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PubMed1992

Maternal cerebral hemodynamics in the supine hypotensive syndrome.

Cerebral hemodynamics were studied in eight nonpregnant women and 24 women in late pregnancy by internal carotid artery velocimetry with a 3.5-MHz continuous-wave Doppler system. Criteria for supine hypotensive syndrome were a mean blood pressure decrease of 15 mmHg and a 2-minute sustained increase in pulse of 20 beats per minute under postural change from the left lateral to supine position. Nonpregnant and normal pregnant controls not meeting these two criteria displayed decreases of 22.9 and 21.7%, respectively, in time-averaged mean peak velocity (mean velocity) in the supine position compared with the left lateral position. Five subjects with subclinical supine hypotensive syndrome who met one of the above criteria showed a 37.0% decrease in internal carotid artery mean velocity in the supine position. Two patients with supine hypotensive syndrome could not tolerate the supine position for more than 6 minutes, at which time internal carotid artery mean velocity fell below 10 cm/second, reverse flow was observed, and they complained of dizziness, nausea, and syncope. Internal carotid artery mean velocity in all women showed no change in the sitting position compared with the left lateral position. These results indicate that the supine position should be avoided in late pregnancy, especially by women with cerebrovascular complications.

Adult↗
PubMed2002

Changing nursery practice gets inner-city infants in the supine position for sleep.

OBJECTIVE: To determine whether an educational intervention to change nursery practice would result in more inner-city parents placing their infants in the supine position for sleep. DESIGN: We conducted semistructured interviews at the 2-week health supervision visit with 1 convenience sample of parents before and a different convenience sample of parents after an educational intervention was conducted to change nursery practice in positioning infants for sleep. SETTING: University hospital clinic located in an urban setting. PARTICIPANTS: Parents of 2-week-old infants at their first health supervision visit in an urban, university-affiliated clinic. All parents who were approached agreed to participate. INTERVENTION: Nurses were instructed to place infants exclusively in the supine position in the nursery and to instruct parents to exclusively place infants in the supine sleeping position at home. MAIN OUTCOME MEASURE: The usual sleeping position in which parents reported placing their 2-week old infants. RESULTS: Before the intervention, 41% of parents reported that a clinician had told them to place their infants to sleep in the supine position compared with 81% after the intervention (odds ratio [OR], 6.1; 95% confidence interval [CI], 3.1-12.3). Before the intervention, 37% of parents reported that the nursery staff placed their infants to sleep in the supine position, compared with 88% after the intervention (OR, 12.5; 95% CI, 5.7-27.7). Before the intervention, 42% of parents reported that they usually placed their infants to sleep in the supine position at home compared with 75% after the intervention (OR, 4.2; 95% CI, 2.1-7.9). CONCLUSION: After an educational intervention to change practice in a well-newborn nursery, many more parents reported placing their infants in the supine position for sleep, which suggests that such an intervention may have an impact on the position in which parents place their children to sleep.

Adolescent↗
PubMed1994

Comparison of supine and prone noninvasive measurements of breathing patterns in fullterm newborns.

The current study was undertaken to ascertain whether shift from supine to prone posture alters the pattern of natural breathing in healthy fullterm newborns. Breathing patterns were measured in the supine and prone posture in 20 healthy fullterm infants using calibrated, noninvasive respiratory inductive plethysmography (RIP). The values for breathing pattern components in supine and prone postures expressed as means (+/- SD) were, respectively, tidal volume (VT), 14.1(+/- 3.2) and 18.9(+/- 4.9)mL; mean inspiratory flow 26.7(+/- 11.5) and 32.8(+/- 13.0)mL/s; and minute ventilation 232(+/- 75) and 288(+/- 96)mL/kg/min (P < 0.01). Less thoracoabdominal incoordination, expressed as the labored breathing index (LBI), occurred with shift from supine to prone posture in infants studied in the active behavioral stage, changing from 2.0(+/- 0.5) to 1.3(+/- 0.4) (P < 0.01). Placement of a facemask-pneumotachograph system increased VT measured with RIP by 26% in the supine, and 18% in the prone posture. Neither respiratory rate nor inspiratory time (Ti) changed with the postural shift. Therefore, change from supine to prone posture improved ventilation and increased respiratory drive as expressed by VT/Ti. Further, thoracoabdominal incoordination which took place during active sleep in the supine posture, lessened with change to the prone posture.

Humans↗
PubMed2005

Comparison of lung area by chest radiograph, with estimation of lung volume by helium dilution during prone and supine positioning in mechanically ventilated preterm infants: a pilot study.

Measurement of lung volume may be useful in determining the degree of lung disease and for optimizing an infant's mechanical ventilator settings. A chest radiograph (CXR) is often used to estimate lung volume, because direct measurement, e.g., functional residual capacity (FRC), is neither practical nor possible in the neonatal intensive care unit. In supinely positioned infants, good correlation was found between lung area determined by CXR and lung volume, e.g., functional residual capacity (FRC). Whether this is true for the prone position is unknown. Since positioning may affect oxygenation and pulmonary function, we studied the relationship between lung area measured from CXR and FRC during both supine and prone positioning in 14 mechanically ventilated preterm infants. Lung area was determined from CXRs using computed radiography and FRCs obtained by helium dilution at end-expiration in both supine and prone positions. Reproducibility of lung area measurements was demonstrated by high correlations between two observers (R2 = 0.92 and 0.99 for supine and prone, respectively). When supine, lung area was 15.4 +/- 3.1 cm2, and FRC was 19.5 +/- 7.3 ml. In prone position, lung area was 16.7 +/- 4.2 cm2, and FRC 23.0 +/- 9.4 ml. There was a moderate to strong positive correlation between lung area and FRC for both positions (supine: r = 0.57, P < 0.03; prone: r = 0.63, P < 0.02). Lung area measured by computed radiography is a reproducible and practical method for estimating lung volume from routine chest X-rays in both supine and prone positions in mechanically ventilated preterm infants.

Female↗
PubMedDate not supplied

Relationship between age and heart rate variability in supine and standing postures: a study of spectral analysis of heart rate.

We compared heart rate variability measures of 11 normal children (4-12 years) to 23 normal adults (21-43 years) to study the effect of age on heart rate variability measures. Children had a significantly higher supine and standing heart rate and lower supine and standing systolic and diastolic blood pressure. Children also had a significantly higher supine standard deviation of HR, supine low frequency (0.01-0.05 Hz) (p < 0.005), supine high frequency (0.2-0.5 Hz) (p < 0.001), and standing high frequency powers (p < 0.005) compared to adults. The ratio of mid frequency (0.07-0.15 Hz) to high frequency power (0.2-0.5 Hz) upon standing was significantly lower in children (p < 0.005). While there was a significant increase of the mid frequency power from supine to standing posture in the adult group (p < 0.02), there was no such significant increase in children. There were also significant negative correlations between age and supine low frequency, mid frequency, and high frequency powers, and standing high frequency power. These findings illustrate a decrease of cholinergic and an increase of adrenergic modulation of heart rate variability with age (4-43 years).

Adrenergic Fibers↗
PubMedDate not supplied

Stroke volume measurement during supine and upright cycle exercise by impedance cardiography.

This study evaluated impedance cardiography (ZCG) estimates of stroke volume (SV) during exercise. Seven subjects were studied at rest and during progressive cycle exercise in supine and upright positions. SV was determined by ZCG (SVZCG) during exercise and for the first 5 cardiac cycles following exercise. SVZCG was compared with separate measurements of SV by CO2 rebreathing (SVCO2). Static blood resistivity (p) was measured at each level of exercise. No significant differences were found between supine exercise and immediate post-exercise values for the peak of the first derivative of the impedance change (dZ/dtmax), left ventricular ejection time (LVET), or SVZCG. Small differences in dZ/dtmax and SVZCG, but not LVET, were found in exercise to post-exercise cycling in the upright position. Intra-individual SVZCG and SVCO2 were moderately correlated (upright mean r = 0.64, supine r = 0.42) from rest to 70% of peak VO2. Similar correlations were found between Pulse-O2 (VO2/heart rate, used as an index to SV) and both SVZCG (upright r = 0.73, supine r = 0.57) and SVCO2 (upright r = 0.8, supine r = 0.65). The ZCG parameters dZ/dtmax and LVET correlated better with Pulse-O2 (dZ/dtmax: upright r = 0.92, supine r = 0.73; LVET: upright r = -0.9, supine r = -0.9). SVZCG calculated with the Kubicek equation performed as well as SVCO2. ZCG might be a superior method if the inversely correlated parameters, dZ/dtmax and LVET, were not expressed as a product to calculate SV.

Adult↗
PubMed2001

[Pronation and supination of the forearm. With special reference to the humero-ulnar articulation].

The development of a kinematic model of the pro- and supination, that can be used to predict the influence of angulations of ulna and radius on the pronation and supination is based on the precise knowledge of the pronation and supination movement. We performed two parallel studies for examining the pronation and supination motion of the human forearm. The first experiment dealt with MRI-studies on 18 probands (36 examined forearms). As a result we observed an evasive movement of the ulna during the rotation of 7, 14 degrees medial. In order to prove whether the evasive movement was caused by a rotation of the humerus or by an evasion in the articulatio humeroulnaris, we carried out a second experiment, using 30 preparations. The measurement of the pro- and supination motion with a fixed humerus was expedited using a special experimental setup which guaranteed that the ulna could move freely. In all cases we found the same magnitude of the evasive motion of the ulna. Therefore we demonstrated, that the ulna performs an evasive motion during the pro- and supination motion of the forearm that influences the kinematic behavior of the pro- and supination motion significantly.

Adult↗
PubMed2002

Pediatric ARDS: effect of supine-prone postural changes on oxygenation.

OBJECTIVE: To determine the effect of repeated prone positioning (supine-prone/prone-supine) on oxygenation in children suffering from ARDS. DESIGN: Single-center prospective case series. SETTING: University pediatric ICU. PATIENTS: Consecutive pediatric patients with severe ARDS (PaO(2)/FiO(2) <200, Murray score >2.5). INTERVENTIONS: Patients were treated as soon as possible with supine-prone/prone-supine positioning every 8 h until clinical improvement or death occurred. MEASUREMENTS AND RESULTS: Twenty-three patients who had ARDS (0.5-months to 12.6-years-old), were placed in the prone position within 56+/-109 h after the diagnosis of ARDS. Prone-supine/supine-prone postural changes were repeated every 8 h for 9.7+/-5.5 days. Changes in PaO(2)/FiO(2) ratio during supine-prone and prone-supine positioning were evaluated. A positive change was defined as an increase of 15% of baseline value. The patient was classified as a responder when the mean increase in the prone position was greater than 15%. There were 18 responders and five non-responders. The responders showed an increase in PaO(2)/FiO(2) ratio of 22%, from 91+/-33 to 112+/-43 (P <0.001), when they were placed from the supine to the prone position. Their PaO(2)/FiO(2) ratio dropped from 109+/- 37 to 94 +/-36, P = 0.011, when changed from the prone to supine position. The overall mortality rate in this series was 48% (11 patients), which was higher in the non-responders (80%) than in the responders (39%), although this difference was not statistically significant (P = 0.95). CONCLUSIONS: The prone position improves oxygenation in a significant proportion of children with ARDS. Although no statistically significant difference was found for the mortality rate, it was higher for the non-responders (80%) vs the responders (39%).

Acute Disease↗
PubMed1994

Effects of supine blood pressure on interpretation of standing up test in 500 patients with diabetes mellitus.

The relationship between fall in blood pressure (BP) on standing and supine BP before standing up was studied in 75 healthy controls and in 500 patients with diabetes mellitus (DM) using conventional BP measurements. The influences of physiological (sex, age, height) and DM-related factors (type, duration, HbA1c-level, use of insulin, oral antidiabetic and anti-hypertensive medication) on BP-fall were assessed. The effects of using a fixed abnormality threshold and a new supine BP-related abnormality definition on interpretation of the test were determined. Highly significant relationships of BP-fall with supine BP were found in control and DM subjects. Slopes did not differ between these groups. Slopes for systolic BP-fall were steeper in type 1 than in type 2 DM patients. A forward stepwise regression procedure revealed that supine BP (explaining 24% of variance) and HbA1c (explaining 1%) had significant influences on systolic BP-fall. Diastolic supine BP explained 14% of diastolic BP-fall, age 3%, and sex 2%. Only supine BP was thus of practical relevance in explaining BP-fall. Taking supine BP into consideration affected test results: of 74 subjects with an abnormal conventional systolic BP-fall, 10 (13.5%) had been misclassified according to the new method, and 4 additional patients had been misclassified as normal. Classification changes were much larger for diastolic BP-fall (63% of conventionally abnormal results were reclassified as normal), but the range of diastolic BP is smaller than for systolic BP, meaning that the measurement error interferes with its clinical utility.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed2005

Does vaginal closure force differ in the supine and standing positions?

OBJECTIVE: This study was undertaken to quantify resting vaginal closure force (VCF(REST)), maximum vaginal closure force (VCF(MAX)), and augmentation of vaginal closure force augmentation (VCF(AUG)) when supine and standing and to determine whether the change in intra-abdominal pressure associated with change in posture accounts for differences in VCF. STUDY DESIGN: Thirty-nine asymptomatic, continent women were recruited to determine, when supine and standing, the vaginal closure force (eg, the force closing the vagina in the mid-sagittal plane) and bladder pressures at rest and at maximal voluntary contraction. VCF was measured with an instrumented vaginal speculum and bladder pressure was determined with a microtip catheter. VCF(REST) was the resting pelvic floor tone, and VCF(MAX) was the peak pelvic floor force during a maximal voluntary contraction. VCF(AUG) was the difference between VCF(MAX) and VCF(REST). T tests and Pearson correlation coefficients were used for analysis. RESULTS: VCF(REST) when supine was 3.6 +/- 0.8 N and when standing was 6.9 +/- 1.5 N--a 92% difference (P < .001). The VCF(MAX) when supine was 7.5 +/- 2.9 N and when standing was 10.1 +/- 2.4 N--a 35% difference (P < .001). Bladder pressure when supine (10.5 +/- 4.7 cm H2O) was significantly less (P < .001) than when standing (31.0 +/- 6.4 cm H2O). The differences in bladder pressure when either supine or standing did not correlate with the corresponding differences in VCF at rest or at maximal voluntary contraction. The supine VCF(AUG) of 3.9 +/- 2.7 N, was significantly greater than the standing VCF(AUG) of 3.3+/-1.9 N. CONCLUSION: With change in posture, vaginal closure force increases because of higher intra-abdominal pressure and greater resistance in the pelvic floor muscles.

Adult↗
PubMed2006

Biomechanic comparison of 3 tendon transfers for supination of the forearm.

PURPOSE: Flexion-pronation of the hand and the forearm is a common deformity when the upper extremity is affected by cerebral palsy. Solutions used to improve the pronation deformity and increase supination include transfer of the flexor carpi ulnaris to the extensor carpi radialis brevis, pronator teres rerouting, and brachioradialis rerouting. The purpose of this study was to compare the biomechanic efficacy of these 3 tendon transfers in simulated supination in cadaveric forearms. METHODS: Ten fresh-frozen adult cadaveric above-elbow upper extremities were used. In each specimen the 3 tendon transfers were performed sequentially in random order and were loaded in increments of 4 N (1 lb) to a maximum of 36 N (8 lb). Measurements were recorded from the starting point of 90 degrees of pronation. Statistical analysis of the data included the Student t test with the Bonferoni correction. RESULTS: For all transfers, supination increased in a nonlinear manner as the load was increased in a nonlinear manner. For the flexor carpi ulnaris transfer, the forearm reached its neutral position at a load of 9 N (2 lb). The forearm continued to rotate to up to 84 degrees of supination with 36 N (8 lb) of load. With the brachioradialis transfer, the forearm reached its neutral position at 13 N (3 lb) of load and continued to rotate to up to 33 degrees of supination with 36 N of load. With the pronator teres transfer, the forearm never reached the neutral position. Under a maximum load of 36 N, only 55 degrees of rotation from full pronation was obtained. CONCLUSIONS: Transfer of the flexor carpi ulnaris to the extensor carpi radialis brevis proved to be the most effective transfer for producing supination in cadavers. The brachioradialis transfer was second best. The pronator teres rerouting was the least effective transfer in effecting simulated supination in this experiment.

Adult↗
PubMed2006

Nonspecific dizziness: frequency of supine hypertension associated with hypotensive reactions on head-up tilt.

The clinical syndrome of supine hypertension associated with orthostatic hypotension (OH) in given individuals is recognized by specialists, but is underdiagnosed in the community. The objective of this study was to assess supine hypertension associated with hypotensive reactions on head-up tilt (SH-HRT) among patients evaluated for nonspecific dizziness. Consecutive patients with nonspecific dizziness were studied with a 10-min supine 30-min head-up tilt test. Supine hypertension (SH) was diagnosed when supine systolic blood pressure (SBP) was > or = 140 mmHg and/or supine diastolic blood pressure (DBP) was > or = 90 mmHg. Hypotensive reactions on tilt (HRT) were diagnosed when SBP decreased by > or = 30 mmHg on tilt and/or DBP decreased by > or = 15 mmHg. Of 430 patients tested, 42 (9.8%) had SH-HRT. The median age was 67 years; 37 had a pretest diagnosis of hypertension, with treatment. The median supine BP was 162/90 mmHg; the median nadir BP on tilt was 118/78 mmHg. Four SH-HRT patterns were recognized: (I) SH with typical neurogenic OH (n = 6), (II) SH with vasovagal reaction on tilt (n = 4), (III) SH with sustained HRT (n = 28), and (IV) SH with mixed orthostatic-vasovagal reaction on tilt (n = 4). Dizziness on tilt occurred in 25% of patients category III (SH with sustained HRT), while appearing universally in other SH-HRT patterns. In conclusion, nonspecific dizziness may be the chief complaint in patients with SH-HRT, a disorder often unrecognized by clinicians. Different patterns of SH-HRT on HUTT may reflect different aberrations in cardiovascular homeostasis and may require differentiated management strategies.

Aged↗
PubMed1999

Comparison of supine and upright positions on autonomic nervous activity in late pregnancy: the role of aortocaval compression.

In order to understand the effect of aortocaval compression on autonomic nervous activity, we compared the effects of supine and upright postures on measures of heart rate variability in late pregnancy. Thirty-two women in late pregnancy and 23 nonpregnant age-matched women were studied. Both time and frequency domain heart rate variability measures were compared between the supine and upright positions, and between pregnant women and controls. The pregnant women had smaller mean RR interval, standard deviation of RR intervals and normalised high-frequency power, and a larger low- to high-frequency power ratio than nonpregnant women in the supine position. When the position was changed from upright to supine in nonpregnant women, the percentage change in the mean RR interval and normalised high-frequency power were increased, whereas the percentage change in the coefficient of variation of RR interval and low- to high-frequency power ratio were decreased. In contrast, the percentage change in normalised high-frequency power was decreased and the percentage change in low- to high-frequency power ratio was increased in pregnant women when the position was changed from upright to supine. These results indicate that the vagal enhancing effect seen in normal subjects when changing position from upright to supine was reversed in women in late pregnancy. Aortocaval compression in the supine position in pregnant women might be responsible for this reversal in the autonomic response to lying down.

Adult↗
PubMed2005

Is the supine position as safe and effective as the prone position for endoscopic retrograde cholangiopancreatography? A prospective randomized study.

BACKGROUND AND STUDY AIMS: Endoscopic retrograde cholangiopancreatography (ERCP) is usually performed with the patient lying in the prone position, on the assumption that this position is optimal for cannulation of the papilla and for obtaining good-quality radiographic images. The supine position, however, may be more comfortable for the patient and may facilitate airway management, and this study aimed to compare the two positions in terms of procedure outcome, safety, and patient tolerance. PATIENTS AND METHODS: Consecutive patients who were undergoing ERCP were randomized to start the procedure in either the prone position or the supine position. Patients under the age of 18 years, intubated patients, and those who had already undergone endoscopic sphincterotomy were excluded. The difficulty of cannulation was assessed using the Freeman score (1=one to five attempts; 2=six to 15 attempts; 3=more than 15 attempts; 4=failure of cannulation). Total procedure time, patient tolerance, willingness to undergo ERCP in the future, and procedure-related adverse cardiorespiratory events (oxygen desaturation, tachycardia, bradycardia) were also recorded. RESULTS: A total of 34 patients were evaluated (21 men, 13 women; mean age 68, range 20-96), 17 patients in each group. Demographic and clinical features, and the indications for the procedure were similar for the two patient groups. The median Freeman score was significantly lower in the prone group compared with the supine group (1 vs. 3, P=0.0047, rank sum test). Biliary cannulation was achieved in all patients in the prone group, but was not achieved in five patients (29%) in the supine group (P=0.052). In four of these five patients, biliary cannulation was successfully achieved after turning the patient into the prone position. The percentage of patients unwilling to repeat the ERCP procedure in the future was higher in the supine group (29% vs. 6%, P=0.087); the mean tolerance score and mean total procedure time were similar in the two groups. Seven patients in the supine group experienced at least one adverse cardiorespiratory event, compared with only one patient in the prone group (41% vs. 6%, P=0.039). CONCLUSIONS: ERCP performed with the patient in the supine position is technically more demanding for operators used to working with patients in the prone position and carries a greater risk of adverse cardiorespiratory events in nonintubated patients.

Adult↗
PubMed2004

Cephalometric comparison of pharyngeal changes in subjects with upper airway resistance syndrome or obstructive sleep apnoea in upright and supine positions.

The aim of the present study was to cephalometrically compare pharyngeal changes between upright and supine positions in patients with upper airway resistance syndrome (UARS) or obstructive sleep apnoea (OSA). Eighty-two OSA patients, 70 men (mean age 49 +/- 11.8 years) and 12 women (45.9 +/- 8.3 years), underwent cephalometric sleep apnoea analysis. One upright and one supine radiograph were taken of each patient (a total of 164 cephalometric radiographs). The results showed no significant changes either in naso- or hypopharyngeal soft tissues between the two positions. In contrast, the shortest distance from the soft palate (ve1-ve2) and the tip of the soft palate (u1-u2) to the posterior oropharyngeal wall was significantly narrower (P < 0.001) in the supine position. Furthermore, in the supine position a slight thickening in the soft palate (sp1-sp2, P < 0.05) was detected with no change in the length of the soft palate (PNS-u1). The form of the tongue changed significantly: it was shorter (Tt-Tgo, P < 0.001; Tt-va, P < 0.001) and thicker (Ts/Tt-Tgo, P < 0.05) in the supine position. The present results suggest that OSA patients are prone to significant narrowing of their oropharyngeal, but not of their naso- or hypopharyngeal, airways in the supine position. Thus, treatment of OSA and UARS patients should mainly be aimed at preventing further oropharyngeal airway narrowing as a result of supine-dependent sleep.

Adolescent↗
PubMed2001

Changes in major blood components after adopting the supine position during haemodialysis.

BACKGROUND: In Japan, haemodialysis (HD) is usually performed with patients in the supine position. However, the effects of changing posture on major blood components have not been investigated in HD patients. It is possible that several fluid components change rapidly when patients change from the upright to the supine position. We therefore investigated the effects of posture on blood component analysis. METHODS: A first blood sample was taken from 10 HD patients 5 min after they adopted a supine position; HD was begun immediately after sampling. Additional blood samples were collected 15 and 30 min later while patients remained in the supine position. On an alternate day, blood samples were taken from these same patients in the supine position, but not during HD. The same procedure was performed in 10 healthy volunteers. RESULTS: Haematocrit significantly decreased in patients undergoing HD at 15 and 30 min into the HD session. Similar decreases were observed in HD patients not undergoing HD and in normal control subjects. Haematocrit changes at 15 min were not significantly different between the three groups. Serum albumin concentrations decreased in the same way as haematocrit. Consequently, the reductions in haematocrit and albumin concentrations in HD patients during the HD session were not attributable to the HD procedure or to end-stage renal disease, but rather were due to the supine position and consequent haemodilution caused by redistribution of water from the extra- to the intravascular space. Finally, WBC counts decreased significantly at 15 min in both HD patient groups and in normal controls. The relative decrease at 15 min was significantly greater in HD patients undergoing HD (61.4% of baseline) than in those not undergoing HD (88.0%) or in normal controls (94.7%). These differences were probably due to previously reported WBC sequestration in the lungs during the early phase of HD. CONCLUSIONS: This study suggests that the change from the upright to the supine positions during HD causes changes in blood components that are critical for quality control determinations.

Adult↗
PubMed1999

Spectral analysis of arterial blood pressure and cerebral blood flow velocity during supine rest and orthostasis.

This study evaluates the effect of orthostasis on the low frequency (LF, 0.04 to 0.15 Hz) fluctuations in the blood flow velocity of the middle cerebral artery (MCAFV) in relation to its arterial blood pressure (ABP) equivalent to further define and quantify this relationship in cerebrovascular regulation. Spectral analysis was performed on 22 healthy subjects during supine rest and head-up tilt. The power in the LF range can be used to quantify the LF fluctuations, and four types of LF power data could be obtained for each individual: LF power of supine MCAFV, LF power of supine ABP, LF power of tilt MCAFV, and LF power of tilt ABP. By comparing LF power of MCAFV with LF power of ABP, two power ratios could be generated to describe the flow-pressure relationship during supine rest and head-up tilt, respectively, supine power ratio (LF power of supine MCAFV/ LF power of supine ABP) and tilt power ratio (LF power of tilt MCAFV/ LF power of tilt ABP). In addition, an index for dynamic autoregulation in response to orthostasis can be calculated from these two power ratios (tilt power ratio/supine power ratio). The authors found that this index was dependent on the extent of orthostatic MCAFV changes, and the dependency could be mathematically expressed (r = 0.61, P = .0001), suggesting its involvement in cerebrovascular regulation. Moreover, these data further support the previous observation that the LF fluctuations of MCAFV might result from modulation of its ABP equivalent, and the modulation effect could be quantified as the power ratio (LF power of MCAFV/ LF power of ABP). These observations could be an important step toward further insight into cerebrovascular regulation, which warrants more research in the future.

Adult↗
PubMed1998

Venous air embolism in sitting and supine patients undergoing vestibular schwannoma resection.

OBJECTIVE: This study retrospectively compares the incidence of venous air embolism (VAE) detection and morbidity in the sitting and supine positions. All patients underwent vestibular schwannoma resection via the retrosigmoid approach by a single surgical team. METHODS: A total of 432 consecutive operations were reviewed, 222 of which were performed with the patients in the sitting position and 210 of which were performed with the patients in the supine position. Charts were reviewed for evidence of intraoperative VAE, intraoperative hypotension secondary to VAE, postoperative morbidity related to VAE, and other variables to compare the groups. RESULTS: This study demonstrated a 28% incidence of VAE detection when patients were in the sitting position compared to a 5% incidence of VAE detection when patients were in the supine position (P < 0.0001). Intraoperative hypotension secondary to VAE was noted in 1.8% of the sitting patients and 1.4% of the supine patients (P=0.72, no significant difference). Postoperative morbidity caused by VAE was noted in one sitting patient (0.5%) (pulmonary edema) and in no supine patients (P=0.48, no significant difference). Blood loss was slightly greater in the supine group, and operative times were similar in both groups, despite that the average tumor size of patients operated on in the sitting position was 2.8 cm versus 2.2 cm in the supine group (P < 0.0001). CONCLUSION: Our results indicate that although there is a higher incidence of VAE detection in sitting patients, the morbidity is not statistically greater. We conclude that because morbidity from VAE is similar in either position, patient positioning should be based on surgical team preference.

Cerebral Veins↗