

The retrorenal colon in the supine and prone patient.

Ninety patients underwent computed tomographic scanning in both the supine and prone positions to show the orientation of the retroperitoneal colon about the kidneys and allow evaluation of changes in colonic position and contents. The data were compared with data on 500 patients scanned only when supine. Particular attention was given to bowel found posterior to the kidneys (retrorenal colon): its frequency of occurrence on 500 scans of supine patients was 1.9%, but 10.0% in the 90 prone patients. Because most invasive renal procedures would not intersect with retrorenal colon located behind the lateral one-third of the kidney, the data were reevaluated after deletion of these patients, giving a frequency in prone patients of 4.7%. This was found exclusively at the level of the lower renal poles, and the involved colon was extensively distended with gas. Attention should be given at fluoroscopy to detect this unusual, posteriorly positioned, air-filled colon before any invasive renal procedure.

Adult↗

PubMed1987

Thermal stimulation of the vestibular labyrinth during orbital flight.

During the European Spacelab mission (SL1) in 1983, caloric testing was performed for the first time in long-term weightlessness. After 2 days into orbital flight an unequivocal caloric nystagmus was observed in both subjects tested which corresponded in both quality and intensity with that measured in one-g conditions on Earth. The subsequent D1 mission enabled the experiment to be repeated on further subjects and with improved measurement procedures. As with the SL1 findings, the observed caloric nystagmus response proved to be equivalent to that measured during baseline testing on Earth. Renewed consideration of peripheral and central mechanisms, which might be involved in the elicitation of the caloric response--both in one-g and zero-g environments--has led to the reopening of a number of associated issues. One important observation which has been addressed by various research groups concerns the influence of the labyrinth's orientation to the gravity vector on the caloric response. The present authors have examined a group of healthy subjects in various body positions in the sagittal plane. The interindividual variability in the response behavior was found to be high; indeed single cases were observed in which the nystagmus response did not invert from the supine to the prone positions. These findings are discussed together with earlier reports in the literature.

Caloric Tests↗

PubMed1996

Influence of varying muscle forces on lumbar intradiscal pressure: an in vitro study.

The purposes of this study were to determine the effect of including muscle forces in the experimental loading of the spine on the intradiscal pressure and to determine whether this effect correlates with previously established in vivo data. We modeled the spine muscles as of five distinct groups and isolated the effect of each group on the intradiscal pressure (L4-L5). Seven human lumbosacral spines were tested in pure flexion/extension, right/left lateral bending, and left/right axial rotation moments. Stimulated muscle activity strongly influenced load-pressure characteristics, especially for the multifidus. Without muscle forces active, pressure increased proportionately with increasing moment. With five pairs of symmetrical constant muscle forces active (80 N per pair) the pressure increased more than 200% in neutral position and did not increase with increasing moment. The pressure without muscle forces and without axial preload was 0.12 MPa, which is about the same found by earlier in vivo studies of anesthetized subjects in prone position. With simulated muscle forces, the pressure was 0.39 MPa and in the range found for non-anesthetized subjects. We conclude that simulating muscle forces substantially affects intradiscal pressure.

Adult↗

PubMed1986

Breathing patterns in infants utilizing respiratory inductive plethysmography.

Respiratory inductive plethysmography (RIP) is a method that can be used to assess breathing patterns in infants without an airway connection. Ribcage and abdomen transducers are used which require gain factor calculation for calibration. We employed a single position graphic (SPG) calibration technique for gain factor calculation in RIP to obtain breathing pattern data for 70 infants in the quietly awake state. The SPG technique utilizes selection of two breaths from a 20s run of breaths with different ribcage/pneumotachograph (RC/PNT) and abdomen/pneumotachograph (AB/PNT) ratios for the gain factor calculation. Validation of gain factors was performed by comparing volumes obtained simultaneously by RIP and PNT. In 46 of the infants, maintenance of gain factor accuracy was confirmed following position reversal. Revalidation after position change could not be accomplished in 24 infants who were aroused into an agitated state. Breathing patterns were collected by RIP alone on the 46 infants who remained accurately calibrated in the supine and prone positions. No significant correlations were found between breathing pattern data and anthropometric characteristics. When the infants were repositioned, no consistent pattern of change could be identified. This study suggests that the SPG technique provides time-efficient and accurate calibration of RIP in the newborn infant. Furthermore, accuracy is maintained through position change if the infant remains in the same behavioral state. Breathing pattern data presented is representative of normative values in the quietly awake state for our study population.

Calibration↗

PubMed2005

Hierarchical organisation of neuro-anatomical constraints in interlimb coordination.

Based on the observation that bimanual finger tapping movements tend toward mirror symmetry with respect to the body midline, despite the synchronous activation of non-homologous muscles, F. Mechsner, D. Kerzel, G. Knoblich, and W. Prinz (2001) [Perceptual basis of bimanual coordination. Nature, 414, 69-73] suggested that the basis of rhythmic coordination is purely spatial/perceptual in nature, and independent of the neuro-anatomical constraints of the motor system. To investigate this issue further, we employed a four finger tapping task similar to that used by F. Mechsner and G. Knoblich (2004) [Do muscle matter in bimanual coordination? Journal of Experimental Psychology: Human Perception and Performance, 30, 490-503] in which six male participants were required to alternately tap combinations of adjacent pairs of index (I), middle (M) and ring (R) fingers of each hand in time with an auditory metronome. The metronome pace increased continuously from 1 Hz to 3 Hz over the course of a 30-s trial. Each participant performed three blocks of trials in which finger combination for each hand (IM or MR) and mode of coordination (mirror or parallel) were presented in random order. Within each block, the right hand was placed in one of three orientations; prone, neutral and supine. The order of blocks was counterbalanced across the six participants. The left hand maintained a prone position throughout the experiment. On the basis of discrete relative phase analyses between synchronised taps, the time at which the initial mode of coordination was lost was determined for each trial. When the right hand was prone, transitions occurred only from parallel symmetry to mirror symmetry, regardless of finger combination. In contrast, when the right hand was supine, transitions occurred only from mirror symmetry to parallel but no transitions were observed in the opposite direction. In the right hand neutral condition, mirror and parallel symmetry are insufficient to describe the modes of coordination since the hands are oriented orthogonally. When defined anatomically, however, the results in each of the three right hand orientations are consistent. That is, synchronisation of finger tapping is determined by a hierarchy of control of individual fingers based on their intrinsic neuro-mechanical properties rather than on the basis of their spatial orientation.

Adult↗

PubMed2004

[Clinical impact of recruitment maneuvers in patients with acute respiratory distress syndrome].

In patients with acute respiratory distress syndrome (ARDS), recruitment maneuvers have been proposed as an adjunct to mechanical ventilation to open up atelectasis and to keep these alveoli open by the application of adequate high levels of positive end-expiratory pressure (PEEP). Though several studies reported that the responsiveness to recruitment maneuvers resulted in a marked improvement of oxygenation with a concomitant decrease in airway pressure and/or inspiratory fraction of oxygen, the performance of recruitment maneuvers still remains a matter of dispute, especially in patients ventilated with a lung protective ventilation strategy. In this review we discuss the pathophysiological background, factors affecting the responsiveness to recruitment maneuvers and their clinical impact in the light of recently published studies. Successful recruitment depends on several factors like the applied recruitment pressure, the level of PEEP set before and after the recruitment maneuver, the stage and the underlying disease of the ARDS, chest wall mechanics and the transpulmonary pressure as well as the positioning of the patient. Regarding the current literature, recruitment maneuvers may be considered as a rescue therapy in the early stage of severe hypoxemic lung failure, if a lung protective ventilation strategy and other additive adjuncts like prone positioning or the application of inhaled vasodilators failed to induce adequate gas exchange.

Acute Disease↗

PubMed1991

Inaccuracies in quantitative radionuclide renal imaging due to patient position or diverging collimation.

Radionuclide renal studies with quantitative measurements in patients confined to intensive care units usually require the use of a 10-inch field-of-view mobile gamma camera and a diverging collimator to image both kidneys simultaneously. The patient must frequently be in the lateral decubitus position so imaging can be performed in the posterior projection. Due to spatial distortion caused by the diverging collimator, variations in detector angulation and kidney depth produce different detection efficiencies for each kidney. Counts in regions of interest over the kidneys were compared as a function of detector angulation and patient position (prone and lateral decubitus). Substantial variations were observed comparing the diverging collimator data to 15-inch field-of view parallel hole acquisitions. Significant variation can also be obtained with parallel hole collimators when the patient's position is changed.

Gamma Cameras↗

PubMedDate not supplied

Changing position does not improve the efficacy of conventional phototherapy.

The aim of this study was to compare the efficacy of position-changing phototherapy with conventional fixed-position phototherapy. Clinically well, term infants with nonhemolytic hyperbilirubinemia were enrolled in the study. After entry into the study, infants were randomly assigned to receive single-direction phototherapy with or without changing from a supine to a prone position or vice versa every 2 h. Phototherapy was initiated when the serum bilirubin concentration was greater than 15 mg/dl and was discontinued when the bilirubin level had declined below 10 mg/dl. Total serum bilirubin concentrations were measured just prior to initiation of phototherapy and at 12-h intervals until phototherapy was discontinued. The rate of bilirubin decline expressed by the first and secondary 24-h declines and overall bilirubin concentration decrease per hour were comparable between the two groups. The rebound in bilirubin levels after cessation of phototherapy was negligible, and none of the infants needed re-phototherapy. We conclude that changing an infant's position at 2-h intervals does not improve the efficacy of conventional single-direction phototherapy.

Breast Feeding↗

PubMed2004

Factors associated with pneumothorax and pneumothorax requiring treatment after percutaneous lung biopsy in 443 consecutive patients.

PURPOSE: To describe patient- and procedure-related factors associated with post-biopsy pneumothorax and those that require intervention. MATERIALS AND METHODS: Patient and procedure data from all lung biopsies performed at a single center between January 2000 and July 2001 were recorded prospectively. Data included patient demographics, lesion size, lesion depth from skin, needle size, number of passes, patient position during biopsy, imaging method used (computed tomography/fluoroscopy), if sedation was used, occurrence of pneumothorax and whether the pneumothorax required treatment. Patient charts were retrospectively reviewed to determine smoking history, as well as previous ipsilateral chest surgery or radiation therapy. Univariate and multivariate analysis was performed, and P <.05 was considered significant. RESULTS: Four-hundred fifty-three biopsies were performed on 443 patients. One-hundred six patients (23.4%) had post-biopsy pneumothorax and 31 patients (6.8% overall, 29.2% of pneumothorax group) required intervention. By univariate analysis, increased patient age, smaller lesion size, increased depth from skin, supine position, and no history of surgery were significant predictors of biopsy-related pneumothorax. However, only increased patient age, supine position, no history of ipsilateral surgery, and history of smoking were associated with pneumothorax that required intervention. By multivariate analysis, increased patient age, smaller lesion size, and no history of surgery predicted pneumothorax; supine position, history of smoking, and no history of ipsilateral surgery predicted which patients with pneumothorax would require treatment. CONCLUSION: Independent risk factors for pneumothorax include increased patient age, smaller lesion size, and no history of surgery. Previous surgery and prone positioning during biopsy appear to provide a "protective effect" against clinically significant post-biopsy pneumothorax.

Adult↗

PubMed2003

[Gas exchange in acute respiratory distress syndrome].

The hypoxemia of acute respiratory distress syndrome (ARDS) depends chiefly upon shunt and ventilation-perfusion (VA/Q) inequality produced by fluid located in the interstitial space, alveolar collapse and flooding. Variables other tham inspired oxygen fraction and the underlying physiological abnormality can influence arterial oxygen partial pressure (PaO2). Changes in cardiac output, hemoglobin concentration, oxygen consumption and alcalosis can cause changes in PaO2 through their influence on mixed venous PO2. Gas exchange (GE) in ARDS may be studied using the inert gas elimination technique (MIGET) which enables to define the distribution of ventilation and perfusion without necessarily altering the FIO2 differentiating shunt from lung units with low VA/Q ratios and dead space from lung units with high VA/Q ratios. Different ventilatory strategies that increase mean airway pressure (positive end-expiratory pressure, high tidal volumes, inverse inspiratory-expiratory ratio, etc) improve PaO2 through increasing lung volume by recruiting new open alveoli and spreading the intra-alveolar fluid over a large surface area. Also prone-position ventilation would result in a marked improvement in GE enhancing dorsal lung ventilation by the effects on the gravitional distribution of pleural pressure and the reduction in the positive pleural pressure that develops in dorsal regions in ARDS. Inhaled nitric oxide (NO) has been shown to increase PaO2 in ARDS patients by inducing vasodilation predominantly in ventilated areas redistributing pulmonary blood flow away from nonventilated toward ventilated areas of the lung thus resulting in a shunt reduction. On the same way inhaled prostaglandins (PGI2 or PGE1) causes selective pulmonary vasodilation improving pulmonary GE. Intravenous almitrine, a selective pulmonary vasoconstrictor, has been shown to increase PaO2 by increasing hypoxic pulmonary vasoconstriction. A synergistic effect was found between inhaled NO and almitrine. In spite of the improval of GE shown by these different techniques on ARDS, no effect was demonstrated on mortality or duration of mechanical ventilation.

Acute Disease↗

PubMed2005

Ventilatory management of acute lung injury and acute respiratory distress syndrome.

CONTEXT: The acute lung injury and acute respiratory distress syndrome are critical illnesses associated with significant morbidity and mortality. Mechanical ventilation is the cornerstone of supportive therapy. However, despite several important advances, the optimal strategy for ventilation and adjunctive therapies for patients with acute lung injury and acute respiratory distress syndrome is still evolving. EVIDENCE ACQUISITION: To identify reports of invasive ventilatory and adjunctive therapies in adult patients with acute lung injury and acute respiratory distress syndrome, we performed a systematic English-language literature search of MEDLINE (1966-2005) using the Medical Subject Heading respiratory distress syndrome, adult, and related text words, with emphasis on randomized controlled trials and meta-analyses. EMBASE and the Cochrane Central Register of Controlled Trials were similarly searched. The search yielded 1357 potential articles of which 53 were relevant to the study objectives and considered in this review. EVIDENCE SYNTHESIS: There is strong evidence to support the use of volume- and pressure-limited lung-protective ventilation in adult patients with acute lung injury and acute respiratory distress syndrome. The benefit of increased levels of positive end-expiratory pressure and recruitment maneuvers is uncertain and is being further evaluated in ongoing trials. Existing randomized controlled trials of alternative ventilation modes, such as high-frequency oscillation and adjunctive therapies, including inhaled nitric oxide and prone positioning demonstrate no significant survival advantage. However, they may have a role as rescue therapy for patients with acute respiratory distress syndrome with refractory life-threatening hypoxemia. CONCLUSIONS: Volume- and pressure-limited ventilation strategies should be used in managing adult acute lung injury and acute respiratory distress syndrome patients. Further research is needed to identify barriers to widespread adoption of this strategy, as well as the role of alternative ventilation modes and adjunctive therapies.

Humans↗

PubMed2000

Pre-, intra-, and postoperative three-dimensional evaluation of adolescent idiopathic scoliosis.

The authors measured and compared the pre-, intra-, and postoperative three-dimensional shape of the spine during corrective surgery to quantify the specific contribution of positioning, anesthesia, surgical exposure, surgical instrumentation, and postural adaptation of the thoracic and lumbar spine. In 58 adolescent girls with idiopathic scoliosis undergoing corrective surgery by a posterior approach, the three-dimensional geometry of the thoracic and lumbar spine was documented in the standing position before and after surgery using a three-dimensional reconstruction technique based on multiplanar radiography, and the intraoperative three-dimensional geometry was measured using a three-dimensional magnetic digitizer before and after installation of the first rod. Prone positioning, anesthesia, and surgical exposure are responsible for a considerable decrease in all curves in the frontal and sagittal plane. Instrumentation with the first rod produces additional substantial and favorable three-dimensional changes with partial restoration of the normal sagittal curves and sagittal shift of the plane of maximum deformity. Although no loss of correction was observed in the frontal plane when patients resumed their standing position, a "spring-back" effect on the spine was noted in the sagittal plane and a loss of three-dimensional correction was seen in the orientation of the plane of maximum deformity. Surgeons can use the knowledge of these various changes to achieve better results by more careful attention to the preoperative positioning of patients and to curve correction in the sagittal plane when instrumentation is applied to the spine.

Adolescent↗

PubMed1995

Chest position and pulmonary deposition of surfactant in surfactant depleted rabbits.

AIMS: To investigate the correlation between chest position and the distribution of surfactant in the lungs of surfactant depleted rabbits, to corroborate current guidelines on the intratracheal instillation of exogenous surfactant in newborns. METHODS: Twelve tracheotomised rabbits, depleted of pulmonary surfactant by saline bronchoalveolar lavage, were given intratracheal 99m Technetium labelled Exosurf in three positions (prone, right side down, and left side down) (n = 4 in each group). They were monitored for 10 minutes using dynamic gamma scintigraphy monitoring. Instillation completed, the lateral lying animals were turned to the opposite side to determine whether redistribution of the surfactant had taken place. The amount of radiolabelled surfactant deposited at the peripheral, central, dorsal and ventral parts of the lungs was then estimated by gamma counting of the lung sections at necropsy. RESULTS: Both gamma scintigraphy and gamma counting showed similar rates and total amount of surfactant accumulation in both lungs of the prone animals. In the lateral lying animals surfactant accumulated at a significantly faster rate in the dependent lungs: the amount of surfactant deposition was three to 14-fold that in the raised lungs (p = 0.017; nested ANOVA). Changing the chest position immediately after instillation did not redistribute the surfactant. In all three groups of animals there was no significant difference in deposition between the peripheral, central, ventral and dorsal parts of the lungs. CONCLUSIONS: Pulmonary distribution of intratracheally instilled surfactant is largely determined by gravity, and changing the chest position after instillation does not result in any redistribution of the surfactant. During the instillation of exogenous surfactant to newborn infants, keeping the chest in the horizontal position may therefore result in the most even distribution of the surfactant in the two lungs. Further deposition studies are required to evaluate the validity of the current recommendations on surfactant administration.

Animals↗

PubMed1990

Influence of static head position on the horizontal nystagmus evoked by caloric, rotational and optokinetic stimulation in the squirrel monkey.

We studied the influence of static head position on the horizontal nystagmus produced by caloric, rotational and optokinetic stimulation in alert squirrel monkeys. Caloric nystagmus is stronger for nose up (NU) than for nose down (ND) pitches; so, for example, slow-phase eye velocity is four times larger in supine than in prone positions. A similarly directed asymmetry occurs in the horizontal vestibulo-ocular (HVOR) responses to long-duration, constant angular-head accelerations, but not to midband (0.1 Hz) sinusoidal head rotations. Consistent with a first-order model of the HVOR, the low-frequency or acceleration gain of the reflex (GA) is equal to the product of the midband velocity gain (GV) and a time constant (TVOR). GV is proportional to the cosine of the angle between the horizontal-canal plane and the plane of rotation, from which it is concluded that signals from the horizontal, but not from the vertical canals contribute to the HVOR. TVOR can be as much as twice as large in NU than in ND positions. GA is proportional to TVOR and it, too, shows a NU-ND asymmetry. The time constant of optokinetic after nystagmus (TOKAN) was also studied. Since TVOR and TOKAN are modified in similar ways by static tilts, it is concluded that head position affects the time constants by way of velocity-storage mechanisms. Evidence is presented that the position-dependent modification of velocity storage is otolith-mediated. The results are used to analyze the mechanisms of caloric nystagmus. The caloric response consists of a convective component (CC), as originally envisioned by Bárány (1906), and a nonconvective component (NC). CC accounts for 75% of the caloric response in the conventional supine testing position. Both components can be affected by the position-dependent modification of TVOR or, equivalently, of GA. It has been suggested that two mechanisms might contribute to NC: 1) a direct thermal effect on hair cells or afferents; or 2) a thermal expansion of labyrinthine fluids that results in a cupular displacement. Both theoretical and experimental evidence indicates that only the first of these mechanisms could result in the steady-state caloric response that is observed in the absence of convection (e.g., in spaceflight and after canal plugging) and that contributes to the prone-supine asymmetry seen in caloric testing.

Animals↗

PubMed1987

Cephalad renal movement during percutaneous nephrostolithotomy.

The change in the position of the kidney during percutaneous nephrostomy is a major concern to urologists who participate in percutaneous stone removal. We report that the majority of kidneys ascend an average of 2.2 cm. when the patient turns from a supine to a prone position. This change in position is more marked on the right side and is more common in male patients. Knowledge of this anatomical variation is important to determine which patients are suitable candidates for percutaneous nephrostolithotomy and to plan a percutaneous approach to a renal or ureteral calculus.

Adult↗