Cerebral oxygen and glucose metabolism and blood flow in mitochondrial encephalomyopathy: a PET study

Cerebral blood flow (CBF), oxygen metabolism (CMRO2), and glucose metabolism (CMRGlc) were measured using positron emission tomography in five patients diagnosed as having mitochondrial encephalomyopathy. The molar ratio between the oxygen and glucose consumptions was reduced diffusely, as CMRO2 was markedly decreased and CMRGlc was slightly reduced. The CBF showed less changes. The CBF increase on hypercapnia was smaller than normal, though this was not significant. CBF with hypocapnia demonstrated a significant reduction compared with the normal. These results suggest that oxidative metabolism is impaired and anaerobic glycolysis relatively stimulated, due to a primary defect of mitochondrial function, and that mild lactic acidosis occurs in brain tissue because of impaired utilisation of pyruvate in the TCA cycle. As these findings appear to indicate directly a characteristic of this disease, such measurements may be a useful tool for assessment of the pathophysiology and for diagnosis of mitochondrial encephalomyopathy.

Lactic acidosis in a Clumber spaniel

A three-year-old female Clumber spaniel was examined because of a history of poor exercisetolerance since puppyhood. The dog had the opportunity for free exercise and rest in its yard at home. Usually the symptoms became more evident when the dog was exercised on a lead. During exercise the dog tired quickly, started to pant and salivate, lay down and was unable to rise. After resting the dog always returned to normal condition rather soon, at the latest within an hour. Except for intermittent polydipsia the dog was otherwise healthy and in good clinical condition.

Association of cerebral dysgenesis and lactic acidemia with X-linked PDH E1 alpha subunit mutations in females

We describe an infant girl who presented at age 4 1/2 months with developmental delay, infantile spasms, hypotonia, and elevated lactate levels in the blood and cerebrospinal fluid. She had minor dysmorphic features. Muscle phosphorus magnetic resonance spectroscopy demonstrated reduced phosphocreatine and increased inorganic phosphate, suggesting a defect in oxidative energy metabolism. Pyruvate dehydrogenase activity in cultured fibroblasts was reduced (0.35 nmol/mg mitochondrial protein/min; controls 0.7-1.1 nmol/mg mitochondrial protein/min). Immunoblotting demonstrated a reduced amount of pyruvate dehydrogenase (PDH) E1 alpha immunoreactive protein with normal amounts of E2 protein. Single-strand conformational polymorphism analysis of E1 alpha cDNA prepared from fibroblasts disclosed an abnormal migration pattern, suggesting heterozygosity for a mutant allele. Dideoxy-fingerprinting of PCR-amplified genomic DNA was used to localize the mutation to exon 10. Direct sequencing demonstrated a novel 13-bp insertion mutation that would lead to premature termination of the protein product. This study further extends the allelic heterogeneity underlying PDH deficiency. The demonstration of bioenergetic abnormalities in muscle emphasizes that hypotonia in PDH deficiency may have combined peripheral and central etiologies. The results further suggest that the association of cerebral dysgenesis with lactic acidemia in females may be a useful clue to PDH deficiency.

Lactic acidosis and diaphragmatic function in vitro

Diaphragm fatigue occurs during heavy exercise. Acidosis leads to skeletal muscle fatigue, yet the diaphragm is not a net producer of either lactic acid or hydrogen ions. We tested the hypothesis that hydrogen ion and lactic acid concentrations similar to those seen in arterial blood at maximal exercise decrease contractility of the in vitro isolated rat diaphragm. Diaphragm strips were exposed to a control solution for 15 min and then to one of the following treatment solutions: control (C, pH = 7.4) or 10 mM lactic acid buffered to pH 7.4 (L74), pH 7.2 (L72), pH 7.1 (L71), or pH 6.8 (L68). After 15 min, the force-frequency relationship of the strip was measured. The strips were then stressed with 75 contractions at 25 Hz (250-ms train duration) at the rate of one per second and the force-frequency curve was measured after 15 min of recovery. The L74, L72, and L71 strips responded similarly to the C strips at all times and frequencies. Decrements in force associated with acidosis were only seen in L68. Within L68, we found decreases in force at stimulation frequencies < 100 Hz. These data suggest that physiologic levels of exogenous hydrogen ions are not a primary cause of in vitro diaphragm fatigue.

Contribution of the respiratory muscles to the lactic acidosis of heavy exercise in COPD

Patients with COPD usually are limited in their exercise tolerance by a limited ventilatory capacity. Lactic acidosis induced by exercise increases the stress on the ventilatory system due to CO2 generated by bicarbonate buffering and hydrogen ion stimulation. Patients with COPD are often observed to increase blood lactate levels at low levels of exercise. We wished to determine whether patients with COPD who experience lactic acidosis do so because of respiratory muscle production of lactate. Eight patients with moderate to severe COPD (FEV1 = 43.5 +/- 11.6% predicted) and 5 healthy subjects performed 10 min of moderate constant work rate exercise either breathing spontaneously or volitionally increasing their ventilation for 5 min to approximate the peak minute ventilation seen during incremental exercise. During volitional increased ventilation, 3% CO2 was added to the inspirate to prevent alkalosis and hypocapnia. In neither the healthy subjects nor the COPD group was the end-exercise lactate level significantly higher during volitional ventilation increase than during spontaneous ventilation. Further, in the COPD patients, the blood lactate levels during volitional ventilation increase were much lower than during maximal exercise (averaging 2.4 vs 5.3 mmol/L) despite similar ventilation levels (averaging 50 and 53 L/min). We conclude that it is unlikely that the respiratory muscles have an important influence on the blood lactate level elevation seen during maximal exercise in COPD patients.

Cardiovascular responses to graded doses of three catecholamines during lactic and hydrochloric acidosis in dogs

We have studied the cardiovascular effects of incremental doses of three catecholamines in dogs subjected to lactic (LAC) and hydrochloric (HCl) acidosis. Fifty-four dogs were allocated randomly to one of three groups: control, LAC and HCl acidosis (n = 18 each group). In the acidotic models, 2 mol litre-1 of lactic acid (4 ml kg-1 h-1) or 2 mol litre-1 of HCl (1 ml kg-1 h-1) was infused i.v. until arterial pH was reduced to 7.00 +/- 0.1. Within each group, six dogs received one of three different drugs in logarithmically incremental doses: adrenaline 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 micrograms kg-1 min-1, noradrenaline 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 micrograms kg-1 min-1 and dobutamine 5, 10, 20, 40, 80, 160 micrograms kg-1 min-1. Cardiovascular variables were monitored, with periodic measurements of plasma electrolyte and lactate concentrations. The pH reduction induced by HCl or lactic acid was associated with a statistically significant increase in mean pulmonary arterial pressure (MPAP), prominent especially in the LAC group where MPAP increased from mean 18 (SD 5) to 27 (6) mm Hg. In the acidotic models, the reduction in myocardial responsiveness to adrenaline or noradrenaline was more prominent than that for the control for corresponding doses of drugs. In the LAC group mean cardiac index decreased significantly from 5.2 (1.8) to 2.2 (0.7) litre min-1 m-2 after infusion of adrenaline 3.2 micrograms kg-1 min-1 and decreased from 5.1 (1.1 to 2.4 (0.9) litre min-1 m-2 after infusion of noradrenaline 3.2 micrograms kg-1 min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in skeletal muscle oxygenation during incremental exercise measured with near infrared spectroscopy

To determine the change in muscle oxygenation in response to progressively increasing work rate exercise, muscle oxyhemoglobin + oxymyoglobin saturation was measured transcutaneously with near infrared spectroscopy in the vastus lateralis muscle during cycle ergometry. Studies were done in 11 subjects while gas exchange was measured breath-by-breath. As work rate was increased, tissue oxygenation initially either remained constant near resting levels or, more usually, decreased. Near the work rate and metabolic rate where significant lactic acidosis was detected by excess CO2 production (lactic acidosis threshold, LAT), muscle oxygenation decreased more steeply. As maximum oxygen uptake (VO2max) was approached, the rate of desaturation slowed. In 8 of the 11 subjects, tissue O2 saturation reached a minimum which was sustained for 1-3 min before VO2max was reached. The LAT correlated with both the VO2 (r = 0.95, P < 0.0001) and the work rate (r = 0.94, P < 0.0001) at which the rate of tissue O2 desaturation accelerated. These results describe a consistent pattern in the rate of decrease in muscle oxygenation, slowly decreasing over the lower work rate range, decreasing more rapidly in the work rate range of the LAT and then slowing at about 80% of VO2max, approaching or reaching a minimum saturation at VO2max.

Bicarbonate therapy in the treatment of lactic acidosis: medicine or toxin?

The metabolic acidosis resulting from poor tissue perfusion is considered to have several significant hemodynamic effects. Correction of the acidosis with sodium bicarbonate seems to be a rational approach to this problem. However, the current medical literature shows little clinical benefit to this tactic. In fact, indiscriminate bicarbonate administration may, itself, have deleterious effects. Concurring with the absence of a consistent therapeutic advantage to the use of sodium bicarbonate in the treatment of lactic acidosis due to inadequate tissue perfusion, the American Heart Association removed the routine use of sodium bicarbonate from the treatment of cardiac arrest in the algorithms of the Advanced Cardiac Life Support course. Although the debate continues, a detailed review of the medical literature does not support the use of sodium bicarbonate in this setting.

Transient organic aciduria and persistent lacticacidemia in a patient with short-chain acyl-coenzyme A dehydrogenase deficiency

A neonate with signs of neurologic dysfunction was noted to have elevated blood lactic acid levels. Organic acid analysis revealed transient elevations in ethylmalonate, methylsuccinate, butyrylglycine, and butyrylcarnitine. Enzyme assay in cultured skin fibroblasts confirmed short-chain acyl coenzyme. A dehydrogenase deficiency. The intermittent nature of the characteristic metabolic markers for this deficiency make diagnosis difficult. The apparent rarity of the disorder may be the result of underdiagnosis.

[Compensating for acidosis: pro]

New insights about the pathophysiology of acidosis as well as the efficacy of various buffer solutions have once again started the discussion about the necessity and indications of buffer therapy. After evaluation of the current literature one has to conclude that the spectrum of indications for application of buffer solution is remarkably small; some indications, however, remain well accepted. It has been shown that acidosis with pH-values above 7.2 has to be buffered only rarely, especially if the underlying disease responds to causal therapy. pH-values under 7.2, however, caused by renal tubular acidosis or by certain types of lactate acidosis, respond to buffer therapy. The choice of buffer solution depends on the pathophysiology of the underlying disease. In particular the application of CO2 generating buffer solutions under the conditions of critically reduced circulation and ventilation remains doubtful. Application of CO2 generating buffers seems to be justified only if intracellular acidosis can be prevented by immediate elimination of carbon dioxide generated by the buffer reaction.

Serial electroencephalograms in a patient with D-lactic acidosis

A patient with previous bowel surgery was followed through the course of her recurrent encephalopathy with biochemically demonstrated D-lactic acidosis by detailed serial electroencephalography (EEG). Although the EEG changes were marked and parallelled the clinical and biochemical abnormalities closely, they were essentially non-specific. This diagnosis should be considered in encephalopathic patients with a history of bowel disease particularly after extensive small bowel resection.

Effect of lactic and CO2 acidosis on neuronal function following glucose-oxygen deprivation in rat hippocampal slices

The present study was designed to determine whether lactate changes the critical pH point at which the recovery of rat population spike is inhibited following glucose-oxygen deprivation and second, which degree of lactic acidosis is similar to the effect of CO2 acidosis. The population spike was recorded from the hippocampal CA1 region after stimulation of the Schaffer collaterals. Slices were randomly perfused with various acidotic solutions for 30 min. During the last 15 min, glucose-oxygen deprivation was combined with the acidotic perfusion. Then the hippocampal slices were perfused with a standard solution of pH 7.4 for 60 min and recovery was compared to the control population spike and expressed as a percentage of the control value. In the control acidotic solution, the critical pH point was 5.0. When 15 mM or 30 mM lactate were added to the control solution, the critical pH point changed to 5.5 or 6.0, suggesting that the inhibition of the population spike was enhanced by lactate in a dose-dependent fashion. The recovery of the population spike was inhibited by exposing the slices to CO2 of 25% or above (pH was 5.76 or below) and this inhibition of recovery associated with CO2 acidosis was the same degree as occurred with 30 mM, namely severe lactic acidosis.

[Reduced oxygen transport capacity as a cause of dyspnea]

A reduction in the capacity of blood to carry oxygen leads to increased extraction of oxygen from the blood by peripheral tissues, and consequently to a decrease in the venous partial pressure of oxygen (pO2). At reduced venous pO2 pre-existing venous-arterial shunts gain in influence on arterial pO2 and arterial pO2 also decreases. In addition, physical exercise leads to lactate acidosis earlier and at lower levels of exercise than in healthy subjects. The low arterial pO2 and the low pH of acidosis are sensed by chemoreceptors of the carotid bodies and neural signals are transmitted to centers of the brain stem, where they are integrated and result in the sensation of shortness of breath (dyspnea). The capacity of the blood to carry oxygen is determined not only by the concentration of hemoglobin but also by the binding characteristics of hemoglobin for oxygen, which can be deduced from its molecular structure. In contrast to cases with acute anemia, dyspnea is often absent in patients in whom anemia develops gradually (down to hemoglobin levels of 7 g/dl). This tolerance is not mediated by pulmonary or cardiac compensatory mechanisms also at work in acute anemia, but is due to increases in the concentration of diphosphoglycerate. This allosteric effector molecule induces, by binding to hemoglobin, a decrease in the affinity of hemoglobin for oxygen, thereby leading to improved release of oxygen from hemoglobin in peripheral tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Natural history and course of acquired lactic acidosis in adults. DCA-Lactic Acidosis Study Group

STUDY OBJECTIVE

To determine the pathogenesis and clinical course of lactic acidosis in adults receiving standard medical care.

DESIGN

Placebo arm of a 5-year prospective, randomized, blinded study comparing placebo and dichloroacetate as specific lactate-lowering therapy. Each patient received intravenous saline placebo in addition to conventional therapy.

SETTING

Intensive care units of 10 tertiary care hospitals in North America.

PATIENTS

One hundred twenty-six patients with lactic acidosis, defined as arterial blood lactate greater than or equal to 5 mmol/L and either arterial pH of less than or equal to 7.35 or base deficit greater than 6 mmol/L. Patients were followed for up to 6 months.

MEASUREMENTS AND MAIN RESULTS

Mean +/- SD demographic entry data for 126 patients included: age 56 +/- 17 years, lactate 10.4 +/- 5.5 mmol/L, pH 7.24 +/- 0.14, calculated base deficit 14.1 +/- 5.4, arterial systolic blood pressure 103 +/- 29 mm Hg, Glasgow Coma score 7.9 +/- 4.9, and APACHE II score 19.2 +/- 8.1. Despite fluids and pressors, 32% of patients had systolic blood pressures of less than or equal to 90 mm Hg in association with sepsis (59%), cardiac failure (18%), or hemorrhage (18%). The most common causes of lactic acidosis in the absence of shock were sepsis (49%), liver disease (15%), and respiratory failure (12%). The median survival was 38.5 hours. Survival at 24 hours was 59%. Arterial pH predicted 24-hour survival better than base deficit or bicarbonate level. Percent survival was 41% at 3 days and 17% at 30 days. Only 21% of patients survived to leave the intensive care unit, and 17% were discharged from the hospital. In patients receiving sodium bicarbonate, neither acid-base nor hemodynamic status improved.

CONCLUSIONS

In this first prospective study of the clinical course of acute lactic acidosis in adults, nearly all subjects had both hemodynamic and nonhemodynamic (metabolic) underlying causes, many of which independently predicted survival and most of which were refractory to standard care.

[Swelling and damage to nerves and glial cells by acidosis]

OBJECTIVE

Development of acidosis is a prominent pathophysiological factor in acute cerebral disorders, such as ischaemia or severe brain trauma. The impairment of the acid-base state in brain parenchyma among others is involved in the development of brain oedema, eventually leading to irreversible damage of neurons and glial cells. In the present study the pathophysiological role of acidosis for cytotoxic cell swelling and damage of glial and neuronal cells was investigated in vitro under conditions found in the ischaemic penumbra in vivo--the still viable perifocal border zone surrounding an infarct with elevated interstitial K(+)- and H(+)-concentrations. Assessment of cell swelling by acidosis was combined with experiments on underlying mechanisms as a basis for therapeutical interventions to inhibit cytotoxic brain oedema in vivo.

METHODS

C6 glioma cells, astrocytes from primary culture, as well as Neuro-2A cells were cultivated, harvested and suspended as single cells under continuous control of pH, pO2, and temperature according to a standard procedure. Cell volume and cell viability were quantified by flow cytometry. Acidosis was induced by isotonic sulfuric- or lactic acid, respectively.

RESULTS

Acidification of the medium led to cell swelling once pH fell below 7.0. Cell viability, however, was not affected by the increasing acidosis down to pH 6.2, while pH 5.6 or below was associated with cell death dependent on the duration of exposure. Acidosis-induced cell swelling was attenuated or completely inhibited by blocking of ion exchange mechanisms, such as the Na+/H(+)-antiporter, or elimination of Na+ ions from the medium.

CONCLUSION

The present results provide new information on the nature of cytotoxic cell swelling and damage in central nervous system by acidosis under consideration of underlying mechanisms. Accordingly, acidosis-induced cell swelling is attributable to activation of ion exchange mechanisms, such as the Na+/H(+)- and Cl-/HCO3(-)-antiporter, in order to maintain a normal cellular acid-base state. This compensation process, however, is associated with the loss of cell volume control by net uptake of osmotic active solutes. Consequently, cell swelling occurring under these conditions is a result of regulatory mechanisms to defend homoeostasis rather than a consequence of cytotoxic cell damage. If cell swelling is inhibited by appropriate treatment, care should be exercised not to enhance the vulnerability of the nerve and glial cells.

[Effect of sodium bicarbonate on lactic acidosis in dogs with hemorrhagic shock]

Several recent studies evaluated alkali therapy for lactic acidosis (LA). We studied the effects of sodium bicarbonate (NaHCO3) on LA due to hemorrhagic shock in dogs. After inducing hemorrhagic shock in twelve mongrel dogs, we divided them into two groups: the first group was treated with 7% NaHCO3 and the second with 4.9% sodium chloride (NaCl). We measured pyruvate, lactate, acetoacetate (AcAc) and 3-hydroxybutyrate (3OHBA) while monitoring hemodynamics and blood gases, and calculated pyruvate/lactate and AcAc/3OHBA ratios. There was no statistically significant difference between the two groups in hemodynamic parameters, except for stroke volume index, and oxygen consumption throughout this experiment. Arterial pH and base excess increased significantly in the NaHCO3 group. The increases of pyruvate and lactate were significantly greater in the NaHCO3 group than in the NaCl group, but the other metabolic data were not significantly different. We did not find that NaHCO3 had greater beneficial effect than NaCl in hemorrhagic shock model, and the use of NaHCO3 for LA due to hemorrhagic shock may not be recommended.

Effects of sodium bicarbonate on striated muscle metabolism and intracellular pH during endotoxic shock

The effects of HCO3Na load on acid-base balance and muscle intracellular bioenergetics have been investigated using 31P-magnetic resonance spectroscopy in an experimental model of endotoxinic shock. Anesthetized, mechanically ventilated, and paralyzed rats (n = 16) were given an intravenous bolus of Escherichia coli lipopolysaccharide (15 mg/kg). When shock was established they were randomly assigned to receive either HCO3Na intravenously (2 mmol/kg in 2 min) or an equimolar saline injection. Lipopolysaccharide induced a significant decrease in the levels of mean arterial pressure (58 +/- 6 vs. 120 +/- 8 mmHg), arterial pH (7.20 +/- .03 vs. 7.35 +/- .01), intracellular pH (6.86 +/- .04 vs. 7.08 +/- .01), a marked hyperlactatemia (7 +/- 3 vs. 1.2 +/- .2 mmol/L) and a drop in the phosphocreatine-inorganic phosphate ratio. In the bicarbonate-loaded rats, mean arterial pressure further decreased whereas it remained unchanged in the saline group. Bicarbonate increased arterial pH and PaCO2 transiently. In the saline group, arterial pH decreased and PaCO2 remained stable. In both groups, intracellular pH and high energy phosphates had a similar evolution. In this model of septic shock, partial correction of arterial pH using HCO3Na did not reduce the metabolic cellular injury in skeletal muscle. Based on these results, HCO3Na may be of limited therapeutic value in severe septic metabolic acidosis.

The use of dichloroacetate in the treatment of overwhelming hypoxic acidosis

Overwhelming hypoxic acidosis due to poor tissue oxygen delivery from low cardiac output, pulmonary failure, and other causes has devastating effects postoperatively on patient outcome. Whereas conventional therapeutics often can not reverse the downward spiral of these patients, dichloroacetate (DCA) has been shown to be beneficial. This study investigated the metabolic and hemodynamic effects of DCA given after the onset of overwhelming hypoxic acidosis in a canine model. A hypoxically ventilated canine model of severe induced acidosis was established and dogs surviving the development of acidosis were randomized to receive DCA or sodium chloride (NaCl) treatment. Dogs receiving DCA after development of hypoxic lactic acidosis showed no further change in metabolic parameters during the 90-minute treatment period (pH, 7.24 to 7.23; HCO3, 17.7 to 18 mmol/L; lactate, 2.04 to 1.05 mM/L); whereas animals receiving an equivalent sodium load showed progressive, significant deterioration in all parameters (pH, 7.24 to 7.12; HCO3, 16.8 to 13.2 mM/L; lactate, 2.05 to 3.55 mM/L). Myocardial blood flow was significantly increased by hypoxia in all dogs. Finally, cardiac output and stroke volume were significantly increased at 90 minutes by DCA versus control. Myocardial oxygen utilization efficiency (LV work/M VO2) was improved during DCA treatment. DCA, a carboxylic acid, increases pyruvate dehydrogenase activity, thereby enhancing lactate use a metabolic substrate. DCA had an ameliorative metabolic effect, and benefitted myocardial performance without a direct inotropic effect. DCA treatment appears to enhance myocardial performance on a metabolic and not primarily inotropic basis, does not increase the "cost" of myocardial work, and warrants further study.

Treatment of biguanide-induced lactic acidosis: reproposal of the "physiological" approach and review of the literature

We report a case of severe biguanide-induced lactic acidosis which did not respond to symptomatic alkali treatment via either intravenous bicarbonate infusion or bicarbonate-dialysis. We thus initiated a therapeutic strategy based on insulin and thiamine only in order to reactivate the pyruvate oxidative pathway, in which both drugs play important roles as cofactors. This original "physiological" approach proved effective, and further alkali administration was unnecessary. Our results prompted a review of the literature on the treatment of biguanide-induced lactic acidosis, a situation in which the absence of precise therapeutic rules can undoubtedly affect both the evolution and the prognosis of the syndrome.

Lactic acidosis and hypoglycaemia in children with severe malaria: pathophysiological and prognostic significance

Serial clinical and metabolic changes were monitored in 115 Gambian children (1.5-12 years old) with severe malaria. Fifty-three children (46%) had cerebral malaria (coma score < or = 2) and 21 (18%) died. Admission geometric mean venous blood lactate concentrations were almost twice as high in fatal cases as in survivors (7.1 mmol/L vs. 3.6 mmol/L; P < 0.001) and were correlated with levels of tumour necrosis factor (r = 0.42, n = 79; P < 0.0001) and interleukin 1-alpha (r = 0.6, n = 34; P < 0.0001). Admission blood venous glucose concentrations were lower in fatal cases than survivors (3.2 mmol/L, vs. 5.8 mmol/L; P < 0.0001). Treatment with quinine was associated with significantly more episodes of post-admission hypoglycaemia when compared with artemether or chloroquine. After treatment, lactate concentrations fell rapidly in survivors but fell only slightly, or rose, in fatal cases. Plasma cytokine levels fluctuated widely after admission. Sustained hyperlactataemia (raised lactate concentrations, 4 h after admission) proved to be the best overall prognostic indicator of outcome in this series. Lactic acidosis is an important cause of death in severe malaria.

Neurodevelopmental abnormalities and lactic acidosis in a girl with a 20-bp deletion in the X-linked pyruvate dehydrogenase E1 alpha subunit gene

We describe a girl with developmental abnormalities of the CNS and a lactic acidosis whose cultured fibroblasts showed a profound deficiency of pyruvate dehydrogenase complex (PDHC) activity (patient = 0.14 nmol/mg protein per minute, controls = 0.7 to 1.1 nmol/mg protein per minute). Immunocytochemistry demonstrated the fibroblast culture to be mosaic, with 14% of cells expressing the PDHC E1 alpha subunit protein in normal amounts and the remaining 86% having no detectable immunoreactive activity. Direct sequencing of cDNA for the X-linked PDHC E1 alpha subunit established that the patient was heterozygous for a 20-bp deletion beginning in the codon for Ser300 of the derived amino acid sequence. The pattern of methylation at the DXS255 locus suggested predominant expression of the X chromosome carrying the mutant allele in the fibroblast culture. There was a good correlation between the residual PDHC activity, the proportion of cells with immunoreactive E1 alpha protein, and the X chromosome inactivation ratio, demonstrating the importance of X-inactivation for expression of this X-linked neurometabolic disease in females.

O2 uptake kinetics above and below the lactic acidosis threshold during sinusoidal exercise

O2 uptake (VO2) kinetics at the onset of a constant work rate exercise are difficult to describe for work rates above the lactic acidosis threshold (LAT), because the steady-state level of VO2 response can usually not be identified. To describe the ability of the O2 transport system to deliver and the cells to utilize O2 above the LAT relative to that below the LAT, we applied a fluctuating (sinusoidal) variation of work rate. After 4 min of constant work at the midpoint of the sinusoidal work rate, a fluctuating work rate, at a period of 4 min, was applied below the LAT for the next 16 min. This was repeated in a range of work rates above the LAT with the same sine-wave amplitude. VO2 response appeared to follow a sinusoidal pattern similar to that of work rate for below- and above-LAT exercise. However, the amplitude of the VO2 response was significantly reduced (5.4 +/- 2.6 vs. 7.6 +/- 1.9 ml.min-1 x W-1, P < 0.01), and the phase lag increased above- compared with below-LAT work rate. VO2/heart rate fluctuations were dramatically reduced, whereas heart rate amplitude decreased and phase lag increased, for above-LAT sinusoidal work rate changes. These results suggest that VO2 kinetics are slowed in the work rate domain above the LAT relative to that below the LAT and that VO2 kinetics could be limited by the O2 transport mechanisms to the exercising muscle.

Carbicarb, sodium bicarbonate, and sodium chloride in hypoxic lactic acidosis. Effect on arterial blood gases, lactate concentrations, hemodynamic variables, and myocardial intracellular pH

The effects of Carbicarb, sodium bicarbonate, and sodium chloride on arterial blood gases, lactate concentrations, hemodynamics, and myocardial intracellular pH were compared in hypoxic lactic acidosis with controlled carbon dioxide elimination. Twenty-one young mongrel dogs were anesthetized, mechanically ventilated, and randomly allocated into one of three treatment groups. After hypoxic lactic acidosis was induced and maintained, 2.5 mEq/kg of one of the agents was infused over 30 min. Arterial blood gases, pH, lactate concentrations, and hemodynamic variables were measured immediately prior to the infusion of the agent and 30 min after the infusion was completed. With sodium bicarbonate administration, there was a significant increase in arterial PCO2 as compared to both Carbicarb or sodium chloride administration. With Carbicarb administration, there was a significant increase in arterial pH, base excess, and cardiac index, without a significant increase in arterial lactate concentration as compared to sodium bicarbonate or sodium chloride administration. Stroke volume index was also increased significantly with decreased heart rate. The data suggest that Carbicarb administration in hypoxic lactic acidosis improved hemodynamics compared with sodium bicarbonate or sodium chloride administration. The increased stroke volume and cardiac contractility appear to be due to improved myocardial intracellular pH.

Comparison of gas exchange, lactate, and lactic acidosis thresholds in patients with chronic obstructive pulmonary disease

During an incremental exercise test, three consequences of the onset of anaerobic metabolism can be observed: rise in blood lactate (lactate threshold, LT); fall in standard bicarbonate (lactic acidosis threshold, LAT); nonlinear increase in CO2 output (V-slope gas exchange threshold, GET). We compared these thresholds in 31 patients with COPD. We found that the GET and LAT overestimated the LT. A better relationship was found between LAT and GET, even though GET was significantly higher than LAT (by 124 ml/min; p < 0.0001). However, since the bias is appreciably greater at lower LAT values (likely because VCO2 kinetics are slower than VO2 kinetics), we separated the studies into two groups: (A) tests where LAT occurred within the first 2 min of the increasing work rate period, and (B) tests where LAT occurred after 2 min. For Group A, there was a substantial bias between LAT and GET (323 ml/min, p < 0.0001), whereas the bias was much smaller (only 5.4%, though statistically significant) for Group B (57 ml/min, p < 0.01). We conclude that when lactic acidosis occurs after the first 2 min of incremental exercise, the GET closely approximates the point at which blood bicarbonate begins to fall.

Exercise in patients with chronic obstructive pulmonary disease

Sporadic visits to the local doctor followed sometimes by changes in oral and inhaled bronchodilators and occasionally by the addition of steroids frequently does little to significantly improve symptoms and function in the disabled patient with COPD. As in other chronic diseases, the management of these patients is facilitated by a team approach in conjunction with general rehabilitation principles. The rationale and practical implementation of such a programme has recently been outlined by the American Association of Cardiopulmonary Rehabilitation. These are multifaceted programmes but a key component, as outlined above, is exercise training. In this brief review the various approaches available have been described. Controversy still reigns regarding the optimal modes of training and there are important differences among the several approaches. Two main groups can be delineated. One emphasises the detailed definition of the impaired physiology with therapeutic measures targeted to specific defects. There is good documentation that, conversely, unstructured programmes that use treadmill and free range walking and cycling also improve endurance for walking. Upper extremity training is of additional benefit. Programmes with as little as three sessions per week of 1-2 hours of low intensity activity have achieved success so we know that simple programmes can be helpful. Moreover, without the necessity for complex testing and training methods these programmes can be implemented with relatively low costs. Future investigations to examine the relationship between improved exercise capacity for walking and arm exercise on the one hand, and the ease of performance of activities of daily living on the other, will help to reinforce the effectiveness of exercise programmes.

Active core rewarming in neurologic, hypothermic patients: effects on oxygen-related variables

OBJECTIVES

To determine in hypothermic patients if a) the decrease in oxygen consumption (VO2) is exclusively dependent on the decrease in metabolic rate, or b) as a consequence of the greater hemoglobin affinity for oxygen, hypothermic tissues have impaired oxygen extraction.

DESIGN

Clinical, prospective study; sequential measurements of oxygen-related variables during active core rewarming.

SETTING

Intensive care unit of a university hospital.

PATIENTS

Twelve patients (44 +/- 16 yrs of age) admitted to the intensive care unit with a core temperature of < 34 degrees C due to severe neurologic damage.

INTERVENTIONS

Rewarming (with heated enemas, gastric infusions, and heated blankets) to increase body temperature at a rate of approximately 1 degree C/hr. Measurements of oxygen-related variables were performed at a baseline of 31.0 +/- 1.1 degrees C, and repeated at each 1 degree C increase to reach a core temperature of approximately 35 degrees C.

MEASUREMENTS AND MAIN RESULTS

Oxygen-related variables of rewarmed patients were allocated into two groups, above or below the observed mean core temperature of 33.1 degrees C recorded for all measurements (n = 45). Comparison of the low core temperature group (31.1 +/- 1.4 degrees C; n = 20) with the high core temperature group (34.7 +/- 0.9 degrees C; n = 25) showed that the group with the lower core temperatures had a significant increase in VO2 index (67 +/- 22 vs. 103 +/- 38 mL/min/m2 [p < .001]), oxygen delivery index (183 +/- 73 vs. 290 +/- 123 mL/min/m2 [p < .001]), and the PO2 value at which hemoglobin was half-saturated with oxygen ([P50] 23 +/- 5.7 vs. 27.7 +/- 5.7 torr [3.0 +/- 0.7 vs. 3.6 +/- 0.7 kPa] [p < .02]). An increase in metabolic acidosis could be observed in the lower temperature group: arterial pH 7.47 +/- 0.15 vs. 7.34 +/- 0.13 (p < .01); base deficit -3.7 +/- 6.7 vs. -8.2 +/- 4.9 mEq/L (p < .02). The oxygen extraction ratio remained unchanged: 0.39 +/- 0.10 vs. 0.38 +/- 0.10 (NS).

CONCLUSIONS

These data show that VO2 was reduced to half of normal values during hypothermia. Active core rewarming produced an average 4.5% increase in VO2 per 1 degree C that was characterized by the wide variation observed in this metabolic response between different patients and for individual cases. Despite the rightward shift of P50 observed during rewarming (mainly due to the Bohr effect), no change was reflected on the oxygen extraction ratio.

Bicarbonate does not increase left ventricular contractility during L-lactic acidemia in pigs

Lactic acidosis decreases left ventricular contractility, but whether bicarbonate increases left ventricular contractility during lactic acidosis in vivo is controversial. Therefore, we measured hemodynamics and left ventricular mechanics before and after bicarbonate administration during L-lactic acid infusion in 15 anesthetized pigs. The pigs were beta-blocked and atrially paced to minimize indirect effects of acidosis on contractility. We measured mean arterial pressure, left ventricular end-diastolic pressure, thermodilution cardiac output, left ventricular pressure (Miller catheter), and left ventricular volume (three orthogonal pairs of ultrasonic crystals). Left ventricular contractility was assessed primarily using the slope (Emax) of the end-systolic pressure-volume relationship. While PCO2 was kept constant, 0.2 M L-lactic acid was infused, which reduced arterial pH to 7.05 +/- 0.06. Animals were then randomized to receive either 1 M NaHCO3 (n = 8), which increased pH to 7.45 +/- 0.11, or an equivalent amount of 1 M NaCl (n = 7). Bicarbonate decreased mean arterial pressure (105 +/- 20 to 95 +/- 39 mm Hg, p < 0.05) but did not increase cardiac output. These effects were not significantly different from the effects of saline. Bicarbonate did not significantly increase Emax (4.2 +/- 0.8 to 4.9 +/- 0.8 mm Hg/ml) and was indistinguishable from saline (5.0 +/- 0.7 to 5.2 +/- 0.7 mm Hg/ml). We conclude that bicarbonate infusion does not directly increase left ventricular contractility during lactic acidemia in pigs within this pH range.

Systemic oxygen extraction can be improved during repeated episodes of cardiac tamponade

We used a tamponade model to study the relationship between oxygen uptake (VO2) and oxygen delivery (DO2) during successive, reversible decreases in blood flow. In 7 pentobarbital-anesthetized and mechanically ventilated dogs, a catheter was introduced via a left thoracotomy into the pericardium to inject and to withdraw saline. Each experiment consisted of three steps. First, cardiac output was reduced by successive pericardial fluid injections until 4 to 6 data points were obtained in the dependent region of the VO2/DO2 plot (step 1). Second, cardiac output was restored by progressive withdrawal of pericardial fluid (step 2). Third, cardiac output was lowered again by reinjection of fluid into the pericardium until death (step 3). Expired gases were collected for determination of VO2. In each animal, critical DO2 (DO2crit), below which VO2 became DO2 dependent, was determined from a plot of VO2 versus DO2. When releasing tamponade, VO2 was restored to baseline. For the 3 steps, DO2crit were 10.5 +/- 2.2 mL/kg/min in step 1, 9.8 +/- 1.8 mL/kg/min in step 2, and 8.3 +/- 1.9 mL/kg/min in step 3 (P < .01 v step 1; P < .05 v step 2, respectively). There was no significant difference in VO2 at DO2crit for the three steps. Hence, critical oxygen extraction ratio (ERO2crit) increased from 60% +/- 12% in step 1 to 64% +/- 11% in step 2 (not significant) and to 73% +/- 12% in step 3 (P < .01). The VO2/DO2 dependency slope was also steeper in step 3 than in step 1 (0.77 +/- 0.31 v 0.54 +/- 0.20, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Lactate oxidation for the detection of mitochondrial dysfunction in human skin fibroblasts

To screen fibroblasts for defects in lactate/pyruvate oxidation, cells were grown to confluence in 25-cm2 flasks, rinsed, and incubated in glucose-free media containing 25 microM L-lactate and 0.1 microCi [D,L-1-14C]lactate. Lactate oxidation was measured as the amount of lactate oxidized in nmol of 14CO2 generated/mg protein/min. Fibroblasts from patients with mitochondrial or peroxisomal disorders had decreased lactate oxidation compared to the control (CON): CON, 1.9 +/- 0.13 nmol/mg/min; neonatal adrenoleukodystrophy (NALD), 0.45 +/- 0.01 (P < 0.001); rhizomelic chondrodysplasia punctata (RCDP), 0.13 +/- 0.002 (P < 0.001); mitochondrial defect of unknown etiology (MIT), 0.77 +/- 0.003 (P < 0.001); pyruvate dehydrogenase (PDH) deficiency, 0.98 +/- 0.02 (P < 0.001). This method is useful for screening fibroblasts for defects in lactate oxidation in patients with mitochondrial or peroxisomal disorders. Confirmation of the site of the defect may then be investigated with specific assays, e.g., PDH, in cellular homogenates: CON, 0.93 +/- 0.02 nmol/mg/min; NALD, 0.55 +/- 0.02; RCDP, 0.44 +/- 0.02; MIT, 0.53 +/- 0.03; PDH deficiency, 0.19 +/- 0.02.

The effect of respiratory and lactic acidosis on diaphragm function

The relative effects of respiratory and metabolic acidosis on diaphragm function are not known. To determine these effects, we compared the effects of respiratory and lactic acidosis on the contractile properties of the diaphragm. We estimated diaphragmatic performance from the change in transdiaphragmatic pressure after supramaximal stimulation of the phrenic nerves in an open-chested, casted-abdomen dog. Similarly, we stimulated the gastrocnemius motor nerve and examined force production and relaxation rate to determine if there was a difference in the response of this skeletal muscle. There was a fall in diaphragm performance with respiratory acidosis (77.1 +/- 16.9 cm H2O versus 93.8 +/- 15.0 cm H2O baseline), but not with lactic acidosis (96.7 +/- 15.7 cm H2O versus 93.8 +/- 15.0 cm H2O baseline); and the gastrocnemius was unaffected by either acidosis. The changes with respiratory acidosis were similar to those seen with diaphragmatic fatigue and had similar relaxation rate changes, suggesting that intracellular pH may play a mechanistic role in respiratory muscle fatigue. In addition, the absence of a respiratory acidosis effect on a non-diaphragmatic skeletal muscle's function represents another physiologic difference between the diaphragm and other skeletal muscles.

A retrospective study of patients with the hereditary syndrome of congenital cataract, mitochondrial myopathy of heart and skeletal muscle and lactic acidosis

The objectives of this study were to describe the course of two forms of an hereditary syndrome characterised by congenital cataract, mitochondrial myopathy of heart and skeletal muscle and lactic acidosis. We also sought to determine clinical, physicochemical and histopathological data which might allow early distinction between the two forms. We compared the ages at which clinical and physicochemical signs appeared in 16 patients. In 5 patients, enzyme-histochemical and ultrastructural data of skeletal muscle were available and muscle fibre composition analysed morphometrically. In any particular family only one form of the syndrome occurred. Amongst the patients who did not survive (range 14-34 years) 4 patients died in the neonatal period and 7 died at a median age of 23 years. The median age of the survivors was 19 years (range 15-42 years). Outflow obstruction of the left ventricle was noted in four deceased patients at variable times prior to death. The other deceased patients were not examined, but the cause of death was invariably heart failure. In none of the surviving patients was outflow obstruction noted. Enzyme-histochemical and ultrastructural findings were not specific for the course of the disease. In one biopsy, taken at the age of 3.5 months from a patient who survived, strong lipid accumulation was noted. Morphometric analysis showed proliferation of the mitochondria in muscle fibres, which increased during the course of the disease.

Respiratory control during exercise in patients with cardiovascular disease

The pathophysiologic mechanism for exertional dyspnea, the main symptom of patients with heart failure, has not been fully clarified. To determine the relationship between exercise hyperpnea and the lactic acidosis in patients with heart failure, we evaluated ventilation during incremental exercise both below and above the lactic acidosis threshold in 16 normal subjects and in 48 patients with cardiovascular disease while expired gas was analyzed continuously. The peak oxygen uptake and oxygen uptake at the lactic acidosis threshold decreased significantly as the New York Heart Association (NYHA) functional class severity increased. the slope of the increase in ventilation to the increase in oxygen uptake (delta VE/delta VO2) at work rates below the lactic acidosis threshold did not differ between normal subjects and patients with heart failure. Above the lactic acidosis threshold, however, the slope of delta VE/delta VO2, which was higher than that below the lactic acidosis threshold in each of four groups, was steeper in patients in NYHA Class II (60.8 +/- 17.9) and Class III (66.5 +/- 21.2) when compared with that in the normal subjects (46.6 +/- 13.5) or the patients in NYHA Class I (46.1 +/- 10.3). The lactic acidosis caused by decreased oxygen transport to working muscles accounts for the higher ventilation during exercise in cardiac patients. These data suggest that the increased ventilation during exercise, which must be related to exertional dyspnea, in patients with cardiovascular disease is primarily the consequence of a stimulus to regulate arterial pH.

[Growth and protein metabolism in chronic metabolic acidosis from experimental renal insufficiency]

Two studies of uremia-induced chronic metabolic acidosis (CMA) were carried out to determine: 1) the level of acidosis beyond which growth failure occurs; 2) the protein metabolism anomalies which are associated with growth failure. Rats rendered uremic by subtotal nephrectomy were fed a diet containing sufficient protein amounts (30% casein) to induce CMA. CMA was left uncorrected in half the rats (group A) and was corrected by administration of bicarbonate in the other half (group B). 1) Fifty-two group A rats were compared with 52 group B rats matched for renal function. Results showed that a) CMA failed to reduce food intake; b) weight gain decreased only when CMA was profound (pH < 7.20) whereas reductions in length gain occurred at less severe levels of acidosis (pH < 7.25) suggesting that bone may be more susceptible to CMA than muscle mass. 2) Protein fractional synthesis rate was evaluated in skeletal muscle after a flooding dose of 3H-phenylalanine in group A rats (pH 7.22 +/- 0.01, HCO3-: 15.2 +/- 0.8 mmol/l) and group B rats matched for renal function. Values were identical in both groups (10.4 +/- 0.5 vs 10.8 +/- 0.5%/day). However, fractional muscle protein accretion rate was decreased in group A rats. These data demonstrate that CMA-associated growth failure in uremia is due to increased breakdown of protein with no change in protein production.

Hemodynamic effects of sodium bicarbonate in critically ill neonates

OBJECTIVE

To analyze the cardiovascular effects of sodium bicarbonate in neonates with metabolic acidosis.

DESIGN

Prospective, open, non-randomized, before-after intervention study with hemodynamic measurements performed before and 1, 5, 10, 20, and 30 min after bicarbonate administration.

SETTING

Neonatal intensive care unit, tertiary care center.

PATIENTS

Sequential sample of 16 paralysed and mechanically ventilated newborn infants with a metabolic acidosis (pH < 7.25 in premature and < 7.30 in term infants, base deficit > -8).

INTERVENTION

An 8.4% sodium bicarbonate solution diluted 1:1 with water (final osmolality of 1000 mOsm/l) was administered in two equal portions at a rate of 0.5 mmol/min. The dose in mmol was calculated using the formula "base deficit x body weight (kg) x 1/3 x 1/2".

MEASUREMENTS AND RESULTS

Sodium bicarbonate induced a significant but transient rise in pulsed Doppler cardiac output (CO) (+27.7%), aortic blood flow velocity (+15.3%), systolic blood pressure (BP) (+9.3%), (+14.6%), transcutaneous carbon dioxide pressure (PtcCO2) (+11.8%), and transcutaneous oxygen pressure (PtcO2) (+8%). In spite of the PaCO2 elevation, pH significantly improved (from a mean of 7.24 to 7.30), and the base deficit decreased (-39.3%). Calculated systemic vascular resistance (SVR) (-10.7%) and diastolic BP (-11.7%) decreased significantly, while PaO2 and heart rate (HR) did not change. Central venous pressure (CVP) (+6.5%) increased only slightly. By 30 min after bicarbonate administration all hemodynamic parameters, with the exception of the diastolic BP, had returned to baseline.

CONCLUSION

Sodium bicarbonate in neonates with metabolic acidosis induces an increase in contractility and a reduction in afterload.

Brain oxidative energy and related metabolism, neuronal stress, and Alzheimer's disease: a speculative synthesis

A reduction in the cerebral metabolic rate of glucose is one of the most predominant abnormalities generally found in the Alzheimer brain, whereas the cerebral metabolic rate of oxygen is diminished only slightly or not at all at the beginning of this dementive disorder. From the cerebral metabolic rates of oxidized glucose and oxygen, the cerebral adenosine triphosphate (ATP) formation rate was calculated in incipient early-onset, incipient late-onset, and stable advanced dementia of the Alzheimer type (DAT). A reduction in ATP formation by various amounts was found, ranging from at least 7% in incipient early-onset DAT, from around 20% in incipient late-onset DAT, and from 35% up to more than 50% in stable advanced dementia. The cerebral diminution in energy availability, along with a loss of functionally important amino acids, ammonia toxicity, supposed membrane damage, dysregulation of Ca2+ homeostasis, and glycogen accumulation in the incipient stages of DAT are assumed to be stress-related abnormalities capable of inducing the formation of heat shock proteins. These events may lead to an enhanced generation of amyloid precursor protein in earlier states of DAT. If abnormally cleaved, amyloid A4 protein may be produced in increased amounts. From the results discussed in this article it is deduced as a speculative synthesis that perturbations in brain oxidative energy and related metabolism may precede the generation of amyloid precursor protein and the formation of plaques in the brain affected by incipient DAT.

Comparative effects of bicarbonate, tris-(hydroxymethyl)aminomethane and dichloroacetate in newborn swine with normoxic lactic acidosis

A total of 20 newborn piglets age 11.5 +/- 0.3 days and weighing 3.7 +/- 0.1 kg were studied under pentobarbital anesthesia. After stabilization following surgical procedures, baseline values for blood gases, base excess (BE), heart rate (HR), aortic pressure (AoP), left-ventricular contractility (LV dP/dtmax), carotid artery flow (CarF) and renal artery flow (RenF) were measured and normal lactic acid 0.2 ml/kg was infused over 1 h and the same parameters repeated. Then sodium bicarbonate (BC, n = 8), Tris-(hydroxymethyl)aminomethane (THAM, n = 6) or dichloroacetate (DCA, n = 6) were infused over 1 h. The doses of BC and THAM were calculated from the standard formula: Mmol = Base deficit x kg x 0.3. DCA was given at a dose of 300 mg/kg. Following lactic acid infusion, pH was 7.00 +/- 0.4 and BE was -20.6 +/- 1.2. Acidosis was associated with a significant (p < 0.05) increase in AoP (+18.6 +/- 7.4%) and decreases in HR (-13.9 +/- 2.7%) and RenF (-43.8 +/- 10.4%). Values of dP/dtmax and CarF were higher during acidosis in all but 3 animals. Following infusion of alkalizing agents pH and BE values were highest with BC and lowest with DCA and the differences were statistically significant (p < or = 0.05). In general, all three alkalizing agents reversed, in part or completely, the changes in cardiovascular parameters associated with acidosis so that following alkali infusion the changes were not statistically significant when compared to baseline values.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectors of hypercarbia during experimental pneumoperitoneum

Hypercarbia occurs during laparoscopy with carbon dioxide (CO2) insufflation. This may be due to increased ventilatory dead space after expansion of the peritoneal cavity with impairment of diaphragmatic excursion, or to increased absorption of CO2 from the peritoneum. To separate these effects, the authors examined the consequences of different insufflating gases and of diminished tissue perfusion on hypercarbia and dead space during pneumoperitoneum. Helium was chosen as an alternate insufflating gas because it is both inert and minimally absorbed. Eight swine (18 to 20 kg) were anesthetized, paralyzed, and mechanically ventilated at constant minute volume. Pneumoperitoneum with helium was maintained at 15 mm Hg for 45 minutes. After desufflation and stabilization for 1 hour, pneumoperitoneum was repeated with CO2. The sequence was again repeated after hemorrhagic shock to constant mean arterial pressure of 50 mm Hg. Data was analyzed by analysis of variance; significance levels are P < 0.01 unless otherwise listed. Arterial PCO2 increased significantly with CO2 insufflation within 15 minutes in normotensive animals and within 30 minutes during hypotension. Arterial pH decrease with CO2 pneumoperitoneum was significant in both groups at 30 minutes. Mixed venous PCO2 also increased with CO2 pneumoperitoneum within 30 minutes. Hypotension did not alter these changes. No significant changes were seen with helium pneumoperitoneum. Neither helium nor CO2 pneumoperitoneum significantly altered dead space. The authors make the following conclusions: 1) Absorption of CO2 from the abdomen during CO2 pneumoperitoneum produces respiratory acidosis, which is not seen with helium insufflation; 2) Pneumoperitoneum does not significantly increase dead space with either gas; 3) Transperitoneal absorption of CO2 is only partly related to perfusion because significant hypercarbia occurs during hemorrhagic shock.

Dependence of maximum performance time on work intensity in patients with a hereditary myopathy with succinate dehydrogenase deficiency

Patients with a hereditary mitochondrial myopathy with succinate dehydrogenase (SDH) deficiency and abnormal lactacidosis during physical exercise have a low work capacity when exercising for about 10-15 min. Their maximum voluntary muscular strength is fairly normal. The relationship between the time (t) and a constant workload (N) that a healthy subject can maximally sustain can be expressed as: log t = beta + alpha log N. For normal subjects the constant alpha is approximately -5 and the constant beta has a large interindividual variation. Of four myopathy patients alpha was determined from two or three maximum bicycle exercise tests of different duration (including ramp- and steady-state tests using a new application of the method of adding submaximal loads to the final maximum workload). The value of alpha varied between -1.0 and -1.81 and beta had low values, both significantly different from those of healthy subjects. The alpha values explain the divergent results that may be obtained with different types of exercise tests in some of these patients, i.e. a normal or moderately reduced capacity in exercise tests of short duration (for example a short Tornvall or a ramp type of test) and a very low exercise capacity in tests of longer duration (for example a steady state type of test with workloads chosen to allow at least two loads). The low absolute value of alpha may be related to the abnormally increased anaerobic metabolism of these patients during exercise, caused by the SDH deficiency.

Protracted metabolic acidosis: the impact of acute ethanol in hemorrhagic shock

The effects of acute ethanol administration on acid-base balance and hemodynamic parameters were studied in a canine model. Ten mongrel dogs, anesthetized and maintained on a volume ventilator, underwent splenic artery ligation 30 minutes prior to study. Group A (N = 5) served as controls. Thirty minutes after drug administration, the animals underwent a 20-cc/kg hemorrhage over 15 minutes. Thirty minutes postphlebotomy, resuscitation was performed with the same volume of homologous blood. Acid-base and hemodynamic parameters were monitored over 3.5 hours. Ethanol levels peaked 60 minutes following administration at 207 +/- 13 mg%. During the entire study, no differences were observed in heart rate, pulmonary capillary wedge pressure, systemic vascular resistance index, pO2, or pCO2, between the two groups. Following hemorrhage, statistically significant decreases in pH, mean arterial pressure (MAP), cardiac index (CI), and left ventricular stroke work index (LVSWI) developed in group A compared to controls. Maximal disparity developed in pH (7.21 +/- 0.05 to 7.33 +/- 0.02, P < 0.01), MAP (67 +/- 11 v 110 +/- 9 torr, P < 0.01), CI (1.69 +/- 0.24 compared to 2.72 +/- 0.19 L/min/M2, and LVSWI (18.7 +/- 1.2 compared to 44.9 +/- 4.8 gr-meter/M2/beat, P < 0.01) at 60, 45, 30, and 75 minutes postphlebotomy. In this study, ethanol directly or indirectly caused an increased metabolic acidosis and myocardial depression in the post-hemorrhage period.

Human muscle fatigue after glycogen depletion: a 31P magnetic resonance study

To differentiate the effects of high energy phosphates, pH, and [H2PO4-] on skeletal muscle fatigue, intracellular acidosis during handgrip exercise was attenuated by prolonged submaximal exercise. Healthy human subjects (n = 6) performed 5-min bouts of maximal rhythmic handgrip (RHG) before (CONTROL) and after prolonged (60-min) handgrip exercise (ATTEN-EX) designed to attenuate lactic acidosis in active muscle by partially depleting muscle glycogen. Concentrations of free intracellular phosphocreatine ([PCr]), adenosine triphosphate ([ATP]), and orthophosphate ([P(i)]) and pH were measured by 31P nuclear magnetic resonance spectroscopy and used to calculate adenosine diphosphate [ADP], [H2PO4-], and [HPO4(2-)]. Handgrip force output was measured with a dynamometer, and fatigue was determined by loss of maximal contractile force. After ATTEN-EX, the normal exercise-induced muscle acidosis was reduced. At peak CONTROL RHG, pH fell to 6.3 +/- 0.1 (SE) and muscle fatigue was correlated with [PCr] (r = 0.83), [P(i)] (r = 0.82), and [H2PO4-] (r = 0.81); [ADP] was 22.0 +/- 5.7 mumol/kg. At peak RHG after ATTEN-EX, pH was 6.9 +/- 0.1 and [ADP] was 116.1 +/- 18.2 mumol/kg, although [PCr] and [P(i)] were not different from CONTROL RHG (P greater than 0.05). After ATTEN-EX, fatigue correlated most closely with [ADP] (r = 0.84). The data indicate that skeletal muscle fatigue 1) is multifactorial, 2) can occur without decreased pH or increased [H2PO4-], and 3) is correlated with [ADP] after exercise-induced glycogen depletion.

Role of tissue hypoxia as the mechanism of lactic acidosis during E. coli endotoxemia

We compared the hemodynamic and metabolic alterations produced in rabbits by similar decreases in cardiac output created by inflating a balloon placed in the right ventricle (n = 6) with those produced by an intravenous bolus of Escherichia coli lipopolysaccharide (LPS; SEP group; n = 6). We measured O2 consumption (VO2), O2 transport (TO2), and O2 extraction ratio (ERO2) for the whole animal and also for the left hindlimb. Both groups experienced similar decreases in cardiac output, systemic TO2, and VO2 and similar increases in ERO2. For the hindlimb, TO2 was similar, but VO2 and ERO2 were lower for the SEP group 30 min after LPS administration (P less than 0.05); however, this difference disappeared during the remainder of the experiment. Arterial lactate concentration was greater (P less than 0.05) for the SEP group. There were no differences in skeletal muscle PO2, measured with a multiwire surface electrode, or in cardiac and skeletal muscle concentrations of high-energy phosphates. We hypothesize that a direct effect of LPS on cellular metabolism may have resulted in greater arterial lactate concentration for the SEP group.

Is the anaerobic threshold truly anaerobic?

This study was done to address the question as to whether there was an exercise metabolic rate below which the O2 supply to the muscles was adequate to meet the O2 requirement and above which the O2 supply was inadequate, ie, an anaerobic threshold (AT). The question was addressed using 2 approaches: (1) The arterial lactate/pyruvate ratio was measured to see if it increased at an O2 uptake (VO2) threshold or continuously as a log function over the entire range of exercise work rates. (2) Anticipating that the VO2 would be affected by reducing O2 supply only for work rates above the AT, the effect of reducing O2 delivery on VO2 for work rates over the entire range of the subject's work capacity was determined. Lactate (L) and pyruvate (P) were measured in arterial blood in 10 normal subjects. The L/P ratio was found not to increase until a threshold work rate was reached, the VO2 being that identified as the AT. Above that VO2, the L/P ratio climbed steeply. Arterial L/P ratio measurements fit a threshold model considerably better than a continuous model, supporting the concept that exercise done at low and moderate work rates can be performed without a change in cell redox state; but redox state does change rapidly in relation to the work rate increase above the AT. In the second study, the cardiorespiratory responses to various levels of exercise were studied in 10 normal subjects before and after carboxyhemoglobin (COHb) was increased to 10% and 20%. The lactic acidosis threshold and VO2 kinetics were examined. Blood lactate concentration increased only above the AT. The AT was systematically decreased by the percent of COHb increase. Importantly, VO2 was reduced and VO2 kinetics were slowed in response to exercise only for the metabolic rates above the AT. These studies demonstrate that lactate increase in response to exercise is O2 flow sensitive, and there is a threshold work rate above which this sensitivity becomes manifest.