Effects of uncompensated and compensated metabolic acidosis on canine diaphragm

We investigated the effects of metabolic acidosis and compensated metabolic acidosis on force of contraction of the diaphragm in anesthetized dogs. Mechanically ventilated animals were prepared with an open thorax. A balloon was positioned beneath the diaphragm to measure transdiaphragmatic pressure (Pdi), and a plaster cast was placed around the abdomen to maintain length and geometry of the diaphragm. The force of contraction was evaluated by measuring Pdi during supramaximal phrenic stimulation at different frequencies and also during spontaneous inspiratory efforts. In 13 dogs with an arterial pH (pHa) of 7.38 and arterial PCO2 (PaCO2) of 36.5 Torr, metabolic acidosis was produced by infusion of HCl until pHa equaled 6.98 and PaCO2 equaled 36.4 Torr. Pdi at all frequencies greater than 10 Hz was significantly reduced (P less than 0.05). The dogs were then hyperventilated until pHa was 7.34 and PaCO2 was 12.8 Torr. Pdi was significantly reduced again at all frequencies (P less than 0.05) except 5 Hz. The percent reduction in Pdi by compensated acidosis was significantly greater at low-frequency stimulation than at high (P less than 0.05). Similar qualitative results were observed during spontaneous inspiratory efforts where Pdi was compared at constant magnitudes of diaphragmatic electromyograms. Twitch characteristics revealed that metabolic acidosis led to a significant shortening of twitch relaxation time (P less than 0.05), and compensated metabolic acidosis added to this effect a significant decrease in twitch amplitude (P less than 0.05).

Effects of neostigmine and salbutamol on diaphragmatic fatigue

We studied the effects of neostigmine and salbutamol on the force generated by the fatigued diaphragm in anesthetized dogs. Mechanically ventilated animals were prepared with an open thorax. A thin-walled latex balloon was positioned beneath the diaphragm to measure transdiaphragmatic pressure (Pdi) and a rigid cast was fixed around the abdomen to limit changes in diaphragmatic length and geometry during contractions. Pdi was the index of force generated by the diaphragm. We measured Pdi during supramaximal phrenic stimulation at different frequencies and during spontaneous inspiratory efforts. The diaphragm was fatigued by repeated phrenic stimulation. Fatigue significantly reduced Pdi at all frequencies of stimulation and during spontaneous contractions (P less than 0.05). The reduction in Pdi was associated with a decrease in peak twitch tension (PTT) to 50% of control (P less than 0.05). Infusion of neostigmine restored PTT to values equivalent with or greater than control (P less than 0.05) and improved Pdi at low stimulation frequencies (P less than 0.05) and during spontaneous inspiratory efforts (P less than 0.05). Infusion of salbutamol had no effect on PTT, but did significantly shortened twitch half relaxation time (P less than 0.05). Salbutamol also had no effect on Pdi during stimulated and spontaneous contractions. We conclude that neostigmine improves force generated by the fatigued diaphragm by increasing twitch amplitude while salbutamol did not have a positive inotropic effect.

Arterial CO2 partial pressure affects diaphragmatic function

The purpose of this study was to examine in an in vivo preparation acute variations of PCO2 on diaphragmatic contractility. Plaster casts were snugly fit around the abdomen of six open-chested dogs, moving the abdominal contents rostrally. Diaphragmatic contractions against this very fixed load in response to phrenic nerve stimulation (supramaximal voltage at 1, 20, 50, and 80 Hz) or during spontaneous inspiratory efforts were virtually isometric (quasi-isometric). Transdiaphragmatic pressure (Pdi) measured by an abdominal balloon was used as an index of diaphragmatic contractility. Arterial PCO2 (PaCO2) was reduced by hyperventilation and raised by increasing PICO2. Pdi values in response to stimulation at 1, 20, 50, and 80 Hz in ranges I (PaCO2 = 0-19 Torr) and II (PaCO2 = 20-34 Torr) did not differ statistically from the control Pdi values (range III; PaCO2 = 35-45 Torr). In range IV (PaCO2 = 46-70 Torr) Pdi values for stimulations of 20, 50, and 80 Hz were significantly lower than control. In range V (PaCO2 = 71-90 Torr), VI (PaCO2 = 91-101 Torr), and VII (PaCO2 greater than or equal to 102 Torr) Pdi values were significantly less than those in range IV at all frequencies of stimulation. In the four dogs measured during spontaneous inspiratory efforts the integrated diaphragmatic electromyogram (Edi) was correlated with the Pdi. As PaCO2 rose (range III to VII), the Pdi values observed at 25, 50, 75, 100% of the maximum Edi (of range III) were significantly lower than the Pdi value of range III.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance liquid chromatographic measurement of exogenous thiosulfate in urine and plasma

A simple technique using reverse-phase ion-pair liquid chromatography for measurement of exogenous thiosulfate is described. Accurate measurement of thiosulfate in plasma and urine was permitted by precolumn derivatization with monobromobimane, a substance that readily yields fluorescent compounds upon reaction with a variety of biologically important nucleophiles including glutathione, cysteine, and sulfite. Using an injection volume of 50 microliters, as little as 0.16 nmol of thiosulfate was reliably measured. The interassay precision of the method was reflected by a coefficient of variation of 7.7% while the coefficient of variation for interassay analysis was 2.6%. Recovery of thiosulfate from plasma was 96.9 +/- 3.2% and greater than 98% from urine. The simplicity, sensitivity, and precision of the method make it ideal for the study of thiosulfate and other important nucleophiles in body fluids.

Isoproterenol and aminophylline improve contractility of fatigued canine diaphragm

We investigated the effects of aminophylline and isoproterenol on diaphragmatic fatigue produced by phrenic stimulation in dogs. With a cast around the abdomen, the diaphragm contracted quasi-isometrically while the thorax was open and the animal was ventilated. We assessed contractility by measuring transdiaphragmatic pressure during supramaximal stimulation of the phrenic nerves at different frequencies and also during spontaneous inspiratory efforts. At doses of 20, 40, and 80 mg/kg, aminophylline significantly improved contractility (p less than 0.01) in a dose-dependent manner during low, but not during high frequency stimulation. The maximal improvement (24%) was observed with 80 mg/kg. With intravenously administered doses of 5 and 10 micrograms/min of isoproterenol, contractility was also significantly enhanced (p less than 0.05) during low frequency stimulation. Maximal improvement (12%) occurred with 5 micrograms/min. Similar results were obtained when spontaneous inspiratory efforts were recorded and transdiaphragmatic pressure was compared at a given diaphragmatic electrical activity before and after administration of each drug. Maximal improvement was 23% with aminophylline and 11% with isoproterenol. Analysis of twitch characteristics revealed that peak tension was increased significantly (p less than 0.025) by both drugs. In addition, isoproterenol caused a marked decrease in the time course of relaxation. We conclude that aminophylline and isoproterenol improve contractility of the fatigued diaphragm by increasing the amplitude of the underlying small twitch. Furthermore, the smaller effect of isoproterenol may be the result of reduced relaxation time of the twitch.

Inhibition of decidual prolactin release by a decidual peptide

Conditioned media from cultures of human decidual explants and aqueous extracts of human decidual tissue contain a factor that causes a reversible dose-dependent inhibition of decidual PRL release in vitro. Decidual explants incubated for 30 min in medium containing 50, 100, and 250 micrograms/ml of a dialyzed and lyophilized preparation of decidual conditioned medium (DCM) released 32.4 +/- 2.7%, 70.9 +/- 4.5%, and 100.0%, respectively, less PRL than control explants. DCM, however, had no measurable effect on the synthesis of decidual PRL or the synthesis and release of trichloroacetic acid-precipitable 35S-labeled proteins. The effect was of short duration and completely reversible. The inhibition of decidual PRL release was not due to PRL, since 500 micrograms/ml human pituitary PRL (a PRL concentration 40 times that in the minimal effective dose of DCM) added to the incubation medium of decidual explants had no effect on the synthesis or release of decidual PRL or trichloroacetic acid-precipitable 35S-labeled decidual proteins. The inhibitory activity eluted from Sephadex G-200 with an apparent molecular weight of 38,000-45,000 daltons, was heat labile, was destroyed by treatment with trypsin, and was unaffected by extraction with acetone-ethanol. These results strongly suggest that the release of decidual PRL is under local control, regulated in part by a factor(s) other than PRL that is released by the decidua.

Direct evidence for the single cell origin of mouse liver cell tumours

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Studies of X-chromosome inactivation with an improved histochemical technique for ornithine carbamoyltransferase

Studies of X-linked enzymes provide an approach to the study of tumour and normal cellular development. We have assessed the technique for the histochemical demonstration of one such enzyme, ornithine carbamoyltransferase (EC 2.1.3.3). Various stages in the Mizutani technique for ornithine carbamoyltransferase were re-examined, and the resulting improved technique applied to normal mice and to mice of the sparse fur strain (Spf) known to have an abnormal form of ornithine carbamoyltransferase inherited as an X-linked characteristic. Positive enzyme activity was present in all hepatocytes from normal mice, the strongest reaction being present in the periportal area with a gradual reduction of activity towards the centrilobular region. No activity was demonstrable in hepatocytes from hemizygous male Spf mice. In heterozygous female Spf mice, there was a clear-cut separation of ornithine carbamoyl-transferase-positive and -negative cells. These were present in very variable proportions in different liver lobes and different animals. Preliminary studies were also carried out using a high pH reaction mixture to detect the abnormal enzyme. These studies demonstrate conclusively the X-linkage of ornithine carbamoyltransferase in mice, showing the mosaic pattern of distribution predicted by the Lyon hypothesis. They show that the Spf strain of mice can be used for studies of both development and tumorigenesis in the liver, and that histochemical study of an animal strain with an X-linked enzyme abnormality provides a powerful investigative tool.

Low-frequency fatigue in isolated skeletal muscles and the effects of methylxanthines

1. A form of skeletal muscle fatigue was examined with isolated animal and human muscle preparations. The possibility that methylxanthines could overcome this was investigated. 2. Prolonged contractile activity resulted in a long-lasting impairment of force generation at low frequencies of stimulation at times when the force at higher frequencies had substantially recovered. This was seen with both fast-twitch and slow-twitch animal muscles and with samples of isolated human muscle. 3. The decrease in low-frequency force was due to a decrease in twitch amplitude, suggesting damage to the processes involved in excitation--contraction coupling. 4. Caffeine and theophylline at concentrations of 1 mmol/l rapidly and completely reversed the effects of this form of fatigue in both animal and human muscle preparations. 5. Agents that potentiate muscle force production could be an effective means of counteracting the effects of an important form of skeletal muscle fatigue, but a clinically useful compound would need to be more potent than the methylxanthines currently in use.

The effect of aminophylline on inspiratory muscle contractility

The effects of aminophylline on diaphragmatic muscle contractility were studied in 8 dogs. The relationships of the electromyographic signal from the diaphragm and the pressures developed by this muscle were compared before and after the administration of aminophylline in doses of 6, 20, 40, 80, and 120 mg/kg. Measurements were made during occluded inspiratory efforts at functional residual capacity. In a second group of 4 dogs the relationships were compared while the rib cage expansion was limited by a plaster cast. Finally, in a third group of 4 dogs after the diaphragm had been paralyzed by phrenicotomy, the relationship of pleural pressure to the electromyographic signal of the intercostal muscles was assessed before and after administration of aminophylline. In all cases, aminophylline progressively shifted the electromyographic pressure relationship up and to the left. This effect became significant (p less than 0.01) at a dose of 20 mg/kg, reached a peak at 80 mg/kg, and then declined at a dose of 120 mg/kg. The amount producing blood concentrations closest to the human therapeutic blood concentration was 20 mg/kg. The peak increase in pressure compared with the control values were 58% in the first group, 27% in the second group, and 52% in the third group (p less than 0.01). We conclude that aminophylline increases respiratory muscle contractility in a dose-related manner. This may have important therapeutic and pathophysiologic implications.

Assessment of palatal height in children

In this study a palatal index (P.I.) was established for 121 randomly selected normal Australian children. Mean P.I. indices were compared in the primary, mixed and permanent dentitions. A subjective assessment of relative palatal height was also carried out by two independent examiners and an attempt was made to examine the reliability of the subjective assessment, and its validity compared with the P.I. Measurements were recorded on stone casts at Level 1 (distal to the primary second molars/second premolars) and Level 2 (between primary first and second molar/first and second premolars). At Level 1 the mean P.I. increased significantly from the primary to the mixed and permanent dentitions. At level 2 the P.I. remained stable. Findings indicate that subjective assessment of relative palatal height was fairly reliable: there was approximately 80% interexaminer and intraexaminer agreements. Subjective assessment of palatal height correlated reasonably well with the P.I.

Chest physical therapy procedures in open heart surgery

Chest physical therapy is now widely used after open heart surgery to prevent secondary pathology in the lungs and to improve the phhysical condition of the patient. A brief overview of cardiac surgery is presented. Factors occurring before, during, and after surgery that contribute to postoperative respiratory insufficiency are outlined, and a comprehensive three-phase treatment program is described. Also, treatment guidelines, precautions, and contraindications are discussed.

Expression of the regulation of cAMP metabolism in somatic cell hybrids

Normal rat liver cells (BRL-1) that respond to isoproterenol (beta+2), prostaglandin E1 (PGE+1) and adenosine (Ado+) with a rise in adenosine 3':5'-monophosphate (cAMP) content have been hybridized with rat hepatoma cells (H35) which do not respond to any of these agonists (beta-2, PGE-1 and Ado-). Both the initial hybrid line (BF5) and a subclone (BF5-1-1) expressed a beta+2, PGE+1, Ado- phenotype. However, full expression of the responsive phenotype in the BF5 line was apparent only if phosphodiesterase activity was blocked, for example, by methylisobutylxanthine (MIX). Direct measurements showed the rate of degradation of cAMP to be 7 times greater in intact BF5 cells than in the BRL-1 parent. In contrast to BF5 cells, the BF5-1-1 cells did not express maximal responsiveness to any of the agonists even in the presence of MIX. The differential accumulation of intracellular cAMP observed with BRL-1, BF5 and BF5-1-1 cells in response to isoproterenol was shown not to be as a result of differential rates of excretion of cAMP. Furthermore, no differences in the apparent affinities of the beta 2-catecholamine receptors for isoproterenol were observed. It is suggested that the increased degradative capacity of BF5 cells accounts for the difference in cAMP accumulation in these cells compared with the BRL-1 parent. The reduced responsiveness of BF5-1-1 cells, however, does not appear to be solely due to increased phosphodiesterase activity. It appears that the beta 2- phenotype may not always be dominant in hybrid crosses of this type as has been reported previously.