Effect Of Postural Changes Research Articles

Effect of postural changes on cardiovascular parameters across gender

Introduction:We investigated the effect of postural changes on various cardiovascular parameters across gender. Twenty-eight healthy subjects (16 male, 12 female) were observed at rest (supine) and subjected to 3 interventions; head-down tilt (HDT), HDT with lower body negative pressure (HDT+ LBNP at −30 mm Hg), and head-up tilt (HUT), each for 10 minutes separated by a 10 minutes recovery period.Methods:Measurements were recorded for heart rate (HR), standard deviation of the normal-to-normal intervals, root mean square of successive differences between the normal-to-normal intervals, heart rate variability-low frequency (LFRRI), heart rate variability-high frequency (HFRRI), low frequency/high frequency ratio (LFRRI/HFRRI), systolic blood pressure (SBP), mean arterial pressure (MAP), diastolic blood pressure (DBP), total peripheral resistance index (TPRI), stroke index (SI), cardiac index (CI), index of contractility (IC), left ventricular work index, and left ventricular ejection time.Results:Across all cardiovascular parameters, there was a significant main effect of the intervention applied but there was no significant main effect of gender across all parameters.Conclusions:The results suggest that there are no specific gender differences in regards to the measured variables under the conditions of this study. Furthermore, these results suggest that in healthy subjects, there appears to be evidence that LBNP partially elicits similar cardiovascular responses to HUT, which supports the use of LBNP as an intervention to counteract the effects of central hypovolemia.

The cerebral venous system and the postural regulation of intracranial pressure: implications in the management of patients with cerebrospinal fluid diversion

Loss of cerebrospinal fluid (CSF) occurs commonly in daily neurosurgical practice. Understanding the altered physiology following CSF loss is important for optimization of patient care and avoidance of complications. There is overwhelming evidence now that the cerebral venous system plays a major role in intracranial pressure (ICP) dynamics especially when one takes into account the effects of postural changes, atmospheric pressure, and gravity on the craniospinal axis as a whole. The CSF and cerebral venous compartments are tightly coupled in two important ways. CSF is resorbed into the venous system, and there is also an evolved mechanism that prevents overdrainage of venous blood with upright positioning known as the Starling resistor. With loss of CSF pressure, this protective mechanism could become nonfunctional which may result in posture-related venous overdrainage through the cranial venous outflow tracts leading to pathologic states. This review article summarizes the relevant anatomic and physiologic basis of the relationship between the craniospinal venous and CSF compartments in the setting of CSF diversion. It is hoped that this article improves our understanding of ICP dynamics after CSF loss, adds a new dimension to our therapeutic methods, stimulates further research into this field, and ultimately improves our care of these patients.

Subclinical pulmonary congestion is prevalent in nephrotic syndrome.

In patients with nephrotic syndrome (NS), the lung is considered an organ protected from the risk of edema. However, data on objectively measured lung water in NS patients is lacking. Here we measured lung water by an ultrasound (US) technique as well as by transthoracic impedance in 42 asymptomatic patients with active NS, in 14 stage G5D CKD patients on chronic hemodialysis, and in 21 healthy individuals. In patients with active NS, the median number of US-B lines (a metric of lung water) after 5 min in a supine position was significantly higher (12; interquartile range: 7-25) compared with that in healthy individuals (4; 2-9) but similar to that in hemodialysis patients (23; 10-39). The difference between NS patients and healthy individuals was significantly amplified (16; 10-35 vs. 4; 2-9) after 60 min of supine resting and significantly attenuated after 5 min of standing (10; 7-25 vs. 3; 1-6). Posture-dependent changes in lung water in patients with active NS were significantly accentuated compared with both hemodialysis patients and healthy individuals. After NS remission, the number of US-B lines was significantly reduced to 5 (4-18) at 5 min and to 6 (5-22) at 60 min approaching the normal range. Lung congestion in patients with active NS was confirmed by transthoracic impedance. Thus, asymptomatic pulmonary congestion is pervasive in patients with NS. A clinical trial is needed to assess the utility of lung US for the management of patients with NS.

Evaluation of Intracranial Pressure in Different Body Postures and Disease Entities.

We currently do not have sufficient knowledge regarding appropriate boundaries between "normal" and "abnormal" intracranial pressure (ICP) in humans. Our objective in this study was to quantify the effects of postural changes on ICP in normal and ill subjects. As a model for normal patients, we included adult patients scheduled for complete removal of a solitary, clearly demarcated, small brain tumor and performed long-term ICP monitoring using a telemetric device. The ill subjects included required invasive ICP monitoring as part of their diagnostic workup or monitoring of the effect of shunt treatment at our department. All patients were included prospectively for a session of monitored changes in body posture. In our preliminary results from 19 patients, we were able to statistically distinguish between patient groups and assumed body postures, highlighting the need for the further characterization of the effects of postural changes on ICP to inform diagnostic and therapeutic decisions.

Patient Specific Hardware-in-the-Loop Testing of Cerebrospinal Fluid Shunt Systems.

The development of increasingly sophisticated cerebrospinal fluid (CSF) shunts calls for test beds that can reproduce an ever larger range of physiologic and pathophysiologic behaviors. In particular, upcoming smart and active devices will require extensive testing under complex dynamic conditions. Herein, we describe a test bed that allows for fast, cost effective, and realistic in vitro testing of active and passive, gravitational and nongravitational CSF shunts based on the hardware-in-the-loop principle. The shunt to be tested is placed in a dynamic in vitro setup that interfaces with a mathematical model of the patient's relevant physiology, which is evaluated numerically in real time. The model parameters can be identified using standard clinical tests. The test bed accounts for posture-dependent behavior and viscoelastic effects. Simulations of infusion tests, of intracranial pressure modulation by cardiovascular action, and of the effects of postural changes show good agreement with published results. Evaluation of valves without and with gravitational units show in modeled sitting patients the expected behavior of overdrainage and avoidance thereof, respectively. Finally, a 24-h test cycle based on recorded patient data elucidates the interaction between patient and shunt system expressed by drainage rate and intracranial pressure during typical daily activities. We envision this test bed as a tool to quantify a shunt's performance within a realistic yet reproducible testing environment. The test bed can improve our understanding of the complex interaction between patient and shunt system and may catalyze the development of active shunts, while reducing the number of necessary in vivo experiments.

Postural change from lateral to supine is an important mechanism enhancing cephalic spread after injection of intrathecal 0.5% plain bupivacaine for cesarean section

BackgroundSpinal anesthesia is widely used for cesarean section, but the factors that affect the spread of the block in pregnant patients are still not fully explained. This study was designed to investigate the effect of postural changes on sensory block level. MethodsThirty patients scheduled for elective cesarean section under combined spinal–epidural anesthesia were randomly allocated into three groups. After intrathecal injection of 0.5% plain bupivacaine 7.5mg, patients in group S were immediately placed in the supine position with left tilt, patients in group L5 were kept lateral for 5min and then turned to the supine position with left tilt, and patients in group L10 were kept lateral for 10min and then turned to the supine position with left tilt. ResultsAt 5min, median cephalad level of sensory block was lower in groups L5 and L10 compared with group S (corrected P<0.001); at 10min, median cephalad sensory block level was lower in group L10 compared with group S (corrected P<0.001) and group L5 (corrected P<0.001), and lower in group L5 compared with group S (corrected P=0.033); at 15 min, median cephalad level of sensory block was lower in group L10 compared with group S (corrected P=0.003) and group L5 (corrected P=0.015). ConclusionsIn our population, using 0.5% plain bupivacaine 7.5mg, postural change from the lateral position to the supine position is an important mechanism enhancing cephalic spread of spinal anesthesia during late pregnancy.

Effect of postural changes on aldosterone to plasma renin ratio in patients with suspected secondary hypertension

AimsTo study the influence of postural changes on aldosterone to renin ratio (ARR) in patients with suspected secondary hypertension and to evaluate the sensitivity and specificity of the recommended seated ARR compared to supine and upright ARR for primary aldosteronism screening. MethodsFifty-three hypertensive patients were prospectively hospitalized for secondary hypertension exploration (age: 51±12, 66% males). After withdrawal of drugs interfering with renin angiotensin system, plasma aldosterone and direct renin concentration were measured in the morning, at bed after an overnight supine position, then out of bed after 1hour of upright position and finally 2hours later after 15minutes of seating. Minimal renin value was set at 5μUI/mL. ResultsReferring to ARR cut-off of 23pg/μUI, the sensitivity of seated ARR was 57.1% and specificity was 92.3%. The negative and positive predictive values were 95.1% and 45.2% respectively. Compared to these results, a cut-off of 19 improved sensitivity to 85.7% with a specificity of 89.7%. Negative and positive predictive values were 98.3% and 41.1% respectively. Seated ARR mean value was lower than supine and upright ARR mean values, due to an overall increase in renin at seating compared to the supine position by factor 1.9 while aldosterone just slightly increased by factor 1.2. Seated ARR correlated to supine and upright ARR: correlation coefficients (r) 0.90 and 0.93 respectively (P<0.001). ConclusionsCurrent recommended measurement of ARR in the seating position is fairly correlated to supine and upright ARR. A suggested cut-off value of 19 instead of 23pg/μUI increased the discriminating power of this test.

Effect of postural changes on inferior vena cava dimensions and its influence on haemodynamics during caesarean section under spinal anaesthesia

The effect of postural changes on inferior vena cava (IVC) dimensions and its influence on intra-operative haemodynamics in term parturients can be studied using abdominal ultrasound by a subcostal approach. Thirty-two term parturients scheduled to undergo elective caesarean section under spinal anaesthesia were recruited in this observational study. End expiratory diameter and collapsibility index of IVC was measured preoperatively in 3 different positions – supine, recumbent with wedge and left lateral positions. End expiratory diameter was significantly high in recumbent (10.79) and left lateral (12.27) compared with supine (9.96) position (P < 0.0001). A greater fall in systolic blood pressure (>20%) was noted in patients with collapsibility index of more than 11.5 in recumbent with wedge position with a positive predictive value of 86%. IVC dimensions change significantly with change in position and collapsibility index in recumbent position can be a useful parameter for predicting hypotension during caesarean section under spinal anaesthesia.

Effect of postural changes on ICP in healthy and ill subjects.

Reference values and physiological measurements of intracranial pressure (ICP) are primarily reported in the supine position, while reports of ICP in the vertical position are surprisingly rare considering that humans maintain the vertical position for the majority of the day. In order to distinguish normal human physiology from disease entities such as idiopathic intracranial hypertension and normal pressure hydrocephalus, we investigated ICP in different body postures in both normal and ill subjects. Thirty-one patients were included: four normal patients following complete removal of a solitary clearly demarcated small brain tumour and fitted with a telemetric ICP monitoring device for long-term ICP monitoring; 27 patients requiring invasive ICP monitoring as a part of their diagnostic work-up or monitoring of shunt treatment effect. ICP was recorded in the following body positions: upright standing, sitting in a chair, supine and right lateral lumbar puncture position. Linear regression of median ICP based on patient posture, group, and purpose of monitoring presented a significant model (p < 0.001), but could not distinguish between patient groups (p = 0.88). Regression of differences in median ICP between body postures and supine ICP as the baseline, presented a highly significant model (p < 0.001) and adjusted R (2) = 0.86. Both body posture (p < 0.001) and patient group (p < 0.001) were highly significant factors. Differences in ICP between body postures enabled us to distinguish the normal group from patient groups. Normal patients appear able to more tightly regulate ICP when switching body postures.

Recumbent deoxygenation in mild/moderate liver cirrhosis: the “Clinodeoxia”. The ortho-clino paradigm

While the effects of postural change on arterial oxygenation have been well documented in normal subjects, and attributed to the relationship of closing volume (CV) to the tidal volume, in liver cirrhosis such postural changes have been evaluated mainly in a rare, peculiar clinical end-stage condition which is characterized by increased dyspnea shifting from supine to upright position ("platypnea"). The latter is associated with worsening of PaO2 ("orthodeoxia"). We evaluated the effects of postural changes on arterial oxygenation in patients affected by mild/moderate liver cirrhosis. We performed pulmonary function tests and arterial blood gas evaluation in sitting and supine positions in 22 patients with mild/moderate liver cirrhosis, biopsy-proved, and 22 matched non-smokers control subjects. Recumbency elicited a decrease of PaO2 (Δ(sup-sit)PaO2) in 19 out of 22 controls and in all but one cirrhotics. The magnitude of this postural change was significantly (p=0.04) greater in cirrhotics (9.6±5.3%) compared to controls (6.7±3.7%). In the subset of cirrhotics younger than 60yrs and with PaO2 greater than 80mmHg in sitting position, the Δ(sup-sit)PaO2 in recumbency further increased to 12±5.8%, significantly (p=0.014) greater than in same subgroup of controls (7.1±3.8%). In mild/moderate liver cirrhosis the postural variations in PaO2 follow the normal trends, but are of greater magnitude probably as a consequence of hypoventilated units of lung for postural and disease-linked tidal airway closure, resulting in more pronounced recumbent hypoxemia ("clinodeoxia").

Effect of postural changes on normal and stenosed common carotid artery using FSI

Gravity associated with postural changes has a strong bearing on haemodynamics of blood flow in arteries. Its effect on stenosed cases has not been widely investigated. In the present study, variation observed in blood flow during postural changes is investigated for different conditions like standing, sleeping and head-down position. A fluid structure interaction study is carried out for idealized normal and 75% eccentric and concentric stenosed common carotid normal artery. The results clearly indicate the effects of altered gravity on flow conditions. It was found to be very significant during head-down position and demonstrated very high arterial blood pressure in stenosed common carotid when compared with normal carotid.

Effect of postural changes on the mechanical ventilation in patients with acute respiratory distress syndrome

Objective To compare the effect of postural changes on the mechanical ventilation in patients with acute respiratory distress syndrome （ ARDS ） .Methods A total of 40 ARDS patients with mechanical ventilation from January 2010 to December 2012 and without contraindications for mechanical ventilation in the prone position were selected , who were divided into the prone position ventilation group and the supine position ventilation group by random number table method , with 20 patients in each group .The changes of vital signs and arterial blood gas before and after mechanical ventilation were compared between the two groups, including the mean airway pressure , plateau pressure and airway resistance three days after treatment . Also, the mechanical ventilation time and the time taken to stay emergency room were compared between the two groups.Results Compared with before treatment , the T, P, MAP and PaCO2 after treatment all decreased in the two groups, with statistically significant differences （P＜0.01）;the PETCO2, pH, PaO2, PaO2/FiO2 after treatment all increased in the two groups , with statistically significant differences （P＜0.01）.There were no statistically significant differences between the two groups in T , P, PETCO2 , MAP, pH, PaO2 , PaCO2 （ P＞0.05）.The PaO2/FiO2 in the prone position ventilation group was （282 ±177;22） three days after treatment , which was higher than that of （245 ±177;21） in the supine position ventilation group three days after treatment , and the difference was statistically significant （t=6.18, P＜0.01）.The mean airway pressure, plateau pressure and airway resistance three days after treatment was （6.8 ±177;0.5） cmH2O, （17.1 ±177;2.0） cmH2O and （14.9 ±177; 1.2）cmH2O/（L±183; s） in the prone position ventilation group, respectively, which was （8.5 ±177;0.9） cmH2O, （20.6 ±177;2.3）cmH2O and （21.1 ±177;0.8）cmH2O/（L±183; s） in the supine position ventilation group , respectively, and the differences were statistically significant （t =7.38, 5.13, 18.83, respectively;P ＜0.01）.The mechanical ventilation time and the time taken to stay emergency room in the prone position ventilation group were shorter than those in the supine position ventilation , and the differences were statistically significant （ t=9.007, 6.379, respectively;P ＜0.01）.Conclusions Prone position ventilation can be more effective in improving oxygenation index and redressing hypoxemia , and has relatively little impact on the patients ’ airway, which is an ideal position of mechanical ventilation . Key words: Respiratory distress syndrome,adult; Position; Mechanical ventilation

The effect of anatomic variations of circle of Willis on cerebral blood distribution during posture change from supination to standing: a model study.

The anatomic variation of Circle of Willis (CoW) has great impact on its compensatory capacity during stroke and cerebral ischemia. In the present study, a series of lumped parameter models were developed and used to simulate the effect of postural changes on the cerebral blood flow in ICA stenosis patients with different anatomic variants of the CoW. The results showed that the asymmetric distribution of cerebral blood flow caused by stenosis was attenuated in standing position in complete and half-complete CoW. However, in incomplete CoW, the decrease in blood flow in the ipsilateral cerebral arteries caused by unilateral ICA stenosis was dramatic in both supine and standing positions, a likely result of inadequate collateral circulation within the CoW. In conclusion, the anatomic variation of CoW plays a significant role in maintaining the balance of cerebral blood supply in patients with ICA stenosis, especially during postural change.

Assessment of regional lung ventilation by electrical impedance tomography in a patient with unilateral bronchial stenosis and a history of tuberculosis

Bronchial stenosis can impair regional lung ventilation by causing abnormal, asymmetric airflow limitation. Electrical impedance tomography (EIT) is an imaging technique that allows the assessment of regional lung ventilation and therefore complements the functional assessment of the lungs. We report the case of a patient with left unilateral bronchial stenosis and a history of tuberculosis, in whom regional lung ventilation was assessed by EIT. The EIT results were compared with those obtained by ventilation/perfusion radionuclide imaging. The patient was using nasal continuous positive airway pressure (CPAP) for the treatment of obstructive sleep apnea syndrome. Therefore, we studied the effects of postural changes and of the use of nasal CPAP. The EIT revealed heterogeneous distribution of regional lung ventilation, the ventilation being higher in the right lung, and this distribution was influenced by postural changes and CPAP use. The EIT assessment of regional lung ventilation produced results similar to those obtained with the radionuclide imaging technique and had the advantage of providing a dynamic evaluation without radiation exposure.

Effects of head down tilt on episcleral venous pressure in a rabbit model

In humans, changing from upright to supine elicits an approximately 10 mmHg increase in cephalic venous pressure caused by the hydrostatic column effect, but episcleral venous pressure (EVP) and intraocular pressure (IOP) rise by only a few mmHg. The dissociation of the small increases in IOP and EVP compared to the larger increase in cephalic venous pressure suggests a regulatory mechanism controlling EVP. The aim of the present study was to determine if the rabbit model is suitable to study the effects of postural changes on EVP despite its short hydrostatic column. In anesthetized rabbits (n = 43), we measured arterial pressure (AP), IOP, and orbital venous pressure (OVP) by direct cannulation; carotid blood flow (BFcar) by transit time ultrasound, heart rate (HR) by digital cardiotachometer, and EVP with a servonull micropressure system. The goal of the protocol was to obtain measurement of supine EVP for ≈10 min, followed by ≈10 min of EVP measurement with the rabbit in a head down tilt. The data were analyzed by paired t-tests and the results reported as the mean ± standard error of the mean. In a separate group of animals (n = 35), aqueous flow was measured by fluorophotometry. This protocol entailed measurement of aqueous flow in the supine position for ≈60 min, followed by ≈60 min of aqueous flow measurement with the rabbit in a head down tilt. From supine to head down tilt, AP and BFcar were unchanged, IOP increased by 2.3 ± 0.4 mmHg (p < 0.001), EVP increased by 2.4 ± 0.4 mmHg (p < 0.001), OVP increased by 2.5 ± 0.2 mmHg (p < 0.001) and HR decreased by 9 ± 3 bpm (p = 0.002). Head down tilt caused no significant change in aqueous flow. Although the hydrostatic column in the rabbit is shorter than humans, the rabbit model permits sufficiently sensitive measurements of the pressures and systemic parameters likely involved in the EVP responses to posture change. The present results indicate directionally similar EVP and IOP responses to tilt as occur in humans and, as in humans, the responses are smaller than would be expected from the change in the hydrostatic column height. Also, as in humans, the model reveals no change in aqueous flow during head down tilt. We conclude the rabbit model is appropriate for studying the mechanisms responsible for the relative immunity of EVP and IOP to posture change.

Using dynamic analysis of Laser-Doppler blood flowmetry to measure nasal mucosa bloody flow in postural changes

The regulation of nasal mucosa blood flow (NMBF) is affected by multiple factors, such as the autonomic nervous system, medications, temperature, humidity, endocrine, even emotional stress and vision. The effects of postural changes on NMBF have been described in numerous studies. However, the results are far from consistent due to different experimental designs. Dynamic analysis of Laser-Doppler blood flowmetry (LDBF) is employed to recognize the effect of postural changes on NMBF. NMBF was continuously measured by LDBF in 14 participants with changing postures (sitting and supine). NMBF was measured in Blood Perfusion Unit (BPU), equivalent to the number of red blood cells multiplied by their mean velocity in a measured volume. NMBF increases significantly in a supine posture compared with that in a sitting posture. Our study demonstrates that NMBF is significantly influenced after initial postural change, suggesting that changes in posture may be regarded as an important factor regulating NMBF.

Effect of postural changes on 3D joint angular velocity during starting block phase

Few studies have focused on the effect of posture during sprint start. The aim of this study was to measure the effect of the modification of horizontal distance between the blocks during sprint start on three dimensional (3D) joint angular velocity. Nine trained sprinters started using three different starting positions (bunched, medium and elongated). They were equipped with 63 passive reflective markers, and an opto-electronic Motion Analysis® system was used to collect the 3D marker trajectories. During the pushing phase on the blocks, norm of the joint angular velocity (NJAV), 3D Euler angular velocity (EAV) and pushing time on the blocks were calculated. The results demonstrated that the decrease of the block spacing induces an opposite effect on the angular velocity of joints of the lower and the upper limbs. The NJAV of the upper limbs is greater in the bunched start, whereas the NJAV of the lower limbs is smaller. The modifications of NJAV were due to a combination of the movement of the joints in the different degrees of freedom. The medium start seems to be the best compromise because it leads, in a short pushing time, to a combination of optimal joint velocities for upper and lower segments.

Cardiac Output Measured with Both Esophageal Doppler Device and Vigileo-FloTrac Device

To the Editor We disagree with Meng et al.'s1 conclusions in their comparison of cardiac output (CO) measurements using both the third-generation Vigileo-FloTrac device (COFT) (Edwards Lifesciences, Irvine, CA) and the esophageal Doppler device (COED). The authors were wrong to assume that the COED was a valid reference. Furthermore, the significant disconcordance between COED and COFT measurements with phenylephrine boluses was predictable. Knapp et al.2 demonstrated that stroke volume initially increases during the first 4 minutes after initiating a phenylephrine infusion, peaks at 19.3 minutes, after which the stroke volume decreases. Schwinn and Reves3 showed that the time course and hemodynamic effects of bolus phenylephrine administration in anesthetized patients ranges from 40 seconds to 55 seconds depending on the dose administered. The patient's underlying volume status,4,5,6 relative density and activation of α- and β-adrenergic receptors, the underlying catecholamine state and cardiac function, and chronic medication use all influence hemodynamic responses to these study interventions. There is interindividual variability in response to anesthetic and a 20% decrease in mean arterial blood pressure after induction hardly guarantees equivalent volume status (especially considering the variable size of the splanchnic reservoir). The χ (Ķ) factor accounting for arterial compliance in the Vigileo-FloTrac (FT) algorithm is updated every minute in the third-generation FT software. Thus, the FT device was using an “unupdated” correction factor because it was trying to make sense of the acutely increased pulse pressure with a phenylephrine bolus. In other words, Meng et al. were testing the FT in a situation for which it had not been intended to perform. Therefore, we could have anticipated study findings given the lack of synchrony between the time course of phenylephrine bolus effects (well below 60 seconds) and the updating interval for the arterial compliance correction factor on the third-generation FT algorithm (60 seconds). Preload-augmenting effects of phenylephrine are generally predominant5–9 and these effects are largely related to splanchnic and abdominal visceral venous constriction5 (in response to α-agonist effects of phenylephrine) resulting in the displacement of blood from a previously nonstressed compartment into the central circulation.5,9,10 Although stroke volume may increase, CO may decrease secondary to an overall negative effect of phenylephrine on the heart rate. Global CO was not directly measured by Meng et al. The implicit assumption with COED-based monitoring is that the proportion of bloodflow in the ascending and descending aorta remains fixed (at a constant 30:70 ratio), despite fluctuations in various hemodynamic variables. Effects of changes in posture have not been formally examined using the esophageal Doppler device.11 Situations altering the proportion of upper lower body bloodflow will affect Doppler-derived values.11 The physiologic effects of an acute bolus of phenylephrine are not dissimilar to those associated with aortic cross-clamping; acute simultaneous increases in preload and afterload. We contend that the esophageal Doppler device assumed ratio of ascending to descending aortic flow (the relative distribution of global cardiac output) will not hold true after a phenylephrine bolus. With an acute phenylephrine bolus, global bloodflow is redirected away from the lower body (splanchnic viscera) toward the vital organs in the upper body (heart and brain). Therefore, when a phenylephrine bolus is used to treat hypotension occurring after the induction of general anesthesia we would expect the COED to decrease (because it is measuring only descending aortic flow) and the COFT to increase (because it is using an “unupdated” arterial compliance correction factor based off a radial arterial monitoring site). In essence, both the devices (esophageal Doppler device and FT) were not accurately measuring the effects of a phenylephrine bolus on global bloodflow. Karthik Raghunathan, MD, MPH Department of Anesthesiology Baystate Medical Center Tufts University School of Medicine Springfield, Massachusetts [email protected] Joshua A. Bloomstone, MD Department of Anesthesiology and Perioperative Medicine Banner Thunderbird Medical Center Glendale, Arizona Valley Anesthesiology Consultants, Ltd Phoenix, Arizona William T. McGee, MD, MHA Division of Critical Care Department of Internal Medicine Baystate Medical Center Tufts University School of Medicine Springfield, Massachusetts

Effect of Postural Change on the Prevalence of Ventilator‐ Associated Pneumonia

Ventilator‐associated pneumonia (VAP) is the most frequent hospital‐acquired infection among ventilated patients. A few studies have shown that postural change for common secretion management was effective in preventing VAP. The purpose of this study was to evaluate factors associated with the development of VAP, focusing on the relationship between VAP and postural change. We performed a retrospective observational study on 111 patients who had been admitted to the emergency room of a university hospital between January 2008 and September 2010. VAP developed in 32 patients (28.8%); compared to the patients without VAP, the ones who developed VAP had higher rates of blood transfusion, enteral nutrition, and continuous infusion of muscle relaxant. Multiple logistic regression analysis revealed that a longer duration of mechanical ventilation was independently associated with the development of VAP. An increase in postural change within 24 h of endotracheal intubation tended to increase the risk for VAP. Our results suggest that early‐stage postural change for mechanically ventilated patients may affect the incidence of VAP; therefore, a postural change must be carefully performed in a high‐risk group. Further studies should be conducted to examine whether postural change may be a risk factor for VAP in patients requiring mechanical ventilation.

Body Context and Posture Affect Mental Imagery of Hands

Different visual stimuli have been shown to recruit different mental imagery strategies. However the role of specific visual stimuli properties related to body context and posture in mental imagery is still under debate. Aiming to dissociate the behavioural correlates of mental processing of visual stimuli characterized by different body context, in the present study we investigated whether the mental rotation of stimuli showing either hands as attached to a body (hands-on-body) or not (hands-only), would be based on different mechanisms. We further examined the effects of postural changes on the mental rotation of both stimuli. Thirty healthy volunteers verbally judged the laterality of rotated hands-only and hands-on-body stimuli presented from the dorsum- or the palm-view, while positioning their hands on their knees (front postural condition) or behind their back (back postural condition). Mental rotation of hands-only, but not of hands-on-body, was modulated by the stimulus view and orientation. Additionally, only the hands-only stimuli were mentally rotated at different speeds according to the postural conditions. This indicates that different stimulus-related mechanisms are recruited in mental rotation by changing the bodily context in which a particular body part is presented. The present data suggest that, with respect to hands-only, mental rotation of hands-on-body is less dependent on biomechanical constraints and proprioceptive input. We interpret our results as evidence for preferential processing of visual- rather than kinesthetic-based mechanisms during mental transformation of hands-on-body and hands-only, respectively.