Blood flow and oxygen consumption in skeletal muscle during sympathetic stimulation

We studied the effects of physiological rates (0-4 Hz) of sympathetic stimulation on blood flow and oxygen consumption of extensor digitorum longus muscles isolated from anesthetized dogs. Observations were made with the preparation at rest and during isometric twitch exercise at 1 and 4 Hz produced by somatic nerve stimulation. Graded increases in sympathetic stimulation rate resulted in graded and sustained reductions in muscle blood flow in all cases. A given rate of sympathetic stimulation reduced muscle blood flow by nearly the same absolute amount regardless of muscle exercise rate. Consequently the curve relating muscle blood flow to muscle oxygen consumption was progressively shifted downward in a parallel fashion with graded increases in sympathetic stimulation rate. Sympathetic stimulation at 0.5 and 1 Hz reduced muscle oxygen consumption during 4-Hz exercise but failed to do so during rest or 1-Hz exercise. Thus even during heavy exercise, local metabolic mechanisms do not override sympathetic vasoconstriction sufficiently to prevent the latter from limiting muscle oxygen consumption. In addition, the functional consequences of sympathetic activation appear to be greater for heavily exercising muscle than resting muscle.     

Blood flow rate, temperature, oxygen tension and consumption in the skin of adults measured by a heated microcathode oxygen electrode

Reliable transcutaneous measurements of arterial oxygen tension are based on a maximum skin blood flow rate which is created by heating the skin, typically at an electrode temperature of 44 to 45 degrees C. This increase in skin blood flow rate creates an arterialization of the oxygen tension in the capillaries and the surrounding tissue. The heat conducted to the skin surface is removed by a combination of convection (skin perfusion) and conduction to the deeper layers of the skin. This heat transport to and through the skin surface causes a measurable temperature profile from the electrode surface to the capillary layer. By a blood flow cessation it is possible to change the temperature profile because the convective part of the heat consumption is eliminated and the conductive part can then be measured and subtracted. Using the forearm as measuring area and a heated tc-PO2 electrode several observations were made. The mean temperature gradient over epidermis down to the capillary layer at an electrode temperature of 43, 44, and 45 degrees C was 2.1, 2.4 and 2.7 degrees C, respectively. The change in temperature profile caused by the blood flow cessation enabled primarily an estimation of the skin blood flow rate by temperature measurements, ranging from 0.07 to 0.24 ml.cm-2.min-1. Increasing blood flow rates correlated to increasing tc-PO2 values. By means of a dynamically, thermally shielded tc-PO2 electrode it was possible to determine the skin blood flow rates in the same arbitrary units computed on the basis of the heat dissipation to the skin surface. Furthermore, it was possible to correlate these blood flow estimations to the cutaneous blood flow rates measured by 133Xe washout technique. By increasing the electrode temperature the cutaneous blood flow rates increased from 12 to 50 ml.(100 g)-1.min-1. It was possible to calculate a conversion factor on the basis of the correlation between the heat determinations of the skin blood flow rate and the 133Xe measurements. Using this conversion factor the highest blood flow rate did not exceed 55 ml.(100 g)-1.min-1. The subcutaneous blood flow rate increased accordingly with increasing electrode temperature. It was concluded that the measured heat consumption of the skin is effected by the heat removing capacity of the cutaneous as well as the subcutaneous blood flow. The cutaneous blood flow, however, was considered predominant in the transport of heat from the skin surface. By 50 times of stripping the skin surface, the cornified epidermal membrane was removed. This procedure increased the tc-PO2 values by on an average 3.6 kPa (27.1 mmHg).(ABSTRACT TRUNCATED AT 400 WORDS)     

Blood flow and oxygen uptake in mammals

Data on the variation of blood flow and oxygen uptake with weightW are reex-amined for mammals at rest. It is concluded that blood flow varies asW ^0.85, while oxygen uptake varies asW ^0.79. The suggestion is made that oxygen uptake for small mammals is often reported with values higher than that given by the above relation, whereas their sleeping consumption is likely appreciably less, i.e., these animals, by their CV and nervous system design, are excitable or “jittery”. In a steady state range of sustainable activity, near universal weight specific blood flow oxygen uptake curves are estimated for mammals of all weights, for the range of states from sleep to peak sustained aerobic activity. It is hoped that these data provide an acceptable experimental data base for study of the design characteristics of tissue perfusion and oxygen transport in the average mammalian microvasculature. This work was carried on under contract with the Army Research Office. That support is gratefully acknowledged.     

Torsion of the pregnant uterus

A 31-year-old woman, with a history of previous cesarean section and right oophorectomy, was admitted for a repeat cesarean section. After the commencement of surgery uterine torsion was diagnosed because of the anterior position of the remaining left ovary and tube, the absence of normal uterovesical peritoneum, and extremely engorged vessels in the lower uterine surface. Posterior classical hysterotomy was performed and a healthy female baby was delivered. Following delivery of the baby and suturing the incision site of the uterus, the contracted uterus was detorted and put back in the pelvic cavity. Extreme uterine torsion of 180 degrees at term is a rare obstetric event. This paper presents a case of uterine torsion at full term pregnancy in which the delivery and repositioning of the uterus was successful.     

Major and collateral components of blood flow to pregnant sheep uterus.

In vivo measurements of vessel diameter, latex injections, and acrylic-cast studies indentified the middle uterine arteries as the main source of blood supply to the pregnant sheep uterus. Collateral circulation stemmed from the dorsal uterine arteries, and the ovarian arteries, and small cervical branches derived from the external iliac arteries (in decreasing order of importance). These morphological observations were related to estimates of collateral flow obtained during isolated, in situ perfusion of the pregnant sheep uterus carried out through the cannulated middle uterine arteries. Collateral blood flow was estimated from the shift of the flow-pressure curve produced by inflation of a balloon catheter advanced into the aorta below the renal arteries. Middle uterine artery flow to one horn increased from 162 +/- 23 ml/min in midgestation to 323 +/- 44 ml/min near term. Collateral uterine blood flow did not change significantly: 82 +/- 15 ml/min in midterm, 74 +/- 9 ml/min near term. Collateral flow consituted a larger fraction of inflow to the horn containing the fetus in 9 of 10 single pregnancies.     

Cerebral blood flow and oxygen consumption in the newborn dog

Cerebral blood flow (CBF), CBF responses to changes in arterial CO2 tension, and cerebral metabolic rate for oxygen (CMRO2) were measured in newborn dogs, by means of a modification of the Kety and Schmidt technique employing 133Xe. Mongrel dogs of 1-7 days of age were paralyzed and passively ventilated with 70% N2O and 30% O2. CBF was derived by analysis of paired serial 20-microliter samples of arterial and of cerebral venous blood from the superior sagittal sinus. At an arterial PCO2 of 36.9 +/- 3.7 Torr and a mean arterial blood pressure of 62 +/- 10 Torr, CBF was 23 +/- 8 ml/min per 100 g. The arteriovenous oxygen content difference averaged 5.6 vol%, and CMRO2 was 1.13 +/- 0.30 ml O2/min per 100 g. CBF increased or decreased by 0.58 ml/min/100 g per Torr change in PCO2. Our results suggest that in the newborn, basal CBF and CBF responses to CO2 are considerably lower than in the adult and parallel the lower metabolic needs of the newborn brain.     

O2 delivery to the pregnant uterus: its relationship to O2 consumption.

Normal sheep were studied at intervals of 3-5 days during the last weeks of pregnancy in order to evaluate variability in rate of O2 consumption (QO2) of the uterus in relation to several variables involved in delivery of O2 to the organ. Among-animal differences of uterine QO2 were statistically significant and directly related to birthweight of the lamb. Among-animal differences of uterine blood flow (UBF) and uterine arteriovenous O2 content difference [C(a-v)O2] also were statistically significant, though neither was related to birthweight, presumably since they tended to vary inversely with one another. In a given ewe relative magnitude of UBF and of C(a-v)O2 was related to maternal arterial O2 content (CaO2), day of pregnancy, and whether the animal carried singlets or twins. Variability in QO2 was most closely related to UBF, although its relations to C(a-v)O2 and CaO2 were significant also. These data suggest there are systematic relationships among variables involved in the delivery of O2 to the uterus of pregnant sheep.