Simulation using novel equipment designed to explain spirometric abnormalities in respiratory disease enhances learning in higher cognitive domains.

Simulation of disorders of respiratory mechanics shown by spirometry provides insight into the pathophysiology of disease but some clinically important disorders have not been simulated and none have been formally evaluated for education. We have designed simple mechanical devices which, along with existing simulators, enable all the main dysfunctions which have diagnostic value in spirometry to be simulated and clearly explained with visual and haptic feedback. We modelled the airways as Starling resistors by a clearly visible mechanical action to simulate intra- and extra-thoracic obstruction. A narrow tube was used to simulate fixed large airway obstruction and inelastic bands to simulate restriction. We hypothesized that using simulators whose action explains disease promotes learning especially in higher domain educational objectives. The main features of obstruction and restriction were correctly simulated. Simulation of variable extra-thoracic obstruction caused blunting and plateauing of inspiratory flow, and simulation of intra-thoracic obstruction caused limitation of expiratory flow with marked dynamic compression. Multiple choice tests were created with questions allocated to lower (remember and understand) or higher cognitive domains (apply, analyse and evaluate). In a cross-over design, overall mean scores increased after 1½ h simulation spirometry (43-68 %, effect size 1.06, P < 0.0001). In higher cognitive domains the mean score was lower before and increased further than lower domains (Δ 30 vs 20 %, higher vs lower effect size 0.22, P < 0.05). In conclusion, the devices successfully simulate various patterns of obstruction and restriction. Using these devices medical students achieved marked enhancement of learning especially in higher cognitive domains.

Exponential protocols for cardiopulmonary exercise testing on treadmill and cycle ergometer.

An extended exponential exercise protocol was validated by comparing submaximal and maximal parameters with those obtained by linear protocol. Normal subjects (n = 16, 20-69 years) undertook maximal exercise tests on treadmill and cycle ergometer. The subjects had a wide range of exercise capacity, and all were accommodated by the protocol. Mean oxygen uptake (V(O2)) agreed between protocols at gas exchange anaerobic threshold (theta) (95% CI of difference -0.1 to +0.06 l min(-1)) and at peak (95% CI of difference -0.1 to +0.1 l min(-1)). Mean pre-thetaDeltaV(O2)/Deltawork rate (W) slope on the cycle ergometer agreed between protocols (95% CI of the difference -0.9 to +0.25 ml min(-1) W(-1)). Post-thetaDeltaV(O2)/DeltaW slope was steeper than pre-theta, and steeper by linear than by exponential protocol (P = 0.0001). It is concluded that the exponential protocol is valid for the measurement of submaximal and maximal exercise parameters in subjects with a wide range of exercise capacity.

Effect of angiotensin converting enzyme inhibition on airway conductance during hypocapnic hyperventilation in normal subjects.

In nine normal subjects, specific airway conductance was measured by whole body plethysmography before and immediately after hypocapnic hyperventilation. This procedure, forced expiratory manoeuvres and arterial blood pressure measurements were carried out before and 4 h after placebo and the angiotensin converting enzyme inhibitor, enalapril, in a double-blind, randomized study design. Bronchoconstriction to hypocapnic hyperventilation was shown by a reduction in specific airway conductance on all occasions (P < 0.001). A reduction in mean blood pressure was obtained after enalapril compared to placebo (P < 0.05). No significant change attributable to enalapril was observed in any lung function measurement either at rest or immediately after hypocapnic hyperventilation, despite an expected enhancement of endogenous angiotensin converting enzyme activity by alkalosis. Inhibition of angiotensin converting enzyme revealed no effect of the endogenous activity of this enzyme on airway calibre either at rest or during the bronchoconstrictor response to hypocapnic hyperventilation.

The use of and attitude to peak flow measurement in general practice.

The use of and attitudes to peak flow meters and monitoring were surveyed in a random sample of general practitioners in Northern Ireland. There was an 87% response. Almost all general practitioners had a peak flow meter or spirometer in their practice but only 48% usually took a meter on home visits. The meters were more likely to be used for the diagnosis and management of asthma than chronic obstructive airways disease. General practitioners felt that meters were more useful when used in the consulting room than for domiciliary monitoring and that domiciliary monitoring was more useful in the management than the diagnosis of asthma. Although 79% of general practitioners felt that domiciliary peak flow measurement was useful for the management of asthma, only 3% of all asthmatic patients were using it. General practitioners' attitudes to peak flow monitoring are positive but they are not actually using them as much as they could.

Validity of peak expiratory flow rate variability for the diagnosis of asthma.

1. The aim of this study was to determine the validity of various numerical indices of peak flow variability as tests for asthma. 2. Normal (n = 24) and asthmatic (n = 123) subjects aged 10-70 years were recruited from the community. Asthma was diagnosed by full clinical assessment and was active during the previous year. Subjects recorded their peak flow immediately after rising in the morning, at 18.00 hours and just before retiring at night for 12 days. 3. The most discriminating index was the highest peak flow variability which occurred within any 1 day during the 12-day recording period, calculated as the difference between the maximum and minimum peak flows expressed as a percentage of the minimum peak flow on that day (the proposed index). This index was < 20% (90th centile) in 96% of the normal subjects and > or = 20% in 89% of the asthmatic subjects. 4. Standard indices of mean peak flow, the forced expiratory volume in 1.0 s and its responsiveness to salbutamol, had much lower sensitivities than peak flow variability. 5. It is concluded that numerical indices of peak flow variability are highly valid tests for asthma. Using an upper limit of normal of 20%, the proposed index of peak flow variability discriminates better than other indices between asthmatic and normal subjects.

Interactive video in medical education: a program on jugular venous pressure and the cardiac cycle.

Interactive video is a new teaching medium that has much potential in medical education. Hitherto, the realization of this potential has been restrained by lack of awareness among medical teachers of the advantageous features provided and how to implement them, while computer specialists lack the required medical knowledge. To facilitate a wider appreciation of interactive video we describe the features offered, emphasizing those which differentiate this method from other teaching methods. These features, and techniques for their implementation which are readily available to non-computer specialists, are illustrated by description of an interactive video program for teaching the assessment of central venous pressure pulsations and their relationship to the electrical, auditory and mechanical events of the cardiac cycle.

Collation of student results in practical class experiments in physiology, using a BBC ECONET computer network.

Funding was provided to Queen's University by the Department of Education and by the Industrial Development Board for Northern Ireland to provide microcomputers for undergraduate use. An allocation from the grant to the Department of Physiology enabled the purchase of 20 BBC Master 128 microcomputers with monitors used as student work-stations connected together by an ECONET network with a file server using a dual floppy disc drive, two printer servers and two demonstrator stations. A BASIC program was written to analyse the students' practical class measurements which they entered manually at their work-station keyboards. Class results were presented to the students in the form of frequency distribution histograms or X/Y graphs. Program modifications to suit different practicals can be made relatively easily. The time taken to analyse data has been shortened. It is easy for the students to get immediate comparison of their own results with those of the rest of the class--particularly advantageous if the student's own experiment did not work. The class can be divided into groups to study different variations of the experiment and provide the data from each group to the whole class. The students' opinions on whether the equipment had (1) improved the teaching of physiology and (2) provided helpful preparation for the use of computers in medical practice were assessed by a questionnaire which showed that a clear majority felt these aims had been fulfilled.

Comparison of the effects of inhaled ipratropium bromide and salbutamol on the bronchoconstrictor response to hypocapnic hyperventilation in normal subjects.

A double blind, placebo controlled comparison was made of the effects of nebulised ipratropium bromide (0.05 and 0.5 mg) and salbutamol (0.25 and 2.5 mg) on lung function and the airway response to hyperventilation in eight normal subjects. Both agents at both doses caused similar baseline bronchodilatation, confirming the presence of resting bronchomotor tone. The overall mean increases as percentages of control were 33% in specific airway conductance (sGaw), 10% in maximal flow after expiration of 50% of vital capacity, and 3.7% in FEV1. Hypocapnia (mean end tidal carbon dioxide tension 2.2 kPa) was produced by three minutes of voluntary hyperventilation and resulted in a mean fall in sGaw of 0.49 s-1 kPa-1 (20%). After inhalation of 0.25 mg salbutamol hypocapnic hyperventilation still produced a mean fall in sGaw of 0.55 s-1 kPa-1, whereas salbutamol 2.5 mg reduced this response to 0.15 s-1 kPa-1 (6%). After both doses of ipratropium the decrease in sGaw caused by hyperventilation was similar to the control. This suggests that bronchoconstriction in response to hypocapnic hyperventilation in normal subjects is not mediated via a cholinergic reflex.

Ventilatory impairment from pre-harvest retted flax.

A new method of retting flax recently developed to suit the United Kingdom climate has allowed the reintroduction of flax growing to this country. The weed killer glyphosate is sprayed on the crop which then rets before harvesting six weeks later. The acute bronchoconstrictor responses of 11 normal subjects to dust from dew retted and from pre-harvest retted flaxes were compared in a double blind crossover fashion. There were no significant differences in the dust levels nor in the size of the dust particles in the experimental dust room. The decreases in pulmonary function after six hours of dust inhalation were significantly larger after pre-harvest retted flax dust than after dew retted flax dust (delta FEV1, -0.21 and -0.40 1; delta MEF50, -0.72 and -1.211/s; delta sGaw (specific airway conductance), -0.17 and -0.65 kPa/s for dew retted and pre-harvest retted respectively). The subjects also reported more symptoms after inhaling pre-harvest retted flax dust. It is concluded that the acute bronchoconstrictor response to flax dust is increased by pre-harvest retting, suggesting an increased risk of byssinosis.

Nontraumatic clostridial myonecrosis, a case report.

Physicians are aware of the association between massively contaminated wounds and clostridial myonecrosis, or gas gangrene. A far less common but equally devastating presentation is that of nontraumatic or spontaneous gas gangrene. The most frequently encountered organism in this rare form of gangrene is Clostridium septicum, and there is a high correlation with hematologic or gastrointestinal malignancy. The mainstays of treatment are intravenous antibiotics, surgical debridement, and hyperbaric oxygen therapy. The prognosis is dependent upon early recognition and institution of treatment.

Branchial challenge of normal subjects with the endotoxin of Enterobacter agglomerans isolated from cotton dust.

Endotoxin produced by a culture of Enterobacter agglomerans isolated from cotton dust was inhaled by 12 normal subjects. No significant airway constriction was obtained in doses equivalent to those experienced in a workshift in a dusty mill. There was a statistically significant difference between this result and the bronchoconstriction that had occurred after flax dust inhalation in the same subjects. It is suggested that Enterobacter agglomerans endotoxin is not the causative agent of the acute bronchoconstriction that follows inhalation of textile dust.

Ventilatory responses of normal subjects to flax dust inhalation: the protective effect of autoclaving the flax.

A homogeneous batch of dew retted hackled flax was divided into two portions. One was untreated and the other was steamed for 45 minutes at 125 degrees C in three pressure/vacuum cycles in an autoclave. Dust was collected when the two flaxes were separately processed by industrial doubler and stapler machines. From untreated flax 7.2 g of dust was collected per kilogram of flax after two processing operations. From the steamed flax 4.4 g of flax was obtained per kilogram after four operations. A method was devised to disperse the dust in a room to produce dust levels similar to those encountered in a dusty mill (4.5-5.7 mg/m3). Twelve normal volunteers from the managerial staff of the linen industry of Northern Ireland inhaled the dust over six hour periods. With the untreated flax decreases were obtained in mean forced expiratory measurements of 7.6% in FEV1 and 4.5% in FVC (p less than 0.01). A double blind crossover comparison of similar levels of untreated and steamed flax dusts showed 30% less impairment of the forced expirations with steamed than with untreated flax (p less than 0.05). If these responses reflect the long term airway effects of flax dust then the steaming of flax may help in reducing byssinosis.

Impairment of flow in routine gravity-fed intravenous infusions to surgical patients.

1. Gravity-fed intravenous infusions were studied in patients by using continuous flow recording and a new resistance-measuring method. 2. A common, though preventable, cause of reduced flow was the gradual deformation of the plastic tubing under the regulator clamp. 3. In many cases there was some constriction of the cannulated vein and in a few this constriction was severe enough to seriously impair the infusion. The severity of the constriction varied periodically. 4. There was no evidence of troble due to a generally raised pressure in the arm veins nor was clotting in the cannula a serious problem. 5. A simple test is described which may be found useful clinically for assessing the difficult infusion.

Effect of a surgically created side-to-side arteriovenous fistula on heat elimination from the human hand and forearm: evidence for a critical role of venous resistance in determining fistular flow.

1. In eight patients with a unilateral fistula between the radial artery and a nearby superficial vein, heat elimination from both hand and forearm, as measured by calorimetry, was always substantially greater on the side of the fistula (a mean excess from hand-plus-forearm 889 J/min). 2. Fistular blood flow measured by hand-plus-forearm plethysmography in these patients averaged 431ml/min. Correlation between fistular blood flow and heat elimination was poor (r = 0.70, P less than 0.06), probably because heat elimination due to the fistula takes place mainly from veins, whose pattern varies from patient to patient. 3. Approximately half of the total increased heat elimination due to the fistula is from the hand. Occlusion of the circulation to the hand caused fistular flow rate to be reduced by about half. This suggests that the main resistance to fistular is venous, proximal veins offering a similar resistance to distal veins. 4. The obligatory heat loss due to fistula is unlikely to embarrass temperature regulation, except in severe cold stress.

The pattern of venous drainage of surgically created side-to-side arteriovenous fistulae in the human forearm.

1. The forearm and hand circulation in nine patients with a surgically created side-to-side fistula between the radial artery and a nearby superficial vein in the lower forearm has been investigated. 2. Dilated veins on the dorsum of the hand communicated with the fistula without intervening valvular obstruction. Skin temperature of both forearm and hand was greater on the side with the fistula in all cases. 3. Inflation of an occlusion cuff distal to the fistula markedly reduced apparent fistular flow. 4. It is concluded that the fistulae result in increased blood flow to the hand by retrograde flow from the fistula into the hand veins. Hand as well as forearm must be included in the plethysmographic measurement of blood flow in such cases.

Measurement by venous occlusion plethysmography of blood flow through surgically created arteriovenous fistulae in the human forearm.

1. Plethysmographs containing the hand plus forearm were used to measure blood flow in patients with a srugically created arteriovenous fistula in one forearm. 2. Apparent flow rate was stable over a limited range of collecting pressures; the absolute value of these pressures varied from patient to patient. 3. After arterial occlusion, blood flow increased by a similar amount on the normal side and on the side with the fistula. 4. Occlusion of fistular flow produced no significant change in heart rate. 5. Fistular flow, estimated as the difference between flow on the two sides, averaged 525 ml/min in seventeen patients.