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Biomedical subjects

S Birch

Publications and source records attributed to S Birch.

At least 127 records · Page 7Linked to original sources
PubMed1983

Effect of positive end-expiratory pressure on breathing patterns of normal subjects and intubated patients with respiratory failure.

The aims of this study included assessment of accuracy of respiratory inductive plethysmography when pulmonary hyperinflation was induced by application of PEEP, and examination of breathing patterns of normal subjects, intubated patients requiring mechanical ventilation and intubated patients immediately before extubation during application of PEEP by demand valve and high gas flow reservoir bag systems. Validation of tidal volume (VT) and end-expiratory level measured with respiratory inductive plethysmography to simultaneous spirometry (SP) was achieved with PEEP levels up to 12.5 cm H2O in 7 normals. In 17 intubated patients, almost all VT values measured with respiratory inductive plethysmography fell within +/- 10% of SP even with 2 to 3 changes of body posture. In normal subjects, increasing levels of PEEP from the demand valve system produced nonprogressive rises of VT and mean inspiratory flow, falls of frequency and fractional inspiratory time (TI/TTOT), and no changes of minute ventilation (Vmin) nor mean expiratory flow. PEEP from the high gas flow reservoir bag system produced nonprogressive rises of VT and rib cage (RC) contribution to VT, and rises of Vmin and mean inspiratory and expiratory flows between 10.0 and 12.5 cm H2O of PEEP. Intubated patients requiring intermittent mandatory ventilation (IMV) had a rapid, shallow breathing pattern unaltered by PEEP levels delivered by either system up to 12.5 cm H2O despite increases of end-expiratory level. Intubated patients who were about to be extubated breathed with patterns closer to ambulatory normal subjects with the exception of their elevated RC contribution to VT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

Effects of partial anti-G suit inflation on thoracic volume and breathing pattern.

The purpose of this study was to determine the changes in thoracic volume and pattern of breathing during partial anti-G suit (PAGS) inflation by respiratory inductive plethysmography (RIP). Nine normal subjects donned the PAGS, with bladders over legs and thighs, and rested for about 10 min in 60 degrees head-up tilt position. The subjects breathed with closed glottis at functional residual capacity while PAGS was suddenly inflated to 140 mmHg using a calves to thighs sequence. The increase in thoracic volume, as measured from deflection of RIP baseline was 252 ml (S.D. 43 ml), which reflected displacement of blood from the lower extremities into the thorax. On resuming normal breathing, thoracic volume returned to baseline level. Breathing pattern was then monitored for a 15 min baseline period, PAGS was inflated, expiratory reserve volume (ERV) was measured by spirometry, and breathing pattern was monitored another 15 min. ERV decreased 227 ml (+/- 60) after PAGS inflation, which did not differ from the change in thoracic volume expected from displacement of blood into the thorax. Breathing pattern was monitored for another 15 min after PAGS was deflated. No changes took place in minute ventilation, tidal volume, frequency, inspiratory time, fractional inspiratory time, and mean inspiratory flow from deflation to PAGS inflation. Thus, 1) increase in thoracic volume produced by displacement of blood from the calves and thighs is balanced by a decrease in gas volume and, 2) no changes in breathing pattern occur after partial anti-G suit inflation, probably because the pulmonary blood vessels and heart are sufficiently distensible to accept a 250 ml volume increment without leakage of fluid into pulmonary tissues.

Adult↗
PubMed1982

Validation of respiratory inductive plethysmography using different calibration procedures.

We devised a new calibration procedure [least squares method (LSQ)] for respiratory inductive plethysmography (RIP) and compared it with our previously reported simultaneous equation method (SEQ) of analyzing data in 2 body positions and with the method of Stagg and associates using the analysis of individual breaths in a single body position. The values from RIP were compared with simultaneous spirometry (SP) in 20 normal subjects placed in the standing (STD), supine (SUP), sitting, prone, semi-recumbent, right lateral decubitus, and left lateral decubitus postures. The LSQ gave the most accurate results followed closely by SEQ. In addition, LSQ was compared with the isovolume angle maneuver (ISV) calibration procedure in supine (ISV-SUP) and standing (ISV-STD) postures. Each of the 10 normal subjects breathed at tidal volumes of 250, 750, and 1,250 ml in the SUP and STD postures. Of the values obtained by the LSQ method, 93% were within +/- 10% of SP in SUP and STD positions. Without a change in the posture in which the calibration was made, 83% of values with ISV-SUP and 90% of values with ISV-STD were within +/- 10% of SP. When body position was changed, 65% of the values obtained with ISV-SUP and 38% of the values obtained with ISV-STD were within +/- 10% of SP. With the LSQ, 45% of isovolume angles in SUP and STD position were within 45 +/- 3 degrees; 40% of isovolume angles with ISV-SUP and 60% with ISV-STD were within 45 +/- 3 degrees when body position was changed from position calibrated. In estimating fractional contribution of rib cage and abdominal compartments. LSQ was comparable to ISV in the standing posture but generally gave lesser values for the rib cage contribution in the supine posture than ISV. The optimal calibration procedure for respiratory inductive plethysmography in terms of accuracy and ease of subject performance is the least squares calibration procedure.

Calibration↗
PubMed1982

Assessment of density dependent flow-volume parameters in nonsmokers and smokers. Measurement with spirometry, body plethysmography and respiratory inductive plethysmography.

The purpose of this investigation was to assess the density-dependent flow-volume components of the forced vital capacity using simultaneous spirometry, respiratory inductive plethysmography, and body plethysmography in the detection of small airway disease. The forced vital capacity was measured during air, helium-oxygen and sulfur-hexafluoride breathing to provide a range of gas density influences. Combining flow measured at the mouth with volume referenced to change in alveolar gas volume as measured by body or respiratory inductive plethysmography during helium-oxygen breathing accentuated the differences between nonsmokers and smokers because of the variable degree of alveolar gas compression occurring over the second half of FVC. The volume of isoflow obtained when comparing the helium and oxygen mixture to air also effectively separated nonsmokers from smokers. The utilization of the high density gas mixture, sulfur hexafluoride-oxygen during the FVC maneuver did not provide useful diagnostic information. Therefore, density-dependent flow-volume information using helium as a test gas alone or compared to air with a variety of analyses is a good approach to detection of early lung disease in smokers.

Adolescent↗
PubMed1982

Assessment of time-volume and flow-volume components of forced vital capacity. Measurement with spirometry, body plethysmography and respiratory inductive plethysmography in nonsmokers and smokers.

The purpose of this investigation was to assess the effectiveness of the time-volume and flow-volume components of the forced vital capacity measured by simultaneous spirometry, respiratory inductive plethysmography, and body plethysmography in detecting small airway disease. Spirometry measured the exit of gas from the lungs, whereas body plethysmography measured both the exit of gas and alveolar gas compression. Respiratory inductive plethysmography, which reflected change in thoracic volume, provided semi-quantitative data f both gas exit and alveolar gas compression which generally lay between spirometry and body plethysmography. In nine nonsmokers and 12 smokers (six with small airway disease as defined by abnormal closing volumes and alveolar uniformity), analysis of forced vital capacity revealed that the only test which differentiated nonsmokers from smokers was the higher spirometric estimation of maximum expiratory flow measured at 25 percent VC in nonsmokers. Combining flow measure at the mouth with volume referenced to change in alveolar gas volume as measured by body or respiratory inductive plethysmography did not differentiate nonsmokers from smokers. Moment analysis performed of forced vital capacity with all of the three devices did not distinguish nonsmokers from smokers. The data in this study and a review of other investigations indicate that the time-volume and flow-volume components of the forced vital capacity on air breathing are not very sensitive in detecting early lung disease in smokers.

Adolescent↗
PubMed1981

Differential effects of methacholine and antigen challenge on gas exchange in allergic subjects.

In order to better characterize the differential effects of nonspecific and specific (antigen) bronchial challenge on gas exchange, seven ragweed-sensitive subjects with a history of asthma underwent progressive inhalation challenge with methacholine and ragweed extract on two different days. For comparable severity of bronchospasm (mean specific airway conductance 0.05 sec-1cm-1H2O for methacholine and 0.06 sec-1cm-1H2O for ragweed), there was a greater decrease in mean arterial oxygen saturation after ragweed (4.7%) than after methacholine challenge (2.7%) (p less than 0.05). While this was not accompanied by differences in static lung volumes, the density-dependent index decreased by 19% after ragweed (p less than 0.001) but remained unchanged after methacholine challenge. These results suggest that a greater involvement of peripheral airways in the bronchospastic response is, at least in part, responsible for the greater decrease in arterial oxygen saturation after ragweed challenge.

Adult↗
PubMed1981

Abnormal mucociliary transport in allergic patients with antigen-induced bronchospasm: role of slow reacting substance of anaphylaxis.

We evaluated the possible role of slow reacting substance of anaphylaxis (SRS-A) in mediating mucociliary dysfunction in allergic asthma. In 6 asymptomatic nonsmokers with ragweed asthma, we measured specific airway conductance (SGaw) and tracheal mucous velocity (TMV) before and after bronchial challenge with ragweed extract, with or without pretreatment with 0.5% and 1% FPL-55712 (SRS-A antagonist). Mean baseline TMV was 8.9 mm/min (SD, 1.1). Placebo and FPL-55712 per se had no effect on TMV. With placebo pretreatment, the doses of ragweed extract that resulted in a decrease in SGaw by more than 35% from baseline, led to an immediate decrease in TMV to 74% of baseline (p less than 0.05), returning to baseline within 2 h. With 0.5% and 1% FPL-55712 pretreatment, doses of ragweed extract that resulted in a similar decrease in SGaw led to an increase in TMV to 130% and 126% of baseline (p less than 0.05), respectively, immediately after antigen challenge and returned to baseline 2 h postchallenge. Inhalation of 1% FPL-55712 immediately after antigen challenge prevented the decrease in TMV. These results indicate that (a) SRS-A liberated during airway anaphylaxis impairs mucous transport, and (b) the antigen-induced increase in TMV after pretreatment with an SRS-A antagonist may reflect a stimulatory effect of other chemical mediators of anaphylaxis.

Adolescent↗
PubMed1980

Deposition of ragweed pollen and extract on nasal mucosa of patients with allergic rhinitis: effect on nasal airflow resistance and nasal mucus velocity.

This study was undertaken to ascertain whether nasal mucus velocity (NMV) could be altered by short-term exposure to antigen. Asymptomatic patients with a history of allergic rhinitis who had a positive cutaneous reaction to ragweed extract were investigated. The plan was to achieve approximately a fourfold elevation of nasal airflow resistance (NAR) with antigen challenge and then obtain serial measurements of NAR and NMV. NMV was not significantly altered when the antigen was introduced by nasal inhalation of (1) ragweed pollen grains, (2) nebulized ragweed extract for 10 breaths, and (3) nebulized ragweed extract for 30 min on each of 3 successive days. When ragweed extract was introduced by direct instillation of the solution into the nose, NMV fell below baseline values at either 0.5 or 1.5 hr, or at both times after administration. Persistence of impairment of mucociliary transport at a time when nasal airway constrictor response had dissipated suggested that a chemical mediator might have been responsible for the alteration of clearance. The failure to demonstrate depression of mucus transport with the inhalation studies might have been due to insensitivity of the radiopaque Teflon disk method or to a qualitatively different allergic reaction to direct instillation of antigen solution.

Adult↗
PubMedDate not supplied

As a matter of fact: evidence-based decision-making unplugged.

The rationale of evidence-based decision-making is to inform the decision-making process with information relevant to the decisions being taken. In this paper the models of research and analytical approaches used to generate the evidence are shown to be generally not 'decision-informing'. The researcher's interest in health care interventions has led to the development and use of designs which strip the research of contextual issues and hence represent a major departure from both the underlying notions of the complex pathways to health and the empirical findings concerning the importance of population context. In this way, the evidence-based approach, dominated by a focus on health outcomes from health care interventions, overlooks the notion that society is not a 'level playing field'. Decisions based on research 'evidence' of this type risk redeploying resources inefficiently and in ways which systematically favour those groups with favourable 'prospects for health' (or non-health care determinants of health), and the conditions that those groups in society tend to suffer from, and away from those groups with less favourable prospects for health. Existing approaches to informing the decision-making process could be enhanced by broadening the scope of the research to incorporate relevant determinants of health in both the specification of the problem and the selection of methods of analysis that enable us to explore the complex pathways to health.

Decision Making↗
PubMedDate not supplied

Performance indicators and performance assessment in the UK National Health Service: implications for management and planning.

Throughout the Western world policy makers are seeking to control the use of health care resources. Often the primary motive for these policies is to control or the total level of public expenditure on health care. One manifestation of such policies in the USA is the use of diagnostic related groups (DRGs), and this instrument is now being adopted in Europe (for example, in France as from January 1986). In Britain, as similar management tool is that of performance indicators, which are basically measures of input and activity. In this article it is argued that management responses to these measures may not lead to greater efficiency in resource utilization. Whilst the use of input and process measures to control resource allocation are better than no controls at all, the achievement of efficiency requires that such measures are supplemented with the assessment of outcomes and analyses of input-output relationships. Such supplementation, for example by using quality-adjusted life years (QALYs), is urgently required if policy makers are not to become disenchanted with the usefulness of existing performance indicators.

Efficiency↗
PubMedDate not supplied

Acupuncture for the treatment of cocaine addiction. Investigation of a needle puncture control.

We conducted a 6-week, single-blind study of acupuncture for cocaine dependence in methadone-maintained patients (N = 40) for the purpose of identifying an appropriate needle puncture control for use in future large-scale clinical trials. Patients were randomly assigned to receive daily acupuncture in three auricular sites plus one body site (LI-4), or in control sites within 2-3 mm of the four active sites. Overall, there was a positive response to treatment on a variety of drug-related and psychosocial measures. Cocaine use decreased significantly for patients in both needle puncture groups. The only statistically significant difference between the two types of needle puncture was on ratings of craving. Subjects rated each type of needle puncture as equally credible and perceived no significant differences on the acute effects of the two types of needle insertions. Power calculations based on these findings suggest that very large sample sizes would be required to detect treatment differences between this control condition and active acupuncture. Alternative controls are suggested, and the challenges inherent in implementing controlled clinical trials of acupuncture are discussed.

Acupuncture Points↗
PubMedDate not supplied

Methodological investigations for a multisite trial of auricular acupuncture for cocaine addiction: a study of active and control auricular zones.

We evaluated objective criteria for defining points for needle insertion prior to conducting a multisite clinical trial of auricular acupuncture for cocaine addiction. Thirty-four cocaine-abusing subjects participated in a study in which the trial's active zones (Shenmen, Liver, Lung, and Sympathetic) and control zones (located on the ear helix) were divided into quadrants and assessed along four dimensions: electrical resistance, skin discoloration, skin topography, and tenderness. Acute effects of needles inserted into points of low electrical resistance in one ear and high electrical resistance in the other were also assessed. Results showed that the active zones had lower overall electrical resistance and more subcutaneous ridges than control zones. Zones did not possess significant variability along any single dimension. Acute effects of needling high and low resistance points were similar, differing only for "fullness." Based on these findings, and in view of the difficulty of accurately measuring electrical resistance at ear points, we do not recommend the use of electrical devices for point determination in the multisite study. At present, there seems to be little scientific basis for the preselection of specific points for needle insertion within auricular zones. Needle placement should be based upon clinical judgement.

Acupuncture Points↗