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PubMed1988

[Radiation loading problems in petrous bone tomography. Experimental research using film dosimetry on the Alderson phantom].

Using film dosimetry and an Alderson skull phantom, the iso-dose distribution during tomography of the petrous bone was investigated. We were particularly concerned with the radiation dose to the lens of the eye, the critical organ in the skull, and to the inner ear, using different types of examination and various positions of the skull. The choice of suitable film material and standardisation against TLD measurements is crucial for the accuracy of film dosimetry, allowing for correction of film blackening in relation to varying energies. Tomography of the petrous bone in the prone position produced a reduction in radiation dose to the eye to only 1 to 4% of the dose incident on the occiput. In this way, and using high definition screen and grinds, it is possible to obtain optimal tomographic images despite drastic reduction of the scattered radiation to the eye. Radiation dose to the inner ear is greatly below any significant somatic does, irrespective of projection or technique. Special measures to reduce radiation to the inner ear are neither effective nor sensible.

Film Dosimetry↗

PubMed1997

Macular hole surgery without face-down positioning. A pilot study.

PURPOSE: To investigate whether postoperative face-down positioning is necessary for successful macular hole repair. BACKGROUND: Although never proven, face-down positioning is strongly considered an important maneuver to achieve macular hole closure. Face-down posturing is inconvenient, and for patients with physical or mental limitations, weeks of face-down positioning may be an impossible task. A gas bubble that completely fills the vitreous cavity will tamponade a macular hole despite head position and may close a macular hole as effectively as a partial gas fill with face-down positioning. If face-down positioning were not necessary, more patients would be eligible to benefit from this surgery. METHODS: Thirty-three consecutive eyes in 31 patients aged 65-79 years with Stage II, III, or IV full-thickness macular holes underwent macular hole surgery with a complete 15% C3F8 vitreous fill. Hole duration varied from 1 month to 10 years; in 21% of eyes, (seven of 33) holes had been present for more than 1 year. All phakic eyes (n = 25) had cataract extraction with intraocular lens insertion when macular hole surgery was done. No patients were positioned face down. RESULTS: The follow-up period was 6-40 months; 73% of the patients have been observed for more than 1 year. Preoperative hole duration did not affect hole closure rate. The success rate after one surgery was 79% (26 of 33 eyes), and with additional vitrectomy surgery, the total success rate was 85% (28 of 33 eyes). Forty-eight percent of eyes attained visual acuity of 20/50. Eighty percent of eyes with preoperative acuity of > 20/100 attained > 20/50 acuity. Significant complications included iris incarceration into the cataract wound during a postoperative fluid-gas exchange (one eye), posterior synechiae (four eyes), intraocular lens capture (two eyes), elevated intraocular pressure (three eyes), and retinal detachment (three eyes). Most of these problems can be avoided or reduced. CONCLUSION: This pilot study suggests that successful macular hole closure is possible without face-down positioning. This technique may be an alternative for patients with macular holes in pseudophakic eyes who are unable to assume face-down posturing. Combining cataract surgery with this technique for macular hole repair is reasonable for phakic patients who cannot maintain prone positioning. Major disadvantages of combined surgery include the morbidity of the second procedure and removal of a visually insignificant cataract. This approach should be considered for those patients unable to tolerate face-down positioning.

Cataract↗

PubMed2000

An approach to ventilation in acute respiratory distress syndrome.

Appropriate management of patients with acute respiratory distress syndrome (ARDS) represents a challenge for physicians working in the critical care environment. Significant advances have been made in understanding the pathophysiology of ARDS. There is also an increasing appreciation of the role of ventilator-induced lung injury (VILI). VILI is most likely related to several different aspects of ventilator management: barotrauma due to high peak airway pressures, lung overdistension or volutrauma due to high transpulmonary pressures, alveolar membrane damage due to insufficient positive end expiratory pressure levels and oxygen-related cell toxicity. Various lung protective strategies have been suggested to minimize the damage caused by conventional modes of ventilation. These include the use of pressure- and volume-limited ventilation, the use of the prone position in the management of ARDS, and extracorporeal methods of oxygen delivery and carbon dioxide removal. Although the death rate resulting from ARDS has been declining over the past 10 years, there is no evidence that any specific treatment or change in approach to ventilation is the cause of this improved survival.

Barotrauma↗

PubMed1992

Human plantarflexor stiffness to multiple single-stretch trials.

The purpose of this investigation was to determine the influence of different stretch velocities, different rates of pre-stretch force development, and different pre-stretch muscle lengths on the intrinsic stiffness exhibited by the quasi-statically contracting active human plantarflexors during multiple single-stretch trials at 20-60% of maximum isometric contraction. Subjects were positioned prone, with the knee flexed 1.57 rad(90 degrees), shank stabilized, and foot secured in a hard plastic orthotic. Slowly increasing isometric plantarflexion force was produced until the plantarflexors were stretched by a rapid 0.2 rad (12 degrees) dorsiflexion movement. Plantarflexion forces and ankle positions were determined during these stretches as well as during resting stretches when the muscle was inactive. Resting forces were subtracted from the active trials, forces converted to torques, and stiffnesses determined for the first 62 ms of the stretch. The slope of the stiffness vs pre-stretch torque relationship averaged 4.30 +/- 0.34 Nm rad-1 Nm-1. Little difference was found between stiffness determined through the single-stretch method and the results of previous studies employing different mechanical inputs. Differences in stiffnesses with different stretching velocities were caused by computational artifact rather than by differences in intrinsic muscular reaction. Faster rates of pre-stretch force increase prior to the stretch resulted in slightly lower stiffnesses. Different pre-stretch muscle lengths apparently did not result in different stiffnesses. The shape of the torque vs displacement curve was remarkably insensitive to the planned manipulations of the testing conditions, responding in a stereotypical manner.

Adult↗

PubMed1984

Effect of posture on extradural pressure.

Extradural pressure was measured in the lateral and the supine positions in three groups of patients using the extradural catheter as a manometer. The groups consisted of 20 pregnant patients at or near term, 10 patients in the period after childbirth and 10 male surgical patients. In every patient, the extradural pressure in the supine position was greater than that in the lateral position. The mean extradural pressures in the lateral and the supine positions were similar in the three groups. It is suggested that the difference between the extradural pressures in the lateral and the supine positions is physiological and occurs irrespective of vena caval compression. Extradural pressure changes are probably the result of postural changes in the cerebrospinal fluid (CSF) pressure. The influence of CSF pressure on extradural pressure was confirmed further by measuring the extradural pressure in the prone position in five pregnant patients.

Adolescent↗

PubMed1978

Regional intrapulmonary gas distribution in awake and anesthetized-paralyzed prone man.

The intrapulmonary distribution of inspired gas (ventilation/unit lung volume, VI), functional residual capacity (FRC), closing capacity (CC), and the slope of phase III were determined in five awake and five anesthetized-paralyzed volunteers who were in the prone position with the abdomen unsupported. After induction of anesthesia-paralysis, FRC was less in four of five subjects and CC was consistently less. At FRC there was no difference in the vertical gradient of regional lung volumes between the awake and anesthetized-paralyzed prone subjects. Also, there was no difference in VI between the two states. The normalized slope of phase III decreased consistently with induction of anesthesia-paralysis, but the vertical distribution of a 133Xe bolus inhaled from residual volume was not different between the two states. The data of the study are compatible with 1) a pattern of expansion of the respiratory system during anesthesia-paralysis and mechanical ventilation different than that during spontaneous breathing and 2) a more uniform intraregional distribution of inspired gas and/or a different sequence of emptying during anesthesia-paralysis.

Adult↗

PubMedDate not supplied

Quality control by portal film analysis in radiotherapy for prostate cancer: a comparison between two different institutions and treatment techniques.

AIMS AND BACKGROUND: Accuracy and reproducibility of patient setup during radiotherapy for prostate cancer were investigated in two different Institutions (A and B), within their Quality Assurance programs. The purpose of the study was to evaluate and compare setup accuracy and reproducibility in Institutions A and B, which adopt different patient positioning and treatment techniques for prostate irradiation. MATERIALS AND METHODS: A retrospective analysis of portal localization films taken during the treatment course was performed: 30 and 21 patients in Institutes A and B, respectively, entered the study. In Institute A, patients were treated in a prone position, utilizing an individualized immobilization cast (either an alpha cradle or a heat and vacuum-formed cellulose acetate cast) with an open table top and individual abdominal wall compressor to minimize small bowel irradiation; a 5-field conformal technique was used. In Institute B, patients were treated in a supine position without any immobilization device; a 6-field BEV-based technique (conformal only for patients treated with a radical aim) was adopted. A total of 598 portal films (420 from Institute A and 178 from Institute B) were analyzed. The mean number of films per patient was 12 (range, 4-29). Systematic and random setup errors were estimated utilizing the statistical method suggested by Bijhold et al. (1992). RESULTS: When patients with a mean (systematic) error larger than 5, 8 and 10 mm in craniocaudal, lateral and posterior-anterior directions, respectively, were compared, no statistically significant difference between the two groups was observed. Similarly, when comparing portal films, a significant difference (P <0.01) appeared only in the craniocaudal direction (errors > 5 mm: Institute A = 24%; Institute B = 11%). In both Institutes, the SD of random and systematic error distribution ranged from 1.8 to 4.2 mm, with a small prevalence of systematic errors. Only for craniocaudal shifts in Institute A was the random error larger than the systematic error, and it was significantly worse than in Institute B (1 SD, 4.2 mm in Institute A vs 1.8 mm in Institute B). CONCLUSIONS: Setup errors observed in Institutes A and B were similar and in accord with data reported in the literature. In Institute B, satisfactory geometrical treatment quality was achieved without patient immobilization. In Institute A, the goal of minimizing small bowel irradiation and prostate motion through the aforementioned technique, which makes patient position less comfortable, did not seem to considerably increase daily setup uncertainty.

Aged↗

PubMed1999

Validation of simple tests of biathlon shooting ability.

The aim of this study was to validate three simple tests of biathlon shooting abilities. Twelve expert biathletes performed visual reaction time tests adapted for the rifle in the standing (RT-S) and prone positions (RT-P), and a tremometer test adapted for the rifle in the standing position (TT-S). Six consecutive days' measurements showed an acceptable reproducibility for these tests (coefficient of variation = 1.2% for RT-S, 1.1% for RT-P and 6.5% for TT-S). A significant difference was observed between TT-S at rest and after roller skiing 2.1 km at 90 % of maximal heart rate. This finding demonstrates the sensitivity of TT-S to discriminate the effects of fatigue on postural control. Among 24 biathletes of regional to expert level, significant correlations were observed between resting RT-P and prone shooting performance after roller skiing (r2 = 0.23; p = 0.01) and between resting TT-S and shooting performance in the standing position after roller skiing (r2 = 0.68; p = 0.0001), demonstrating the specificity of these tests. From these results, we conclude that TT-S is a valid field test of biathlon shooting performance.

Adult↗

PubMed1978

Influence of head position on the prognosis of experimental subarachnoid hemorrhage.

Autogenous blood was injected repeatedly into the intracranial subarachnoid space of cats, the heads of which were placed in one of four positions (prone, supine, left side down, and right side down). Epidural pressures, mean aortic blood pressures, and pulse rates were measured, and their responses to the repeated injections were analyzed. The distribution of the injected blood was different among the four groups. The cats in the sulpine position had the greatest amounts of blood in the posterior fossa and tolerated the injections least well. The position of the head at the time of a subarachnoid hemorrhage may influence the prognosis; positions that favor accumulations of blood around the brain stem carry the greatest risk.

Animals↗

PubMed2005

Ventilatory strategies in patients with sepsis and respiratory failure.

Patients with sepsis may require mechanical ventilation due to the acute respiratory distress syndrome (ARDS). It has become increasingly accepted that mechanical ventilation can contribute to lung injury in these patients. The modern concept of ventilator-induced lung injury is described in the context of alveolar over-distention (volutrauma), alveolar de-recruitment (atelectrauma), and biochemical injury and inflammation to the lung parenchyma (biotrauma). To avoid over-distention lung injury, the tidal volume should be set at 6 mL/kg predicted body weight and plateau pressure should be limited to 30 cm H2O. This has been shown to afford a survival benefit. Although setting positive end-expiratory pressure (PEEP) to zero is likely harmful during mechanical ventilation of patients with ARDS, evidence is lacking for a survival benefit if a high PEEP level is set compared with a modest level of PEEP. Although adjunctive measures such as recruitment maneuvers, prone position, and inhaled nitric oxide may improve oxygenation, evidence is lacking that these measures improve survival.

Journal Article↗

PubMed2004

Regulation of regional lung perfusion by nitric oxide.

Improved oxygenation has previously been shown in patients with acute lung injury when ventilated in prone position. We hypothesized that this was due to higher regional production of nitric oxide in dorsocaudal lung regions. We measured nitric oxide synthase mRNA expression and nitric oxide production by citrulline assay in ventral and dorsal lung tissue from patients. In volunteers, regional lung perfusion in prone and supine postures was assessed by single photon emission computed tomography using (99m)Tc macroaggregated albumin before and after inhibition of nitric oxide synthase by N(G)-monomethyl-L-arginine infusion. Nitric oxide synthase mRNA expression and nitric oxide production were significantly higher in dorsal compared with ventral lung regions. In supine posture, lung perfusion was shifted to ventral parts during nitric oxide synthase inhibition, whereas in the prone posture lung perfusion remained unchanged. Our results suggest a role for endogenous nitric oxide in regulation of regional pulmonary perfusion.

Acid-Base Equilibrium↗

PubMedDate not supplied

The role of 3D spiral CT in early gastric carcinoma.

PURPOSE: The purpose of this study is to assess the role of 3D imaging using spiral CT for the detection and evaluation of early gastric carcinoma (EGC). METHOD: Thirty-one patients with EGC underwent 3D and axial imaging using spiral CT, and all cases were confirmed at surgery. According to the pathologic specimens, one patient (3.2%) had type I, five (16.1%) had type IIb, 13 (42.0%) had type IIc, three (9.6%) had types IIc + IIb, three (9.6%) had types IIc + III, two (6.5%) had types IIa + IIc, two (6.5%) had types IIb + IIc, and two (6.5%) had types IIb + III. Spiral CT was first performed with 3 mm collimation, 4.5 mm/s table feed, and a 1 mm reconstruction interval in the supine position after intravenous injection of Buscopan and ingestion of gas. The 3D shaded surface display renderings were performed, analyzed, and graded as excellent, good, or poor. Axial CT scanning was performed with 5 mm collimation, 7 mm/s table feed, and a 5 mm reconstruction interval in the prone position after ingestion of water. RESULTS: With use of axial CT images, 20 of 31 tumors (64.5%) were detected. Tumors were suspected in two cases, but nine were not detected. With use of 3D images, 29 of 31 tumors (93.5%) were detected (p < 0.05). Of the 31 cases of EGC, excellent 3D images were obtained in 6 patients (19.3%), good 3D images in 21 (67.7%), and poor 3D images in 2 (6.5%). In the two cases with poor images, the tumor was confined to the mucosal layer and the types were EGC IIc + IIb. In the remaining two cases (6.5%), the tumors were not detected by 3D images. In one case, the tumor was confined to the mucosal layer, and in the other it was located in the pyloric antrum. Both tumors were EGC type IIc. The two cases not detected by 3D imaging were also not detected by axial CT scanning. CONCLUSION: The detection rate of EGC is higher using 3D imaging than axial CT scan alone.

Adult↗

PubMed1987

Treatment of retinal detachments due to macular holes.

Seven cases of retinal detachment due to macular holes in myopic eyes with posterior vitreous detachment were treated by exchanging liquid vitreous with an intravitreal gas bubble (40% SF6 + 60% air in one case, SF6 alone in six cases). All patients were positioned face down until the bubble absorbed. No cryotherapy, diathermy, or photocoagulation was used to create a chorioretinal adhesion. the retina reattached in six cases, with follow-up periods ranging from 6 to 24 months. One case failed because the patient was unable to maintain a prone position.

Female↗

PubMed2007

Insights in pediatric ventilation: timing of intubation, ventilatory strategies, and weaning.

PURPOSE OF REVIEW: Mechanical ventilation is a common intervention provided by pediatric intensivists. This fact notwithstanding, the management of mechanical ventilation in pediatrics is largely guided by a few pediatric trials along with careful interpretation and application of adult data. RECENT FINDINGS: A low tidal volume, pressure limited approach to mechanical ventilation as established by the Acute Respiratory Distress Syndrome Network investigators, has become the prevailing practice in pediatric intensive care. Studies by these investigators suggest that high positive end expiratory pressure and recruitment maneuvers are not uniformly beneficial. High frequency oscillatory ventilation continues to be evaluated in an attempt to provide 'open lung' ventilation. Airway pressure release ventilation is a newer mode of ventilation that may combine the 'open lung' approach with spontaneous breathing. Prone positioning was demonstrated in a recent pediatric trial to have no effect on outcome, while calfactant was found to potentially improve outcomes in pediatric acute respiratory distress syndrome. Ventilator weaning protocols may not be as useful in pediatrics as in adults. Systemic corticosteroids decrease the incidence of post extubation stridor and may reduce reintubation rates. SUMMARY: Mechanical ventilation with pressure limitation and low tidal volumes has become customary in pediatric intensive care units, and this lung protective approach will continue into the foreseeable future. Further investigation is warranted regarding use of high frequency oscillatory ventilation, airway pressure release ventilation, and surfactant to assist pediatric intensivists in application of these therapies.

Child↗

PubMed2002

Spatial orientation of caloric nystagmus.

The spatial orientation of the slow-phase eye velocity of caloric nystagmus was investigated in cynomolgus monkeys after all six semicircular canals had been plugged. Normal animals generate responses that have dominant convective components produced by movement of the endolymph in the lateral canal toward or away from gravity. As a result, the direction of horizontal slow-phase velocity induced by cold-water irrigation changes direction with changes in head position with regard to gravity. Plugging produced a dense overgrowth of bone that blocked the flow of endolymph, but the end organs were intact. Robust caloric nystagmus was elicited after recovery, but the horizontal (yaw) component was now always toward the stimulated (ipsilateral) side, regardless of head position re gravity. The induced caloric nystagmus had strong spatial orientation properties after canal plugging. With animals upright, the three-dimensional velocity vector of the caloric nystagmus was close to the yaw axis with small vertical and roll components. Roll components became stronger in supine and prone positions and vertical components were enhanced in the right- and left-side down positions. In each instance, the addition of the roll and vertical components moved the velocity vector of the nystagmus closer to the spatial vertical. Modeling supported the postulate that the caloric nystagmus after canal plugging is influenced by three factors: (1) a reduction in neural activity in the ampullary nerves on the stimulated side due to cooling of the nerves; (2) contraction of the endolymph in the closed space between the cupula and the plug due to cooling, which resulted in deflection of the cupula and hair cells toward the plug (ampullofugal deflection); and (3) alignment of eye velocity to gravity due to the orientation properties of velocity storage. Although convection is the most prominent factor in producing caloric responses in the normal state, our results suggest that alteration of nerve activity due to thermal effects, endolymph contraction or expansion, and velocity storage are also likely to contribute to the total response.

Animals↗

PubMed2002

Changes in organ perfusion and weight ratios in post-simulated microgravity recovery.

Head-down tilt models have been used as ground-based simulations of microgravity. Our previous animal research has demonstrated that there are significant changes in fluid distribution within 2 h after placement in a 45 degrees head-down tilt (45HDT) position and these changes in fluid distribution were still present after 14 days of 45HDT. Consequently, we investigated changes in fluid distribution during recovery from 16 days of 45HDT. Changes in radioactive tracer distribution and organ/body weight ratio were examined in rats randomly assigned to a 45HDT or prone control group. The 45HDT rats were suspended for 16 days and then allowed to recover at the prone position 0, 77, 101, or 125 h post-suspension. Animals were injected with technetium-labeled diethylenetriamine pentaacetate (99mTcDTPA, MW=492 amu, physical half-life of 6.02 h) and then killed 30 min post-injection. Lungs, heart, liver, spleen, kidneys, and brain were harvested, weighed, and measured for radioactive counts. Statistical analyses included two-way analysis of variance (ANOVA) that compared 45HDT versus controls at the four experimental time points. The organ weight divided by the body weight ratio for the brain, heart, kidneys and liver in the 45HDT rats was significantly different than the control rats, regardless of time (treatment). There was no difference between the different time points (time). The average 99mTcDTPA count divided by the organ weight ratio values for the heart, liver, and spleen were significantly higher in the 45HDT group than the control group. The average counts for the heart and spleen were significantly higher at 77, 101, and 125 h than at time zero. We conclude that the major organs have different recovery patterns after 45HDT for 16 days in the rat.

Adaptation, Physiological↗

PubMed2000

Utility of intravenously administered contrast material at CT colonography.

PURPOSE: To determine if intravenously administered contrast material improves overall reader confidence in the assessment of the colon, large-bowel wall conspicuity, and diagnostic accuracy in the detection of colorectal polyps and cancers at computed tomographic (CT) colonography. MATERIALS AND METHODS: Two hundred patients underwent CT colonography in both supine and prone positions. A five-point scale was used to assess the effect of contrast enhancement on overall reader confidence and bowel wall conspicuity. Eighty-one patients underwent CT colonography with complete colonoscopic or surgical correlation; diagnostic accuracy was compared in 48 patients who received contrast material and 33 who did not. RESULTS: Bowel preparation was ideal in 38 (19%) of 200 patients. Enhanced prone CT images had significantly better scores for reader confidence (4.9 +/- 0.1 vs 4.6 +/- 0.1, P: <.005) and bowel wall conspicuity (4.6 +/- 0.2 vs 4.2 +/- 0.2, P: <.005) compared with those of nonenhanced prone images despite no significant difference in bowel distention (3.8 +/- 0.2 vs 3.9 +/- 0. 1, P: =.8). Enhancement significantly improved the ability to depict medium (6-9-mm) polyps (75% vs 58%, P: <.05). Three large (10-19-mm) polyps were detected only with contrast enhancement; two remained submerged despite dual positioning. CONCLUSION: The use of intravenously administered contrast material significantly improved reader confidence in the assessment of bowel wall conspicuity and the ability of CT colonography to depict medium polyps in suboptimally prepared colons.

Adult↗

PubMedDate not supplied

Advanced gastric carcinoma: the role of three-dimensional and axial imaging by spiral CT.

BACKGROUND: The purpose of this study was to assess the role of three-dimensional (3D) and axial imaging by spiral computed tomography (CT) in the evaluation of advanced gastric carcinoma (AGC). METHODS: Sixty patients with AGC underwent 3D and axial imaging by spiral CT. Among them, 40 cases were confirmed by surgery. The remaining 20 cases showed typical findings of AGC with upper gastrointestinal series and gastroscopy that were proved by endoscopic biopsy. Spiral CT was performed with 3-mm collimation, 4. 5-mm/s table feed, and 1.5-mm reconstruction interval in the supine position after ingestion of gas. Three-dimensional images using the shaded surface display (SSD) technique were analyzed and graded (excellent, good, or poor). A second dual-phase spiral CT scan was performed with 5-mm collimation, 7-mm/s table feed, and 5-mm reconstruction interval in the prone position after ingestion of water. RESULTS: Among 60 cases of AGC, there were two cases (3.4%) of Borrmann type 1, 12 cases (20.0%) of Borrmann type 2, 32 cases (53.3%) of Borrmann type 3, 11 cases (18.3%) of Borrmann type 4, and three cases (5.0%) of Borrmann type 5. Of the 60 cases of AGC, excellent 3D images were obtained in nine patients (15.0%), good 3D images in 39 (65.0%), and poor 3D images in 12 (20.0%). Among the 12 patients with poor images, cancers were located at the pyloric antrum in eight cases (66.7%), were AGC Borrmann type 4 in three cases (25.0%), and early gastric carcinoma (EGC)-mimicking lesion (AGC Borrmann type 5) in one case (8.3%). Cancers involving the antrum tended to show poor images (p < 0.05). Using axial images, Borrmann's classification based on tumor morphology was accurately identified in 41 cases (68.3%); however, using 3D imaging, 52 cases (86.7%) were accurately classified (p < 0.05). In 40 cases receiving surgery, good correlation between axial CT image and pathology occurred in 70.0% of T class and 72.5% of N class. CONCLUSIONS: Three-dimensional images of AGC by spiral CT data were good or excellent in 80%, and combining 3D images with axial CT imaging improved the accuracy in classifying Borrmann type and tumor staging.

Adenocarcinoma↗