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Biomedical subjects

L Adams

Publications and source records attributed to L Adams.

At least 163 records · Page 9Linked to original sources
PubMed1985

Arterial oxygen desaturation during treadmill and bicycle exercise in patients with chronic obstructive airways disease.

Nine men with severe chronic obstructive airways disease (COAD), known to desaturate on exercise, performed a 6 min self-paced walk on a treadmill, followed by a bicycle exercise with workloads adjusted to mimic the oxygen consumption achieved on the treadmill. During both exercises, ventilation, oxygen consumption, carbon dioxide production, PaO2, PaCO2, pH and arterial lactate were measured and subjective breathlessness recorded. A reasonable match of oxygen consumption between the two exercises was achieved. In all subjects PaO2 fell to a lower level during treadmill compared with bicycle exercise. Ventilation, carbon dioxide production and arterial lactate were higher during bicycle exercise. Subjective breathlessness was greater during bicycle exercise, in proportion to the higher ventilation on the bicycle. The greater anaerobiosis occurring on the bicycle led to acidosis and an increased ventilation, minimizing the exercise fall in PaO2. Bicycle testing may seriously underestimate exercise desaturation occurring during level walking in patients with severe COAD.

Aged↗
PubMed1985

The measurement of breathlessness induced in normal subjects: validity of two scaling techniques.

The intensity of breathlessness induced by ventilatory stimulation resulting from hypercapnia, hypoxia or exercise has been quantified in normals by using the two different sensory scaling techniques of linear visual analogue scaling and ratio magnitude estimation. In naive individuals both techniques show good face validity. When related to ventilation, quantification of breathlessness is moderately reproducible with both methods, even when subjects are kept in ignorance of the pattern of ventilatory stimulation. There is a small within- and large between-subject variability with both scaling techniques; possible factors responsible are discussed. The reproducibility of visual analogue scaling when related to ventilation is independent of the nature of the ventilatory stimulus and is maintained over intervals as long as 1 week when memory for the score given is unlikely to be an important factor. The difficulties of interpreting subjective estimates of perceived breathlessness are discussed, together with the relative merits of the two scaling techniques.

Adult↗
PubMed1985

Breathlessness during different forms of ventilatory stimulation: a study of mechanisms in normal subjects and respiratory patients.

This study investigates the mechanisms underlying the perception of breathlessness induced by hypoxia and hypercapnia in both naive normal subjects and patients with respiratory mechanical problems. In normal subjects separately receiving both oscillating hypercapnic and hypoxic ventilatory stimulation, equivalent peak stimulus intensities in end-tidal gas were associated with a 'damped' ventilatory response when the frequency of stimulation was increased. A concomitant fall in peak breathlessness levels on a visual analogue scale was recorded in each case. In normal subjects and patients, the voluntary copying of a ventilatory pattern recorded during oscillating hypercapnic stimulation was associated with a marked diminution or complete absence of breathlessness despite equivalent levels of peak ventilations achieved. Voluntary copying of hypercapnic stimulated ventilation was not associated with any demonstrable change in the distribution of muscle movements between the chest wall and abdomen. These results suggest that the intensity of breathlessness depends on the level of effective reflex stimulation of the respiratory-related neurones in the medulla. They cannot be explained solely in terms of perception of afferent neural information arising from either chemoreceptors or respiratory mechanoreceptors.

Abdomen↗
PubMed1984

Respiratory impairment induced by smoking in children in secondary schools.

A longitudinal study was carried out from 1975 to 1979 in a cohort of 405 secondary school children. At yearly intervals they underwent a series of tests of pulmonary function designed to monitor lung development; some of these tests are relatively sensitive indicators of early abnormalities. A self administered questionnaire provided details of smoking habits and respiratory symptoms. The prevalence of smoking increased with age; most of those smoking at 16 had already been smoking, at least experimentally, at 13. Taking up smoking was clearly associated with the early onset of cough, production of phlegm, and shortness of breath on exertion. After two years of smoking more than a few cigarettes a day the children who smoked appeared considerably less healthy than their non-smoking peers and showed some evidence of early obstruction of the airways.

Adolescent↗
PubMed1984

Is the voluntary control of exercise in man necessary for the ventilatory response?

The ventilatory response to electrically induced exercise (EEL) was studied in eighteen normal subjects and compared with the response to performing the same exercise voluntarily (EV). EEL was produced by surface electrode stimulation of the quadriceps and hamstring muscles so as to cause a pushing movement at 1 HZ against a spring load; this produced no pain or discomfort. Matching of EV to EEL was achieved by subjects copying a tension signal recorded during EEL and displayed on a storage oscilloscope. There were no differences between the resting states measured before either form of exercise. The ventilatory response (change in ventilation as a ratio of the change in CO2 elimination) was similar in the two types of exercise. The increases in ventilation and CO2 elimination were greater with EEL. Small but significant increases in the gas exchange ratio and serum lactate were found for EEL but not for EV, suggesting an increase in anaerobic metabolism in EEL. End-tidal PCO2 showed little change in either form of exercise. In some runs end-tidal PCO2 rose, but insufficiently to account for the ventilatory response as judged by the response to inhaled CO2. In two subjects arterial blood samples showed small and inconsistent changes in both Pa,CO2 and PaO2 for EV and EEL. pH and base excess changes also were consistent with more anaerobiosis with EEL compared to EV. The first ten breaths of exercise were used to study the on transient. In EV, expiratory duration shortened and ventilation increased significantly on the first breath but CO2 elimination did not increase until the second breath; in EEL, these variables did not change significantly until the second breath. For the remainder of the on transient the pattern of the ventilatory response was similar for EV and EEL. By the end of the on transient both EV and EEL had reached approximately 80% of their final steady-state values. These results suggest that a normal ventilatory response can occur in the absence of a drive to exercise from the cortex.

Adult↗
PubMed1984

The role of spinal cord transmission in the ventilatory response to exercise in man.

The ventilatory response to electrically induced exercise was studied in thirteen patients with traumatic spinal cord transection at or about the level of T6. The steady-state and on-transient responses to this exercise were compared with those obtained in eighteen normal subjects (Adams, Garlick, Guz, Murphy & Semple, 1984). Exercise was produced by surface electrode stimulation of the quadriceps and hamstring muscles so as to produce a pushing movement at 1 HZ against a spring load. At rest there was no significant difference between normals and patients, except that the patients had a lower CO2 elimination (VCO2) and end-tidal PCO2 (PET,CO2) and a higher heart rate. On exercise the mean rise in VCO2 for the patients was 172 ml min-1 (S.D. 72), and for the normals was 287 ml min-1 (S.D. 143). The corresponding mean changes in ventilation (VI) were 4.4 l min-1 (S.D. 2.2) and 7.6 l min-1 (S.D. 3.2). However, the ventilatory equivalent for CO2 (delta VI/delta VCO2) in the steady state was not significantly different between patients (26.0, S.D. 5.9) and normals (28.5, S.D. 7.4). In the steady state there was a mean rise in PET,CO2 of 0.9 mmHg (S.D. 1.4) in the normals, and 3.2 mmHg (S.D. 2.7) in the patients, but there was overlap between the two groups. In many experimental runs in both groups, PET,CO2 did not rise, and sometimes fell. Where PCO2 did rise, the ventilatory response to exercise could not be accounted for on the basis of the ventilatory sensitivity to CO2 inhalation. From arterial sampling in three of the patients it was found that when PET,CO2 rose, the corresponding change in Pa,CO2 was less. During the on transient, there was a significant rise in both VCO2 and VI by the second breath in both groups. At the end of the on transient the normal subjects had achieved 84% (S.D. 40) of the steady-state increase in VCO2 and 88% (S.D. 24) of the increase in VI. The corresponding values for the patients were 67% (S.D. 17) and 77% (S.D. 16) respectively; these differences between normals and patients are significant. The increase of VI during the on transient in the patients was achieved almost entirely by an increase in tidal volume whereas in normals, an increase in respiratory rate was a more important component. We conclude therefore that in man, spinal cord transection with a presumed loss of muscle afferents allows a ventilatory response to electrically induced exercise that cannot be explained by classical chemoreception.(ABSTRACT TRUNCATED AT 400 WORDS)

Carbon Dioxide↗
PubMed1983

Patterns of smoking: measurement and variability in asymptomatic smokers.

Measurements of patterns of puffing (cigarette-holder pneumotachograph) and ventilation (plethysmography) were made in ten asymptomatic smokers during the smoking of a cigarette, on four separate occasions. There were marked individual differences and these were consistent over 3-5 weeks. In itself, the pattern of smoking could be responsible for a threefold variation in smoke intake. Puffing but not inhalation became less intense as a cigarette was smoked. It was not possible to predict indices of absorption from smoking patterns. Certain smoking patterns, e.g. small puff volume, low puff frequency, short duration of inhalation and expulsion of volume between puff and inhalation, may be less harmful than others and this may explain why some individuals remain healthy despite a lifetime of smoking.

Adolescent↗
PubMed1982

Selective management of flail chest and pulmonary contusion.

Four hundred and twenty-seven patients with severe blunt chest trauma were treated resulting in (1) flail chest, (2) pulmonary contusions, (3) pneumothorax, (4) hemothorax, or (5) multiple rib fracture. The need for endotracheal intubation and mechanical ventilation was determined selectively by standard clinical criteria. Avoidance of fluid overload and vigorous pulmonary toilet was attempted in all patients. Three hundred and twenty-eight patients were treated by nonintubation; 318 patients (96.6%) had a successful outcome, while ten required intubation. Only one patient died. The 99 patients who required intubation and mechanical ventilation had a high mortality because of associated shock and head injury; however, the total mortality for the entire group of patients was 6.5%, with only 1.4% mortality caused by pulmonary injury. The incidence of pneumonia was high (51%), but there was only a 4% incidence of tracheostomy complications. Flail chest and pulmonary contusion without flail chest occurred in 95 and 135 patients, respectively. Half of the flail chest patients were intubated, but 69.5% were intubated less than three days. Twenty per cent of the patients with pulmonary contusion required mechanical ventilation, usually for less than three days. This study demonstrates that patients with severe blunt chest trauma can be managed safely by selective intubation and mechanical, ventilation and that the incidence of complications associated with controlled mechanical ventilation can be greatly reduced.

Adolescent↗
PubMed1981

Kainate lesion dissociates striatal dopamine receptor radioligand binding sites.

Kainic acid lesion of rat striata reduces the specific dopamine receptor binding of the butyrophenone antagonist [3H]spiperone and the butyrophenone-like antagonist [3H]domperidone by 56% and 59% respectively. Significantly greater decreases in binding were observed with the agonist [3H]N-propylnorapomorphine (NPA) and the antagonist [3H]flupentixol which showed 79% and 73% losses of high affinity binding respectively. These data indicate that, in part, [3H]spiperone and [3H]domperidone label distinct dopamine receptors with different neuronal localizations from those labeled by [3H]flupentixol and [3H]NPA. Our data is consistent with the hypothesis that [3H]flupentixol and [3H]NPA bind preferentially to adenylate cyclase-linked dopamine (D1) receptors.

Animals↗
PubMed1981

Effects of cyanide antidotes used with sodium nitroprusside infusions: sodium thiosulphate and hydroxocobalamin given prophylactically to dogs.

Cyanide antidotes were given to dogs before an infusion of sodium nitroprusside 1.5 mg kg-1 for 1 h. Dogs given thiosulphate 75 mg kg-1 had significantly lower plasma and red cell cyanide concentrations while plasma thiocyanate concentrations were significantly increased in comparison with control. These changes were associated with only minimal disturbance of tissue oxygenation. There was no effect on red cell cyanide or thiocyanate concentrations in dogs treated with hydroxocobalamin 1.5 mg kg-1, but plasma cyanide concentrations were significantly greater than in those receiving no antidote although there was less evidence of impaired oxygenation. There was no evidence of a synergistic action between thiosulphate and hydroxocobalamin. The vascular response to nitroprusside was unchanged in the thiosulphate-treated dogs, but was significantly greater in those given hydroxocobalamin. The implications for prophylaxis and treatment of cyanide poisoning following nitroprusside overdose are discussed.

Animals↗
PubMed1981

The evaluation of a photometer (the Radiometer OSM2) for the determination of haemoglobin concentration and per cent oxyhaemoglobin and carboxyhaemoglobin in blood.

Haemoglobin concentration and its saturation with oxygen and carbon monoxide were estimated in identical blood samples using an automated two-wavelength photometer (the Radiometer OSM2) and standard methods. The instrument was easy to operate and maintain and, in general, was accurate and repeatable. At carboxyhaemoglobin levels below 1.5%, however, the precision of the instrument was poor.

Carboxyhemoglobin↗
PubMed1980

An evaluation of the clinical potential of a comprehensive model of human respiration in artificially ventilated patients.

1. We have investigated the feasibility of accurately simulating the respiratory function of artificially ventilated patients, using a computer model of the respiratory system. Twelve patients artificially ventilated after uncomplicated cardiac bypass surgery was studied. 2. The basic information required to simulate individual ventilated subjects was measured or derived. A program was written to enable key model parameters to be adjusted automatically to match model predictions to these clinical measurements. On completion of this matching procedure all the variables computed by the model were compared with patient values (measured or derived) and their accuracy was assessed. 3. The matching algorithm successfully optimized parameters of the model representing metabolic activity, tissue respiratory quotient, venous admixture, physiological dead space and total body bicarbonate to match measured values for oxygen consumption, carbon dioxide production, Pa, O2, PaCO2, and arterial HCO3- respectively. Other variables compared arise from the solution of equations within the model and correlation between model and patient values is generally good (r greater than 0.9). However, values of Pv-, O2 correlate less well (r = 0.85). Factors affecting the accuracy of patient simulation are discussed and some deficiencies analysed. 4. The creation of an accurate, steady-state representation of a patient by the model opens up the possibility of using it interactively as an aid to clinical management. Some possible future developments of the technique are discussed.

Blood↗
PubMed1979

Some physiological and metabolic effects of sodium nitroprusside and cyanide in the dog.

The cardiovascular and acid-base changes following equivalent i.v. bolus doses of sodium nitroprusside (SNP) and potassium cyanide (KCN) have been studied in two groups of anaesthetized dogs. In a third group, the metabolic changes produced by i.v. infusion of SNP 1.5 mg kg-1 at a constant rate over 1 h have been studied. In contrast to a decrease in arterial pressure following SNP, hypertension and tachycardia occurred after the administration of KCN, with hyperventilation and an increase in packed cell volume. During infusion of SNP, increases in plasma cyanide concentrations were associated with an increase in arterial base deficit, plasma lactate and excess lactate and a decrease in oxygen consumption. The occurrence of lactic acidosis with SNP 1.5 mg kg-1 suggests that this may be the maximum safe dose for short term infusion. However, all these changes reversed spontaneously following discontinuation of SNP, indicating that base deficit is an adequate metabolic monitor during administration of SNP.

Acid-Base Equilibrium↗
PubMed1979

Metabolism of sodium nitroprusside and cyanide in the dog.

Blood cyanide (HCN) and thiocyanate (SCN) concentrations were measured at intervals in anaesthetized dogs given bolus doses of sodium nitroprusside (SNP) 1 mg kg-1 or potassium cyanide 1.07 mg kg-1 and in animals infused with SNP 1.5 mg kg-1 for 1 h. Cyanide appeared rapidly in the red cells to give peak concentrations which accounted for more than 90% of the total blood HCN. A delay between the peak plasma and red cell HCN concentrations confirmed that some of the SNP was degraded in the plasma. Comparison of HCN and SCN concentrations with those measured previously in patients receiving an infusion of SNP suggests that the degradation of SNP and detoxication of HCN may be more rapid in the dog. The various pathways of HCN detoxication are discussed in relation to the reduced formation of SCN in dogs receiving SNP compared with those receiving KCN.

Animals↗