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PubMed2004

Colpocystoproctography in the upright and supine positions correlated with dynamic MRI of the pelvic floor.

PURPOSE: To test whether there are statistically significant differences between measurement results on colpocystoproctography in the upright and the supine positions, and to correlate these results with dynamic MRI. PATIENTS AND METHODS: Seven patients with pelvic floor descent had received colpocystoproctography in the upright and supine positions and, additionally, dynamic MRI of the pelvic floor. Bladder neck position, angle of urethral inclination, posterior vesicourethral angle, and vaginal vault position were measured at relaxed pelvic floor and at pelvic strain. Differences between the measurement results of each parameter in the upright and supine position on colpocystoproctography were calculated and correlated with the measurement results from the dynamic MRI. RESULTS: At pelvic strain, bladder neck position, angle of urethral inclination, posterior vesicourethral angle and vaginal vault position measurements showed no statistically significant differences between colpocystoproctography in the upright and supine positions or dynamic MRI. For the bladder neck height at pelvic floor relaxation, significant differences were found between colpocystoproctography in the upright and supine positions, and colpocystoproctography in the upright position versus dynamic MRI. CONCLUSION: At pelvic strain, measurement data from dynamic MRI are not statistically different from data from colpocystoproctography either in supine and upright positions.

Aged↗
PubMed1994

A cephalometric and electromyographic study of upper airway structures in the upright and supine positions.

Obstructive sleep apnea (OSA) is characterized by recurrent upper airway obstruction during sleep, usually in the supine position. To investigate the relationship between upper airway size and genioglossus (GG) muscle activity, upright and supine cephalograms were obtained in 20 OSA patients and 10 symptom-free control subjects. Tongue electromyographic (EMG) recordings were obtained with surface electrodes, and pressure transducers were placed in the 10 symptom-free controls. The tongue cross-sectional area increased 4.3% (p < 0.05), and the oropharyngeal area decreased 36.5% (p < 0.01) when the OSA patients changed their body position from upright to supine. No changes were observed in the tongue area, but soft palate thickness increased (p < 0.01) when the control subjects changed from the upright to the supine position. Furthermore, the oropharyngeal cross-sectional area decreased 28.8% (p < 0.01) despite a 34% increase (p < 0.05) in resting GG EMG activity. Posterior tongue pressure increased 17% (p < 0.05) with the change from upright to supine. On the basis of these findings, we propose that body posture has a substantial effect on upper airway structure and muscle activity. This postural effect should be taken into account when assessing upper airway size in the erect posture (conventional cephalography) and in the supine position (computed tomography). The vertical and anteroposterior position of the tongue and its relationship to airway size may be more important than soft palate size in the pathogenesis of OSA.

Airway Resistance↗
PubMed2002

Effects of prone and supine posture on cardiopulmonary function after experimental chlorine gas lung injury.

BACKGROUND: Chlorine gas may induce severe acute lung injury. Improvement of pulmonary gas exchange in patients and animals with acute lung injury nursed in the prone position was observed in recent years. The purpose of this study was to evaluate the effects of prone and supine positions on pulmonary and cardiovascular functions following experimental chlorine gas lung injury. METHODS: Twenty anesthetized and mechanically ventilated pigs were exposed to chlorine gas (400 p.p.m. in air) for 20 min in the supine position, then assigned randomly to ventilation in the supine or prone positions (n=10 in each group). Hemodynamics, gas exchange, lung mechanics and oxygen transport were evaluated for 5 h. RESULTS: All animals showed severe pulmonary dysfunction immediately after chlorine gassing with a threefold increase in pulmonary vascular resistance index, a drop in arterial oxygenation (12.3+/-1.3 kPa to 5.4+/-0.7 kPa) and a fall in lung-thorax compliance (22+/-1 ml cmH2O-1 to 8+/-2 ml cmH2O-1). Venous admixture (Qs/Qt) improved in animals in the prone position while there was no change in the supine position (prone 32+/-11% vs. supine 42+/-9% at 5 h,P<0.05). Lung-thorax compliance improved significantly with time in the prone group only (P<0.01). Oxygen delivery increased significantly in prone animals compared with animals nursed in the supine posture (P<0.001). CONCLUSION: Immediate prone positioning after chlorine gas injury not only inhibited deterioration of gas exchange but was also associated with improved pulmonary function and oxygen transport.

Administration, Inhalation↗
PubMed1996

Reduced arterial O2 saturation during supine exercise in highly trained cyclists.

Performance of intense dynamic exercise in highly trained athletes is associated with a reduced arterial haemoglobin saturation for O2 (SaO2) and lower arterial PO2 (PaO2). We hypothesized that compared with upright exercise, supine exercise would be accompanied by a smaller reduction in SaO2 because of a lower maximal O2 uptake (VO2max) and/or a more even ventilation-perfusion distribution. Eight elite bicyclists completed progressive cycle ergometry to exhaustion in both positions with concomitant determinations of ventilatory data, arterial blood gases and pH. During upright cycling VO2max averaged 75 +/- 1.6 mL O2 min-1 kg-1 (+/-SEM) and it was 10.6 +/- 1.7% lower during supine cycling (P < 0.001). Also the maximal pulmonary and alveolar ventilation were lower during supine cycling (by 15 +/- 2% and 21 +/- 3%, respectively; P < 0.001) which related to a 0.8 +/- 0.1 L lower tidal volume (P < 0.001). In all subjects and independent of work posture PaO2 and SaO2 decreased from rest to exhaustion (from 99 +/- 3 to 82 +/- 2 Torr and 98.1 +/- 0.2 to 95.2 +/- 0.4%, respectively; P < 0.001); alveolar-arterial PO2 difference increased from 6 +/- 2 to 37 +/- 3 Torr in both body positions. At exhaustion arterial PCO2 was lower in upright than in supine (33.4 +/- 0.6 vs. 35.9 +/- 0.9 Torr; P < 0.01), suggesting a greater relative hyperventilation in upright. Arterial pH was similar in upright and supine at rest (both 7.41 +/- 0.01) and at exhaustion (7.31 +/- 0.01 vs. 7.32 +/- 0.01, respectively). We conclude that despite a lower Vo2max and supposedly an improved ventilation-perfusion distribution, altering body position from upright to supine does not influence arterial O2 desaturation during intense exercise.

Adult↗
PubMed2000

Achieving haemodynamic baseline values with Finapres in elderly subjects during supine rest.

BACKGROUND: Clear guidelines for the resting time necessary to achieve stable blood pressure (BP) levels are scant in gerontology research. Therefore, we aimed to determine the minimum period required for obtaining haemodynamic baseline values in elderly subjects during supine rest. In addition, we evaluated the effect of cardiovascular morbidity, such as diastolic heart failure, and the effect of complex comorbidity of geriatric patients, on haemodynamic changes during supine rest. METHODS: A total of 17 healthy subjects, 18 heart failure patients with normal systolic function and 24 geriatric patients, aged 70 years and more, participated. After an overnight fast, changes in systolic BP (SBP), diastolic BP (DBP), heart rate (HR), and stroke volume (SV) were determined by Finapres beat-to-beat non-invasive BP monitoring during a 20-min supine rest. The procedure was repeated in the healthy subjects and geriatric patients on a second day. RESULTS: Complete BP stabilization was reached in each group within 5 min of supine rest, as SBP remained essentially unchanged and DBP did not change significantly anymore after the fourth minute. In the heart failure patients, HR decreased and SV increased until the twelfth minute of rest. The SBP, DBP, HR, and SV changes during supine rest showed good reproducibility. CONCLUSIONS: A span of 5 min of supine rest ensured achievement of reliable and reproducible baseline BP values by Finapres in elderly subjects. However, we recommend at least 12 min of rest to obtain full haemodynamic stability in elderly patients with diminished cardiac compliance and diastolic function.

Adaptation, Physiological↗
PubMed1999

Short-term morbidity and infant mortality among infants who slept supine at 1 month of age--a follow-up report.

Following evidence that prone sleeping is causally related to sudden infant death syndrome (SIDS), intervention campaigns to avoid prone sleeping in many countries have led to a large reduction in SIDS and total infant mortality. The supine position has been recommended for healthy infants in several countries. The objective of this report was to determine how usual sleep position at 1 month relates to morbidity indicators at 1 month and 12 weeks and to SIDS and postneonatal mortality using a prospective population-based live birth cohort in Tasmania, Australia. Eligible infants were the one-fifth of Tasmanian live births at higher risk of SIDS using a perinatal score. From 1 January 1988 to 31 December 1995, 9826 (89% of eligible) infants participated in the home interview. Fifty-three eligible infants died of SIDS, 51 (96%) with hospital interview data and 35 (81% of those eligible for home visit) with home visit data. The main outcome measures were SIDS, postneonatal mortality and parentally reported infant morbidity. The postneonatal mortality rates (cases per 1000 live births) by usual sleep position at 1 month of age were supine 1.60 [95% CI 0.04, 8.87], side 2.87 [1.79, 4.35], prone 10.27 [5.62, 17.18] and other (including no usual position) 6.37 [0.16, 34.98]. None of the study infants who slept supine died of SIDS at a later time. Of 25 morbidity indicators studied, only noisy breathing was increased for supine compared with side-sleeping babies. In this study, there was no evidence to suggest that supine sleeping at 1 month of age was associated with an increase in important short-term morbidity or postneonatal mortality. These findings provide further support for the recent recommendations of the American Academy of Pediatrics that healthy infants should preferably sleep in the supine position.

Analysis of Variance↗
PubMed2001

Supine fall in lung volumes in the assessment of diaphragmatic weakness in neuromuscular disorders.

OBJECTIVE: To determine whether diaphragmatic function can be determined by noninvasive respiratory indices in neuromuscular disease. DESIGN: Vital capacity (VC) and mouth pressure generated during a maximal static inspiratory effort (Pi max) were measured with patients in both sitting and supine positions. SETTING: Rehabilitation hospital. PATIENTS: Twenty-four patients with generalized neuromuscular disease. MAIN OUTCOME MEASURES: Changes in indices from sitting to supine position were compared with invasive diaphragmatic function indices consisting of transdiaphragmatic pressures during maximal sniff (Pdi sniff) and the ratio of gastric pressure (Pga) increases over transdiaphragmatic pressure (DeltaPga/DeltaPdi) during quiet breathing. RESULTS: The fall in VC in the supine position was greater in the 15 patients who had spontaneous paradoxical diaphragmatic motion (DeltaPga/DeltaPdi < 0) than in the 9 patients who did not. Specificity and sensitivity of a greater than 25% supine fall in VC for the diagnosis of diaphragmatic weakness (DeltaPga/DeltaPdi < 0 and/or Pdi sniff < 30cmH2O) were 90% and 79%, respectively. Stepwise multiple regression analysis of Pdi sniff showed that both the supine fall in VC and Pi max were associated with diaphragmatic weakness (R(2) =.66; p <.0001). These factors contributed 52% and 14% of the Pdi sniff variance, respectively. CONCLUSIONS: Simple VC measurement in the sitting and supine positions may be helpful in detecting severe or predominant diaphragmatic weakness.

Adult↗
PubMed2004

Supine position is safe and effective for percutaneous nephrolithotomy.

BACKGROUND AND PURPOSE: The prone position has been widely adopted in conventional percutaneous nephrolithotomy (PCNL). Following its introduction in 1998, we changed our routine practice of PCNL from the prone to the supine position, which had numerous benefits and was safe and effective. Tract formation and stone fragmentation and retrieval were accomplished with the patient supine. PATIENTS AND METHODS: We report our experience with 62 patients (67 renoureteral units) treated in the supine position and describe the technique in detail. RESULTS: The primary stone clearance rate was 76%, and the mean number of sessions of PCNL was 1.3. There was no procedure-related major complication. There were also no splanchnic injuries. One kidney loss (emergency nephrectomy for control of hemorrhage) was noted but was not directly related to the procedure (profuse bleeding after accidental traction on the balloon nephrostomy tube by the patient 1 week after PCNL). Modification of positioning was made to suit the body build of Chinese patients. CONCLUSION: There are several advantages to the supine position for the patient and the urologist, with greater versatility of stone manipulation along the whole upper urinary tract. There are a few limitations of the supine position, but they can be overcome. Performing PCNL with the patient in the supine position is a sound alternative to the conventional prone position.

Adult↗
PubMed1997

Cardiac axis change between prone and supine positioning may contribute to differences in 99Tc(m)-MIBI myocardial SPET imaging.

The aims of this study were to assess the effect of prone and supine positioning on 99Tc(m)-MIBI myocardial SPET images and the contribution of cardiac axis change. We compared 227 tomograms of patients imaged in the prone position with 227 tomograms of the same patients imaged in the supine position. For each tomographic session, the axis angle of the heart was recorded using an in-house program. The results showed a significant change in the cardiac axis angle of 9 degrees in the transaxial plane (P < 0.001). This change in the cardiac axis correlated with differences in cardiac wall activity (wall activity when the patient was imaged in the prone position minus wall activity when the patient was imaged in the supine position). Our results suggest that factors other than diaphragmatic movement and attenuation could account for the differences in wall activity observed when patients are imaged prone versus supine. Differences in the intensity of photon attenuation in the heart itself, depending on the cardiac axis, could be a contributing factor. Quantitation of the variation in wall activity leads us to suggest that 99Tc(m)-MIBI SPET should be performed in the prone position to allow better visualization of the inferior and the septal walls. The anterior and lateral walls are better studied in the supine position. Images acquired in both the prone and supine positions would allow the best assessment of all walls.

Coronary Disease↗
PubMed2005

Prone SPECT myocardial perfusion imaging is associated with less cardiac drift during the acquisition duration than imaging in the supine position.

BACKGROUND AND AIM: Cardiac cranial drift, a slow vertical upward displacement seen during the acquisition of myocardial single photon emission tomography (SPECT), is a source of image artefacts that may lead to erroneous interpretation. Changes in breathing pattern and depth throughout image acquisition are believed to cause cardiac cranial drift. As the physiology of respiration probably differs with postural changes, we hypothesized that cardiac drift may be different for supine vs. prone acquisitions. Our aim was to assess the magnitude of cardiac displacement for prone and supine SPECT acquisitions in patients undergoing stress myocardial perfusion imaging. METHODS: We enrolled prospectively 15 subjects undergoing exercise myocardial perfusion imaging. Subjects had post-stress images acquired in both the prone and supine positions. Motion was assessed in the horizontal (x) and vertical (y) axes for both camera heads at all 64 projections at which images were obtained. Pixel displacement (number of pixels from the baseline of zero) in either the cranial/caudal or left/right direction was quantified using the automated camera motion correction algorithm. RESULTS: Supine imaging was associated with more cranial drift than prone imaging (1.20+/-0.40 pixels vs. 0.92+/-0.24 pixels, P<0.05). There was no significant difference in cardiac displacement in the horizontal axis (1.03+/-0.5 pixels vs. 1.12+/-0.22 pixels, P=NS). CONCLUSIONS: Prone imaging is associated with less cardiac cranial drift than imaging in the supine position, suggesting that the former is associated with a more constant and reliable diaphragmatic breathing pattern. Acquisitions in the prone position may thus be associated with fewer motion artefacts than supine acquisitions for cardiac SPECT imaging.

Adult↗
PubMed2003

Episcleral venous pressure in younger and older subjects in the sitting and supine positions.

PURPOSE: Intraocular pressure is higher in older than younger subjects during the day and night. We attempted to determine whether episcleral venous pressure could explain the difference in the sitting and supine positions. PARTICIPANTS AND METHODS: We compared episcleral venous pressure, intraocular pressure, and blood pressure in a group of younger subjects aged 18 to 30 years and in a group of older subjects aged 65 years or older. The above measurements were performed in the sitting position and after 15 minutes in the supine position. RESULTS: The main difference between the groups was their systemic conditions. Comparing both groups, episcleral venous pressure and intraocular pressure were not different in the sitting position. However, in the supine position, episcleral venous pressure (9.6 vs. 8.3 mm Hg) (P < 0.01) and intraocular pressure (17.1 vs. 15.6 mm Hg) (P < 0.05) were higher in the older group. Statistically, a within-group analysis showed a significant increase in intraocular pressure in the supine position for both the younger (+ 0.8 mm Hg) (P < 0.001) and older subjects (+ 1.8 mm Hg) (P < 0.02). This was associated with an increased episcleral venous pressure in younger (+ 0.4 mm Hg) (P < 0.001) and older subjects (+1 mm Hg) (P < 0.02). There was no gender difference in intraocular pressure and episcleral venous pressure. No differences were found for intraocular pressure and episcleral venous pressure in subjects having certain systemic conditions. Blood pressure was higher for older subjects (P < 0.001). It decreased in the supine position for both groups (P < 0.001). CONCLUSION: Intraocular pressure and episcleral venous pressure were not different in the younger and older group in the sitting position. They were higher in the supine position for older subjects. There was no gender difference.

Aged↗
PubMed2006

Comparison of different extubation techniques in lumbar surgery: prone extubation versus supine extubation with or without prior injection of intravenous lidocaine.

The aim of this study was to evaluate the incidence of coughing and breath holding in patients undergoing lumbar surgery extubated in prone position, supine position, or supine position with intravenous lidocaine before extubation. About 105 ASA I to II patients undergoing lumbar surgery were extubated in prone position in group P (n = 35), in supine position in group S (n = 35) and in supine position with intravenous 1.5 mg/kg lidocaine 10 minutes before extubation in group SL (n = 35). The number of patients who coughed and demonstrated breath holding was noted at emergence period. The time of loss of monitoring while repositioning the patient was recorded. The frequency of cough in group S was higher compared with group P at 1 minute after extubation (P = 0.008). Two and three minutes after extubation, the patients in group S demonstrated higher cough incidence compared with groups P and SL (P < 0.05). The incidence of breath holding in the first 6 minutes was lower in group P (n = 11) compared with groups S (n = 29) and SL (n = 25)(P = 0.001). The loss of monitoring time was longer in groups S (62 +/- 40 s) and SL (53 +/- 39 s) when compared with group P (0 s) (P < 0.01). Prone emergence and supine emergence with intravenous lidocaine provides an alternative approach to conventional supine emergence and prone extubation offers less cough and breath holding and continuation of monitoring.

Adult↗
PubMed2004

Positive end-expiratory pressure affects regional redistribution of ventilation differently in prone and supine sheep.

OBJECTIVE: To examine interactions between positive end-expiratory pressure (PEEP) and posture on regional distribution of ventilation and to compare measurements of regional ventilation with two aerosols: a wet fluorescent microsphere aerosol (FMS, median mass aerodynamic diameter 1.1 microm) and a dry Tc-labeled carbon particle aerosol (Technegas, TG, median mass aerodynamic diameter approximately 0.1 microm). DESIGN: Experimental study. SETTING: Academic laboratory. SUBJECTS: : Anesthetized and mechanically ventilated sheep (n = 16). INTERVENTIONS: Four conditions were studied: prone or supine posture with or without 10 cm H2O PEEP. MEASUREMENTS AND MAIN RESULTS: Comparisons of FMS and TG were made in five animals. The median correlation coefficient of the two ventilation tracers was .95 (range, .91-.96). The mean ventilation per unit weight of dry lung for horizontal planes was almost identical whether measured with TG or FMS. The distribution of ventilation was assessed by analyzing deposition of aerosol in about 1,000 lung regions per animal. Distribution of ventilation down the vertical axis was linear in prone (the slope indicated a dorsal-to-ventral three-fold difference in ventilation) but unimodal in supine animals with the mode in the center of the lung. Redistribution of ventilation with 10 PEEP differed between posture, shifting the mode in supine toward dependent lung regions while eliminating the dorsal-to-ventral gradient in prone. The regional heterogeneity in ventilation was greater in supine sheep at both levels of PEEP, and this was due mostly to greater isogravitational heterogeneity in supine than in prone position. CONCLUSIONS: The wet fluorescent microsphere aerosol was as reliable as Technegas for high-resolution measurements of regional ventilation. The markedly different effects of 10 PEEP in supine and prone sheep may have important implications for gas exchange both in noninjured and injured lungs.

Administration, Inhalation↗
PubMed2000

Skin hemodynamics during change from supine to lateral position.

The purpose of this study was to identify the skin hemodynamics during the position change from supine to lateral in patients with neurodegenerative diseases. The participants were 19 patients with neurodegenerative diseases and 12 healthy volunteers. The alteration in the total concentration of oxyhemoglobin and deoxyhemoglobin, indicative of change in blood volume, was measured in the skin of the left flank by using a portable noninvasive tissue oxygen monitor by near-infrared spectroscopy. The positions were changed from the left and right lateral with a return to the supine between each procedure. In healthy volunteers, total hemoglobin concentration (skin blood volume) increased when the position changed from supine to left lateral and decreased when changed from supine to right lateral. The decreased skin blood volume gradually recovered after a change from the supine to the right lateral position in healthy volunteers. However, it did not recover in three sporadic olivopontocerebellar atrophy (OPCA) patients with marked autonomic dysfunction and one Parkinsonian patient with severe orthostatic hypotension. Our study identified that the intracutaneous blood was changing dynamically during the position change from supine to lateral and was regulated by autonomic nerve function.

Autonomic Pathways↗
PubMed1998

Alveolar oxygen uptake and femoral artery blood flow dynamics in upright and supine leg exercise in humans.

We tested the hypothesis that the slower increase in alveolar oxygen uptake (VO2) at the onset of supine, compared with upright, exercise would be accompanied by a slower rate of increase in leg blood flow (LBF). Seven healthy subjects performed transitions from rest to 40-W knee extension exercise in the upright and supine positions. LBF was measured continuously with pulsed and echo Doppler methods, and VO2 was measured breath by breath at the mouth. At rest, a smaller diameter of the femoral artery in the supine position (P < 0. 05) was compensated by a greater mean blood flow velocity (MBV) (P < 0.05) so that LBF was not different in the two positions. At the end of 6 min of exercise, femoral artery diameter was larger in the upright position and there were no differences in VO2, MBV, or LBF between upright and supine positions. The rates of increase of VO2 and LBF in the transition between rest and 40 W exercise, as evaluated by the mean response time (time to 63% of the increase), were slower in the supine [VO2 = 39.7 +/- 3.8 (SE) s, LBF = 27.6 +/- 3.9 s] than in the upright positions (VO2 = 29.3 +/- 3.0 s, LBF = 17.3 +/- 4.0 s; P < 0.05). These data support our hypothesis that slower increases in alveolar VO2 at the onset of exercise in the supine position are accompanied by a slower increase in LBF.

Adult↗
PubMed2000

Supine lower body negative pressure exercise simulates metabolic and kinetic features of upright exercise.

Exercise within an artificial gravity environment may help prevent microgravity-induced deconditioning. We hypothesized that supine lower body negative pressure (LBNP) exercise simulates physiological and biomechanical features of upright exercise. Walking (4.5 +/- 0.3 km/h) and running (8.0 +/- 1.0 km/h) while supine within a LBNP exerciser were compared with walking and running while upright. Eight healthy subjects exercised for 5 min at each of the four posture/gait conditions. LBNP of 52 +/- 4 mmHg generated one body weight of supine ground reaction force (GRF). Gait parameters and GRFs were measured during the third minute of exercise, and heart rate and oxygen consumption were measured during the fifth minute. Oxygen consumption during supine LBNP treadmill exercise [walking: 14.6 +/- 0.9; running: 32.2 +/- 1.6 (SE) ml. min(-1). kg(-1)] was similar to that during upright treadmill exercise (walking: 15.1 +/- 0.9; running: 34.0 +/- 1.9 ml. min(-1). kg(-1)). Heart rate for supine LBNP exercise (grand mean: 133 +/- 11 beats/min) was also similar to that for upright exercise (136 +/- 11 beats/min). Footward forces integrated over each stride (330.5 +/- 34.4 vs. 319. 1 +/- 29.6 N. s) and rate of force generation (26,483 +/- 4,310 vs. 25,634 +/- 4,434 N/s) were similar for upright and LBNP exercise, respectively. Our collective results indicate that supine exercise within LBNP can simulate the physiological stress and GRFs that are generated during upright gait.

Adult↗
PubMed2001

Distribution of pulmonary ventilation using Xe-enhanced computed tomography in prone and supine dogs.

Xe-enhanced computed tomography (CT; Xe-CT) is a method for the noninvasive measurement of regional pulmonary ventilation in intact subjects, determined from the washin and washout rates of the radiodense, nonradioactive gas Xe, as measured in serial CT scans. We used the Xe-CT ventilation method, along with other quantitative CT measurements, to investigate the distribution of regional lung ventilation and air content in healthy, anesthetized, mechanically ventilated dogs in the prone and supine postures. Vertical gradients in regional ventilation and air content were measured in five mongrel dogs in both prone and supine postures at four axial lung locations. In the supine position, ventilation increased with dependent location, with a mean slope of 7.3%/cm lung height, whereas no ventilation gradients were found at any location in the prone position. These results agree quantitatively with other published studies. In addition, six different animals were studied (3 supine, 3 prone) to examine the longitudinal distribution of ventilation and air content. The prone lungs were more uniformly inflated compared with the supine, which were less well expanded at the base than apex. Ventilation index, a measure of regional ventilation relative to whole lung ventilation, increased steeply from apex to base in the supine animals, whereas it was again more uniform in the prone condition. We conclude that the Xe-CT method provides a reasonable, quantitative measurement of regional ventilation and promises to be a valuable tool for the noninvasive determination of regional lung function.

Animals↗
PubMed2005

Marked differences between prone and supine sheep in effect of PEEP on perfusion distribution in zone II lung.

The classic four-zone model of lung blood flow distribution has been questioned. We asked whether the effect of positive end-expiratory pressure (PEEP) is different between the prone and supine position for lung tissue in the same zonal condition. Anesthetized and mechanically ventilated prone (n = 6) and supine (n = 5) sheep were studied at 0, 10, and 20 cm H2O PEEP. Perfusion was measured with intravenous infusion of radiolabeled 15-microm microspheres. The right lung was dried at total lung capacity and diced into pieces (approximately 1.5 cm3), keeping track of the spatial location of each piece. Radioactivity per unit weight was determined and normalized to the mean value for each condition and animal. In the supine posture, perfusion to nondependent lung regions decreased with little relative perfusion in nondependent horizontal lung planes at 10 and 20 cm H2O PEEP. In the prone position, the effect of PEEP was markedly different with substantial perfusion remaining in nondependent lung regions and even increasing in these regions with 20 cm H2O PEEP. Vertical blood flow gradients in zone II lung were large in supine, but surprisingly absent in prone, animals. Isogravitational perfusion heterogeneity was smaller in prone than in supine animals at all PEEP levels. Redistribution of pulmonary perfusion by PEEP ventilation in supine was largely as predicted by the zonal model in marked contrast to the findings in prone. The differences between postures in blood flow distribution within zone II strongly indicate that factors in addition to pulmonary arterial, venous, and alveolar pressure play important roles in determining perfusion distribution in the in situ lung. We suggest that regional variation in lung volume through the effect on vascular resistance is one such factor and that chest wall conformation and thoracic contents determine regional lung volume.

Animals↗