Optimizing cerebral oxygenation during cardiac surgery: a review of experimental and clinical investigations with near infrared spectrophotometry

OBJECTIVES

Near-infrared spectrophotometry (NIRS) is a promising method for non-invasive monitoring of cerebral oxygenation and hemodynamics. This paper reviews studies in which we aimed to validate NIRS in an experimental model of cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) (validation study), use the method in experimental settings to optimize cerebral oxygenation during CPB (oxygenation study), and test its utility during routine cardiac surgery (clinical study).

METHODS

Validation study: Forty 8-10 kg piglets underwent 60 min of DHCA at 15 degrees C, were extubated on the first postoperative day, and sacrificed on the 4th postoperative day for histologic investigations. During CPB and DHCA, the animals were investigated by NIRS (monitoring of cerebral oxygenated hemoglobin (HbO2) and oxidized cytochrome aa3 (Cytox)) and magnetic resonance spectroscopy (MRS) (monitoring of cerebral adenosine triphosphate (ATP) and phosphocreatine (PCr). Oxygenation study: A normoxic (n = 5) and a hyperoxic group (n = 5) of piglets underwent 120 min of DHCA and 6 h of reperfusion with NIRS monitoring. Neuronal damage was evaluated by histology. Clinical study: Patients (n = 41) undergoing routine cardiac surgery were investigated by NIRS and neuropsychological testings.

RESULTS

Validation study: Reductions of CytOx and HbO2 values were closely correlated with decreases in ATP, PCr, and pHi. The changes in CytOx and PCr showed the strongest correlation (r = 0.623). Maximal CytOx reduction during DHCA predicted brain damage. Oxygenation study: Histology revealed a significant increase in brain damage in the normoxic group. Cytox and HbO2 tended to be lower during DHCA (p = 0.16). Clinical study: During CPB, arterial PCO2, pH and temperature were closely related to CytOx and HbO2. Patients who suffered from neuropsychological deficits had a lower CytOx minimum compared to those without these.

CONCLUSIONS

NIRS measurements, especially the CytOx signal, correlate well with high energy phosphates and have a high sensitivity to predict histologic brain damage. NIRS is an important and useful tool in studies investigating cerebral oxygenation during CPB. The CytOx signal predicted impaired neuropsychological outcome in patients. Therefore, the CytOx signal holds much interest for future studies.

Brain hemodynamic changes in preterm infants after maintenance dose caffeine and aminophylline treatment

OBJECTIVE

To investigate the acute effects of low-dose caffeine and aminophylline on cerebral blood flow in preterm infants, using both near-infrared spectroscopy (NIRS) and cerebral Doppler ultrasonography.

METHODS

Preterm infants with a gestational age of <32 weeks and birth weight of <1,500 g were randomized to receive either caffeine or aminophylline treatment for apnea of prematurity. The study period went from 30 min before to 60 min after the administration of the maintenance dose of pure caffeine (2.5 mg/kg once a day) or aminophylline (1.25 mg/kg twice a day). NIRS was used to measure changes in oxygenated hemoglobin (O(2)Hb), deoxygenated hemoglobin (HHb), oxidized-reduced cytochrome aa3 (CtOx), and mean cerebral oxygen saturation (SmO(2) = O(2)Hb/total Hb). Changes in cerebral blood volume (DeltaCBV) after caffeine or aminophylline administration were calculated. Cerebral blood flow velocity (CBV) in the pericallosal artery was evaluated by cerebral Doppler ultrasounds.

RESULTS

Data collected by NIRS and cerebral Doppler ultrasounds did not show significant differences before and after caffeine treatment. We observed a significant increase in O(2)Hb and HHb concentration and in CBV at 30 min after the infusion of aminophylline, which tended to return to baseline at the end of the study period.

CONCLUSION

Caffeine does not significantly affect brain hemodynamics, while aminophylline induces a significant transient increase in O(2)Hb and HHb concentration and CBV.

Pulsatility does not change cerebral oxygenation during cardiopulmonary bypass

BACKGROUND

To determine the effect of pulsatility during cardiopulmonary bypass (CPB) on cerebral oxygenation, we measured oxyhaemoglobin (HbO2), deoxyhaemoglobin (Hb) and oxidised cytochrome aa3 (CtO2) with near-infrared spectroscopy (NIRS) in 14 patients electively scheduled for cardiac surgery.

METHODS

Cerebral oxygenation was measured during steady state CPB at a core temperature of 32 degrees C. Non-pulsatile flow and pulsatile flow were performed for 10 min each.

RESULTS

After 14 min of CPB, HbO2, Hb and CtO2 were significantly below prebypass values. HbO2 and CtO2 did not alter with changing flow patterns. Hb significantly increased both during the period of nonpulsatile (median: -0.7 vs. 0.25 micromol/l; P<0.05) and pulsatile flow (median: 0.25 vs. 0.5 micromol/l; P<0.001). This increase was independent of flow pattern.

CONCLUSIONS

Neither oxygenated haemoglobin, nor intracellular oxygenation, represented by CtO2, indicated a beneficial effect of pulsatile perfusion during hypothermic CPB. These results, however, are only valid for short time effects within 10 min before rewarming from CPB and patients without flow-limiting stenoses of the carotid artery.

Changes in cerebral blood volume and cerebral oxygenation during periodic breathing in term infants

The present study is an analysis of changes in cerebral oxygenation and cerebral blood volume (CBV) during periodic breathing in healthy term infants by means of near infrared spectroscopy (NIRS). Polygraphy included electrocardiogram, electrooculogram, heart rate, oxygen saturation, side stream capnography, two respiratory effort sensors, a movement sensor, and NIRS. During periodic breathing analysis of behaviour of total haemoglobin (cHbtot), deltaCBV, the haemoglobin oxygenation index (cHbD), and cytochrome oxidase (CytOx) was performed. In ten healthy term infants 30 cycles of periodic breathing with a mean of 10 apnoeas per cycle were analysed. Corresponding cyclical variations of cHbD appeared in 98%, cyclical variations of cHbtot appeared in 42% of all apnoeas. During phases of apnoea, a mean decrease of cHbD of -3.45 micromol/l occurred 1.75 seconds after onset of apnoea, and a mean decrease of cHbtot of -0.79 micromol/occurred 0.74 seconds after onset of apnoea. During these apnoeas, the deltaCBV was -44 microl/100 g brain. During phases of ventilation, there was an increase of cHbD and cHbtot to the pre-apnoeic levels. There was a tendency that CytOx values decreased during periodic breathing, the amount of decrease was -0.32 micromol/l. In conclusion, the present study was able to show for the first time that there is cyclical desaturation and reoxygenation of cerebral blood during periodic breathing. Cyclical changes in CBV in association with periodic apnoea occurred only in 42% of apnoea.

The effects of cell ageing on metabolism in rainbow trout (Oncorhynchus mykiss) red blood cells

The effects of cell age on metabolism in the nucleated red blood cells of rainbow trout (Oncorhynchus mykiss) were examined. Red blood cells were separated according to age using fixed-angle centrifugation. The mean erythrocyte haemoglobin concentration in old red blood cells was found to be 120 % of that in young red blood cells. In young red blood cells, the activities of the mitochondrial enzymes citrate synthase and cytochrome oxidase were 135–200 %, respectively, of those measured in old red blood cells. The activity of the glycolytic enzyme lactate dehydrogenase in young red blood cells was 170 % of that in old red blood cells, whereas the activity of the glycolytic enzyme pyruvate kinase was not significantly affected by cell age. In addition, young red blood cells consumed over twice as much O(2) and devoted 50 % more O(2) to protein synthesis and the activity of Na(+)/K(+)-ATPase than old red blood cells. Red blood cell age did not significantly affect the rate of lactate production. This study shows that ageing in rainbow trout nucleated red blood cells is accompanied by a significant decline in aerobic energy production and the processes it supports, as well as a corresponding increase in the glycolytic contribution to metabolism.

The activity of cytochrome oxidase is increased in circulating lymphocytes of patients with chronic obstructive pulmonary disease, asthma, and chronic arthritis

We have previously shown that the activity of cytochrome oxidase (CytOx) in skeletal muscle of patients with chronic obstructive pulmonary disease (COPD) was higher than in healthy control subjects. The mechanisms and implications of this observation were unclear. In particular, it was not known if this abnormality can occur also in: (1) cell types other than muscle cells, and (2) other chronic inflammatory diseases. To obtain further insight into these questions, we measured the activity of CytOx in circulating lymphocytes in patients with stable COPD (n = 17), bronchial asthma (n = 6), or chronic arthritis (n = 5), and in healthy control subjects (n = 8). We found that, compared with healthy subjects (280 +/- 117 nKat/microg protein), patients with COPD showed increased CytOx activity (430 +/- 150 nKat/microg protein, p = 0.01) in lymphocytes. Further, this activity was negatively related to the degree of airflow obstruction present in these patients (r = -0.53, p < 0.05). We also found that the activity of CytOx in circulating lymphocytes was higher than normal in patients with chronic arthritis (411 +/- 130 nKat/microg protein, p < 0.05) and, particularly, in patients with bronchial asthma (1,667 +/- 1,027 nKat/microg protein, p < 0.001). These results show that the increased CytOx activity previously reported in skeletal muscle of patients with COPD is also detected in other cell types (such as circulating lymphocytes) and in other chronic inflammatory diseases (such as bronchial asthma and chronic arthritis). The mechanisms and implications of these findings deserve further investigation.

Neonatal intensive care applications of near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is a noninvasive technique for assessing cerebral hemodynamic variables and oxidative status in the neonatal intensive care setting. It can be performed for extended periods of time at the bedside without interfering with routine patient care. NIRS appears to have the ability to not only assess relative changes in oxygenated and deoxygenated hemoglobin, total hemoglobin, and cytochrome aa3, but it can also produce estimates of cerebral blood volume and cerebral blood flow. Research data document significant changes in these hemodynamic variables with patient activity and clinical interventions in both premature and term infants. NIRS may evolve into an important diagnostic and prognostic tool for neonatal neurologic outcome.

Near infrared spectroscopy-measured changes in cerebral blood volume and cytochrome aa3 in newborn lambs exposed to hypoxia and hypercapnia, and ischemia: a comparison with changes in brain perfusion and O2 metabolism

OBJECTIVES

Validation of near infrared spectroscopy (NIRS)-measured changes in cerebral blood volume (deltaCBV) and cytochrome aa3 (deltaCytaa3) as estimators of changes in brain perfusion and oxygenation in the newborn lamb during hypoxia and hypercarbia, and additional hypotension.

METHODS AND MATERIALS

In 33 newborn lambs brain perfusion assessed by carotid artery blood flow (deltaQcar: ml/min)and cerebral metabolic rate of oxygen (deltaCMRO2: ml O2/min) were related to NIRS-derived deltaCBV (ml/100 g) and deltaCytaa3 (microM) during combined hypoxia and hypercarbia and additional hypotension. Combined hypoxia and hypercapnia was induced by ventilation with 6-8% of O2 and 10% of CO2 during 30 min, and additional hypotension ( < 35 mmHg for 5 min) was induced by careful withdrawal of blood.

RESULTS

CBV increased during hypoxia and hypercarbia, decreased during additional hypotension and was related to deltaQcar: (0.009 ml/100 g change per ml/min Qcar: P < 0.0001). Cytaa3 increased during hypoxia and hypercarbia, decreased during subsequent additional hypotension andshowed a reverse relationship with deltaCMRO2 (-1.65 microM change per ml O2/min CMRO2: P <0.0001). Cytaa3 remained above baseline during reperfusion.

CONCLUSIONS

deltaCBV estimates changes in brain perfusion, but overestimates brain perfusion during hypotension. The pattern of deltaCytaa3 suggests less oxygen utilisation by brain tissue during hypoxia and subsequent reperfusion.

A comparison of the monitors INVOS 3100 and NIRO 500 in detecting changes in cerebral oxygenation

BACKGROUND

Measurements of cerebral haemoglobin oxygenation of 2 near-infrared spectroscopy devices (INVOS 3100 and NIRO 500) were compared during and after hypocapnia.

METHODS

Fifteen awake, healthy volunteers, who hyperventilated to obtain end-tidal CO2 (EtCO2) values of approximately 20 mmHg, were studied. During hyperventilation and 8 min thereafter, EtCO2, INVOS 3100 (RSO2 = regional cerebral oxygenation) and NIRO 500 recordings (HbO2 = oxyhaemoglobin, Hb = deoxyhaemoglobin, Hb-diff = HbO2-Hb, CtO2 = oxidised cytochrome oxidase aa3) were analysed.

RESULTS

Hyperventilation induced a significant decline in EtCO2 from 30.5 to 14.7 mmHg (P < 0.001) and RSO2 from 67.1% to 62.7% (P = 0.025). At hypocapnia, only Hb (+1.61 +/- 0.48 mumol/L; P < 0.001) and Hb-diff (-3.01 +/- 2.0 mumol/L; P < 0.001) indicated a decline in cerebral haemoglobin oxygenation. Within 8 min after hyperventilation, both EtCO2 and RSO2 normalised to values insignificantly different from baseline. In contrast, Hb and Hb-diff remained significantly different (Hb: +2.52 +/- 1.28 mumol/l; P < 0.001, Hb-diff: -4.31 +/- 4.0 mumol/L; P < 0.001). A correlation with EtCO2 was found for RSO2 (R = 0.35; P < 0.001) and CtO2 (R = 0.42; P < 0.001). All volunteers were continuously awake and none presented clinical symptoms of cerebral hypoxia.

CONCLUSION

Changes in cerebral haemoglobin oxygenation state were reflected more accurately by INVOS 3100 than NIRO 500. The cause may be the different technology of the monitors, since INVOS 3100 eliminates the contribution of extracranial oxygenation.

Effects of L-carnitine on erythrocyte acyl-CoA, free CoA, and glycerophospholipid acyltransferase in uremia

We studied the effects of L-carnitine treatment in the acyl flux of erythrocyte membranes from uremic patients. We found a significantly lower relative proportion of long-chain acyl-CoA (LCCoA) to free CoA (FCoA) in patients than in control subjects. In addition, patients had reduced activities of both carnitine palmitoyltransferase (CPT) and glycerophospholipid acyltransferase (LAT; CoA dependent), and increased ratios of long-chain acylcarnitine (LCAC) to free carnitine in their erythrocytes. These data support the hypothesis that acyl-trafficking is altered in erythrocytes in uremia. After treatment with L-carnitine, we observed a significant increase in CPT and LAT activities as well as in the LCCoA-FCoA ratio, and a significant decrease in the ratio of LCAC to free carnitine. These results support the conclusion that L-carnitine supplementation improves erythrocyte flux in uremic patients.

Cerebral oxygenation during cardiopulmonary bypass

Cerebral fractional oxygen extraction (FOE) was monitored in 30 children, using near infrared spectroscopy during cardiopulmonary bypass, to investigate the effect of hypothermia and circulatory arrest. One group of children (n = 15) underwent profound hypothermia with total circulatory arrest (n = 8) or continuous flow (n = 7). Another group (n = 15), of whom only one had circulatory arrest, underwent mild (n = 6) or moderate (n = 9) hypothermia. The mean FOE (SD) before bypass was 0.35 (0.12) and this correlated negatively with the preoperative arterial oxygen content (r = -0.58). Between the stage of cooling on bypass and cold bypass there was a reduction in FOE in all groups. Between cold bypass and rewarming there was an increase in FOE only in the groups with continuous flow. In the circulatory arrest group, the FOE remained low during rewarming and was significantly lower than that of the continuous flow group. No patients died and none had neurological abnormalities postoperatively. Apparent changes in oxidised cytochrome oxidase concentration were also monitored using near infrared spectroscopy. There was a fall in cytochrome aa3 on starting cardiopulmonary bypass, but there were no significant differences in the changes in cytochrome aa3 between any stage in any of the patient groups. Using this non-invasive technique, cooling was shown to reduce cerebral FOE. During rewarming on bypass there was an increase in cerebral FOE only in patients who had had continuous flow bypass. In contrast, the cerebral FOE in those with circulatory arrest remained constant after arrest and during the duration of the study. This may have implications for the timing of hypoxic brain injury.

Platelet mitochondrial respiratory chain function in Parkinson's disease

Reports on mitochondrial respiratory chain (MRC) complex I (CI) dysfunction in the substantia nigra in Parkinson's disease (PD) support the oxidative stress hypothesis in the neuropathogenesis of PD. Studies in peripheral tissue have found variable decreased CI and occasionally other complex activity suggestive of systemic impairment of MRC function in PD; however, MRC activity may be influenced by numerous variables. We conducted spectrophotometric measurements of MRC function in platelet mitochondrial preparations in 13 individuals with PD and 9 age-matched controls (CON) and have identified additional variables that may affect MRC activity. Mean CI, CIII, CIV, and citrate synthase (CS) activities were similar between PD and CON. CIII and CIV, specific and CS-corrected, activities were significantly positively correlated with CI in combined and individual group data, with the exception of CIII CS-corrected and CIV specific activities in CON and PD, respectively. CIII and CS specific activities were negatively correlated with age in CON, but varied randomly in PD. In PD, CIII specific activity was 1.4-fold higher in those with a history of environmental risk factors for PD and CIV specific activity was lower in those with a positive family history of PD [8.34 +/- 0.74 (n = 4) vs. 12.4 +/- 1.1 (SEM) min-1 mg-1; p = 0.046]. Group heterogeneity, variables affecting enzyme activity, and intrinsic properties of cells may thus contribute to conflicting data in studies of MRC function in platelets and other tissues.

Higher hematocrit improves cerebral outcome after deep hypothermic circulatory arrest

BACKGROUND

Various degrees of hemodilution are currently in clinical use during deep hypothermic circulatory arrest to counteract deleterious rheologic effects linked with brain injury by previous reports.

MATERIAL AND METHODS

Seventeen piglets were randomly assigned to three groups. Group I piglets (n = 7) received colloid and crystalloid prime (hematocrit < 10%), group II piglets (n = 5) received blood and crystalloid prime (hematocrit 20%), group III piglets (n = 5) received blood prime (hematocrit 30%). All groups underwent 60 minutes of deep hypothermic circulatory arrest at 15 degrees C with continuous magnetic resonance spectroscopy and near-infrared spectroscopy Neurologic recovery was evaluated for 4 days (neurologic deficit score 0, normal, to 500, brain death; overall performance category 1, normal, to 5, brain death). Neurohistologic score (0, normal, to 5+, necrosis) was assessed after the animals were euthanized on day 4.

RESULTS

Group I had significant loss of phosphocreatine and intracellular acidosis during early cooling (phosphocreatine in group I, 86.3% +/- 26.8%; group II, 117.3% +/- 8.6%; group III, 110.9% +/- 2.68%; p = 0.0008; intracellular pH in group I, 6.95 +/- 0.18; group II, 7.28 +/- 0.04; group III, 7.49 +/- 0.04; p = 0.0048). Final recovery was the same for all groups. Cytochrome aa3 was more reduced in group I during deep hypothermic circulatory arrest than in either of the other groups (group I, -43.6 +/- 2.6; group II, -16.0 +/- 5.2; group III, 1.3 +/= 3.1; p < 0.0001). Neurologic deficit score was best preserved in group III (p < 0.05 group II vs group III) on the first postoperative day, although this difference diminished with time and all animals were neurologically normal after 4 days. Histologic assessment was worst among group I in neocortex area (group I, 1.33 +/- 0.3; group II, 0.22 +/- 0.1; group III, 0.40 +/- 0.2, p < 0.05, group I vs group II; p = 0.0287, group I vs group III).

CONCLUSION

Extreme hemodilution during cardiopulmonary bypass may cause inadequate oxygen delivery during early cooling. The higher hematocrit with a blood prime is associated with improved cerebral recovery after deep hypothermic circulatory arrest.

Recent developments in cerebral monitoring--near-infrared light spectroscopy. An overview

A recent development has been the resurgence of interest in the concept of near-infrared light spectroscopy as a method of monitoring cerebral perfusion. Although this technique has been in use for 40 years, the principle has been primarily employed in peripheral pulse oximetry. Infrared light of wavelengths 600-1300 nanometres (nm) penetrate human tissue to a depth of several centimetres. Within the human brain this light is attenuated by the chromophores oxyhaemoglobin, deoxyhaemoglobin and also oxidised cytochrome a3. Positioning a near-infrared light source and a photodetector in a side by side configuration detects light attenuated and reflected in a parabolic path through the scalp, skull and brain tissue.

Non-invasive measurement of cardiac oxygenation and haemodynamics during transient episodes of coronary artery occlusion and reperfusion in the pig

1. The non-invasive method of near-infrared spectroscopy was used to measure myocardial oxygenation and haemodynamics in response to left anterior descending coronary artery occlusion in a porcine model. 2. Near-infrared spectroscopy measures changes in haemoglobin (and myoglobin) oxygenation and blood volume to yield information on tissue perfusion and flow. It also measures the redox state of cytochrome aa3, thus providing information about intracellular oxygen utilization. 3. Left anterior descending coronary artery occlusion was induced to produce periods of ischaemia lasting between 24s and 13.5 min (n = 13). The changes in deoxyhaemoglobin, oxyhaemoglobin and cytochrome aa3 measured during occlusion were all highly significant compared with baseline variation. In all occlusions (n = 13) a rapid decrease in oxyhaemoglobin concentration (-75.83 +/- 3.27 mumol/l, mean +/- SEM) with a simultaneous increase in deoxyhaemoglobin of 9.27 +/- 1.69 mumol/l was measured. The total haemoglobin concentration also fell by -71.3 +/- 5.32 mumol/l. Cytochrome aa3 was also reduced during occlusion (-8.35 +/- 1.044) mumol/l. 4. Over the range 24-60s occlusion, the magnitude of the fall in total haemoglobin and oxyhaemoglobin correlated with the duration of occlusion (P < 0.003 and 0.013 respectively). For total haemoglobin only the magnitude of the fall correlated with the increase upon release of occlusion (r = 0.89, P < 0.003). 5. Release of occlusion (n = 8) resulted in an immediate increase in the concentration of deoxyhaemoglobin at 9.88 +/- 1.06s, then total haemoglobin at 13.62 +/- 1.23s and finally oxyhaemoglobin at 29.75 +/- 5.96s. The difference between the timing of the maxima after reperfusion is significant (P < 0.002 and P < 0.007 respectively). Moreover, the time for the deoxyhaemoglobin signal to reach maximum values was found to correlate with the duration of occlusion (P < 0.04). This could be indicative of the PO2 of the ischaemic tissues and an immediate off-loading of oxygen from oxyhaemoglobin. The results are reliable, reproducible and sensitive enough to detect the kinetics of haemoglobin oxygenation from a beating heart in situ.

Effects of a diet low in copper on copper-status indicators in postmenopausal women

To study the effects of low copper intake in older individuals, 12 postmenopausal women, aged 63.1 +/- 8.8 y, were fed a diet containing 9 micromol (0.57 mg) Cu/d for 105 d, followed by a copper-repletion period of 35 d during which the diet was supplemented with 31.5 micromol (2.0 mg) Cu/d. Plasma copper and ceruloplasmin did not change significantly during copper depletion but ceruloplasmin decreased during copper repletion. Erythrocyte superoxide dismutase activity dropped significantly during low copper intake from 3450 to 2600 U/g hemoglobin, but did not increase during copper repletion. Platelet cytochrome c oxidase activity changed significantly (P<0.0001) from 1740 to 810 U/g protein during copper depletion, then increased to 1000 U/g protein during copper repletion. Erythrocyte glutathione peroxidase activity responded similarly. Clotting factor VIII activity increased significantly during copper depletion, then dropped during copper repletion. Low copper intakes did not induce the changes in serum cholesterol and hematology generally found in copper-deficient animal models. These results indicate that a paradigm shift may be needed in evaluating copper status in adult humans. Sensitive indicators of copper include functional activities of platelet cytochrome c oxidase, platelet copper, glutathione peroxidase, and clotting factor VIII. Plasma copper, ceruloplasmin, and cholesterol are relatively insensitive indicators. Also, the recovery from mild copper depletion may require more aggressive intervention tha 2 mg Cu/d for 35 d.

Reduced carnitine palmitoyl transferase activity and altered acyl-trafficking in red blood cells from hemodialysis patients

We measured carnitine palmitoyl transferase activity, free carnitine, and long chain acyl carnitine levels in erythrocytes from 15 uremic patients and 25 controls. Carnitine palmitoyl transferase levels in patients were significantly lower than in controls. The levels of free carnitine and long chain acyl carnitines as well as the long chain acyl carnitine/free carnitine ratio were significantly higher in patients than in controls. Our results suggest that hemodialysis causes alteration in the acyl-trafficking in red blood cells membrane.

Correlation between NIR spectroscopy and pulse oximetry in the fetus

At the Women's University Hospital Würzburg, pulse oximetry as well as Near Infrared Spectroscopy (NIR) measurements are performed on the fetus during labor in order to compare both methods. Changes of oxygen saturation seem to be positively correlated to concentration changes of oxidized hemoglobin measured by NIR, partially correlated to those of total hemoglobin, and partially correlated negatively to those of reduced hemoglobin. No correlation was found between oxygen saturation changes and those of cytochrome aa3, perhaps due to a longer lagtime. Pulse oximetry as well as NIR Spectroscopy may prove helpful tools for fetal surveillance. Both must be studied particularly with reference to FBA and fetal outcome before clinical decisions can be influenced by these methods.

Compensatory elevation of complex II activity in Leber's hereditary optic neuropathy

AIMS

To evaluate the mitochondrial respiratory enzyme activities in blood cells of Leber's hereditary optic neuropathy (LHON) with 11778 point mutation of mitochondrial DNA.

METHODS

Assays for the activities of NADH-cytochrome c reductase (complex I+complex III), succinate-cytochrome c reductase (complex II+complex III), and cytochrome c oxidase (complex IV) on blood cell mitochondria of seven LHON patients and 15 normal controls.

RESULTS

There was no statistically significant difference in NADH-cytochrome c reductase and cytochrome c oxidase activities between LHON patients and controls, but activities of succinate-cytochrome c reductase in LHON patients was significantly elevated compared with normal controls.

CONCLUSION

The observations that the activity of NADH-cytochrome c reductase is normal but that of succinate-cytochrome c reductase is increased in LHON patients with 11778 point mutation of mitochondrial DNA indicate an elevation of complex II activity, which may be due to a nuclear compensatory effect for defects of the respiratory function of mitochondria.

The influence of arterial carbon dioxide on cerebral oxygenation and haemodynamics during ECMO in normoxaemic and hypoxaemic piglets

OBJECTIVE

To investigate the cerebrovascular response to changes in arterial CO2 tension during extracorporeal membrane oxygenation (ECMO) in normoxaemic and hypoxaemic piglets.

METHODS

Four groups of six anaesthetized, paralysed and mechanically ventilated piglets: group 1-normoxaemia without ECMO, group 2-ECMO after normoxaemia, group 3-hypoxaemia without ECMO, and group 4-ECMO after hypoxaemia, were exposed successively to hypercapnia and hypocapnia. Changes in cerebral concentrations of oxyhaemoglobin (cO2Hb), deoxyhaemoglobin (cHHb), (oxidized-reduced) cytochrome aa3 (cCyt.aa3) and blood volume (CBV) were continuously measured using near infrared spectrophotometry. Heart rate, arterial O2 saturation, arterial blood pressure, central venous pressure, intracranial pressure (ICP) and left common carotid artery blood flow (LCaBF) were measured simultaneously.

RESULTS

Hypercapnia resulted in increased CBV, cO2Hb and ICP in all groups, while cHHb was decreased. No changes in LCaBF were found. Hypocapnia resulted in decreased cO2Hb and increased cHHb except in group 3. LCaBF decreased in all groups except group 2. CBV decreased only in groups 2 and 4. No effect on ICP was observed in any of the groups. The other variables showed no important changes either during hypercapnia or hypocapnia. ECMO after hypoxaemia resulted in a greater response of cO2Hb and cO2Hb and cHHb during hypocapnia. The effect of hypercapnia on CBV while on ECMO was greater than without ECMO.

CONCLUSION

Since cerebrovascular reactivity to CO2 remains intact during ECMO in piglets, it is important to keep arterial CO2 tension stable and in normal range during clinical ECMO.

Reduced copper enzyme activities in blood cells of children with cystic fibrosis

Cystic fibrosis patients are at risk for nutrient deficiencies from malabsorption related to exocrine pancreatic insufficiency. This research examined the copper homeostasis of children with cystic fibrosis. Our objective was to measure cytochrome oxidase and copper-zinc superoxide dismutase activities in mononuclear cells, neutrophils, and erythrocytes of adolescents with cystic fibrosis, as well as plasma copper and ceruloplasmin. Thirteen adolescents with pancreatic insufficiency caused by cystic fibrosis were compared with 10 age- and sex-matched control subjects. Serum copper concentrations and ceruloplasmin measurements were not significantly different between the two groups. Cytochrome oxidase activity was significantly lower in the mononuclear cells and copper-zinc superoxide dismutase activity was significantly lower in the neutrophils and erythrocytes of the cystic fibrosis group. Other measures of trace element status such as hemoglobin concentration, serum ferritin, serum zinc, glutathione peroxidase activity, and manganese superoxide dismutase activity were not different between the two groups. Reductions in the activity of two copper-dependent enzymes suggest abnormal copper homeostasis in this population.