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PubMed2006

Benign paroxysmal positional vertigo due to a simultaneous involvement of both horizontal and posterior semicircular canals.

From April 2001 to November 2003, we investigated 8 patients with benign paroxysmal positional vertigo (BPPV) that was suspected to simultaneously affect both the horizontal and posterior semicircular canals (HSCC and PSCC). These cases showed typical vertical-torsional nystagmus induced by the Dix-Hallpike maneuver, followed by a horizontal nystagmus. They also showed a direction-changing geotropic or apogeotropic positional nystagmus triggered by lateral head rotations in the supine position. Using the three-dimensional analysis of the positional nystagmus, the rotation axis of the positional nystagmus had a component perpendicular to the plane of PSCC and another component perpendicular to the plane of HSCC. All these findings suggest that BPPV in these patients was a combination of posterior and horizontal canal BPPV. The observation of a vertical-torsional positional nystagmus should prompt the specialist to perform not only the canalith repositioning procedure, but also to execute lateral head turns in the supine position.

Adult↗

PubMed2004

Age at death, season, and day of death as indicators of the effect of the back to sleep program on sudden infant death syndrome in the United States, 1992-1999.

BACKGROUND: In June 1992, the American Academy of Pediatrics Task Force on Infant Positioning and Sudden Infant Death Syndrome (SIDS) made its first recommendation concerning placing infants in a supine position. Since the publication of this recommendation, SIDS rates in the United States have declined 44%. Before this recommendation, SIDS had a marked seasonal pattern and was noted to occur more frequently on weekends. OBJECTIVE: The objective of this study was to determine if significant changes in SIDS rates have occurred in age at death (0-27 days vs 1-6 months vs 7-11 months), season of death, and weekday of death since the implementation of the recommendations for supine positioning of infants for sleep. DESIGN: United States natality and mortality data were used for the years 1992 through 1994. United States linked infant birth and death certificate files were used for the years 1995 through 1999. Season of death was calculated from month of death and was ordered for analysis from winter to fall to spring to summer; day of death was ordered from Monday to Sunday and additionally analyzed as weekend (Saturday and Sunday) vs weekday (Monday through Friday). RESULTS: During the 8 years, 28 548 deaths were attributed to SIDS among residents of the United States. The average annual decrease in the SIDS rate for neonates aged 0 to 27 days was 6.6%; for infants aged 1 to 6 months, 9.0%; and for infants aged 7 to 11 months, 6.1%. The average decline in seasonal rates from winter to summer was 11.2% per season. A significant interaction between year of death and season indicated a diminishing rate of seasonal variation. The odds ratio for weekend vs weekday SIDS deaths was 0.98 (95% confidence interval, 0.96-1.01). There was no significant interaction between year of death and weekday of death, which indicates no change in the relationship since the implementation of the supine sleeping recommendations. CONCLUSIONS: These data provide insights into the effect of the supine sleep recommendations on SIDS. The reduction in seasonal variation of SIDS suggests advantages conferred by supine sleeping in colder seasons.

Age Distribution↗

PubMed1990

[Change in the zone of apposition of the human diaphragm associated with ventilatory movement].

The movement of the cephalic margin of the zone of apposition (ZOA) of the diaphragm associated with ventilatory movement was measured using ultrasonography in 24 healthy subjects and 45 patients with various pulmonary diseases. A transducer was placed on the lower chest wall, and movement of the cephalic margin of ZOA was measured during maximal inspiratory maneuver and expiratory maneuver from end expiratory position in supine and sitting positions in healthy subjects, and in the supine position in patients. In healthy subjects, there was a linear relationship between inspiratory or expiratory volumes and movement of the cephalic margin of ZOA. Movement in the supine position during vital capacity maneuver was 103.0 +/- 15.6 (mean +/- SD), 106.6 +/- 17.2, 108.5 +/- 18.2, and 114.8 +/- 16.3 mm on the left anterior, right anterior, left posterior, and right posterior axillary lines, respectively. In the supine position, movement on the right posterior axillary line was significantly larger than that measured on other axillary lines (p less than 0.05). Movement during maximal inspiratory maneuver in the supine position was significantly larger than that in the sitting position (p less than 0.01). Movement during maximal expiratory maneuver in the supine position was significantly smaller than that in the sitting position (p less than 0.01). Patients showed decreased movement and great differences in movement between the left and right anterior axillary lines. Seven patients out of 28 with normal spirograms showed decreased movement on either or both sides. These data suggest that: 1) the movement of the cephalic margin of ZOA reflects diaphragm displacement; and 2) difference in ventilatory function of right and left hemithorax can be detected by movement of the cephalic margin of ZOA.

Diaphragm↗

PubMed1986

Diuretic treatment in decompensated cirrhosis and congestive heart failure: effect of posture.

The diuretic effect of the supine position was evaluated in six patients with cirrhosis and ascites and six with congestive cardiac failure. After fasting overnight in bed the patients received bumetanide 1 mg intravenously and were then immediately randomly assigned to either bed rest in the supine position or normal daily activity in the upright position for the next six hours. Two days later the procedure was repeated, the patients being assigned to the other posture. The diuretic response was similar in patients with heart failure and cirrhosis, and was significantly greater in the supine than in the upright position: mean 1133 v 626 ml/6 h (p less than 0.01). The natriuresis was similarly larger during recumbency: mean sodium 96 v 45 mmol(mEq)/6h (p less than 0.01), and the excreted potassium in six hours was similar in both postures. The glomerular filtration rate was 100 and 66 ml/min (p less than 0.01) and heart rate 76 and 83 beats/min (p less than 0.01) in the supine and upright positions respectively. Plasma concentrations of noradrenaline, renin, and aldosterone were all raised even when the patient adopted the supine position, and a further significant rise was observed during the upright position. The results suggest that the attenuated response to intravenous bumetanide in the upright position and during normal daily activity may be due to the activation of several homeostatic mechanisms that may reduce the excretion of water and salt.

Adult↗

PubMed1995

The Tasmanian SIDS Case-Control Study: univariable and multivariable risk factor analysis.

A population-based retrospective case-control study has been conducted in Tasmania since October 1988. Study measurements pertained to the scene of death of last sleep, as well as a verbal questionnaire on relevant exposures. From 1 October 1988 to 1 October 1991, 62 cases of sudden infant death syndrome (SIDS) occurred. Case response rate for retrospective interviews was 94% (58/62). The initial control response rate was 84% (101/121). After stratification for maternal age and birthweight, there was no increase in risk associated with the usual side position (odds ratio [OR] 1.05 [0.27, 5.02]), compared with the supine position (OR 1.00, reference). The prone position was associated with increased risk [OR 5.70 (1.67, 25.58)], relative to the supine position. In the final multivariable model, predictors of SIDS in this study were usual prone position (P < 0.001), maternal smoking (P = 0.008), a family history of asthma (P = 0.045) and bedroom heating during last sleep (P = 0.039). Protective factors were maternal age over 25 years (P = 0.013) and more than one child health clinic attendance (P = 0.003). The results provide further support for current health education activities which aim to inform parents of modifiable risk factors for SIDS, including the prone sleeping position, thermal stress and infant exposure to tobacco smoke.

Breast Feeding↗

PubMed2002

Developmental neurotransmitter pathology in the brainstem of sudden infant death syndrome: a review and sleep position.

Developmental studies on neurotransmitters and their receptors in sudden infant death syndrome (SIDS) infants and controls are reviewed, including comparison between the prone and supine positions at death. In SIDS infants, there are an increase of glial fibrillary acidic protein (GFAP)-positive astrocytes in the brainstem, an increase of substance P (SP) in the medulla and pons, a decrease of tyrosine hydroxylase (TH)-positive catecholaminergic neurons in the ventrolateral medulla (VLM), and vagal nuclei in the medulla oblongata and basal ganglia, a decrease of tryptophan hydroxylase (TrH)-positive serotonergic neurons in the periaqueductal gray matter (PAG), and decreases of 5-hydroxytryptamine 1A (5-HT1A) and 5-HT2A receptor immunoreactivities in the VLM and vagal nuclei in the medulla oblongata. These findings may be the result of chronic or repeated hypoxia and at the same time suggest hypofunction or immaturity of cardiorespiratory regulation. In contrast, 5-HT1A and 5-HT2A receptor immunoreactivities are increased in the PAG of SIDS infants. These increased immunoreactivities may reflect delayed neuronal maturation or a developmental abnormality of the nocicetive reaction of cardiorespiratory and arousal control in SIDS. Also, there are no differences of brainstem gliosis and catecholaminergic neuron changes between the prone and supine positions. Therefore, these changes may be predisposing factors for SIDS.

Astrocytes↗

PubMed1999

Redistribution of basic drugs into cardiac blood from surrounding tissues during early-stages postmortem.

The objective of this study was to elucidate the mechanism(s) responsible for increases in the concentrations of basic drugs in cardiac blood of bodies in a supine position during early-stages postmortem. The concentrations of basic drugs in cardiac blood and other fluids and tissues of three individuals who had used one or more basic drugs were examined. The results were compared with those obtained in experiments using rabbits. In the first case, autopsy of whom was performed approximately 12 h after death, methamphetamine was detected and its concentrations were in the order: lung >> pulmonary venous blood > blood in the left cardiac chambers (left cardiac blood) >> pulmonary arterial blood > blood in the right cardiac chambers (right cardiac blood). In the second case, autopsy of whom was performed approximately 9 h after death, methamphetamine and morphine were detected and their concentrations in the left cardiac blood were roughly twice those in the right cardiac blood. The methamphetamine and morphine concentrations in the lung were 2 to 4 times higher than those in cardiac blood samples. In the third case, autopsy of whom was performed approximately 2.5 days after death, the pulmonary veins and arteries were filled with chicken fat clots. Toxicological examination revealed the presence of four basic drugs: methamphetamine, amitriptyline, nortriptyline and promethazine. Their concentrations in the lung were 5 to 300 times higher than those in cardiac blood, but postmortem increases in the concentrations of these drugs in the cardiac blood were not observed. In the animal experiments, rabbits were given 5 mg/kg methamphetamine intravenously or 20 mg/kg amitriptyline subcutaneously and sacrificed 20 min or 1 h later, respectively. The carcasses were left in a supine position at the ambient temperature for 6 h after or without ligation of the large vessels around the heart. For the groups with ligated vessels, the mean ratios of the drug concentrations in both left and right cardiac blood samples 6 to 0 h postmortem were about 1, whereas in those without ligated vessels, these ratios were about 2 and 1, respectively. The order of the methamphetamine and amitriptyline concentrations in blood and tissue samples were roughly: lungs > myocardium and pulmonary venous blood > cardiac blood, inferior vena caval blood and liver. Our results demonstrate that when bodies are in a supine position, (1) basic drugs in the lungs diffuse rapidly postmortem into the left cardiac chambers via the pulmonary venous blood rather than simply diffusing across concentration gradients, and (2) basic drugs in the myocardium contribute little to the increases in their concentrations in cardiac blood during the early postmortem period.

Adult↗

PubMed2001

Critical analysis of cerebrovascular autoregulation during repeated head-up tilt.

BACKGROUND AND PURPOSE: Cerebrovascular autoregulation has been described with a phase lead of cerebral blood flow preceding changes in cerebral perfusion pressure (CPP), but there has been less focus on the effect of CPP on cerebral vascular resistance. We investigated these relations during spontaneous fluctuations (control) and repeated head-up tilt. METHODS: Eight healthy adults were studied in supine rest and repeated tilt with 10-second supine, 10 seconds at 45 degrees head-up tilt for a total of 12 cycles. Cerebral blood flow was estimated from mean flow velocity (MFV) by transcranial Doppler ultrasound, CPP was estimated from corrected finger pressure (CPP(F)), and cerebrovascular resistance index (CVRi) was calculated in the supine position from CPP(F)/MFV. Gain and phase relations were assessed by cross-spectral analysis. RESULTS: In the supine position, MFV preceded CPP(F), but changes in CVRi followed CPP(F). Gain and phase relations for CPP(F) as input and MFV as output were similar in supine and repeated tilt experiments. Thus, changes in cerebrovascular resistance must have had a similar pattern in the supine and tilt experiments. CONCLUSIONS: Cerebrovascular autoregulation is achieved by changes in resistance in response to modulations in perfusion pressure whether spontaneous or induced by repeated tilt. The phase lead of MFV before CPP(F) is a mathematical and physiological consequence of the relation the input variable (CPP(F)) and the manipulated variable (cerebrovascular resistance) that should not be taken as an indication of independent control of cerebral blood flow.

Adult↗

PubMed2006

Posture-induced changes in intracranial pressure: a comparative study in patients with and without a cerebrospinal fluid block at the craniovertebral junction.

OBJECTIVE: The aim of this study was to determine posture-induced changes in intracranial pressure (ICP) when patients with hydrocephalus or idiopathic intracranial hypertension remained supine for 1 hour and then sat up and remained sitting for 3 hours. METHODS: Continuous ICP was monitored using a fiberoptic extradural sensor in: 1) 259 patients with hydrocephalus or idiopathic intracranial hypertension with free cerebrospinal fluid (CSF) flow through the craniovertebral junction and Sylvian aqueduct, 2) 20 patients with hydrocephalus secondary to aqueductal stenosis with free CSF flow through the craniovertebral junction, and 3) 97 patients with hydrocephalus associated with Chiari malformation. The maximum ICP difference (DeltaICP) was calculated as the difference between mean ICP in the supine position and minimum ICP value after changing body position. The mean ICP difference (DeltaICPmean) was calculated as the difference between the mean ICP in the supine position and the mean ICP while the patient was in a sitting position. RESULTS: In the complete sample, the median of DeltaICP was 13 mm Hg (interquartile range 10-17). The median of DeltaICPmean was 8 mm Hg (interquartile range 5-11). Both DeltaICP and DeltaICPmean were significantly greater in patients without obstruction in the craniospinal junction than in those with Chiari malformation (P = 0.005 and P = 0.014, respectively). No differences were found in DeltaICP or DeltaICPmean between patients with Sylvian aqueduct stenosis and those without (P = 0.777 and P = 0.346, respectively). CONCLUSION: ICP reduction after a change in body position is significantly greater in patients with free CSF flow through the craniospinal junction than in those with Chiari malformation, indicating the difficulty or impossibility of CSF displacement into the spinal canal in the latter.

Adult↗

PubMed2003

Effects of sleep position, sleep state and age on heart rate responses following provoked arousal in term infants.

Previous studies have suggested that autonomic dysfunction may be involved in Sudden Infant Death Syndrome (SIDS). The major risk factors for SIDS are the prone sleeping position and maternal smoking. Our aim was to examine the effects of sleeping position and maternal smoking on the postnatal maturation of autonomic function by examining heart rate responses following arousal in healthy term infants. Twenty-four infants (11 born to mothers who smoked during pregnancy and 13 to mother who did not smoke) were studied using daytime polysomnography and multiple measurements of arousal threshold (cm H(2)O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep (AS) and quiet sleep (QS). We demonstrated no difference between smoking and non-smoking groups of infants in any of our measurements, and thus combined data from the groups. Baseline (BHR) was elevated in the prone compared to the supine position in quiet sleep (QS) at 2-3 weeks (p<0.001) and 5-6 months (p<0.001), and in active sleep (AS) at 2-3 and 5-6 months (p<0.05). BHR was significantly elevated in AS compared to QS in the supine position at all ages (p<0.01) and in the prone position at 2-3 (p<0.001) and 5-6 months (p<0.05). Increases in heart rate (deltaHR%) following arousal were significantly greater in the supine compared to the prone position in QS at 2-3 weeks (p<0.05) and in AS at both 2-3 (p<0.01) and 5-6 months (p<0.05). DeltaHR% was significantly greater in AS compared to QS in both supine (p<0.05) and prone (p<0.001) positions at 2-3 weeks and in the supine position at 2-3 months (p<0.001). We conclude that sleep state, sleep position and postnatal age affect the cardiac responses following arousal from sleep in healthy term infants. Impairment of heart rate control in the prone position may be important in understanding the increased risk for SIDS in this position.

Adolescent↗

PubMed1990

[Influences of changing vertical dimension, occlusal contacts of bite plane and body position on masticatory muscle activities].

The Bite plane therapy has been accepted to be useful for treatment of the patients with the stomatognathic dysfunction. The purpose of this study is to make clear the influences of changing the vertical dimension and occlusal contacts of the bite plane on masticatory muscle activities in order to improve the bite plane therapy. The full arch bite plane with an interincisal distance of 5 mm was fabricated for each one of 30 subjects without stomatognathic dysfunction. The EMG activities were recorded from the anterior part of the temporal muscles, the masseter muscles and the anterior belly of the digastric muscles bilaterally while the subject exerted tapping and maximal voluntary clenching in a postural position. Four kinds of experiments were performed as follows. In Exp. 1, integrated EMG activities of each muscle were compared with and without the bite plane. In Exp. 2, the influences of changing the vertical dimension of the bite plane (2.5 mm, 5 mm and 7.5 mm) were tested in 17 subjects. In Exp. 3, the influences of changing the location of occlusal contacts of the bite plane were studied in 12 subjects. In Exp. 4, the influence of changing the body positions on EMG activities and mandibular positions was compared in 30 subjects between the sitting and supine positions. Furthermore, the influence of the same factor was compared with and without the bite plane which was adjusted in each position. The results were summarized as follows: 1. Wearing the bite plane mainly reduced activities of the temporal muscles. 2. The bite plane with an interincisal distance of 5 mm was most effective in reducing activities of the temporal muscles. 3. Wearing the bite plane with anterior occlusal contacts reduced activities of the elevator muscles significantly. 4. Significant differences in activities of the temporal and digastric muscles were recognized between the two body positions when the bite plane was not applied. However, no significant difference was recognized when the bite plane was inserted. Furthermore, those differences were correlated with the difference in the antero-posterior mandibular displacement between the two body positions while the subject tapped the teeth. These results suggest the possibility to control masticatory muscle activities by applying the bite plane with the proper vertical dimension and occlusal contacts. In addition, it is necessary to take a suitable body position for the patient who has a difference in the mandibular displacement between the sitting and supine positions when applying the bite plane.

Dental Occlusion↗

PubMed1999

Methodological parameters influence the detection of right-to-left shunts by contrast transcranial Doppler ultrasonography.

BACKGROUND AND PURPOSE: Contrast transcranial Doppler ultrasonography is a new method to detect intracardiac right-to-left shunts, such as the patent foramen ovale. However, the methodology of the procedure varies considerably among investigators. This study was undertaken to assess the influence of methodological parameters on the results of the contrast transcranial Doppler examination in the detection of right-to-left shunts. METHODS: A total of 72 patients (mean age, 58.2+/-14.7 years) had a contrast transcranial Doppler ultrasonography examination. To study the influence of methodological factors, patients with evidence of a right-to-left shunt underwent repeated examinations with modified procedures. Parameters under investigation were the timing of the Valsalva maneuver, the dose of the contrast medium, and the patient's posture during the examination. RESULTS: The median contrast signal count was 58.5 and 48.0 (P<0.001) and the median latency of the first intracranially detected contrast signal was 12.5 and 8.5 seconds (P=0.05) when the Valsalva maneuver was performed 5 and 0 seconds after the start of the injection, respectively. Reducing the contrast medium dose from 10 to 5, 2.5, and 1.2 mL resulted in a decline of the median signal count from 54.5 to 28.5, 20.5, and 12.0 (P<0.01), respectively, while the latency of the first contrast signal increased from 13.3 to 14.0, 14.6, and 15.0 seconds (P<0.05). The sitting position also produced a lower signal count than the supine position (P<0.02). CONCLUSIONS: This study demonstrates that several essential methodological parameters influence the results of the contrast transcranial Doppler ultrasonography examination. Therefore, it is necessary to standardize the procedure to permit comparable quantitative assessments of the shunt volume. The findings of the present study suggest that 10 mL of contrast medium be injected with the patient in the supine position and that the Valsalva maneuver be performed 5 seconds after the start of the injection.

Adult↗

PubMed2000

The three-dimensional vestibulo-ocular reflex during prolonged microgravity.

Single-case, longitudinal studies of the three-dimensional vestibulo-ocular response (VOR) were conducted with two spaceflight subjects over a 180-day mission. For reference, a control study was performed in the laboratory with 13 healthy volunteers. Horizontal, vertical and torsional VOR was measured during active yaw, pitch and roll oscillations of the head, performed during visual fixation of real and imaginary targets. The control group was tested in the head-upright position, and in the gravity-neutral, onside and supine positions. Binocular eye movements were recorded throughout using videooculography, yielding eye position in Fick co-ordinates. Eye velocity was calculated using quaternion algebra. Head angular velocities were measured by a head-mounted rate sensor. Eye/head velocity gain and phase were evaluated for the horizontal, vertical and torsional VOR. The inclination of Listing's plane was also calculated for each test session. Control group gain for horizontal and vertical VOR was distributed closely around unity during real-target fixation, and reduced by 30-50% during imaginary-target trials. Phase was near zero throughout. During head pitch in the onside position, vertical VOR gain did not change significantly. Analysis of up/down asymmetry indicated that vertical VOR gain for downward head movement was significantly higher than for upward head movement. Average torsional VOR gain with real-target fixation was significantly higher than with imaginary-target fixation. No difference in phase was found. In contrast to vertical VOR gain, torsional VOR gain was significantly lower in the gravity-neutral supine position. Spaceflight subjects showed no notable modification of horizontal or vertical VOR gain or phase during real-target fixation over the course of the mission. However, the up/down asymmetry of vertical VOR gain was inverted in microgravity. Torsional VOR gain was clearly reduced in microgravity, with some recovery in the later phase. After landing, there was a dip in gain during the first 24 h, with subsequent recovery to near baseline over the 13-day period tested. Listing's plane appeared to remain stable throughout the mission. The findings reflect various functions of the otolith responses. The reduced torsional VOR gain in microgravity is attributed to the absence of the gravity-dependent, dynamic stimulation to the otoliths (primarily utricles). On the other hand, the reversal of vertical VOR up/down gain asymmetry in microgravity is attributed to the off-loading of the constant 1-g bias (primarily to the saccules) on Earth. The observed increase in torsional VOR gain from the 1st to the 6th month in microgravity demonstrates the existence of longer-term adaptive processes than have previously been considered. Likely factors are the adaptive reweighting of neck-proprioceptive afferents and/or enhancement of efference copy.

Eye Movements↗

PubMed1999

Body position, membrane diffusing capacity and pulmonary capillary blood volume in chronic bronchitis and pulmonary emphysema.

BACKGROUND: The effect of body position on diffusing capacity and its components, membrane diffusing capacity (Dm) and pulmonary capillary blood volume (Vc), in patients with chronic obstructive pulmonary disease (COPD) has remained elusive. This study was designed to evaluate the effect of body position on diffusing capacity for carbon monoxide (DLco), Dm and Vc in male patients with chronic bronchitis and pulmonary emphysema. METHODS: Pulmonary function tests including spirometry and lung volume were assessed in the erect position, and DLco, Dm and Vc were measured in the erect and supine positions in a random order in 17 men with chronic bronchitis and 19 men with pulmonary emphysema. RESULTS: Spirometry results and lung volumes were comparable between both groups of patients; however, significantly lower values of DLco and Kco (DLco corrected by alveolar volume, VA) were observed in the emphysema than in the bronchitis group. In the bronchitis group, Kco and Vc were significantly higher in the supine than in the erect position, but Dm was significantly lower in the supine position. Alternation of body position did not significantly affect DLco and its components in the emphysema group. DLco, Kco and Vc in both the erect and supine positions were significantly higher in the bronchitis than in the emphysema group. Vc-SE (SE, the data in the supine minus those in the erect position) was also significantly higher in the bronchitis group. In the bronchitis group, DLco-SE was significantly correlated with Dm-SE and Vc-SE. However, Kco-SE was highly correlated with Dm-SE. In the emphysema group, DLco-SE and Kco-SE were highly correlated with Vc-SE only. CONCLUSIONS: An increase in Vc in the supine position may account for the postural effect on Kco in bronchitis patients. In patients with pulmonary emphysema, decreased DLco and an absence of postural effect on DLco and its components may be due to a widespread abnormality of the pulmonary capillary bed. These findings may be of value in elucidating the difference in mechanisms of impaired gas exchange between patients with chronic bronchitis and pulmonary emphysema.

Aged↗

PubMed1985

Respiratory drive in nonsmokers and smokers assessed by passive tilt and mouth occlusion pressure. Response to rebreathing carbon dioxide.

The purpose of the present investigation was to assess respiratory center function in smokers using (1) measurement of mouth occlusion pressure during carbon dioxide rebreathing and (2) noninvasive measurement of breathing pattern during passive upright tilt. The breathing patterns of 20 normal nonsmokers and 20 smokers without major obstruction of the airways were monitored noninvasively with respiratory inductive plethysmography for 15 minutes in the supine position and then after 90 degrees head-up passive tilt to the standing position. In nonsmokers, significant increases from supine to standing positions included the following: (1) minute ventilation from 6.22 +/- 1.47 to 7.32 +/- 1.16 L/min (p less than 0.05); (2) tidal volume from 368 +/- 93 to 462 +/- 108 ml (p less than 0.01); and (3) mean inspiratory flow from 263 +/- 61 to 320 +/- 43 ml/sec (p less than 0.01). Responses of smokers to tilt were variable; 14 showed changes similar to nonsmokers, but six showed no increase of ventilation and respiratory drive upon tilting. The latter also showed blunted response to rebreathing carbon dioxide in the supine position as estimated by plotting mouth occlusion pressures against end-tidal carbon dioxide tension. These data suggest that disturbances of respiratory center control are common in smokers without major obstruction of the airways.

Adult↗

PubMed2004

[The influence of the supine and prone positions in the esophageal pH monitoring in very low birth weight infants].

BACKGROUND: Scarce information is available on the effects of body's positioning in the number and the duration of gastroesophageal reflux episodes in very low birth weight infants. AIM: To evaluate the influence of prone compared to supine positions on the frequency and duration of acid gastroesophageal reflux episodes in very low birth weight infants and study the role of body position in the occurrence of exams with reflux index > or = 5% and > or = 10%. METHODS: Sixty one prolonged esophageal pH monitoring exams were retrospectively analyzed. The difference between the prone and supine position exam duration was not longer than 3 hours. The reflux index was evaluated for the total period of the exam (reflux index total) and for each period in the two positions. The total number of reflux episodes, the number of reflux episodes > 5 minutes and the longest reflux episode were evaluated for each period in the two positions. These parameters were compared in accordance with body positioning, for each one of the three reflux index total categories: reflux index total < 5%, > or = 5% and > or = 10%. The frequencies of exams with reflux index total > or = 5% and reflux index total > or = 10% were compared for both positions. RESULTS: The number of hours in prone (11.2 +/- 1.0) and in supine (11.2 +/- 1.1) position were not different. All the prone positions monitoring parameters were significantly lower than the supine ones, in the three reflux index total categories. In the supine position, 32.7% (20/61) and 27.8% (17/61) of the exams, which were normal in prone, became abnormal, taking into account reflux index > or = 5% and > or = 10%, respectively, obtained for each position. CONCLUSIONS: In prone position, there is a significant decrease in number and duration of acid reflux episodes in very low birth weight infants. Supine position promotes a significant increase in the number of esophageal pH monitoring exams with reflux index > or = 5% and > or = 10%, making easier the diagnose of the gastroesophageal reflux disease.

Esophagus↗

PubMed2002

Influence of head position on thermal stress in newborns: simulation using a thermal mannequin.

The influence of head position on thermal stress was assessed by using a heavily clothed thermal mannequin in three different body positions [supine, face straight up (FSU); supine, face to the side (FTS); prone, FTS] and with or without the head covered by a bonnet. The mannequin was exposed to air temperatures of 29, 32, 34, and 36 degrees C. When the head is uncovered, body or head position has no impact on heat loss. When the head is covered, dry heat loss from the mannequin as a whole (and that from the head in particular) is lower (-0.35 to -0.40 W) in the FTS position than in the FSU position as a result of decreased heat loss from the surface area of the face in contact with the mattress. In the FTS position and with the head covered, there was no difference in heat loss between the prone and supine positions. The results suggest that in heavily clothed newborns whose head is covered by a bonnet, thermal stress depends on the head position.

Clothing↗

PubMed1998

Effects of posture on blood flow diversion by hypoxic pulmonary vasoconstriction in dogs.

We used differential excretion of sulphur hexafluoride from the left and right lung to measure blood flow diversion by hypoxic pulmonary vasoconstriction (HPV) in the prone and supine positions in dogs (n = 9). Gas exchange was assessed using the multiple inert gas elimination technique. Blood flow diversion from the hypoxic (3% oxygen) left lung was mean 70.7 (SD 11.2)% in the supine compared with 57.0 (12.1)% in the prone position (P < 0.02). The supine position was associated with increased perfusion to low VA/Q regions (P < 0.05). The increased flow diversion with hypoxia in the supine position was associated with more ventilation to high VA/Q regions (P < 0.05). We conclude that flow diversion by hypoxic pulmonary vasoconstriction is greater in the supine position. This effect could contribute to the variable response in gas exchange with positioning in patients with ARDS.

Animals↗