Power spectral analysis for autonomic influences in heart rate and blood pressure variability in fetal lambs

Kimura, Yoshitaka; Okamura, Koji; Watanabe, Takanori; Murotsuki, Jun; Suzuki, Taku; Yano, Masahiro; Yajima, Akira

doi:10.1152/ajpheart.1996.271.4.h1333

Cited by 41 publications

(48 citation statements)

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“…Power within the L frequency range was increased significantly in the nimesulide-treated fetuses. Power in the low-frequency range is influenced both by sympathetic and parasympathetic activity, although previous experiments by Kimura et al (20), suggest that beta-adrenergic blockade in the fetal sheep had a greater influence on L power than did cholinergic blockade (20). In that study, beta blockade reduced L power 78%, while cholinergic blockade reduced power in this frequency range 61% (20).…”

Section: Discussionmentioning

confidence: 62%

“…In 7 control and in 5 nimesulide-treated fetuses, we quantified the power spectra of the variations in fetal heart rate, using methods similar to that reported by Kimura and coworkers (20) and later supported by studies by Li and coworkers (21). Five-minute epochs of fetal femoral or lingual arterial blood pressure, sampled at a rate of 60 Hz at the time of experimentation, were analyzed for heart period using LabView ver.…”

Section: Methodsmentioning

confidence: 99%

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Blockade of PGHS-2 inhibits the hypothalamus-pituitary-adrenal axis response to cerebral hypoperfusion in the sheep fetus

Wood¹,

Fraites²,

Keller‐Wood³

2009

American Journal of Physiology-Regulatory, Integrative and Comp

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Wood CE, Powers Fraites M, Keller-Wood M. Blockade of PGHS-2 inhibits the hypothalamus-pituitary-adrenal axis response to cerebral hypoperfusion in the sheep fetus. Am J Physiol Regul Integr Comp Physiol 296: R1813-R1819, 2009. First published March 18, 2009 doi:10.1152/ajpregu.90917.2008.-Decreases in fetal blood pressure stimulate homeostatic stress responses that help return blood pressure to normal levels. Fetal hypothalamus-pituitary-adrenal (HPA) axis responses to hypotension are mediated by chemoreceptor and baroreceptor reflexes and ischemia of the fetal central nervous system. Indomethacin, a nonselective inhibitor of prostaglandin endoperoxide synthase (PGHS)-1 and -2, attenuates the HPA response to hypotension in the fetus. The present study was designed to test the hypothesis that selective inhibition of PGHS-2 also inhibits the HPA response to cerebral hypoperfusion. We studied 13 chronically catheterized fetal sheep (126 -136 days gestation). Five fetal sheep were subjected to intracerebroventricular infusion of nimesulide (0.01 mg/ day), a specific inhibitor of PGHS-2, and eight were treated with vehicle (DMSO in water) for 5 days. Each fetus was subjected to a 10-min period of brachiocephalic occlusion, which decreased carotid arterial pressure ϳ75% and reflexively increased fetal plasma concentrations of ACTH, POMC, cortisol, and femoral arterial pressure, and decreased fetal heart rate. Nimesulide significantly inhibited the ACTH response to the BCO, while significantly augmenting the reflex cardiovascular response and altering fetal heart rate variability consistent with increased sympathetic nervous system activity. The results of this study demonstrate that the activity of PGHS-2 in the brain is a necessary component of the fetal HPA response to cerebral hypoperfusion in the late-gestation fetal sheep. These results are consistent with those of recent study, in which we demonstrated that the preparturient increase in fetal ACTH secretion depends upon PGHS-2 activity within the fetal brain. adrenocorticotropin; cortisol; fetus; blood pressure EICOSANOIDS HAVE BEEN LONG recognized for their importance as signaling molecules in the fetus (7). Plasma concentrations of PGE 2 are much higher in the late-gestation fetus than in the postnatal animal (7), and the concentrations increase prior to normal parturition in this species. The pattern of increase of fetal plasma PGE 2 , combined with the observation that exogenous PGE 2 stimulates fetal hypothalamus-pituitary-adrenal (HPA) axis activity (7), led to the hypothesis that PGE 2 secreted by the placenta acts as a hormone to stimulate fetal HPA axis activity prior to spontaneous parturition (34). Although the endogenous plasma concentrations of PGE 2 are high compared with plasma concentrations postnatally, intracarotid arterial infusion of PGE 2 , producing plasma concentrations within the range of that occur endogenously prior to spontaneous parturition, failed to increase fetal HPA axis activity (11). From the results of that study, we conclude...

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Section: Discussionmentioning

confidence: 62%

Section: Methodsmentioning

confidence: 99%

Blockade of PGHS-2 inhibits the hypothalamus-pituitary-adrenal axis response to cerebral hypoperfusion in the sheep fetus

Wood¹,

Fraites²,

Keller‐Wood³

2009

American Journal of Physiology-Regulatory, Integrative and Comp

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“…Using a 64-ch MCG, Fukushima, et al found that the activity of the sympathetic and parasympathetic nervous systems, as evaluated from the LF/HF ratio, were enhanced at gestational ages of 32 weeks and later, 13) consistent with previous reports of a conversion point at 32 weeks of gestation. 22,23) We found that the ANS activity, as evaluated by the CV and LF/ HF ratio using SAVP-ECG, was remarkably enhanced just after birth. Akselrod, et al discovered characteristic 0.1-Hz and 0.3-Hz frequency band levels (spectral peaks) in a spectral analysis of the heart rate variability in animals.…”

Section: )mentioning

confidence: 81%

Development and Significance of a Fetal Electrocardiogram Recorded by Signal-Averaged High-Amplification Electrocardiography

et al. 2009

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SummaryAlthough ultrasonic diagnostic imaging and fetal heart monitors have undergone great technological improvements, the development and use of fetal electrocardiograms to evaluate fetal arrhythmias and autonomic nervous activity have not been fully established. We verified the clinical significance of the novel signal-averaged vector-projected high amplification ECG (SAVP-ECG) method in fetuses from 48 gravidas at 32-41 weeks of gestation and in 34 neonates. SAVP-ECGs from fetuses and newborns were recorded using a modified XYZ-leads system. Once noise and maternal QRS waves were removed, the P, QRS, and T wave intervals were measured from the signal-averaged fetal ECGs. We also compared fetal and neonatal heart rates (HRs), coefficients of variation of heart rate variability (CV) as a parasympathetic nervous activity, and the ratio of low to high frequency (LF/HF ratio) as a sympathetic nervous activity. The rate of detection of a fetal ECG by SAVP-ECG was 72.9%, and the fetal and neonatal QRS and QTc intervals were not significantly different. The neonatal CVs and LF/HF ratios were significantly increased compared with those in the fetus. In conclusion, we have developed a fetal ECG recording method using the SAVP-ECG system, which we used to evaluate autonomic nervous system development. (Int Heart J 2009; 50: 161-171)

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“…The spectral analysis showed an increase in the relative power of low frequencies and a decrease in the relative power of high frequencies of the RRI spectrum. The ranges for LF and HF we used have been validated for the analysis of autonomic influences in heart rate variability in fetal sheep by Kimura et al (21). Although these authors used cycles/beat in their analysis, the frequency ranges for LF and HF are equivalent when expressed in Hertz.…”

Section: Discussionmentioning

confidence: 99%

“…Power spectral analysis of RRI variability was performed on data from the same file used for the sequence method using fast-Fourier transform and the data integrated over a specified frequency range. The frequency ranges used have been validated for the fetal sheep to represent sympathetic and parasympathetic cardiac modulation (LF, 0.025-0.31 Hz; HF, 0.5-1.25 Hz) (21). Power of RRI spectra in the LF (LF RRI) and HF (HFRRI) range were calculated in normalized units, and the ratio of LFRRI/HFRRI was used as an estimation of sympathovagal balance (31).…”

Section: Animal Studiesmentioning

confidence: 99%

Mild chronic hypoxemia modifies expression of brain stem angiotensin peptide receptors and reflex responses in fetal sheep

Pulgar¹,

Hong²,

Jessup³

et al. 2009

American Journal of Physiology-Regulatory, Integrative and Comp

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The effects of chronic mild hypoxemia on the binding of angiotensin receptors in selected brain stem nuclei and reflex responses were studied in fetal sheep. Fetal and maternal catheters were placed at 120 days' gestation, and animals received intratracheal maternal administration of nitrogen (n ϭ 16) or compressed air in controls (n ϭ 19). Nitrogen infusion was adjusted to reduce fetal brachial artery PO2 by 25% during 5 days. Spontaneous baroreflex sensitivity and spectral analysis of the pulse interval were analyzed during the 5 days hypoxemia period using 90 min of daily recording. Brains of control and hypoxemic animals were collected, and brain stem angiotensin receptor binding was studied by in vitro autoradiography at 130 days of gestation. After 5 days of hypoxemia, some animals in each group were submitted to one complete umbilical cord occlusion during 5 min. [125 I]sarthran binding showed that chronic mild hypoxemia significantly increases angiotensin type 1 receptor, angiotensin type 2 receptor, and ANG-(1-7) angiotensin receptor binding sites in the nucleus tractus solitarius and dorsal motor nucleus of the vagus (P Ͻ 0.05). Hypoxemia induced lower baroreflex sensitivity and a higher low frequency-to-high frequency ratio in the fetus, consistent with a shift from vagal to sympathetic autonomic cardiac regulation. Cord occlusion to elicit a chemoreflex response induced a greater bradycardic response in hypoxemic fetuses (slope of the initial fall in heart rate; 11.3 Ϯ 1.9 vs. 6.4 Ϯ 1.2 beats ⅐ min Ϫ1 ⅐ s Ϫ1 , P Ͻ 0.05). In summary, chronic mild hypoxemia increased binding of angiotensin receptors in brain stem nuclei, decreased spontaneous baroreflex gain, and increased chemoreflex responses to asphyxia in the fetus. These results suggest hypoxemia-induced alterations in brain stem mechanisms for cardiovascular control.fetus; hypoxemia; baroreflex OXYGEN DEPRIVATION IMPOSES diverse challenges to fetal development, with changes in the autonomic cardiovascular control via baroreflex and chemoreflex pathways playing a major role as a survival strategy (16). In fetal sheep, acute episodes of hypoxemia induce a redistribution of cardiac output to maintain blood flow and oxygen delivery to the heart and brain (14). This response is initiated by stimulation of peripheral chemoreceptors and maintained by endocrine mechanisms involving secretion of hormones such as catecholamines, neuropeptide Y, arginine vasopressin, and cortisol (11). During acute severe hypoxia, i.e., complete occlusion of the umbilical cord, fetuses respond with a fall in heart rate (FHR) and an increase in blood pressure. This acute FHR during hypoxia represents a key fetal adaptation, believed to help reduce myocardial work and oxygen requirements (11). This initial bradycardia, which is mediated by chemoreflex vagal pathways (5, 17, 23), occurs before the increase in blood pressure and is an indication of the severity of the hypoxic insult (5). Recently, it was reported that the slope of the initial bradycardia increases during short ...

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Power spectral analysis for autonomic influences in heart rate and blood pressure variability in fetal lambs

Cited by 41 publications

References 0 publications

Blockade of PGHS-2 inhibits the hypothalamus-pituitary-adrenal axis response to cerebral hypoperfusion in the sheep fetus

Blockade of PGHS-2 inhibits the hypothalamus-pituitary-adrenal axis response to cerebral hypoperfusion in the sheep fetus

Development and Significance of a Fetal Electrocardiogram Recorded by Signal-Averaged High-Amplification Electrocardiography

Mild chronic hypoxemia modifies expression of brain stem angiotensin peptide receptors and reflex responses in fetal sheep

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