Influence Of Postural Changes Research Articles

Influence of posture during gliding flight in the flying lizard Draco volans

The agamid lizards of the genus Draco are undoubtedly the most renown reptilian gliders, using their rib-supported patagial wings as lifting surfaces while airborne. Recent investigations into these reptiles highlighted the role of body posture during gliding, however, the aerodynamics of postural changes in Draco remain unclear. Here, we examine the aerodynamics and gliding performances of Draco volans using a numerical approach focusing on three postural changes: wing expansion, body camber, and limb positioning. To this aim, we conducted 70 three-dimensional steady-state computational fluid dynamics simulations of gliding flight and 240 two-dimensional glide trajectory calculations. Our results demonstrate that while airborne, D. volans generates a separated turbulent boundary layer over its wings characterized by a large recirculation cell that is kept attached to the wing surface by interaction with wing–tip vortices, increasing lift generation. This lift generating mechanism may be controlled by changing wing expansion and shape to modulate the generation of aerodynamic force. Furthermore, our trajectory simulations highlight the influence of body camber and orientation on glide range. This sheds light on how D. volans controls its gliding performance, and conforms to the observation that these animals plan their glide paths prior to take off. Lastly, D. volans is mostly neutral in pitch and highly maneuverable, similar to other vertebrate gliders. The numerical study presented here thus provides a better understanding of the lift generating mechanism and the influence of postural changes in flight in this emblematic animal and will facilitate the study of gliding flight in analogous gliding reptiles for which direct observations are unavailable.

Influence of postural changes on nasal resistance in patients with obstructive sleep apnea.

Increased nasal resistance (NR) can augment upper airway collapse in patients with obstructive sleep apnea (OSA). Posture change can lead to altered nasal resistance. Our study aimed to investigate the influence of posture changes on NR in patients with OSA. Healthy controls without subjective nasal obstruction (apnea-hypopnea index (AHI) < 5 events/h), patients with OSA and subjective nasal obstruction, and patients with OSA and no subjective nasal obstruction were recruited. NR was measured by active anterior rhinomanometry in sitting, supine, left-lateral, and right-lateral postural positions. Total NR and postural change-related NR increments were calculated and compared among groups. In total, 26 healthy controls and 72 patients with OSA (mean AHI 39.7 ± 24.8 events/h) were recruited. Of patients with OSA, 38/72 (53%) had subjective nasal obstruction. Compared with controls, patients with OSA and no subjective nasal obstruction had lower total NR (inspiration, p = 0.037; expiration, p = 0.020) in the supine postural position. There was no difference in sitting, left-lateral, and right-lateral total NR among groups. Total NR was higher in lateral compared to sitting posture in both patients with OSA and in controls. The NR increment for sitting to supine postural change was significantly lower in patients with OSA (inspiration, p = 0.003; expiration, p = 0.005) compared with controls. The change in NR showed no statistically significant difference among groups in supine-left or supine-right postural change. Patients with OSA had lower supine total NR and lower total NR increment in the sitting to supine postural change, which may be related to a different posture-related NR regulatory mechanism. This study provides a new exploratory direction for the compensatory mechanism of the upper airway to collapse during sleep.

Personalised gravitational loading of the cervical spine from biplanar X-rays for asymptomatic and clinical subjects in neutral standing position

BackgroundAs a leading cause of disability with a high societal and economic cost, it is crucial to better understand risk factors of neck pain and surgical complications. Getting subject-specific external loading is essential for quantifying muscle forces and joint loads but it requires exertion trials and load cells which are uncommon in clinical settings. MethodsThis paper presents a method to compute the gravitational loading at four levels of the cervical spine (C3C4, C4C5, C5C6, C6C7) in neutral standing position from biplanar radiographs exclusively. The resulting load was decomposed in local disc frames and its components were used to compare different populations: 118 asymptomatic subjects and 46 patients before and after surgery (anterior cervical discectomy and fusion or total disc replacement). Comparisons were performed at C6C7 and the upper level adjacent to surgery. FindingsSignificant changes in gravitational loading were observed with age in healthy subjects as well as in patients after surgery and have been associated with changes in posture. InterpretationThis approach quantifies the influence of postural changes on gravitational loading on the cervical spine. It represents a simple way to obtain necessary input for muscle force quantification models in clinical routine and to use them for patient evaluation. The study of the subsequent subject-specific spinal loading could help further the understanding of cervical spine biomechanics, degeneration mechanisms and complications following surgery.

Spinal cord injury affects the interplay between visual and sensorimotor representations of the body.

The brain integrates multiple sensory inputs, including somatosensory and visual inputs, to produce a representation of the body. Spinal cord injury (SCI) interrupts the communication between brain and body and the effects of this deafferentation on body representation are poorly understood. We investigated whether the relative weight of somatosensory and visual frames of reference for body representation is altered in individuals with incomplete or complete SCI (affecting lower limbs’ somatosensation), with respect to controls. To study the influence of afferent somatosensory information on body representation, participants verbally judged the laterality of rotated images of feet, hands, and whole-bodies (mental rotation task) in two different postures (participants’ body parts were hidden from view). We found that (i) complete SCI disrupts the influence of postural changes on the representation of the deafferented body parts (feet, but not hands) and (ii) regardless of posture, whole-body representation progressively deteriorates proportionally to SCI completeness. These results demonstrate that the cortical representation of the body is dynamic, responsive, and adaptable to contingent conditions, in that the role of somatosensation is altered and partially compensated with a change in the relative weight of somatosensory versus visual bodily representations.

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.

9B.07

Objective: The aldosterone to renin ratio(ARR)is currently the most reliable available means of screening for Primary aldosteronism. It could be measured in the supine, seating or upright positions. The Endocrine Society and recent French guidelines recommended screening primary aldosteronism by the measurement of ARR in the seating position. The aim of this work is to study the influence of postural changes on ARR in patients with suspected secondary hypertension & to evaluate sensitivity and specificity of seated ARR compared to supine and upright ARR.Design and method: 43 patients were prospectively hospitalized for secondary hypertension exploration (age 51 ± 16,5; SBP/DBP:139 ± 12/85 ± 9mmHg, number of antihypertensive drugs:2 ± 1). After a conventional washout of drugs interfering with renin angiotensin aldosterone system, plasma aldosterone concentration was measured by RIA method(Normal values: 40–175ng/l)and direct renin concentration(DRC)with CLIA method (Normal values: 4,2–59.7 μUI/l). Aldosterone and renin samples were collected in the morning, at bed after an overnight supine position, then out of bed after 1 hour of upright position and finally 2 hours later after 15 minutes in seating position. When DRC was <5 μUI/l it was counted 5 μUI/l as recommended. Results: Referring to ARR cut-off value of 23pg/μUI, the sensitivity of seated ARR was 50% with a specificity of 96.5%. The negative predictive value was 80% and the positive predictive value was 87.5%. Compared to these results, a cut-off value of 19pg/μUI improved sensitivity to 85.7% with a specificity of 89.6%. Negative predictive value and positive predictive value were 92.8%and80% respectively. Seated ARR mean value(17 ± 15pg/μUI/l) was lower than supine and upright ARR, respectively measured at 23 ± 20pg/μUI and 24 ± 20pg/μUI. This could be explained by an overall increase in DRC at seating compared to the supine position with a mean increase by factor 2.2 (53 μUI/l vs 24 μUI/l), whereas at the same time, aldosterone just slightly increased by a factor 1.05(235ng/l vs 223ng/l). Seated ARR correlated to supine and upright ARR with correlation coefficients (r)of 0.89 and 0.93 respectively (p < 0,0001). Conclusions: Current recommended measurement of ARR in the seating position is fairly correlated to ARR in supine and upright positions. However, even if the recommended cut-off value of 23pg/μUI offers a good specificity, a suggested cut-off value of 19pg/μUI increases the discriminating power of this test.

The Influence of Posture Change on Ocular Blood Flow in Normal Subjects, Measured by Laser Speckle Flowgraphy

Purpose: To investigate, using laser speckle flowgraphy (LSFG), the autoregulation of ocular blood flow (BF) in response to posture change.Methods: This study comprised 20 healthy volunteers (mean age 30.0 ± 8.5). The mean blur rate (MBR) of the ocular circulation in the subjects was assessed in both a sitting and a supine position every 2 min over the course of 10 min. Baseline measurements of the MBR at the optic nerve head (ONH) and the choroid were taken in a sitting position. Increases in the MBR ratio in a supine position were calculated with reference to this baseline. Intraocular pressure (IOP), systemic blood pressure and heart rate in the brachial artery were also recorded.Results: In the ONH, the MBR ratio increased significantly over the baseline after 2 min (104.8 ± 5.0%, p = 0.001) and 4 min (104.4 ± 5.6%, p = 0.005), in a supine position, but decreased to the initial level after only 6 min. In the choroid, on the other hand, while the MBR ratio also increased significantly after 2 min in a supine position (113.7 ± 8.1%, p < 0.001), it kept this significant increase over the time course of 10 min. After 10 min in a supine position, IOP increased significantly (p < 0.001), systolic blood pressure decreased significantly (p < 0.001), but diastolic blood pressure did not change significantly compared to the baseline. (p = 0.07)Conclusions: ONH and choroidal circulation have significantly different hemodynamics in response to posture change in healthy volunteers. This finding suggests that LSFG enables us to assess the autoregulation of BF in the ONH.

Influence of postural changes on the variations of blood volume in hemodialysis and reincidence post-dialysis blood volume

The aim of the present work is to study the possible increment of blood volume, in the seated as well as the lying position, and to analyse the influence of changes of posture on the changes of blood volume during the hemodialysis. 17 patients were studied, evaluating the variations of the hematocrit in the extracorporeal circuit on entry into the dialyzer, by means of a photometric system (Crit-Line Instrument, Izasa). Every 15 minutes the values of the hematocrit were taken and heir repercussion in the blood volume in different changes of posture. Initially all of the patients improved their blood volume, both seated and lying down. During the session of hemodialysis and ultrafiltration, with the patient in a seated position, an important drop in the blood volume was noticed; this was the case in the 1st, 2nd and 3rd hours. This drop improved when the patient adopted a lying position and there was a "reincidence of post-dialysis blood volume" at the end. According to these results, the supine posture improves the refill, confirming that the patients position influences the vascular refill.

1911 脊椎圧迫骨折による姿勢変化が隣接脊椎に及ぼす力学的影響の筋骨格モデルによる検討(OS19.計算ソリッドバイオメカニクス(3),オーガナイズドセッション)

1911 脊椎圧迫骨折による姿勢変化が隣接脊椎に及ぼす力学的影響の筋骨格モデルによる検討(OS19.計算ソリッドバイオメカニクス(3),オーガナイズドセッション)

A211 脊椎圧迫骨折による姿勢変化が隣接脊椎に及ぼす力学的影響の筋骨格モデルを用いた検討(A2-3 生体のモデリング・シミュレーション)

A211 脊椎圧迫骨折による姿勢変化が隣接脊椎に及ぼす力学的影響の筋骨格モデルを用いた検討(A2-3 生体のモデリング・シミュレーション)

1211 脊椎圧迫骨折による姿勢変化が隣接脊椎に及ぼす力学的影響の検討(OS12-3 脊椎バイオメカニクス・人工股関節,オーガナイズドセッション:12 人間・生物・植物等に関するエンジニアリングの研究)

1211 脊椎圧迫骨折による姿勢変化が隣接脊椎に及ぼす力学的影響の検討(OS12-3 脊椎バイオメカニクス・人工股関節,オーガナイズドセッション:12 人間・生物・植物等に関するエンジニアリングの研究)

Ultrasound morphologic parameters of female stress incontinence

The study compared ultrasound parameters of the lower urinary tract with patients' age, number of previous pregnancies as well as the grade of incontinence. Furthermore, the influence of postural changes was studied. Ultrasonographic examination of the vaginal introitus was performed on 222 patients using a 5 MHz scanner. The transducer was inserted along the body axis and a vertical plane was defined. Urinary stress incontinence was found to be associated with the occurrence of cystoceles, the finding of a funnel-like opening of the proximal urethra, an increased retrovesical angle beta, and finally with a descent of the bladder neck. However, there was no significant correlation between urethral length and the grade of stress incontinence. In patients without urinary incontinence, the retrovesical angle as well as the position of the bladder neck were strongly related to parity but did not correlate with the patients' age. There was no significant difference between parameters when the patients were straining in a prone or half-prone position. Sonomorphological pelvic floor disorder is based on previous pregnancies and correlates well with urinary stress incontinence.

Influence of postural changes on the dynamics of swallowing

Influence of postural changes on the dynamics of swallowing

The Influence of Postural Changes on Gastroesophageal Reflux and Barrier Pressure in Nonfasting Individuals

There is controversy regarding optimal body positioning (i.e., head-up, head-down) in awake nonfasting individuals to minimize the risk for pulmonary aspiration of gastric contents as the result of gastroesophageal reflux (GER). In the present study, we investigated GER and intragastric-esophageal barrier pressure by means of multichannel intraluminal impedance measurement and intragastric-esophageal manometry in awake, nonfasting volunteers randomly positioned in a 20 degrees head-up position, the supine position, and a 20 degrees head-down position. No significant difference among positions was found with respect to number of GER episodes per person (0/1/1) or intragastric-esophageal barrier pressure (15.6/19.6/19.4 mm Hg). We conclude that specific body positioning is useless in the prophylaxis of GER in awake nonfasting individuals. Tilting of nonfasting individuals to the head-up or head-down position recommended for prevention of regurgitation of gastric contents does not influence the frequency of gastroesophageal reflux.

Influence of posture change on intrarenal arterial resistive index measurement.

We investigated the influence of posture change on intrarenal arterial resistive index measurement in 80 subjects (38 male, 42 female). Three interlobar arteries in the superior, middle, and inferior parts of the right kidney in each subject were examined by color Doppler ultrasound in two different positions (left lateral decubitus and supine). Based on the movement of the kidney caused by posture change, 23 subjects were classified as having a highly mobile kidney (group I) and the other 57 subjects were classified as not having a highly mobile kidney (group II). Fifty-eight kidneys (72.5%), 19 in group I (82.6%) and 39 in group II (68.4%), showed higher resistive index values in the lateral decubitus position than in the supine position. The influence of posture change on resistive index measurement was significant ( p < 0.001 for all subjects, p < 0.01 for group I, p < 0.05 for group II). The ranges of resistive index differences caused by posture change were 0-0.13 for group I and 0-0.11 for group II. The difference in resistive index caused by posture change was not significant between groups. Posture change is a potential confounding factor for intrarenal resistive index measurement.

Excessive exercise ventilation in moderate left heart dysfunction. Influence of postural changes in central haemodynamics and blood gases.

To evaluate the relative importance of pulmonary congestion and peripheral hypoxia as causes for the excessive exercise ventilation in left heart dysfunction, seven patients with excessive ventilation and distinct left heart dysfunction during moderate exercise (LHD), and seven control patients with essentially normal exertional functions (CTR), had ventilation, central haemodynamics, arterial and mixed venous blood gases examined at rest and exercise, 32 W (25-40) in the LHD group and 44 W (33-49) in the CTR group, in lying and sitting positions. Change from lying to sitting exercise, led to fall in pulmonary artery wedge pressure (PAWP) from 31.0 +/- 5.5 to 8.8 +/- 5.0 mmHg in the LHD group, compared with from 13.7 +/- 1.0 to 2.1 +/- 2.4 mm Hg in the controls, while ventilation/O2 intake ratio (V/VO2) and physiological dead space/tidal volume ratio (VD/VT) showed a tendency to rise, from 36.3 +/- 8.8 to 39.2 +/- 7.4, and from 0.35 +/- 0.11 to 0.39 +/- 0.09, respectively, in the LHD group, and from 27.5 +/- 3.1 to 28.7 +/- 5.3, and from 0.19 +/- 0.09 to 0.21 +/- 0.12 in the controls. Mixed venous O2 tension (PvO2) showed a marked decline from 3.60 +/- 0.33 to 3.26 +/- 0.36 kPa in the LHD group, as compared with from 3.94 +/- 0.28 to 3.71 +/- 0.29 kPa in the controls, while the calculated physiologic shunt (Qs/Qt) suggested improved alveolo-arterial gas exchange. The data fit in with recent studies ascribing the excessive exercise ventilation to a combination of signals from hypoxia-induced changes, particularly in the exercising muscles, and augmented ergoreflex and central and peripheral chemoreceptor activity, partly to changes in the integrated control of ventilation and circulation, not to mechanisms related to pulmonary congestion.

Difficulties in estimating muscle forces from muscle cross-sectional area. An example using the psoas major muscle.

Most biomechanical models use muscle cross-sectional area (CSA) as an indicator of maximum isometric muscle force. In general, there are multiple estimates of CSA for the same muscle. For example, numerous studies have estimated the CSA of the psoas major muscle using different subject populations and positions. However, few studies have combined the available information to obtain an overall estimate of CSA or investigated the effect different subject characteristics may have on CSA. In the present update, nine studies that reported psoas major CSA or physiologic CSA were compared with respect to subject characteristics, methodology, and results. Corrections to cadaveric data were made to adjust physiologic CSA to CSA. Comparison of reported values for living subjects indicated that females have smaller mean CSA than males for the psoas major muscle and that body size does not significantly influence muscle CSA in males. Areas derived from cadaveric data were smaller than similar studies on living subjects, possibly because of subject age, removal of tendinous and fatty components of fascicles, and lack of detailed data for fascicle angles in the supine position. Results indicate that researchers who use muscle CSA in biomechanical models should carefully assess the appropriateness of the data used, particularly in relation to potential sex differences and the influence of postural changes on CSA.

Effect of postural changes on human lymphatic capillary pressure of the skin.

1. The influence of postural changes on cutaneous lymphatic capillary pressure and venous pressure was measured at the dorsum of the foot in twelve healthy volunteers. Measurements were performed in the supine and sitting positions. 2. Lymphatic skin capillaries were visualized by fluorescence microlymphography with fluorescein isothiocyanate (FITC)-Dextran 150000. Subsequently a lymphatic capillary was punctured with a glass micropipette and pressure was measured using the servo-nulling technique. Lymphatic capillary pressure, venous pressure, heart and respiration rates were recorded simultaneously. 3. Mean lymphatic capillary pressure was significantly higher (P = 0.0096) in the sitting (9.9 +/- 3.0 mmHg) than in the supine (3.9 +/- 4.2 mmHg) position. There was no significant difference (P = 0.09) between lymphatic capillary pressure and venous pressure (6.8 +/- 3.4 mmHg) in the supine position. During sitting mean lymphatic capillary pressure was significantly lower (P = 0.0022) than mean venous pressure (53.3 +/- 4.1 mmHg). The smaller increase in lymphatic capillary pressure may be caused by the discontinuous fluid column in the lymphatic system and enhanced orthostatic contractile activity of lymphatic collectors and precollectors. Spontaneous low frequency pressure fluctuations occurred in 89% of recordings during sitting, which was significantly (P = 0.02) higher than in the supine position (54%). 4. The present results support the suggestion of enhanced intrinsic contractile activity of lymph precollectors and collectors in the dependent position. This mechanism is primarily responsible for the propulsion of lymph from the periphery to the thoracic duct during quiet sitting, when extrinsic pumping by the calf muscles is not active.

Alterations of skin microcirculatory rhythmic oscillations in different positions of the lower extremity.

Microcirculatory vasomotion is considered to be an important mechanism promoting and facilitating the transfer of blood cells through skin capillaries. Since skin vulnerability of the leg is closely associated with gravitational factors and skin micro-circulation, we investigated by a laser Doppler apparatus influence of postural changes on skin blood flow oscillations in lower limbs of healthy volunteers. Our data show a marked decrease in microcirculatory oscillation amplitudes at a frequency 7.6 (+/- 0.6) min-1 after lowering the leg. This could be reversed by the application of compressive bandage. Our study points toward a potentially important mechanism of microcirculatory impairment during orthostasis.

Biliary Sludge

Biliary sludge has been for many years a poorly defined entity, usually with low amplitude, nonshadowing echoes within the most dependent part of the gallbladder, which shift under the influence of postural changes. From a sonographic point of view, the detection of sludge implies the coexistence of small-sized, solid components and of a gel-like embedding material. The chemical nature of biliary sludge has recently been recognized to be predominantly composed of a coaggregate of cholesterol monohydrate crystals and liquid crystalline droplets, and in some cases, such as obstructive jaundice or symptomatic liver diseases, by bilirubin granules, all embedded in a gel matrix of mucous glycoproteins. From a pathogenic point of view, biliary sludge is often associated with biliary stasis, or with conditions characterized by impaired gallbladder contraction, such as prolonged total parenteral nutrition, fasting, and pregnancy. Other causes include mucus hypersecretion, which may favor cholesterol nucleation and crystal growth, and bile infection. Sludge may be an intermediate step in the formation of different types of stones. From an epidemiological point of view, sludge is quite rare in the asymptomatic, free-living population, but may be common in selected series of symptomatic patients. From a clinical point of view, sludge often has a fluctuating course, including frequent disappearances and reappearances, suggesting that the early stages of gallstone formation are reversible.