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A R Cummin

Publications and source records attributed to A R Cummin.

15 recordsLinked to original sources
PubMed1992

Estimates of mean alveolar PCO2 during steady-state exercise in man: a theoretical study.

The partial pressure of carbon dioxide in arterial blood is an important operator in the control of breathing, by actions on peripheral and central chemoreceptors. In experiments on man we must often assume that lung alveolar PCO2 equals arterial PCO2 and obtain estimates of the former derived from measurements in expired gas sampled at the mouth. This paper explores the potential errors of such estimates, which are magnified during exercise. We used a published model of the cardiopulmonary system to simulate various levels of exercise up to 300 W. We tested three methods of estimating mean alveolar PCO2 (PACO2) against the true value derived from a time average of the within-breath oscillation in steady-state exercise. We used both sinusoidal and square-wave ventilatory flow wave forms. Over the range 33-133 W end-tidal PCO2 (P(et)CO2) overestimated PACO2 progressively with increasing workload, by about 4 mmHg at 133 W with normal respiratory rate for that load. PCO2 by a graphical approximation technique (PgCO2; "graphical method") underestimated PACO2 by 1-2 mmHg. PCO2 from an experimentally obtained empirical equation (PnjCO2; "empirical method") overestimated PACO2 by 0.5-1.0 mmHg. Graphical and empirical methods were insensitive to alterations in cardiac output or respiratory rate. End-tidal PCO2 was markedly affected by respiratory rate during exercise, the overestimate of PACO2 increasing if respiratory rate was slowed. An increase in anatomical dead space with exercise tends to decrease the error in P(et)CO2 and increase the error in the graphical method. Changes in the proportion of each breath taken up by inspiration make no important difference, and changes in functional residual capacity, while important in principle, are too small to have any major effect on the estimates. Changes in overall alveolar ventilation which alter steady-state PACO2 over a range of 30-50 mmHg have no important effect. At heavy work loads (200-300 W), P(et)CO2 grossly overestimates by 6-9 mmHg. The graphical method progressively underestimates, by about 5 mmHg at 300 W. A simulated CO2 response (the relation between ventilation and increasing PCO2) performed at 100 W suggests that a response slope close to the true one can be obtained by using any of the three methods. The graphical method gave results closest to the true absolute values. Either graphical or empirical methods should be satisfactory for detecting experimentally produced changes in PACO2 during steady-state exercise, to make comparisons between different steady-state exercise loads, and to assess CO2 response in exercise.(ABSTRACT TRUNCATED AT 400 WORDS)

Arteries↗
PubMed1992

Ventilatory responsiveness to carbon dioxide below the normal control point in conscious normoxic humans.

A recently developed CO2 pulse technique was used to test for ventilatory sensitivity to CO2 in four normal men following 2 min voluntary hyperventilation down to an end-tidal CO2 tension (PETCO2) of 20 mmHg (2.7 kPa). Pure CO2 was injected into the inspiratory limb of a breathing circuit at 0.4 l.min-1 for 30 s and any small ventilatory response was detected against background noise by ensemble-averaging of multiple runs. Following hyperventilation, ventilation was initially often above control and apnoea was not seen. In one subject, the ventilatory response to the CO2 pulse was barely detectable either before or after hyperventilation. In another subject, there was a response to pulses given before hyperventilation and 3 and 5.5 min after hyperventilation but not 30 s after hyperventilation when PETCO2 was about 25 mmHg (3.3 kPa) and rising. In the two remaining subjects ventilatory responses were seen to CO2 pulses started 30 s after hyperventilation, although PETCO2 following the pulse remained some 5 mmHg (0.7 kPa) below baseline. We conclude that in some subjects the PETCO2 threshold lies well below the normal PETCO2. The technique is tedious for the experimental subject because of the large number of repetitions required and, therefore, unsuitable for a study on a large number of subjects.

Adult↗
PubMed1991

Hypoxia following voluntary hyperventilation during exercise in man.

The importance of carbon dioxide in the control of ventilation during exercise was tested by emptying CO2 stores by voluntary hyperventilation. Healthy subjects were studied after 3 min hyperventilation down to an end-tidal PCO2 of about 20 mmHg on a background of steady exercise at 75 W. Control runs were performed when the hyperventilation was made isocapnic by the addition of CO2. Following hypocapnic hyperventilation, there was a period when ventilation fell below control and this was accompanied by a fall in end-tidal PO2 (minimum 48 mmHg) and oximeter reading (minimum 73%). Ventilation rapidly returned to baseline following isocapnic hyperventilation and hypoxia was not seen. A mathematical simulation suggested that brain PCO2 recovered more slowly than arterial PCO2 and that at the times that ventilation was depressed central chemoreceptor PCO2 would have been low. We conclude that CO2 provides a crucial drive for maintaining adequate ventilation during steady exercise and that the central chemoreceptor may be involved.

Adolescent↗
PubMed1991

Suction drainage: a new approach to the treatment of empyema.

Thirteen patients with empyema thoracis were treated with a new suction drainage technique. The method entails passing a catheter into the empyema cavity under ultrasound guidance and using strong suction to drain loculated pus. Eight patients had no recurrence after a single treatment and one patient had no recurrence after two treatments. The procedure was a useful palliative measure in two patients with malignant disease who subsequently died. In one patient failure of the lung to expand after the procedure showed the need for thoracotomy. In one other patient the empyema recurred and decortication was required.

Adolescent↗
PubMed1990

Local anaesthesia for fibreoptic bronchoscopy: transcricoid injection or the "spray as you go" technique?

Local anaesthesia for fibreoptic bronchoscopy should be given by a safe technique that is not unpleasant to the patient and should provide acceptable conditions for the bronchoscopist. Single injection transcricoid local anaesthesia was compared with the "spray as you go" technique in patients having day case fibreoptic bronchoscopy. Patients were randomised to receive either 100 mg lignocaine by a single cricothyroid puncture or 240 mg lignocaine instilled through the bronchoscope under direct vision. Further doses were given by the operator to both groups as required. The 30 patients receiving transcricoid lignocaine coughed less (3.56 (SD 3.1) coughs/min) than the 32 patients receiving lignocaine through the bronchoscope (5.89 (4.8)/min) despite receiving a lower total dose of lignocaine (322 (25.9) v 451 (20.9) mg). Cricothyroid puncture was not associated with any complications and was not unpleasant for the patients.

Administration, Topical↗
PubMed1990

The effect of almitrine on the steady-state ventilatory response to carbon dioxide at rest and during exercise in man.

Almitrine has potential as a tool for testing the physiological role of the peripheral chemoreceptor. The effects of almitrine on CO2 chemosensitivity were studied at rest and during light exercise using a constant inflow technique that avoids the hyperoxia of rebreathing methods. The steady-state ventilatory response to CO2 was measured in two groups of six normal men before and 150 min after 100 mg oral almitrine bismesylate or placebo. One group was studied at rest, the other while pedalling at 50 W. The resting group showed a significant increase in CO2 response slope after almitrine when compared with placebo but there was no significant change in the response intercept. During exercise the individual results were very variable and after almitrine no significant change was seen in either the response slope or intercept. Control ventilation was not affected by almitrine in either group. Even in the absence of marked hyperoxia the effect of almitrine on CO2 sensitivity at rest in small. The lack of effect at 50 W is against any important role for the peripheral chemoreceptor during light exercise but other interpretations are possible.

Adult↗
PubMed1989

Sedation for fibreoptic bronchoscopy: comparison of alfentanil with papaveretum and diazepam.

Sedation for fibreoptic bronchoscopy should produce optimal conditions for the operator, patient comfort and rapid recovery allowing early discharge home. We have compared a regimen producing 'light' sedation with a more traditional regimen producing 'deep' sedation. Seventy-six patients undergoing fibreoptic bronchoscopy under topical anaesthesia were randomized to receive either light sedation with the short acting opiate, alfentanil (median dose 1.1 mg, range 0.5-2.6 mg) or deep sedation with a combination of papaveretum (median dose 10 mg, range 5-15 mg) and diazepam (median dose 8 mg, range 0-20 mg). Both techniques gave equally good operating conditions, although patients given alfentanil coughed less than those given papaveretum and diazepam (U = 2.814 P less than 0.01). Patients recorded their degree of apprehension on a visual analogue scale prior to sedation and the actual degree of comfort experienced after recovery. There was no significant difference between apprehension or comfort between the groups. This was despite a higher degree of amnesia for an irrelevant object shown during the bronchoscopy in the deeply sedated group (chi 2 = 21.084 P less than 0.001). Patients given alfentanil performed significantly better in a modified Romberg test (chi 2 = 4.357 P less than 0.05) and a visualisation test (t = 3.035 P less than 0.01) two hours after the bronchoscopy. Alfentanil produced good operating conditions, patient comfort, less cough and a more rapid recovery, compared to the deep sedation regimen, and is an ideal sedative for fibreoptic bronchoscopy.

Aged↗
PubMed1987

Ventilatory responses to inhaled carbon dioxide at rest and during exercise in man.

1. Rapid steady-state CO2 responses were determined in six normal subjects at rest and five subjects at four different work loads up to 125 W, by injecting pure CO2 at constant flow into a small mixing chamber in the inspiratory limb of a breathing circuit. 2. The time course of the response of ventilation (V) and mean alveolar PCO2 (PACO2) was checked in separate experiments, where the flow rate of injected CO2 was changed abruptly and the effects were followed for 10 min. 3. V and PACO2 were measured every breath, and the results ensemble-averaged for each subject (two or three runs per subject) and then for the groups as a whole, in 30 s or 60 s time bins. 4. PACO2 during exercise was estimated by graphical reconstruction from the sloping alveolar plateau, and separately by the empirical equation of Jones, Robertson & Kane [1]. At rest, PACO2 was assumed equal to end-tidal PCO2 (PetCO2). 5. With the constant inflow technique, 4 min was required to reach steady-state V and PACO2 during exercise, and 6 min at rest. 6. At rest, with 4 min steps (doubtful steady state) the averaged CO2 response was concave up. With 6 min steps the response was almost linear. In neither case was the deviation from linearity statistically significant. 7. During exercise, the averaged CO2 responses were essentially isocapnic at work loads greater than 75 W with either method of deriving PACO2.

Adult↗
PubMed1986

Ventilatory sensitivity to inhaled carbon dioxide around the control point during exercise.

Rapid steady-state CO2 responses were determined in five normal adults at rest and at up to six levels of exercise by injecting pure CO2 at a constant flow into the inspiratory limb of a breathing circuit. Ventilation (V) was measured with a dry gas meter and PCO2 at the mouth was recorded by a mass spectrometer. Mean alveolar PCO2 (PACO2) was taken as equal to end-tidal PCO2 at rest, and during exercise was derived graphically from the sloping alveolar plateaus. The accuracy of the latter method was checked in separate experiments against arterial PCO2 (PaCO2). The mean results showed a linear relationship between change in PACO2 and change in V for work loads ranging from rest to 75 W (r = 0.94-0.98). Above 75 W the response became concave down with an initial essentially isocapnic phase. This suggests that during exercise there is a large increase in CO2 sensitivity about the control point.

Blood Gas Analysis↗
PubMed1986

Ventilation and cardiac output during the onset of exercise, and during voluntary hyperventilation, in humans.

Three normal subjects performed rest--exercise transitions on a cycle ergometer, from rest to unloaded pedalling (0 W), 50, 100 and 150 W. Each experiment was performed in triplicate, with randomized work load order, in two sessions. Ventilation was obtained breath-to-breath by integration of a pneumotachygraph signal, and cardiac output beat-to-beat by a new development of the Doppler technique. Results were bin-averaged in 4 s bins over the first 20 s, and compared to resting values. Both ventilation and cardiac output increased significantly in the first 2 s. This initial rise in ventilation was due entirely to an increase in rate, the subsequent rise mainly to increase in tidal volume. Cardiac output increased predominantly through change in rate with smaller increases in stroke volume. A striking feature was a tendency for ventilation and cardiac output responses to be biphasic with an initial rise followed by a slight fall at the 14 s mark, and a subsequent rise, at all work loads. Overall correlation between ventilation and cardiac output was therefore high (r = 0.92). Six normal subjects hyperventilated for 45 s voluntarily, (a) at rate 24/min and normal tidal volume; (b) at normal rate and tidal volume of 1.5 l; (c) at rate 24/min and tidal volume of 1.5 l. Cardiac output, averaged over 10-45 s, rose by 0.4, 0.5, and 1.0 l min-1 respectively, with falls in end-tidal PCO2 of 4, 6, and 8 mmHg. Six normal subjects hyperventilated for 60 s with rate 24/min and tidal volume of 1.4 l, and end-tidal PCO2 maintained at 38 +/-2 mm Hg. Cardiac output, averaged from 10-60 s, rose by 1.0 l min-1. With increased rate and tidal volume, whether isocapnic or hypocapnic, cardiac output responses showed an overshoot with a peak value at about 30 s. The hypothesis of 'cardiodynamic hyperpnoea' considers a possible effect of increasing cardiac output on ventilation. The effects of ventilation on cardiac output must also be considered. We propose an extended hypothesis involving stable positive feed-back.

Adult↗
PubMedDate not supplied

Effect on ventilation of carbon dioxide delivered in early inspiration in man.

Four subjects breathed an air-CO2 mixture, obtained by injecting pure CO2 0.4 l.min-1 into the inspiratory line of an open breathing circuit. The effects of injecting CO2 directly into the tubing (Fenn-Craig technique, FC), with a resulting large CO2 bolus in early inspiration, were compared with those of injecting into a mixing chamber (MC) and thus spreading the CO2 load more evenly over inspiration. Ensemble averaging of three experiments for MC and FC in each subject was used to clarify the relatively small changes in ventilation (V), about 5 l.min-1, and end-tidal PCO2 (PETCO2), about 5 mmHg, which were produced by the stimulus. Change in V and in PETCO2 were both systematically less for MC than FC, by about 1 l.min-1 and 0.5 to 1 mmHg respectively, suggesting that the CO2 load to the alveoli was larger for FC, with V then appropriately higher by the normal CO2 response. The increased CO2 load in FC could be accounted for by the lower proportion of CO2 left in the dead space, compared to MC. Thus, in man breathing air, no systematic effect on CO2 sensitivity was produced by an early inspiratory bolus of CO2.

Administration, Inhalation↗