Ejection Force Research Articles

Assessment of Atrial Function

This article discusses the traditional and more recent echocardiographic measures that have been employed to evaluate atrial function. Conventional parameters commonly used and reported in the literature include the study of the various phases of atrial activity using atrial volume measurements, the peak A wave velocity, its velocity time integral (VTI) and the fraction of atrial contribution (all obtained from transmitral flow), as also the atrial ejection force. Newer parameters for atrial function assessment include Doppler tissue imaging (DTI) including segmental atrial contractility using colour Doppler tissue imaging (CDTI) and estimates of atrial strain and strain rate.

Divergent effects of ephedrine and phenylephrine on cardiovascular hemodynamics of near‐term fetal sheep exposed to hypoxemia and maternal hypotension

We hypothesized that the administration of ephedrine and phenylephrine for maternal hypotension modifies cardiovascular hemodynamics in near-term sheep fetuses. At 115-136 days of gestation, chronically instrumented, anesthetized ewes with either normal placental function or increased placental vascular resistance after placental embolization were randomized to receive boluses of ephedrine (n = 12) or phenylephrine (n = 12) for epidural-induced hypotension after a short period of hypoxemia. Fetal cardiovascular hemodynamics were assessed by Doppler ultrasonography at baseline, during hypotension and after vasopressor treatment. During hypotension, fetal PO(2) decreased and proximal branch pulmonary arterial and pulmonary venous vascular impedances increased. Additionally, in the embolized fetuses, the time-velocity integral ratio between the antegrade and retrograde blood flow components of the aortic isthmus decreased. These parameters were restored to baseline conditions by ephedrine but not by phenylephrine. With phenylephrine, weight-indexed left ventricular cardiac output and ejection force decreased in the non-embolized fetuses, and the proportion of isovolumetric contraction time of the total cardiac cycle was elevated in the embolized fetuses. After exposure to hypoxemia and maternal hypotension, ephedrine restored all fetal cardiovascular hemodynamic parameters to baseline. Phenylephrine did not reverse fetal pulmonary vasoconstriction or the relative decrease in the net forward flow through the aortic isthmus observed in fetuses with increased placental vascular resistance. Moreover, fetal left ventricular function was impaired during phenylephrine administration.

Stereolithography mold life extension using gas‐assisted injection

PurposeThe purpose of this work is to extend the life of plastic injection molds made by stereolithography through the use of gas‐assist technology.Design/methodology/approachPolypropylene parts were made by injection molding in stereolithography molds with and without gas‐assist technology. The mold life was evaluated by observing the number of parts produced before the breakage of each of small core pins and the ejection force was measured.FindingsWhen using gas‐assisted injection molding (GAIM), the core pin life was approximately doubled, the average cavity pressure and the average mold temperature were reduced, and there was a three‐fold increase in ejection force. Also, the core pin location had a very dramatic effect on the life.Research limitations/implicationsThis study suggests research into understanding the relationship between ejection force and mold failure, testing the mechanical properties of the parts and identifying reliable design rules for parts produced by GAIM. Research into other low pressure injection techniques and the viability of using a wider set of polymer materials also appears promising.Practical implicationsThe result of this research encourages molders who have abandoned the use of stereolithography tools after a few unsuccessful attempts to consider using GAIM with stereolithography molds.Originality/valueThis is a novel use of GAIM technology to extend the lives of molds fabricated by stereolithography.

Echocardiographic assessment of left atrial ejection force and kinetic energy in chronic heart failure

There is limited information regarding left atrial (LA) systolic adaptation to chronic heart failure (HF) in humans. Therefore, the aim of our study was to determine the LA ejection force (LAEF) and kinetic energy in patients with HF. 58 HF patients (63.8% in NYHA II) and 48 controls were studied. LA volumes were echocardiographically determined using the biplane area-length method. LA systolic function was assessed with the: (a) active emptying volume (ACTEV) and fraction (ACTEF), (b) ejection force (kdynes/m2), calculated with Manning's method [LAEF = 0.5 * rho * mitral orifice area * A2; rho: blood density, Alpha: late transmitral flow velocity] and a modification incorporating parameters of LA function [LAEFm = 0.5 * rho * LA volume at onset of atrial systole * ACTEF * A2/VTl A], and (c) kinetic energy [LA-ke (kdynes.cm/m2) = 0.5 * rho * ACTEV * A2]. LA maximal volume and ACTEV were lower (42.9 +/- 14.4 vs. 59.7 +/- 14.7 cm3, P < 0.0001; 10.9 +/- 3.3 vs. 13 +/- 3.3 cm3, P = 0.0001, respectively), whereas ACTEF (%) was higher (36.3 +/- 7 vs. 29.3 +/- 7.6 cm3, P < 0.0001) in controls than HF. LAEF, LAEFm, and LA-ke were lower in controls than HF (7.68 +/- 5.1 vs. 10.16 +/- 3.7 kdynes/m2, P = 0.006; 3.63 +/- 2.05 vs. 5.02 +/- 1.74 kdynes/m2, P = 0.0004; 2.41 +/- 1.91 vs. 3.99 +/- 2.1 kdynes.cm/m2, P < 0.0004, respectively). Despite the decreased LA systolic shortening, overall LA systolic performance is augmented in chronic HF due to LA dilation.

Investigation on the Densification Mechanism of Warm Compaction

Warm compaction is a low cost process to make high density and high performance iron base powder metallurgy parts. Based on results obtained from the dynamic compacting curve, ejection force curve, X-ray diffraction, micro-hardness of iron powder, friction condition and lubricant properties, densification mechanism of warm compaction can be drawn. In the initial stage, the rearrangement of powder particles is the main factor. It contributes more in the densification of warm compaction than that in cold compaction. However, in the later stage, the plastic deformation of powder particles is the primary factor. The increase in plasticity at high temperature can harmonize the secondary rearrangement of powder particles. During the compaction, the polymer lubricant has great contribution to the densification of the powder, since it improves the lubricating condition and effectively decreases the friction in the forming process and thus enhances the compact density. The dynamic compacting curve of warm compaction can be divided into three phases. The first is the particle rearrangement dominant phase; the percentage of particle rearrangement in warm compaction is higher than that in cold compaction by 15-31%. The second is the elastic deformation and plastic deformation dominant phase. The third is the plastic deformation dominant phase. The study of the powder densification mechanism can direct engineers in designing and producing warm compaction powders for high density parts.

Cardiovascular hemodynamics and umbilical artery N‐terminal peptide of proB‐type natriuretic peptide in human fetuses with growth restriction

To test our hypothesis that human fetal N-terminal peptide of proB-type natriuretic peptide (NT-proBNP) secretion is increased in proportion to the severity of fetal cardiovascular compromise in intrauterine growth restriction. This prospective cross-sectional study consisted of 42 growth-restricted fetuses who underwent Doppler ultrasonographic examination of cardiovascular hemodynamics within 7 days before delivery. Group 1 fetuses (n = 13) had normal umbilical artery (UA) velocimetry. Group 2 fetuses (n = 15) had abnormal UA and normal ductus venosus (DV) velocimetry. In Group 3 fetuses (n = 14), both UA and DV velocimetries were abnormal. At delivery, an UA blood sample was obtained for assessment of NT-proBNP. Normal values for UA NT-proBNP were determined in 49 neonates (control group) with uncomplicated pregnancy and delivery. Group 3 fetuses demonstrated greater (P < 0.05) UA and descending aorta pulsatility indices (PIs) and greater DV, left hepatic vein (LHV) and inferior vena cava PIs for veins (PIVs) than fetuses in Groups 1 and 2. Weight-indexed cardiac outputs and ventricular ejection forces were similar among the groups. Group 3 fetuses had higher (P < 0.05) UA NT-proBNP concentration than fetuses in Groups 1 and 2. In the control group, the 95(th) percentile value of UA NT-proBNP was 518 pmol/L. In Group 3, 13/14 neonates demonstrated abnormal UA NT-proBNP levels. The corresponding incidences were 4/13 and 7/15 in Groups 1 and 2. Significant positive correlations were found between UA, DV and LHV PIVs and UA NT-proBNP concentrations. In human fetal growth restriction, increased cardiac afterload and pulsatility in DV blood velocity waveform pattern are associated with elevated UA NT-proBNP concentrations.

Left Αtrial Remodeling in Patients Younger than 70 Years with Diastolic and Systolic Heart Failure

We sought to determine left atrial (LA) volume and systolic function (LA remodeling) in younger (<70 years) patients with systolic and diastolic heart failure (HF). In all, 32 patients with diastolic HF (left ventricular [LV] ejection fraction > or = 0.50), 26 patients with systolic HF (LV ejection fraction < 0.50), and 48 control subjects were studied. LAlpha volume (cm(3)/m(2)) was echocardiographically determined at mitral valve opening (maximal), mitral valve closure (minimal), and atrial systole (electrocardiographic Rho wave) using the biplane area-length method. The LA active emptying fraction (%) and ejection force (kdyne/m(2)) served as indices of LA systolic function. LA maximal volume was greater in systolic HF than diastolic HF and in the latter greater than control (68.6 +/- 13.8 vs 52 +/- 11.6 vs 42.9 +/- 14.4, respectively, P < .0001). Active emptying fraction was similar between diastolic HF and control, and greater than systolic HF (31.5 +/- 8.1 vs 36.3 +/- 7 vs 26.6 +/- 6.2, respectively, P < .0001), whereas LA ejection force was similar in diastolic and systolic HF and greater than control (5.05 +/- 1.3 vs 4.98 +/- 2.17 vs 3.63 +/- 2.05, respectively, P = .001). Vmax was related to body surface area, brain natriuretic peptide, and LV mass in diastolic HF (multiple R2 = 0.74) and to diastolic blood pressure, LV mass, and early to late transmitral flow velocity ratio in systolic HF (multiple R2 = 0.96). LA remodeling is more severe in systolic HF than diastolic HF and governed by different mechanisms. This may be of significant clinical relevance regarding the morbidity and mortality of these two conditions.

Left Atrial Contractile Function Is Persistently Augmented in Newly Diagnosed Asymptomatic Hereditary Hemochromatosis Subjects Despite One Year Therapy

We have previously shown that left atrial (LA) contractile function in newly diagnosed asymptomatic hereditary hemochromatosis (HH) subjects with modest iron overload is significantly augmented than control subjects despite the lack of detectable left ventricular (LV) relaxation abnormalities. However, the therapeutic effect of phlebotomy in this population has never been monitored. We monitored LA function and LV diastolic function of this population using 2D and Doppler echocardiography over 12-month therapy. We recruited 22 newly diagnosed asymptomatic HH subjects ages 48±11 (mean±SD). All HH subjects had HEF C282Y homozygosity and and underwent follow up echocardiography at 6-month and 12-month of phlebotomy treatment. The HH subjects showed significantly higher normalized active emptying volume (AEV-N; 7.5±2.8 vs 5.5±1.9 ml/m2), active emptying fraction (AEF; 41.6±10.0 vs 34.2±10.2%), ejection force (AF; 15.2±5.9 vs 10.3±4.1 kdyne), and kinetic energy (KE; 25.1±15.9 vs 14.0±7.1 kerg) of LA at baseline (data are HH vs controls, P<0.05 for all). Despite the significant reduction of iron overload during 12-month therapy, no significant changes in the LA contractile function were noted in HH subjects [AEV-N(ml/m2);8.4±5.6, AEF(%);43.8±13.7, AF(kdyne);14.5±8.3, KE(kerg);28.1±14.8, data are at 12-month(n=18)]. The indices of LV relaxation were not changed. Our results suggest that augmentation of LA contractile function is persistent in asymptomatic HH subjects despite one year therapy of iron removal. Further investigation is needed to determine the therapeutic effect.

Green Body Behaviour of High Velocity Pressed Metal Powder

High velocity compaction (HVC) is a production technique with capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts. Several investigations indicate that high-density components can by obtained using HVC. Other characteristics are low ejection force and uniform density. Investigated here are green body data such as density, tensile strength, radial springback, ejection force and surface flatness. Comparisons are performed with conventional compaction using the same pressing conditions. Cylindrical samples of a pre-alloyed water atomized iron powder are used in this experimental investigation. The different behaviour of HVC-pressed green bodies compared to conventional pressed green bodies are analysed and discussed. The HVC process in this study resulted in a better compressibility curve and lower ejection force compared to conventional quasi static pressing. Vertical scanning interferometry (VSI) measurements show that the HVC process gives flatter sample surfaces.

2A1-E02 板バネ関節および劣駆動機構を有するロボットフィンガ(ロボットハンドの機構と把握戦略)

This paper presents the development of simple structure and light weight robot finger which can grasp various shapes of objects by self adapting to their shapes. This finger was designed for grasping object which is used in daily life, in order to use for prosthesis. This finger consists of three phalanges, interconnected by the joints of leaf spring. The three phalanges are driven by a single tendon. First, mathematical model of the finger was constructed in order to optimize dimensional design for distributed forces to each phalanx. Second, finger was made and grasping experiment was made. Finally, the results of maximum ejection force for the finger are presented.

Wall friction measurement and compaction characteristics of bentonite powders

This paper presents a new method (referred to as direct method) for measuring wall friction during powder compaction and ejection. The accuracy for wall friction force measurement by both new and conventional methods (referred to as indirect method) were first studied according to the theory of error propagation. The error sources for compact density measurement in both methods were also examined. Based on the accuracy in the measurement of wall friction force and compact density, the direct method is compared favorably to the indirect method. Two bentonites, Black Hills bentonite and Zhi-Hsing bentonite which were considered as the candidate buffer materials for the geological disposal of high-level radioactive wastes were adopted to conduct a series of compaction and ejection tests. The compaction characteristics of bentonite blocks were expressed in terms of compressibility curve, wall friction ratio and friction index. The Gurnham's equation was used to describe the compressibility curve. The effects of the aspect ratio of block on the friction ratio and friction index are discussed from both experimental and theoretical point of views. Ejection profiles of the compacted bentonite blocks during ejection phase were presented. The proposed measuring method is validated by comparing the readings of ejection force recorded by both upper load cell and ring-type load cell.

Left Atrial Anatomy and Function After Conversion From Atrial Fibrillation in Hypertrophic Hearts

The aim of the study was to evaluate the influence of left ventricular (LV) hypertrophy on left atrial (LA) electrical and mechanical function after cardioversion atrial fibrillation (A-Fib) of brief duration. Study group A included 100 patients with a first diagnosis of hypertension who had a moderate LV hypertrophy. The patient population included 64 men and 36 women with a mean age of 55 +/-7 years who were hospitalized because of A-Fib and were cardioverted with external DC shock. Control group B included 100 patients without cardiac hypertrophy cardioverted because of lone A-Fib. Atrial function and size were assessed by Doppler echocardiography and the following parameters were measured: transmitral peak A velocity, atrial filling fraction, atrial ejection force, peak E velocity, deceleration time, and isovolumic relaxation time, LA maximal and minimal volume, and LV cardiac mass index. Baseline echocardiography showed that LA diameters and volumes were enlarged in all patients during A-Fib. After the restoration of sinus rhythm LA diameters and volumes decreased and the reduction was more evident in group B compared to group A. LA function as a continuous variable was negatively related to LV mass index (r = -0.77), LA diameter (r = -0.66 and r = -0.69 for the superoinferior diameter), LA maximal volume (r = -0.61) and LA minimal volume (r = -0.55) (all p<0.01). Atrial ejection force as a continuous variable was positively related to age (r =0.78), peak A wave velocity (r =0.71), systolic blood pressure (r =0.51), and IVRT (r =0.41) (all p<0.01). Hypertrophy influenced the recovery of atrial function after cardioversion of A-Fib. Atrial function was reduced in patients with LV hypertrophy even after A-Fib of brief duration.

Right atrial size and function in patients with pulmonary hypertension associated with disorders of respiratory system or hypoxemia

Pulmonary hypertension (PH) determines various adaptive changes in right ventricular (RV) geometry which may progressively lead to hypertrophy, mechanical dysfunction and dilatation with pump failure. Right atrium (RA) is theoretically involved in this physiopathological process, but its role has never been investigated. We hypothesized that RA increases volume and function to assist RV during the chronic pressure overload exposition due to PH. We prospectively enrolled 66 consecutive patients referred to our echolab with a diagnosis of PH [defined as pulmonary artery systolic pressure (PASP) >30 mmHg] associated with disorders of the respiratory system and/or hypoxemia and normal RV systolic function. Ejection force was taken up as index of RA systolic function and calculated according to the Manning's formula. Thirty-three healthy subjects for whom PH was definitely excluded by echoDoppler evaluation were used as controls. PASP was 42+/-10 and 20+/-8 mmHg in PH patients and controls, respectively; p=0.00001). In comparison with controls, PH patients exhibited higher RA volume (37+/-13 vs 32+/-13 ml, p=0.04) and RA ejection force (6.7+/-3.0 vs 3.5+/-1.8 Kdynes, p=0.00001). Both variables were positively related to PASP (r=0.23 and 0.48, p=0.02 and 0.00001, respectively). In patients with chronic PH, RA size and systolic function significantly increase and parallel signs of activation of the Frank-Starling mechanism in both right chambers. The magnitude of these phenomena is positively related to PASP levels.

Effects of Condensing Agent and Nuclease on the Extent of Ejection from Phage λ

We have recently demonstrated, that DNA ejection from bacteriophage lambda can be partially or completely suppressed in vitro by external osmotic pressure. This suggests that DNA ejection from phage is driven by an internal mechanical force consisting of DNA bending and DNA-DNA electrostatic repulsion energies. In the present work we investigate the extent to which DNA ejection is incomplete at zero osmotic external pressure when phage is opened with its receptor in vitro. The DNA fragment remaining in the capsid and the tail that is no longer bent or compressed -and hence for which there is no internal driving force for ejection- is shown not to be ejected. We also demonstrate that DNA can be "pulled" out from the capsid by DNase I acting as a DNA binding protein or spermine acting as a DNA condensing agent. In particular, cryo electron microscopy and gel electrophoresis experiments show the following: (i) DNA ejection from bacteriophage lambda incubated in vitro with its receptor is incomplete at zero external osmotic force, with several persistence lengths of DNA remaining inside the phage capsid, if no nuclease (DNase I) or DNA condensing agent (spermine) is present in the host solution; (ii) in the presence of both DNase I and spermine in the host solution, 60% (approximately 29 kbp) of wild-type lambda DNA (48.5 kbp) remains unejected inside the phage capsid, in the form of an unconstrained toroidal condensate; (iii) with DNase I added, but no spermine, the ejection is complete; (iv) with spermine, but without DNase I added, all the DNA is again ejected, and organized as a toroidal condensate outside.

Diastolic dysfunction in stunned myocardium: a state of abnormal excitation–contraction coupling that is limited by Na+–H+ exchange inhibition

The systolic and diastolic effects of myocardial stunning were studied to evaluate the contributions of the endocardial and epicardial segments of the ventricular myocardial band, and determine if preconditioning by Na+-H+ exchange (NHE) inhibition effected post-stunning dysfunction. Thirteen Yorkshire-Duroc pigs (27.3-38.2 kg) underwent 15 min of mid-LAD clamping. Seven had no protective measures and six were pretreated with IV Cariporide 5 mg/kg 15 min before ischemia. Sonomicrometer crystals evaluated systolic dysfunction (impaired regional shortening) and diastolic dysfunction (contraction extending into early diastole). Before ischemia, contraction started first on the endocardial side followed 82+/-23 ms later by the subepicardium. Endocardial shortening stopped first, coinciding with negative dP/dt onset, while epicardial shortening phase persisted for 92+/-33 ms more during occurrence of rapid LVP descent and development of peak negative dP/dt. Ischemia produced paradoxical bulging of both segments. Sixty minutes after ischemia systolic segment shortening recovered 36+/-24% of baseline values without pretreatment, compared to 75.8+/-15% with Cariporide (p<0.05). Global ejection force (maximum dP/dt) fell 32+/-20% in the unprotected group, but was maintained by Cariporide pretreatment. Diastolic dysfunction always showed continued endocardial contraction into early diastole (occupying 38+/-16% of diastole in untreated hearts), whereas Cariporide treatment reduced this dysfunction to 5+/-10% (p<0.05). Persistent diastolic dysfunction raised left ventricle end diastolic pressure (LVEDP) 4 mmHg in untreated hearts, whereas Cariporide returned LVEDP to normal. Less elevation of creatine kinase MB (CK-MB) and conjugated dienes followed Cariporide pretreatment. Temporary LAD ischemia alters the normal sequential pattern of contraction responsible for ejection and suction by (a) reducing systolic contractile force, and (b) prolonging endocardial contraction into early diastole to disrupt the normal endocardial-epicardial sequence responsible for ventricular suction. NHE inhibition before ischemia limits postischemic systolic and diastolic dysfunction by re-establishing the expected shortening sequences within the ventricular myocardial band model.

The effect of genome length on ejection forces in bacteriophage lambda

A variety of viruses tightly pack their genetic material into protein capsids that are barely large enough to enclose the genome. In particular, in bacteriophages, forces as high as 60 pN are encountered during packaging and ejection, produced by DNA bending elasticity and self-interactions. The high forces are believed to be important for the ejection process, though the extent of their involvement is not yet clear. As a result, there is a need for quantitative models and experiments that reveal the nature of the forces relevant to DNA ejection. Here, we report measurements of the ejection forces for two different mutants of bacteriophage λ, λb221cI26 and λcI60, which differ in genome length by ∼30%. As expected for a force-driven ejection mechanism, the osmotic pressure at which DNA release is completely inhibited varies with the genome length: we find inhibition pressures of 15 atm and 25 atm, for the short and long genomes, respectively, values that are in agreement with our theoretical calculations.

Fluidity and Tableting Characteristics of a Powder Solid Dispersion of the Low Melting Drugs Ketoprofen and Ibuprofen with Crospovidone

ABSTRACTA powder solid dispersion system (SD) of ketoprofen (KP) or ibuprofen (IP), which possess low melting points, plus crospovidone (CrosPVP), have good fluidity characteristics and can be used to formulate tablets. Tablets of KP or IP in the SD of adequate hardness within a narrow weight range can be prepared by direct compression. Addition of microcrystalline cellulose (MCC) resulted in greater hardness characteristics and less variation in tablet weight. Forces during the tableting process were measured with a tableting process analyzer (TabAll) equipped with a single-punch for determining capping and sticking properties during the tableting process. Pressure transmission ratio from the upper to the lower punch and die wall force were increased by adding 1% magnesium stearate (MS) to the SD. Ejection force decreased when MS was added to the SD. When tablets of the IP SD were prepared without excipient, scraper pressure (SP) was large, resulting in sticking. However, addition of 1% MS, lowered the SP value and eliminated sticking. Thus, an SD of compounds with a low melting point such as KP or IP is suitable for tablet manufacture by direct compression with the addition of 1% MS.

Die wall lubricated warm compaction behavior of non-lubricant admixed iron powders

The phenomena of die wall lubricated warm compaction of non-lubricant admixed iron powders were researched, and its mechanism of densification was discussed. Water atomized powder obtained from the Wuhan Iron and Steel Corporation was used. With compacting and sintering, compared with cold compaction, the density of warm compacted samples increases by 0.07 – 0.22 g/cm3 at the same pressed pressure. The maximum achievable green density of warm compacted samples is 7.12 g/cm3 at 120 °C, and the maximum sintered density is 7.18 g/cm3 at 80 °C. Compared with cold compaction, the ejection force of warm compaction is smaller; the maximum discrepancy is about 7 kN. The warm compacted mechanism of densification of iron powders can be obtained; heating the powder contributes to improving plastic deformation of powder particles, and accelerating the mutual filling and rearrangement of powder particles.

PHYSIOLOGY OF LACTATION

29 May 2005 Dear Editor, I was interested in the report of deaths of two infants aged 6 weeks and five others mainly males near 6 weeks after birth all while at the breast. I would like to suggest a possible cause that does not seem to have been considered. The two died of asphyxia diagnosed as due to ‘oro nasal obstruction’. They were both ‘at risk’ babies with inexperienced mothers not concentrating on the baby's feeding in the critical 6 weeks period during which the baby learns to coordinate breathing with feeding and the mother's let down (draught) reflex stabilizes. Baby 1 was a male full-term, first-born baby delivered by Caesarean section for fetal distress showing some respiratory distress after delivery. The primiparous mother was absorbed in a film in a picture theatre when the baby became restless having started suckling stimulating the milk let down reflex. Mother assumed that restlessness was due to a bowel action and put him back on the breast after 15 min by which time it is not uncommon for a second let down to occur. This was followed by apnoea and post-mortem showed that the baby had died of asphyxia, which could have been from laryngeal obstruction. Baby 2 was a male born 2 weeks early with respiratory distress up to the 7th day and followed by readmission to hospital with jaundice. The mother was shopping with the baby in a sling and when he became restless having started breast-feeding in the sling, she continued upstairs shopping until she noticed that he had stopped breathing. Death and post-mortem 4 days later showed ‘diffuse alveolar damage’. My study of the let down (draught) reflex recorded by mothers and published 50 years ago in The Archives of Disease in Childhood, Vol. 29, No. 143, 1954, showed the developing pattern of the let down reflex. In the first weeks of lactation, milk is usually already down when the baby is put to the breast, but the reflex takes a few seconds for let down by 6 weeks often with considerable force of milk ejection that can confuse the baby's feeding and breathing control. This was when these babies suffocated. Ultrasound studies in University of Western Australia by Donna Ramsay et al. are confirming multiple let downs, but there have not been reliable studies yet of the force and variability in this highly emotional few weeks. This is often not recognized by primiparae who do not experience the let down sensation that often only becomes felt in the 3rd to 6th week. A forceful gush of milk could have been very dangerous for these babies recovering from early respiratory distress with impaired respiratory reflex response, being nursed in difficult even horizontal positions with mother's attention distracted. I now have a number of breast-fed great grand children with many books on rearing babies, attending groups and advised by lactation experts, but they do not seem to get taught the basic physiology of lactation and methods of helping the baby to adjust to the reflex in the first important 6 weeks. I do not wish to suggest that a neonatal paediatric great grandmother should be interfering and scaring mothers, but it would help to give them some gentle education in lactation physiology.

Microtubule movements on the arms of mitotic chromosomes: polar ejection forces quantified in vitro.

During mitosis, "polar ejection forces" (PEFs) are hypothesized to direct prometaphase chromosome movements by pushing chromosome arms toward the spindle equator. PEFs are postulated to be caused by (i) plus-end-directed microtubule (MT)-based motor proteins on the chromosome arms, namely chromokinesins, and (ii) the polymerization of spindle MTs into the chromosome. However, the exact role of PEFs is unclear, because little is known about their magnitude or their forms (e.g., impulsive vs. sustained, etc.). In this study, we employ optical tweezers to bring about the lateral interaction between chromosome arms and MTs in vitro to directly measure the speed and force of the PEFs developed on chromosome arms. We find that forces are unidirectional and frequently exceed 1 pN, with maximum forces of 2-3 pN and peak velocities of 63 +/- 41 nm/s; the movements are ATP-dependent and exhibit a characteristic noncontinuous motion that includes displacements of >50 nm, stalls, and backwards slippage of the MT even under low loads. We perform experiments using antibodies to the chromokinesins Kid and KIF4 that identify Kid as the principal force-producing agent for PEFs. At first glance, this motor activity appears surprisingly weak and erratic, but it explains how PEFs can guide chromosome movements without severely deforming or damaging the local chromosome structure.