Retrosplenial cortex inactivation selectively impairs navigation in darkness

There is an emerging consensus that retrosplenial and posterior parietal cortex importantly contribute to navigation. Several theories of navigation have argued that these cortical areas, particularly retrosplenial cortex, are involved in path integration. In an effort to characterize the role of retrosplenial cortex in active navigation, the effects of temporary inactivation of retrosplenial cortex on spatial memory performance were evaluated in light and dark testing conditions. Inactivation of retrosplenial cortex selectively resulted in behavioral impairments when animals were tested in darkness. These data support the hypothesis that retrosplenial cortex contributes to navigation in darkness, perhaps by providing mnemonic associations of the visual and nonvisual environment that can be used to correct for cumulative errors that occur during path integration.

Superior colliculus and active navigation: role of visual and non-visual cues in controlling cellular representations of space

To begin investigation of the contribution of the superior colliculus to unrestrained navigation, the nature of behavioral representation by individual neurons was identified as rats performed a spatial memory task. Similar to what has been observed for hippocampus, many superior collicular cells showed elevated firing as animals traversed particular locations on the maze, and also during directional movement. However, when compared to hippocampal place fields, superior collicular location fields were found to be more broad and did not exhibit mnemonic properties. Organism-centered spatial coding was illustrated by other neurons that discharged preferentially during right or left turns made by the animal on the maze, or after lateralized sensory presentation of somatosensory, visual, or auditory stimuli. Nonspatial movement-related neurons increased or decreased firing when animals engaged in specific behaviors on the maze regardless of location or direction of movement. Manipulations of the visual environment showed that many, but not all, spatial cells were dependent on visual information. The majority of movement-related cells, however, did not require visual information to establish or maintain the correlates. Several superior collicular cells fired in response to multiple maze behaviors; in some of these cases a dissociation of visual sensitivity to one component of the behavioral correlate, but not the other, could be achieved for a single cell. This suggests that multiple modalities influence the activity of single neurons in superior colliculus of behaving rats. Similarly, several sensory-related cells showed dramatic increases in firing rate during the presentation of multisensory stimuli compared to the unimodal stimuli. These data reveal for the first time how previous findings of sensory/motor representation by the superior colliculus of restrained/anesthetized animals might be manifested in freely behaving rats performing a navigational task. Furthermore, the findings of both visually dependent and visually independent spatial coding suggest that superior colliculus may be involved in sending visual information for establishing spatial representations in efferent structures and for directing spatially-guided movements.

The effect of chest wall transcutaneous electrical nerve stimulation on dyspnoea

We studied the effects of transcutaneous electrical nerve stimulation (TENS) over the chest wall on breathlessness in normal subjects during exercise. Eleven male subjects performed a progressive incremental exercise test to break point on four consecutive days. TENS (continuous form, frequency 100 Hz, pulse width 200 microseconds) was applied during three of these tests-over the second intercostal spaces during inspiration ('in phase' with the underlying inspiratory muscle contraction) or expiration ('out of phase' with contraction) or over the deltoid muscles during inspiration (control), and not on the fourth occasion in random order. Breathlessness (Borg scale), heart rate, respiratory frequency, tidal volume, minute ventilation and minute oxygen uptake were measured. No significant differences were found for any of the measured variables between the four study days. We conclude that TENS under these circumstances has no effect on the sensation of breathlessness or on the measured physiological variables in normal subjects during exercise.

Resting energy expenditure, substrate use, and video tapes

OBJECTIVE

To investigate the effect of watching different types of video on energy expenditure.

DESIGN

Randomised study assessing a "pleasant," an "amusing," an "exciting," and no video film clips.

SUBJECTS

12 volunteers who did not know the purpose of the study.

MAIN OUTCOME MEASURES

Changes in energy expenditure, substrate use, heart rate, and aural temperature during each film clip.

RESULTS

Energy expenditure was raised slightly (0.21 kJ/day) during the "exciting" film. Individual responses varied greatly.

CONCLUSION

Watching different types of video seems to have little effect on resting metabolic rate.

Significance of solitary and multiple esophageal ulcers in patients with AIDS

We endoscopically evaluated odynophagia and/or dysphagia in 23 patients with acquired immunodeficiency syndrome (AIDS). Eleven patients (48%) were found to have esophageal ulcers. Seven of them had deep, sharply demarcated, well-circumscribed ulcer craters with raised edges; in two the ulcer extended to the muscularis propria. Ulcers were single in four patients, multiple in six, and unspecified in one. Biopsies were nondiagnostic. In eight patients, mycobacterial, viral, and fungal cultures were negative. Specific infections diagnosed in three patients were treated with appropriate agents. Ulcers were treated symptomatically, and seven patients received therapy for suspected viral etiology. Symptoms remained unchanged in five patients, improved in three, and resolved in two. Fifty-five percent of patients died within 3.6 months (mean) of diagnosis. Large solitary and multiple esophageal ulcers are common in AIDS patients with odynophagia and dysphagia.

Breathing pattern awake and asleep in patients with myotonic dystrophy

Patients with myotonic dystrophy often have an irregular pattern of breathing at rest, implying abnormality of breathing control. No central medullary defect has been found in such patients. We postulated that irregular breathing in myotonic dystrophy due to abnormal central respiratory output would persist during slow-wave sleep. We examined the patterns of breathing whilst awake and asleep in seven patients with myotonic dystrophy, seven similarly weak nonmyotonic subjects and seven normal controls. Polysomnography was performed, and the coefficients of variation (CoV) of the breath intervals were analysed during different stages of sleep. The myotonic group showed significantly greater variation in breath intervals than the other two groups whilst awake (median CoV 37 vs 18% for nonmyotonics) and during light sleep (31 vs 13%). This difference was not evident during slow-wave sleep (median CoV 12 vs 9% in nonmyotonic). We conclude that irregular breathing in patients with myotonic dystrophy whilst awake and during light sleep, does not persist during slow-wave sleep. These results suggest that "behavioural" influences play a role in the abnormal breathing pattern found in myotonic dystrophy. The source of the irregular breathing is unlikely to be found in the medulla, but may originate from forebrain influences.

Breathing pattern awake and asleep in patients with myotonic dystrophy

Patients with myotonic dystrophy often have an irregular pattern of breathing at rest, implying abnormality of breathing control. No central medullary defect has been found in such patients. We postulated that irregular breathing in myotonic dystrophy due to abnormal central respiratory output would persist during slow-wave sleep. We examined the patterns of breathing whilst awake and asleep in seven patients with myotonic dystrophy, seven similarly weak nonmyotonic subjects and seven normal controls. Polysomnography was performed, and the coefficients of variation (CoV) of the breath intervals were analysed during different stages of sleep. The myotonic group showed significantly greater variation in breath intervals than the other two groups whilst awake (median CoV 37 vs 18% for nonmyotonics) and during light sleep (31 vs 13%). This difference was not evident during slow-wave sleep (median CoV 12 vs 9% in nonmyotonic). We conclude that irregular breathing in patients with myotonic dystrophy whilst awake and during light sleep, does not persist during slow-wave sleep. These results suggest that "behavioural" influences play a role in the abnormal breathing pattern found in myotonic dystrophy. The source of the irregular breathing is unlikely to be found in the medulla, but may originate from forebrain influences.

The effect of severe head injury on whole body energy expenditure and its possible hormonal mediators in children

This study examines the effects of severe head injury in children on whole body energy expenditure and the mediators that influence this. One hundred five serial measurements of whole body energy expenditure and plasma adrenaline, triiodothyronine, glucagon, cortisol, insulin, and growth hormone concentrations were made in 18 children aged 2-15 y receiving neurointensive care for severe head injury. Energy expenditure was measured using indirect calorimetry by a modified Douglas bag technique, and hormones were measured by RIA or radioenzymatic assay. Energy expenditure varied markedly between and within children (mean 97% of predicted, range 60-137%) and was significantly lower in the four children with a poor outcome (p = 0.03). Within each child there were statistically significant positive relationships between energy expenditure and adrenaline (p < 0.0001), triiodothyronine (p < 0.0001), and glucagon (p < 0.0001). However, there was evidence that the effect of adrenaline on energy expenditure was attenuated. This may be due to the effects of the cerebral trauma itself on central nervous influences on energy expenditure, to interactions between hormones, or to a global impairment of O2 utilization by the body's tissues.

Hormonal and metabolic profiles in subjects with obstructive sleep apnea syndrome and the acute effects of nasal continuous positive airway pressure (CPAP) treatment

Nocturnal secretion of growth hormone is impaired in patients with obstructive sleep apnea (OSA), but the metabolic consequences have not been reported. We measured blood levels of the hormones insulin, C-peptide, growth hormone, cortisol and glucagon together with the intermediary metabolites of carbohydrate (glucose, pyruvate, lactate, alanine) and lipid metabolism [glycerol, nonesterified fatty acids (NEFA), 3-hydroxybutyrate] in six obese nondiabetic men with OSA on two nights. In the first study, the untreated subjects showed frequent apneas and consequent hypoxemia. The hormone and metabolite concentrations were compared with those obtained on the following night when the subjects were treated effectively with nasal continuous positive airway pressure (CPAP). There were no significant differences in the concentrations of insulin, C-peptide, cortisol or glucagon. We confirmed a marked reduction in growth hormone concentrations in OSA, with a significant increase on the CPAP night. The nocturnal profiles of glucose, pyruvate, lactate, alanine and glycerol showed no differences between the two nights, but concentrations of NEFA and 3-hydroxybutyrate, both products of lipolysis, were significantly greater on the treatment night. Because growth hormone has a lipolytic action, the results suggest that suppression of secretion of growth hormone in untreated OSA results in impaired lipolysis, which is rapidly reversed by nasal CPAP.

Recovery of 13C in breath from infused NaH13CO3 increases during euglycaemic hyperinsulinaemia

1. The effect of euglycaemic hyperinsulinaemia on the recovery of 13C in expired CO2 has been assessed in six normal subjects. Each was studied on three occasions: once with a 6 h primed constant infusion of NaH13CO3 combined with a euglycaemic hyperinsulinaemic clamp for the last 3 h (study 1), once with a 6 h primed constant infusion of NaH13CO3 alone (study 2) and once with a 6 h infusion of normal saline combined with a hyperinsulinaemic clamp for the last 3 h (study 3). Measurements of 13C enrichment of expired CO2 were made in the third and sixth hour of each infusion. 2. There was no significant increase in enrichment during study 3 (3 h 0.00047 +/- 0.00016 versus 6 h 0.00069 +/- 0.00028 atom per cent excess) with potato-starch-derived D-glucose used to maintain euglycaemia. 13C recovery increased in the sixth hour of both study 1 and 2 (study 1: 3 h 74.4 +/- 2.0 versus 6 h 85.5 +/- 2.6%, P < 0.01; study 2: 3 h 72.1 +/- 2.4 versus 6 h 81.7 +/- 1.4%, P < 0.01). There was no significant difference in recovery between studies 1 and 2. 3. These results suggest that increased recovery during a sequential euglycaemic clamp is predominantly time-dependent. Studies which use this technique to examine the effect of insulin on substrate oxidation should take this into account.

The effect of controlled-release salbutamol on sleep and nocturnal oxygenation in patients with asthma and chronic obstructive pulmonary disease

Patients with asthma or chronic obstructive pulmonary disease (COPD) may have falls in oxygen saturation at night. We have investigated the effect of a long acting beta agonist (salbutamol CR) on nocturnal oxygen saturation (SaO2) in asthma and COPD. Eleven asthmatic and 14 COPD patients in stable condition were randomly allocated to 8 mg salbutamol CR or placebo twice daily in a double-blind, cross-over study. FEV1 at entry was 71.5% predicted in the asthmatic patients and 36% predicted in the COPD group. Each treatment period lasted 7 days, at the end of which measurements of ventilatory function and detailed sleep studies were performed. There was a significant improvement in morning FEV1 in the asthmatic patients when on active treatment and a small, but non-significant improvement in the COPD group. Sleep architecture and oxygenation were similar on placebo and on active treatment in both groups. We conclude that salbutamol CR has no significant effect on nocturnal oxygenation or sleep pattern in patients with mild asthma or moderately severe COPD.

The impact of metformin therapy on hepatic glucose production and skeletal muscle glycogen synthase activity in overweight type II diabetic patients

The effect of metformin therapy on glucose metabolism was examined in eight overweight newly presenting untreated type II diabetic patients (five males, three females). Patients were treated for 12 weeks with either metformin (850 mg x 3) or matching placebo using a double-blind crossover study design; patients were studied at presentation and at the end of each treatment period. Insulin action was assessed by measuring activation of skeletal muscle glycogen synthase (GS) before and during a 4-hour hyperinsulinemic euglycemic clamp (100 mU.kg-1 x h-1). Metformin therapy was associated with a significant decrease in fasting blood glucose (6.8 +/- 0.6 v 8.3 +/- 0.9 mmol.L-1, P < .01) and glycosylated hemoglobin ([HbA1] 7.7% +/- 0.4% v 8.5% +/- 0.5%, P < .01) levels. Fasting hepatic glucose production (HGP) was also significantly decreased following metformin therapy (1.98 +/- 0.13 v 2.41 +/- 0.20 mg.kg-1 x min-1, P < .02), whereas fasting insulin and C-peptide concentrations remained unaltered. The decrease in basal HGP correlated closely with the decrease in fasting blood glucose concentration (r = .92, P < .001). Insulin-stimulated glucose uptake was assessed using the hyperinsulinemic euglycemic clamp technique and was increased post-metformin (3.8 +/- 0.6 v 3.1 +/- 0.7 mg.kg-1 x min-1, P < .05). This was primarily the result of increased nonoxidative glucose metabolism (1.1 +/- 0.6 v 0.4 +/- 0.6 mg.kg-1 x min-1, P < .05); oxidative glucose metabolism did not change. Metformin had no measurable effect on insulin activation of skeletal muscle GS, the rate-limiting enzyme controlling muscle glucose storage.(ABSTRACT TRUNCATED AT 250 WORDS)

Do nonesterified fatty acids regulate skeletal muscle protein turnover in humans?

We examined whether elevated plasma nonesterified fatty acid (NEFA) levels exert a direct effect on protein metabolism by measuring [2H5]phenylalanine skeletal muscle exchange and whole body turnover. [2H5]phenylalanine was infused (0.5 mg.kg-1 x h-1) for 300 min in seven healthy subjects on two occasions. Intralipid (10%; 30 ml/h) or 0.154 mol/l NaCl was infused in random order from 120 min. Measurements were taken during basal (90-120 min) and infusion (270-300 min) periods. Intralipid infusion increased plasma NEFA levels [1.31 +/- 0.13 vs. 0.49 +/- 0.05 (SE) mmol/l; P < 0.05] and forearm NEFA uptake [45 +/- 76 vs. -51 +/- 44 nmol . 100 ml forearm-1 x min-1; P < 0.05]. Serum insulin and blood ketone body levels were similar with the two treatments. Elevated plasma NEFA levels were associated with a comparable decrease in forearm phenylalanine uptake (11 +/- 2 vs. 17 +/- 2 nmol x 100 ml forearm-1 x min-1; lipid vs. control, P < 0.05) and release (20 +/- 2 vs. 26 +/- 3 nmol x 100 ml forearm-1 x min-1; lipid vs. control, P < 0.05). However, there were no significant changes in net forearm phenylalanine exchange and whole body phenylalanine turnover. Therefore, elevated plasma NEFA levels were associated with a comparable decrease in the rates of skeletal muscle protein synthesis and breakdown but did not appear to influence overall protein balance, as assessed using [2H5]phenylalanine.

The role of plasma non-esterified fatty acids during exercise in type 2 diabetes mellitus

Elevated fasting plasma non-esterified fatty acid (NEFA) levels have been reported in Type 2 diabetes. We examined whether such changes persist during low-grade exercise and influence carbohydrate metabolism. Eight Type 2 diabetic patients with moderate glycaemic control and eight healthy controls received the anti-lipolytic agent, acipimox, or placebo on separate occasions before exercising for 45 min at 35% pre-determined VO2max. Fasting plasma NEFA levels were similar (0.40 +/- 0.06 (SEM) and 0.45 +/- 0.05 mmol l-1; healthy and Type 2 diabetic subjects) following placebo, and increased to comparable levels with exercise (0.73 +/- 0.07 and 0.73 +/- 0.10 mmol l-1). Acipimox lowered basal NEFA levels (0.14 +/- 0.03 and 0.28 +/- 0.04 mmol l-1; both p < 0.05 vs placebo), and prevented the rise with exercise. Blood glucose (p < 0.001) and serum insulin (p < 0.01) levels were higher in the Type 2 diabetic patients (vs controls) for both treatments. Whole body lipid oxidation increased from baseline to a comparable degree with exercise following placebo (3.2 +/- 0.3 and 2.8 +/- 0.3 mg kg-1 min-1; healthy and Type 2 diabetic subjects, both p < 0.02). Although less marked, the same was also observed following acipimox (2.0 +/- 0.4 and 2.1 +/- 0.5 mg kg-1 min-1; both p < 0.05). Carbohydrate oxidation increased with exercise in both subject groups, but with no significant difference between the treatments. Thus, the metabolic response to low-grade exercise was normal in Type 2 diabetic patients with moderate glycaemic control, but occurred against a background of hyperinsulinaemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid and lipoprotein metabolism in familial combined hyperlipidaemia during treatment of sporadic phaeochromocytoma: a case study

Lipid metabolism was evaluated during management of phaeochromocytoma in a 41 year old non-obese post-menopausal women with familial combined hyperlipidaemia. The main effect of the excess catecholamine secretion on lipid metabolism was increased lipolytic activity, lower serum triglyceride and increased HDL cholesterol concentrations, compared with findings following removal of the tumour. Before removal of the tumour, the use of beta blockers alone led to marked deterioration of the hyperlipidaemic state, and combined alpha and beta blockade additionally led to a marked reduction in fat oxidation and lipoprotein lipase activity. Overactivity of the adrenergic system leads to changes in lipid metabolism in phaeochromocytoma. Treatment of the phaeochromocytoma may lead to worsening of hyperlipidaemia pre-existing in such individuals.

Effect of increased free fatty acid supply on glucose metabolism and skeletal muscle glycogen synthase activity in normal man

1. Experimental elevation of plasma non-esterified fatty acid concentrations has been postulated to decrease insulin-stimulated glucose oxidation and storage rates. Possible mechanisms were examined by measuring skeletal muscle glycogen synthase activity and muscle glycogen content before and during hyperinsulinaemia while fasting plasma non-esterified fatty acid levels were maintained. 2. Fasting plasma non-esterified fatty acid levels were maintained in seven healthy male subjects by infusion of 20% (w/v) Intralipid (1 ml/min) for 120 min before and during a 240 min hyperinsulinaemic euglycaemic clamp (100 m-units h-1 kg-1) combined with indirect calorimetry. On the control day, 0.154 mol/l NaCl was infused. Vastus lateralis muscle biopsy was performed before and at the end of the insulin infusion. 3. On the Intralipid study day serum triacylglycerol (2.24 +/- 0.20 versus 0.67 +/- 0.10 mmol/l), plasma nonesterified fatty acid (395 +/- 13 versus 51 +/- 1 mumol/l), blood glycerol (152 +/- 2 versus 11 +/- 1 mumol/l) and blood 3-hydroxybutyrate clamp levels [mean (95% confidence interval)] [81 (64-104) versus 4 (3-5) mumol/l] were all significantly higher (all P less than 0.001) than on the control study day. Lipid oxidation rates were also elevated (1.07 +/- 0.07 versus 0.27 +/- 0.08 mg min-1 kg-1, P less than 0.001). During the clamp with Intralipid infusion, insulin-stimulated whole-body glucose disposal decreased by 28% (from 8.53 +/- 0.77 to 6.17 +/- 0.71 mg min-1 kg-1, P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of intravenous metformin on glucose metabolism during hyperglycaemia in type 2 diabetes

A stepped intravenous metformin infusion was used in conjunction with the hyperglycaemic clamp technique to study the dose-response relationship of plasma metformin concentration with hepatic glucose production and peripheral glucose disposal in nine patients with Type 2 diabetes. The study was of double-blind crossover design, using NaCl infusion as control. Plasma metformin concentrations spanning the therapeutic range (1.64 +/- 0.13 mg l-1 and 6.57 +/- 0.61 mg l-1) were achieved. No differences in peripheral glucose disposal were demonstrated when compared with NaCl infusion (3.4 +/- 0.1 vs 3.6 +/- 0.2 (+/- SE) mg kg-1 min-1 and 3.4 +/- 0.2 vs 3.3 +/- 0.2 mg kg-1 min-1, respectively). There was also no difference in basal hepatic glucose production during metformin and NaCl infusion (2.7 +/- 0.3 vs 2.8 +/- 0.2 mg kg-1 min-1). No acute effect of metformin on hepatic glucose production or peripheral glucose disposal was observed, implying that a chronic persistent effect is more important in these respects than immediate effects consequent upon changes in plasma drug level.

An evaluation of the Deltatrac indirect calorimeter by gravimetric injection and alcohol burning

We evaluated a 'state of the art' open hood type of indirect calorimeter (Deltatrac, Datex) to determine its stability and precision, and related these to in vivo measurements made with the same type of calorimeter. Three Deltatrac Metabolic Monitors were investigated at two centres over a period of twelve months by two methods of recovery: (i) gravimetric injection of a nitrogen/CO2 gas mix and (ii) ethanol burning using the manufacturers approved apparatus. We compared machine variation with in vivo variation in measurements of oxygen uptake and carbon dioxide production at rest in healthy subjects. The Deltatrac recovery of both oxygen and carbon dioxide was on average 4.8% and 4.7% higher respectively for the alcohol burning method. We suspected that this apparent over-recovery was because the alcohol burner produced a resistance to the airflow generated across the canopy. By gravimetrically injecting the gas mix into the canopy hose whilst the alcohol burner was attached we were able to confirm this error. There was no significant change in recovery for any of the Deltatracs by either method over the year of evaluation. The between-study variation for the machine and in vivo measurements were less than 4%, and the within-study variations were less than 6% and less than 7%, respectively. These studies re-emphasise that careful evaluation of commercially produced indirect calorimeters is essential before clinical measurements are made.

Role of plasma non-esterified fatty acids during and after exercise

1. The importance of circulating non-esterified fatty acids as a substrate during and after low-grade exercise has been examined by using a nicotinic acid analogue to inhibit lipolysis. Seven healthy men received acipimox or placebo on separate occasions. After 90 min, bicycle exercise was performed for 45 min (40% of pre-determined maximum oxygen uptake), followed by a 60 min recovery period. 2. The plasma concentration of non-esterified fatty acids increased during exercise after placebo (320 +/- 80 to 630 +/- 110 mumol/l) and remained elevated in the post-exercise period. Basal concentrations were lower after acipimox (100 +/- 10 mumol/l; P less than 0.05); they declined to 60 +/- 10 mumol/l during exercise and remained at this level for the rest of the study. 3. Lipid oxidation increased from 0.8 +/- 0.1 to 4.2 +/- 0.5 mg min-1 kg-1 during exercise after placebo (P less than 0.001) and remained elevated in the post-exercise period (1.2 +/- 0.1 mg min-1 kg-1). It was lower after acipimox, but still increased from 0.3 +/- 0.1 to 2.3 +/- 0.2 mg min-1 kg-1 with exercise. Carbohydrate oxidation was increased after acipimox compared with after placebo, but only reached significance during the post-exercise period (P less than 0.05). 4. Although acipimox abolished the rise in the plasma concentration of non-esterified fatty acids during exercise, there was only a 50% decrease in the rate of lipid oxidation. This suggests that an alternative source of non-esterified fatty acids makes an important contribution to the supply of lipid for oxidation during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Value of nocturnal oxygen saturation as a screening test for sleep apnoea

The sensitivity and specificity of overnight recording of arterial oxygen saturation (SaO2) in routine clinical practice was evaluated in 41 subjects who were being investigated for possible sleep apnoea-hypopnoea syndrome. SaO2 was measured with an ear probe oximeter (Biox IIa) and chart recorder during an "acclimatisation" night immediately before a detailed polysomnographic study. The recordings were classified by two observers as positive, negative, or uninterpretable. Twelve of the 41 patients had the obstructive sleep apnoea syndrome when defined in terms of an apnoea-hypopnoea index greater than 15 events an hour on the second night. The sensitivity of nocturnal SaO2 on the acclimatisation night when the diagnostic criterion was an apnoea-hypopnoea index of greater than 5, greater than 15, and greater than 25/h was 60%, 75%, and 100% respectively. Corresponding values for specificity were 95%, 86%, and 80%. Oximetry alone therefore allowed recognition of a moderate or severe sleep apnoea syndrome. In routine practice an appreciable number of equivocal results is likely and repeat oximetry or more detailed polysomnography will then be required if clinical suspicion is high.

A video system for investigating breathing disorders during sleep

A system has been developed for investigating breathing during sleep that superimposes physiological signals on a video image of the patient, with the combined image plus sound recorded on video tape for later analysis. Signals normally displayed include oxygen saturation, airflow, chest wall motion, electroencephalogram, and electrooculogram; but others can be recorded if desired. The information is displayed on a timebase appropriate for the recognition and analysis of respiratory events during sleep. In addition, use is made of normally invisible video lines to record the analogue voltage waveforms so that on replay this information can be displayed on a fast timebase for analysing the more rapidly changing waveforms of electrophysiological signals. The system allows detailed polysomnography to be performed in the normal ward setting with the subject monitored overnight by the nursing staff. Subsequent analysis of the synchronised video, audio, and analogue signals allows measurement of the conventional indices obtained by polysomnography and aids their interpretation.

Breathing during sleep in patients with myotonic dystrophy and non-myotonic respiratory muscle weakness

Sleep apnoea and hypopnoea have been reported in myotonic dystrophy, but it is unclear whether this is simply attributable to the respiratory muscle weakness which is common in this condition. We therefore investigated whether breathing and oxygenation during sleep were more abnormal in patients with myotonic dystrophy than in patients with non-myotonic muscle weakness. Seven subjects were studied in each of three groups: normal controls, myotonic dystrophy and non-myotonic weakness. Patients in the latter group were chosen to represent a similar range of severity of respiratory muscle weakness to those with myotonic dystrophy. Detailed polysomnography was performed; the severity of breathing disorders during sleep was quantified in terms of the frequencies of apnoea and hypopnoea and the degree of arterial desaturation. The myotonic patients showed more frequent apnoea and hypopnoea and more severe desaturation than the other two groups; the results in the non-myotonic patients were generally intermediate. The results suggest that abnormal breathing during sleep is common in myotonic dystrophy and is not due solely to the direct effects of respiratory muscle weakness. Somnolence, which is a well recognized symptom of myotonic dystrophy, was not clearly attributable to the sleep apnoea/hypopnoea syndrome nor to abnormal sleep architecture in the myotonic patients.

Lung function in patients with diabetes mellitus

Lung function was assessed in 35 nonsmoking adults with insulin dependent diabetes mellitus and 34 matched control subjects. The tests included spirometry, lung volumes, CO transfer factor and maximum respiratory pressures. Additionally, in subjects under 35 years of age (20 patients and 18 controls) measurements of CO transfer factor were obtained during exercise at three different workloads. Random blood glucose and glycosylated haemoglobin were measured and each patient's diabetic history was recorded. The total lung capacity (TLC) in the patients was lower than those recorded for the controls (P less than 0.05) but there were no significant differences in respiratory muscle strength between the groups. In the young group of patients (less than 35 years) the transfer factor for CO (TLCO) was similar but the volume corrected transfer coefficient (KCO) was higher at rest than in the controls (P less than 0.02). The KCO remained high in these patients during exercise. The older patients (greater than 35 years) showed a lower TLCO (P less than 0.01) with a similar KCO to the controls. The association of a reduction in TLC and higher KCO in the young patients suggests an extrapulmonary mechanism of lung volume restriction. This is not attributable to muscle weakness but might be due to limited expansion of the rib cage. In older patients any tendency for KCO to rise may be masked by disease-related changes in the pulmonary microvasculature.

Adverse effect of additional weight on exercise against gravity in patients with chronic obstructive airways disease

The effects of an acute, artificially simulated increase in body weight on exercise performance were examined in 14 patients of normal weight (mean (SD) body mass index 22.3 (2.7)), age 61 (8) years) with chronic obstructive airways disease (FEV1 1.2 (0.5) 1; vital capacity (VC) 2.9 (0.6) 1), and in six normal subjects with similar age and sex distribution. The patients performed a six minute walking test and a symptom limited step climbing test both with and without an additional 10 kg weight (two leaded aprons). The normal subjects performed a step test with and without the additional weight. Ventilation (VE) and oxygen consumption (VO2) were measured during step climbing. Resting spirometric values were not altered by the additional weight. In the patients the median number of steps climbed fell from 67.5 when they were unweighted to 44.5 when they were weighted. Mean VE and VO2 were increased during weighted step climbing by 14% and 13% but the maximum levels of VE and VO2 achieved were similar during unweighted and weighted exercise (VE 36.8 (8.6) and 37.3 (10.2) 1 min-1, VO2 1.35 (0.3) and 1.41 (0.4) 1 min-1 respectively). The normal subjects were readily able to complete 150 steps both with and without the additional weight. In the patients the six minute walking distance fell only slightly with the extra weight, from 554 (SD 61) to 540 (62) m. A subsidiary study was carried out in six healthy younger subjects in which VE and VO2 were measured during a 5.6 km/h six minute treadmill walk at zero incline. The additional weight did not alter VE or VO2 during exercise. In conclusion, a small acute increase in body weight substantially worsened the already reduced "uphill" exercise performance in patients with chronic obstructive airways disease because of its effect on ventilation and oxygen consumption. These results suggest that modest weight loss might benefit patients with chronic obstructive airways disease even though they may be only slightly above their ideal body weight.