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Biomedical subjects

M J Tobin

Publications and source records attributed to M J Tobin.

At least 73 records · Page 4Linked to original sources
PubMed1997

Effect of elastic loading on variational activity of breathing.

To examine the effect of elastic loading on variational activity of breathing, we studied 11 healthy subjects breathing at rest and with inspiratory elastic loads of 9 and 18 cm H2O/L, applied randomly for 1 h each. Compared with rest, a load of 18 cm H2O/L decreased gross variability, quantitated as standard deviation, of tidal volume (VT) and expiratory time (TE) (p < 0.01 in both instances) but increased that of inspiratory time (TI) (p < 0.03). The autocorrelation coefficients at a lag of 1 breath for each breath component were not altered by elastic loading, although the number of breath lags with significant serial correlations for TE tended to increase with a load of 18 cm H2O/L (p = 0.08). A load of 18 cm H2O/L decreased only the fraction of variational activity of VT and TE due to uncorrelated, random behavior (white noise), while it increased that fraction for TI (p < 0.05 in each instance); the correlated and oscillatory fractions did not change. Uncorrelated random behavior constituted > 87% of the variance of each breath component, correlated behavior represented 3 to 11%, and oscillatory behavior represented < 1.5% during both rest and loaded breathing. Elastic loading changed the gross variability of each primary breath component by altering the random fraction of variational activity; it had no significant effect on the structured, correlated fraction. We speculate that the observed changes in variational activity may reflect an attempt by the controller to compensate for the increased load while simultaneously minimizing load-induced dyspnea.

Adult↗
PubMed1997

Comparison of assisted ventilator modes on triggering, patient effort, and dyspnea.

In 11 ventilator-dependent patients, we undertook a head-to-head comparison of patient-ventilator interaction during four ventilator modes: assist-control ventilation (ACV), intermittent mandatory ventilation (IMV), pressure support (PS), and a combination of IMV and PS. Progressive increases in IMV rate and PS level each decreased inspiratory pressure-time product (PTP) (p < 0.0001). These reductions in PTP were greater with PS than with IMV at lower but proportional levels of maximal assistance (p < 0.005). When PS 10 cm H2O was added to a given level of IMV, greater reductions in PTP were achieved not only during intervening (PS) breaths (p < 0.001), but also during mandatory (volume-assisted) breaths (p < 0.0005); this additional unloading during mandatory breaths was proportional to the decrease in respiratory drive (dP/dt) during intervening breaths (r = 0.67, p < 0.0001). Maximal unloading occurred with ACV, achieving more than a fivefold decrease in PTP compared with unassisted breathing. Decreases in PTP were confined to the post-trigger phase, and PTP of the post-trigger phase correlated with dP/dt (r = 0.78, p < 0.0001). Effort during the trigger phase remained constant despite marked changes in drive and intrinsic positive end-expiratory pressure (PEEPi). Ineffective triggering occurred with all modes, and wasted PTP increased with increasing levels of assistance as a result of the accompanying decrease in drive and increase in volume. Breaths preceding nontriggering efforts had shorter respiratory cycle times (p < 0.0005) and expiratory times (p < 0.0001) and higher PEEPi (p < 0.0001), indicating that neural-mechanical asynchrony resulted from inspiratory activity commencing prematurely before elastic recoil pressure had fallen to a level that could be overcome by a patient's muscular effort. Thus, increases in the level of ventilator assistance produced progressive decreases in inspiratory muscle effort and dyspnea,which were accompanied by increases in the rate of ineffective triggering.

Aged↗
PubMed1997

Effect of hyperoxic hypercapnia on variational activity of breathing.

Dysrhythmias of breathing occur in several clinical disorders, but their mechanistic basis is obscure. To understand their pathophysiology, factors responsible for the variability of breathing need to be defined. We studied the effect of hyperoxic hypercapnia (CO2) on the variational activity of breathing in 14 volunteers before and after delivering CO2 nonobstrusively via a plastic hood. Compared with air, CO2 increased the gross variability of minute ventilation (VI) and tidal volume (VT), and decreased that of inspiratory time (TI) and expiratory time (TE) (all p < 0.03). CO2 increased the autocorrelation coefficient at a lag of one breath for VI (p < 0.05), the number of consecutive breath lags having significant autocorrelation coefficients for VI and VT (both p < 0.01), and the cycle time of oscillations in VI (p = 0.03) and VT (p = 0.04). Uncorrelated random behavior constituted > or = 80% of the variance of each breath component, correlated behavior represented 9 to 20%, and oscillatory behavior represented < 1% during both air and CO2. CO2 increased the correlated behavior of volume components, which was accompanied by development of low-frequency oscillations with a cycle time consistent with central chemoreceptor activation.

Adult↗
PubMed1997

Relationship between transdiaphragmatic and mouth twitch pressures at functional residual capacity.

The clinical application of transdiaphragmatic twitch pressure (Pdi,tw) response to phrenic nerve stimulation has been hindered by the requirement for placement of oesophageal and gastric balloons. Investigators have reported that mouth twitch pressure (Pmo,tw) estimates Pdi,tw accurately at lung volumes above and below functional residual capacity (FRC). However, it is not known whether Pmo,tw estimates Pdi,tw accurately when stimulation is performed at FRC during relaxed conditions. The aim of this study was to develop a simple method whereby measurements of Pmo could be used to predict oesophageal twitch pressure (Poes,tw) and possibly Pdi,tw at FRC. The study was performed in 11 healthy volunteers during phrenic nerve stimulation. At FRC, 9 of the 11 subjects showed a poor correlation between Pmo,tw and Poes,tw, and between Pmo,tw and Pdi,tw, probably due to varying degrees of glottic closure. Stimulations performed while subjects maintained an inspiratory flow of approximately 50 mL x s(-1), or at the point of reattaining FRC during an inspiration preceded by a limited exhalation, produced good correlations between Pmo,tw and Poes,tw (r=0.97 in both instances) and Pmo,tw and Pdi,tw (r=0.96 and r=0.95, respectively), with a steep slope. The respective slopes for the Pmo,tw Poes,tw relationship were 0.88 and 0.94, and for the Pmo,tw Pdi,tw relationship, 0.59 and 0.54. Unfortunately, these manoeuvres produced a significant increase in transpulmonary pressure (3.6+/-0.6 (SE) and 5.6+/-1.4 cmH2O, respectively), suggesting change in diaphragmatic length. Stimulations delivered while subjects performed an inspiratory effort or during exhalation against a high resistance preceded by a limited inhalation could not be used to predict Poes,tw and Pdi,tw from Pmo,tw. In conclusion, although transdiaphragmatic and oesophageal twitch pressure could be predicted from mouth twitch pressure during some inspiratory manoeuvres mouth twitch pressure was not reliable for the prediction of the oesophageal and transdiaphragmatic twitch pressure at functional residual capacity during relaxed conditions in healthy volunteers.

Adult↗
PubMed1996

Bone lead levels and delinquent behavior.

OBJECTIVE: To evaluate the association between body lead burden and social adjustment. DESIGN: Retrospective cohort study. SETTING: Public school community. PARTICIPANTS: From a population of 850 boys in the first grade at public schools, 503 were selected on the basis of a risk scale for antisocial behavior. All of the 850 boys who scored in the upper 30th percentile of the distribution on a self-reported antisocial behavior scale were matched with an equal number drawn by lot from the lower 70% of the distribution. From this sample, 301 students accepted the invitation to participate. EXPOSURE MEASURE: K x-ray fluorescence spectroscopy of tibia at subjects' age of 12 years. MAIN OUTCOME MEASURES: Child Behavior Checklist (CBCL), teachers' and parents' reports, and subjects' self-report of antisocial behavior and delinquency at 7 and 11 years of age. RESULTS: Subjects, teachers, and parents were blind to the bone lead measurements. At 7 years of age, borderline associations between teachers' aggression, delinquency, and externalizing scores and lead levels were observed after adjustment for covariates. At 11 years of age, parents reported a significant lead-related association with the following CBCL cluster scores: somatic complaints and delinquent, aggressive, internalizing, and externalizing behavior. Teachers reported significant associations of lead with somatic complaints, anxious/depressed behavior, social problems, attention problems, and delinquent, aggressive, internalizing, and externalizing behavior. High-lead subjects reported higher scores in subjects' self-reports of delinquency at 11 years. High-lead subjects were more likely to obtain worse scores on all items of the CBCL during the 4-year period of observation. High bone lead levels were associated with an increased risk of exceeding the clinical score (T > 70) for attention, aggression, and delinquency. CONCLUSION: Lead exposure is associated with increased risk for antisocial and delinquent behavior, and the effect follows a developmental course.

Analysis of Variance↗
PubMed1996

Monitoring during mechanical ventilation.

Approximately half of the patients admitted to an ICU are admitted for the purposes of monitoring rather than interventional therapy. In the last decade, significant technologic advances have enhanced monitoring capacities, and the understanding of the pathophysiology of respiratory failure has improved pari passu, allowing clinicians to employ monitors in a more intelligent manner. This article deals with new developments in arterial blood gas monitoring, pulse oximetry, capnometry, and monitoring of neuromuscular function and pulmonary mechanics, emphasizing issues most relevant to mechanical ventilation.

Blood Gas Analysis↗
PubMed1996

Comparison of magnetic and electrical phrenic nerve stimulation in assessment of diaphragmatic contractility.

Unlike the standard electrical approach, cervical magnetic stimulation of the phrenic nerves is less painful and achieves a constant degree of diaphragmatic recruitment, features that should enhance its applicability in a clinical setting. An unexplained phenomenon is the greater transdiaphragmatic twitch pressure (Pditw) with magnetic vs. electrical stimulation. We hypothesized that this greater Pditw is due to coactivation of extradiaphragmatic muscles. Because impedance to rib cage expansion is increased at high lung volumes and efficiency of extradiaphragmatic muscles is less than that of the diaphragm, we reasoned that the difference between electrical Pditw and magnetic Pditw would be less evident at high volumes than at end-expiratory lung volume. In human volunteers, magnetic Pditw and electrical Pditw were 37.7 +/- 1.9 (SE) and 32.3 +/- 2.2 cmH2O, respectively, at end-expiratory lung volume (P < 0.005) and 24.0 +/- 2.9 and 27.2 +/- 2.8 cmH2O, respectively, at one-half inspiratory capacity (not significant); at total lung capacity, magnetic Pditw was less than electrical Pditw (10.6 +/- 0.8 and 16.2 +/- 2.9 cmH2O, respectively; P < 0.05). Magnetic stimulation caused significant extradiaphragmatic muscle depolarization and rib cage expansion, whereas electrical stimulation caused virtually no extradiaphragmatic muscle depolarization and rib cage deflation. Despite these differences, the induction of respiratory muscle fatigue produced reductions in both electrical and magnetic Pditw values (P < 0.01), which were of similar magnitude and closely correlated (r = 0.96). In conclusion, magnetic stimulation recruits both extradiaphragmatic and diaphragmatic muscles, and it is equally as effective as electrical stimulation in detecting diaphragmatic fatigue.

Adult↗
PubMed1996

Aerosol delivery from a metered-dose inhaler during mechanical ventilation. An in vitro model.

Successful bronchodilator therapy with a metered-dose inhaler (MDI) in intubated, mechanically ventilated patients requires adequate delivery of aerosol to the lower respiratory tract. We determined the effect of ventilator mode, inspiratory flow pattern, humidity, and spontaneous respiratory effort on albuterol delivery in a model of the trachea and bronchi. The model was ventilated through an endotracheal tube during controlled mechanical ventilation (CMV), assist control (AC), pressure support (PS), and continuous positive airway pressure (CPAP), separately with a dry and humidified ventilator circuit. Delivery of albuterol administered by a MDI and spacer on filter placed at the ends of the bronchi was measured by spectrophotometry (246 nm). Under dry conditions and with a frequency of 10 breaths/min, albuterol delivery with CMV (VT, 800 ml; 30.3 +/- 3.4%), AC (VT, 800 ml; 31.9 +/- 1.3%), PS 10 cm H2O (VT, 700 ml; 28.8 +/- 4.5%), or PS 20 cm H2O (VT, 800 ml; 30.9 +/- 1.8%) was lower than that observed with simulated spontaneous breaths with CPAP (VT, 800 ml; 39.2 +/- 1.4%) (p < 0.01 for all modes). Delivery was greater under dry (28.8 to 39%) than under humidified conditions (15.9 to 20.2%) (p < 0.005 in all modes). Albuterol delivery showed a linear correlation with both inspiratory time and duty cycle (r > 0.91). Lower respiratory tract delivery of aerosol from a MDI varied from 4.9 to 39.2%. We conclude that in addition to other known factors such as dose, type of spacer, and its position the technique of administering MDIs in mechanically ventilated patients markedly influences lower respiratory tract aerosol delivery.

Aerosols↗
PubMed1996

Dose-response to bronchodilator delivered by metered-dose inhaler in ventilator-supported patients.

In nonintubated patients, metered-dose inhalers (MDIs) are accepted as the most convenient, efficient, and cost effective method of administering inhaled bronchodilators. Recent studies have demonstrated the efficacy of MDIs in ventilator-supported patients; however, the optimal dose of a bronchodilator from a MDI is unknown. We determined the response to increasing doses of albuterol administered by a MDI and cylindrical spacer to 12 mechanically ventilated patients with chronic obstructive pulmonary disease (COPD). Four, eight, and 16 puffs of albuterol were given at 15-min intervals. Rapid airway occlusion were performed before and at 5-min intervals after albuterol for 80 min. Respiratory mechanics were also measured for 60 min in another group of seven patients with COPD who received four puffs of albuterol. Significant decrease in airways resistance occurred after administration of albuterol (p < 0.001). The decrease in airway resistance with four puffs of albuterol was comparable to that observed with cumulative doses of 12 puffs (p = 0.12) and 28 puffs (p = 0.25). Heart rate increased significantly (p < 0.01) after a cumulative dose of 28 puffs. The decrease in airway resistance was sustained for 60 min in the group that received only four puffs of albuterol (p < 0.003). In conclusion, four puffs of albuterol given by a MDI and spacer provided the best combination of bronchodilator effect and safety in stable mechanically ventilated patients with COPD.

Administration, Inhalation↗
PubMed1996

Serum albuterol levels in mechanically ventilated patients and healthy subjects after metered-dose inhaler administration.

In mechanically ventilated patients, systemic blood levels of inhaled drugs reflect absorption from the lower respiratory tract alone since, unlike nonintubated patients, oropharyngeal and gastrointestinal absorption cannot occur. To determine the efficiency of aerosol administration by a metered-dose inhaler (MDI), we measured serum albuterol levels after administration by a MDI and spacer to nine mechanically ventilated patients (10 puffs) and to 10 healthy subjects (six puffs). Serum albuterol levels (+/- SEM) quantitated by high-performance liquid chromatography and electrochemical detection were: 0.09 +/- 0.04 mg/ml/puff at baseline, 0.66 +/- 0.10 at 5 min, 0.98 +/- 0.10 at 10 min, 0.56 +/- 0.08 at 15 min, and 0.37 +/- 0.03 at 30 min in mechanically ventilated patients versus zero at baseline, 0.89 +/- 0.12 at 5 min, 1.27 +/- 0.13 at 10 min, 0.84 +/- 0.09 at 15 min, and 0.53 +/- 0.07 at 30 min in control subjects (p > or = 0.07 at 5, 10, and 30 min; p < or = 0.05 at baseline and at 15 min). Area under the curve (AUC0-30) in the mechanically ventilated patients was 16.8 +/- 1.4 versus 23.4 +/- 1.9 ng/ml/puff x min in control subjects (p = 0.014). In summary, administration of albuterol with a MDI achieved a profile of serum levels in mechanically ventilated patients similar to that in healthy control subjects, but the peak serum level and systemic bioavailability (AUC0-30) were lower in the patients. In conclusion, serum levels reliably assess lower respiratory tract deposition of albuterol, and show that MDIs are more efficient for aerosol delivery in mechanically ventilated patients than was previously reported in studies using radiolabeled aerosols.

Aged↗
PubMed1996

Bronchodilator delivery with metered-dose inhalers in mechanically-ventilated patients.

Metered-dose inhalers (MDIs) provide several advantages over nebulizers, including ease of administration, decreased cost, reliability of dosing, and freedom from contamination. However, this method of aerosol delivery has been considered ineffective in mechanically-ventilated patients because most of the aerosol deposits in the endotracheal tube and ventilator circuit. A smaller amount of aerosol from a MDI is deposited in the lower respiratory tract of mechanically-ventilated patients than in ambulatory patients, although recent studies show that a significant bronchodilator effect can still be achieved. When employed optimally, significant bronchodilation occurs with as little as 4 puffs of a sympathomimetic aerosol. Multiple factors influence the efficacy of MDIs in mechanically-ventilated patients. The method of connecting the MDI canister to the ventilator circuit has a marked effect on aerosol delivery, and other factors include the timing of MDI actuation, ventilator mode, tidal volume, circuit humidity, and duty cycle. With a proper technique of administration, a MDI serves as an effective, convenient, and safe method for delivering bronchodilator aerosols in mechanically-ventilated patients.

Administration, Inhalation↗
PubMed1996

Rural psychiatric services.

OBJECTIVE: The objective was to describe and evaluate a community mental health service developed during 1991-1992 in an attempt to meet the mental illness needs of an isolated rural community. The setting was the Grampians health region in Western Victoria: this region has an area of 45,000 square kilometers and a population of 182,000. METHOD: The method involved firstly describing the evolution of the service delivery model. This comprised a team of travelling psychiatrists and community psychiatric nurses which succeeded in providing a combined inpatient and outpatient service which was integrated with general practitioners. Secondly, diagnostic and case load descriptions of patients receiving service were compared for both the inpatient and outpatient settings. RESULTS: The results were that reduced reliance on inpatient beds and increased consumer satisfaction were achieved. CONCLUSION: It was concluded that on initial evaluation of the service it was seen to be meeting its objective of treating the seriously mentally ill in an isolated rural community-based setting.

Adolescent↗
PubMed1995

Vulvovaginal candidiasis: topical vs. oral therapy.

Vulvovaginal candidiasis is extremely common. It may be treated with topical or oral antifungal medications. Topical therapy is efficacious and well-tolerated in most women. Oral therapy should be reserved for rare cases of severe and recalcitrant infection but should not be used in pregnant women, patients with diabetes or those using concomitant medications. An understanding of the pharmacotherapeutic characteristics of both oral and topical medications is a vital element in ensuring a favorable therapeutic outcome.

Administration, Oral↗
PubMed1995

A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group.

BACKGROUND: Weaning patients from mechanical ventilation is an important problem in intensive care units. Weaning is usually conducted in an empirical manner, and a standardized approach has not been developed. METHODS: We carried out a prospective, randomized, multicenter study involving 546 patients who had received mechanical ventilation for a mean (+/- SD) of 7.5 +/- 6.1 days and who were considered by their physicians to be ready for weaning. One hundred thirty patients had respiratory distress during a two-hour trial of spontaneous breathing. These patients were randomly assigned to undergo one of four weaning techniques: intermittent mandatory ventilation, in which the ventilator rate was initially set at a mean (+/- SD) of 10.0 +/- 2.2 breaths per minute and then decreased, if possible, at least twice a day, usually by 2 to 4 breaths per minute (29 patients); pressure-support ventilation, in which pressure support was initially set at 18.0 +/- 6.1 cm of water and then reduced, if possible, by 2 to 4 cm of water at least twice a day (37 patients); intermittent trials of spontaneous breathing, conducted two or more times a day if possible (33 patients); or a once-daily trail of spontaneous breathing (31 patients). Standardized protocols were followed for each technique. RESULTS: The median duration of weaning was 5 days for intermittent mandatory ventilation (first quartile, 3 days; third quartile, 11 days), 4 days for pressure-support ventilation (2 and 12 days, respectively), 3 days for intermittent (multiple) trials of spontaneous breathing (2 and 6 days, respectively), and 3 days for a once-daily trial of spontaneous breathing (1 and 6 days, respectively). After adjustment for other covariates, the rate of successful weaning was higher with a once-daily trial of spontaneous breathing than with intermittent mandatory ventilation (rate ratio, 2.83; 95 percent confidence interval, 1.36 to 5.89; P < 0.006) or pressure-support ventilation (rate ratio, 2.05; 95 percent confidence interval, 1.04 to 4.04; P < 0.04). There was no significant difference in the rate of success between once-daily trials and multiple trials of spontaneous breathing. CONCLUSIONS: A once-daily trial of spontaneous breathing led to extubation about three times more quickly than intermittent mandatory ventilation and about twice as quickly as pressure-support ventilation. Multiple daily trials of spontaneous breathing were equally successful.

Acute Disease↗