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PubMed1979

[Orthopedic methods used in the treatment of scoliosis].

This paper describes the various technics of orthopedic surgery currently used to correct scoliosis and maintain correction. Among corrective methods they illustrate the use of the Cotrel plaster corset (E.D.F.) preceded by passive bipolar traction and autoelongation. Once correction is achieved, it must be maintained to the end skeletal growth; this is done with various types of orthopedic corsets (Lyonnais, La Padula, Milwaukee), which are used according to the patient's age and anatomical type of deformity. The authors discuss in particular the forces that are applied to the occiput and mandible with the Milwaukee corset (Logan, Cochran and Waugh), the values being recorded in diverse situations including the upright stance, ambulation, sitting position, position, supine position, and sleep (Galante, 1970). The authors also made a comparative study of the conventional Milwaukee corset (with broad chin bearing) versus the Milwaukee with hyoid bearing; and finally they illustrate the results obtained by Andriacchi and his associates in selecting the Milwaukee corset for patients with idiopathic scoliosis on the basis of the mathematical model of the rachis.

Casts, Surgical↗

PubMed1989

[Study on the genesis of posturally induced crackles from hemodynamic data--in patients with ischemic heart disease having normal respiratory function].

The presence of fine crackles is suggestive of heart failure in patients without pulmonary disease. We have been interested in the clinical observation that fine crackles are frequently detected when posture was changed from sitting to supine positions or in patients going from sitting position to supine position with passive legs elevation in patients without obvious evidence of heart failure. We named these crackles, "the posturally induced crackles (PIC)". We have already reported that PIC was frequently detected in patients with ischemic heart disease. The present study was performed to estimate the mechanism of the genesis of PIC and to clarify its significance. Seventy-three patients with ischemia heart disease were included in this study. Pulmonary sounds were auscultated in sitting and supine positions and during passive elevation of both legs in a supine position. Patients were divided into 3 groups according to the presence or absence of fine crackles, i.e., those in whom fine crackles were not detected in either position (PIC (-)), those in whom fine crackles were detected in a supine position or during passive elevation of both legs, but not in a sitting position (PIC (+)), and those in whom fine crackles were detected even in a sitting position (Persistent crackles). We measured various hemodynamic parameters (cardiac index, RA pressure, PA pressure and PAW) and parameters of pulmonary circulation (pulmonary blood volume, pulmonary "venous" compliance) in these 3 groups and comparisons were made between them.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Volume↗

PubMed1996

An increase in infant cranial deformity with supine sleeping position.

Abnormalities of the occipital cranial suture in infancy can cause significant posterior cranial asymmetry, malposition of the ears, distortion of the cranial base, deformation of the forehead, and facial asymmetry. Over the past 2 years, we have noted a dramatic increase in the incidence of deformation of the occipital skull in our tertiary referral center. Our patient referral base has not changed appreciably over the past 5 years and patients have been referred from the same primary practitioner base. The timing of this increase correlates closely with the acceptance in our area of recommended changes in sleeping position to supine or side positioning for infants because of the fear of sudden infant death syndrome (SIDS). A total of 51 infants with occipital cranial deformity, with a mean age of 5.5 months at presentation, have been evaluated and treated by a single craniofacial surgeon in the 16-month period from September 1993 to December 1994. Older infants were treated with continuous positioning by the parent keeping the infant off the involved side. Younger infants and those with poor head control were treated with a soft-shell helmet. Mean timing of initial diagnosis and start of treatment was 5.5 months. Mean duration of helmet for positional treatment was 3.8 months. To date, only 3 of 51 patients have required surgical intervention, and other patients demonstrated spontaneous improvement of all measured parameters. Follow up has ranged from 8 to 24 months. We believe that most occipital plagiocephaly deformities are deformations rather than true cranio-synostoses. Despite varying amounts of suture abnormality evidenced on computed tomographic scans, most deformities can be corrected without surgery. In cases where progression of the cranial deformity occurs, despite conservative therapy, surgical intervention should be undertaken at approximately 1 year of age. The almost universal acceptance in the State of North Carolina of positioning neonates on their backs to avoid SIDS, may well increase the incidence of these deformities in the future.

Cranial Sutures↗

PubMedDate not supplied

Comparison of heteronymous monosynaptic Ia facilitation in young and elderly subjects in supine and standing positions.

BACKGROUND: The control of posture and balance is a primary concern among the elderly. Postural instability has been identified as a contributor to the greater incidence of falling among this segment of the population. One important neuromuscular mechanism identified as important in the control of posture and balance is the segmental reflex system. The purpose of this study was to examine the role of presynaptic inhibition in modulating the reflex system in young and elderly subjects. METHODS: To estimate the influence of body position on presynaptic inhibition to the soleus motor pool between young and elderly subjects, 11 young (mean age=23.9 yrs.) and 9 elderly (mean age=72.1 yrs.) subjects were examined in two different body positions: supine and standing. This study utilized the heteronymous facilitation protocol, as described by Hultborn et al. (1987), to estimate presynaptic inhibition of the Ia afferent pathway onto the soleus alpha-motoneuron pool. Maximal soleus H-reflex (H-max) and motor response (M-max) amplitudes were determined prior to testing at each condition, and the H-max/M-max ratio at each body position was determined. To estimate presynaptic inhibition at each body position, subjects received 24 test soleus H-reflex stimuli ( approximately 15% M-max), and 24 soleus H-reflexes conditioned by stimulation of the ipsilateral femoral nerve. RESULTS: Results demonstrated a significant decrease in H-max/M-max ratio from supine (66.1%) to standing (56.8%) for the young subjects, whereas the elderly subjects demonstrated no changes in the H-max/M-max ratio between body positions (39.8% supine; 39.8% standing). The conditioning stimulus produced a significant change in the test reflex for the young subjects during supine testing (51.1% increase) but not standing (3.4% increase). The elderly subjects demonstrated no significant changes in the test reflex produced by the heteronymous conditioning at either condition (17.6% increase supine; 4.9% increase standing). CONCLUSIONS: These results demonstrate differential effects of both H-reflex modulation and heteronymous conditioning for elderly subjects when compared with young adults. These differences may be an adaptive phenomenon of the aging neuromuscular system, exemplified by a decreased ability to modulate the reflex system in the elderly group.

Adult↗

PubMed2004

Short- and long-term reproducibility of autonomic measures in supine and standing positions.

Autonomic nervous tests and heart rate variability (HRV) have been used to assess cardiac autonomic function and to evaluate long-term prognosis. The aim of this study was to evaluate the short- and long-term reproducibility of HRV parameters and autonomic nervous tests according to body position (supine or standing). The study group consisted of 26 healthy subjects. Autonomic nervous tests and HRV were performed twice during the day and the results were averaged. The protocol was then repeated 3 days after each examination and also after 6 and 24 months. Autonomic nervous tests included deep breathing, Valsalva manoeuvre and isometric muscle exercise (handgrip), as well as blood pressure and heart rate in response to standing. ECG recordings were taken for 10 min during spontaneous breathing for HRV analysis. We found that the reproducibility of some parameters of the autonomic nervous test were independent of body position [E/I ratio (heart rate response to deep breathing)], whereas other parameters were dependent on body position (Valsalva manoeuvre and blood pressure response to sustained handgrip). In addition, within-day measurements of those parameters varied from non-reproducible (Valsalva ratio, handgrip and blood pressure response to standing) to moderately reproducible [E/I ratio and 30/15 ratio (heart rate response to standing)]. Among the HRV parameters, we found that total power (TP), low (LF)- and high (HF)-frequency were reproducible not only for measurements made within the same day, but also during short- and long-term observations, and only the LF/HF ratio was dependent on body position. We conclude that only a few autonomic nervous tests are reproducible in the short- and long-term. Because HRV parameters obtained during spontaneous respiration showed high reproducibility for measurements made within the same day as well as in the short- and long-term, they should be used instead of autonomic nervous tests when long-term observations are carried out in a healthy population.

Adult↗

PubMed2003

[Effects of body position changes on frequency domain correlative cardiogram in pilots].

OBJECTIVE: To study the effects of the body position changes on FCG in pilots so as to explore the possibility of using FCG as an indicator of medical monitoring and medical support. METHOD: 65 pilots were examined in 4 different body positions, i.e. supine position, head-down position, standing position and sitting position. Twelve channel routine electrocardiogram was recorded synchronously, and their complaints were also recorded. RESULT: The grade distribution and abnormal cases of the FCG varied with the body positions. The orders of changing magnitude were: the standing position, the head-down position, the sitting position and the supine position. The changes accorded with that of 12 channels routine ECG synchronously recorded and complaints of the subjects. CONCLUSION: The FCG was an objective index representing the cardiac functional status.

Adult↗

PubMed2006

The amplitude of the Achilles tendon reflex in infants is related to body position.

In this study, we investigated whether the Achilles tendon reflex (ATR) in healthy infants is modulated by changes in body position (prone vs. supine). The amplitude of the ATR was compared at postnatal day 1, months 2, 3 and 6, while infants were placed in prone and supine position. The ATR was considered "positive" when at least 1 of 20 tendon taps evoked a visible contraction of the ankle plantar flexor muscles. At 6 months, the amplitude and latency of the ATR were evaluated by electromyographic (EMG) recordings of the (lateral and medial) gastrocnemius muscle, with the infant in prone and supine position. At postnatal day 1, the clinical ATR response was more frequently present in prone than supine position (14/16 or 88% vs. 4/16 or 25%, respectively, p < 0.01). From 2 months onwards, the frequencies of positive ATRs were no longer significantly different between prone (14/14 or 100%) and supine position (10/14 or 67%). However, based on the EMG recordings at 6 months, the ATR amplitude was higher in prone compared to supine position (n=8, median 5.5 mV, range 4.7-6.6 mV; and median 3.8 mV, range 2.3-5.6 mV, p < 0.05). We conclude that the ATR response in healthy infants is more pronounced in prone than in supine position, either when clinically (visually) assessed during routine tendon tapping or when neurophysiologically assessed during surface EMG recording.

Achilles Tendon↗

PubMed2003

Effect of changing patient position from supine to prone on the accuracy of a Brown-Roberts-Wells stereotactic head frame system.

OBJECTIVE: Despite the growing popularity of frameless image-guided surgery systems, stereotactic frame systems are widely accepted by neurosurgeons and are commonly used to perform biopsies, functional procedures, and stereotactic radiosurgery. We investigated the accuracy of the Brown-Roberts-Wells stereotactic frame system when the mechanical load on the frame changes between preoperative imaging and the intervention because of different patient position: supine during imaging, prone during intervention. METHODS: We analyzed computed tomographic images acquired from 14 patients who underwent stereotactic biopsy, deep brain stimulator implantation, or radiosurgery. Two images were acquired for each patient, one with the patient in the supine position and one in the prone position. The prone images were registered to the respective supine images by use of an intensity-based registration algorithm, once using only the frame and once using only the head. The difference between the transformations produced by these two registrations describes the movement of the patient's head with respect to the frame. RESULTS: The maximum frame-based registration error between the supine and prone positions was 2.8 mm; it was more than 2 mm in two patients and more than 1.5 mm in six patients. Anteroposterior translation is the dominant component of the difference transformation for most patients. In general, the magnitude of the movement increased with brain volume, which is an index of head weight. CONCLUSION: To minimize frame-based registration error caused by a change in the mechanical load on the frame, stereotactic procedures should be performed with the patient in the identical position during imaging and intervention.

Brain Diseases↗

PubMed2003

[The study of the relationship between obstructive sleep apnea syndrome and positional nasal resistance].

OBJECTIVE: To study the nasal resistance in different position and its possible relationship to obstructive sleep apnea syndrome (OSAS). METHOD: The positional rhinomanometry and the detection of polysomnography were performed in 14 normal subjects, 20 snoring patients and 40 patients with OSAS. RESULT: The study reveals that: 1. the nasal resistance in seated position and in supine position of the patients with OSAS but without nasal diseases or snoring patients without nasal disease were higher than that of the normal group (P < 0.05). 2. The nasal resistance in seated position and in supine position of the patients with both OSAS and nasal disease were higher than that of the snoring patients with nasal disease (P < 0.05). 3. The nasal resistance in supine position was higher than the nasal resistance in seated position in all the groups (P < 0.05), even in the patients with OSAS (P < 0.01). 4. The AHI, waken intervals, snoring index of the patients both with OSAS and nasal disease were higher than those of the patients only with OSAS. CONCLUSION: Nasal resistance increased in the patients with snoring or OSAS and increased more in the supine position. Nasal resistance may be an important factor in the pathogenesis of OSAS.

Adult↗

PubMed2004

Predictive value of Kushida index and acoustic pharyngometry for the evaluation of upper airway in subjects with or without obstructive sleep apnea.

Acoustic pharyngometry is a relatively new noninvasive method that quantifies geometrically complexed pharyngeal dimensions. Our study aimed to investigate the predictability and usefulness of acoustic pharyngometry in diagnosis of obstructive sleep apnea (OSA), and we developed a prospective clinical trial in 16 subjects without apnea and 54 subjects with apnea. All seventy subjects received polysomnography (PSG) to assess the sleep architecture, including breathing and the degree of apnea hypopnea index. Acoustic pharyngometry was performed in four body positions (sitting, supine, right and left lateral) while awake with tidal breathing in addition to morphometric measurements (Kushida index) of oral cavity. This study shows that the cross-sectional area and volume of the upper airway is smaller in the supine position than any other positions. As well, the oropharyngeal junction area of the supine position is the most predictive parameter to discriminate between subjects with or without OSA. Acoustic pharyngometry can be a clinically useful tool for localizing the narrowed portion of the upper airway and predicting obstructive sleep apnea.

Acoustics↗

PubMed2002

Venous air emboli occur during release of positive end-expiratory pressure and repositioning after sitting position surgery.

UNLABELLED: We studied the effect of positive end-expiratory pressure (PEEP) release and positioning on the occurrence of venous air embolism (VAE). Eighteen consecutive patients (8 women, 10 men; ASA grade I-III) undergoing neurosurgery in the sitting position were studied. After induction of anesthesia ventilation was controlled with a PEEP of 5 cm H(2)O in an oxygen-air gas mixture. A transesophageal echocardiographic (TEE) probe was inserted. Preoperatively, a patent foramen ovale was excluded in all patients. TEE monitoring was performed during surgery, during PEEP release at the end of surgery with the patient still in the sitting position, and during change of the patient position into the supine position. The severity of VAE was differentiated as follows: grade 1 = only microbubbles; grade 2 = microbubbles and decrease of end-tidal carbon dioxide partial pressure (PETCO(2)) by more than 1.5 mm Hg; grade 3 = microbubbles combined with a decrease of PETCO(2) by more than 1.5 mm Hg, and a decrease of mean arterial blood pressure by at least 20 mm Hg. During surgery, VAE with a grade of 1, 2 or 3 occurred in 7, 4, and 2 patients, respectively. After PEEP release, VAE of grades 1, 2, and 3 were observed in 7, 2, and 1 patients, respectively. During repositioning from sitting to supine position, VAE of grades 1, 2, and 3 was observed in 6, 1, and 1 patients, respectively. The patient with VAE grade 3 needed inotropic support until 2 h after surgery to maintain sufficient blood pressure. No patient showed any sign of paradoxical arterial embolism or cardiac dysfunction. We conclude that VAE occurs not only during surgery in the sitting position, but also with release of PEEP and during repositioning to the supine position. IMPLICATIONS: This study shows that venous air embolism (VAE) occurs not only during surgery in the sitting position but also during positive end-expiratory pressure release and repositioning of the patient into the supine position. Continuous monitoring for VAE should be performed until the patient is returned to the supine position.

Adult↗

PubMed1990

[Influence of change in dental chair position on circulation kinetics. 1. Effects on rate x pressure product].

The rate x pressure product is a product of the systolic blood pressure and heart rate and is widely used in clinical medicine as an index of the cardiac oxygen supply-demand balance. Employing 20 healthy male subjects, we studied the changes in the rate x pressure product due to a body position change from the sitting position to the supine position in a dental chair. The following results were obtained: 1. The change from the sitting position caused a 10% decrease in the rate x pressure product, and this value did not return to the initial sitting position value even after 5 min in the supine position. 2. The heart rate tended to decrease due to the position change. 3. Immediately after the position change, the systolic blood pressure decreased significantly (p less than 0.05), but it tended to return to the initial value with the lapse of time. The lower rate x pressure product in the supine position suggests that the supine position is more advantageous than the sitting one in treatment of the elderly and patients with cardiovascular diseases from the viewpoint of the systemic cardiovascular kinetics.

Blood Pressure↗

PubMed1997

Mechanism of posturally induced crackles as predictor of latent congestive heart failure.

We investigated the role of changes in pulmonary function in posturally induced crackles (PIC) in 76 patients with various heart diseases. Regional ventilation was evaluated by spirometric gated ventilation scanning using 133Xe in 23 of these patients and its relationship to PIC was analyzed. A change from the sitting to the supine position was associated with a significant decrease in the percent functional residual capacity (FRC, p < 0.01) and significant increases in closing volume (CV), CV/vital capacity (VC) and closing capacity (CC)/FRC (p < 0.01) in the PIC-positive subjects. CV, CV/VC and CC/FRC did not differ significantly between PIC-positive (n = 37) and PIC-negative (n = 39) subjects in the sitting position, but in the supine position, these values were significantly higher in the PIC-positive group than in the PIC-negative group (CV: p < 0.05, CV/VC and CC/FRC: p < 0.01). These results suggest that airway closure was markedly increased in PIC-positive subjects in the supine position compared with PIC-negative subjects. Regional ventilation (V) was assessed in the sitting and the supine position from right lateral images divided into 9 segments from the base to the apex of the lung using spirometric gated ventilation scanning. There was no significant difference in regional ventilation in the sitting position between PIC-negative (n = 11) and PIC-positive (n = 12) subjects; in the supine position, regional ventilation decreased significantly at the base in the PIC-positive group. Findings suggest that PIC at the base of the lungs may be related to airway closure at the base of the lungs in the supine position in PIC-positive subjects.

Adult↗

PubMed1996

Reproducibility and condylar position of a physiologic maxillomandibular centric relation in upright and supine body position.

Better understanding of the physiologic features of the masticatory system has led to the evolution of the concept of maxillomandibular centric relation from the mechanical to physiological bases. However, the reproducibility of physiologic methods for centric relation determination has been criticized. In this clinical study the swallowing technique was modified to establish a physiologic centric relation in a reproducible manner. Condylar and disk positioning and reproducibility of the proposed modified swallowing technique (MST) were compared with the same parameters of a traditional technique, namely, the chin point guidance technique (CGT). Both techniques were studied with the patient in the upright and supine positions. Three interocclusal records were obtained for each technique-position combination for each of the 30 patients. The recorded maxillomandibular relations were analyzed on the three-dimensional analyzer. MST positioned the condyles in a more superoanterior position than did CGT, which was interpreted as a better seating of the condyles and disk in the articular fossae. There was no significant difference in reproducibility between MST and CGT on x, y, or z axes (p > 0.05), indicating that it is possible to establish a physiologic centric relation in a reproducible manner. The term "functional centric area" was proposed in this study to define a neuromuscularly determined centric occlusal scheme.

Adult↗

PubMed1995

The effect of maternal posture on fetal cerebral oxygenation during labour.

OBJECTIVE: To measure the effect of changes in maternal posture on fetal cerebral oxygenation during normal labour. DESIGN: A prospective study comparing changes in the fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume, measured by near infrared spectroscopy, in women with effective epidural analgesia when moved from the left lateral to the supine position during labour. SETTING: A London teaching hospital obstetric unit. SUBJECTS: Fourteen women during uncomplicated labour at term. RESULTS: When compared with the left lateral position, the supine position was associated with a significant decrease in the mean concentration of fetal cerebral oxyhaemoglobin of 1.12 (SD 1.0, 95% CI 0.49 to 1.75) mumol. 100 g-1 (P < 0.01) without any significant change in the mean concentration of deoxyhaemoglobin and cerebral blood volume. These changes were associated with a significant decrease in the mean cerebral oxygen saturation of 8.3 (SD 8.8, 95% CI 1.5 to 15.1)% (P < 0.05, n = 9). CONCLUSION: Changes in maternal posture during labour, in women with effective epidural analgesia, are associated with a significant decrease in fetal cerebral oxygenation.

Adult↗

PubMed1999

Influence of patient positioning on dose-volume histogram and normal tissue complication probability for small bowel and bladder in patients receiving pelvic irradiation: a prospective study using a 3D planning system and a radiobiological model.

PURPOSE: A prospective study was undertaken to evaluate the influence of patient positioning (prone position using a belly board vs. supine position) on the dose-volume histograms (DVHs) of organs of risk, and to analyze its possible clinical relevance using radiobiological models. METHODS AND MATERIALS: From November 1996 to August 1997 a computed tomography (CT) scan was done in the prone position using a belly board and in supine position in 20 consecutive patients receiving postoperative pelvic irradiation because of rectal cancer. Using a three-dimensional (3D) planning system (Helax, TMS) the DVH for small bowel, bladder, a standard planning target volume (PTV) of postoperative irradiation of rectal cancer, the intersection of volume of PTV and small bowel (PTV intersection V(SB), respectively, of PTV and bladder (PTV intersection V(B)) were defined in each axial CT slice. The normal tissue complication probability (NTCP) was determined by the radiobiological model of Lyman and Kutcher using the tolerance data of Emami. For evaluation of late toxicity alpha/beta ratio was 2.5; for evaluation of acute toxicity, it was 10. Total dose was 50.4 Gy (1.8 Gy/fraction) (ICRU 50). RESULTS: Using the prone position compared to the supine position, the median volume of PTV intersection V(B) was reduced by 18.5 cm3 (62%). Median dose (related to the reference dose) to the bladder was 44.5% (22.4 Gy) in prone and 66.05% (33.3 Gy) in supine position (p<0.001). Median V(B) within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose was significantly lower in the prone position when compared to the supine position. Using the radiobiological models, however, there was no difference of NTCP between prone position or supine position. In the prone position, median volume of PTV intersection V(SB) was reduced by 32.5 cm3 (54%). The median dose to small bowel was 30.85% (15.4 Gy) in the prone position and 47.35% (23.9Gy) in the supine position (p<0.001). Significant differences between prone and supine position were found for median V(SB) within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose. According to the method of Lyman, median NTCP of small bowel was significant lower in prone than in supine position. CONCLUSION: The prone position with a standard belly board should be the standard positioning technique for patients receiving adjuvant postoperative radiation therapy following surgery of rectal cancer. Both irradiated volume and total dose to the organs of risk can be reduced significantly. As a consequence of this, radiation induced toxicity will be minimized.

Adult↗

PubMed2003

Nasal obstruction and sleep-disordered breathing: the effect of supine body position on nasal measurements in snorers.

OBJECTIVE: Nasal obstruction is considered to be a potential etiological factor in sleep-disordered breathing. However, a significant correlation between nasal measurements and obstructive sleep apnea has not been demonstrated so far. The aim of this study was to investigate the relationships between nasal resistance, nasal volumes and selected sleep parameters using nasal measurements performed in both seated and supine positions. We also investigated whether snoring patients in our clinical sample showed increased positional or decongestive nasal mucosal changes. MATERIAL AND METHODS: Forty-one snoring men on a waiting list for correction of nasal obstruction underwent polysomnography, anterior rhinomanometry and acoustic rhinometry. Nineteen non-snoring control subjects were also recruited. Nasal measurements were performed in a seated position, after lying down in a supine position and, after decongestion of nasal mucosa, in a seated position again. RESULTS: In the overall patient group, nasal volume at a distance 2-4 cm from the nares in the supine position correlated inversely with apnea-hypopnea index (AHI) (r = -0.32, p < 0.05) and oxygen desaturation index (ODI) (r = -0.49, p < 0.05). In the non-obese patients, total nasal resistance measured in a supine position correlated with AHI (r = 0.50, p < 0.05) and ODI (r = 0.58, p < 0.05) and supine nasal volumes were also inversely correlated with ODI. No significant correlations were found between baseline nasal measurements performed in a seated position and sleep parameters. Postural or decongestive changes in nasal measurements were not increased in snoring patients compared with control subjects. CONCLUSION: The relationship found between nasal measurements and sleep parameters suggests that nasal obstruction does augment airway collapse.

Adult↗

PubMed1999

Postural differences in cardiac dynamics during quiet and active sleep in low birthweight infants.

To study the effects of body position (supine versus prone) on changes in cardiac inter-beat interval during quiet and active sleep, 6-h continuous electrocardiographic recordings and simultaneous minute-by-minute behavioural activity state assignments were made in 61 healthy, growing, low birthweight infants. The infants weighed 795-1600 g at birth and ranged between 30-38 wk in postconceptual age. Infants were randomly assigned to the supine or prone position for the first 3 h of each study; the position was reversed for the second 3 h. Higher heart rates and lower time and frequency domain measures of inter-beat interval variability were observed in the prone position as compared to the supine position, during both quiet and active sleep. In addition, an analysis of consecutive increases and decreases in the instantaneous heart rate revealed a lower incidence of sustained accelerations or decelerations in the prone position. Although consistent findings concerning inter-beat interval variability and sleeping position were obtained from all analytic techniques, the differences derived from analysis of consecutive inter-beat changes were the most robust. These differences in multiple measures of cardiac rate and rhythm between prone and supine positions suggest that autonomic control of the heart is altered by body position, the net effect on heart rate being increased sympathetic dominance.

Autonomic Nervous System↗