Left atrial mechanics evaluated by two-dimensional strain analysis: alterations in essential hypertension

BACKGROUND

Hypertension is a cardiovascular risk factor that predisposes to cardiac structural alterations namely increased left ventricular (LV) wall thickness, reduced LV compliance and diastolic dysfunction, with consequent left atrial (LA) dilation and functional impairment. In this article, we evaluated differences in left atrial structure and function using two-dimensional speckle tracking echocardiography in patients with hypertension compared with controls.

METHODS

This was a retrospective cross-sectional study of 208 hypertensive patients and 157 controls who underwent a comprehensive transthoracic echocardiogram. Patients with hypertension were stratified by the presence of left ventricular hypertrophy (LVH).

RESULTS

Non-LVH hypertension patients had lower left atrial reservoir strain (LAS RES ) (34.78 ± 29.78 vs. 29.78 ± 6.08; P  = 0.022) and conduit strain (LAS CD ) (19.66 ± 7.29 vs. 14.23 ± 4.59; P  = 0.014) vs. controls despite similar left atrial volumes (LAV) . Left atrial contractile strain (LAS CT ) was not significantly different between non-LVH hypertension patients and controls (15.12 ± 3.77 vs. 15.56 ± 3.79; P  = 0.601). Left atrial mechanical dispersion was significantly higher in the LVH group compared with the non-LVH hypertension group (42.26 ± 13.01 vs. 50.06 ± 14.95; P  = 0.009). In multivariate regression analysis, LVH correlated with left atrial mechanical dispersion ( P  = 0.016). An age-hypertension interaction independently correlated with LAS CT ( P  < 0.001).

CONCLUSION

Hypertension results in functional left atrial changes even before development of LV hypertrophy and structural left atrial changes with increased left atrial volume. We demonstrate both a likely hypertension-associated left atrial myopathy that prevents age-related compensatory increase in left atrial contractile function, and impact of LVH in hypertension on left atrial dyssynchrony.

Alterations in Left Atrial Strain in Breast Cancer Patients Immediately Post Anthracycline Exposure

AIMS

With improved diagnosis and treatments, a greater percentage of breast cancer patients are achieving long-term survival. Consequently, long-term cardiotoxicity secondary to chemotherapy has become more prevalent, warranting improved cardiac surveillance. We evaluated changes in left atrial (LA) strain in breast cancer patients immediately post anthracycline (AC) therapy to assess its utility as a marker of diastolic dysfunction.

METHODS

This was a prospective cohort study of 128 consecutive human epidermal growth factor receptor 2 (HER2)-negative breast cancer patients who underwent transthoracic echocardiography prior to and immediately post AC treatment. Traditional left ventricular (LV) systolic and diastolic parameters and LA volumes were evaluated; additionally, LV global longitudinal strain (LV GLS) and LA phasic strain were measured.

RESULTS

All patients had normal LV ejection fraction (>53%) post AC, though LV GLS was significantly reduced. Peak E and é velocities were reduced post AC, with no change in LA volumes. LA reservoir strain (LASRES 34.8% vs 31.5%, p<0.001) and conduit strain (LASCD 17.2% vs 14.4%, p<0.001) were significantly lower post AC and correlated modestly with LV diastolic parameters. Reduction in LA strain post AC was evident even in patients with preserved LV systolic and diastolic function. More patients demonstrated alteration in diastolic function (≥15% reduction in LASRES from baseline) (32%) compared to alteration in systolic function (≥15% reduction in LV GLS) (23%).

CONCLUSIONS

LA strain is a promising marker of early diastolic dysfunction. We demonstrate its potential utility in surveillance of breast cancer patients treated with AC.

Echocardiographic Assessment in Patients Recovered from Acute COVID-19 Illness

Coronavirus (COVID-19) infections have spread rapidly worldwide and posed an immense public health problem. COVID-19 infection can affect the cardiovascular system both acutely and in patients followed up some period after COVID-19 infection. The aim of this study was to evaluate left ventricular (LV) and right ventricular (RV) function by echocardiography in COVID-19 recovered patients (hospitalized and non-hospitalized). Forty-two patients who recovered from COVID-19 but had ongoing symptoms were included in this retrospective observational cross-sectional study. Patients were followed-up at a median time of 112 days from confirmed COVID-19 diagnosis and a comprehensive echocardiogram was performed. COVID-19 patients were age- and sex-matched to healthy controls. Traditional TTE parameters and advanced echocardiographic parameters including two-dimensional LV global longitudinal strain (GLS) and RV free wall strain (FWS) were measured. LV volumes and LV ejection fraction were similar in COVID-19 patients and controls; however, LV GLS was significantly worse in the COVID-19 group (p = 0.002). Similarly, RV volumes and traditional RV function parameters were similar, but RV FWS (p = 0.009) and RV global strain (p = 0.015) were reduced. Alterations in LV and RV strain were observed in both hospitalized and non-hospitalized patients. In the subset of COVID-19 patients without any co-morbidities (n = 30), LV GLS remained reduced compared to controls. According to multivariate analysis, COVID-19 infection was the only independent determinant of reduced LV GLS (p = 0.012), while COVID-19 infection, diastolic blood pressure, and RV fractional area change were determinants of RV FWS. In this observational study, prior COVID-19 infection demonstrated LV dysfunction in patients with persistent symptoms. Abnormal LV strain was evident in both hospitalized and non-hospitalized patients, suggesting that these changes are independent of the severity of COVID-19 infection at presentation. The use of LV GLS in COVID-19 patients could have potential clinical utility to support the indication for cardiac magnetic resonance imaging in patients with possible COVID-19 related myocarditis. Future longitudinal studies are needed to evaluate its correlation with adverse cardiovascular events.

Left atrial strain in cardiac surveillance of bone marrow transplant patients with prior anthracycline exposure

BACKGROUND

Bone marrow transplantation (BMT) has significantly improved survival rates in various hematological malignancies. However, this has led to an increased prevalence of long-term cardiotoxicity, particularly in those with prior anthracycline (AC) therapy.

OBJECTIVES

To evaluate changes in left atrial (LA) volume and function, including LA strain, in BMT patients with prior AC exposure and evaluate its utility as a marker of diastolic dysfunction.

METHODS

This was a cross-sectional analysis of 79 BMT patients with prior AC exposure who underwent a comprehensive surveillance transthoracic echocardiogram compared to age-matched healthy volunteers. Left ventricular (LV) and LA parameters were evaluated between the 2 groups. BMT patients were stratified using traditional measures of diastolic function and additionally utilizing LA strain.

RESULTS

LV systolic dysfunction with reduced LVEF (13/79) or global longitudinal strain (29/79) was present in BMT patients. There were no differences in LA volumes between the two groups. LA reservoir strain (30.1 ± 11.2% vs 34.1 ± 9.6%, p < 0.001) and LA conduit strain (13.6 ± 8.4% vs 17.0 ± 10.5%, p < 0.001) were reduced in the BMT group compared to controls. LA reservoir strain had modest correlation with mitral annular e' velocity (r = 0.468, p < 0.001). Using current diastolic function guidelines, 26/79 BMT patients had evidence of diastolic dysfunction. However, utilizing LA reservoir strain, an additional 35 patients were identified.

CONCLUSIONS

LA strain can identify early diastolic dysfunction in BMT patients with prior AC treatment. With diastolic dysfunction known to precede systolic dysfunction post AC, changes in LA reservoir strain may identify more patients with cardiac dysfunction, prompting increased surveillance and treatment.

The utility of strain imaging in the cardiac surveillance of bone marrow transplant patients

OBJECTIVE

To evaluate the utility of two-dimensional multiplanar speckle tracking strain to assess for cardiotoxicity post allogenic bone marrow transplantation (BMT) for haematological conditions.

METHODS

Cross-sectional study of 120 consecutive patients post-BMT (80 pretreated with anthracyclines (BMT+AC), 40 BMT alone) recruited from a late effects haematology clinic, compared with 80 healthy controls, as part of a long-term cardiotoxicity surveillance study (mean duration from BMT to transthoracic echocardiogram 6±6 years). Left ventricular global longitudinal strain (LV GLS), global circumferential strain (LV GCS) and right ventricular free wall strain (RV FWS) were compared with traditionl parameters of function including LV ejection fraction (LVEF) and RV fractional area change.

RESULTS

LV GLS (-17.7±3.0% vs -20.2±1.9%), LV GCS (-14.7±3.5% vs -20.4±2.1%) and RV FWS (-22.6±4.7% vs -28.0±3.8%) were all significantly (p=0.001) reduced in BMT+AC versus controls, while only LV GCS (-15.9±3.5% vs -20.4±2.1%) and RV FWS (-23.9±3.5% vs -28.0±3.8%) were significantly (p=0.001) reduced in BMT group versus controls. Even in patients with LVEF >53%, ~75% of patients in both BMT groups demonstrated a reduction in GCS.

CONCLUSION

Multiplanar strain identifies a greater number of BMT patients with subclinical LV dysfunction rather than by GLS alone, and should be evaluated as part of post-BMT patient surveillence. Reduction in GCS is possibly due to effects of preconditioning, and is not fully explained by AC exposure.

Malignant melanoma of brown bullhead (Ameiurus nebulosus) in Lake Memphremagog, Vermont/Quebec

In 2012, brown bullhead (Ameiurus nebulosus) with large, raised, black growths were first reported from multiple areas within the Vermont portion of Lake Memphremagog. Subsequent surveys conducted from 2014 to 2017 at two sites within the lake indicated a prevalence of 30% in adult brown bullhead 200 mm and above total length. These lesions ranged from slightly raised smooth black areas to large nodular areas on the body surface and fins and within the oral cavity. Microscopically, these lesions were determined to be malignant melanoma with invasion into surrounding hypodermis, skeletal muscle and bone as well as metastases to gill, ovary and intestine. Liver neoplasms were also observed in 8% of the bullhead collected from Lake Memphremagog in 2015. Neither skin nor liver neoplasms were noted in Ticklenaked Pond, a site used for comparison.

Hardwood tree growth after eight years on brown and gray mine soils in west virginia

Surface coal mining in Appalachia disturbs hundreds of hectares of land every year with the removal of valuable and ecologically diverse eastern deciduous forests. After the passage of the Surface Mining Control and Reclamation Act in 1977, coal mine operators began planting a variety of grasses and legumes as a fast and economical way to reestablish a permanent vegetative cover to meet erosion and site stabilization requirements. However, soil compaction and competitive forage species have arrested the recolonization of native hardwood tree species on these reclaimed sites. Three 2.8-ha demonstration plots were established at Catenary Coal's Samples Mine in Kanawha County, West Virginia, of weathered brown sandstone and unweathered gray sandstone. Half of each plot was compacted. Each plot was hydroseeded with a low-competition herbaceous cover and planted with 11 hardwood tree species. After eight growing seasons, average tree volume index was nearly 10 times greater for trees grown in the brown sandstone treatments, 3853 cm, compared with 407 cm in gray sandstone. Trees growing on compacted treatments had a lower mean volume index, 2281 cm, than trees growing on uncompacted treatments, 3899 cm. Average pH of brown sandstone was 5.2 to 5.7, while gray sandstone was 7.9. The gray sandstone had much lower fine soil fraction (<2-mm) content (40%) than brown sandstone (70%), which influenced nutrient- and water-holding capacity. Brown sandstone showed significantly greater tree growth and survival and at this stage is a more suitable topsoil substitute than gray sandstone on this site.

Survival and growth of hardwoods in brown versus gray sandstone on a surface mine in West Virginia

Surface mining in West Virginia removes the eastern deciduous forest and reclaiming the mined land to a productive forest must consider soil depth, soil physical and chemical properties, soil compaction, ground cover competition, and tree species selection. Our objective was to evaluate tree survival and growth in weathered brown sandstone and in unweathered gray sandstone. Brown and gray sandstone are often substituted when insufficient native topsoil is available for replacement. Three 2.8-ha plots were constructed with either 1.5 or 1.2 m of brown sandstone, or 1.5 m of gray sandstone at the surface. Half of each plot was compacted with a large dozer. Percent fines (<2 mm) in the upper 20 cm was 61% for brown sandstone and 34% in gray. Brown sandstone's pH was 5.1, while gray sandstone's pH was around 8.0. In March 2005, 2-yr-old seedlings of 11 hardwood species were planted. After 3 yr, tree survival was 86% on 1.5-m gray sandstone, 67% on 1.5-m brown sandstone, and 82% on 1.2-m brown sandstone. Survival was 78% on noncompacted and 79% on compacted areas. Average volume of all trees (height x diameter(2)) was significantly greater on brown sandstone (218 cm(3)) than gray sandstone (45 cm(3)) after 3 yr. Black locust (Robinia pseudoacacia L.) had the highest survival (100%) and significantly greater volume (792 cm(3)) than all other tree species. Survival of the other 10 species varied between 65% for tulip poplar (Liriodendron tulipifera L.) and 92% for redbud (Cercis canadensis L.), and volume varied between 36 cm(3) for white pine (Pinus strobes L.) and 175 cm(3) for tulip poplar. After 3 yr, brown sandstone appears to be a better topsoil material due to the much greater growth of trees, but tree growth over time as these topsoils weather will determine whether these trends continue.

Different pathophysiology of impaired glucose tolerance in first-degree relatives of individuals with type 2 diabetes mellitus

To assess whether an increased genetic predisposition for type 2 diabetes mellitus (T2DM) influences the contributions of insulin resistance and impaired insulin secretion to impaired glucose tolerance (IGT), 437 subjects not known to have T2DM underwent an oral glucose tolerance test and a 3-hour hyperglycemic clamp. Plasma insulin responses and insulin sensitivity were compared between all subjects (unselected for demographic or anthropometric characteristics) who had normal glucose homeostasis and no first-degree T2DM relative (n = 133), IGT with a first-degree T2DM relative (IGT/FH+, n = 74), or IGT without a first-degree T2DM relative (IGT/FH-, n = 50). Compared with those with normal glucose homeostasis, first- and second-phase plasma insulin responses were reduced approximately 45% and 30%, respectively (both P < .001), in IGT/FH+, whereas insulin sensitivity was only approximately 20% reduced (P = .011). In contrast, in IGT/FH-, first-phase plasma insulin responses were only approximately 20% reduced (P = .016), second-phase plasma insulin responses were not reduced, but insulin sensitivity was approximately 40% reduced (P < .001). The IGT/FH+ group differed significantly from the IGT/FH- group by having 25% to 30% lower first-phase plasma insulin responses (P = .026) and 25% to 30% greater insulin sensitivity (P = .027). Adjustment for obesity abolished the differences in insulin resistance but not plasma insulin responses. However, when the IGT groups were stratified into subgroups based on body mass index (BMI), first-phase plasma insulin responses were approximately 30% lower in IGT/FH+ with a BMI of at least 27 kg/m(2) (P = .018) but similar in IGT/FH+ with a BMI less than 27 kg/m(2) compared with the corresponding IGT/FH- subgroups. We conclude that, in IGT, an increased genetic predisposition for T2DM increases the contribution of impaired insulin secretion to its pathophysiology. This effect is enhanced by obesity.

Metabolic fate of plasma glucose during hyperglycemia in impaired glucose tolerance: evidence for further early defects in the pathogenesis of type 2 diabetes

We examined the intracellular metabolic fate of plasma glucose during a hyperglycemic clamp in impaired glucose-tolerant (IGT; n = 21) and normal glucose-tolerant subjects (n = 10) using a combination of [3-(3)H]glucose infusion with measurement of [(3)H]water formation and indirect calorimetry. IGT was associated with approximately 35% reduced first-phase insulin responses, normal second-phase insulin response, and 25-30% reduced insulin sensitivity, resulting in approximately 35% reduced plasma glucose disposal. This was coupled with approximately 55% reduced storage of plasma glucose (P < 0.01) and approximately 15-20% reduced glycolysis of plasma glucose (P < 0.03), accounting for approximately 75 and 25% of the reduction in glucose disposal, respectively. Decreased glucose oxidation accounted for virtually all the decrease in glycolysis. Therefore, nonoxidative glycolysis of plasma glucose in IGT was similar to that in NGT (P > 0.9) and accounted for an increased proportion of systemic glucose disposal (P < 0.05). We conclude that, in IGT, decreased disposal of plasma glucose involves mainly decreased glycogen synthesis and to a lesser extent decreased glycolysis, which is accounted for by decreased glucose oxidation. An increased proportion of plasma glucose hence undergoes nonoxidative glycolysis, representing a novel early abnormality in the pathogenesis of T2DM.

A new approach to optimizing urea clearances in hemodialysis and continuous ambulatory peritoneal dialysis

Recent studies suggest that the relationship of the net normalized protein catabolic rate (which is the normalized protein equivalent of nitrogen appearance [nPNA]) to the weekly clearance of urea normalized to total body water (Kt/V urea) in patients on continuous ambulatory peritoneal dialysis (CAPD) is curvilinear, rather than linear, as has been thought. The authors have reexamined the relationship of nPNA to weekly Kt/V urea in a CAPD population by cross-sectional analysis to see if the curvilinear definition of the relationship is as good as or better than the usual linear description. They also examined this relationship in the hemodialysis populations at the Dialysis Clinics Inc. in Columbia, Missouri, and in the Renal Kidney Disease Program in Minneapolis, Minnesota. It seems obvious that there should be a plateau of nPNA in each therapy because extension of linear regressions would predict protein intakes of normal individuals exceeding 8 g/kg/body weight/day. The authors compared their findings to other published results. Intuitively and analytically, the curvilinear relationships seem likely. The authors observed that the nPNA plateau is achieved at lower Kt/V in patients on CAPD than in those on hemodialysis, which is compatible with the peak concentration hypothesis. Asymptotes for CAPD and hemodialysis are similar. Weekly Kt/V urea requirements to achieve nPNA values at 95% of the asymptote are greater than those usually delivered. However, such nearly complete elimination of uremic appetite suppression may not be practical or necessary for achieving acceptable nutritional status and long-term survival in most patients. Optimum therapy may be well above adequate therapy relative to minimizing appetite suppression by uremia.

Lean body mass estimation by creatinine kinetics, bioimpedance, and dual energy x-ray absorptiometry in patients on continuous ambulatory peritoneal dialysis

Lean body mass (LBM), which is fat free body mass, can be used as an index of nutritional status. We evaluated three techniques for LBM estimation, including dual energy x-ray absorptiometry (DEXA), creatinine kinetics (CrKin), and bioimpedance (BI) in 10 patients on continuous ambulatory peritoneal dialysis (CAPD). Two different formulae were applied for BI LBM estimation, Segal (S) and Deurenberg (D). Mean values (+/- SEM) of LBM estimated were 48.2 +/- 3.6, 46.12 +/- 2.87, 43.32 +/- 3.87, and 41.27 +/- 4.26 by DEXA, BI-S, BI-D, and CrKin, respectively. LBM by CrKin was significantly lower than that by DEXA and BI-S values. There was no statistically significant difference between DEXA and BI-S values. Statistically significant correlations were found between LBM values by all methods. Particularly strong correlations were found between DEXA versus BI-S (r = 0.976) and BI-S versus BI-D (r = 0.98). Because clinical assessment of hydration status is inaccurate, and both BI and DEXA measure excess extracellular water in LBM, falling muscle mass may be missed by these techniques. The CrKin technique for estimating LBM at normal body fluid volumes (dry weight) may be a better index of nutritional status in patients on CAPD because this may truly reflect the dry LBM and changes in muscle mass. Both DEXA and BI include excess body water in LBM and may mask malnutrition in the presence of subclinical or clinical overhydration, which is common in patients on peritoneal dialysis.

Comparison of different measurements of lean body mass in normal individuals and in chronic peritoneal dialysis patients

To evaluate different methods of measuring lean body mass (LBM) in chronic peritoneal dialysis (CPD) patients, we first made comparisons in seven normal subjects. Seven methods (total body potassium [TBK] counting, bioelectrical impedance with calculations according to Segal and Deurenberg, near-infrared interactance with and without exercise level included as a variable, anthropometric measurements, and creatinine kinetics) were compared with the standard method of underwater weighing (UW) for measuring LBM. Significant correlations with LBM measured by UW (r > 0.938) were found with LBM measured by all other methods. Compared with UW, the best result in normals was found with TBK as it had high r values, small y-intercepts, and slopes of regression lines close to unity in both measurements of LBM and %LBM; in addition, fat-free mass index by TBK best approximated that by UW and TBK had the lowest mean prediction error with UW. In 11 patients on CPD, LBM was measured by all the above methods except UW. Significant correlations of all methods with LBM measured by TBK used as the reference standard were noted (all r > 0.76) in the CPD population. The LBM measured by creatinine kinetics correlated best (by kilograms or percentage of body weight [%BW]) with LBM from TBK compared with the other methods in which values tended to be higher. The fat-free mass index by creatinine output was nearest to the fat-free mass index by TBK. The root mean square prediction error was lowest between LBM by creatinine output and that by TBK. The findings support the concept of measuring creatinine outputs in CPD patients for estimates of LBM as an index of nutritional status as well as for creatinine clearances as an index of adequacy. Total body potassium and creatinine output measurements of LBM reflect the LBM at normal body fluid volumes ("dry weight") and may be better indices of nutrition in dialysis patients than the other techniques, which include excess fluid in the LBM.

Anesthetic management of patients with pheochromocytomas: a report of three cases

The perioperative management of patients with pheochromocytoma is a challenge to even the most seasoned practitioner. Preoperative preparation, close monitoring, and anticipation of hemodynamic changes is critical for a successful outcome.

A peptidergic circuit for reproductive behavior

A projection from the medial amygdaloid nucleus to the hippocampus and septum probably uses vasopressin as a transmitter. The nucleus synthesizes vasopressin and activation of the nucleus has a hippocampal effect that is completely blocked by a vasopressin antagonist. The afferent and efferent projections of this peptidergic nucleus suggest a possible role for the system in sexual behavior. Stimulation of the nucleus inhibits the output of the hippocampus in both genders and reorganizes behavior for a period of 15-20 min. In males, the effect of peptidergic activation is to produce a behavior that resembles the post-ejaculatory interval in coitus. This state is characterized by an EEG that resembles slow-wave sleep and by ultrasonic vocalizations at a characteristic frequency of 22 kHz. Castration in either gender causes depletion of the peptide from the target fields and eliminates the peptidergic signal in the hippocampus after about 15 weeks. The effects of castration in males can be reversed by testosterone replacement. The fluctuation of estrogen levels in rat plasma during the estrus cycle happens too quickly to impact the peptidergic system, and thus there is no significant change in the strength of the peptidergic signal among the proestrus, estrus, metestrus and diestrus stages. This fact permits study of the physiology of the system without concern for stage of estrus but does not permit conclusions regarding its function in females.

A simplified method for autoregulation of blood flow in the extracorporeal membrane oxygenation circuit

The ability of autoregulate blood flow in the extracorporeal membrane oxygenation (ECMO) circuit is critical to prevent cavitation and air embolism. Conventional circuits have used a spring-loaded mechanical switching device that interrupts the flow of power to the roller head when falling venous return collapses the venous bladder. This device has been less than desirable due to being poorly adjustable, subject to sporadic flow in periods of hypovolemia, and not commercially available. An improved alternative is reported using a commercially available pressure monitor and computerized switching device, which, when attached to the venous reservoir or bladder, has the ability to autoregulate blood flow in the ECMO circuit by smoothly regulating the roller head velocity. Experience with this system in the laboratory employing a swine model, and in 35 infants, is reported without device-related complications.

Providers assume responsibility for overpayment in liability cases

The Health Care Financing Administration (HCFA) has informed hospitals that they can no longer bill or file liens against liability proceeds involving Medicare beneficiaries. HCFA also told providers that before they request conditional payment from Medicare, they must provide their fiscal intermediaries with complete information about any payments received from primary payers, or else reimburse Medicare for any overpayments. This article examines situations in which providers can be held liable for Medicare overpayment and explains how to lessen the facility's risk.

Assessment of the agglutination test for tuberculosis

A new whole cell agglutination test for active tuberculosis, for which encouraging results have recently been reported, has been carried out on the serum of 112 subjects. The results have been disappointing; the test had no predictive value in the diagnosis of active tuberculosis.

Timing of intraventricular haemorrhage

The detection of the onset of intraventricular haemorrhage (IVH) during life is a necessary preliminary to understanding the cause of this condition. In 10 infants of very low birthweight treated with serial transfusions of adult blood the proportions of transfused cells circulating after each transfusion were compared with the proportion of transfused cells found in the intraventricular clot at necropsy. This allowed the timing of IVH to be restricted retrospectively to the period between consecutive blood transfusions. In addition, the proportional changes of transfused cells produced by infusion of a known red cell mass allow changes in the babies' original red cell mass to be followed during life. A fall in this value occurred in 8 infants dying with IVH and was taken to indicate haemorrhage. Comparison of the two methods in 9 infants suggested that, while in some cases intraventricular bleeding occurs rapidly, in others it takes place over a period of time. The interval between birth and the onset of haemorrhage was directly proportional to the gestational age of the infant.