Improved growth of bifidobacteria by cocultivation with Lactococcus lactis subspecies lactis.

Cultivation of bifidobacteria in milk is a difficult and industrially valuable task. In this paper, we report the finding of a novel technique to improve the growth of bifidobacteria in dairy products and the results of mechanism studies. The growth of bifidobacteria in skim milk medium was found to be stimulated upon cocultivation with certain strains of Lactococcus lactis ssp. lactis. Bifidobacterium growth-stimulating (BGS) activity was observed on a wide range of bifidobacterial species. Bifidobacterium growth-stimulating activity was associated with the ability to grow in skim milk medium and the presence of a cell wall-anchored proteinase (PrtP) in Lc. lactis ssp. lactis. Studies on one strain, Lc. lactis ssp. lactis MCC857, showed that crude PrtP extracts and casein hydrolysates exhibited BGS activity. The casein hydrolysate BGS activity was found in the low molecular weight fraction by HPLC separation. A combination of 2 AA, Met and Leu, was found to account for a large portion of the casein hydrolysate BGS activity. In conclusion, this cocultivation system is highly efficient and industrially applicable for the production of fermented milk with high cell counts of bifidobacteria.

Computational hemodynamic analysis in congenital heart disease: simulation of the Norwood procedure.

Hypoplastic left heart syndrome (HLHS) is a congenital heart disease which should be treated at neonate. Even now, its operation is one of the greatest challenges. However, currently there are no quantitative standards to evaluate and predict the outcome of the therapy. In this study, computational fluid dynamics (CFD) was used to estimate the performance of first stage HLHS surgery, the Norwood operation. An image data transfer system was developed to convert clinical images into three-dimensional geometry. To confirm software applicability, a validation process was carried out to eliminate any influence of numerical procedures. The velocities derived from echocardiography measurements were used as boundary conditions, and pressure waves measured by a cardiac catheter simultaneous with an electrocardiogram (ECG) were employed to validate the results of CFD simulation. Calculated results were congruent with the in vivo measurement results. The blood flow circulations were successfully simulated and the distribution of blood flow in each vessel was estimated. Time-varying energy losses (EL), local pressure and wall shear stress (WSS) were analyzed to estimate clinical treatment. The results indicated that pulsatile simulation is essential in quantitative evaluation. Computational hemodynamics may be applied in the surgical optimization for the treatment of HLHS.

Probiotics in the treatment of Japanese cedar pollinosis: a double-blind placebo-controlled trial.

BACKGROUND: Probiotic bacteria may be effective in the treatment of allergic inflammation and food allergy, but efficacy and underlying mechanisms remain unclear. OBJECTIVE: The present study investigated the effects of probiotic strain Bifidobacterium longum BB536 in the treatment of Japanese cedar pollinosis (JCPsis). METHODS: In a randomized, double-blind, placebo-controlled trial, 44 JCPsis subjects received BB536 or placebo for 13 weeks during the pollen season. Subjective symptoms and self-care measures were recorded daily and blood samples were taken before and during intervention to measure blood levels of parameters related to JCPsis. RESULTS: BB536 intake was associated with a significant reduction in number of subjects prematurely terminated due to severe symptoms and pollinosis medication (P=0.0057 vs. placebo group). Comparison of subjective symptom scores indicated significant decreases in rhinorrhea, nasal blockage and composite scores in the BB536 group compared with the placebo group. Comparison of medical scores showed marked improvements in all symptoms on BB536 intake. A T-helper type 2 (Th2)-skewed immune response occurring along with pollen dispersion was observed. BB536 significantly suppressed increases in plasma thymus- and activation-regulated chemokine and tended to suppress elevations of Japanese cedar pollen (JCP)-specific IgE. CONCLUSION: These results suggest the efficacy of BB536 in relieving JCPsis symptoms, probably through the modulation of Th2-skewed immune response.

Immunostimulatory oligodeoxynucleotide from Bifidobacterium longum suppresses Th2 immune responses in a murine model.

We have reported previously that novel immunostimulatory sequence (ISS) oligodeoxynucleotide (ODN) BL07S from a probiotic strain of Bifidobacterium longum inhibited immunoglobulin (Ig) E production in vitro. However, whether ISS-ODNs from probiotics regulate T helper type 2 (Th2)-polarized immune reactions in vivo remains unclear. To evaluate the inhibitory effects of ODN BL07S on type I allergic response, BALB/c mice were injected with or without ODN BL07S in the presence of ovalbumin (OVA) on days 0 and 14. Serum Ig levels (IgE, IgG1 and IgG2a) and cytokine levels (interferon (IFN)-gamma, interleukin (IL)-12, IL-4, IL-5, IL-10 and IL-13) were investigated in splenocyte cultures from days 14-28. Production of OVA-specific and total IgE were significantly suppressed by administration of ODN BL07S, but not by ODN BL06S, a non-ISS-ODN. Compared to controls, ODN BL07S induced significantly lower levels of Th2 cytokines (IL-4 and IL-5) in splenocyte cultures, and significantly higher levels of serum OVA-specific IgG2a. These effects of ODN BL07S on modulation of Th2 immune response were dose-dependent. The present results demonstrate that ODN BL07S from genomic DNA of B. longum BB536 prevents antigen-induced Th2 immune responses in vivo, suggesting that ISS-ODNs from probiotics might be useful in preventing allergic disease.

By-side impurities in chloronaphthalene mixtures of the Halowax series: all 135 chlorodibenzofurans.

One hundred twenty five congeners of CDF off 135 theoretically possible were quantified in seven of various type Halowax formulations but still 45 co-eluted under the gas chromatographic conditions applied. The total CDFs concentration of Halowax formulations was between 250 and 16,000 ng/g. The compositional profile of CDF homologue groups of the Halowaxes frequently followed a degree of chlorination of the parent chloronaphthalene mixture and an exception was Halowax 1031. The compositional profile of many isomers of trichlorodibenzofuran, found and often highly abundant, was characteristic to majority of the formulations examined, and each of them demonstrated to have its own pattern but mysterious to explain remained Halowax 1031. In term of dioxin-like toxicity the most potent due to CDFs content was Halowax 1014 with 210 ng TCDD TEQ/g and next was Halowax 1013 with 36 ng TEQ/g, while between 1.3 and 5.0 ng TEQ/g were for other formulations. A tentative estimation made implies that the net total CDFs production due to manufacture of the technical CNs in the XX century could reach an amount between 420 kg (median) and 825 kg (mean), and for most toxic dioxin-like congeners between 705 g (median) and 5700 g (mean) TCDD TEQ, while for the worst case of Halowax 1014 alone scenario it could be 750 kg of the total CDFs and 16 kg of TCDD TEQ for most toxic congeners.

By-side impurities in chloronaphthalene mixtures of the Halowax series: all 75 chlorodibenzo-p-dioxins.

A by-side chlorodibenzo-p-dioxins (CDDs) has been identified as impurity in concentration between 1.5 and 370 ng/g in the Halowax formulations of all type. Halowax 1014 was relatively richer in number of CDD congeners detected when compared to six other CN formulations examined. Amongst the mono- to tri-CDDs, the most prevalent in the Halowaxes were 1- and 2-MoCDD, and especially they were abundant in the formulations of a lower than a higher degree of chlorination. Amongst the tetra- to octaCDD only 1,2,3,4-/1,2,4,6-/1,2,4,9-/ 1,2,3,8-TeCDD, 1,2,3,4,6,7,8-HpCDD and OcCDD were found in all the Halowaxes, and 1,2,3,4,6,7,9-HpCDD remained undetected only in Halowax 1099 and 1013, while most of TeCDDs, PeCDD, and HxCDDs were absent in a majority of the formulations examined. The compositional profile of 1,2,3,4-/1,2,4,6-/1,2,4,9,-/1,2,3,8-TeCDD and OcCDD congeners found in the Halowaxes seem to indicate, that after an initial in situ formation of mono- and di-CDDs during CNs synthesis, a further increase of reaction time, temperature, and pressure can lead to successive chlorination of the already established chlorodibenzo-p-dioxin molecule, and so to enrichment in 1,2,3,4-/ 1,2,4,6-/1,2,4,9,-/1,2,3,8-TeCDD but also OcCDD content for most of the final products obtained. Nevertheless, also due to the co-synthesis of chlorophenols in the Halowaxes, their condensation reactions could also contribute to the formation of CDDs. In term of dioxin-like toxicity the most potent due to CDDs content was Halowax 1014 with 0.95 ng TCDD TEQ/g, and between 0.00068 and 0.058 ng/g were for other formulations. A rough estimation made implies that a net CDDs production due to manufacture of the technical CNs in the XX century could reach an amount between 3.0 and 12.6 kg, while for most toxic dioxin-like constituents between 5.25 and 24 g TCDD TEQ, For the worst case scenario and involvement of Halowax 1014 only the net total CDDs production was estimated to be 1.5 kg, and for highly-toxic congeners 71 g TCDD TEQ. All these figures are much lower when compared to co-production of CDFs.

By-side impurities in chloronaphthalene mixtures of the Halowax series: all 209 chlorobiphenyls.

202 congeners of chlorobiphenyl (CB) with 109 single-resolved compounds and 93 co-eluting, which represented from mono- to deca-CB were quantified as by-side impurities in all seven and of various type the technical chloronaphthalene (CN) formulations of the Halowax series. IUPAC No. 104, 145, 159, 169, 184, 186, and 188 were undetected (<0.05-<0.7 ng/g). The total CBs content of the Halowax formulations ranged between 220 and 640,000 ng/g, and lower chlorinated Halowaxes 1031 (27% Cl) and 1000 (35% Cl) were two to three orders of magnitude more contaminated with CBs than higher chlorinated Halowax 1001, 1099, 1013, 1014, and 1051 (49-70% Cl). The profile of CB homologue groups of the Halowaxes changed and followed somehow a degree of chlorination of the parent CN mixture. For Halowax 1031 and 1000, a decreasing trend in proportion from mono- to deca-CB was evident, while for Halowax 1001, 1099, 1013, 1014, and 1051 the relative proportions between the CB homologue groups varied somehow. Evidently content of lower chlorinated mono- and di-CBs highly decreased and steadily increased tri- to octa-CBs and they become dominating homologues in Halowax formulations in parallel with an increase of the content of higher molecular weight CN constituents, respectively. Among planar non- and mono-ortho CBs, total concentrations in Halowax formulations were detected in the range of 2.0-2600 ng/g, and only 3,3',4,4',5,5'-HxCB (no. 169) was undetected (<0.05ng/g). Detection of by-side CBs in technical Halowaxes demonstrate clearly that those formulations apart from a massive introduction of dioxin-like CNs become in the past also an early source of environmental pollution with CBs, which proceeded for around 20-30 years use of original CB formulations.

Effects of milk products fermented by Bifidobacterium longum on blood lipids in rats and healthy adult male volunteers.

The effects of milk products fermented by Bifidobacterium longum strain BL1, a probiotic strain, on blood lipids in rats and humans were studied. Rats were fed a cholesterol-enriched experimental diet, supplemented with lyophilized powders of 1) acid milk (control), 2) milk fermented with a mixed culture of ordinary yogurt starters composed of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (SL), and 3) bifidobacterium milk fermented with the probiotic B. longum strain BL1, respectively. The bifidobacterium milk feeding brought about significant lowering of the serum concentrations of total cholesterol, low-density lipoprotein cholesterol, and triglycerides, in comparison with the control, while no change in high-density lipoprotein cholesterol concentration was observed. On the other hand, supplementation with SL milk resulted in only slight, nonsignificant decreases in serum lipid concentrations in comparison with the control. In the human study, 32 subjects with serum total cholesterol ranging from 220 to 280 mg/dl were randomly assigned to two treatments: 1) intake of a low-fat drinking yogurt prepared with ordinary yogurt starters composed of S. thermophilus and L. delbrueckii subsp. bulgaricus (P-group) and 2) intake of a low-fat drinking yogurt prepared with the two ordinary yogurt starters plus B. longum strain BL1 (B-group). After intake for 4 wk at 3 x 100 ml/day, reduction of serum total cholesterol was observed in approximately half of the B-group subjects; a particularly significant decrease in serum total cholesterol was found among subjects with moderate hypercholesterolemia (serum total cholesterol > 240 mg/dl). However, the serum lipid concentrations in the P-group subjects were almost stable during the experimental periods. The present results indicate the potential of the probiotic B. longum strain BL1 in serum lipid improvement.

Overexpression of a DEAD box/RNA helicase protein, rck/p54, in human hepatocytes from patients with hepatitis C virus-related chronic hepatitis and its implication in hepatocellular carcinogenesis.

Hepatitis C virus (HCV) infection is the most common cause of chronic hepatitis, which frequently progresses to hepatocellular carcinoma. The pathogenesis of its persistent infection and tumour progression has not been fully characterized yet. The RCK gene was previously cloned at the breakpoint of the t(11;14)(q23;q32) chromosome translocation observed in human B-cell lymphoma cell line RC-K8. The RCK protein, rck/p54, which is a 54-kDa cytoplasmic protein belonging to the DEAD box/RNA helicase family, is considered to facilitate the translation of mRNA(s) of genes for cell proliferation and malignant transformation not only in B-cell lymphomas having the t(11;14) translocation but also in other solid tumours. The aim of this work was to examine the involvement of rck/p54 in carcinogenesis of hepatocellular carcinoma from HCV-related chronic hepatitis. We examined the expression of rck/p54 in 29 cases of HCV-related chronic hepatitis and eight cases of hepatocellular carcinoma by immunohistochemistry and Western blot analysis. Twenty-six of 29 cases with HCV-related chronic hepatitis and all cases with hepatocellular carcinoma tested overexpressed rck/p54 protein. The expression of rck/p54 was lowered by treatment with IFN-alpha in two cases who showed the decrease in HCV RNA levels. These findings suggest that rck/p54 protein is possibly involved in the replication of HCV genomes in hepatocytes and in tumourigenesis of hepatocellular carcinomas.

Video-assisted cardioscopy for infectious endocarditis.

We successfully resected vegetation of infectious endocarditis in right ventricular outflow tract using a video-assisted cardioscopy without ventriculotomy. Video-assisted cardioscopy provided clear and precise visualization of vegetation on the anterior wall of right ventricular outflow. This technique is effective to visualize remote intra-cardiac structures, and to facilitate repairs, while avoiding the need for extended cardiac incisions.

Long-term histological prognosis and serum fibrosis markers in chronic hepatitis C patients treated with interferon.

BACKGROUND: Interferon (IFN) therapy is effective in 20-40% of patients with chronic hepatitis C, but the relationship between histological changes and the response to interferon is still unclear. We investigated the long-term histological prognosis and the changes of serum fibrosis markers after interferon therapy relation to the response. METHODS AND RESULTS: One hundred and eighteen patients with chronic hepatitis C who received interferon therapy were divided into four groups based on the detection of viremia and the serum alanine aminotransferase (ALT) level after treatment. A histological examination was performed by using the histological activity index and the criteria of the METAVIR score. Serum fibrosis markers were used to measure the levels of hyaluronic acid and type IV collagen 7s. Responders, whose serum ALT levels became normal after treatment, demonstrated histological improvement. Histological improvement was more rapid in sustained virological responders with hepatitis C virus (HCV) RNA seronegativity than in biochemical responders with HCV-RNA seropositivity. Only sustained virological responders exhibited histological cure. In partial responders, whose serum ALT levels decreased to less than twice the upper of normal, and non-responders whose serum ALT levels were not reduced, liver fibrosis was unchanged or showed progression. Serum fibrosis markers increased with progression of the histological stage and varied depending on the response to interferon. CONCLUSION: Normalization of serum ALT levels after interferon therapy led to a histological improvement, and that with viral clearance achieved histological cure. Serum fibrosis markers were useful indicators for long-term according to the response of IFN therapy.

Body mass index for chronic hemodialysis patients: stable hemodialysis and mortality.

Body mass index (BMI) is used as a reference for weight control programs in the general population and in morbidity and mortality studies in diabetes patients. However, the implications of BMI in chronic hemodialysis patients is unclear. We studied the BMI of chronic hemodialysis patients, focusing on problems encountered during outpatient hemodialysis therapy and on 2-year mortality. Outpatients with chronic hemodialysis (n = 258; 144 men, 114 women) were divided into four groups: (i) patients with stable hemodialysis; (ii) patients with marked hypotension requiring catecholamine infusion during hemodialysis; (iii) patients with excessive interdialysis weight gain requiring occasional additional hemodialysis; and (iv) patients with troublesome hemodialysis due to other causes. The statistical differences between the average BMI among these groups were evaluated, and were subdivided into sex, age and the duration of hemodialysis history. The 2-year mortality rates of these patients were also studied according to their BMI. In patients under 60 years of age, those with excessive interdialysis weight gain had statistically larger BMI (23.2; n = 35) compared to patients with good hemodialysis control (20.1; n = 178), regardless of gender and hemodialysis history. The mortality rate was at a minimum at approximately 20 BMI in patients under 60 years of age. However, lower BMI was associated with a greater mortality rate in patients 60 years or over. For chronic hemodialysis patients, the BMI associated with stable hemodialysis and minimum mortality is approximately 20, in those under 60 years of age. The BMI of aged hemodialysis patients should be considered separately in morbidity and mortality studies.

[Surgical techniques and results of right ventricular [correction of venericular] outflow tract reconstruction with pedicled autologous tissue].

From 1987 to 2000, 44 patients underwent anatomic repair of anomalies with pulmonary outflow obstruction by using pedicled autologous tissue in reconstructing the pulmonary outflow tract. Twenty-four patients had tetralogy of Fallot with pulmonary atresia (TOF/PA), from 1.7 years to 12.9 years of age (mean 9.0 years). In the group of TOF/PA, slit-widening method was performed in 22, autologous pericardial flap was used in 1, and atrial appendage was used in 4 patients. Eight patients had transposition of the great arteries with ventricular septal defect and pulmonary stenosis (TGA type III), from 9 months to 9.2 years of age (mean 4.5 years). All of the patient with TGA type III under went direct PA-RV anastomosis (natural route non-conduit repair). Three patients had truncus arteriosus, from 1 month to 7.8 years of age (mean 4.5 years). In the group of the truncus, atrial appendage was used in 1 and direct PA-RV anstomosis was made in 2 patients. Six patients had Rastelli's conduit obstruction, from 6.6 years to 20.3 years of age (mean 13.9 years). The conduit was removed and outflow tract was reconstructed with direct PA-RV anastomosis in 5 and using atrial appendage in 1 patients. There was one hospital death (2%) and no late deaths. In 31 patients whose follow-up time exceed 5 years, 7 patients (23%) were found to have pressure gradient more than 40 mmHg at the pulmonary outflow tract. None of the patients with TGA who underwent natural route non-conduit repair developed late stenosis at the pulmonary out flow tract.

Anomalous origin of innominate artery from right pulmonary artery in DiGeorge Syndrome.

We experienced a case of anomalous origin of innominate artery from right pulmonary artery (isolated innominate artery). This patient was a 2-month-old baby girl weighing 3.2 kg with DiGeorge syndrome, who was diagnosed with perimembranous ventricular septal defect, atrial septal defect, and patent ductus arteriosus. This type of anomaly is exceedingly rare.

Transxiphoid approach for intracardiac repair using video-assisted cardioscopy.

Video-assisted cardioscopy (VAC) is a novel tool for providing clear visualization of small intracardiac structures and achieving complete repair in minimally invasive surgery. Between July 1999 and July 2000, 12 patients with atrial septal defect and ventricular septal defect underwent surgical repair using a combined procedure with the transxiphoid approach and VAC in our institution. The mean skin incision was 5.4 cm, and the postoperative courses of all the patients were uneventful without any complications. The mean hospital stay was 8.3 days and 1 patient (8.3%) needed blood products. Our experience showed the technical feasibility and acceptable surgical results of transxiphoid approach using a VAC.

Assisted venous drainage cardiopulmonary bypass in congenital heart surgery.

BACKGROUND: A novel active venous drainage perfusion circuit was designed to achieve effective venous return through small venous cannulas. The efficacy and safety of this new system was investigated and compared with a conventional gravity drainage system. METHODS: Four hundred consecutive patients undergoing open heart repair of congenital heart lesions by one surgeon were studied. The first 200 patients were supported by gravity drainage and the next 200 patients were supported by assisted venous drainage. No patient in the time period was excluded from the study. RESULTS: The two groups did not differ significantly in weight, bypass time, or cross-clamp time. Priming volumes were less in the assisted group than in the gravity group (576+/-232 mL versus 693+/-221 mL, p < 0.001). Venous cannula size was smaller in the assisted group when compared with the gravity group (33.2F+/-7.4F versus 38.5F+/-7.1F, p < 0.001). There was a trend to lower operative mortality in the assisted drainage group (5 of 200, 2.5% versus 11 of 200, 5.5%; p = 0.10). Hospital stay and pulmonary, infectious, and neurologic complications were comparable in both groups. Cardiac complications were less common in the assisted group than in gravity group (22 of 200, 11% versus 38 of 200, 19%; p = 0.017). Hematologic complications were less common in the assisted group than the gravity group (6 of 200, 3% versus 19 of 200, 9.5%; p < 0.01). CONCLUSIONS: These findings suggest that assisted venous drainage is safe in congenital heart operations and facilitates the use of smaller venous cannulas.

Creatine kinase isoforms in the seminal plasma and the purified human sperm.

In previous conventional reports sperm and seminal plasma were not well separated and therefore it was highly probable that isoform (CK-BB) of seminal plasma was determined together with that of sperm. The authors developed a method to purify sperm specimen free from seminal plasma. Human sperm was purified by means of the continuous-step density gradient centrifugation with an inner column and the subsequent modified swim-up procedure. CK isoforms in the purified sperm and the seminal plasma were analyzed by ion exchange chromatography and electrophoresis. The purified sperm contained mitochondrial CK-MiMi as well as cytosolic CK, of which isoform was almost occupied by CK-MM but CK-BB was not detected. On the other hand, CK isoform in the seminal plasma was detected as CK-BB alone. CK activity in human sperm and seminal plasma were 2.0 +/- 0.7 x 10(-6) IU/10(6) sperm and 661 +/- 360 IU/L, respectively. CK activity in the seminal plasma gave no correlation with the semen parameters.

Endovascular stent graft treatment of a pulmonary artery pseudoaneurysm.

A 5-year-old girl with pulmonary atresia, ventricular septal defect, hypoplastic pulmonary arteries, and multiple pulmonary artery reconstructive procedures presented with an enlarging pulmonary artery pseudoaneurysm. A previous attempt to occlude the aneurysm was unsuccessful and the aneurysm continued to enlarge. We describe the percutaneous placement of an endovascular stent graft to occlude the aneurysm. This novel use of a covered graft effectively treated a potentially lethal problem without reoperative thoracotomy or sternotomy.

Muscle contraction and relaxation described by tactile stiffness.

We developed a tactile sensor system that measures the stiffness of objects (tactile stiffness) and used it to describe the time course of muscle contraction and relaxation. We examined fatigue resistance of the latissimus dorsi muscle (LDM), which is preconditioned for cardiomyoplasty. Time to peak, ripple of LDM, and time constant were calculated from the time course of LDM contraction and relaxation as described by tactile stiffness. We compared conditioned and unconditioned LDMs using these 3 parameters. The time course can be described by tactile stiffness. Tactile stiffness fell exponentially during LDM relaxation. In mean values, time to peak increased 230%, ripple decreased 20%, and time constants increased 424%. Significant differences were shown in 3 parameters between conditioned and unconditioned LDMs (p < 0.05). Our tactile sensor system can describe the time course of LDM contraction and relaxation. Examining the difference in time courses, we might detect the level of LDM preconditioning for cardiomyoplasty.

Frank-Starling mechanism retains recirculation fraction of myocardial Ca(2+) in the beating heart.

Myocardial Ca(2+) handling in excitation-contraction coupling is the second primary determinant of energy or O(2) demand in a working heart. The intracellular and extracellular routes remove myocardial Ca(2+) that was released into the sarcoplasma with different Ca(2+): ATP stoichiometries. The intracellular route is twice as economical as the extracellular route. Therefore the fraction of total Ca(2+) removed via the sarcoplasmic reticulum, i.e., the recirculation fraction of intracellular Ca(2+) (RF), determines the economy of myocardial Ca(2+) handling. RF has conventionally been estimated as the exponential decay rate of postextrasystolic potentiation (PESP). However, we have found that PESP usually decays in alternans, but not exponentially in the canine left ventricle beating above 100 beats/min. We have succeeded in estimating RF from the exponential decay component of an alternans PESP. We previously found that the Frank-Starling mechanism or varied ventricular preload did not affect the economy of myocardial Ca(2+) handling. Then, to account for this important finding, we hypothesized that the Frank-Starling mechanism would not affect RF at a constant heart rate. We tested this hypothesis and found its supportive evidence in 11 canine left ventricles. We conclude that RF at a constant heart rate would remain constant, independent of the Frank-Starling mechanism.