Post‐natal developmental changes in the length‐tension relationship of cat papillary muscles.

Davies, P.; Dewar, J.; Tynan, Michael; Ward, Robert E.

doi:10.1113/jphysiol.1975.sp011181

Cited by 67 publications

(26 citation statements)

References 12 publications

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“…The positive inotropic effect of pacing-induced tachycardia has been demonstrated previously in unanesthetized lamb fetuses and in neonatal cat and lamb myocardial muscle strips in vitro (1,8,23). The current study provides further developmental evidence of an increase of left ventricular contractile function during tachycardia during the neonatal period ( Fig.…”

Section: Discussionsupporting

confidence: 82%

“…The 'data from the present study ( Fig. 3 and 4) and others (1,8) would suggest that some of the postnatal increase of contractile function and cardiac output may occur as a result of the inotropic effect of an increase in heart rate; however, the magnitude of the increase in contractile function, which occurs . , Fig.…”

Section: Discussionsupporting

confidence: 57%

“…Multiple recent investigations in vitro have demonstrated that atrial pacing-induced tachycardia is associated with a small but significant increase in left ventricular contractile function in conscious adult humans and dogs (9, 17-19, 28, 33). Although there is some information available concerning the effect of a heart rate increase on left ventricular contractility in the unanesthetized lamb fetus (1, 23) and in neonatal cat and lamb heart muscle in vitro (1,8), to our knowledge there is no such information available in conscious neonates of any species. Therefore, we studied the effect of a pacing-induced heart rate increase on left ventricular contractile function in conscious newborn lambs.…”

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confidence: 99%

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The Effect of Atrial Pacing-Induced Tachycardia on Left Ventricular Contractile Function in Conscious Newborn and Adult Sheep

Fisher¹,

Gross²

1983

Pediatr Res

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SummaryIn order to determine if an increase in heart rate is associated with an increase of left ventricular contractile function during the neonatal period we recorded phasic and mean aortic blood pressure. left atrial mean or left ventricular end diastolic Dressure. phasic left ventricular blood pressure, aortic blood flow velocity and the instantaneous first derivatives of left ventricular blood pressure (dP/dt) and aortic blood flow velocity (dV/dt) during pacing-induced tachycardia in conscious newborn and adult sheep. There was a significant positive linear correlation between heart rate and both indices of contractility (dP/dt and dV/dt) in both age groups. Left ventricular end diastolic pressure was unchanged except for a decrease at the most rapid heart rate in the newborns. There was no change in aortic mean blood pressure during the study. Our data demonstrate that an increase of heart rate is associated with an increase of left ventricular contractile function in conscious neonatal and adult sheep. Investigations of the effects of potential inotropic agents on left ventricular contractile performance in newborns and adults must evaluate the independent effect of any simultaneously occurring increase in heart rate.The positive inotropic effect of an increase of contraction frequency was originally demonstrated in vitro by Bowditch (5). Multiple recent investigations in vitro have demonstrated that atrial pacing-induced tachycardia is associated with a small but significant increase in left ventricular contractile function in conscious adult humans and dogs (9, 17-19, 28, 33). Although there is some information available concerning the effect of a heart rate increase on left ventricular contractility in the unanesthetized lamb fetus (1, 23) and in neonatal cat and lamb heart muscle in vitro (1,8), to our knowledge there is no such information available in conscious neonates of any species. Therefore, we studied the effect of a pacing-induced heart rate increase on left ventricular contractile function in conscious newborn lambs. As species variability has been reported in adults (25) we also performed a pacing study in conscious adult sheep. MATERIALS AND METHODSSurgical technique. We operated on 1 1 Western newborn lambs 1-25 (9 + 2, mean + S.E.) days after birth and on 8 nulliparous female adult sheep. The lambs weighed 6.5 f 0.6 g. We anesthetized the animals with 1-2% fluothane (Halothane), intubated the trachea, and ventilated the lungs with an animal ventilator (Methomatic, Pittman-Moore). We performed a thoracotomy in the left fourth intercostal space and inserted polyvinyl catheters (inside diameter, 0.10 cm; outside diameter, 0.15 cm) into the ascending aorta via the left internal thoracic artery and into the left atrium through a purse-string suture in the atrial appendage. The catheters were closed after they were filled with heparin. We sutured a pair of stainless steel pacing wires (#A5633 hookup wire, Cooner Wire Co., Chatsworth, CA) to the left atrial epicardium. Through a separate incis...

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Section: Discussionsupporting

confidence: 82%

Section: Discussionsupporting

confidence: 57%

mentioning

confidence: 99%

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The Effect of Atrial Pacing-Induced Tachycardia on Left Ventricular Contractile Function in Conscious Newborn and Adult Sheep

Fisher¹,

Gross²

1983

Pediatr Res

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“…80% reduction of total vascular or systemic and ductal resistance) (3 1). Several studies suggest that isolated premature myocardium is less capable of generating tension than is that of the mature animal (10,14,32). Consequently, the high cardiac output and the preservation of LV performance in preterm lambs with PDA may have been facilitated by the reduction of impedance to ejection into the lower resistance combined systemic and pulmonary vascular beds.…”

Section: Discussionmentioning

confidence: 99%

The Contractility and Performance of the Preterm Left Ventricle before and after Early Patent Ductus Arteriosus Occlusion in Surfactant- Treated Lambs

et al. 1985

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ABSTRAm. The influence of left-right ductal shunting on early hemodynamic responses, namely left ventricular performance, contractility, and systemic perfusion was evaluated in nine preterm lambs (120 days gestational age) treated with surfactant. Blood gases were maintained in the physiological range using mechanical ventilation; hemodynamic and blood flow measurements (radionuclide labeled microspheres) were obtained before and after occlusion of the patent ductus arteriosus with a catheter balloon. The mean left-right ductal shunt before occlusion (1.2 h postnatal age) was 59 f 11% SD. Left ventricular output was increased in all lambs with PDA (pre: 306 f 106 versus post: 155 f 31 ml/min/kg; p < 0.001); effective systemic blood flow and organ blood flows did not change. The left ventricle end-diastolic volume was increased in all and decreased following ductal occlusion (pre: 2.0 f 0.4 verus post: 1.5 f 0.2 ml/kg;p < 0.01). Cardiac rate, ejection fraction, and contractility (peak dP/dt) did not change. Right-left ductal shunting was not detected in six similarly treated lambs. Thus, during the 1st h of life the hemodynamic profile of preterm lambs with patent ductus arteriosus was characterized by large magnitude left-right shunt and a "high" cardiac output state sufficient to maintain unchanged systemic perfusion. The increased left ventricle output was accomplished by increasing end-diastolic volume (Frank-Starling mechanism), but left ventricle contractility remained unchanged. We speculate that the preterm left ventricle may be unable to sustain the high level of pump performance and contractility required to compensate for the ductal "steal" of systemic blood flow. (Pediatr Res 19: 1053-1058,1985 Abbreviations PDA, patent ductus arteriosus LV, left ventricleThe persistently PDA represents a major challenge for the preterm cardiovascular system undergoing the fetal transition to extrauterine life. It has been well demonstrated that left-right Supported by Grants 590 GL03 and 676 IG from the American Heart Associaton, Greater Los Angeles Affiliate and NIH Grant HD 12714. 10 ductal shunting adversely affects the cardiopulmonary status of such infants (1-5). Recent advances using assisted ventilation and surfactant therapy have made it possible to study early postnatal cardiovascular adaptation in premature animals under acceptable physiological conditions (6, 7). Early cardiovascular adjustments to left-right ductal shunting have been infrequently studied under such circumstances (8, 9). Various studies suggest that the increased metabolic and oxygen requirements of the term newborn are provided by increasing LV performance and "contractile state" (10-12). However, it is unclear whether the immature LV of the preterm has sufficient "reserve" capacity to undergo these transitional circulatory adjustments, particularly when additional pathological LV volume load and left-right ductal shunting are present (10,(13)(14)(15).A prior study of 2-h-old preterm lambs (120-124 days gestational age) with left-right d...

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“…The study of Nakanishi and Jarmakani (2) suggeststhat the role of the sarcoplasmic reticulum in cardiac contraction in the newborn and near-term fetus is less than in the adult. Furthermore, several investigators (3)(4)(5)(6)(7)(8)(9)(10) have shown that the neonatal myocardium develops less force than the adult myocardium and myofibrillar and sarcoplasmic reticulum contents increase with development. However, these studies were performed using neonatal or near-term fetal an imals and contractile system in the early mammalian fetus has not been stud ied extensively.…”

Section: Ica)o Extracellular Calciummentioning

confidence: 99%

Development of Myocardial Contractile System in the Fetal Rabbit

Nakanishi¹,

Okuda²,

Kamata³

et al. 1987

Pediatr Res

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ABSTRACf. Developmental changes in the myocardial contractile system were evaluated in the fetus at 18, 21, and 28 days of gestation (full term 31 days) and in 3-to 5-day-old newborn rabbits. Mechanical function was studied using the isolated arterially perfused heart. Perfusion with ryanodine (10-5 M), an inhibitor of Ca release from the sarcoplasmic reticulum, decreased contractile force and increased the time to peak tension in the 28-day fetus and newborn but these changes were minimal in the 18-and 21-day fetus. Postextrasystolic potentiation, which is thought to be caused by Ca release from the sarcoplasmic reticulum, was observed in the 28-day fetus and the newborn, but was not significant in the 18-and 2l-day fetus . An ultrastructural study showed poorly developed sarcoplasmic reticulum and myofibrils in the 18-and 21-day fetus. Although the maximum developed tension observed at high extracellular calcium increased with development, the relative value of developed tension at various extracellular calcium was similar in the three fetal groups and only in the newborn the extracellular calcium-developed tension curve shifted to the right. Myofibrillar yield increased with development but sensitivity of myofibrillar ATPase activity to Ca was similar in the fetus and newborn. These data suggest that 1) the sarcoplasmic reticulum does not function significantly in the 18-and 21-day fetus, 2) although sarcoplasmic reticulum starts to function at late gestation, it does not cause significant changes in intracellular calcium in the fetal period, 3) myocardial contractility remains similar in the fetus from the 18th to 28th day of gestation and major changes in contractility occur after birth. tPediatr Res 22: 201-207, 1987) Abbreviations DT, developed tension +dT/dt(max), maximal rate of tension development TPT, time to peak tension IhRT, half relaxation time PES, paired electric stimulation RT, resting tension ICa)o, extracellular calciumIn the adult myocardium, a relatively small Ca influ x across the sarcolemma induces the subsequent release of greater Received November 3,1986; accepted March 27, 1987. Correspondence Toshio Nakanishi, M.D., Pediatric Cardiology, Heart Institut e of Japan , Tokyo Women's Medical College, 10 Kawadacho, Shinjuku , Tokyo, Japan .Supported by Research Grant 59480241 and 59570411 from the Japan ese Ministry of Education, Science, and Culture and by a grant-in-aid from the Japan Research Promotion Society for Cardiovascular Diseases. amounts of Ca from the sarcoplasmic reticulum, which then activates the myofilaments (I ). The study of Nakanishi and Jarmakani (2) suggeststhat the role of the sarcoplasmic reticulum in cardiac contraction in the newborn and near-term fetus is less than in the adult. Furthermore, several investigators (3-10) have shown that the neonatal myocardium develops less force than the adult myocardium and myofibrillar and sarcoplasmic reticulum contents increase with development. However, these studies were performed using neonatal or near-term fetal an imal...

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Post‐natal developmental changes in the length‐tension relationship of cat papillary muscles.

Cited by 67 publications

References 12 publications

The Effect of Atrial Pacing-Induced Tachycardia on Left Ventricular Contractile Function in Conscious Newborn and Adult Sheep

The Effect of Atrial Pacing-Induced Tachycardia on Left Ventricular Contractile Function in Conscious Newborn and Adult Sheep

The Contractility and Performance of the Preterm Left Ventricle before and after Early Patent Ductus Arteriosus Occlusion in Surfactant- Treated Lambs

Development of Myocardial Contractile System in the Fetal Rabbit

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