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PubMedDate not supplied

Comparison of magnetometer and inductance plethysmography derived Konno-Mead diagrams during CO2 rebreathing.

Magnetometers measure changes in antero-posterior diameters of the rib cage and abdomen while respiratory inductance plethysmography (RIP) measures changes in chest wall cross-sectional area. We compared Konno-Mead diagrams derived from isovolume calibrated magnetometers and RIP in the DC-mode during room air and CO2 rebreathing in the sitting and supine positions. Chest wall configurations obtained during quiet tidal breathing were similar in both sitting and supine positions. During CO2 stimulated breathing, however, derived chest wall configurations were at times dissimilar. The RIP per cent rib cage contribution to tidal volume was greater than that of magnetometers during room air and CO2 rebreathing in both sitting and supine positions. Changes in end expiratory levels measured by magnetometers and RIP during CO2 rebreathing are in general proportionate to each other; however, the magnetometers usually depicted quantitatively greater decreases in abdominal end expiratory levels during rebreathing. We conclude that the qualitative and quantitative assessment of chest wall configurations and volume displacement vary depending on the method used. RIP by including lateral wall motion may more accurately reflect compartmental displacements, while magnetometers by solely measuring antero-posterior diameter may better reflect changes in abdominal volume and thus diaphragm configuration.

Adult↗

PubMed1995

Restraint-induced stress in pregnant mice--degree of immobilization affects maternal indices of stress and developmental outcome in offspring.

Maternal stress on gestational day 8 (GD8) in the CD-1 mouse can induce a syndrome of fetal anomalies, including encephalocele, supernumerary ribs, fused ribs and vertebral anomalies. Two forms of restraint were compared for their ability to induce these defects. The two types of restraint differed in the degree of mobility afforded the dam during confinement, either total restraint in a supine position or a less confining restraint in which restrained dams could move from a supine to a non-supine position, but could not turn from front to back. Dams were exposed to either form of restraint for 12 h on GD8 and their near-term fetuses examined for external and skeletal abnormalities. As both types of restraint precluded normal eating and drinking, an additional control group deprived of food/water was included for evaluation. Cohorts of dams were restrained for 3, 6 or 12 h on GD8 and end points commonly used to gauge the degree of stress evaluated. These included serum corticosterone level and the weight of body, spleen and thymus. Stress-induced analgesia, as measured by the tail-flick procedure, was monitored in these same dams as an additional non-invasive measure of stress. Both types of restraint induced greater and longer-lasting weight loss than food/water deprivation. Both also produced more fetal anomalies than observed in the offspring of caged controls or food/water deprived dams. Both forms of restraint equally elevated serum corticosterone levels above the increase exhibited by the food/water deprived dams. The most pronounced difference between the two types of restraint concerned the degree of analgesia. The type limiting mobility the most, caused much greater analgesia after 6 and 12 h of restraint although the dams subjected to the other form of restraint were significantly more analgesic than the food/water deprived dams by 12 h. Dams restrained in the supine position exhibited slightly greater weight loss, more analgesia and produced significantly more offspring with anomalies.

Analysis of Variance↗

PubMedDate not supplied

The effect of posture on the induction of epidural anesthesia for peripheral vascular surgery.

BACKGROUND AND OBJECTIVES: A study was done to determine whether a difference existed in the quality and time to maximum anesthesia between the induction of lumbar epidural anesthesia in the sitting and supine position in patients undergoing infrainguinal arterial reconstruction. METHODS: An epidural catheter was inserted at L3-L4 in 40 patients who were randomly assigned to two groups. In group 1, with the patient sitting, 3 mL lidocaine 1.5% with 5 micrograms/mL epinephrine was given as a test dose, followed 3 minutes later by 12 mL bupivacaine 0.75% injected over 2 minutes through the catheter. After remaining in the sitting position for 5 minutes, the patient was placed supine and the quality of anesthesia assessed at 3-minute intervals for 30 minutes. Anesthesia was assessed by loss of sensation to pinprick and the Bromage scale for loss of motor function. In group 2, after placement of the catheter, the patient was immediately placed supine, the same doses of local anesthesia were given at the same time intervals as in group 1, and the onset of anesthesia was similarly assessed. In addition to a comparison between groups in the quality and time to maximum anesthesia, a correlation was sought between these variables and the age, weight, height, and body surface area (BSA) of the patients in each group. RESULTS: The demographically similar groups showed no difference in maximum cephalad spread of anesthesia (median, interquartile range; group 1: T4, T2.5-T6; group 2: T4, T2.5-T7), motor block (group 1: 3, 2-4; group 2: 4, 4-6), or time to maximum motor block (mean +/- SD; group 1, 17.4 +/- 8.7 minutes; group 2, 17.9 +/- 6.8 minutes). The time to maximum cephalad spread of anesthesia was shorter in group 1 (13.8 +/- 6.9 minutes; group 2, 18.6 +/- 6.6 minutes; P = .03). Neither the age nor weight of the patients in either group had any influence on the quality and time to maximum anesthesia. There was, however, a significant correlation between the height (r = 0.48, P = .0303) and BSA (r = 0.48, P = .0318) of the patients in group 1 and the time to maximum cephalad spread of anesthesia. CONCLUSIONS: When lumbar epidural anesthesia was induced in the sitting rather than supine position, the time to maximum cephalad spread was shorter and correlated directly with the height and BSA of the patient. The position of the patient during induction had no effect on the final level of cephalad spread and degree of motor block.

Age Factors↗

PubMed2005

Cyclotorsional eye movements during a simulated PRK procedure.

PURPOSE: Eye alignment is a serious concern when performing corneal surface ablation. Although several excimer lasers monitor horizontal and vertical movements, little is known about the potential impact of cyclotorsional movements. Dynamic cyclotorsions have been measured on 10 emmetropic subjects during a simulated PRK treatment. METHODS: Cyclotorsional eye movements were measured using a 3D videoculographic system (SMI) in 10 emmetropic subjects in upright and supine position. The subjects were wearing an eyelid speculum and were asked to fixate on a 1 degrees red spot. The fixation target was either in focus or optically degraded by electronic filters. Data were collected at the University Eye Clinic, Torino, Italy, and the different setting measurements were compared using Student's t-test for paired data. RESULTS: Cyclotorsions were significantly higher when subjects were fixating an optically degraded stimulus (upright: P=0.04; supine: P=0.0002). The cyclotorsional movements ranged from -13 to 17 degrees. A significant difference in eye orientation was present when changing from the upright to the supine position (P=0.03). Even when correcting for this positional error, significantly higher cyclotorsional movements were detected in the supine position (in focus: P=0.0043; optically degraded: P=0.0008). The torsional range was from -14.85 to 14.55 degrees. CONCLUSIONS: The high range of cyclotorsional eye movements during a simulated PRK procedure suggests that 3D tracking could improve surface ablation results when treating high astigmatism or when wavefront guided.

Adult↗

PubMed1999

Newborns spontaneous arm movements are influenced by the environment.

The spontaneous arm movements of 28 healthy full-term newborn infants were observed for 1 min in four different environmental conditions: each infant was placed in a vertical position in a bathtub filled with water with the water level up to her or his neck in a vertical position in water with the water level up to her or his waist in a supine position out of the water in a vertical position out of the water. It was hypothesised that these different environmental constraints would influence the infants spontaneous activity. From video recordings spontaneous arm movements were categorised according to the classifications of Hannan (Hannan TE. Young infant's hand and finger expressions: An analysis of category reliability. In: Field T, Fogel A, editors. Emotion and Early Interaction. New Jersey: Elbaum 1982;253-265). The statistical analyses showed, firstly, that the frequency of occurrence of various arm movements is greater out of the water than in the water. Secondly, for those out of the water the frequency of occurrence of various arm movements is greater in the vertical position in comparison to the supine position. Thirdly, the infants showed more active arm movements (more upward movements) in the vertical position out of the water in comparison to the two water and supine conditions. These findings lead to the conclusion that different environmental constraints influenced the spontaneous arm movements.

Arm↗

PubMed2002

Observations on intraoperative somatosensory evoked potential (SEP) monitoring in the semi-sitting position.

BACKGROUND: Former case reports suggest that monitoring of median nerve somatosensory evoked potentials (M-SEP) is unreliable in patients operated in the semi-sitting position due to the occurrence of evoked potential changes unrelated to neurological damage. This study was designed to analyze these changes in greater detail and confirm that these changes are not caused by neurological damage. METHODS: M-SEP monitoring findings of 50 patients with surgery in the semi-sitting position were analyzed and compared with a group of 50 patients who underwent surgery in the supine position. M-SEP amplitudes and latencies at distinct steps of the monitoring procedure were used for further analysis. In 10 of the 50 semi-sitting patients, M-SEP were recorded additionally after surgery with the anesthetized patient in the supine position. RESULTS: Significant M-SEP changes occurred in the semi-sitting patients only. An amplitude loss of greater than 50% on at least one side was observed in 24 patients. The magnitude and the time course of the amplitude loss was considerably variable. A complete loss of the evoked potential was not observed in any case. In all 10 patients, M-SEP recovered completely when recorded in the supine position. CONCLUSIONS: In about half of the patients with M-SEP monitoring in the semi-sitting position, a significant amplitude loss occurs which is unrelated to neurological damage and presumably caused by subdural gas collections. There is no characteristic pattern of M-SEP changes which enables a differentiation of these 'artificial' alterations from true events. The only appropriate criterion to indicate an impending neurological damage in these patients seems to be a complete loss of the M-SEP potential.

Adolescent↗

PubMed2003

Contributions of upper airway mechanics and control mechanisms to severity of obstructive apnea.

The contributions of pharyngeal mechanical abnormalities, flow demand, and compensatory effectiveness to obstructive sleep apnea severity were determined in 82 patients. Flow demand was estimated from mean inspiratory flow on continuous positive airway pressure. Mechanical load on upper airway muscles was estimated from minimal effective continuous positive airway pressure, flow demand, and minimum flow observed during brief pressure dial downs. Compensatory effectiveness was estimated by relating polysomnographic severity and mechanical load. Mechanical load was more severe in men, in supine position, and in older and heavier patients. Higher flow demand contributed significantly to mechanical load in men and in those who are obese. At the same mechanical load, severity was independent of age, sex, or body mass index but was greater in the supine position and in REM sleep. Mechanical load accounted for only 34% of variability in severity. Eighty-two percent of patients experienced periods of stable breathing despite mechanical loads that would produce continuous cycling without compensation. I conclude that most patients can adequately compensate for the abnormal mechanics, at least part of the time. Higher flow demand contributes to severity in men and in obesity. Severity is largely due to factors other than mechanical load. Compensatory effectiveness is impaired in the supine position and in REM sleep, but not by age, sex, or body mass index.

Adult↗

PubMed2002

Effect of body position on arterial oxygen tension in the elderly.

BACKGROUND: It is well known that body position can have an effect on gas exchange though the magnitude of this effect has not been studied thoroughly in the elderly. OBJECTIVES: This study analyzes the effect body position change has on arterial oxygen tension (PaO(2)) and arterial carbon dioxide tension (PaCO(2)) in healthy elderly. METHODS: We tested 46 "lung-healthy" elderly, including 30 women and 16 men, 67-88 years of age. Blood was drawn from the radial artery first in the sitting position and subsequently in the supine position. Spirometry was performed. RESULTS: Mean (SD) sitting PaO(2) was 10.53 kPa (1.22), whereas mean supine PaO(2) was 9.85 kPa (1.33). The difference between sitting and supine PaO(2) was 0.68 kPa (0.86) and was statistically significant. Sitting PaCO(2) was 5.06 kPa (0.47) and supine PaCO(2) was 5.05 kPa (0.54). The difference between sitting and supine PaO(2) correlated positively with FEV(1)/FVC %, negatively with the corresponding difference between sitting and supine PaCO(2), and negatively with BMI. CONCLUSIONS: We conclude that the significant difference in PaO(2) in sitting and supine positions clearly shows that the position needs to be considered both when attempting to establish reference values and when evaluating gas exchange in elderly persons. The positional changes in oxygenation are related to the corresponding change in PaCO(2), and to FEV(1)/FVC % and BMI.

Aged↗

PubMed2006

Effect of supine knee position on obstructive sleep apnea.

We previously reported a case of a middle-aged man whose obstructive sleep apnea (OSA) was virtually eliminated when he slept in the supine "knees up" position. In this study, we attempt to replicate this phenomenon in a group of volunteers with previously diagnosed OSA. Results indicated no significant improvement in OSA when sleeping supine knees up. Examination of distribution of within subjects' change [calculated as Respiratory Disturbance Index (RDI) in the "knees down" position vs RDI in the knees up position] indicated a trend for improvement in the latter (p=0.12, two-tailed probability). These results suggest that knee position is unlikely to be a robust intervention for OSA though they allow for the possibility that some patients may have a moderation of their condition by such a manipulation.

Female↗

PubMed1981

[Plasma catecholamines, metabolic substrates, aerobic and anaerobic capacity during exercise in supine and sitting position (author's transl)].

The influence of a graduated bicycle ergometric test in supine and sitting position on the work capacity, the plasma catecholamines, the carbohydrate (glucose and lactate) and lipid metabolism (free fatty acids and glycerol) and the heart rate and oxygen intake was examined in six healthy subjects. The work capacity is approx. 30% higher in sitting position. In supine position, adrenaline and nor-adrenaline are lower at rest, at all submaximum levels and during maximum ergometric exercise. Glucose, free fatty acids and glycerol show no differences dependent on the body position at the same submaximum levels, only the lactate level is approx. 30% higher (200 Watt) in supine position. During maximum graduated exercise in sitting position the glucose level is 10% higher than in supine position, the free fatty acids show no difference; the lactate level is approx. 37% higher, the glycerol level approx. 40% than in supine position. The heart rate and the oxygen intake don't show any position dependent differences at rest and at the same submaximum levels. During maximum ergometric exercise they are 15% (heart rate) and about 30% (oxygen intake) higher than in supine position, corresponding to a higher exercise level.

Adult↗

PubMed2003

Infant position in neonates receiving mechanical ventilation.

BACKGROUND: Several body positions other than standard supine position have been used in patients undergoing intensive care for reducing the incidence of pressure ulcers of the skin, contractures or ankylosis and for improving the patient's well being. In patients from different age groups undergoing mechanical ventilation (MV), it has been observed that particular positions such as prone position may improve some respiratory parameters. Benefits from these positions have not been clearly defined in Neonatology, a field where it is common that patients require mechanical ventilation sometimes during extended time periods. OBJECTIVES: To assess the effects on both short and long-term outcomes of different positioning of newborn infants receiving MV. SEARCH STRATEGY: Databases searched (up to January 2002) were the Oxford Database of Perinatal Trials, CINAHL, MEDLINE, EMBASE and Cochrane Controlled Trials Register (The Cochrane Library, Issue 1, 2002). Hand searches of proceedings of the Society for Pediatric Research from 1990 to January 2002 were used to identify unpublished studies. SELECTION CRITERIA: Randomised or quasi randomised clinical trials comparing different positions in newborns receiving mechanical ventilation. DATA COLLECTION AND ANALYSIS: Three independent and unblinded reviewers assessed the trials for inclusion in the review and extracted the data. Data were double-checked and entered into the Review Manager software. MAIN RESULTS: Ten trials involving 164 infants were included in this review. Several positions were compared: prone vs. supine, prone vs. lateral right, lateral right vs. supine, lateral left vs. supine, lateral right vs. lateral left and good lung dependent vs. good lung uppermost. Apart from one of the two studies that compared lateral right vs. lateral left positions, all the included studies had a crossover design. Comparing prone vs. supine position, an increase in arterial P02 in the prone position of between 2.75 and 9.72 mm Hg (95%CI) was observed (one trial). When % hemoglobin oxygen saturation was measured with pulse oximetry, improvement in the prone position was from 1.17 to 4.36% (typical effect based on four trials). It was not possible to establish whether this effect remained once the intervention was stopped. Negative effects from the interventions were not described, although this issue was not studied enough. Effects of position on other outcomes were not statistically significant; however, these cannot be excluded considering the small numbers that were studied. REVIEWER'S CONCLUSIONS: The prone position was found to slightly improve the oxygenation in neonates undergoing mechanical ventilation. However, we found no evidence concerning whether particular body positions during mechanical ventilation of the neonate are effective in producing sustained and clinically relevant improvements.

Humans↗

PubMed2002

Symptom predictability of reflux-induced respiratory disease.

Gastroesophageal reflux disease (GERD) often is associated with pulmonary problems such as asthma as well as recurrent and nocturnal cough. Dual-probe 24-hr pH monitoring may assist in establishing a correlation between these symptoms and GERD-related symptoms. To determine if any specific symptom was predictive of aspiration, this study was undertaken. Ambulatory dual-probe esophageal pH monitoring was performed on 133 patients who had upper airway and additional symptoms for GERD. All patients had esophageal manometric studies of the lower esophageal sphincter (LES), the upper esophageal sphincter (UES), and the esophageal body before dual-probe pH monitoring was performed. Using two assembled glass probes, the distal and the proximal sensors were placed 5 cm above the proximal border of the LES and 1 cm below the lower border of the UES, respectively. Patients were classified into three groups: proximal and distal probe positive (group I), proximal probe negative and distal probe positive (group II) and proximal and distal probe negative (Group III) Upper airway and additional symptoms plus manometry results of the LES, body and UES study were compared between groups. In addition, positive distal probe patients (groups I and II) were compared for distal fraction of time at pH < 4 and number of reflux episodes at each probe position. A positive distal probe result was defined as an abnormal DeMeester score (> 14.8). A proximal probe test result was considered positive if percent time pH < 4.0 was > 1.1 for total, 1.7 for upright, and 0.6 for supine positions. The ages of the subjects ranged from 18 to 83 years (mean age: 50.5 +/- 1.5 years). Groups I, II, and III included 16 patients, 38 patients, and 79 patients, respectively. Group I had a significantly higher incidence of nocturnal cough than the other two groups. (P < 0.05). The manometric data revealed between groups that LES pressure (LESP) for groups I and II was significantly lower than LESP for group III (P = 0.003). Cricoid pressure, pharyngeal pressure, length, and relaxation of UES were not different between groups. Fraction of reflux time for group I was significantly higher than for group II in the supine position and at mealtime (P < 0.05). The number of reflux episodes for group I was significantly higher at meal time (P < 0.01). In conclusion, nocturnal cough is strongly predictive of proximal esophageal reflux. Proximal reflux episodes are significantly more frequent in the supine position and correlate well with the high predictive value of nocturnal cough.

Adolescent↗

PubMed2001

Lung mechanics in individuals with spinal cord injury: effects of injury level and posture.

Individuals with spinal cord injury (SCI) exhibit reduced lung volumes and flow rates as a result of respiratory muscle weakness. These features have not, however, been investigated in relation to the combined effects of injury level and posture. Changes in forced vital capacity (FVC), forced expiratory volume in 1 s (FEV(1)), FEV(1)/FVC, forced expiratory flow at 50% vital capacity (FEF(50)), inspiratory capacity (IC), and expiratory reserve volume (ERV) were assessed by injury level in the seated and supine positions in 74 individuals with SCI. The main findings were 1) FVC, FEV(1), and IC increased with descending SCI level down to T(10), below which they tended to level off; 2) supine values of FVC and FEV(1) tended to be larger in the supine compared with the seated posture down to injury level T(1), caudad to which they were less than when seated; 3) IC increased proportionately more down to injury level L(1), below which it declined slightly and plateaued; 4) ERV was measurable even at high cervical injuries, was generally smaller in the supine position, reached peak values in both positions at T(10) injury level, and then rapidly declined at lower levels; 5) when subjects were separated according to current, former, and never smokers, only formerly smoking paraplegic individuals demonstrated spirometric values significantly less than paraplegic individuals who never smoked. Changes in spirometric measurements in SCI are dependent on injury level and posture. These findings support the concept that the increase in vital capacity in supine position is related to the effect of gravity on abdominal contents and increase in IC.

Adult↗

PubMed2006

Hemodynamic, autonomic and neurohormonal behaviour of familial amyloidotic polyneuropathy and neurally mediated syncope patients during supine and orthostatic stress.

Orthostatic intolerance (OI) syndromes are frequent and share symptoms like dizziness and orthostatic syncope. Their pathophysiology however seems to be different. The aim of our work was to evaluate autonomic and hemodynamic behaviour in patients with familial amyloidotic polyneuropathy and neurally mediated syncope in supine position and after acute orthostatic passive stress. We studied 12 patients with autonomic failure (group A), 12 patients with neurally mediated syncope (group B) and 16 aged matched normal controls (group C), in supine position and during the first 10 min of head-up tilt test (HUTT). Beat-by-beat blood pressure and heart rate were continuously monitored and digitised at 500 Hz. The baroreceptor alfa-index gain (vagal reflex-BRG), high frequency of RR variability (HFRR, vagal tonus) and low frequency of systolic arterial pressure variability (LFSAP, sympathetic tone) were calculated. Catecholamines, plasma brain (BNP) and atrial natriuretic (ANP) peptides were also measured. Hemodynamic data were derived and calculated by the non-invasive modelflow method. During supine position, cardiac output (CO) and stroke volume (SV) were similar in all groups. Mean arterial pressure (MAP) and BNP were higher in group A. Noradrenaline (NOR), BRG, HFRR and LFSAP were extremely low in this group. BRG and adrenaline (ADR) were higher in group B than in controls. Within the first 10 min of HUTT, there was a huge drop of CO, SV and MAP in group A, maintenance of very low levels of neurohormones and lack of autonomic function. HR, LFSAP and ADR had a higher rise at HUTT in group B compared with controls (p<0.01) but a significant decrease of BRG was noted (p<0.05). ANP or BNP did not change with tilt in any group. Different orthostatic intolerance syndromes may show important hormonal, autonomic and hemodynamic differences during supine rest and enhanced after passive orthostatism.

Adult↗

PubMed2007

Hypotension induced by lateral decubitus or supine spinal anaesthesia in elderly with low ejection fraction undergone hip surgery.

OBJECTIVE: The aim of the study was to assess the effect of low ejection fraction (EF) on hypotension during lateral or supine position of spinal anaesthesia in patients older than 75 years old. METHODS: We analyzed 41 patients who had undergone hip surgery between August 2000 and October 2001 in the Aydin SSK State Hospital retrospectively. Patients older than 75 years of age and an EF less than 50% were selected and spinal anaesthesia was performed with hyperbaric bupivacaine 0.5%, lateral decubitus or supine position. The patients were divided into two groups: Group I (unilateral group, n = 23) and Group II (supine group, n = 18). History of hypertension, diabetes mellitus, and ASA status, preoperative value of EF and cardiac index, and intraoperative hypotension, bradycardia, ephedrine use, and maximal sensorial block levels were recorded. RESULTS: The age range of patients was between 75 and 103. The maximal sensorial block level was evaluated due to lower or higher than thoracic sixth segment for each patient in intraoperative period. The sensorial block level higher than thoracic sixth segment were determined 2 patient in Group I and 14 patients in Group II (p = 0.001). Hypotension was observed in five patients in Group I and 10 patients in Group II (p = 0.015). In Group I, the number of ephedrine used patient was lower than Group II (p = 0.015). CONCLUSIONS: Elderly patients with low EF were more likely to predispose to higher sensorial block level and hypotension was more common during spinal anaesthesia with supine position compared to lateral decubitus position.

Aged↗

PubMed1992

Randomized, double-blind, placebo-controlled crossover trial of pirenzepine in patients with gastroesophageal reflux.

A muscarinic receptor subtype 1 (M1) antagonist, pirenzepine, recently has been shown to be relatively free of the usual anticholinergic side effects on esophageal smooth muscle and thus has been implicated for the treatment of gastroesophageal reflux disease (GERD). However, the effect of pirenzepine on GERD remains to be defined. Thirteen patients who demonstrated GERD in a baseline 24-hr ambulatory intraesophageal pH monitoring study were randomized in a double-blind crossover fashion to receive pirenzepine and placebo. An ambulatory 24-hr intraesophageal pH monitor was used to assess reduction in reflux (esophageal pH less than 4.0) with respect to position (upright vs supine), to total number of reflux episodes, and to episodes greater than 5 min. A significant effect for pirenzepine was seen for episodes greater than 5 min (t = 2.61, P = 0.023) and a trend towards significance was seen for total (upright and supine positions combined) percent time of reflux (t = 2.13, P = 0.055). Although not statistically significant, pirenzepine consistently showed greater reduction in all parameters of reflux tested. A greater reduction in percent time of reflux in supine vs upright positions (pirenzepine: 58.9% vs 21.4%; placebo: 43.6% vs 7.3%) may be clinically important in prevention of esophageal injury due to reflux in the recumbent position. Pirenzepine may provide a unique alternative for some GERD patients who may be refractory to other therapies of GERD.

Adult↗

PubMed1998

Recurrent supine syncope: an unusual manifestation of the neurally mediated faint.

INTRODUCTION: Syncope occasionally may occur in the supine patient due to severe brady- or tachyarrhythmia. However, recurrent syncope upon assumption of the supine position as a result of a neurally mediated reflex mechanism has not been reported previously. METHODS AND RESULTS: Two young patients, both of whom had significant systemic illnesses, experienced recurrent episodes of presyncope and/or syncope shortly after assuming the supine position. During ambulatory ECG monitoring, symptoms were provoked only by lying down and were associated with transient bradycardia. Head-up tilt table testing was undertaken as part of the syncope evaluation and was nondiagnostic in both cases. However, both patients exhibited a transient cardioinhibitory response with reproduction of typical symptoms upon return of the table to the supine position ("reverse tilt"). During follow-up (8 and 14 months), both patients improved with pharmacologic treatment (disopyramide in one case and midodrine in the other). CONCLUSION: Presyncope or syncope upon lying down can be an unusual manifestation of the neurally mediated faint.

Adult↗

PubMed1984

Platelet number and platelet volume in healthy young men during exercise and changes in posture.

In ten healthy young men, alterations in platelet number (B-Thro) and mean platelet volume (MPV) during 15 min of moderate exercise on a bicycle ergometer and 30 min of rest in supine position were determined. During exercise B-Thro increased 10.9% and MPV increased 1.5%. During rest in supine position B-Thro decreased 8.7% whereas MPV was unchanged. From concomitant alterations in leucocyte number, erythrocyte number and concentration of albumin it is concluded that part of the alterations in B-Thro is caused by transfer of water between the vascular system and the interstitial compartment and part is the result of a release of platelets from reservoirs during exercise and a sequestration of platelets in reservoirs during rest in supine position. The alteration in MPV during exercise is explained by a larger average volume of platelets being released from reservoirs when compared with the average volume of platelets already circulating.

Adult↗