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Biomedical subjects

G Lister

Publications and source records attributed to G Lister.

At least 19 recordsLinked to original sources
PubMed2001

Cardiorespiratory events recorded on home monitors: Comparison of healthy infants with those at increased risk for SIDS.

CONTEXT: Home monitors designed to identify cardiorespiratory events are frequently used in infants at increased risk for sudden infant death syndrome (SIDS), but the efficacy of such devices for this use is unproven. OBJECTIVE: To test the hypothesis that preterm infants, siblings of infants who died of SIDS, and infants who have experienced an idiopathic, apparent life-threatening event have a greater risk of cardiorespiratory events than healthy term infants. DESIGN: Longitudinal cohort study conducted from May 1994 through February 1998. SETTING: Five metropolitan medical centers in the United States. PARTICIPANTS: A total of 1079 infants (classified as healthy term infants and 6 groups of those at risk for SIDS) who, during the first 6 months after birth, were observed with home cardiorespiratory monitors using respiratory inductance plethysmography to detect apnea and obstructed breathing. MAIN OUTCOME MEASURES: Occurrence of cardiorespiratory events that exceeded predefined conventional and extreme thresholds as recorded by the monitors. RESULTS: During 718 358 hours of home monitoring, 6993 events exceeding conventional alarm thresholds occurred in 445 infants (41%). Of these, 653 were extreme events in 116 infants (10%), and of those events with apnea, 70% included at least 3 obstructed breaths. The frequency of at least 1 extreme event was similar in term infants in all groups, but preterm infants were at increased risk of extreme events until 43 weeks' postconceptional age. CONCLUSIONS: In this study, conventional events are quite common, even in healthy term infants. Extreme events were common only in preterm infants, and their timing suggests that they are not likely to be immediate precursors to SIDS. The high frequency of obstructed breathing in study participants would likely preclude detection of many events by conventional techniques. These data should be important for designing future monitors and determining if an infant is likely to be at risk for a cardiorespiratory event.

Airway Obstruction↗
PubMed2000

Assessment of muscle flap sensibility by evoked potentials in the rat.

This study investigated whether the sensory-to-motor reinervation of the muscle flap provides a better sensory recovery of an overlying skin graft. Fifty-four animals were studied in three groups of 18 rats each: group I (control): 1 cm of the gastrocnemius muscle motor nerve was excised and no repair was performed; group II (motor-to-motor repair): the motor nerve of the gastrocnemius flap was transected and repaired; group III (sensory-to-motor repair): the motor nerve of the gastrocnemius muscle and sural nerve were transected and their distal and proximal ends, respectively, were repaired. At follow-up periods of 6, 12, and 24 weeks, evaluation of hair growth, muscle atrophy, and sensory evoked potentials was performed. Somatosensory evoked potentials (SSEP) at 6 weeks in the sensory-to-motor repair (group III) revealed a significant (P < 0. 05) increase (104.4% +/- 22.9) in the relative response of peak-to-peak potentials when compared with group I (46.6% +/- 19) and group II (51.8% +/- 14.0). Muscle flap stimulation was most prominent at 6 weeks in sensory-to-motor reinvervated flaps (group III 133.1% +/- 25.4; group I 84.9% +/- 20.2). In this study, sensory-to-motor nerve repair significantly improved the sensibility of skin flaps at 6 weeks. Denervated flaps presented with 3 months of sensory recovery delay.

Animals↗
PubMed2000

Robotic assistance in microsurgery.

The purpose of this study was to introduce a new robotic system for microsurgical procedures of the eye, ear, brain, face, and hand. The design and main features of the Robot Assisted MicroSurgery (RAMS) work station are described. In addition, compatibility with the operating-room table is assessed. The engineering components of the RAMS work station consist of a laptop computer, a joystick, a mouse, slave robot, VME and amplifier chassis, and safety control box. The mechanical part of the RAMS, the slave robot, is designed to simulate movements of the human upper extremity, which has five joints and six degrees of motion. The robot has a zero backlash in five joints, and can sustain full extension of loads over three pounds. The arm measures 2.5 cm in diameter, and it is 34.6 cm long from its base to its tip. The arm and its base weigh 2.5 kg. Motors and encoders on the robot are easily removable, allowing for the arm to be sterilized in an autoclave. Assessment of robotic positioning, time for setup, relative precision, and possible problems in the operating field are compared with human-assisted microsurgical procedures. Robotic arm positioning on the operating-room table differs for each type of procedure. For those involving the hand and upper extremity, the robotic arm base occupies 35 percent of the operating table; this is only 10 to 15 percent for human-assisted procedures. The setup time for robot-assisted procedures is longer than for human-assisted surgery. However, microsurgical manipulations with the RAMS are more rapid than the surgeon's motions. Therefore, depending on the type of procedure, the total operating time is comparable to human-assisted procedures. The movement of the RAMS was found to be more precise, in attempting to perform vascular and neural anastomoses. The authors conclude that concurrent use of the remote-controlled RAMS as a microsurgical assistant is applicable in microsurgery, with the advantages of greater precision and more rapid microsurgical manipulation. However, the long-term cost effectiveness of using this system as an assistant in microsurgery warrants further investigation.

Anastomosis, Surgical↗
PubMed2000

Comparison of apnea identified by respiratory inductance plethysmography with that detected by end-tidal CO(2) or thermistor. The CHIME Study Group.

As part of the Collaborative Home Infant Monitoring Evaluation (CHIME) we compared apnea identified by a customized home monitor using respiratory inductance plethysmography (RIP) with simultaneously recorded polysomnography-acquired nasal end-tidal CO(2) (PET(CO(2))) and nasal/oral thermistor in 422 infants during overnight laboratory recordings to determine concordance between techniques, sources of disagreement, and capacity of RIP to detect obstructed breaths within an apnea. Among 233 episodes of apnea identified by at least one method as >/= 16 s, 120 were observed by the CHIME monitor, 219 by PET(CO(2)), and 163 by thermistor. The positive predictive value of the CHIME-identified apnea was 89.2% (95% CI 83, 95) and 73% (95% CI 65, 81) for PET(CO(2)) and thermistor, respectively. However, the sensitivity of the CHIME monitor in identifying events detected by the other methods was only approximately 50%. Among 87 apnea events identified by all three techniques, no two methods showed high agreement in measurement of apnea duration: RIP and PET(CO(2)) (ICC = 0.54), RIP and thermistor (ICC = 0.13), PET(CO(2)) and nasal thermistor (ICC = 0.41). Among the 179 breaths identified by RIP as obstructed, 79.9% were judged to be obstructed on the PET(CO(2)) and 80.4% were judged to be obstructed on the thermistor channel. Among 238 breaths identified on PET(CO(2)) as obstructed, 54.2% were determined to be obstructed by RIP. Among 204 breaths identified on thermistor as obstructed, 55. 4% were determined to be obstructed by RIP. Reasons for discrepancies in apnea detection among channels included body movement, partial airway obstruction, and obstructed breaths. Despite these limitations the CHIME monitor provides an opportunity to record physiological data previously unavailable in the home.

Apnea↗
PubMed1999

Longitudinal assessment of hemoglobin oxygen saturation in healthy infants during the first 6 months of age. Collaborative Home Infant Monitoring Evaluation (CHIME) Study Group.

Limitations in home monitoring technology have precluded longitudinal studies of hemoglobin oxygen saturation during unperturbed sleep. The memory monitor used in the Collaborative Home Infant Monitoring Evaluation addresses these limitations. We studied 64 healthy term infants at 2 to 25 weeks of age. We analyzed hemoglobin oxygen saturation by pulse oximetry (SpO(2)), respiratory inductance plethysmography, heart rate, and sleep position during 35, 127 epochs automatically recorded during the first 3 minutes of each hour. For each epoch baseline SpO(2) was determined during >/=10 s of quiet breathing. Acute decreases of at least 10 saturation points and <90% for >/=5 s were identified, and the lowest SpO(2) was noted. The median baseline SpO(2) was 97.9% and did not change with age or sleep position. The baseline SpO(2) was <90% in at least 1 epoch in 59% of infants and in 0.51% of all epochs. Acute decreases in SpO(2) occurred in 59% of infants; among these, the median number of episodes was 4. The median lowest SpO(2) during an acute decrease was 83% (10th, 90th percentiles 78%, 87%); 79% of acute decreases were associated with periodic breathing, and >/=16% were associated with isolated apnea. With the use of multivariate analyses, the odds of having an acute decrease increased as the number of epochs with periodic breathing increased, and they lessened significantly with age. We conclude that healthy infants generally have baseline SpO(2) levels >95%. The transient acute decreases are correlated with younger age, periodic breathing, and apnea and appear to be part of normal breathing and oxygenation behavior.

Female↗
PubMed1998

Effects of rate and amplitude of breathing on respiratory system elastance and resistance during growth of healthy children.

Intrinsic properties of lung and chest wall tissues can lead to breathing rate (frequency [f]) and amplitude (tidal volume [VT]) dependence of respiratory system resistance (R) and elastance (E). To explore these dependencies on R and E within physiological limits of tidal volume and breathing frequencies during early childhood. we measured airway opening pressure (Pao) and flow (V'ao) in 15 anesthetized, paralyzed, intubated, and mechanically ventilated healthy children (age 1 day to 72 months; weight 2.5-21 kg) at multiple combinations of VT (6, 10, and 14 mL/kg) and frequency (10, 20, and 30 breaths/min). In each instance, R and E were estimated by multiple linear regression applied to the tracheal pressure, flow, and volume (V), assuming a simple series R-E model. R decreased substantially with increasing frequency and weight (Wt), but was unaffected by changes in VT (R = 764Wt(-0.91) x f(-0.57)). E decreased sharply with increasing Wt, was lower at higher VT, and was slightly, yet significantly, increased at higher frequency (E = 2,905Wt(-1.38) x VT(-0.18) x f(0.11)). Such frequency dependence of R and E is consistent with stress adaptive, or viscoelastic, properties of respiratory tissues. The small V dependence of E is similar to that observed in other species under healthy conditions and presumably reflects the combined nonlinear pressure-volume relationships of the healthy parenchymal and chest wall tissues. Lack of VT dependence of R at high inspiratory flow rates suggests that turbulent flows are either not an important form of energy dissipation in the lower airways of children or they are counterbalanced by a decrease in tissue damping at high VT. The above regression models represent the first attempt to quantify simultaneously the separate effects of lung growth as well as rate and amplitude of breathing on R and E. Similar equations based on a larger sample of healthy subjects can provide normative R and E values for comparison with mechanically ventilated children with lung disease.

Airway Resistance↗
PubMed1998

Advantages of sharp adventitial dissection for microvascular anastomoses.

Adventitia is usually removed from arteries to simplify microvascular anastomoses. Some surgeons peel the adventitia away bluntly whereas others trim the adventitia sharply with scissors. We used a rat cremaster flap for intravital microscopy to evaluate these two techniques. Animals with unmanipulated vessels, without anastomosis or adventitial removal, served as controls. Fifty-four rats were studied in three groups of 18 rats. Functional capillary density, red blood cell velocity, diameter of the flap's feeding artery (A1), microthrombi formation, and neutrophilic activity were studied for 5 hours following anastomosis, and 24 and 72 hours later. Histological changes in blunt and sharply prepared arteries were compared with control vessels. After blunt preparation, capillary perfusion was reduced to 61% of control values (p < 0.05) and A1 diameter was reduced to 77% of control values (p < 0.05). Capillary perfusion and A1 diameter were unchanged in sharply prepared arteries. Architectural changes in the vessel wall were more profound, and neutrophilic activity was increased in bluntly prepared arteries. In this study, sharp preparation of small arteries was beneficial compared with blunt preparation.

Anastomosis, Surgical↗
PubMed1998

Microcirculatory hemodynamics during the acute phase of free vascularized muscle allograft rejection.

This study investigated the microcirculatory pattern during acute rejection of a vascularized free muscle graft. Using a new rat cremaster muscle free flap model, isograft transplantation was done between genetically identical Lewis rats (N = 23) and allograft transplantation across a major histocompatibility barrier (Lewis Brown Norway [RT-11 + n] to Lewis [RT-11] rats; N = 24). At days 1, 3, 5, and 7 posttransplantation, microcirculatory measurements were taken of vessel diameter, red blood cell velocity, endothelial edema index, leukocytic-endothelial interaction (rolling, adhering, and transmigrating leukocytes), and capillary perfusion. In the allografts at 5 days the lumen obstruction was 27% greater (p < 0.05) than onset. The number of perfused capillaries decreased by 36% compared with isografts at day 5 (p < 0.05). The number of adhering leukocytes increased significantly in allografts both at day 1 (71%; p < 0.05) and at day 3 (77%; p < 0.05). At day 3, transmigrating leukocytes rose significantly (p < 0.05). Allograft histology showed myocytic destruction and lymphocytic infiltration at day 5. Our results suggest that the microcirculatory signs of acute muscle allograft rejection occurred 24 hours after transplantation, and preceded histological signs of rejection. The critical time for microvascular survival of muscle allografts was 3 days. This procedure allows us to distinguish events related to transplantation trauma from rejection phenomena.

Acute Disease↗
PubMed1998

Agreement among raters in assessment of physiologic waveforms recorded by a cardiorespiratory monitor for home use. Collaborative Home Infant Monitoring Evaluation (CHIME) Study Group.

There are numerous reports of cardiorespiratory patterns in infants on home monitors, but no data to determine whether "experts" agree on the description of these patterns. Therefore, we evaluated agreement among four experienced investigators and five trained technicians who assessed independently the same sample of physiologic waveforms recorded from infants enrolled in a multicenter study. The monitor used respiratory inductance plethysmography and recorded waveforms for apnea > or = 16 s or a heart rate < 80 beats/min for > or = 5 s. The investigators and technicians initially assessed 88 waveforms. After additional training, the technicians assessed another 113 additional waveforms. In categorizing waveforms as apnea present or absent, agreement among technicians improved considerably with additional training (kappa 0.65 to 0.85). For categorizing waveforms as having bradycardia present versus absent, the trends were the same. Agreement in measurement of apnea duration also improved considerably with additional training (intraclass correlation 0.33-0.83). Agreement in measurement of bradycardia duration was consistently excellent (intraclass correlation 0.86-0.99). Total agreement was achieved among technicians with additional training for measurement of the lowest heart rate during a bradycardia. When classifying apnea as including > or = 1, > or = 2, > or = 3, or > or = 4 out-of-phase breaths, agreement was initially low, but after additional training it improved, especially in categorization of apneas with > or = 3 or > or = 4 out-of-phase breaths (kappa 0.67 and 0.94, respectively). Although researchers and clinicians commonly describe events based on cardiorespiratory recordings, agreement amongst experienced individuals may be poor, which can confound interpretation. With clear guidelines and sufficient training raters can attain a high level of agreement in describing cardiorespiratory events.

Female↗
PubMed1997

Venous and arterial reflex responses to positive-pressure breathing and lower body negative pressure.

We examined the relative importance of arteriolar and venous reflex responses during reductions in cardiac output provoked by conditions that increase [positive end-expiratory pressure (PEEP)] or decrease [lower body negative pressure (LBNP)] peripheral venous filling. Five healthy subjects were exposed to PEEP (10, 15, 20, and 25 cmH2O) and LBNP (-10, -15, -20, and -25 mmHg) to induce progressive but comparable reductions in right atrial transmural pressure (control to minimum): from 5.9 +/- 0.4 to 1.8 +/- 0.7 and from 6.5 +/- 0.6 to 2.0 +/- 0.2 mmHg with PEEP and LBNP, respectively. Cardiac output (impedance cardiography) fell less during PEEP than during LBNP (from 3.64 +/- 0.21 to 2.81 +/- 0.21 and from 3.39 +/- 0.21 to 2.14 +/- 0.24 l.min-1.m-2 with PEEP and LBNP, respectively), and mean arterial pressure increased. We observed sustained increases in forearm vascular resistance (i.e., forearm blood flow by venous occlusion plethysmography) and systemic vascular resistance that were greater during LBNP: from 19.7 +/- 2.91 to 27.97 +/- 5.46 and from 20.56 +/- 2.48 to 50.25 +/- 5.86 mmHg.ml-1.100 ml tissue-1.min (P < 0.05) during PEEP and LBNP, respectively. Venomotor responses (venous pressure in the hemodynamically isolated limb) were always transient, significant only with the greatest reduction in right atrial transmural pressure, and were similar for LBNP and PEEP. Thus arteriolar rather than venous responses are predominant in blood volume mobilization from skin and muscle, and venoconstriction is not intensified with venous engorgement during PEEP.

Adult↗
PubMed1997

Hepatic and gastrointestinal oxygen and lactate metabolism during low cardiac output in lambs.

We previously observed young lambs to be more tolerant of hypoxia; compared with older lambs, they accumulate lactate at a slower rate during comparable reduction in cardiac output, and have a greater percent decrease in cardiac output before onset of systemic lactate accumulation. To determine the mechanism of lactic acidosis and the cause for this "tolerance," we reduced cardiac output progressively in seven chronically catheterized conscious lambs (16.4 + 5.1 d) and measured hepatic and gastrointestinal (GI) blood flow (radioactive microspheres) and delivery, uptake, and extraction of lactate and O2. Hepatic O2 consumption declined proportionately below a critical hepatic O2 delivery (approximately 2 mL O2/min/kg), corresponding to the systemic O2 delivery associated with the onset of systemic lactate accumulation. As hepatic O2 delivery decreased below the critical value, there was initially net hepatic lactate uptake and then a change to net production when the O2 delivery decreased below approximately 1 mL O2/min kg. The GI tract had net lactate production at rest, but surprisingly switched to lactate uptake as cardiac output decreased. The mechanism of lactic acidosis was failure of hepatic lactate uptake to increase despite increased hepatic lactate delivery, as reported in adults subjects. However, in contrast, there was "true" hepatic dysfunction and lactate production only at the lowest levels of cardiac output, after onset of systemic lactate accumulation. Moreover, we speculate that tolerance of young lambs to hypoxia is at least due to two factors: 1) hepatic lactate uptake is maintained beyond the "critical" O2 delivery and fall in hepatic O2 consumption, and 2) there is a switch to lactate uptake by the GI tract serving to buffer the lactate.

Acidosis, Lactic↗
PubMed1997

Infant polysomnography: reliability. Collaborative Home Infant Monitoring Evaluation (CHIME) Steering Committee.

Infant polysomnography (IPSG) is an increasingly important procedure for studying infants with sleep and breathing disorders. Since analyses of these IPSG data are subjective, an equally important issue is the reliability or strength of agreement among scorers (especially among experienced clinicians) of sleep parameters (SP) and sleep states (SS). One basic issue of this problem was examined by proposing and testing the hypothesis that infant SP and SS ratings can be reliably scored at substantial levels of agreement, that is, kappa (kappa) > or = 0.61. In light of the importance of IPSG reliability in the collaborative home infant monitoring evaluation (CHIME) study, a reliability training and evaluation process was developed and implemented. The bases for training on SP and SS scoring were CHIME criteria that were modifications and supplements to Anders, Emde, and Parmelee (10). The kappa statistic was adopted as the method for evaluating reliability between and among scorers. Scorers were three experienced investigators and four trainees. Inter- and intrarater reliabilities for SP codes and SSs were calculated for 408 randomly selected 30-second epochs of nocturnal IPSG recorded at five CHIME clinical sites from healthy full term (n = 5), preterm (n = 4), apnea of infancy (n = 2), and siblings of the sudden infant death syndrome (SIDS) (n = 4) enrolled subjects. Infant PSG data set 1 was scored by both experienced investigators and trained scorers and was used to assess initial interrater reliability. Infant PSG data set 2 was scored twice by the trained scorers and was used to reassess inter-rater reliability and to assess intrarater reliability. The kappa s for SS ranged from 0.45 to 0.58 for data set 1 and represented a moderate level of agreement. Therefore, rater disagreements were reviewed, and the scoring criteria were modified to clarify ambiguities. The kappa s and confidence intervals (CIs) computed for data set 2 yielded substantial inter-rater and intrarater agreements for the four trained scorers; for SS, the kappa = 0.68 and for SP the kappa s ranged from 0.62 to 0.76. Acceptance of the hypothesis supports the conclusion that the IPSG is a reliable source of clinical and research data when supported by significant kappa s and CIs. Reliability can be maximized with strictly detailed scoring guidelines and training.

Humans↗
PubMed1996

Randomized outcome trial of human milk fortification and developmental outcome in preterm infants.

Despite potential benefits, human milk may fail to meet preterm infants' nutrient requirements. We tested the hypothesis that fortified breast milk, fed alone or with preterm formula, would improve neurodevelopment and growth at 18-mo follow-up without adverse short-term clinical or biochemical consequences. Two hundred seventy-five preterm infants from two medical centers (birth weight < 1850 g; mean gestation 29.8 +/- 2.7 wk) whose mothers chose to provide breast milk were randomly assigned to receive for a mean of 39 d a multinutrient fortifier or control supplement containing phosphate and vitamins. Breast milk comprised 47.6% and 46.4% of enteral intake in fortified and control groups, respectively; preterm formula supplements were used when insufficient breast milk was available. Overall, there were no significant growth advantages with fortification; although, when breast milk exceeded 50% of intake, fortification promoted faster weight gain (an advantage of 1.6 g.kg-1.d-1; 95% CI: 0.1, 3.1; P < 0.05). Compared with control infants, the fortified group showed 1) higher plasma urea from week 2 (P = 0.04), 2) higher plasma calcium (mean 2.34 +/- 0.01 compared with 2.27 +/- 0.02 mmol/L; P = 0.003), 3) a greater rise in alkaline phosphatase by week 6 (P = 0.04), 4) more clinical infections (suspected plus proven; 43% compared with 31%, P = 0.04), 5) a nonsignificantly increased incidence of necrotizing enterocolitis (5.8% compared with 2.2%, P = 0.12), and 6) higher white cell and platelet counts. Developmental scores at 18 mo were slightly but not significantly higher in the fortified group. This study confirmed that breast milk fortifiers can improve short-term growth (when breast milk intakes are high); but beneficial effects on long-term development remained unproven. Future research is required to evaluate potential adverse consequences and explore more optimal fortification strategies.

Acid-Base Equilibrium↗
PubMed1995

Hemodynamic variations between end-to-side and end-organ flap systems.

This study aimed to evaluate microcirculatory differences between anatomic arrangements of the intact side flow and the end flow systems. The cremaster muscle tube-flap model was employed. Fifty male Sprague-Dawley rats were studied in two experimental groups of 25 animals each. The end-to-side vascular system was compared with end-organ flaps during acute (6 hours) and chronic (1, 3, 7, and 14 days) observation periods. Standard microcirculatory measurements were taken in all groups including vessel diameters, red blood cell velocities, and capillary densities. End-to-side flaps presented with stable flow hemodynamics over a 14-day period. In end-organ flaps we found acute venous congestion, alterations in arterial and venous flow velocities, and a significant decline in capillary perfusion.

Abdominal Muscles↗
PubMed1995

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Cost Control↗