Relationship of arterial pressure and heart rate in fetal, new‐born and adult sheep.

Dawes, G. S.; Johnston, Barbara M.; Walker, David W.

doi:10.1113/jphysiol.1980.sp013516

Cited by 94 publications

(52 citation statements)

References 14 publications

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“…This reflex is active but functionally immature at 36 wk and still relatively weak at 40 wk (27). If the threshold for baroreflex activation is slow to reset to the usual postnatal range, dynamic variations in pressure may be wider than expected and remain so for much longer than is normal after birth, as we observed (28).…”

Section: Discussionsupporting

confidence: 53%

Abnormal Circulatory Stress Responses of Preterm Graduates

2007

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Preterm birth and chronic lung disease may increase the risk of hypertension and cardiovascular disease in infancy and adolescence. Here we looked for evidence of early circulatory dysfunction associated with these perinatal complications. We compared infants born at term (n ϭ 12) with those born preterm with an uncomplicated neonatal course (n ϭ 12) or diagnosed with bronchopulmonary dysplasia (BPD) (n ϭ 10). We measured blood pressure (BP) (Finometer), and heart rate (HR) responses to 4 min of breathing 4% CO 2 during quiet sleep. Hypercapnia accelerated HR and increased BP of term infants. Preterm infants either (i) had an exaggerated pressor but little or no HR response to CO 2 (healthy or mild-moderate BPD) or (ii) had a diminished pressor response and accompanying decrease in HR (severe BPD). Short-term reflex cardiovascular control was consequently altered by premature birth, with potentially more serious aberrations associated with severe BPD. Most anomalies had not resolved by the time infants born preterm reached term age; some may be early signs of emerging long-term cardiovascular dysfunction. W ith the impressive increase in survival of very preterm and low birth weight infants come new challenges. Evidence already indicates that this "new generation" of children and adolescents may have accelerated disease onset later in life (1). One factor contributing to their higher risk of cardiovascular disease may be abnormal vascular and circulatory development (2-4). Cardiovascular activity is normally carefully regulated, but if some or all of the central and peripheral regulatory mechanisms involved fail to develop normally, perfusion, growth, and function may be compromised. In exceptional circumstances during infancy, persistent serious dysfunction could result in a sudden catastrophic decrease in BP and HR or prevent autoresuscitative recovery, culminating in sudden infant death syndrome (SIDS) (5,6). In other cases, dysfunction may be relatively benign, although there may still be side effects with adverse consequences of their own.We know relatively little about how BP and HR control develops, and the potentially adverse effects of fetal and perinatal stress. A better understanding of these issues could lead to new therapies or strategies to prevent neonatal complications and improve long-term outcome. In the study described here, we looked for evidence that development of neonatal circulatory control is altered by common perinatal complications (7). We studied three different groups of newborn infants: those born normally at term, those born preterm but otherwise healthy, and infants born very preterm suffering from chronic lung disease (BPD). Infants with BPD are at particularly high risk of long-term cardiovascular complications and SIDS (8 -10). We compared BP and HR responses of these infants to a routine physiologic stress (breathing a low concentration of CO 2 for several minutes) commonly used to unmask autonomic anomalies (11). Normally, acute exposure to CO 2 increases BP and HR ...

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Section: Discussionsupporting

confidence: 53%

Abnormal Circulatory Stress Responses of Preterm Graduates

2007

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“…Although there have been other investigations into the efferent limb of the arterial baroreflex control of heart rate during postnatal maturation in rabbits, swine and sheep (Bloor, 1964;Dawes et al 1980;Tomomatsu & Nishi, 1982;Palmisano et al 1989;Segar et al 1992;Patton & Hanna, 1994), many of these have been conducted on anaesthetised or sedated, paralysed and artificially ventilated animals, or have evaluated only a portion of the heart rate-blood pressure relationship, making the results difficult to interpret. Taken together, there is no generalised agreement as to whether the gain of the arterial baroreflex decreases remains constant or increases with postnatal maturation.…”

Section: Discussionmentioning

confidence: 99%

Renin and Heart Rate Responses to Haemorrhage are Age Dependent in Conscious Lambs

Smith

Basati

Şener

et al. 2000

Experimental Physiology

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The present experiments were carried out in conscious lambs (1‐2 weeks old, n= 9) and older sheep (11‐12 weeks old, n= 11) to determine whether the cardiovascular and endocrine responses to 0, 10 and 20% haemorrhage were developmentally regulated. The major novel finding of our study is that throughout the first 3 months of postnatal life, there is a similar decrease in mean arterial pressure and a similar restoration of pressure to pre‐haemorrhage levels, for the same degree of blood loss, yet the mechanisms used to restore pressure appear to be age dependent as follows. In lambs, but not in older sheep, heart rate increased for 1 h after 20% haemorrhage. Activation of the renin‐angiotensin system was also greater and more prolonged in lambs than in older sheep following haemorrhage, and occurred at a lesser degree of blood loss. Plasma arginine vasopressin responses to haemorrhage were, however, similar in both age groups. These data provide new information that some of the mechanisms used to restore arterial pressure following blood volume depletion appear to be age dependent.

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“…In animal studies, it is shown that the BR is impaired in the fetus and the newborn and develops further during postnatal life (7)(8)(9). The impairment in BR function is due to maturational changes in the autonomic pathways (10).…”

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confidence: 99%

Cardiovascular Autonomic Regulation in Preterm Infants: The Effect of Atropine

et al. 2004

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To study cardiovascular autonomic control, we assessed the effect of atropine on heart rate (HR) and blood pressure (BP) variability in 12 preterm infants (range 26 -32 wk) before intubation for respiratory insufficiency. Spectral power analysis of R-R interval and systolic BP (SBP) series were estimated in a low-frequency (LF; 0.04 -0.15 Hz) and high-frequency (HF; 0.4 -1.5 Hz) band and evaluated for a 10-min period before and a 10-min period after atropine sulfate (0.01 mg/kg). Baroreceptor reflex (BR) functioning was estimated using transfer function analysis at LF (coherence, gain, and phase). Atropine resulted in a significant 12% increase in steady-state HR (p Ͻ 0.01) and unchanged SBP. For R-R interval series, the total spectral power decreased 6-fold (p Ͻ 0.01), which was predominantly due to a reduction in the LF band (16-fold; p Ͻ 0.01). In contrast, we observed a significant increase (25%; p Ͻ 0.05) in total spectral power of SBP series partly as a result of an increase in HF power. The LF power of SBP series was not altered. The median LF transfer gain (BR sensitivity) between SBP and R-R interval decreased from 4.2 to 1.4 ms/mm Hg (p Ͻ 0.01) after atropine. The LF phase relationship (BP leads R-R interval fluctuations bỹ 4 s) was not changed after atropine. In conclusion, even in preterm infants in distress, atropine modulates HR and BP variability, suggesting that BR-mediated parasympathetic control of heart rate is of significance for cardiovascular control at that age. The baroreceptor reflex (BR) is the most important regulatory mechanism in the short-term control of heart rate (HR) and blood pressure (BP). The BR buffers sudden changes in systemic BP by adapting HR and peripheral vascular resistance. These responses of HR and vascular resistance are mediated by the efferent parasympathetic and sympathetic limb of the BR. As both systems are involved, studies on the BR give information on autonomic cardiovascular regulation (1,2).Data about the ontogeny of the BR and functional maturation in the human infant are limited. This is partly caused by the limited experimental (pharmacologic or mechanical) possibilities to challenge the BR in neonates. Passive head-up tilt test has been applied to neonates to measure responses in BP, HR, and limb blood flow to body tilting. In preterm infants (26 -38 wk gestation), passive head-up tilt resulted in significant vasoconstriction of the lower limb with a slight fall in aortic BP and unchanged HR (3). The inadequate ability to maintain BP and the lack of tachycardia suggest that preterm infants lack the full integrated BR response as seen in adults. In term infants, however, a fall in systolic BP (SBP) was observed in conjunction with tachycardia and a fall in limb blood flow, suggesting the presence of active reflex vasoconstriction (4). In a recent study, BR maturation was studied longitudinally in preterm infants, using a beat-to-beat analysis of R-R interval series and noninvasively measured SBP (5). BR sensitivity (the R-R interval change in millisecon...

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Relationship of arterial pressure and heart rate in fetal, new‐born and adult sheep.

Cited by 94 publications

References 14 publications

Abnormal Circulatory Stress Responses of Preterm Graduates

Abnormal Circulatory Stress Responses of Preterm Graduates

Renin and Heart Rate Responses to Haemorrhage are Age Dependent in Conscious Lambs

Cardiovascular Autonomic Regulation in Preterm Infants: The Effect of Atropine

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