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Biomedical subjects

F Stein

Publications and source records attributed to F Stein.

At least 19 recordsLinked to original sources
PubMed2001

Energy metabolism, nitrogen balance, and substrate utilization in critically ill children.

BACKGROUND: Critically ill patients are characterized by a hypermetabolic state, a catabolic response, higher nutritional needs, and a decreased capacity for utilization of parenteral substrate. OBJECTIVE: We sought to analyze the relation between a patient's metabolic state and their nutritional intake, substrate utilization, and nitrogen balance (NB) in mechanically ventilated, critically ill children receiving parenteral nutrition. DESIGN: This was a cross-sectional study in which resting energy expenditure (REE) and NB were measured and substrate utilization and the metabolic index (MI) ratio (REE/expected energy requirements) were calculated. RESULTS: Thirty-three children (mean age: 5 y) participated. Their average REE was 0.23 +/- 0.10 MJ x kg(-1) x d(-1) and their average MI was 1.2 +/- 0.5. Mean energy intake, protein intake, and NB were 0.25 +/- 0.14 MJ x kg(-1) x d(-1), 2.1 +/- 1 g x kg(-1) x d(-1), and -89 +/- 166 mg x kg(-1) x d(-1), respectively. Patients with an MI >1.1 (n = 19) had a higher fat oxidation than did patients with an MI <1.1 (n = 14; P < 0.05). Patients with lipogenesis (n = 13) had a higher carbohydrate intake than did patients without lipogenesis (n = 20; P < 0.05). Patients with a positive NB (n = 12) had a higher protein intake than did patients with a negative NB (n = 21; P < 0.001) and lower protein oxidation (P < 0.01). CONCLUSIONS: Critically ill children are hypermetabolic and in negative NB. In this population, fat is used preferentially for oxidation and carbohydrate is utilized poorly. A high carbohydrate intake was associated with lipogenesis and less fat oxidation, a negative NB was associated with high oxidation rates for protein, and a high protein intake was associated with a positive NB.

Adolescent↗
PubMed2001

Orthostatic intolerance and motion sickness after parabolic flight.

Because it is not clear that the induction of orthostatic intolerance in returning astronauts always requires prolonged exposure to microgravity, we investigated orthostatic tolerance and autonomic cardiovascular function in 16 healthy subjects before and after the brief micro- and hypergravity of parabolic flight. Concomitantly, we investigated the effect of parabolic flight-induced vomiting on orthostatic tolerance, R-wave-R-wave interval and arterial pressure power spectra, and carotid-cardiac baroreflex and Valsalva responses. After parabolic flight 1) 8 of 16 subjects could not tolerate 30 min of upright tilt (compared to 2 of 16 before flight); 2) 6 of 16 subjects vomited; 3) new intolerance to upright tilt was associated with exaggerated falls in total peripheral resistance, whereas vomiting was associated with increased R-wave-R-wave interval variability and carotid-cardiac baroreflex responsiveness; and 4) the proximate mode of new orthostatic failure differed in subjects who did and did not vomit, with vomiters experiencing comparatively isolated upright hypocapnia and cerebral vasoconstriction and nonvomiters experiencing signs and symptoms reminiscent of the clinical postural tachycardia syndrome. Results suggest, first, that syndromes of orthostatic intolerance resembling those developing after space flight can develop after a brief (i.e., 2-h) parabolic flight and, second, that recent vomiting can influence the results of tests of autonomic cardiovascular function commonly utilized in returning astronauts.

Adult↗
PubMed2001

Effect of acute exposure to hypergravity (GX vs. GZ) on dynamic cerebral autoregulation.

We examined the effects of 30 min of exposure to either +3GX (front-to-back) or +GZ (head-to-foot) centrifugation on cerebrovascular responses to 80 degrees head-up tilt (HUT) in 14 healthy individuals. Both before and after +3 GX or +3 GZ centrifugation, eye-level blood pressure (BP(eye)), end tidal PCO2 (PET(CO2)), mean cerebral flow velocity (CFV) in the middle cerebral artery (transcranial Doppler ultrasound), cerebral vascular resistance (CVR), and dynamic cerebral autoregulatory gain (GAIN) were measured with subjects in the supine position and during subsequent 80 degrees HUT for 30 min. Mean BP(eye) decreased with HUT in both the GX (n = 7) and GZ (n = 7) groups (P < 0.001), with the decrease being greater after centrifugation only in the GZ group (P < 0.05). PET(CO2) also decreased with HUT in both groups (P < 0.01), but the absolute level of decrease was unaffected by centrifugation. CFV decreased during HUT more significantly after centrifugation than before centrifugation in both groups (P < 0.02). However, these greater decreases were not associated with greater increases in CVR. In the supine position after centrifugation compared with before centrifugation, GAIN increased in both groups (P < 0.05, suggesting an autoregulatory deficit), with the change being correlated to a measure of otolith function (the linear vestibulo-ocular reflex) in the GX group (r = 0.76, P < 0.05) but not in the GZ group (r = 0.24, P = 0.60). However, GAIN was subsequently restored to precentrifugation levels during postcentrifugation HUT (i.e., as BP(eye) decreased), suggesting that both types of centrifugation resulted in a leftward shift of the cerebral autoregulation curve. We speculate that this leftward shift may have been due to vestibular activation (especially during +GX) or potentially to an adaptation to reduced cerebral perfusion pressure during +GZ.

Adult↗
PubMed2000

Final report of the FOPE II Pediatric Subspecialists of the Future Workgroup.

The report of the Pediatric Subspecialists of the Future Workgroup of the Second Task Force on Pediatric Education reviews the critical changes of the past 2 decades that have affected the provision of pediatric subspecialty services, education of pediatric health care providers, and the acquisition and application of new knowledge. The report considers the future needs that will determine the ability of pediatric subspecialists to meet identified goals. Recommendations for change in the education, role, and financing of the pediatric subspecialist are reported together with those of other workgroups. Pediatrics 2000;106(suppl):1224-1244; pediatric subspecialist, pediatric subspecialist workforce, education pediatric subspecialist, research pediatric subspecialist.

Certification↗
PubMed1999

Respiratory system mechanics in patients receiving aerosolized ribavirin during mechanical ventilation for suspected respiratory syncytial viral infection.

Respiratory syncytial virus (RSV) is an important respiratory pathogen for infants. Aerosolized ribavirin (AR) has been used in mechanically ventilated (MV) patients with RSV bronchiolitis. The purpose of this study was to measure respiratory system mechanics (RSM) in pediatric patients requiring MV and receiving AR for suspected RSV. Patients were prospectively randomized to receive AR, either at a regular dose (RD) (6 g/300 mL over 18 hr/day) or a high dose (HD) (6 g/100 mL over 2 hr, three times a day). To measure changes in RSM, a passive exhalation technique was used before and after each dose of AR; time constant (tc) in s, resistance (Rrs) in cmH(2)O/mL/kg/s, and quasistatic compliance (Crs) in mL/cmH(2)O/kg were measured. Airway pressure and flow signals were obtained and analyzed using a pneumotachograph, a differential pressure transducer, and a computer interface. Statistical analysis was done by Mann-Whitney and Wilcoxon rank tests. Thirteen patients were enrolled: 5 patients in the HD group (mean age of 52 months), and 8 patients in the RD group (mean age of 10 months). Four and 5 patients were positive for RSV by ELISA in the HD and RD groups, respectively. The RSM in the HD group were: tc, 0.58 +/- 0.15 s and 0.55 +/- 0.20 s before and after AR, respectively; Rrs, 0.03 +/- 0. 03 cmH(2)0/mL/kg/s and 0.02 +/- 0.02 cmH(2)0/mL/kg/s, respectively; and Crs, 0.63 +/- 0.21 mL/cmH(2)O/kg and 0.70 +/- 0.13 mL/cmH(2)O/kg, respectively. In the RD group, the RSM were: tc, 0.37 +/- 0.12 s and 0.31 +/- 0.10 s before and after AR, respectively; Rrs, 0.03 +/- 0.02 cmH(2)0/mL/kg/s and 0.02 +/- 0.01 cmH(2)0/mL/kg/s, respectively (P < 0.05); and Crs, 0.46 +/- 0.20 mL/cmH(2)O/kg and 0.46 +/- 0.19 mL/cmH(2)O/kg, respectively. We conclude that the use of AR for bronchiolitis in infants and young children during mechanical ventilation does not worsen RSM.

Administration, Inhalation↗
PubMed1999

Rectal-scalp temperature difference predicts brain death in children.

When brain death in children occurs, commonly the scalp feels cold despite a normal core temperature. This phenomenon might reflect absent cerebral blood flow and metabolic activity. The authors, therefore, measured rectal-scalp temperature differences in critically ill comatose children to test the hypothesis that a particular temperature difference may correlate with clinical brain death. In a prospective cohort study set in a pediatric intensive care unit, rectal-scalp, rectal-abdomen, and rectal-mastoid temperatures in critically ill comatose children older than 18 months of age were measured before and during brain death evaluations. Twelve children were enrolled. Clinical criteria for brain death were met by seven patients, and five patients survived. All of the seven children who died had rectal-scalp temperature differences greater than 4 degrees C (mean = 6.7, range = 6.0-7.4) at the time of clinical brain death. No survivor had a rectal-scalp temperature difference of 4 degrees C at any time (mean = 3.4, range = 2.9-3.9). Rectal-scalp temperature differences of those who died and those who survived were significantly different at the P < 0.005 level. Rectal-abdomen and rectal-mastoid temperature differences did not correlate with clinical brain death or rectal-scalp temperature difference. In this preliminary study a rectal-scalp temperature difference of greater than 4 degrees C correlates with clinical criteria for brain death in children.

Biomarkers↗
PubMed1999

Chronic survival of calves implanted with the DeBakey ventricular assist device.

The DeBakey ventricular assist device (VAD) is a miniaturized, electromagnetically driven axial flow pump capable of generating in excess of 10 L/min output. The VAD was evaluated in 19 calves during experiments designed to test iterative modifications in the system and to determine the safety of the DeBakey VAD for intermediate to long-term implant. Five of the animals died or were euthanized during the perioperative period (i.e., Days 1-5) due to complications associated with bleeding (n = 3), sudden cardiac arrest (n = 1), or pump occlusion due to a muscle remnant associated with coring (n = 1). The remaining 14 animals survived from 7-145 days. Ten of the 14 animals survived 30 or more days, and 2 animals survived 93 and 145 days before elective euthanasia. Pump function was evaluated in the 14 calves that survived beyond the perioperative period. Pump output at implantation averaged 3 L/min while output at 100 days (n = 2) averaged 4.22 L/min. The electrical current did not change across time during the study, indicating normal operation of the bearings. Pumps consumed less than 10.5 W of power for all support durations. Hemolysis did not occur; the average daily plasma free hemoglobin varied from 2.0 to 8.0 mg/dl. Evaluation of serum biochemical data showed that implantation of the DeBakey VAD in calves with normal hearts did not impair end organ function; BUN, creatinine, and total bilirubin varied minimally within the normal range. The white blood cell count of implanted animals remained within the normal range throughout the study.

Animals↗
PubMed1999

Vertical shift in cerebral autoregulation curve: a graded head-up tilt study.

According to the classical theory of cerebral autoregulation, cerebral blood flow (CBF) will be maintained at a near-constant level for cerebral perfusion pressure (CPP) within the range of 60-150 mmHg. In recent years, however, studies with contradicting results have demonstrated a change in CBF when the level of CPP had not changed significantly. It is suggested that a shift in the autoregulation curve may have taken place along the horizontal axis or along the vertical axis. This paper describes previously unreported findings of a graded head-up tilt (HUT) study which was designed as a preliminary experiment to test the protocol for possible use on astronauts upon returning from space-flight. Data from this study tend to support the findings of previous studies regarding possible shifts in the cerebral autoregulation curve. Five female and four male healthy volunteers were exposed to HUT for 5 minutes at each angle of 30 degrees, 60 degrees, and 90 degrees. Throughout the test, cerebrovascular and cardiovascular responses were evaluated by use of continuous acquisition of mean flow velocity (MFV) from the right middle cerebral artery with transcranial Doppler sonograhy, mean arterial blood pressure (MABP, Finapres) and heart rate (HR, ECG). Based on the last 60 seconds of data at each tilt angle and baseline, the percentage changes in MFV from baseline were found to be similar to those in MABP at the level of the brain (MABPbrain), and both were significant (p<0.05) at the 60 degrees (-9.1 +/- 7% for MABP brain, -9.8 +/- 5% for MFV) and 90 degrees (-13 degrees +/- 8%, -12.0 +/- 6%) positions. Heart rate (HR) increased significantly (p<0.05) from the baseline at 30 degrees (6.3 +/- 5%) through 90 degrees (23.3 +/- 8%). The trend toward decreasing MFV in normal subjects, even while MABP brain remained within the normal limits of cerebral autoregulation, may suggest a downward shift of the cerebral blood flow plateau in the classic cerebral autoregulation curve.

Adult↗
PubMed1998

Influence of phase duration of biphasic waveforms on defibrillation energy requirements with a 70-microF capacitance.

BACKGROUND: Phase duration of biphasic shocks may be an important determinant of defibrillation success. The purpose of this study was to investigate the effect of changing phase duration of biphasic pulses delivered by 70-microF capacitors on defibrillation energy requirements. This may be clinically relevant for the optimization of implantable cardioverter-defibrillator design and programming. METHODS AND RESULTS: Defibrillation thresholds (DFTs) were determined for 13 waveforms in 13 pigs by application of a 70-microF capacitance and a transvenous/submuscular lead system. In part I, phase-1 duration varied, preserving a phase-1/phase-2 duration ratio of 60%/40%. The phase-1 durations were 1, 2, 3, 4, 5, and 6 ms. The DFT was lowest (22.9+/-7 J) for phase 1=3 ms compared with phase 1=1 ms (36.4+/-7.5 J), 2 ms (25+/-6.5 J), 4 ms (25+/-7.6 J), 5 ms (30.7+/-7.3 J), or 6 ms (32.9+/-8.1 J) (P<.001). In part II, phase-1 duration was 3 ms but phase-2 duration varied: 0.7, 1.3, 2, 2.7, 3.3, 4, and 6 ms. Significant DFT minima were found at phase 2=2 ms (22.5+/-4.2 J) and phase 2=4 ms (22.5+/-4.2 J) compared with phase 2=0.7 ms (31.7+/-9.3 J), phase 2=3.3 ms (26.7+/-6.1 J), or phase 2=6 ms (28.3+/-6.8 J) (P<.05). CONCLUSIONS: The strength-duration curve of biphasic defibrillation shocks demonstrates a single optimum for phase-1 duration. In contrast, two optima with minimal energy requirements were found for phase-2 duration. Optimization of both phases of low-capacitance biphasic shocks may reduce energy requirements for defibrillation.

Animals↗
PubMed1998

[Effects of extracorporeal ultrasound shockwaves on the relatively mature embryos of the teleost Oryzias latipes].

Exposure to low-energy ultrasound shock waves (1000 impulses at a frequency of 2/sec and an energy density of 0.08 mj/mm2; peak positive/negative pressure 16/-7 MPa; pulse duration about 10 musec) led to the following alterations in the cells and tissues of stage 35 embryos of Oryzias latipes ranked according to their extent: (1) In various tissues, especially in the trunk musculature, orthodox mitochondria were transformed into condensed (= low energy) mitochondria. (2) Nuclear envelopes and sarcoplasmatic reticulum of muscle fibres as well as endoplasmatic reticulum of epidermal ionocytes were often vesicularly dilated. (3) Muscle fibres in the trunk musculature began to separate from each other. Epidermal intercellular spaces were enlarged and increased in number. (4) Destruction of vessels and haematomas were observed in the circulatory system of the yolk sac. (5) Necroses up to total disintegration were found in various organs of the body cavity (intestine, liver, spleen). The less serious alterations (1 and 2) occurred in organs completely surrounded by other tissues. Major damages (4 and 5), however, affected only organs with free outer and inner surfaces, probably explained by cavitation and jet stream phenomena within the adjacent fluids.

Age Factors↗
PubMed1997

[Selenium in phenylketonuria patients. Effects of sodium selenite administration].

PATIENTS AND METHOD: 17 patients (8 female, 9 male; age 8.2 +/- 3.7 years) with phenylketonuria under phenylalanin restricted diet were investigated prior to and after 3 months of selenium substitution (sodium selenite, 115 micrograms Se/m2 BSA/d). Different parameters in blood were determined: selenium, glutathione peroxidase (Gpx) activity, thyroid hormones, blood cell count, lymphocytic antigen expression, muscle function and -enzymes, cardiac ultrasound. RESULTS: The main significant results of selenium substitution are: increased plasma-selenium, blood cell selenium, plasma-Gpx activity and left ventricular cardiac index as well as decreased plasma thyroxin, free thyroxin, reverse triiodthyronin, total cholesterol, mean erythrocyte and thrombocyte volume and lymphocytic CD2 expression. CONCLUSION: The data indicate metabolic and functional signs of selenium deficiency in patients with phenylketonuria without selenium substitution. We conclude that, despite of lacking clinical symptoms, a selenium supply in phenylketonuria patients under diet is necessary and should be performed with usefull peroral sodium selenite (115 micrograms Se/m2 BSA/d) initially, followed by a dosage between 30 and 60 micrograms Se/m2 BSA/d).

Antioxidants↗
PubMed1997

Complexity of middle cerebral artery blood flow velocity: effects of tilt and autonomic failure.

We examined spectral fractal characteristics of middle cerebral artery (MCA) mean blood flow velocity (MFV) and mean arterial blood pressure adjusted to the level of the brain (MAPbrain) during graded tilt (5 min supine, -10 degrees, 10 degrees, 30 degrees, 60 degrees, -10 degrees, supine) in eight autonomic failure patients and age- and sex-matched controls. From supine to 60 degrees, patients had a larger drop in MAPbrain (62 +/- 4.7 vs. 23 +/- 4.5 mmHg, P < 0.001; means +/- SE) and MFV (16.4 +/- 3.8 vs. 7.0 +/- 2.5 cm/s, P < 0.001) than in controls. From supine to 60 degrees, there was a trend toward a decrease in the slope of the fractal component (beta) of MFV (MFV-beta) in both the patients and the controls, but only the patients had a significant decrease in MFV-beta (supine: patient = 2.21 +/- 0.18, control = 1.99 +/- 0.60; 60 degrees: patient = 1.46 +/- 0.24, control = 1.62 +/- 0.19). The beta value of MAPbrain (MAPbrain-beta; 2.19 +/- 0.05) was not significantly different between patients and controls and did not change with tilt. High and low degrees of regulatory complexity are indicated by values of beta close to 1.0 and 2.0, respectively. The increase in fractal complexity of cerebral MFV in the patients with tilt suggests an increase in the degree of autoregulation in the patients. This may be related to the drop in MAPbrain. The different response of MFV-beta compared with that of MAPbrain-beta also indicates that MFV-beta is related to the regulation of cerebral vascular resistance and not systemic blood pressure.

Adult↗
PubMed1997

Cerebrovascular and cardiovascular responses to graded tilt in patients with autonomic failure.

BACKGROUND AND PURPOSE: Patients with autonomic nervous system failure often experience symptoms of orthostatic intolerance while standing. It is not known whether these episodes are caused primarily by a reduced ability to regulate arterial blood pressure or whether changes in cerebral autoregulation may also be implicated. METHODS: Eleven patients and eight healthy age- and sex-matched control subjects were studied during a graded-tilt protocol. Changes in their steady state middle cerebral artery mean flow velocities (MFV), measured by transcranial Doppler, brain-level mean arterial blood pressures (MABPbrain), and the relationship between the two were assessed. RESULTS: Significant differences between patients and control subjects (P < .05) were found in both their MFV and MABPbrain responses to tilt. Patients' MFV dropped from 60 +/- 10.2 cm/s in the supine position to 44 +/- 14.0 cm/s at 60 degrees head-up tilt, whereas MABPbrain fell from 109 +/- 11.7 to 42 +/- 16.9 mm Hg. By comparison, controls' MFV dropped from 54 +/- 7.8 cm/s supine to 51 +/- 8.8 cm/s at 60 degrees, whereas MABPbrain went from 90 +/- 11.2 to 67 +/- 8.2 mm Hg. Linear regression showed no significant difference in the MFV-MABPbrain relationship between patients and control subjects, with slopes of 0.228 +/- 0.09 cm.s-1.mm Hg-1 for patients and 0.136 +/- 0.16 cm.s-1.mm Hg-1 for control subjects. CONCLUSIONS: The present study found significant differences between patients and control subjects in their MFV and MABPbrain responses to tilt but no difference in the autoregulatory MFV-MABPbrain relationship. These results suggest that patients' decreased orthostatic tolerance may primarily be the result of impaired blood pressure regulation rather than a deficiency in cerebral autoregulation.

Adult↗
PubMed1997

Transfer function analysis of cerebral autoregulation dynamics in autonomic failure patients.

BACKGROUND AND PURPOSE: Autonomic nervous system diseases affect systemic blood pressure regulation. Patients with autonomic nervous system diseases have consistently larger drops in blood pressure associated with standing than the normal population. Autonomic dysfunction and/or these changes in blood pressure may affect dynamic cerebral autoregulation. METHODS: Heart rate, mean blood flow velocity (MBFV) of the middle cerebral artery via transcranial Doppler ultrasound, mean arterial blood pressure adjusted to brain level (MABPbrain) via Finapres, and end tidal CO2 were measured continuously during graded tilt (after 5 minutes in supine position as baseline, -10 degrees, +10 degrees, +30 degrees, +60 degrees, -10 degrees, and supine recovery) in autonomic failure patients and their age- and sex-matched control subjects. The dynamic response of MBFV to spontaneous variations in MABPbrain was investigated by cross-spectral analysis. The transfer gain and phase relationships between MBFV and MABPbrain were determined from the final 256 beats of each 5-minute-tilt segment. The transfer gain was normalized to mean MABPbrain and MBFV and then converted to decibels (dB). RESULTS: MBFV variation (0.03 to 0.14 Hz) preceded MABPbrain by similar phase angles in patients and control subjects and in all tilt conditions (patients: 31 +/- 5 degrees; control subjects: 30 +/- 5 degrees; mean +/- SEM). Patients had a higher supine gain than control subjects (P < .05). Both patients and control subjects showed a significant decrease in gain with tilt and by 60 degrees the patients were not different from the control subjects (supine to 60 degrees: patients = 5.23 +/- 0.77 to -1.65 +/- 0.89 dB; control subjects = 1.74 +/- 0.82 to -1.80 +/- 0.62 dB). CONCLUSIONS: These data indicate an altered, yet present, autoregulatory response with autonomic failure.

Autonomic Nervous System Diseases↗
PubMed1995

Simultaneous cerebrovascular and cardiovascular responses during presyncope.

BACKGROUND AND PURPOSE: Presyncope, characterized by symptoms and signs indicative of imminent syncope, can be aborted in many situations before loss of consciousness occurs. The plasticity of cerebral autoregulation in healthy humans and its behavior during this syncopal prodrome are unclear, although systemic hemodynamic instability has been suggested as a key factor in the precipitation of syncope. Using lower body negative pressure (LBNP) to simulate central hypovolemia, we previously observed falling mean flow velocities (MFVs) with maintained mean arterial blood pressure (MABP). These findings, and recent reports suggesting increased vascular tone within the cerebral vasculature at presyncope, cannot be explained by the classic static cerebral autoregulation curve; neither can they be totally explained by a recent suggestion of a rightward shift in this curve. METHODS: Four male and five female healthy volunteers were exposed to presyncopal LBNP to evaluate their cerebrovascular and cardiovascular responses by use of continuous acquisition of MFV from the right middle cerebral artery with transcranial Doppler sonography, MABP (Finapres), and heart rate (ECG). RESULTS: At presyncope, MFV dropped on average by 27.3 +/- 14% of its baseline value (P < .05), while MABP remained at 2.0 +/- 27% above its baseline level. Estimated cerebrovascular resistance increased during LBNP. The percentage change from baseline to presyncope in MFV and MABP revealed consistent decreases in MFV before MABP. CONCLUSIONS: Increased estimated cerebrovascular resistance, falling MFV, and constant MABP are evidence of an increase in cerebral vascular tone with falling flow, suggesting a downward shift in the cerebral autoregulation curve. Cerebral vessels may have a differential sensitivity to sympathetic drive or more than one type of sympathetic innervation. Future work to induce dynamic changes in MABP during LBNP may help in assessing the plasticity of the cerebral autoregulation mechanism.

Adolescent↗
PubMed1994

Simultaneous transcranial Doppler and arterial blood pressure response to lower body negative pressure.

Microgravity induces fluid shifts which can alter the cardiovascular responses of astronauts both during space flight and on return to Earth. The decrease in orthostatic tolerance in astronauts returning from a weightless environment can be modelled in ground-based studies using lower body negative pressure (LBNP). This study examined the physiological changes induced by LBNP and determined a reliable method of predicting the onset of presyncope to enable evaluation of countermeasures for loss of orthostatic tolerance, such as glycerol-induced hyperhydration. Six healthy male subjects, aged 18 to 45 years, were each subjected to two LBNP tests, with or without glycerol ingestion. Continuous, non-invasive measurements of middle cerebral artery blood flow velocities (CBF) by transcranial Doppler, arterial blood pressure (Finapres ABP), ECG and LBNP box pressures were recorded during each test. Negative pressure was increased in three minute intervals until symptoms of presyncope were observed. An increase in heart rate (HR), a relatively constant mean ABP and a steady decline in mean CBF were consistently observed as the box pressure was decreased. The continuous on-line measurements clearly showed consistent dynamic changes in both CBF and ABP waveforms in response to changes in LBNP. At the onset of presyncope, sudden drops in mean ABP, HR and mean CBF were typically noted, the latter providing the earliest indication of presyncope. The time required to re-establish original baseline values of CBF and ABP after release of box pressure varied widely from six to over ten minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Nosocomial infections in the pediatric intensive care unit.

Pediatric intensive care units have contributed considerably to the management of children with severe diseases and life-threatening conditions. The use of mechanical ventilation, invasive monitoring, and indwelling catheters increase the risk for nosocomial infection. Improving infection control practices and surveillance can significantly reduce the incidence of nosocomial infections.

Bacteremia↗