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References for Best Sleep Positions

These are references for the web page "Best Sleeping Positions".


Am Rev Respir Dis. 1991 Sep;144(3 Pt 1):499-503.
Influence of posture and sustained loss of lung volume on pulmonary function in awake asthmatic subjects.
Ballard RD, Pak J, White DP.
Departments of Medicine, Denver Veterans Administration Medical Center, CO 80220.
Nocturnal worsening occurs commonly in the asthmatic patient population and contributes substantially to the morbidity and even mortality of asthma. However, no physiologic process has yet been identified as the major contributor to this pattern. Sleep is typically associated with both the supine posture and substantial decrements in lung volume, and both have been proposed to have a role in the pattern of nocturnal worsening. To assess the effects of posture and sleep-associated reductions in functional residual capacity on pulmonary function, eight asthmatic patients were first monitored overnight in a horizontal volume-displacement body plethysmograph to determine mean FRC during sleep for each subject. We then compared, during wakefulness, the effects on FEV1 and methacholine responsiveness from chest wall and abdomen strapping (to maintain FRC at mean sleep levels) for 6 h in the supine and upright postures. FEV1 was significantly decreased after strapping in the supine posture (2.54 +/- 0.36 versus 3.38 +/- 0.29 L on control day, p = 0.0001) but was not affected by strapping in the upright posture (3.07 +/- 0.30 versus 3.34 +/- 0.31 L on control day, not significant, NS). Bronchial responsiveness to methacholine was not altered after strapping in either posture. These observations suggest that the supine posture, in conjunction with the reduction in lung volume associated with sleep, may contribute to the nocturnal worsening of asthma.

Asthma and allergies in wheezing children

Pediatrics. 2004 May;113(5):1216-22.
The bedding environment, sleep position, and frequent wheeze in childhood.
Ponsonby AL, Dwyer T, Trevillian L, Kemp A, Cochrane J, Couper D, Carmichael A.
National Centre for Epidemiology and Population Health, Australian National University, Canberra ACT, Australia.
OBJECTIVE: Synthetic quilt use has been associated with increased childhood wheeze in previous studies. Our aim was to examine whether the adverse effect of synthetic quilt use on frequent wheeze differed by usual sleep position.
DESIGN, SETTING, AND PARTICIPANTS: A population-based cross-sectional study of 6378 (92% of those eligible) 7-year-olds in Tasmania, Australia, was conducted in 1995. Exercise-challenge lung function was obtained on a subset of 414 children from randomly selected schools. EXPOSURE
MEASURES: Child bedding including pillow and overbedding composition and usual sleep position by parental questionnaire.
OUTCOME MEASURES: Frequent wheeze (>12 wheeze episodes over the past year), using the International Study of Asthma and Allergies in Childhood parental questionnaire, and baseline and postexercise forced expiratory volume in 1 second lung-function measures.
RESULTS: Frequent wheeze (n = 117) was positively associated with synthetic quilts, synthetic pillows, electric blankets, and sleeping in a bottom bunk bed but did not vary by sleep position. In a nested case-control analysis, the association between synthetic quilt use and frequent wheeze differed by sleep position. Among children who slept supine, synthetic (versus feather) quilt use was associated with frequent wheeze (adjusted odds ratio: 2.37 [1.08, 5.23]). However, among nonsupine sleepers, overlying synthetic quilt use was not associated with frequent wheeze (adjusted odds ratio: 1.06 [0.60, 1.88]). This difference in quilt effect by sleep position was highly significant. Similarly, synthetic quilt use was associated with lower postexercise forced expiratory volume in 1 second measures among supine but not nonsupine sleeping children.
CONCLUSION: An increasing focus on the bedding environment immediately adjacent to the nose and mouth is required for respiratory disorders provoked by bedding, such as child asthma characterized by frequent wheeze.

Asthma (nocturnal)

Curr Opin Pulm Med. 1996 Jan;2(1):48-59.
Nocturnal asthma: physiologic determinants and current therapeutic approaches.
D'Alonzo GE, Ciccolella DE.
Temple University Health Sciences Center, Philadelphia, PA 19140, USA.
Asthma has a tendency to destabilize at night in patients that are diurnaly active and try to sleep at night. As asthma worsens, the expression of this disease seems to increase at night. Additionally, nocturnal asthmatics have increased airway hyperresponsiveness and likely more active inflammation at night as compared with the daytime. Although the cause of nocturnal asthma cannot be completely explained, there do appear to be a variety of internal body circadian rhythms that play a role in this disease. Also, noncircadian rhythmic influences such as sleep, supine posture, snoring, and gastroesophageal reflux cannot be dismissed. Directing therapy, perhaps in unique ways, may be essential for the control of nocturnal asthma. Patients on inhaled corticosteroid therapy or nonsteroidal anti-inflammatory agents often persist in asthmatic disease expression at night. Long-acting bronchodilator therapy, either by inhalation or with sustained-release tablets, is often added to inhaled anti-inflammatory therapy for more complete 24-hour disease control. Using existing therapies but employing chronotherapeutic strategies is likely to improve the overall asthma management. By focusing on nocturnal asthma, we may be able to improve our understanding of this disease and more effectively control it over each 24-hour period.

Back pain in pregnancy

Am J Reprod Immunol. 1992 Oct-Dec;28(3-4):251-3.
Nocturnal low back pain in pregnancy: polysomnographic correlates.
Fast A, Hertz G.
Department of Physical Medicine and Rehabilitation, St. Vincent's Hospital and Medical Center, New York, NY 10011.
Thirteen women in late stages of pregnancy underwent a polysomnographic study. Eight women (61%) complained of mild nocturnal back pain or back discomfort. Five women (39%) did not complain of nocturnal back pain. The two groups did not differ in total bed time, total sleep time, sleep latency, and wake after sleep onset (WASO). A significant decrease in rapid eye movement (REM) sleep and an increase in stage 2 were observed in the pain group. The same group had a statistically significant decrease in the basal O2 saturation level. The pain group also spent a longer time sleeping in the supine position. We hypothesize that a prolonged stay in the supine position leads to obstruction of the vena cava. In the presence of inadequate collateral circulation, increased pressure and venostasis in combination with a decrease in basal oxygen saturation may lead to hypoxemia, compromise the metabolic supply of the neural structures, and result in pain. It appears, therefore, that the vascular system plays an important role in the pathogenesis of pain. The role played by the disturbed sleep architecture in the production of pain remains to be established. It is possible that the changes observed in sleep architecture result from pain rather than contribute to pain production.

Bruxism and swallowing

Sleep. 2003 Jun 15;26(4):461-5.
Association between sleep bruxism, swallowing-related laryngeal movement, and sleep positions.
Miyawaki S, Lavigne GJ, Pierre M, Guitard F, Montplaisir JY, Kato T.
STUDY OBJECTIVE: To describe the relationships of sleep bruxism to swallowing and sleep positions.
DESIGN: Controlled descriptive study.
SETTING: Polysomnography and audio-video recordings were done in a hospital sleep laboratory.
PARTICIPANTS: Nine patients with sleep bruxism and 7 normal subjects were matched for age and sex. Interventions: n/a.
MEASUREMENTS AND RESULTS: During sleep, patients with sleep bruxism showed a higher frequency of rhythmic masticatory muscle activity episodes (6.8 +/- 1.0 [SEM]/h) than did normals (0.5 +/- 0.1/h, p < 0.01). Swallowing-related laryngeal movements occurred more frequently in sleep of patients with sleep bruxism (6.8 +/- 0.8/h) than in normals (3.7 +/- 0.3/h, p < 0.01). In both groups, during sleep, close to 60% of rhythmic masticatory muscle activity episodes were associated with swallowing. In sleep bruxism patients, 68% of swallowing events occurred during rhythmic masticatory muscle activity episodes, while only 10% of swallowing events were associated with rhythmic masticatory muscle activity in normal subjects. Sleep bruxism patients and normals spent 95.5% and 87.3% of sleeping time in the supine and lateral decubitus positions, respectively. In both groups, up to 96% of rhythmic masticatory muscle activity and swallowing were observed in the supine and lateral decubitus position. In sleep bruxism patients, although sleeping time did not differ between the 2 sleeping body positions, 74% of rhythmic masticatory muscle activity and swallowing events were scored in the supine position compared to 23% in the lateral decubitus position.
CONCLUSIONS: During sleep, rhythmic masticatory muscle activity is often associated with swallowing. In sleep bruxism patients, most of these oromotor events are observed in the supine position. The physiologic link between rhythmic masticatory muscle activity and swallowing and the clinical relevance of sleep position in sleep bruxism management need to be investigated.

Bruxism, clenching episodes and gastroesophageal reflux

Am J Orthod Dentofacial Orthop. 2004 Nov;126(5):615-9.
Relationships among nocturnal jaw muscle activities, decreased esophageal pH, and sleep positions.
Miyawaki S, Tanimoto Y, Araki Y, Katayama A, Imai M, Takano-Yamamoto T.
Department of Orthodontics and Dentofacial Orthopedics, Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan.
The purpose of this study was to examine the relationships among nocturnal jaw muscle activities, decreased esophageal pH, and sleep positions. Twelve adult volunteers, including 4 bruxism patients, participated in this study. Portable pH monitoring, electromyography of the temporal muscle, and audio-video recordings were conducted during the night in the subjects' homes. Rhythmic masticatory muscle activity (RMMA) episodes were observed most frequently, with single short-burst episodes the second most frequent. The frequencies of RMMA, single short-burst, and clenching episodes were significantly higher during decreased esophageal pH episodes than those during other times. Both the electromyography and the decreased esophageal pH episodes were most frequently observed in the supine position. These results suggest that most jaw muscle activities, ie, RMMA, single short-burst, and clenching episodes, occur in relation to gastroesophageal reflux mainly in the supine position.

Chronic respiratory insufficiency patients

Intensive Care Med. 2009 Feb;35(2):306-13. Epub 2008 Sep 16.
Sleep and non-invasive ventilation in patients with chronic respiratory insufficiency.
Ambrogio C, Lowman X, Kuo M, Malo J, Prasad AR, Parthasarathy S.
University of Torino, Turin, Italy.
OBJECTIVE: Noninvasive ventilation with pressure support (NIV-PS) therapy can augment ventilation; however, such therapy is fixed and may not adapt to varied patient needs. We tested the hypothesis that in patients with chronic respiratory insufficiency, a newer mode of ventilation [averaged volume assured pressure support (AVAPS)] and lateral decubitus position were associated with better sleep efficiency than NIV-PS and supine position. Our secondary aim was to assess the effect of mode of ventilation, body position, and sleep-wakefulness state on minute ventilation (V(E)) in the same patients.
DESIGN: Single-blind, randomized, cross-over, prospective study.
SETTING: Academic institution.
PATIENTS AND PARTICIPANTS: Twenty-eight patients.
MEASUREMENTS AND RESULTS: Three sleep studies were performed in each patient; prescription validation night, AVAPS or NIV-PS, and crossover to alternate mode. Sleep was not different between AVAPS and NIV-PS. Supine body position was associated with worse sleep efficiency than lateral decubitus position (77.9 +/- 22.9 and 85.2 +/- 10.5%; P = 0.04). V(E) was lower during stage 2 NREM and REM sleep than during wakefulness (P < 0.0001); was lower during NIV-PS than AVAPS (P = 0.029); tended to be lower with greater body mass index (P = 0.07), but was not influenced by body position.
CONCLUSIONS: In patients with chronic respiratory insufficiency, supine position was associated with worse sleep efficiency than the lateral decubitus position. AVAPS was comparable to NIV-PS therapy with regard to sleep, but statistically greater V(E) during AVAPS than NIV-PS of unclear significance was observed. V(E) was determined by sleep-wakefulness state, body mass index, and mode of therapy.

Cough (nocturnal) and coughing attacks

Chest. 1995 Aug;108(2):581-5.
Intractable cough associated with the supine body position. Effective therapy with nasal CPAP.
Bonnet R, Jurres R, Downey R, Hein H, Magnussen H.
Loma Linda University, Division of Pulmonary and Critical Care Medicine, CA 92354, USA.
We describe five patients with severe nocturnal cough and daytime somnolence in whom the coughing attacks are triggered by assuming the supine body position. Quantity and quality of the nocturnal cough were evaluated in the sleep laboratory with and without nasal continuous positive airway pressure (N-CPAP). Air flow characteristics were assessed using flow volume and airway resistance loops. Airway anatomy was evaluated bronchoscopically. In all five patients, the cough had a barking quality. Flow-volume loops showed an expiratory collapse phenomenon in two of the patients. Endoscopically, all five patients had signs of airway collapse. All patients had difficulty falling asleep because of coughing and were awakened by it frequently. Sleep times ranged from 2.5 to 4.5 h per night. With N-CPAP pressures ranging from 5 to 13 cm H2O, all five patients had clinically significant improvement in their symptoms. Their sleep times increased to a range of 5 to 7.5 h per night and the daytime somnolence markedly improved or resolved. All five patients requested a N-CPAP unit for home use. We conclude that a cough that is predominantly associated with or exacerbated by the supine body position may be treated effectively with N-CPAP.

GERD (gastroesophageal reflux disease)

Am J Gastroenterol. 1999 Aug;94(8):2069-73.
Influence of spontaneous sleep positions on nighttime recumbent reflux in patients with gastroesophageal reflux disease.
Khoury RM, Camacho-Lobato L, Katz PO, Mohiuddin MA, Castell DO.
Department of Medicine, Graduate Hospital, Philadelphia, Pennsylvania 19146, USA.
OBJECTIVE: Body position has been shown to influence postprandial and fasting gastroesophageal reflux (GER) in patients and normal volunteers when they are assigned to lie in a prescribed position. No published studies have evaluated the effect of spontaneous sleeping positions on recumbent reflux in patients with GER.
METHODS: Ten patients, three female and seven male (mean age 47.6 yr, range 30-67 yr) with abnormal recumbent esophageal pH <4 on 24-h pH-metry participated. A standardized high fat dinner (6 PM) and a bedtime snack (10 PM) were administered to all patients. GER during spontaneous sleep positions was assessed with a single channel pH probe placed 5 cm above the lower esophageal sphincter (LES) and with a position sensor taped to the sternum. Data were recorded with a portable digital data logger (Microdigitrapper-S, Synectics Medical) and analyzed for recumbent percent time pH <4 and esophageal acid clearance time in each of four sleeping positions. Time elapsed between change in sleeping position and GER episodes was also calculated.
RESULTS: Right lateral decubitus was associated with greater percent time pH <4 (p < 0.003) and longer esophageal acid clearance (p < 0.05) compared to the left, supine, and prone. GER episodes were more frequent in the supine position (p < 0.04) and occurred within 1 min after change in sleeping position 28% of the time.
CONCLUSIONS: The left lateral decubitus position is preferred in patients with nocturnal GER. Measures to aid patients in sleeping in this position should be developed.

Zhonghua Wai Ke Za Zhi. 1999 Feb;37(2):71-3, 3.
[Can esophagogastric anastomosis prevent gastroesophageal reflux]
[Article in Chinese]
Wang Q, Liu J, Zhao X, Lei J, Cong Q, Li W, Li B, Wang F, Cao F, Zhang X, Zhang H, Zhang H.
Depatment of Thoracic Surgery, Fourth Hospital of Hebei Medical University, Shijiazhuang 050011.
OBJECTIVE: To investigate the possible anti-reflux function of esophagogastric anastomosis in the patients after receiving resection of cardiac cancer.
METHODS: One hundred and ninety-two patients were studied by video-assisted gastroscopy, manometry, 24-h pH esophageal monitoring, radioscintigraphy and scanning electron microscopy.
RESULTS: Abnormalities were found in 90.2% of patients through endoscopy. Resting pressure in esophageal body was higher than that in normal controls, and in the stomach, lower. Twenty-four hour pH monitoring demonstrated that gastroesophageal reflux (GER) did not occur when the patients slept in semi-reclining position, and occurred in all patients when slept in supine position. Scintigraphic study showed that 2/3 of the patients had reflux, occurrence of which was not affected by the length of postoperative period. Scanning electron microscopic examination showed that degeneration, exfoliation of esophageal mucosal epithelial cell, and derangement of micro-fold and inflammatory oedema of cytomembrane may be directly caused by reflux.
CONCLUSIONS: GER exists in the majority of the patients after esophagogastrectomy and esophagogastrostomy for cardiac cancer. The occurrence of GER is not affected by the length of postoperative period. Some detecting methods fail to show the existence of GER, and 24-h pH monitoring is the most reliable method for detecting GER. Sleep in semireclining position is an effective method of preventing GER in postoperative patients.

Geriatric inpatients

Age Ageing. 2008 Sep;37(5):526-9. Epub 2008 May 16.
Severe nocturnal hypoxaemia in geriatric inpatients.
Hjalmarsen A, Hykkerud DL.
Department of Medicine, Pulmonary Division, University Hospital of North Norway, N 9038 Tromso, Norway.
BACKGROUND: Oxygen levels are decreased in older people especially in the supine position, and during sleep. Geriatric inpatients often suffer from stroke and heart disease. Respiratory control may be substantially affected.
OBJECTIVE: the aim of this study was to examine oxygen levels during night in inpatients on geriatric medical wards to find out if they needed nocturnal oxygen therapy.
DESIGN: prospective observational study. Setting/Participants: we consecutively examined 133 patients with SpO(2) >or=92% in sitting position by an overnight -8-h pulse oximetry. Patients with severe obesity, dementia or pulmonary disease were excluded. The test was performed at least 4 days after the event in stroke cases. Outcome Variables: ninety two patients, m/f 43/49, with mean age 78.3 +/- 6.9 SD completed the test. Sixty six patients suffered from stroke; 34 left-sided and 19 right-sided stroke. Nine patients suffered from a heart disease only, and 17 patients suffered from other diseases.
RESULTS: according to the guidelines for long-term oxygen therapy recommendations for nocturnal oxygen therapy, we found that 26% of the patients fulfilled the criteria of SpO(2) <or=90% for >or=30% of the time. There was a significant positive correlation between age and the amount of time with SpO(2) between 80 and 84% (0.215, P < 0.05). Diagnosis or severeness of disease did not significantly affect nocturnal SpO(2) %. The 1-year survival rate was 75% in group I (hypoxaemic) versus 84% in group II (normoxaemic) (NS).
CONCLUSION: nearly 30% of the inpatients in geriatric medical wards suffered from severe oxygen-requiring nocturnal hypoxaemia irrespective of diagnosis.

Heart failure patients with central sleep apnea/Cheyne-Stokes (irregular) respiration

Sleep Med. 2010 Feb;11(2):143-8. Epub 2010 Jan 21.
Impact of sleeping position on central sleep apnea/Cheyne-Stokes respiration in patients with heart failure.
Joho S, Oda Y, Hirai T, Inoue H.
Second Department of Internal Medicine, Toyama University Hospital, Toyama, Japan.
BACKGROUND: The present study determines the influence of sleeping position on central sleep apnea (CSA) in patients with heart failure (HF).
METHODS: The apnea/hypopnea index (AHI) during different body positions while asleep was examined by cardiorespiratory polygraphy in 71 patients with HF (ejection fraction <45%).
RESULTS: Twenty-five of the patients having predominantly CSA (central apnea index 10/h) with a lower obstructive apnea index (<5/h) were assigned to groups with positional (lateral to supine ratio of AHI <50%, n=12) or non-positional (ratio > or = 50%, n=13) CSA. In the non-positional group the BNP level was higher, the ejection fraction was lower and the trans-tricuspid pressure gradient was higher than in the positional group. Multiple regression analysis revealed more advanced age (p=0.006), log(10)BNP (p=0.017) and lung-to-finger circulation time (p=0.020) as independent factors of the degree of positional CSA. Intensive treatment for HF changed CSA from non-positional to positional in all eight patients tested. Single night of positional therapy reduced CSA (p<0.05) and BNP level (p=0.07) in seven positional patients.
CONCLUSION: As cardiac dysfunction progresses, severity of CSA also increases and positional CSA becomes position-independent. Positional therapy could decrease CSA, thereby having a valuable effect on HF.

Sleep.2006 Aug 1;29(8):1045-51.
Lateral sleeping position reduces severity of central sleep apnea / Cheyne-Stokes respiration.
Szollosi I, Roebuck T, Thompson B, Naughton MT.
Department of Allergy Immunology and Respiratory Medicine, Alfred Hospital, Melbourne, Australia.
INTRODUCTION: The influence of sleeping position on obstructive sleep apnea severity is well established. However, in central sleep apnea with Cheyne Stokes respiration (CSA-CSR) in which respiratory-control instability plays a major pathophysiologic role, the effect of position is less clear.
STUDY OBJECTIVES: To examine the influence of position on CSA-CSR severity as well as central and mixed apnea frequency.
METHODS: Polysomnograms with digitized video surveillance of 20 consecutive patients with heart failure and CSA-CSR were analyzed for total apnea-hypopnea index, mean event duration, and mean oxygen desaturation according to sleep stage and position. Position effects on mixed and central apnea index, mean apnea duration, and mean desaturation were also examined in non-rapid eye movement sleep.
RESULTS: Data are presented as mean +/- SEM unless otherwise indicated. Group age was 59.9 +/- 2.3 years, and total apnea-hypopnea index was 26.4 +/- 3.0 events per hour. Compared with supine position, lateral position reduced the apnea-hypopnea index in all sleep stages (Stage 1, 54.7 +/- 4.2 events per hour vs 27.2 +/- 4.1 events per hour [p < .001]; Stage 2, 43.3 +/- 6.1 events per hour vs 14.4 +/- 3.6 events per hour [p < .001]; slow-wave sleep, 15.9 +/- 6.4 events per hour vs 5.4 +/- 2.9 events per hour [p < .01]; rapid eye movement sleep, 38.0 +/- 7.3 events per hour vs 11.0 +/- 3.0 events per hour [p < .001]). Lateral position attenuated apnea and hypopnea associated desaturation (supine 4.7% +/- 0.3%, lateral 3.0% +/- 0.4%; p < .001) with no difference in event duration (supine 25.7 +/- 2.8 seconds, lateral 26.9 +/- 3.4 seconds; p = .921). Mixed apneas were longer than central (29.1 +/- 2.1 seconds and 19.3 +/- 1.1 seconds; p < .001) and produced greater desaturation (6.1% +/- 0.5% and 4.5% +/- 0.5%, p = .003). Lateral position decreased desaturation independent of apnea type (supine 5.4% +/- 0.5%, lateral 3.9% < or = 0.4%; p = .003).
CONCLUSIONS: Lateral position attenuates severity of CSA-CSR. This effect is independent of postural effects on the upper airway and is likely to be due to changes in pulmonary oxygen stores. Further studies are required to investigate mechanisms involved.

Irregular or periodic breathing

J Appl Physiol. 1993 May;74(5):2198-204.
Pattern of breathing and upper airway mechanics during wakefulness and sleep in healthy elderly humans.
Hudgel DW, Devadatta P, Hamilton H.
Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109.
Elderly subjects are known to be prone to periodic breathing in sleep. Because periodic breathing may be associated with changes in upper airway caliber, we hypothesized that oscillations in upper airway caliber contribute to the increased prevalence of sleep-related periodic breathing in the elderly. We tested this hypothesis by measuring upper airway resistance, ventilatory variables, and the pattern of variation of these variables in groups of body size-matched young and elderly healthy individuals during wakefulness and stage 2 non-rapid-eye-movement sleep. No major differences existed between the two groups during either wakefulness or sleep in mean upper airway resistance or ventilation values. However, ventilation was more variable during sleep in the elderly; this variability was oscillatory in the majority of elderly subjects at an average rate of 0.04 breaths/cycle or one cycle approximately every 24 s. Oscillations in upper airway resistance during sleep were associated with reciprocal oscillations in tidal volume and/or minute ventilation at the same frequency. Those subjects who had significant oscillations in upper airway resistance had more apneas and hypopneas than those subjects without such oscillations. Oscillations in resistance and ventilation occurred in the supine but not in the lateral body position. We conclude that the wide oscillations in upper airway resistance present during sleep in supine healthy elderly subjects produce a fluctuating mechanical limitation of ventilation, which may contribute to periodic breathing.


Eur J Obstet Gynecol Reprod Biol. 2003 Aug 15;109(2):128-32.
Normal pregnancy and oxygenation during sleep.
Trakada G, Tsapanos V, Spiropoulos K.
Division of Obstretrics and Gynecology, University of Patras Medical School, Patras 26 500, Greece.
Pregnancy is associated with significant alterations in respiratory function. Changes during pregnancy include reduced functional residual capacity (FRC) and residual volume (RV), increased alveolar-arterial difference for oxygen (A-alphaPO2) and in the supine position, reduced cardiac output. In conjunction with sleep-related apneas or hypopneas, these could lead to maternal oxygen desaturation during sleep. Because of the conflicting data from sleep studies in late pregnancy, we performed complete polysomnography on 11 pregnant women at 36 weeks of gestation and again postpartum. We also measured the PaO2, every 2h. The frequency of apneas and hypopneas was significantly lower during pregnancy compared with that on the postpartum control night. PaO2 levels in the supine position, during sleep, were also significantly lower during pregnancy compared to the postpartum period. No correlation was observed between PaO2 levels and apneas or hypopneas or percent of REM sleep.

Sleep apnea

Eur J Orthod. 2004 Jun;26(3):321-6.
Cephalometric comparison of pharyngeal changes in subjects with upper airway resistance syndrome or obstructive sleep apnea in upright and supine positions.
Ingman T, Nieminen T, Hurmerinta K.
Department of Pedodontics and Orthodontics, Institute of Dentistry, Biomedicum Helsinki, University of Helsinki, Finland.
The aim of the present study was to cephalometrically compare pharyngeal changes between upright and supine positions in patients with upper airway resistance syndrome (UARS) or obstructive sleep apnea (OSA). Eighty-two OSA patients, 70 men (mean age 49 +/- 11.8 years) and 12 women (45.9 +/- 8.3 years), underwent cephalometric sleep apnea analysis. One upright and one supine radiograph were taken of each patient (a total of 164 cephalometric radiographs). The results showed no significant changes either in naso- or hypopharyngeal soft tissues between the two positions. In contrast, the shortest distance from the soft palate (ve1-ve2) and the tip of the soft palate (u1-u2) to the posterior oropharyngeal wall was significantly narrower (P < 0.001) in the supine position. Furthermore, in the supine position a slight thickening in the soft palate (sp1-sp2, P < 0.05) was detected with no change in the length of the soft palate (PNS-u1). The form of the tongue changed significantly: it was shorter (Tt-Tgo, P < 0.001; Tt-va, P < 0.001) and thicker (Ts/Tt-Tgo, P < 0.05) in the supine position. The present results suggest that OSA patients are prone to significant narrowing of their oropharyngeal, but not of their naso- or hypopharyngeal, airways in the supine position. Thus, treatment of OSA and UARS patients should mainly be aimed at preventing further oropharyngeal airway narrowing as a result of supine-dependent sleep.

Fortschr Neurol Psychiatr. 2000 Feb;68(2):93-6.
[The relationship between sleep position and therapeutic effect of the Esmarch-Scheine appliance in sleep apnea syndromes]
[Article in German]
Yoshida K.
Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kyoto University, Japan.
Recently an oral appliance is being used increasingly for the treatment of sleep apnea syndrome. But the success rate of oral appliance therapy shows large interindividual difference, and which factors influence its efficiency remain uncertain. To elucidate the influence of the sleep posture on the therapeutic effect of the Esmarch device, 58 patients with sleep apnea syndrome were investigated polysomnographically before and after insertion of the device. The sleep position during each apnea was classified into three types; supine, lateral and prone. The mean apnea index (25.6 +/- 18.7) decreased significantly (p < 0.0001) after insertion of the device (11.5 +/- 12.6). The number of apneas (in the supine and prone) positions was significantly reduced from 18.0 +/- 16.7 and 2.0 +/- 3.6 to 5.0 +/- 11.2, p < 0.001, and 0.3 +/- 0.4, p < 0.005, respectively, but that in the lateral position was slightly increased from 5.6 +/- 9.4 and 6.2 +/- 8.9. The percent of apneas was 70.3% for supine, 21.9% for lateral, and 7.8% for prone before therapy and 43.5%, 53.9% and 2.6%, respectively after therapy. The results indicated that the effectiveness of oral appliance therapy can differ greatly with the sleep posture. The sleep posture recorded polysomnography may be important for choice of oral appliance therapy and its prognosis.

Intern Med. 1995 Dec;34(12):1190-3.
Effect of prone position on apnea severity in obstructive sleep apnea.
Matsuzawa Y, Hayashi S, Yamaguchi S, Yoshikawa S, Okada K, Fujimoto K, Sekiguchi M.
First Department of Internal Medicine, Shinshu University School of Medicine, Matsumoto.
We describe a patient with obstructive sleep apnea (OSA) whose apnea-hypopnea index (AHI) improved remarkably in the prone position accompanied by an improved sleep quality, despite a higher AHI in the supine position and even in the lateral position. Magnetic resonance imaging revealed the most dilated upper airway in the prone position, which suggests the role of anatomical narrowing of the upper airway as an important component in the pathophysiology of positional apnea patients. Further studies are needed to determine the therapeutic efficacy of a prone sleeping position in patients with OSA.

Thorax. 1992 Jul;47(7):524-8.
Effects of posture on flow-volume curves during normocapnia and hypercapnia in patients with obstructive sleep apnea.
Miura C, Hida W, Miki H, Kikuchi Y, Chonan T, Takishima T.
First Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
BACKGROUND: A high ratio of forced expiratory to forced inspiratory maximal flow at 50% of vital capacity (FEF50/FIF50) may identify upper airway dysfunction. Since hypercapnia increases the motor activity of airway dilating muscles its effects on the maximum expiratory and inspiratory flow-volume curves (MEIFV) in patients with obstructive sleep apnea and in normal subjects in different postures was studied.
METHODS: The effects of posture on the maximum expiratory and inspiratory flow-volume curves during the breathing of air and 7% carbon dioxide in 11 patients with obstructive sleep apnea were compared with those in nine normal subjects. Measurements were made in the sitting, supine, and right lateral recumbent positions. Forced expiratory flow at 50% vital capacity (FEF50), forced inspiratory flow at 50% vital capacity (FIF50) and FEF50/FIF50 were determined.
RESULTS: In the normal subjects FEF50, FIF50, and FEF50/FIF50 were not affected by change in posture or by breathing carbon dioxide. In the patients there was a fall in FIF50 and an increase in FEF50/FIF50 when breathing air in the supine position compared with values in the seated and lateral position. While they were breathing carbon dioxide there was a slight increase in FEF50 when patients were seated or in the lateral position compared with values during air breathing. Hypercapnia abolished the effects of posture on FEF50/FIF50. Values for FEF50/FIF50 in the supine position while they were breathing air correlated with the apnoeic index but not with other polysomnographic data.
CONCLUSION: In patients with obstructive sleep apnea the upper airway is prone to collapse during inspiration when the patient is supine, even when awake; this tendency can be reversed by breathing carbon dioxide.

Am J Otolaryngol. 1985 Sep-Oct;6(5):373-7.
Sleeping position and sleep apnea syndrome.
Kavey NB, Blitzer A, Gidro-Frank S, Korstanje K.
Four patients who were evaluated for hypersomnia-sleep apnea syndrome were found in all-night sleep studies to have obstructive or mixed apneas related to their sleeping positions. All four were available for comprehensive follow-up and were subsequently restudied while avoiding the supine position. Supine, prone, and lateral decubitus apnea indices were calculated for each patient for each night. The supine sleeping position was associated with significantly more apneas than the non-supine positions. Keeping these patients off their backs when they slept was effective treatment. Additionally, when results of surgical or pharmacologic treatments of apnea are evaluated, positional apnea indices should be considered.

Sleep paralysis and terrifying hallucinations

J Sleep Res. 2008 Dec;17(4):464-7. Epub 2008 Aug 5.
'The devil lay upon her and held her down'. Hypnagogic hallucinations and sleep paralysis described by the Dutch physician Isbrand van Diemerbroeck (1609-1674) in 1664.
Kompanje EJ.
Department of Intensive Care, Erasmus MC University Medical Center Rotterdam, Rotterdam, The Netherlands.
Hypnagogic and hypnopompic hallucinations are visual, tactile, auditory or other sensory events, usually brief but sometimes prolonged, that occur at the transition from wakefulness to sleep (hypnagogic) or from sleep to wakefulness (hypnopompic). Hypnagogic and hypnopompic hallucinations are often associated with sleep paralysis. Sleep paralysis occurs immediately prior to falling asleep (hypnagogic paralysis) or upon waking (hypnopompic paralysis). In 1664, the Dutch physician Isbrand Van Diemerbroeck (1609-1674) published a collection of case histories. One history with the title 'Of the Night-Mare' describes the nightly experiences of the 50-year-old woman. This case report is subject of this article. The experiences in this case could without doubt be diagnosed as sleep paralysis accompanied by hypnagogic hallucinations. This case from 1664 should be cited as the earliest detailed account of sleep paralysis associated with hypnagogic illusions and as the first observation that sleep paralysis and hypnagogic experiences occur more often in supine position of the body.

J Sleep Res. 2002 Jun;11(2):169-77.
Situational factors affecting sleep paralysis and associated hallucinations: position and timing effects.
Cheyne JA.
Department of Psychology, University of Waterloo, Waterloo, Ontario, Canada.
Sleep paralysis (SP) entails a period of paralysis upon waking or falling asleep and is often accompanied by terrifying hallucinations. Two situational conditions for sleep paralysis, body position (supine, prone, and left or right lateral decubitus) and timing (beginning, middle, or end of sleep), were investigated in two studies involving 6730 subjects, including 4699 SP experients. A greater number of individuals reported SP [with terrifying hallucinations] in the supine position than all other positions combined. The supine position was also 3-4 times more common during SP than when normally falling asleep. The supine position during SP was reported to be more prevalent at the middle and end of sleep than at the beginning suggesting that the SP episodes at the later times might arise from brief microarousals during REM, possibly induced by apnea. Reported frequency of SP was also greater among those consistently reporting episodes at the beginning and middle of sleep than among those reporting episodes when waking up at the end of sleep. The effects of position and timing of SP on the nature of hallucinations that accompany SP were also examined. Modest effects were found for SP timing, but not body position, and the reported intensity of hallucinations and fear during SP. Thus, body position and timing of SP episodes appear to affect both the incidence and, to a lesser extent, the quality of the SP experience.

Snoring, hypopneas and apneas

Am J Respir Crit Care Med. 1994 Jan;149(1):145-8.
Effect of posture on upper airway dimensions in normal human.
Jan MA, Marshall I, Douglas NJ.
Respiratory Medicine Unit, University of Edinburgh, United Kingdom.
Posture has a major effect on breathing during sleep. Snoring, hypopneas, and apneas are all more common lying than sitting and more common supine than in a lateral lying position. Because the effect of the lateral lying position on upper airway caliber has not previously been studied, we examined this in 20 normal awake subjects and also determined the effect of neck position. The acoustic reflection technique was used. Pharyngeal cross-sectional areas (CSA) fell significantly from the sitting to supine position (oropharyngeal junction, from 1.65 +/- [SEM] 0.6 cm to 1.31 +/- 0.07 cm), but there was no difference in CSA between the supine and lateral positions for oropharyngeal junction (1.36 +/- 0.06 cm), mean pharyngeal area, maximal pharyngeal area, or pharyngeal volume. Neck hyper-extension significantly increased pharyngeal CSA (e.g., oropharyngeal junction null position 1.51 +/- 0.08, hyper-extension 1.94 +/- 0.11 cm), but there was no significant effect of neck flexion on airway CSA. These results confirm that in normal awake subjects, pharyngeal areas are smaller lying than sitting but also showed no significant difference between CSA in the supine and lateral lying positions. The study also demonstrates that the upper airway caliber increases with neck extension in conscious adults.

Stroke patients with sleep apnea

Stroke. 2008 Sep;39(9):2511-4. Epub 2008 Jul 10.
High prevalence of supine sleep in ischemic stroke patients.
Brown DL, Lisabeth LD, Zupancic MJ, Concannon M, Martin C, Chervin RD.
Cardiovascular Center - Stroke Program, 1500 E. Medical Center Drive - SPC#5855, Ann Arbor, MI 48109-5855, USA.
BACKGROUND AND PURPOSE: Sleep apnea is very common after stroke and is associated with poor outcome. Supine sleep is known to exacerbate apneas in the general sleep apnea population. We therefore investigated the pattern of sleep positions in the acute stroke period.
METHODS: Inpatients with acute ischemic stroke underwent full polysomnography that included continuous monitoring of sleep positions. Sleep apnea severity was measured using the apnea-hypopnea index (AHI). Stroke severity was measured by the NIH Stroke Scale (NIHSS) at the time of study enrollment by certified study personnel. Percent total sleep time spent in the supine position was calculated and compared by stroke severity based on a median split of NIHSS using a Wilcoxon rank-sum test.
RESULTS: Of the 30 patients, the median age was 67. The median AHI was 23 (IQR: 6, 47). Twenty-two patients (73%) had sleep apnea with an AHI >/=5. The vast majority of sleep time among the stroke cases was spent supine, with a median percent sleep time spent supine of 100 (IQR: 62, 100). The majority (63%) of subjects spent no time asleep in any of the nonsupine positions (prone, left, right). Median percent sleep time supine was 100 (IQR: 100, 100) in those with a higher NIHSS and 63 (IQR: 51, 100) in those with a lower NIHSS (P<0.01).
CONCLUSIONS: Given the high prevalence of supine sleep identified, research into positional therapy for stroke patients with sleep apnea seems warranted.

Stroke (elderly patients)

Age Ageing. 1994 Sep;23(5):405-10.
The effects of pressure and shear on skin microcirculation in elderly stroke patients lying in supine or semi-recumbent positions.
Schubert V, Horaud J.
Department of Geriatric Medicine, Huddinge University Hospital, Sweden.
The effects of external pressure and shear on the skin microcirculation over the sacral area, which is known as a high risk area for pressure sore formation, were studied in 30 elderly patients. The skin blood cell flux (SBF) was measured using the laser Doppler technique, with the patient first at rest in lateral position, then lying for 30 minutes in supine or semi-recumbent 45 degrees position, and finally in lateral position. Elderly high-risk patients (G2), most of them more than two years post-stroke, had a lower body mass index and a reduced sacral skin-fold compared with non-risk patients (G1). The SBF in G2 decreased 28% in supine and 14% in 45 degrees position, whereas the SBF in G1 increased 35% in supine and 13% in 45 degrees position. Spontaneous movements up to seven times per 30 minutes were registered, even during sleep, and were evident by direct observation of the recorded charts as a temporary SBF increase. The risk for skin ischaemic damage over the sacral area of elderly risk patients was evident in both positions, especially with the patients lying in supine position. When increasing the upper body slope in G2 from horizontal to 45 degrees, an inability to recover a satisfactory blood supply after the ischaemic insult was found. Discomfort from compressive and shear forces initiates changes in posture, even in elderly patients prone to tissue breakdown. Occasional relief of pressure was in most patients followed by temporary increase in skin blood flow with concomitant temperature increase. This most probably protected them from developing skin lesions.

Tuberculosis (pulmonary) treated by thoracoplasty

Respiration. 1993;60(6):325-31.
Nocturnal oxygen saturation and sleep quality in long-term survivors of thoracoplasty.
Brander PE, Salmi T, Partinen M, Sovijorvi AR.
Department of Pulmonary Medicine, University of Helsinki, Finland.
The extent and the predictors of nocturnal hypoxemia were studied in 9 men and 11 women treated for pulmonary tuberculosis by thoracoplasty 30-54 years previously. The patients had a scoliotic (Cobb) angle of 4-53 degrees. Median values for pulmonary function were: forced expiratory volume in 1 s 1.2 liters (49% of the predicted value), vital capacity 1.9 liters (54%), total lung capacity 3.6 liters (62%), and supine waking partial pressure for arterial oxygen 9.7 kPa. Four patients were hypercapnic. The patients' mean nocturnal SaO2 ranged from 83 to 94% (median 91.8%), and the SaO2 level below which the patients spent 10% of the total nocturnal recording time ranged from 78 to 92% (median 89.4%). A multiple stepwise linear regression analysis identified supine waking SaO2 as a significant predictor of nocturnal O2 desaturation, accounting for about 80% of the variability in nocturnal SaO2 levels; lung function values and Cobb angle were not significant independent predictors. The sleep quality, assessed by EEG, was good. It is concluded that in thoracoplasty patients with mild hypoxemia during wakefulness, the degree of sleep-related oxygen desaturation was modest and closely related to the waking level of SaO2.

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