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Background: Limb electrodes for the 12 lead ECG are routinely placed on the torso during exercise stress testing or when limbs are clinically inaccessible. It is unclear whether such electrode modification produces ECG changes in healthy male or female subjects that are clinically important according to the 2009 AHA, ACCF, HRS guidelines. We therefore measured whether ECG modification produced clinically important or false positive ECG changes e.g., appearance of Q waves in leads V(1-3), ST changes greater than 0.1 mV, T wave changes greater than 0.5 mV (frontal plane) or 1 mV (transverse plane), QRS axis shifts or alterations to QTc/P-R/QRS intervals., Methods: The 12 lead ECG was measured in 18 healthy and semi-recumbent subjects using the standard and Takuma modified limb placements., Results: In the frontal plane we demonstrate that the modification of limb electrode placement produces small Q, R and T wave amplitude and QRS axis changes that are statistically but not clinically significant. In the transverse plane it produces no statistically or clinically significant changes in the ECG or in ST segment morphology, P-R, QRS or QTc intervals., Conclusions: We provide better and more robust evidence that routine modification of limb electrode placement produces only minor changes to the ECG waveform in healthy subjects. These are not clinically significant according to the 2009 guidelines and thus have no effect on the clinical specificity of the 12 lead ECG., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)

Objective: The etiology of oligohydramnios-related pulmonary hypoplasia is not understood but is known to involve chronic lung liquid loss. We tested the hypothesis that low amniotic pressure in oligohydramnios disturbs the normal tracheal-amniotic pressure gradient to increase lung liquid loss and impair lung development., Study Design: Chronic pharyngeal catheterization with drainage to the exterior was used in 15 fetal sheep to mimic reduced amniotic pressure at the upper airway in the presence of normal amniotic fluid volume., Results: Pharyngeal pressures relative to amniotic pressures were negative in all drained fetuses (mean +/- SE -3.0 +/- 0.6 mm Hg), in contrast to positive pressures in controls (0.7 +/- 0.1 mm Hg). There was no significant difference in lung weight or deoxyribonucleic acid relative to body weight, or in lung morphometry, between 10 fetuses drained for 10 to 21 days and their control cotwins., Conclusion: Mimicking low amniotic pressure in the upper airway by chronic fetal pharyngeal drainage does not impair lung development in fetal sheep.

To investigate the recent suggestion that fetal hypoxemia and acidemia in polyhydramnios are secondary to raised amniotic pressure, 5 to 15 L of normal saline solution was infused intraamniotically at 100 ml/min in seven ewes. Amniotic pressure increased linearly by 1.0 +/- 0.013 (mean +/- SEM) mm Hg per liter infused. Infusion of 15 L produced a mean rise in amniotic pressure of 15.2 +/- 1.2 mm Hg (p less than 0.001) but no significant change in fetal pH, PCO2, PO2, fetal heart rate, or mean arterial pressure. A similar rise in amniotic pressure and lack of change in blood gas values occurred in two control ewes infused intraperitoneally. Rupture of the membranes occurred in two of three amnioinfusions of 15 L. We conclude that acute amnioinfusion raises amniotic pressure in sheep but does not alter fetal blood gas status.

The mechanism of oligohydramnios-related pulmonary hypoplasia (PH) is not understood, but is known to involve chronic loss of lung liquid. In order to investigate the recent suggestion that fetal breathing movements are absent or diminished in oligohydramnios-related PH, we made continuous recordings of fetal breathing movements (FBM) during chronic lung drainage in tracheostomized fetal sheep. FBM remained present throughout the drainage period. There was no significant difference in the number or duration of FBM epochs in tracheostomized fetuses compared to controls, although there was a slight reduction in incidence between 126 and 133 days (P = 0.02). PH in the fetuses undergoing chronic lung liquid drainage was confirmed by significant reductions in lung weight, volume, DNA, and total airspace, and in altered maturation. This study is consistent with other data suggesting that inhibition of FBM is not the primary mechanism of oligohydramnios-related pulmonary hypoplasia.

We measured the effects of 2 minutes of vibroacoustic stimulation on the activity of unanesthetized fetal sheep in utero. We were unable to detect any changes in activity after stimulation with a model 5C electrolarynx. With more powerful stimulation using a mechanical oscillator, fetal electrocortical activity desynchronized. Fetal breathing and eye movements changed with electrocortical activity and there was an increase in nuchal muscle activity. Stimulation caused a small decrease in fetal heart rate. Responses to stimulation were not seen in four of the five fetuses with bilateral cochlear ablation. These results indicate that in fetal sheep the auditory apparatus is necessary for the detection of vibroacoustic stimuli. The difference in responsiveness of the sheep and human fetus appears to be because of a difference in central processing after detection of the stimulus.

The safety of vibroacoustic stimulation (VAS), which produces marked changes in fetal heart rate, movements and behavioural state, remains unclear. In order to determine whether VAS is associated with catecholamine release, we measured plasma noradrenaline and adrenaline in 13 appropriately grown normoxaemic fetuses between 28 and 40 weeks gestation immediately before and 60 and 75 s after VAS. Over this time interval, VAS is known to increase fetal heart rate. There was no significant change in either noradrenaline (median change = +0.06 ng/ml, P = 0.26) or adrenaline levels (median change = +0.03 ng/ml, P = 0.4). This study suggests that sympathoadrenal activation is not part of the fetal response to VAS. These findings do not support the recent suggestion that VAS may be deleterious to the fetus by provoking sudden release of catecholamines.

In intact fetal lambs near term there was a statistically significant relation between regular small uterine contractions and a change to high-voltage fetal electrocortical activity (excess above chance 15%) or arrest of breathing (excess 12%). Isocapnic hypoxia also arrested fetal breathing. After brain stem transection there was no relation between uterine contractions and the fetal electrocortical activity, but isocapnic hypoxia increased the rate and depth of fetal breathing. Similarly uterine contractions were to a small extent associated with the initiation of fetal breathing movements which continued for about as long as the contraction. We conclude that the occasional effects of uterine contractions are consistent with diminished fetal cranial oxygen supply.