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PubMed2001

Acute effects of melatonin administration on cardiovascular autonomic regulation in healthy men.

BACKGROUND: Previous studies have suggested that melatonin, a major pineal hormone, possibly modulates the autonomic nervous system in animals. The aim of this study was to examine the effects of melatonin administration on heart rate variability (HRV) in human beings. METHODS: In 26 healthy men, melatonin (2 mg) or placebo was randomly administered. Power spectral analysis of HRV and blood pressure monitoring were performed in the supine position before and 60 minutes after administration and in the standing position 60 minutes after administration. Plasma catecholamine levels were also assessed. RESULTS: No differences in any baseline parameters were found between the two groups. Compared with placebo, melatonin administration within 60 minutes increased R-R interval, the square root of the mean of the squared differences between adjacent normal R-R intervals, high-frequency power, and low-frequency power of HRV and decreased the low-frequency to high-frequency ratio and blood pressure in the supine position (all P <.01). Plasma norepinephrine and dopamine levels in the supine position 60 minutes after melatonin administration were lower compared with placebo (P <.05 and P <.01, respectively). Standing up resulted in the decrease of HRV and the increase of blood pressure and plasma catecholamine levels in both administration groups, and the differences between the groups found in the supine position disappeared. CONCLUSIONS: These findings indicate that melatonin administration increased cardiac vagal tone in the supine position in awake men. Melatonin administration also may exert suppressive effects on sympathetic tone.

Blood Pressure↗
PubMedDate not supplied

Effects of backrest elevation and position on pulmonary artery pressures.

This repeated measures study identified each subject's baseline range of fluctuation in pulmonary artery pressures and used this information to evaluate the effects of changes in backrest elevation (0 degrees and 30 degrees) and position (supine and lateral) on pulmonary artery pressures. Sixteen hemodynamically stable patients were studied. Six measures of pulmonary artery pressure were obtained with subjects in the supine (flat) position. Pulmonary artery systolic pressures fluctuated from 2-16 mm Hg, pulmonary artery diastolic pressures from 0-11 mm Hg, and pulmonary artery mean pressures from 0-13 mm Hg. Only pulmonary artery diastolic pressures were not altered in a statistically significant way with backrest elevation. Even though backrest elevation produced clinically significant changes (those exceeding the subject's baseline range of fluctuation) in some subjects, no other changes in parameters of hemodynamic status were observed. These results suggest that pulmonary artery pressures may be obtained with backrests elevated. Since position changes produced both statistically and clinically significant changes in all pulmonary artery pressures, the use of lateral positions during pulmonary artery pressure measurement is not recommended.

Adult↗
PubMed2000

Difference in human cardiovascular response between upright and supine recovery from upright cycle exercise.

Cardiovascular responses were examined in seven healthy male subjects during 10 min of recovery in the upright or supine position following 5 min of upright cycle exercise at 80% peak oxygen uptake. An initial rapid decrease in heart rate (fc) during the early phase of recovery followed by much slower decrease was observed for both the upright and supine positions. The average fc at the 10th min of recovery was significantly lower (P < 0.05) in the supine position than in the upright position, while they were both significantly greater than the corresponding pre-exercise levels (each P < 0.05). Accordingly, the amplitude of the high frequency (HF) component of R-R interval variability (by spectrum analysis) in both positions was reduced with a decrease in mean R-R interval, the relationship being expressed by a regression line--mean R-R interval = 0.006 x HF amplitude + 0.570 (r = 0.905, n = 28, P < 0.001). These results would suggest that the slower reduction in fc following the initial rapid reduction in both positions is partly attributable to a retardation in the restoration of the activity of the cardiac parasympathetic nervous system. Post-exercise upright stroke volume (SV, by impedance cardiography) decreased gradually to just below the pre-exercise level, whereas post-exercise supine SV increased markedly to a level similar to that at rest before exercise. The resultant cardiac output (Qc) and the total peripheral vascular resistance (TPR) in the upright and supine positions returned gradually to their respective pre-exercise levels in the corresponding positions. At the 10th min of recovery, both average SV and Qc were significantly greater (each P < 0.005) in the supine than in the upright position, while average TPR was significantly lower (P < 0.05) in the supine than in the upright position. In contrast, immediately after exercise, mean blood pressure dropped markedly in both the supine and upright positions, and their levels at the 10th min of recovery were similar. Therefore we concluded that arterial blood pressure is maintained relatively constant through various compensatory mechanisms associated with fc, SV, Qc, and TPR during rest and recovery in different body positions.

Adult↗
PubMedDate not supplied

The relationship between the parturient's positions and perceptions of labor pain intensity.

BACKGROUND: While the effect of the maternal position on reducing labor pain has been studied, the data presented to date have not been conclusive. OBJECTIVES: To determine if maternal position reduced the intensity of labor pain during cervical dilatation from 6 to 8 centimeters. METHOD: Pain intensity was measured using the visual analogue scale (VAS) on 39 primiparous and 19 multiparous women (N = 58) who alternately assumed the sitting and supine positions for 15 minutes during cervical dilatation from 6 to 8 centimeters. RESULTS: The pain scores for the sitting position were significantly lower than those for the supine position. The Wilcoxon signed-ranks test showed the VAS scores for the (a) total labor pain ("total" being defined as both abdominal and lumbar pain) during contraction (p =.011), (b) continuous total labor pain (p =.001), (c) lumbar pain during contraction (p <.001), and (d) continuous lumbar pain (p <.001) in the sitting position (significantly lower than in supine position). The diminished pain scores were greater than 13 millimeters, which is the minimum clinically significant change in patient pain severity as measured with the 100 millimeter VAS. The largest decrease occurred in lower back pain. No significant differences were found for abdominal pain scores in either the sitting or supine positions. CONCLUSION: The sitting position offers an effective method to relieve lower back labor pain during cervical dilatation from 6 to 8 centimeters. Similar relief was experienced for women who reported pain only on contraction as well as those with continuous pain.

Adult↗
PubMed1992

Effects of age and posture on plasma active renin and plasma inactive renin in normal subjects.

To investigate the effects of age and posture on plasma active and inactive renin, we measured the plasma active renin concentration (ARC) and inactive renin concentration (IRC) in 81 healthy subjects. The subjects were divided into five groups according to age and body position at the time the blood was taken. Group I included 15 five-day-old newborns in a supine position. Group H included 18 adults, aged from 20 to 50 years, who were in a supine position. Group III included 21 adults, over 50 years old, who were in a supine position. Group IV included 20 adults, aged from 20 to 50 years, who were in an upright position. Group V included 19 adults, over 50 years old, who were in an upright position. Twelve subjects were included in Groups II and IV. Plasma active renin was measured by the amount of angiotensin I general when an exogenous renin substrate was added. Plasma inactive renin was activated by trypsin. The results showed that, in a supine position, both ARC and IRC were significantly higher in newborns (Group I) than in the two adult groups (Groups II and III). The mean of the ARC/TPRC (total plasma renin concentration) ratio was lower in adults over 50 years old (Group III) than in those from 20 to 50 years old (Group II), but the difference was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1999

Arterial oxygen saturation in severely disabled people: effect of oral feeding in the sitting position.

Control of the circulatory and respiratory systems is especially important in severely disabled people. The purpose of this study was to clarify the response of hemoglobin oxygen saturation level (SpO(2)), pulse rate, and respiratory rate during oral feeding in severely disabled persons. Continuous measurement of these variables was done by pulse oximetry and respiratory inductance plethysmography under two experimental settings in eight severely disabled persons aged 14-28 yrs. Setting I consisted of the following three procedures: (a) a 30-min period in the supine position, (b) a 50-min period in a sitting position, and (c) a 30-min period in the supine position. Setting II consisted of the following four procedures: (a) a 30-min period before the meal in the supine position, (b) a nonspecified period in a sitting position during which the meal was taken, (c) a 30-min period after the meal in the same sitting position, and (d) a 30-min period in the supine position. Results showed that mean SpO(2) level decreased and mean pulse rate increased during the meal in almost all subjects. In many cases, pulse rate and SpO(2) level did not return to baseline values in the sitting position after the meal. These findings indicate that oral feeding of severely disabled persons in a sitting position places considerable stress on the circulatory system, the effects of which may last after the meal in some cases.

Adolescent↗
PubMed2004

Cardiac autonomic balance and QT dispersion during head-up tilt testing in diabetics with and without sensory neuropathy.

BACKGROUND: Cardiovascular autonomic dysfunction is associated with higher mortality in diabetics. However, detection methods of early cardiac diabetic dysautonomia, and its correlation with severity of sensory neuropathy, have not been described. METHODS: We analyzed the heart rate variability (HRV) by spectral analysis and QT dispersion in 23 diabetics with and without sensory neuropathy, and in 5 age-matched controls, in the supine position and during head-up tilt testing (HUT). Diabetics were divided into 3 groups according to the degree of sensory neuropathy. RESULTS: In the spectral analysis of HRV, the high frequency components in the supine position decreased as a function of severity of the neuropathy. High frequency in diabetics was significantly decreased in the supine position, even in absence of sensory neuropathy. The low/high frequency ratio (L/H) in the supine position was similar among controls and the 3 patient groups. L/H in diabetics with moderate or severe neuropathy did not increase from the supine to the upright position. Baseline QT dispersion increased proportionally to the severity of sensory neuropathy and, in patients without apparent sensory neuropathy, QT dispersion increased significantly during HUT. CONCLUSIONS: The spectral analysis of HRV and measurements of QT dispersion, before and during HUT, were reliable detection methods of early abnormalities in autonomic balance and may predict a risk of sudden cardiac death in diabetics.

Aged↗
PubMed2001

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

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

Adult↗
PubMed2006

Evaluation of a brief cardiovascular autonomic screen.

OBJECTIVE: To test the validity and practicality of a simple, rapid autonomic cardiovascular evaluation (RACE). INTRODUCTION: Assessment of the autonomic nervous system is costly and time consuming. Consequently, briefer measures are often utilized as evaluations of autonomic function. We therefore set out to assess the validity and practicality of a simple, rapid autonomic cardiovascular evaluation protocol which mimicked the bedside evaluations used in many healthcare centers. DESIGN/METHODS: Every eligible patient undergoing full autonomic testing (FAT) in our laboratory was enrolled. The protocol, performed blinded to FAT results, consisted of one breath in the supine position, and supine and standing (1 and 3 min) pressures and pulse. Results were scored for cardiac variation during the breath, a drop in pressure during the stand. Pulse increase was also scored. Aggregate RACE score was regressed against a similarly scored FAT. RESULTS: The single breath response correlated poorly with the standard response to deep breathing with convergent results in only 26/37 patients, with a specificity of 30%, and sensitivity of 85%. HR and BP changes standing showed little regression against matching values during FAT. Only 5/11 patients who met the criteria for postural tachycardia syndrome by FAT demonstrated a >20 bpm increase in HR by 3 min standing. Finally, aggregate scores for FAT and RACE correlated poorly. DISCUSSION: The RACE does not satisfy the criteria to serve as a robust dysautonomia screen. Full autonomic testing provides more complete and accurate information than simple bedside assessment.

Adolescent↗
PubMed2004

Right lateral decubitus position reduces QT dispersion in patients with chronic heart failure.

A greater QT dispersion in patients with chronic heart failure (CHF) appears to be a non-invasive marker of susceptibility to malignant ventricular arrhythmias. We evaluated whether QT dispersion in CHF patients is modified by the patients' recumbent position. In 12 CHF patients, and age and sex-matched 12 normal subjects, a single 12-lead surface ECG was recorded in each postural position [left lateral decubitus position (L), supine position (S), and right lateral decubitus position (R)]. In normal subjects, the QT dispersion was comparable in the three recumbent positions [L: 47+/-15 (SD) ms, S: 40+/-9 ms, R: 38+/-14 ms, P=NS]. In contrast, in CHF patients, QT dispersion was significantly shorter in R than those in L and S (L: 93+/-42 ms*, S: 81+/-29 ms*, R: 63+/-24 ms, *P <.05 vs. R). In conclusion, reclining in R reduces the prolonged QT dispersion in CHF patients.

Aged↗
PubMed1995

Delayed posterior interosseous nerve palsy.

A rare case of delayed posterior interosseous nerve palsy that developed 39 years after an unreduced anterior dislocation of the radial head is reported. The posterior interosseous nerve was compressed and narrowed at the arcade of Frohse. Radial head resection and release of the arcade was done. The paralysis continued to recover 6 weeks after operation. The nerve, at the arcade of Frohse, was susceptible to compression by the dislocated radial head, especially in the supinated position. Repeated supination and pronation movement over time may have led to developmental changes that caused the delayed nerve palsy.

Adult↗
PubMed1982

Effect of posture on gastro-oesophageal reflux in the newborn.

The effect of posture on gastro-oesophageal reflux was studied by giving 72 orogastric tube feeds to 18 low birthweight babies. Each infant was studied in each of 4 positions: prone, supine, right, and left lateral. Brilliant blue was added to feeds and reflux was determined by staining of a cotton thread opposite the holes in a feeding tube passing from the nose to the distal oesophagus. A comparison of the prone and supine positions showed that significantly less reflux occurred in the prone position.

Enteral Nutrition↗
PubMed1988

Regulation of end-expiratory lung volume during exercise.

We determined the effects of exercise on active expiration and end-expiratory lung volume (EELV) during steady-state exercise in 13 healthy subjects. We also addressed the questions of what affects active expiration during exercise. Exercise effects on EELV were determined by a He-dilution technique and verified by changes in end-expiratory esophageal pressure. We also used abdominal pressure-volume loops to determine active expiration. EELV was reduced with increasing exercise intensity. EELV was reduced significantly during even mild steady-state exercise and during heavy exercise decreased an average of 0.71 +/- 0.3 liter. Dynamic lung compliance was reduced 30-50%; EELV remained greater than closing volume. Changing the resistance to airflow (via SF6-O2 or He-O2 breathing) during steady-state exercise changed the peak gastric and esophageal pressure generation during expiration but did not alter EELV; breathing through the mouthpiece produced similar effects during exercise. EELV was significantly reduced in the supine position. With supine exercise active expiration was not elicited, and EELV remained the same as in supine rest. With CO2-driven hyperpnea (7-70 l/min), EELV remained unchanged from resting levels, whereas during exercise, at similar minute ventilation (VE) values EELV was consistently decreased. At the same VE, treadmill running caused an increase in tonic gastric pressure and greater reductions in EELV than either walking or cycling. We conclude that both the exercise stimulus and the resultant hyperpnea stimulate active expiration and a reduced FRC. This new EELV is preserved in the face of moderate changes in mechanical time constants of the lung. This reduced EELV during exercise aids inspiration by optimizing diaphragmatic length and permitting elastic recoil of the chest wall.

Adult↗
PubMed1985

The effect of positional changes on oxygenation in patients with pleural effusions.

In unilateral parenchymal pulmonary disease, arterial oxygenation decreases when the patient is positioned such that the abnormal lung is dependent; however, few studies have evaluated the effect of the body position on oxygenation in patients with unilateral or asymmetric pleural effusions. To our knowledge, no previous study has evaluated the possible transient effects of changing position on the level of arterial oxygen saturation (SaO2) in such patients. Accordingly, we studied ten normoxic patients spontaneously breathing room air, who had asymmetric pleural effusions as documented by chest x-ray film and physical examination. We monitored pulse, respiratory rate, and blood pressure every five minutes and SaO2 by ear oximetry continuously while patients were in the following positions: sitting; supine; and left and right lateral decubitus. The mean SaO2 was 95 percent and 94.3 percent in the sitting and supine positions, respectively. Mean SaO2 fell to 93.4 percent when the patients were positioned so that the side with the largest pleural effusion was dependent. When the side with the pleural effusion was down, the mean SaO2 was significantly lower than in either the sitting position or with the side with the pleural effusion up. We could find no significant relationship between the size of the pleural effusion and the amount of arterial oxygen desaturation. We conclude that there is a decrease in SaO2 in normoxic patients when the side with the larger pleural effusion is dependent; however, this decreased SaO2 does not appear to be clinically significant in patients with normal SaO2.

Aged↗
PubMed2005

Effects of electrical muscle stimulation on oxygen consumption.

Electrical muscle stimulation (EMS) devices are being marketed as weight/ fat loss devices throughout the world. Commercially available stimulators have the ability to evoke muscle contractions that may affect caloric expenditure while the device is being used. The aim of this study was to test the effects of two different EMS devices (Abtronic and Feminique) on oxygen consumption at rest. Subjects arrived for testing after an overnight fast, had the devices fitted, and then positioned supine with expired air measured to determine oxygen consumption. After a 10-minute acclimation period, oxygen consumption was measured for 20 minutes with the device switched off (resting) then 20 minutes with the device switched on (stimulated). There were no significant differences (p > 0.05) in oxygen consumption between the resting and stimulated periods with either the Abtronic (mean +/- SD; resting, 3.40 +/- 0.44; stimulated, 3.45 +/- 0.53 ml of O(2).kg(-1).min(-1)) or the Feminique (resting, 3.73 +/- 0.45; stimulated, 3.75 +/- 0.46 ml of O(2).kg(-1).min(-1)). In summary, the EMS devices tested had no effect on oxygen consumption during muscle stimulation.

Calorimetry, Indirect↗
PubMed2002

Increased signal intensity in the normal glenoid labrum in MR imaging: diagnostic pitfalls caused by the magic-angle effect.

PURPOSE: To determine the effect of the magic-angle effect on the MR signal in the posterosuperior portion of the glenoid labrum. METHODS: MR imaging of 15 arthroscopically evaluated shoulders, five with posterosuperior labrum injury and ten intact, was retrospectively reviewed. In the first part of the study, the signal intensity of the posterosuperior labrum on gradient-recalled echo (GRE) T2*-weighted axial images was correlated with the arthroscopy findings. The second part of the study was designed to illustrate the orientation-dependent signal that occurs in the posterosuperior labrum of three asymptomatic volunteers when imaged in the conventional supine position and in a position similar to Trendelenburg's. Another three volunteers were examined with GRE T2*-weighted axial images to assess the echo-time (TE)-dependent signal in the labrum. RESULTS: The signal increase in the posterosuperior labrum was identified not only in the injured labra but also in nine of 10 intact labra. In the volunteers' studies, the signal in the posterosuperior labrum changed according to the examinees' positions (conventional supine or similar to Trendelenburg's) and according to TE. CONCLUSIONS: Increased signal intensity due to the magic-angle effect may be misdiagnosed as a labrum injury. Awareness of this pitfall is particularly important in MR imaging of throwing athletes whose posterosuperior labra are frequently injured by posterosuperior glenoid impingement.

Adolescent↗
PubMed2002

Cheyne-Stokes respiration during sleep: a possible effect of body position.

BACKGROUND: Cheyne-Stokes Respiration (CSR) is a common finding in Chronic Heart Failure and Stroke patients. The body position effect during sleep on obstructive breathing abnormalities is well known. However, the effect of body position during sleep on breathing abnormalities of central type like CSR has not been well documented. MATERIAL/METHODS: Six sleep studies (two complete Polysomnographic (PSG) evaluations and four Pulse Oximetry recordings (PO)), were carried out in a 57-year-old female patient with a recent Cerebro Vascular Accident (CVA who had both Obstructive Sleep Apnea (OSA) and CSR. RESULTS: The first PSG was carried out two months post-stroke and revealed a severe, continuous CSR pattern during Non Rapid Eye Movements (NREM) sleep (mainly with central apneas), and Obstructive Sleep Apnea (OSA) during Rapid Eye Movements (REM) sleep, independent of body position: Supine Respiratory Disturbance Index (SRDI) = 85.2 and Lateral RDI (LRDI) = 95.4. A second PSG was performed three months later after an overall clinical improvement and showed a complete disappearance of CSR during NREM sleep and OSA during REM sleep in her lateral posture (LRDI = 0), while the RDI in the supine posture was only slightly improved (SRDI = 73.2). The CSR pattern was less severe and was characterized mainly by central hypopneas. Two PO recordings between the PSG studies showed similar improvement trends. Two additional PO recordings, two and three weeks after the last PSG (the first one with the patient lying supine and the second one with the patient lying on her side throughout the night), revealed a further significant improvement in the supine posture (SRDI = 37.5). CONCLUSIONS: The results of this study suggest that body posture may play a role not only in the prevalence and severity of obstructive breathing disorders, but also in CSR, a central type of breathing abnormalities during sleep.

Cheyne-Stokes Respiration↗