SUMMARY1. Foetal breathing movements, electrocortical activity, arterial pressure and heart rate were recorded continuously in chronically catheterized sheep, 97-145 days pregnant.2. With increasing gestational age there was a fall in heart rate of 0*67 beats/day and a rise in arterial pressure of 0-46 mmHg/day.3. Hypoxaemia in the foetus was induced by allowing the ewe to breathe low oxygen mixtures, 9 % 02 with 3 % CO2 in N2. In the younger foetuses there was an initial rise in heart rate whereas in the older foetuses there was a fall. After the end of hypoxia there was a persistent tachycardia in both groups. In the older foetuses there was a rise of arterial pressure. 4. Two vagotomized older foetuses showed cardiovascular responses similar to those of the younger foetuses.5. Foetal breathing movements were abolished by hypoxaemia in twenty-two of twenty-five experiments. In the three exceptional experiments there was a small rise in Pa co2 6. The proportion of time occupied by low voltage electrocortical activity in the foetus was reduced by hypoxaemia.7. Hypercapnia was induced by giving the ewe 4-6 % CO2 with 18 % 02 in N2 to breathe. After an initial slight fall the foetal heart rate increased and there was a small rise in foetal arterial pressure.8. The proportion of time occupied by low voltage electrocortical activity and breathing movements was increased by hypercapnia.9. Maternal hyperoxia, induced by giving 50 % 02 in N2, did not significantly increase foetal breathing movements unless the ewe was in labour. In labour the foetuses had lower Pa 02 values initially and a reduced incidence of foetal breathing, both of which were increased by maternal hyperoxia.

N umerous pathologic states are characterized by altered vascularity (number of blood vessels per unit tissue volume) or perfusion (expressed as volume blood flow [in milliliters per second] per unit tissue mass [in milliliters per kilogram per second]). No easily available clinical tool exists for quantification of tissue or organ blood flow and perfusion.Perfusion estimation with use of near-infrared spectroscopy, MRI, or CT has been attempted, but there are several challenges for clinical adoption. Near-infrared spectroscopy provides no visual display to indicate the anatomic site where tissue oxygenation is being measured. MRI allows imaging but is inherently expensive, temporally and spatially limited, and dependent on the type of sequence used (arterial spin labeling or blood oxygenation level-dependent). CT requires ionizing radiation and a tracer. US would therefore be an obvious candidate for noninvasive volumetric perfusion imaging that can be performed in most clinical settings. With a validated method, the ability to understand where organ perfusion has changed versus absolute measurements (against a known reference range), or as relative measurements (eg, in response to therapy or surgery, including transplantation), would be valuable for detecting perfusion changes and determining their severity and lead to earlier interventions. These would have obvious applications in emergency care, transplantation, and oncology, where estimation of perfusion would be a useful additional diagnostic tool.Power Doppler US has advantages for flow quantification because of its ability to depict low-velocity signals and multidirectional flow and its lack of aliasing (1). Sources of error include signal attenuation due to depth and patient habitus and tissue inhomogeneity, which reduces the possibility for comparison over time or between patients. To compensate, a technique called

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Objectives Three-dimensional (3D) umbilical cord blood volume flow measurement with the intention of providing a straightforward, consistent, and accurate method that overcomes the limitations associated with traditional pulsed-wave Doppler flow measurement and provides a means by which to recognize and manage at-risk pregnancies. Methods The first study involved 3D ultrasound volume flow measurements in seven healthy ewes whose pregnancies ranged from 18 to 19 weeks’ gestation (7 singletons). Sonographic umbilical arterial and venous flow measurements from each fetus were compared to the corresponding average measured arterial/venous flow to assess feasibility of measurement in a static vessel. A second complementary study involved 3D ultrasound volume flow measurements in seven healthy women whose pregnancies ranged from 17.9 to 36.3 weeks’ gestation (6 singletons, 1 twin). Umbilical venous flow measurements were compared to similar flow measurements reported in the literature. Pregnancy outcomes were abstracted from the medical records of the recruited patients. Results In the fetal sheep model, arterial/venous flow comparisons yielded errors of 10% or less for eight out of the nine measurements. In the clinical study, venous flow measurements showed agreement with the literature over a range of gestational ages. Two of the seven patients in the clinical study demonstrated lower flow than anticipated for gestational age; one was subsequently diagnosed with intrauterine growth restriction and the other with preeclampsia. Conclusions Accurate measurements of umbilical blood volume flow can be performed with relative ease in both the sheep model and in humans using the proposed 3D ultrasound flow measurement technique. Results encourage further development of the method as a means for diagnosis and identification of at-risk pregnancies.

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