Effect of young sibling visitation on respiratory syncytial virus activity in a NICU.

OBJECTIVE: To determine whether the restriction of young sibling (<13 years) visitation in the neonatal intensive care unit (NICU) during the respiratory syncytial virus (RSV) season was associated with a reduction in the rate of RSV infection among NICU patients. STUDY DESIGN: A retrospective chart review of all RSV positive infants from the 2001-2010 RSV seasons. The 2001-2006 RSV seasons (group 1) contained 639 admissions and the 2007-2010 (group 2, with sibling restriction) contained 461 admissions. Groups were compared by using the Fisher's Exact Test. RESULTS: There was a reduction of RSV positive infants from 6.7% in Group 1 to 1.7% in Group 2 (P<0.0001). There was a reduction of symptomatic infants from the number of infants with symptomatic RSV infection from 23/639 infants with young sibling visitation to 2/461 (P<0.001). CONCLUSION: Exclusion of young sibling visitors <13 years of age during RSV season was associated with a significant reduction in the number of RSV positive infants in the NICU.

Diagnostic ionizing radiation exposure in premature patients.

OBJECTIVE: Concern regarding the magnitude and consequences of diagnostic radiation exposure in premature infants in neonatal intensive care units (NICUs) has increased as survival of premature infants has improved. Radiation exposure is not often rigorously monitored in NICU patients. The purpose of this observational study was to quantify the amount of ionizing radiation exposure in infants <33 weeks gestational age and to identify the indications for diagnostic imaging. STUDY DESIGN: We conducted a retrospective review of 215 premature infants who were <33 weeks gestation and who received central venous line (CVL) placement during their NICU stay during the period from 2006 to 2011. Absorbed ionizing radiation was estimated using the method of Puch-Kapst and colleagues (2009) and compared with recommended radiation exposure limits. All infants were 29.2±2.3 weeks (mean±s.d.) and 1262±433 g birth weight. RESULT: Subjects received 15±15 radiographs (4.4±2.9 for CVL placement, 5.7±9.8 for gastrointestinal (GI) evaluations and 5.2±9.3 for respiratory indications). Eleven infants (5.1%) received more than the maximum recommended radiation from radiographs (>1000 µSv). Inclusion of fluoroscopic procedures increased to 26 the number of infants (12.1%) who received more than the maximum recommended 1000 µSv. CONCLUSION: Ionizing radiation exposure that exceeded the recommended maximum in premature infants at high risk for long-term sequelae occurred in 12.1% of infants who were <33 weeks gestation and who were cared for in our NICU over the past 5 years. CVL placement accounted for 22% of this radiation exposure. GI evaluations accounted for the greatest amount of ionizing radiation exposure. We suggest that the increased use of other imaging strategies may reduce total ionizing radiation exposure in this vulnerable population.

Poractant alfa and beractant treatment of very premature infants with respiratory distress syndrome.

OBJECTIVE: Comparison of the differences between availability of animal-derived surfactant preparations used to treat premature infants is incomplete. The objective of this study was to assess the short-term treatment efficacy of the two most commonly used surfactant preparations in the United States, beractant (100 mg kg(-1) initial and subsequent doses) and poractant alfa (200 mg kg(-1) initial and 100 mg kg(-1) subsequent doses), in very premature, mechanically ventilated infants <30 weeks gestation with respiratory distress syndrome (RDS). STUDY DESIGN: Inborn infants at two institutions, open label, 1:1, randomized controlled trial. Level of respiratory support for first 72 h of life. Morbidities of prematurity observed during the neonatal intensive care unit hospitalization. RESULT: We studied 52 infants 24 0/7 to 29 6/7 weeks gestation; 25 received poractant alfa (27.1±1.6 weeks, birth weight of 930±231 g) and 27 received beractant (26.7±1.7 weeks, P=0.343 and birth weight 900±271 g, P=0.668). Respiratory support for the first 72 h of life was lower in the poractant alfa than beractant group for mean airway pressure (MAP, P=0.003) and respiratory index (MAP × FiO(2), P=0.032). Infants in the poractant alfa group had a greater number of infants extubated at 48 (13/25 vs 6/27, P=0.027) and 72 h (15/25 vs 8/27, P=0.029) than the beractant group. Although the study was not powered to detect morbidities of prematurity, the prevalence of PDA and air leaks was less in the infants treated with poractant alfa than in those treated with beractant. Rates of bronchopulmonary dysplasia (8/23 vs 11/22, P=0.303) or death (2/25 [corrected] vs 5/27, P=0.272) were similar in the infants treated with poractant alfa and beractant, respectively. CONCLUSION: This study suggests significant short-term benefits to the use of the larger initial dose of poractant alfa than beractant in very premature infants with RDS. Further studies involving a larger number of preterm infants are needed to assess long-term effects.

VATS management of an enlarging multicystic pneumatocele.

A multicystic pneumatocele progressively enlarged when the patient required positive pressure ventilation for an intercurrent respiratory syncytial virus infection. Video Assisted Thoracoscopic Surgery was used to visualize the pneumatocele for cannulation. One chamber of the pneumatocele was cannulated with a pigtail catheter and another large chamber ruptured, without cannulation. The multicystic pneumatocele resolved with this therapy.

Maturation-dependent differences in regulation of sarcoplasmic reticulum Ca(2+) ATPase in sheep myocardium in response to pressure overload: a possible mechanism for maturation-dependent systolic and diastolic dysfunction.

We have previously demonstrated that pressure-overload hypertrophy in adult sheep is associated with myocardial dysfunction whereas that in young lambs is associated with normal contractility. To probe for possible mechanisms of these age-dependent differences, we assessed mRNA expression of genes encoding critical components of myocardial Ca(2+) handling in the same animal model. We studied left ventricular myocardium of young and adult sheep with short-term (48 h) and long-term (6 wk) pressure overload induced by ascending aortic constriction. Six weeks of pressure overload induced the significant left ventricular hypertrophy (36 and 39% increase in left ventricular/body weight ratio in lambs and sheep, respectively). The Ca(2+) ATPase and Na(+)/Ca(2+) exchanger mRNA decreased with pressure overload only in the adult (p < 0.05). Ca(2+) channel mRNA was slightly increased by pressure overload regardless of age (p < 0.05). Calsequestrin, sarcoplasmic reticulum Ca(2+) release channel, or myosin heavy-chain mRNA levels did not significantly differ. In adult sheep after 6 wk of pressure overload, decreases in load-adjusted midwall shortening (systolic dysfunction) and prolongation of relaxation time constant (diastolic dysfunction) correlated with decreases in Ca(2+)-ATPase mRNA. The sarcoplasmic reticulum Ca(2+)-ATPase protein level and Ca(2+) uptake activity of isolated sarcoplasmic reticulum vesicles were depressed only in the adult with pressure-overload hypertrophy but not in the young. We demonstrated age-dependent differences in mRNA expression of Ca(2+)-handling protein genes in response to pressure overload, which preceded the occurrence of hypertrophy and myocardial dysfunction. Thus, altered expression of Ca(2+)-handling protein genes may be one of the primary responses to pressure overload rather than a phenomenon secondary to myocardial hypertrophy.

Effects of chronic heparin administration on coronary vascular adaptation to hypertension and ventricular hypertrophy in sheep.

BACKGROUND: Hypertension decreases myocardial perfusion capacity in adults for several reasons, including insufficient coronary angiogenesis with left ventricular (LV) hypertrophy, arteriolar hypertrophy, and altered vasomotion. Heparin influences growth factors that promote angiogenesis and vasodilation and inhibit arteriolar wall thickening. METHODS AND RESULTS: Adult sheep were given heparin 200 U/kg body wt SC twice daily throughout 6 weeks of LV and coronary hypertension from a progressively constricted ascending aortic band (n=14). They were compared with untreated sheep with (n=13) and without (n=13) aortic stenosis. After 6 weeks, maximum myocardial perfusion was measured during adenosine infusion in the conscious state by the microsphere method. Sheep with aortic stenosis had less maximum coronary flow per gram, less conductance reserve, and thicker arteriolar walls in the LV and nonhypertrophied right ventricle. Capillary density decreased in the LV endomyocardium and remained unchanged in the right ventricle. Heparin-treated sheep had significant partial normalization of coronary conductance reserve and maximum perfusion in both ventricles and capillary density in the LV endomyocardium. Arteriolar wall thickness was unchanged. Compared with untreated sheep with aortic stenosis, in heparin-treated sheep LV FGF-2 protein increased 2-fold, whereas FGF-2 mRNA remained unchanged. VEGF mRNA and protein increased 3-fold and 1.4-fold, respectively, whereas TGF-beta(1) mRNA declined 3-fold. CONCLUSIONS: Heparin administration during LV hypertension increases heparin-binding angiogenic factors FGF-2 and VEGF in the LV and ameliorates decreases in LV perfusion capacity and capillary density.

Effect of young age on coronary adaptations to left ventricular pressure overload hypertrophy in sheep.

OBJECTIVES: This study attempted to determine the effect of young age on changes in coronary conductance and capillary density with left ventricular pressure overload hypertrophy. Mechanisms responsible for age differences in perfusion capacity were examined. BACKGROUND: Hypertension in adults causes alterations in the coronary vasculature, resulting in diminished coronary perfusion capacity and myocardial ischemia. These processes are worsened in adults by advanced age. Young age may provide advantages in coronary adaptation to hypertension. METHODS: Coronary conductance was examined in conscious chronically instrumented 10-week old lambs and adult sheep with progressive ascending aortic stenosis of 6-week's duration and age-matched control sheep by means of the microsphere technique and vasodilators. Capillary density was measured post-mortem. RESULTS: Adult sheep with aortic stenosis had a decrease in left ventricular subendomyocardial capillary density by 17% and maximal coronary conductance with adenosine by 67%. In the nonhypertrophied right ventricle, maximal coronary conductance was depressed by 47%, whereas capillary density was normal, implying an effect of coronary hypertension on resistance vessels. In contrast, lambs with aortic stenosis maintained normal left ventricular capillary density, maximal coronary conductance and coronary reserve and had relatively little impairment of conductance in the right ventricular coronary bed (-15%, p = NS). Similar responses were found with other vasodilators, isoproterenol and chromonar. CONCLUSIONS: Young age confers advantages to coronary adaptation to left ventricular pressure overload, including angiogenesis proportionate to hypertrophy, resulting in normal capillary density and coronary conductance. There is also less hypertension-induced impairment of coronary conductance distinct from the effects of hypertrophy.

Transition from compensated hypertrophy to intrinsic myocardial dysfunction during development of left ventricular pressure-overload hypertrophy in conscious sheep. Systolic dysfunction precedes diastolic dysfunction.

BACKGROUND: Patients with aortic stenosis have a period of compensated left ventricular hypertrophy but may eventually develop congestive heart failure. Previous experimental studies showed either normal myocardial contractility in mild short-term pressure overload or myocardial dysfunction with severe pressure overload. Transition from compensated left ventricular hypertrophy to myocardial dysfunction has not been experimentally demonstrated in an adult large animal. Controversial issues in pressure-overload hypertrophy include whether the left ventricular dysfunction is due to insufficient hypertrophy (afterload mismatch) or to intrinsic myocardial dysfunction and whether diastolic dysfunction precedes systolic dysfunction. METHODS AND RESULTS: We induced left ventricular hypertrophy (41% increase in left ventricular to body weight ratio) by gradually tightening a hydraulic constrictor around the ascending aorta in 9 chronically instrumented conscious sheep. Afterload (end-systolic stress) elevation remained constant (approximately 33% greater than baseline) by adjustment of the aortic constrictor over 6 weeks, gradually increasing left ventricular pressure (from 117 +/- 6 to 163 +/- 5 mm Hg) as hypertrophy developed. Four sets (baseline, 2 weeks, 4 weeks, and 6 weeks) of serial hemodynamic studies were performed in each animal with beta-blockade, first with and then without aortic constriction to mechanically match loading conditions. Stepwise methoxamine infusion was performed to obtain load-independent assessment of myocardial contractility. Midwall shortening (P < .05) and shortening rate (P < .05) at mechanically matched loading conditions showed that myocardial dysfunction developed between the fourth and the sixth week. Shortening-preload-afterload (P < .05) and shortening rate-preload-afterload (P < .05) relations, load-independent contractility indices based on the systolic myocardial stiffness concept, also revealed depressed myocardial contractility at the sixth week. Time constant of left ventricular isovolumic relaxation and diastolic myocardial stiffness constant did not change over the 6 weeks. CONCLUSIONS: Transition from normal myocardial contractility to myocardial dysfunction was demonstrated. This transition occurred even when the elevation of afterload remained constant as hypertrophy incompletely adapted to increasing left ventricular pressure. Systolic dysfunction preceded diastolic dysfunction in this model.

Response of the hypertrophied left ventricle to tachycardia: importance of maturation.

Pressure overload left ventricular (LV) hypertrophy (LVH) induces ventricular dysfunction during stress, which is commonly attributed to diminished myocardial capillary density and ischemia. Immature hearts with LVH have a normal coronary flow reserve and capillary density. The purpose of this study was to determine 1) whether young lambs with LVH had an abnormal response to chronotropic stress, 2) whether nonischemic mechanisms contributed to the abnormal response, and 3) whether the age at which LVH was induced affected the response. We assessed LV endomyocardial function, perfusion, and Ca(2+)-adenosinetriphosphatase (ATPase) mRNA levels in chronically instrumented lambs with and without LVH and adult sheep with and without LVH. Rapid pacing induced diastolic dysfunction, increased time constant of isovolumic relaxation using an iterative fit (tM), and elevated LV diastolic pressures in young lambs and adult sheep with LVH. During pacing, tM was greater in the adult sheep with LVH than in the young lambs with LVH. Ca(2+)-ATPase mRNA levels were 79% less in adult sheep with LVH than in those without. Ca(2+)-ATPase mRNA levels in lambs with and without LVH and adult sheep without LVH were similar. Diastolic dysfunction occurred in the absence of subendomyocardial hypoperfusion, suggesting a nonischemic mechanism. In adult sheep with LVH diastolic dysfunction was associated with a marked reduction in Ca(2+)-ATPase mRNA levels.

Different responses of extent and velocity of contraction to dobutamine in conscious sheep.

The shortening- and shortening rate-preload-afterload relations, based on the concept of the myocardial end-systolic stress-strain relation (ESSSR), are a newly developed load- and size-independent assessment of myocardial contractility. The purpose of this study was to apply this assessment to compare extent and velocity of myocardial contraction during graded infusions of dobutamine. Seven chronically instrumented unsedated sheep were studied at rest and during graded infusions of dobutamine (2.5-20 micrograms.kg-1.min-1). The ESSSR were linear over a wide range of load alterations, whereas the end-systolic pressure-diameter relations (ESPDR) were generally nonlinear. Midwall shortening rate (SRm) at common preload and afterload representing contraction extent increased with each dose of dobutamine through 20 micrograms.kg-1.min-1. In contrast, midwall shortening (Sm) increased through dobutamine 5 micrograms.kg-1.min-1 but not at higher dobutamine infusion rates. Conventional endocardial shortening and the slope of the ESPDR, fitted to a linear model, exhibited responses similar to Sm. The velocity of circumferential endocardial fiber shortening (Vcf,c), Vcf,c-afterload relation, and maximum first derivative of left ventricular pressure exhibited responses similar to SRm. Thus both the extent and velocity of contraction increased at low doses of dobutamine, whereas only the velocity increased at high doses. Potential mechanisms for the saturated response of the extent of contraction include 1) shorter systolic time for contraction due to earlier onset of relaxation and 2) the utilization of myocardial contractile energy for left ventricular wall deformation at small cavity volumes at high doses of dobutamine.

Age-dependent ventricular response to pressure overload. Considerations for the arterial switch operation.

Success with the arterial switch operation for D-transposition of the great arteries and the concept of left ventricular suitability for systemic work stimulated this literature review of the age-dependent mechanisms in normal cardiac growth and pressure-induced left ventricular hypertrophy. Normal postnatal myocardial growth is markedly influenced by hemodynamic factors. It consists of an early hyperplastic phase of both myocytes and capillaries that is followed by a myocyte hypertrophic phase. Similarly, imposition of a pressure overload induces both myocyte hyperplasia/hypertrophy and increased angiogenesis in neonates, but only myocyte hypertrophy at a later age. The functional consequences of ventricular hypertrophy are the result of adaptive and nonadaptive changes resulting from the overload stimulus, for example, induction of protooncogene expression, myosin isoenzyme shifts, degree of coronary perfusion, responsiveness to beta-adrenergic stimulation, and myocyte capacity to re-accumulate or sequester cytosolic calcium. Strikingly, both the capacity and the rapidity of left ventricular hypertrophy decrease with increasing age. This experimental information supports the current use of primary arterial switching for neonates with D-transposition of the great arteries and the use of "rapid" two-stage arterial switching in infants more than 3 to 4 weeks of age; it raises some concern about the practice of late retraining of the left ventricle in cases of failed atrial inversion operation.

Transient coronary stenosis associated with arrhythmia and ischemia 24 hours after reperfusion.

We examined the electrophysiologic sequelae of transient reductions in coronary blood flow (CBF) in conscious dogs. Animals were instrumented to measure arterial pressure, heart rate, repetitive extrasystole threshold (RET), and CBF before coronary stenosis, during 90 minutes of a 50% reduction in CBF, and at 1, 24, 48, and 72 hours after reperfusion. RET was decreased at 24 and 48 hours but returned to baseline by 72 hours after reperfusion. Frequent ventricular ectopic activity (VEA), absent during the control period, was noted during stenosis and at 1, 24, and 48 hours after reperfusion. beta-Adrenergic blockade (metoprolol) normalized the decreased RET at 24 hours. Addition of alpha 1-adrenergic blockade (prazosin) abolished VEA. Endocardial blood flow in the posterior papillary muscle of the left ventricle was reduced by 52 +/- 9% during stenosis, was similar to baseline levels by 1 hour after reperfusion, and decreased by 39 +/- 5% at 24 hours. We conclude that episodes of modest coronary artery stenosis may be followed by electrophysiologic changes indicative of increased vulnerability to malignant ventricular arrhythmias.

A time-course study of the effects of pentobarbital, fentanyl, and morphine chloralose on myocardial mechanics.

Cardiovascular physiological studies in anesthetized animals may be confounded by the hemodynamic actions of the anesthetic agents themselves. To identify an anesthetic regimen that does not significantly influence cardiovascular physiology, the hemodynamic responses of 28 dogs were studied. Animals were equally divided among groups with 1) no anesthesia (i.e., trained conscious preparation), 2) pentobarbital sodium, 3) fentanyl citrate, and 4) a combination of morphine sulfate and alpha-chloralose. Anesthesia was maintained for 3 h. Data were acquired with the use of ultrasound imaging of the heart in conjunction with invasive pressure measurements. Left ventricular ejection phase indexes and end-systolic force-velocity relations were used to evaluate the effects of each anesthetic agent on overall systolic performance and myocardial contractility. Compared with the conscious animals, pentobarbital profoundly depressed systolic performance (P less than 0.05 vs. control) because of a reduction in myocardial contractility (P less than 0.01) and an increase in left ventricular afterload (end-systolic wall stress, P less than 0.05). Fentanyl increased myocardial contractility (P less than 0.05) but also tended to increase afterload with the net result that overall systolic performance remained unchanged. Morphine-chloralose did not affect overall ventricular systolic performance or its individual determinants. Pentobarbital and fentanyl also caused progressive time-dependent deteriorations in all parameters of systolic function during prolonged anesthesia. In contrast, cardiac function was stable for greater than or equal to 3 h after induction of morphine-chloralose anesthesia. The hemodynamic profile of dogs anesthetized with morphine-chloralose most closely resembled that of the conscious animals. Morphine-chloralose is recommended when prolonged anesthesia is required for studies of cardiovascular physiology.

Myocardial function in immature and mature sheep with pressure-overload hypertrophy.

The effect of pressure-overload left ventricular hypertrophy (LVH) on myocardial function is controversial. A major factor in the controversy may be the age at which the pressure overload was induced. The goal of this study was to determine whether the age at which the LVH was induced affected systolic myocardial function. We studied lambs (n = 8) and sheep (n = 7) with LVH induced by constricting the ascending aorta and their sham-operated controls (n = 7 and n = 7). This new, unsedated, ovine model of LVH was large enough to accommodate chronic surgical implantation of instrumentation and the induction of pressure-overload hypertrophy in both young and adult age groups. Solid-state intraventricular pressure transducers and sonomicrometer crystal were used to assess instantaneous left ventricular pressure and dimensions. Myocardial contractility was assessed with midwall shortening at common preload and afterload. Load alterations were induced by graded infusion of methoxamine. There was depressed myocardial function in adult sheep with LVH compared with adult controls. Lambs with and without LVH had normal left ventricular myocardial function, similar to adult controls. Similar results were obtained in studies after beta-adrenergic receptor blockade. We conclude that maturation decreases the ability of the myocardium to maintain normal contractility in the presence of pressure-overload hypertrophy.

Myocardial angiogenesis and coronary perfusion in left ventricular pressure-overload hypertrophy in the young lamb. Evidence for inhibition with chronic protamine administration.

In contrast to young growing animals, pressure-overload hypertrophy in adults is frequently associated with diminished myocardial capillary density and maximal coronary flow per gram. To determine the role of angiogenesis in maintaining perfusion capacity in the hypertrophying heart, the angiogenesis inhibitor protamine sulfate was administered to young lambs during the development of left ventricular (LV) pressure-overload hypertrophy. Baseline and maximum (adenosine) myocardial perfusion was measured in four groups of chronically instrumented 10-week-old lambs subjected to 1) ascending aortic bands since the age of 4 weeks (LVH group, n = 10), 2) sham operation at the age of 4 weeks (SHAM group, n = 8), 3) aortic bands and twice daily injections of protamine since the age of 4 weeks (LVH + P group, n = 9), 4) sham operation and injection of protamine (SHAM + P group, n = 8). Capillary density was measured postmortem. Peak LV pressure and the LV/body weight ratio were similarly increased in LVH and LVH + P compared with sham-operated lambs (p less than 0.001). In LVH lambs, LV capillary number increased by 32% compared with sham-operated lambs (p less than 0.05), and capillary density, coronary flow reserve, and minimal coronary resistance remained normal. In contrast, LVH + P lambs had no significant increase over SHAM lambs in LV capillaries and total maximum coronary flow. The LVH + P lambs had lower LV subendomyocardial capillary density and higher minimal coronary resistance per gram (p less than 0.05 versus LVH lambs). Right ventricular capillary density and minimal resistance were similar in all groups. These findings support the hypotheses that myocardial angiogenesis with pressure-overload hypertrophy is important in maintaining maximal LV coronary flow in the young and that impairment of angiogenesis results in diminished coronary flow capacity.

Preload dependence of fiber shortening rate in conscious dogs with left ventricular hypertrophy.

Employing the new concept of systolic myocardial stiffness, this study addresses the questions of linearity of the end-systolic stress-strain relations in left ventricular hypertrophy and the preload dependence of fiber shortening rate. Pressure overload hypertrophy was induced in six puppies by banding the ascending aorta. Ultrasonic crystals were implanted for measurement of short axis and wall thickness in the six dogs with hypertrophy and in five control dogs. A pressure catheter was inserted through the apex for left ventricular pressure measurement. Load was altered by graded infusions of phenylephrine in the setting of beta-adrenergic blockade. Linearity of the end-systolic stress-strain relations was observed in all cases, and preload-corrected shortening rate-afterload relations were derived from these stress-strain relations. Without preload correction, mid wall and endocardial shortening rate were depressed (p less than 0.05 and p less than 0.005, respectively) in the hypertrophy group. However, with preload correction at 35 g/cm2, there was no significant difference in shortening rate between the control and hypertrophy groups at afterloads of 150, 200 and 250 g/cm2. Endocardial shortening rate at a preload of 25 versus 35 g/cm2 demonstrated a preload dependence in both the control (p less than 0.04) and the hypertrophy group (p less than 0.01). Mid wall shortening rate displayed a preload dependence only in the hypertrophy group (p less than 0.05). It is concluded that end-systolic stress-strain relations are linear in control conditions and in hypertrophy, fiber shortening rate is preload-dependent and, thus, shortening rate-afterload relations currently used to assess myocardial contractility need to be modified to account for these preload effects.

Application of the systolic stiffness concept to assess myocardial function in developing hypertension.

The concept of end-systolic myocardial stiffness permits the quantification of preload effects on fiber shortening and changes in the slope (max Eav) of the end-systolic stress-strain relation, which, if linear, reflect changes in the inotropic state. As an application of this new concept, the end-systolic stress-strain and shortening-afterload relations were evaluated on the basis of data from dogs studied during development of perinephritic hypertension. End-systolic stress-strain relations were linear before and 2 weeks after the induction of hypertension and the end-systolic pressure-diameter relations were not always linear. The shortening-afterload relations obtained directly from raw data points displayed enhanced contractility in the hypertensive state under beta-adrenergic receptor blockade. However, the preload-corrected shortening-afterload relations demonstrated that contractility was unchanged in hypertension. Hypertensive hearts operated at higher preload than normotensive hearts at any afterload levels. This discrepancy between the conventional method without preload-correction and the preload-corrected analysis indicates the importance of preload-correction on shortening-afterload relations in hypertension.

Sympathetic augmentation of cardiac function in developing hypertension in conscious dogs.

To determine the alterations in left ventricular (LV) function and the mechanisms involved that occur during the development of perinephritic hypertension, dogs were instrumented with a miniature LV pressure transducer, aortic and left atrial catheters, and ultrasonic crystals to measure LV diameter in the short and long axes and wall thickness. At 2 wk after initiation of perinephritic hypertension, increases (P less than 0.05) were observed in LV systolic pressure, LV end-diastolic pressure, both short- and long-axis end-diastolic diameters, calculated LV end-diastolic volume, stroke volume, global average LV systolic wall stress, first derivative of LV pressure (LV dP/dt), and ejection fraction, whereas mean velocity of circumferential fiber shortening (Vcf) and rate of change of LV short-axis diameter (LV dD/dt) rose but not significantly. At three levels of matched preload and afterload induced by the administration of graded doses of phenylephrine, Vcf, LV dD/dt, and LV dP/dt increased in hypertension compared with the same levels of preload and afterload before hypertension. When the loading conditions in the normotensive and hypertensive dogs were matched, either after ganglionic blockade or beta-adrenergic blockade, both isovolumic and ejection-phase indexes of LV function remained similar before and after hypertension. Thus we conclude that 1) LV function in intact, conscious dogs with early hypertension is enhanced, and 2) the major mechanism for the increase in LV function involves the sympathetic nervous system.