Electricity production from municipal solid waste using microbial fuel cells.

The organic content of municipal solid waste has long been an attractive source of renewable energy, mainly as a solid fuel in waste-to-energy plants. This study focuses on the potential to use microbial fuel cells to convert municipal solid waste organics into energy using various operational conditions. The results showed that two-chamber microbial fuel cells with carbon felt and carbon felt allocation had a higher maximal power density (20.12 and 30.47 mW m(-2) for 1.5 and 4 L, respectively) than those of other electrode plate allocations. Most two-chamber microbial fuel cells (1.5 and 4 L) had a higher maximal power density than single-chamber ones with corresponding electrode plate allocations. Municipal solid waste with alkali hydrolysis pre-treatment and K3Fe(CN)6 as an electron acceptor improved the maximal power density to 1817.88 mW m(-2) (~0.49% coulomb efficiency, from 0.05-0.49%). The maximal power density from experiments using individual 1.5 and 4 L two-chamber microbial fuel cells, and serial and parallel connections of 1.5 and 4 L two-chamber microbial fuel cells, was found to be in the order of individual 4 L (30.47 mW m(-2)) > serial connection of 1.5 and 4 L (27.75) > individual 1.5 L (20.12) > parallel connection of 1.5 and 4 L (17.04) two-chamber microbial fuel cells . The power density using municipal solid waste microbial fuel cells was compared with information in the literature and discussed.

Effects of different SRT on anaerobic digestion of MSW dosed with various MSWI ashes.

This study investigated different solid retention time (SRT) on municipal solid waste (MSW) anaerobic digestion with various MSW incinerator fly ash (FA) and bottom ash (BA) addition. Results showed that biogas production rates (BPRs, ≈ 200 to ≈ 400 mL/gVS) with organic loading rate of ≈ 0.053 gVS/gVS(reactor) (Day 1-435, SRT 20 days, SRT20) at FA 1g/d (FA1), BA 12 g/d (BA12) and BA 24 g/d (BA24) dosed bioreactors increased after adaptation. BPRs with SRT10 and SRT5 decreased while BPRs with SRT40 showed to increase compared to initial BPRs (≈ 200 mL/gVS) with SRT20. SRT5 operation reduced the BPRs (≈ 10 - ≈ 90 mL/gVS) significantly and only BA12 and BA24 dosed bioreactors could recover the BPRs (≈ 100 - ≈ 200 mL/gVS) after SRT20 operation (Day 613-617) compared to FA1 and FA3 and control. Released levels of Co, Mo and W at BA12 and BA24 dosed bioreactors showed most potential to improve MSW anaerobic digestion.

Effects of micro-nano and non micro-nano MSWI ashes addition on MSW anaerobic digestion.

This study aims at investigating the effects of micro-nano municipal solid waste (MSW) incinerator (MSWI) fly ash (FA) and bottom ash (BA) on the MSW anaerobic digestion. Results showed that suitable micro-nano and non micro-nano MSWI ashes addition (FA/MSW 3, 6, 18 and 30 g g(-1) VS and BA/MSW 12, 36, 60 and 120 g g(-1) VS) could enhance the biogas production compared to the control. It was particularly found to have the highest biogas production at the micro-nano MSWI BA/MSW ratio of 36 g g(-1) VS (∼193 mL g(-1) VS MSW, ∼3.5 times to the control). Micro-nano MSWI FA and BA added bioreactors had the higher biogas production than the corresponding non micro-nano MSWI FA and BA added ones. Suitable MSWI ashes addition could improve the biogas production due to the released metals levels suitable for the MSW anaerobic digestion particularly found in the micro-nano added bioreactors.

Effects of spiked metals on the MSW anaerobic digestion.

This study aimed to investigate the effects of eight metals on the anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) in bioreactors. Anaerobic bioreactors containing 200 mL MSW mixed completely with 200 m L sludge seeding. Ca and K (0, 1000, 2000 and 6,000 mg L(-1)) and Cr, Ni, Zn, Co, Mo and W (0, 5, 50 and 100 mg L(-1)) of various dose were added to anaerobic bioreactors to examine their anaerobic digestion performance. Results showed that except K and Zn, Ca (~728 to ~1,461 mg L(-1)), Cr (~0.0022 to ~0.0212 mg L(-1)), Ni (~0.801 to ~5.362 mg L(-1)), Co (~0.148 to ~0.580 mg L(-1)), Mo (~0.044 to ~52.94 mg L(-1)) and W (~0.658 to ~40.39 mg L(-1)) had the potential to enhance the biogas production. On the other hand, except Mo and W, inhibitory concentrations IC(50) of Ca, K, Cr, Ni, Zn and Co were found to be ~3252, ~2097, ~0.124, ~7.239, ~0.482, ~8.625 mg L(-1), respectively. Eight spiked metals showed that they were adsorbed by MSW to a different extent resulting in different liquid metals levels and potential stimulation and inhibition on MSW anaerobic digestion. These results were discussed and compared to results from literature.

Modeling biogas production from organic fraction of MSW co-digested with MSWI ashes in anaerobic bioreactors.

This study aims at investigating the effects of MSW incinerator fly ash (FA) and bottom ash (BA) on the anaerobic co-digestion of OFMSW with FA or BA. It also simulates the biogas production from various dosed and control bioreactors. Results showed that suitable ashes addition (FA/MSW 10 and 20 g L(-1) and BA/MSW 100 g L(-1)) could improve the MSW anaerobic digestion and enhance the biogas production rates. FA/MSW 20 g L(-1) bioreactor had the higher biogas production and rate implying the potential option for MSW anaerobic co-digestion. Modeling studies showed that exponential plot simulated better for FA/MSW 10 g L(-1) and control bioreactors while Gaussian plot was applicable for FA/MSW 20 g L(-1) one. Linear and exponential plot of descending limb both simulated better for BA/MSW 100 g L(-1) bioreactor. Modified Gompertz plot showed higher correlation of biogas accumulation than exponential rise to maximum plot for all bioreactors.

Novel modeling concept for evaluating the effects of cadmium and copper on heterotrophic growth and lysis rates in activated sludge process.

A new modeling concept to evaluate the effects of cadmium and copper on heterotrophic growth rate constant (mu(H)) and lysis rate constant (b(H)) in activated sludge was introduced. The oxygen uptake rate (OUR) was employed to measure the constants. The results indicated that the mu(H) value decreased from 4.52 to 3.26 d(-1) or by 28% when 0.7 mg L(-1) of cadmium was added. Contrarily the b(H) value increased from 0.31 to 0.35 d(-1) or by 11%. When adding 0.7 mg L(-1) of copper, the mu(H) value decreased to 2.80 d(-1) or by 38%. The b(H) value increased to 0.42 d(-1) or by 35%. After regression, the inhibitory effect was in a good agreement with non-competitive inhibition kinetic. The inhibition coefficient values for cadmium and copper were 1.82 and 1.21 mg L(-1), respectively. The relation between the b(H) values and heavy metal concentrations agreed with exponential type well. The heavy metal would enhance b(H) value. Using these data, a new kinetic model was established and used to simulate the degree of inhibition. It was evident that not only the inhibitory effect on mu(H) but also that the enhancement effect on b(H) should be considered when heavy metal presented.

Biostabilization assessment of MSW co-disposed with MSWI fly ash in anaerobic bioreactors.

Municipal solid waste incinerator (MSWI) fly ash has been examined for possible use as landfill interim cover. For this aim, three anaerobic bioreactors, 1.2m high and 0.2m in diameter, were used to assess the co-digestion or co-disposal performance of MSW and MSWI fly ash. Two bioreactors contained ratios of 10 and 20 g fly ash per liter of MSW (or 0.2 and 0.4 g g(-1) VS, that is, 0.2 and 0.4 g fly ash per gram volatile solids (VS) of MSW). The remaining bioreactor was used as control, without fly ash addition. The results showed that gas production rate was enhanced by the appropriate addition of MSWI fly ash, with a rate of approximately 6.5l day(-1)kg(-1)VS at peak production in the ash-added bioreactors, compared to approximately 4l day(-1)kg(-1)VS in control. Conductivity, alkali metals and VS in leachate were higher in the fly ash-added bioreactors compared to control. The results show that MSW decomposition was maintained throughout at near-neutral pH and might be improved by release of alkali and trace metals from fly ash. Heavy metals exerted no inhibitory effect on MSW digestion in all three bioreactors. These phenomena indicate that proper amounts of MSWI fly ash, co-disposed or co-digested with MSW, could facilitate bacterial activity, digestion efficiency and gas production rates.

Solubility of heavy metals added to MSW.

This paper aims to investigate the six heavy metal levels (Cd, Cr, Cu, Pb, Ni and Zn) in municipal solid waste (MSW) at different pHs. It intends to provide the baseline information of metals solubility in MSW co-disposed or co-digested with MSW incinerator ashes in landfill or anaerobic bioreactors or heavy metals contaminated in anaerobic digesters. One milliliter (equal to 1mg) of each metal was added to the 100ml MSW and the batch reactor test was carried out. The results showed that higher HNO3 and NaOH were consumed at extreme pH of 1 and 13 compared to those from pH 2 to 11 due to the comparably higher buffer capacity. Pb was found to have the least soluble level, highest metal adsorption (%) and highest partitioning Kd (lg(-1)) between pH 3 and 12. In contrast, Ni showed the highest soluble level, lowest metal adsorption (%) and lowest Kd (lg(-1)) between pH 4 and 12. Except Ni and Cr, other four metals seemed to show the amphibious properties as comparative higher solubility was found in the acidic and basic conditions.

Comparisons of grey and neural network prediction of industrial park wastewater effluent using influent quality and online monitoring parameters.

In this study, Grey model (GM) and artificial neural network (ANN) were employed to predict suspended solids (SSeff) and chemical oxygen demand (CODeff) in the effluent from a wastewater treatment plant in industrial park of Taiwan. When constructing model or predicting, the influent quality or online monitoring parameters were adopted as the input variables. ANN was also adopted for comparison. The results indicated that the minimum MAPEs of 16.13 and 9.85% for SSeff and CODeff could be achieved using GMs when online monitoring parameters were taken as the input variables. Although a good fitness could be achieved using ANN, they required a large quantity of data. Contrarily, GM only required a small amount of data (at least four data) and the prediction results were even better than those of ANN. Therefore, GM could be applied successfully in predicting effluent when the information was not sufficient. The results also indicated that these simple online monitoring parameters could be applied on prediction of effluent quality well.

Recurrent cardiac myxoma with multiple distant metastasis and malignant change.

A 37 year-old female underwent open heart surgery for a left atrial myxoma. The post-operative course was uneventful and she was discharged two weeks later. She had regular monthly follow-up in the outpatient department until 10 months postoperatively when she was readmitted to the orthopedic ward for excision of a left ankle tumor. Two days after admission, she developed severe orthopnea. The initial diagnosis was heart failure, and she was transferred to the medical ward for treatment. Transthoracic and transesophageal echocardiography revealed a recurrent left atrial tumor. Because of acute obstruction of the mitral valve and deterioration of her condition, she underwent emergent open heart surgery. The recurrent atrial tumor was excised; histopathologic examination revealed a myxoid sarcoma. Multiple tumors were found on this admission, including a mass in the neck and in the left forearm; computed tomography revealed a brain tumor in the left posterior frontal lobe and a chest wall tumor. She died two months later. Recurrent cardiac myxoma with multiple distant metastasis may have a malignant potential. Because of the potential for tumor recurrence, long-term and regular follow-up is mandatory.

Expression pattern in a modified equalized kidney cDNA library of hypertensive rat.

BACKGROUND: Genes with important functions and rarely expressed would probably more easily be cloned from a modified equalized kidney cDNA library for further investigation. METHODS: A kidney cDNA library of a spontaneously hypertensive rat was synthesized by a modified equalization method. Inserts of random clones were amplified by PCR and sequenced. Sequences were compared against a nonredundant database in GenBank. The cDNA profile was compared with an expression profile of a mouse renal proximal tubule cDNA library. Seven clones were analyzed by Northern blot analysis. The cDNA ends of two novel genes were amplified by PCR, sequenced and analyzed. RESULTS: 336 cDNA clones were analyzed and grouped into 323 species of transcript with 77 species similar to previously reported genes. Northern blot analysis identified one kidney-specific, one rarely expressed and lung-specific, and another relatively testis-specific gene. Two novel genes were cloned. One was 4.1 kb in length and encoded a 390-amino acid zinc-finger protein. Another was 2.5 kb and encoded a 474-amino acid protein of unknown function. Compared with the expression profile of a mouse renal proximal tubule cDNA library, this kidney library had a lower proportion of ribosomal genes and had a greater proportion of genes for signal transduction and DNA or RNA binding. CONCLUSIONS: Rare or novel genes could be more easily isolated from this library for molecular study of hypertension and renal pathophysiology.

Effect of different recumbent positions on spectral indices of autonomic modulation of the heart during the acute phase of myocardial infarction.

OBJECTIVE: To examine which recumbent position can lead to the highest vagal modulation in patients during the acute phase of myocardial infarction. DESIGN: Descriptive study. SETTING: Intensive care unit in a medical center. PATIENTS: A total of 52 patients admitted to the intensive care unit because of acute myocardial infarction (AMI), 41 patients with coronary artery disease (CAD), and 28 patients with patent coronary arteriogram. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Heart rate variability analysis was performed in patients with AMI, patients with CAD, and patent coronary controls in supine, left lateral decubitus, and right lateral decubitus positions in random order. In the right lateral decubitus position, the vagal modulation was the highest and the sympathetic modulation was the lowest among three recumbent positions in three groups of patients. When the position was changed from supine to right lateral decubitus, the increase in vagal modulation was greater in patients who had more severely depressed vagal modulation in the supine position and the rate of increase was the greatest in patients with AMI, followed by patients with CAD and patent coronary controls. Detailed analysis showed that the vagal enhancing and sympathetic suppression effect of the right lateral decubitus position applied to patients with Q wave myocardial infarctions. CONCLUSIONS: The right lateral decubitus position can lead to the highest vagal modulation and the lowest sympathetic modulation among three recumbent positions in patients with Q wave myocardial infarction. The right lateral decubitus position can be used as an effective vagal enhancer in patients with Q wave myocardial infarction but without severe bradycardia or atrioventricular block.

Biphasic changes in autonomic nervous activity during pregnancy.

To understand the sequential response of the autonomic nervous system to pregnancy, we studied heart rate variability in 23 first trimester, 23 second trimester and 21 third trimester pregnant women. Twenty non-pregnant women were recruited as controls. Time and frequency domain measures of heart rate variability in three recumbent positions were compared. We found that normalized high-frequency power in the supine position increased significantly in the first trimester (42.2 (95% confidence interval (CI) 5.4) nu (normalized unit); P < 0.05) compared with non-pregnant controls (33.0 (6.0) nu), and then decreased progressively in the second (27.3 (6.7) nu) and third (21.8 (6.0) nu; P < 0.05) trimesters. The low-/high-frequency power ratio in the supine position decreased significantly in the first trimester (0.8 (0.3); P < 0.05) compared with that of non-pregnant controls (1.1 (0.3)) and increased progressively in the second (1.5 (0.4)) and third (2.1 (0.8); P < 0.05) trimesters. When the position was changed from the supine to the right lateral decubitus, the percentage change in normalized high-frequency power correlated significantly and negatively with normalized high-frequency power in the supine position in non-pregnant controls (r = -0.56, P = 0.01) and in pregnant women in the first (r = -0.44, P = 0.034), second (r = -0.68, P < 0.001) and third (r = -0.68, P < 0.001) trimesters. These results indicate that autonomic nervous activity shifted towards a lower sympathetic and higher vagal modulation in the first trimester, and changed towards a higher sympathetic and lower vagal modulation in the third trimester as gestational age increased. The balance between the haemodynamic changes of pregnancy and aortocaval compression caused by the enlarging gravid uterus may be responsible for the biphasic changes in autonomic nervous activity during pregnancy.

Cloning a novel metallophosphoesterase gene from a kidney cDNA library of hypertensive rat.

BACKGROUND AND PURPOSE: Genetic and environmental factors may contribute to the pathogenesis of essential hypertension. To facilitate genetic studies of hypertension and renal disorders, we sought to clone novel genes from a modified, equalized kidney (MEK) cDNA library of a spontaneously hypertensive rat (SHR). METHODS: A kidney cDNA library of an SHR was synthesized using the modified equalization method. Inserts of 350 random clones were amplified by polymerase chain reaction (PCR) and sequenced, of which 246 were presumably unknown after being compared against a nonredundant database in the GenBank. The cDNA ends of clone 38S were obtained by rapid amplification of cDNA ends, sequenced, and then analyzed with Translate, Prosite, Profile, SignalP, and TMpred programs. RESULTS: The full-length cDNA was 938 bp, and translated into a 182-amino acid protein. The deduced protein had a metallophosphoesterase domain, a signal peptide at its amino end, a protein kinase C phosphorylation site, and a transmembrane domain. Northern blot analysis revealed that this gene was expressed in the heart, brain, spleen, lungs, liver, skeletal muscles, kidneys and testes of Sprague-Dawley rats. A putative protein of Arabidopsis thaliana shares 62% homology with protein 38S, but the two proteins differ in terms of function and structure. CONCLUSIONS: Our results support that protein 38S is a novel membrane metallophosphoesterase, although its function in the kidneys remains to be elucidated. This study also demonstrates the feasibility of using PCR to clone novel genes from our MEK cDNA library.

Role of electrophysiological studies and arrhythmia intervention in repairing Ebstein's anomaly.

BACKGROUND: Repairing Ebstein's anomaly without correction of associated arrhythmia may result in sudden death. Catheter or surgical ablation is indicated for various symptomatic tachyarrhythmias in Ebstein's anomaly. METHODS: Between October 1973 and October 1997, 30 patients with Ebstein's anomaly underwent surgical repair in our hospital. Tricuspid valve replacement was performed in 13 patients, tricuspid annuloplasty and valvuloplasty in the remaining 17 patients. Preoperative electrophysiological studies were performed in 11 patients after 1980. Concomitant arrhythmia ablation was done in 10 patients: 4 for Wolff-Parkinson-White syndrome, 2 for atrioventricular (AV) nodal reentrant tachycardia, one for ventricular tachycardia and 3 for paroxysmal atrial flutter and fibrillation. RESULTS: No mortality or major morbidity occurred in those patients undergoing arrhythmia intervention. There were 7 deaths in total; 6 died suddenly, and the other died of purulent mediastinitis. None of the 6 sudden deaths underwent preoperative electrophysiological evaluation. The functional recovery was good in all survivals. CONCLUSIONS: We conclude that detailed preoperative electrophysiological evaluation in patients with Ebstein's anomaly is mandatory. Aggressive surgical intervention of the associated arrhythmias in addition to anatomic correction can reduce the sudden death in Ebstein's anomaly.

Characteristic findings of body surface potential map during ventricular repolarization in patients with coronary heart disease.

The objective of the present study was to investigate the characteristics of body surface potential map (BSPM) findings during ventricular repolarization in patients with coronary artery disease (CAD). A total of 108 consecutive patients, 99 men and 9 women with angina pectoris and positive treadmill exercise test results as well as angiographically documented CAD underwent BSPM study in a fasting state. Their ages ranged from 30 to 70 years. There were 13 patients with right coronary artery (RCA) lesions, 37 with left anterior descending artery (LAD) lesions, 5 with left circumflex artery (LCX) lesions, 17 with both RCA and LAD lesions, 12 with both LCX and LAD lesions, and 24 with 3-vessel disease. The BSPMs were obtained by using the heart potential map system designed by Toyama et al. There were 59 lead points on the anterior chest wall and 28 on the back. The BSPMs in isopotential distribution were made every one msec throughout the ventricular activation period. The distribution of positive and negative potentials, potential maximum and potential minimum, polarity of potential distribution, and the reversal of potential distribution during ventricular repolarization were analyzed. The following information on BSPMs was obtained: (1) In early ventricular repolarization, the negative potential and the potential minimum appeared abnormally on the anterior thorax. The potential abnormality displayed on the right portion or the inferior portion in patients with RCA lesions, on the middle portion or the left portion in patients with LAD lesions, and on the left-superior portion or the left-middle portion in patients with LCX lesions. In patients with multi-vessel disease, the abnormal potential distribution showed a combined pattern of individual vessel lesions. (2) In some cases, the multipolar potential distribution appeared abnormally during the initial stage and the peak of the T wave. (3) The reversal of potential distribution was observed in about half of the patients. The characteristic findings of the BSPM during ventricular repolarization, including abnormal potential distribution, multipolar potential distribution and reversal of potential distribution, will be of clinical value in patients with CAD.

Return of autonomic nervous activity after delivery: role of aortocaval compression.

We have compared measures of heart rate variability (HRV) in 15 women in late pregnancy before and 3 months after delivery and in 20 non-pregnant controls, to study the effect of aortocaval compression on autonomic nervous activity. Normalized high-frequency power was used as an index of vagal activity and the low-/high-frequency power ratio as index of sympathovagal balance. We found that the decrease in vagal activity and increase in sympathovagal balance before delivery returned to normal 3 months after delivery. Percentage changes in vagal activity and sympathovagal balance 3 months after delivery in the left lateral decubitus position were least among three recumbent positions. The relief of aortocaval compression as a result of delivery of the fetus may be the main cause of return of autonomic nervous activity 3 months after delivery. Postpartum hormonal changes may also contribute to return of autonomic nervous activity after delivery.

Effect of acupuncture at nei-kuan on left ventricular function in patients with coronary artery disease.

Effect of acupuncture at Nei-Kuan (EH-6) on left ventricular ejection fraction (LVEF) was examined in 22 patients with angiographically proved coronary artery disease (CAD) and 22 normal subjects. Serial equilibrium radionuclide angiography was done to measure LVEF at 4 different times (at baseline, at 1 to 15 minutes, and 16 to 30 minutes during acupuncture, and immediately after acupuncture). One week later, each patient had an identical imaging protocol with acupuncture performed at a dummy point. Our results showed that in normal subjects, the mean values of LVEF did not change significantly during or after acupuncture. In contrast, in patients with CAD, the mean values of LVEF in the initial 15 minutes of acupuncture significantly increased from baseline (42.5 +/- 15.6% vs. 40.6 +/- 15.4%, p < 0.05). The increase persisted through the next 15 minutes of acupuncture and 15 minutes after acupuncture, but became insignificant at one week. Thus, acupuncture at Nei-Kuan can temporarily improve LV function in patients with CAD.

Implications of an early reversal pattern of body surface potential maps in coronary artery disease.

During early ventricular depolarization, the normal body surface potential map (BSPM) has a maximal potential that is greater than the absolute value of the minimal potential; this reverses in late depolarization, so that the absolute value of the minimal potential is greater. Nevertheless, an abnormal "early reversal" BSPM pattern has been observed in some patients with cardiovascular disease. To investigate the implications of this abnormal pattern, BSPMs were studied in 100 patients with angiographically proven coronary artery disease (CAD). There were 57 patients (57%; group A) with an abnormal early reversal pattern and 43 (43%; group B) without this early reversal pattern. A significant (> 70% narrowing) CAD lesion was observed in a significantly higher proportion of group A (97%) than group B (77%) patients, although the number of involved coronary arteries was not significantly different between the two groups. The maximal extent of the abnormal negative potential was significantly greater in group A (21.2 +/- 9.6 cm2) than in group B (12.2 +/- 7.5 cm2). The abnormal negative potential lasted significantly longer in group A (22.1 +/- 12.1 msec) than in group B (14.4 +/- 9.2 msec). Similarly, the minimal potential lasted significantly longer in group A (20.1 +/- 11.3 msec) than in group B (11.8 +/- 7.1 msec). These findings suggest that the abnormal early reversal BSPM pattern is a valuable indicator of extensive myocardial lesions and the severity of CAD.

Comparison of supine and upright positions on autonomic nervous activity in late pregnancy: the role of aortocaval compression.

In order to understand the effect of aortocaval compression on autonomic nervous activity, we compared the effects of supine and upright postures on measures of heart rate variability in late pregnancy. Thirty-two women in late pregnancy and 23 nonpregnant age-matched women were studied. Both time and frequency domain heart rate variability measures were compared between the supine and upright positions, and between pregnant women and controls. The pregnant women had smaller mean RR interval, standard deviation of RR intervals and normalised high-frequency power, and a larger low- to high-frequency power ratio than nonpregnant women in the supine position. When the position was changed from upright to supine in nonpregnant women, the percentage change in the mean RR interval and normalised high-frequency power were increased, whereas the percentage change in the coefficient of variation of RR interval and low- to high-frequency power ratio were decreased. In contrast, the percentage change in normalised high-frequency power was decreased and the percentage change in low- to high-frequency power ratio was increased in pregnant women when the position was changed from upright to supine. These results indicate that the vagal enhancing effect seen in normal subjects when changing position from upright to supine was reversed in women in late pregnancy. Aortocaval compression in the supine position in pregnant women might be responsible for this reversal in the autonomic response to lying down.