Portable liquid oxygen and exercise ability in severe respiratory disability.

BACKGROUND: The development of portable liquid oxygen systems, capable of delivering high flow rate oxygen for long periods, justifies reassessment of the value of supplemental oxygen to aid exercise tolerance in patients with chronic respiratory insufficiency. The type of exercise test and the low oxygen flow rates previously used may account for the variable and often poor responses to supplemental oxygen reported in earlier studies. METHODS: The walking tolerance of 30 patients with severe respiratory disability was measured while they were breathing air and increasing doses of supplemental oxygen (2, 4, 6 1/min) by using both the standard six minute walking test and an endurance walking test. To assess the initial learning effect and repeatability of the walking tests, three six minute walks and three endurance walks were performed on day 1 and a single walk of each type on days 2, 3, and 14. In addition, oxygen dosing studies were performed on days 2 and 3 after the initial baseline walking tests. Each dosing study comprised four endurance walking tests or four six minute walking tests with patients breathing either air at a flow rate of 4 1/min from a portable cylinder or supplemental oxygen at a flow rate of 2, 4 or 6 1/min from a portable liquid oxygen supply. The order of the tests was randomised. Walking distance with each flow rate of oxygen was compared with walking distance with patients carrying cylinder air and for the initial unburdened walks. Breathlessness was assessed by visual analogue scoring on completion of each walk. RESULTS: Exercise ability and breathlessness were significantly improved with supplemental oxygen and this benefit outweighed the reduction in performance resulting from carrying the portable device. Supplemental oxygen at flow rates of 2, 4, and 6 1/min increased mean endurance walking distances by 37.9%, 67.7% and 85.0% and six minute walking distances by 19.2%, 34.5%, and 36.3% by comparison with distances when the patient was carrying air with a flow rate of 4 1/min. The additional work of carrying the portable gas supply reduced endurance walking distance by 22.2% and six minute walking distance by 14.1% by comparison with a baseline unburdened walk. Comparison of supplemental oxygen at 2, 4, and 6 1/min with the baseline unburdened performance showed increased endurance walking distances of 7.3%, 30.4%, and 43.9% and six minute walking distances of 2.3%, 15.5%, and 17.0%. Walking distance was increased by more than 50% by comparison with an unburdened walk in seven patients with the endurance walking test but in only three patients with the six minute walking test. The benefit was similar in patients with obstructive and with interstitial lung disease. Individual responses were variable and only desaturation during the baseline walk in patients with obstructive lung disease had any predictive value for benefit with oxygen. CONCLUSION: As there was no clear relation between response to oxygen therapy and the patients' characteristics, assessment for supplemental oxygen therapy will depend on exercise testing. It is suggested that portable oxygen should be considered only if a patient shows a 50% improvement in exercise ability with high flow rate oxygen (4-6 1/min) by comparison with an unburdened walk.

A comparison of the pharmacological and mechanical properties in vitro of large and small pulmonary arteries of the rat.

1. The mechanical and pharmacological properties of small pulmonary arteries (100-300 microns normalized lumen diameter) were directly compared with those of the left main pulmonary artery (1-2 mm) from the rat. The active and passive length-tension characteristics and responses to a variety of agonists and antagonists were dependent on arterial diameter. 2. Maximum contractile function was obtained in both groups of vessels when stretched so as to give an equivalent transmural pressure of 30 mmHg. This is substantially lower than that found for systemic vessels, and reflects the normal low pulmonary arterial pressure. 3. Noradrenaline was a powerful vasoconstrictor in large but not small pulmonary arteries (P less than 0.001). In contrast, bradykinin produced a significantly greater response in the small arteries (P less than 0.001). In comparison with large pulmonary arteries, small arteries were more sensitive to noradrenaline (P less than 0.05) and 5-hydroxytryptamine (P less than 0.001), less sensitive to endothelin-1 (P less than 0.001) and had the same sensitivity to prostaglandin F2 alpha. 4. The mechanism that maintains the low arterial tone of the pulmonary circulation is unknown, but it may involve the release of relaxing factors from the endothelium. In this preparation, basal resting tone could not be demonstrated in either large or small arteries. 5. Acetylcholine-induced relaxation of pre-contracted pulmonary arteries was reduced or absent in the small artery, despite histological evidence of an intact endothelium. In large arteries pre-contracted with prostaglandin F2 alpha, acetylcholine (100 mumol/l) caused 88.2% relaxation compared with 25.2% in the small artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Inositol 1,4,5-trisphosphate- and guanosine 5'-O-(3-thiotriphosphate)-induced Ca2+ release in cultured airway smooth muscle.

1. The interaction between inositol 1,4,5-trisphosphate (InsP3) and guanosine 5'-O-(3-thio triphosphate) (GTP gamma S) releasable calcium (Ca2+) pools was examined using 45Ca effluxes in permeabilized cultured airway smooth muscle cells from rabbit trachea. 2. Addition of InsP3 or GTP gamma S caused a concentration-dependent release of intracellular Ca2+. The release of Ca2+ by InsP3 was much greater than with GTP gamma S. Pretreatment with maximally effective InsP3 (10 microM) abolished the GTP gamma S-induced Ca2+ release, whereas pretreatment with 100 microM GTP gamma S reduced the InsP3-induced Ca2+ release by 25%. 3. Ryanodine (100 microM), also gave a large release of intracellular Ca2+. After pretreatment with 100 microM ryanodine, GTP gamma S did not induce Ca2+ release, and InsP3-induced Ca2+ release was reduced by 76%. 4. Caffeine (50 mM), produced a slow release of intracellular Ca2+. Pre-exposure to 50 mM caffeine had no effect on the GTP gamma S-induced Ca2+ release but reduced the InsP3 releasable Ca2+ by 58%. 5. Pretreatment with ryanodine abolished the caffeine-induced Ca2+ release, and addition of caffeine before ryanodine reduced the ryanodine-induced Ca2+ release by 64.4%. 6. These results suggest that there are at least three pools of Ca2+ present within airway smooth muscle cells. The largest pool is released by InsP3 or ryanodine, another is released either by a high concentration of InsP3 or on application of GTP gamma S, and the third by InsP3 alone. Ca2+ may be able to move from the GTP gamma S-sensitive pool into the InsP3- and ryanodine-sensitive pool when this becomes depleted. In contrast, the opposite movement of Ca2 + cannot occur.

The effect of aminophylline on function and intracellular pH of the rat diaphragm.

We studied the effect of aminophylline on twitch tension (TT) and intracellular pH (pHi) in isolated rat diaphragm strips that were fatigued, hypercapnic, or hypoxic. Superfused muscles were directly stimulated at 0.5 Hz. The pHi was measured from distribution volumes of dimethyl-oxazolidinedione. Fatigue was induced by intermittent tetanic stimulation. Hypercapnia and hypoxia were produced by altering superfusate carbon dioxide tension (PCO2) or oxygen tension (PO2). Aminophylline (1.0 mmol.l-1) reversed the twitch decay seen during fatigue or hypercapnic acidosis, and caused partial recovery of twitch depression during hypoxia. Muscle fatigue was not due to an intracellular acidosis. Both hypercapnia and hypoxia lowered pHi. Aminophylline did not alter pHi in unstimulated muscles, but caused a significant fall in pHi in stimulated muscles that were fatigued or hypoxic. High dose aminophylline improved twitch tension in diaphragm strips that were fatigued, acidotic, or hypoxic. Twitch potentiation was not due to an intracellular alkalosis. Aminophylline lowered pHi in stimulated muscle, and thus, theoretically, could sometimes be harmful in the treatment of muscle fatigue.

Identification and characterization of the gene encoding the major structural protein of insect iridescent virus type 22.

The major structural protein (MSP--apparent molecular weight 49,000) of insect iridescent virus type 22 (isolated from blackflies--Simulium spp.) was resolved from disrupted, purified virus particles by SDS-PAGE and transferred to nitrocellulose by Western blotting. The portion of the blot containing the MSP was identified and excised. Tryptic peptides, generated by digestion in situ, were purified by HPLC. Three of these peptides were sequenced and an oligonucleotide gene probe was designed using one of them. A SalI clone of IV22 DNA was identified as MSP-specific by hybridization. DNA from this and an overlapping DNA clone was sequenced and a large open reading frame was positively identified as the MSP coding sequence by comparison with the tryptic peptide sequences. The molecular weight of the predicted protein product of this gene is 51,993, comparable with the apparent weight obtained by SDS-PAGE. In infected Spodoptera frugiperda (Sf) cells MSP is synthesized from 12 hr postinfection onwards. The identification of this gene and analysis of its expression opens the way to elucidating the control of late gene expression in an insect iridescent virus.

Staphylococcal pneumonia, pneumatoceles, and the toxic shock syndrome.

A case of community acquired staphylococcal pneumonia is reported with the unusual complication, in an adult, of multiple pneumatoceles. Recognition of this prevented inappropriate management. The patient also developed the toxic shock syndrome. In contrast to infants with pneumatoceles, recovery of lung function has been poor.

The mechanism of action of endothelin-1 on small pulmonary arterial vessels.

The effect of endothelin-1, a recently isolated vasoconstrictor peptide, was studied in preparations of pulmonary arterial vessels from the rat. Contraction was measured in large (1-2 mm diameter) and small (150-350 microns diameter) vessels on a Mulvany-Halpern myograph. Endothelin-1 was found to be one of the most potent vasoconstrictors yet described in these isolated pulmonary vessels. The contraction elicited was dose dependent, of slow onset, and prolonged. There was significant difference in sensitivity between the two vessel types, with an EC50 of 8.9 nM for the artery, and 33.1 nM for the smaller vessels. The endothelin-1 stimulated contraction was predominantly dependent on extracellular [Ca2+]. However 34.7% of the contraction in the pulmonary artery and 18.5% in the resistance vessel could be obtained in Ca2+ free (EGTA containing) solution. This extracellular Ca2+ independent fraction was sensitive to depletion of intracellular stores by pretreatment with caffeine or noradrenaline in the artery but not the arteriole. The extracellular Ca2+ dependent fraction was not affected by Ca2+ channel blockade with dihydropydridines or verapamil, but was inhibited by application of cadmium or lanthanum. The contraction was not altered by inhibition of Na+/H+ exchange.

The effect of pH and hypoxia on function and intracellular pH of the rat diaphragm.

We studied the relationship between contractile function and intracellular pH (pHi) in the isolated rat diaphragm when superfusate PCO2 was changed during hyperoxia or hypoxia. Superfused diaphragm strips were field stimulated at 0.5 Herz, and twitch tension (TT) was recorded. The pHi was calculated from the volume distribution of a weak acid, dimethyl-oxazolidinedione. In hyperoxia, hypercapnic acidosis (pH 7.06-6.63) depressed diaphragm pHi and TT, whereas hypocapnic alkalosis (pH 7.82-8.15) increased pHi but did not significantly affect TT. TT was maximum at physiological pHi (7.06), but in hyperoxic hypercapnic muscles substantial force was still generated at pHi values as low as 6.44. Hypoxia (PO2 30-38 mm Hg) markedly reduced TT; this effect was slightly exacerbated by hypercapnia and attenuated by hypocapnia. Hypoxia lowered pHi by about 0.2 units, which was insufficient to account for the hypoxic contractile failure. Knowledge of the hyperoxic muscle TT/pHi relationship suggests that, in other contexts, caution should be exercised in attributing severe muscle fatigue or force loss to modest falls in pHi.

A comparison of contractile function in large and small pulmonary arterial vessels of the rat.

The contractile function of rat pulmonary arterial vessels, ranging in internal diameter from 100 to 2000 microns, was studied in vitro using a small vessel myograph. It was found that vessels with a diameter of 200-400 microns produced considerably more force for a given intervention than those either smaller (less than 100-2000 microns) or larger (400-2000 microns). It is suggested that these vessels may play an important role in the generation of pulmonary vascular resistance.

Effects of heparin on inositol 1,4,5-trisphosphate and guanosine 5'-O-(3-thio triphosphate) induced calcium release in cultured smooth muscle cells from rabbit trachea.

The effects of heparin on intracellular calcium release in monolayers of permeabilised cultured rabbit smooth muscle cells were determined using 45Ca effluxes. Low molecular weight heparin inhibited inositol 1,4,5-trisphosphate (InsP3) induced Ca2+ release (IC50 = 0.8 microgram/ml), but not guanosine 5'-O-(3-thio triphosphate) (GTP gamma S) stimulated Ca2+ release. Only a small inhibition was noted with high molecular weight heparin and de-N-sulphated heparin, although chondroitin sulphate A potently inhibited the InsP3 response. These results indicate the competitive and specific nature of the heparin effect and give information about the structure of the InsP3 site.

In vitro buffering capacity of cardiac and skeletal muscle tissue in normotensive and hypertensive rats. Assessment using PCO2 equilibration of homogenates.

Experiments were performed to assess the in vitro buffering capacity (physicochemical buffering) of cardiac and skeletal muscle tissue in normotensive and hypertensive rats using the techniques of PCO2 equilibration of tissue homogenates. We have previously shown (Oldershaw PJ, Cameron IR. Int J Cardiol 1988;18:131-141 and Int J Cardiol 1988;18:143-149) that the ability of myocardial cells to regulate intracellular pH is improved in association with left ventricular hypertrophy (induced by experimental hypertension) and this study purports to investigate the role of physicochemical buffering in this improved control. Rats were made hypertensive using the technique of sub-diaphragmatic aortic constriction and left for 1 or 4 weeks at which time samples of left ventricular and skeletal muscle tissue were taken for analysis; sham-operated animals were used as controls. The tissue was homogenised and in vitro buffering capacity assessed using PCO2 equilibration. The slope of the log PCO2-pH plot was calculated for each tissue and taken as a measure of buffering capacity. In control animals, in vitro buffering was greater in skeletal than cardiac muscle (slopes 1.89 +/- 0.5 cf. 1.64 +/- 0.06 P less than 0.05). In association with hypertension of 1 or 4 weeks duration the buffering capacity of left ventricular tissue increased to 2.00 +/- 0.08 (P less than 0.01) at 1 week and to 2.05 +/- 0.06 (P less than 0.01) at 4 weeks. There was no comparable change in the buffering capacity of skeletal muscle tissue. At least part of the observed in vivo changes in intracellular pH control may therefore be explicable on the basis of improved intracellular physicochemical buffering.

The repeatability and validity of respiratory resistance measured by the forced oscillation technique.

Measurement of forced expiratory volume in one second (FEV1) is commonly used in bronchial challenge testing in laboratory and epidemiological studies but has certain disadvantages. We have therefore studied the repeatability and validity of a derived measurement of respiratory resistance (Ros) obtained with the Siregnost FD5 impedance oscillometer (Siemens). Repeatability was estimated in 25 non-asthmatics and 28 asthmatics and compared with that of PEFR, FEV1 and specific conductance. PEFR and FEV1 were the most repeatable. Repeatability for measurements with the oscillometer as measured by the intraclass correlation coefficient for a single measurement was 0.75 for non-asthmatics, but was less good for asthmatics (intraclass correlation coefficient 0.56). To assess the validity of respiratory resistance measured during a histamine bronchial challenge test a sample of 20 hospital personnel was studied on four occasions, FEV1 and Ros both being measured twice. Ros changed at lower doses of histamine than FEV1, but the intraclass correlation coefficient for repeatability of change only reached 0.6 at an absolute dose of 3.41 mumol histamine. The estimated provocation dose of histamine producing a 35% fall in Ros was 8.70 mumol (95% range for a single measurement +/- 1.11 doubling doses), that producing a 10% fall in FEV1 was 8.32 mumol (95% range +/- 1.04 doubling doses) and a 20% fall in FEV1 11.48 mumol (95% range +/- 1.11 doubling doses). Measurements obtained with the Siregnost FD5 oscillometer are repeatable. The use of Ros during bronchial challenge testing is valid, but shows insufficient advantage over FEV1 to support its use in epidemiological studies.

Analysis of transcription initiation in the Panolis flammea nuclear polyhedrosis virus polyhedrin gene.

The nucleotide sequence of the polyhedrin gene of Panolis flammea multiple nucleocapsid polyhedrosis virus (PfMNPV) has been determined. The coding sequences of this gene shared 82% similarity at the DNA level and 88% similarity at the protein level with the polyhedrin gene from Autographa californica (Ac) MNPV. A single nucleotide deviation from the consensus transcription initiation sequence for baculovirus very late genes was identified in the PfMNPV polyhedrin gene. RNA was prepared from Mamestra brassicae larvae infected with PfMNPV and compared with RNA harvested at 24 h post-infection from AcMNPV-infected Spodoptera frugiperda cells using Northern blotting with an AcMNPV polyhedrin gene-specific probe. The PfMNPV mRNA was estimated to be 1.0 kb compared with a larger size of 1.15 kb for the AcMNPV polyhedrin mRNA. A cDNA copy of the 5' end of the PfMNPV polyhedrin mRNA was made using the technique of primer extension and sequenced to demonstrate that the point of transcription initiation was similar to that of AcMNPV polyhedrin mRNA.

Conservation of polyhedrin gene promoter function between Autographa californica and Mamestra brassicae nuclear polyhedrosis viruses.

The DNA sequence of the polyhedrin gene of the Mamestra brassicae multiple nucleocapsid nuclear polyhedrosis virus (MbMNPV) was determined and compared with the polyhedrin genes of Autographa californica (Ac) and Panolis flammea (Pf) MNPVs. Using this information, a transfer vector was constructed based on the EcoRI I fragment of AcMNPV in which the polyhedrin promoter was replaced by the homologous region extending 481 nucleotides upstream from the MbMNPV polyhedrin coding sequence. The Escherichia coli lacZ gene was also included downstream from the putative MbMNPV promoter. Cotransfection of this transfer vector with wild-type AcMNPV DNA produced stable recombinant viruses expressing the lacZ gene under the control of the MbMNPV polyhedrin promoter. The levels of beta-galactosidase produced by these recombinants in infected cells were 30% lower than the expression level obtained from viruses with the authentic AcMNPV promoter in front of the lacZ gene. The MbMNPV promoter has thus been shown to function efficiently in the genetic environment of AcMNPV. The implications of this finding for the release of genetically manipulated baculovirus insecticides and for the construction of baculovirus multiple expression vectors are discussed.

Effect of changing dietary sodium on the airway response to histamine.

The airway response to histamine has been shown to be related to the 24 hour urinary excretion of sodium. To assess whether this relation is likely to represent a direct causal association a randomised double blind crossover trial of slow sodium (80 mmol/day) was compared with placebo in 36 subjects having a low sodium diet. The dose of histamine causing a 20% fall in FEV1 (PD20) was 1.51 doubling doses lower when the men were taking sodium than when they were taking placebo (p less than 0.05). On the basis of PD10 values, the difference in men was 1.66 doubling doses of histamine (p less than 0.05). There was no corresponding effect in women. Regressing PD10 against urinary excretion of electrolytes with data from the two occasions during the trial and the measurements made before the trial showed a significant association with sodium excretion after allowance had been made for any effect associated with potassium or creatinine excretion, the latter being a marker of the completeness of the urine collection. Again there was no corresponding effect among women. These findings are compatible with the differences in regional mortality data for England and Wales, which show a relation between asthma mortality and regional per person purchases of table salt for men but not for women.

The effects of short-term hypertensive left ventricular hypertrophy on intracellular pH and intracellular electrolytes in rats.

Experiments were performed to assess the effect of left ventricular hypertrophy (induced by experimental hypertension) on intracellular pH (pHi) and intracellular electrolytes in left ventricular tissue. They were undertaken on: (1) hypertensive rats (hypertension being induced by either: (a) subdiaphragmatic aortic constriction, (b) unilateral renal artery clipping, or (c) unilateral renal artery clipping with contralateral nephrectomy); (2) sham-operated rats for the above 3 subgroups; and (3) control (unoperated) rats. Intracellular pH and intracellular electrolytes were measured in left ventricular, right ventricular and skeletal muscle tissue from these animals. Intracellular pH control was assessed by exposing a number of animals in each group to an acute respiratory acidosis (by varying the concentration of inspired PCO2). In association with left ventricular hypertrophy (secondary to hypertension), left ventricular pHi became significantly alkaline in all experimental hypertensive groups compared with control values; pHi control (in response to an acidosis) was also significantly improved. There was no change in resting levels of pHi or pHi control in right ventricular or skeletal muscle tissue in any hypertensive group. There was no change in resting levels of pHi or pHi control in left ventricular, right ventricular or skeletal muscle tissue from sham-operated animals. This suggests that these changes are the result of hypertrophy per se, rather than due to a generalised mechanism secondary to hypertension and operating on all tissues. There was no change in intracellular electrolyte concentration or content in association with hypertension in any tissue or group studied.

The effects of long-standing hypertensive left ventricular hypertrophy on intracellular pH and intracellular electrolytes in rats.

Experiments were performed to assess the effect of long-standing (4-8 weeks) left ventricular hypertrophy (induced by experimental hypertension) on intracellular pH (pHi) and intracellular electrolytes in left ventricular tissue. They were undertaken on: (1) hypertensive rats (hypertension being induced by either (a) subdiaphragmatic aortic constriction, (b) unilateral renal artery clipping, or (c) unilateral renal artery clipping with contralateral nephrectomy); (2) sham-operated rats for the above 3 subgroups; and (3) control (unoperated) rats. In this study the hypertension (and therefore the hypertrophy) was of long (4-8 weeks) duration. Intracellular pH and intracellular electrolytes were measured in left ventricular, right ventricular and skeletal muscle tissue from these animals. Intracellular pH control was assessed by exposing a number of animals in each group to a respiratory acidosis (by varying the concentration of inspired PCO2). As described previously [Oldershaw PJ, Cameron IR, Int J Cardiol 1988;18:131-141], in the earlier stages of left ventricular hypertrophy (1-4 weeks duration) left ventricular pHi was significantly alkaline at normal levels of extracellular pH. At this late stage, with the exception of animals with aortic constriction, pHi had returned to control values. There was no change in resting levels of pHi in right ventricular or skeletal muscle tissue in any hypertensive group. The improved control of pHi in left ventricular tissue observed with hypertrophy of short duration (1-4 weeks [Oldershaw PJ, Cameron IR. Int J Cardiol 1988;18:131-141]) persisted in all experimental groups at this stage (4-8 weeks) after the onset of development of left ventricular hypertrophy. There was no change in pHi control in right ventricular or skeletal muscle tissue. Neither was there any change in intracellular electrolyte concentrations or content in association with hypertension in any tissue or group studied.

Effect of verapamil on polycythaemia secondary to hypoxia in rats.

1. Polycythaemia occurs in man secondary to chronic hypoxaemia, and may lead to morbidity from hyperviscosity of the blood. Hypoxaemic rats develop similar changes. We have investigated the effect of the calcium antagonist verapamil upon the polycythaemic response to hypoxia in rats. 2. Control groups of 10 male rats breathed air in an environmental chamber for 28 days. Hypoxic groups breathed a normobaric atmosphere of 10% oxygen for 6 h each day, and air for the remaining 18 h. Control and hypoxic groups were treated with intraperitoneal or subcutaneous water, or with intraperitoneal or subcutaneous water plus verapamil. 3. On day 28, packed cell volume (PCV) was measured by a microhaematocrit technique and red cell mass (RCM) by dilution of injected 51Cr-labelled rat erythrocytes. 4. PCV and RCM were significantly higher in all the hypoxic groups compared with the control groups (P less than 0.01 in each case). 5. PCV and RCM were significantly lower in the hypoxic groups treated with intraperitoneal or subcutaneous verapamil than in the hypoxic groups treated with intraperitoneal or subcutaneous water (P less than 0.01). There were no significant differences between PCV and RCM in verapamil- and water-treated normoxic control groups. Verapamil had no effect on the shift of the oxygen/haemoglobin dissociation curve produced by hypoxia. 6. Verapamil reduces the polycythaemic response to repeated intermittent hypoxia in rats. Venesection is usually performed for excessive secondary polycythaemia in man. Our results suggest a possible therapeutic role for verapamil in such individuals.