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Biomedical subjects

A R Hohimer

Publications and source records attributed to A R Hohimer.

At least 55 records · Page 3Linked to original sources
PubMed1985

Effect of acute hypoglycaemia on cerebral metabolic rate in fetal sheep.

Studies were carried out in 11 fetal sheep four days after surgery for insertion of catheters and electrocortical leads. After a 3 h control period an insulin infusion was given to the ewe and maintained for the next 4 h. Fetal arterial glucose fell from 0.85 +/- 0.10 to 0.57 +/- 0.06 mM (SEM) while oxygen content was unchanged (3.80 +/- 0.24 to 3.75 +/- 0.21 mM). Cerebral uptake of oxygen and glucose were determined from samples drawn simultaneously from the axillary artery and sagittal vein and cerebral blood flow (microsphere technique). There was no significant change in uptake of either oxygen or glucose by the fetal brain. We conclude that a rapid fall in fetal glucose levels with no change in oxygen content does not result in decrease in cerebral metabolism measured over a short term.

Animals↗
PubMed1985

The effect of indomethacin on breathing movements and cerebral blood flow and metabolism in the fetal sheep.

Indomethacin, a cyclo-oxygenase inhibitor, stimulates virtually continuous breathing movements in the fetal sheep. We measured blood flow (radioactive microsphere distribution) to major brain regions and analyzed arterial and sagittal vein blood samples for oxygen and carbon dioxide tensions, pH and for oxygen contents and glucose concentrations in 13 fetal lambs between 122-132 days of gestation. The measurements were done before and again after 4 to 5 h of an indomethacin infusion. We found that indomethacin caused a mild arterial acidosis and hypoxemia and a 23 +/- 6% (SEM, P less than 0.01) decrease in blood flow to the cerebral hemispheres. Similar decreases were also observed in all other brain regions except for the cerebellum. Arteriovenous concentration differences for both oxygen and glucose widened such that there was no significant change in cerebral metabolism. Sagittal vein hydrogen ion concentration was 44.3 +/- 0.06 nmoles 1(-1) during control and rose by 4.5 +/- 1.4 nmol.1(-1) (P less than 0.01) with the indomethacin. These results are consistent with the hypothesis that one mechanism by which indomethacin augments the incidence of fetal respiratory efforts is by stimulating central chemoreceptors.

Animals↗
PubMed1984

Effect of exercise on uterine blood flow in the pregnant Pygmy goat.

Pygmy goats in the last third of pregnancy were trained to walk on a treadmill at rates up to 2.0 mph and up an inclination of 0-15 degrees. Electromagnetic flowmeters were placed unilaterally on a uterine artery, and measurements were made while the goats were standing quietly on the treadmill and during 5 min of exercise. Blood flow fell during exercise in all five animals studied, and this reduction was proportional to the level of exertion. At the highest level of exercise that these animals would voluntarily perform, uterine artery blood flow fell by 32 +/- 3 (SE) % (P less than 0.001) from control. In four additional animals the radioactive microsphere technique was used to measure uterine blood flow at rest and after 5-7 min of exercise. In these animals, exercise caused total uterine blood flow to fall by 18 +/- 10%; cotyledonary (placental) blood flow fell by 8 +/- 13%, while myoendometrial blood flow decreased by 52 +/- 12% (P less than 0.05). Thus nonplacental portions of the pregnant Pygmy goat uterus suffer major reductions in blood flow during exercise. This vasoconstriction may be due to exercise per se or to concomitant hypocapnia or hyperthermia. Singleton and twin kids born to animals that exercised were of normal birth weight.

Animals↗
PubMed1984

Hemodynamics in the guinea pig after anesthetization with ketamine/xylazine.

The resting hemodynamics were determined in 8 guinea pigs after they were anesthetized with ketamine/xylazine. Measurements were made of blood pressure, heart rate, cardiac output, arterial blood gases, and pH. These measurements were obtained initially at 4 to 5 hours after an injection (IM) of ketamine HCl (25 mg) and xylazine (0.15 mg) was given to anesthetize the animals for catheterization (period 1), again 5 days after the operation (period 2), and finally 4 to 5 hours after a 2nd injection of ketamine/xylazine (period 3). There were no differences in heart rates, respiratory rates, or cardiac outputs among the 3 study periods. However, arterial blood pressure was slightly, but significantly, lowered after, and presumably due to, instrumentation (62 +/- 4 mm of Hg, P less than 0.05) when compared with the 5-day postoperative period (67 +/- 7 mm of Hg) or after the readministration of anesthetics (66 +/- 7 mm of Hg). The partial pressure of carbon dioxide in the arterial blood was slightly lower (4 mm of Hg, P less than 0.05) in both acutely postanesthetic periods (period 1 and period 3) than in the same animals at postoperative day 5 (period 2). This study has demonstrated that resting hemodynamics measured shortly after this anesthesia with ketamine/xylazine are not largely different from those in chronically instrumented animals.

Anesthesia, General↗
PubMed1983

The effect of induced maternal hypercapnia on gross fetal body movements.

Gross fetal body movements and fetal heart rate were studied serially during the last trimester of pregnancy by real-time ultrasound in 11 healthy women during the inhalation of 4% carbon dioxide in air. We observed that induction of maternal hypercapnia during the last 10 weeks of pregnancy had no effect on the percentage of time of gross fetal body movements or on fetal heart rate accelerations.

Carbon Dioxide↗
PubMed1983

Cerebral blood flow and metabolism during morphine-induced stimulation of breathing movements in fetal lambs.

Brain blood flow increased in the fetal lamb during morphine-induced stimulation of breathing. The increase in flow was 60% in the cerebral hemispheres and the cerebellum, and 100% in the midbrain plus rhinencephalon, pons, medulla and cervical spinal cord. Oxygen content of arterial blood decreased in all experiments and the arterial carbon dioxide tension increased in all but one of the experiments. The increase in cerebral blood flow observed is predicted by the changes in arterial oxygen content and carbon dioxide tension. Cerebral oxygen consumption and glucose utilization were not changed by morphine treatment. These results suggest that there is no direct effect of morphine upon cerebral blood flow and metabolism in the fetal lamb during morphine-stimulated breathing.

Animals↗
PubMed1983

Progesterone-induced hyperventilation in the guinea pig.

Progesterone-induced hyperventilation has thus far not been reported in animals other than humans. Accordingly we investigated the effects of chronic progesterone treatment on ventilation in guinea pigs. Virgin female guinea pigs were divided into those treated with cholesterol as controls (C), progesterone (P), or estrogen plus progesterone (E&P). All hormones were administered in silastic capsules placed subcutaneously for 28 days. On day 28 arterial blood gases and respiratory rates were determined. Arterial pH was elevated in P- and E&P-treated animals compared with controls (7.43 +/- 0.04 and 7.43 +/- 0.03 vs 7.39 +/- 0.05, respectively, P less than 0.05). Arterial PCO2 was reduced in both progesterone-treated groups compared to controls (33.9 +/- 5.8 (P), 33.1 +/- 2.8 (E&P), 38.0 +/- 4.3 (C)), and was correlated with systemic progesterone concentrations in animals receiving E&P (r = -0.85, P less than 0.01) but not in animals receiving P alone (r = -0.07, P = N.S.). Arterial [HCO-3], PO2 and respiratory rates were not different between groups. We conclude that chronic progesterone administration produces hyperventilation in guinea pigs, and that estrogen facilitates this action of progesterone.

Animal Diseases↗
PubMed1983

Central chemical regulation of breathing movements in fetal lambs.

In 12 chronically prepared fetal lambs between 126 and 136 days of gestation, 17 ventriculocisternal perfusions (123 microliter/min) were performed. The concentration of bicarbonate ([HCO3-]) in the mock cerebrospinal fluid (CSF) perfusate was altered to manipulate the [HCO3-] in the cerebral ventricles. These perfusions did not systematically alter fetal arterial PCO2, PO2, pH, heart rate or mean blood pressure. Fetal breathing movements (FBM) were noted as rhythmic negative intrathoracic pressures with reference to amniotic fluid pressure. The incidence of FBM was determined and expressed as the percent of the 3 h observation period during which breathing movements were present. Perfusions with mock CSF having an approximately normal [HCO3-], resulted in cisternal [HCO3-] of 23.9 +/- 0.8 (SEM) meq/L and an incidence of fetal breathing movements (FBM) of 22.1 +/- 10.0%. Perfusions with an elevated [HCO3-] in the mock CSF increased the cisternal [HCO3-] to 30.7 +/- 0.4 meq/L and lowered the incidence of FBM to 0.6 +/- 0.2%. Perfusions with a lowered [HCO3-] mock CSF decreased the cisternal [HCO3-] to 17.3 +/- 0.8 meq/L and increased the incidence of FBM to 45.7 +/- 6.8%. These perfusions did not alter the relative incidence of low voltage (LV) versus high voltage (HV) electrocortical (ECOG) state. In 4 animals, low [HCO3-] perfusions induced FBM in the normally apneic HV ECOG state. We conclude that in the near-term fetal lamb, central chemoreceptors can modulate the incidence of rhythmic respiratory efforts, that tonic afferent stimuli arising from these receptors are critical for the generation of spontaneous FBMs and that central acidosis is capable of evoking FBMs in the normally apneic HV ECOG state.

Animals↗
PubMed1983

Cerebral metabolism in hypoglycemic and hyperglycemic fetal lambs.

To investigate the mechanism whereby glucose affects fetal breathing movements (FBM), cerebral metabolism was studied in 12 unanesthetized fetal lambs, during fasting-induced hypoglycemia and after a subsequent fetal infusion of glucose. Preductal arterial and sagittal sinus blood samples were analyzed for glucose and oxygen concentrations and for blood gases and pH. Measurements of regional brain blood flow were made with radioactive microspheres. Maternal fasting of 24- to 36-h duration resulted in a decrease in fetal blood glucose from 1.061 +/- 0.085 mmol X l-1 to 0.664 +/- 0.053 (P less than 0.001). Although cerebral glucose and O2 uptake remained unchanged, sagittal sinus CO2 partial pressure (Pco2) and [H+] were significantly decreased and may have contributed to the observed decrease in FBM. A 2-h infusion of glucose to the fetuses of fasted animals resulted in an increase in blood glucose to 2.452 +/- 0.173 mmol X l-1. Cerebral O2 consumption was again unchanged; however, cerebral glucose consumption was significantly increased as were sagittal sinus Pco2 and [H+], which may have contributed to the observed increase in FBM. These findings are consistent with the hypothesis that glucose affects the incidence of FBM in part by altering the environment of central chemoreceptors.

Animals↗
PubMed1983

Regional distribution of blood flow during mild dynamic leg exercise in the baboon.

Five chair-restrained baboons were trained with operant techniques and a food reward to perform dynamic leg exercise. Cardiac output and blood flows to most tissues were determined by radioactive microsphere distribution. After 2 min of exercise mean arterial blood pressure had increased by 11 +/- 3% (SE), heart rate by 34 +/- 7%, cardiac output by 50 +/- 12%, and O2 consumption by 157 +/- 17%. The blood flow to exercising leg muscle increased by 585 +/- 338% and to the myocardium by 35 +/- 19%. Blood flow to torso and limb skin fell by 38 +/- 4 and 38 +/- 6%, respectively, and similar reductions occurred in adipose tissue blood flow. Nonworking skeletal muscle blood flow decreased by 30 +/- 10%. Renal blood flow was lowered by 16 +/-2%. The lower visceral organs had more variable responses, but when grouped together total splanchnic blood flow fell by 21 +/- 9%. Blood flow to the brain was unchanged with exercise, whereas spinal cord perfusion increased 23 +/- 3%. Thus during short dynamic exercise baboons redistributed blood flow away from skin, fat, nonworking muscles, and visceral organs to supply the needs of exercising muscles. Our data suggest the baboon is a useful animal model for investigating vascular responses of tissues, such as torso skin, adipose, individual visceral organs, and the spinal cord, that cannot be examined in humans.

Adipose Tissue↗
PubMed1982

Effects of glucose concentration on fetal breathing movements and electrocortical activity in fetal lambs.

Tracheal pressure and electrocortical activity were recorded in 10 unanesthetized fetal lambs in utero to determine the effect on fetal breathing movements (FBMs) of fasting and a subsequent infusion of glucose. The incidence of FBMs decreased significantly from 37.9% +/- 4.3% during fed control studies to 23.6% +/- 3.6% (P less than 0.05) after 24 to 36 hours of maternal fasting, with a related fall in fetal blood glucose. A 2-hour infusion of glucose to the fetuses of fasted animals resulted in a significant increase in FBMs to 39.5% +/- 4.9%, but only to a level similar to that in the fed control studies despite a twofold increase in the fetal concentration of glucose above fed control values. Changes in the incidence of FBMs paralleled the changes in fetal low-voltage electrocortical activity with alterations in glucose. In conclusion, FBM, although correlated with the concentration of glucose, may be influenced more by fetal hypoglycemia than hyperglycemia. Glucose appears to affect the incidence of FBM by altering the incidence of low-voltage electrocortical activity.

Animals↗
PubMed1981

Ventriculocisternal cerebrospinal perfusion in unanesthetized fetal lambs.

Methods have been developed for the placement of cannulas in the lateral cerebral ventricle and cisternum magnum of the fetal lamb. Three to seven days after surgery, perfusion of the cerebral ventricular system was carried out in unanesthetized lambs in utero. Artificial cerebrospinal fluid (CSF) was perfused at 123 microliter/min for 4-5 h with no change in fetal arterial O2 pressure, CO2 pressure, pH, mean arterial blood pressure, or heart rate. The preparation is suitable for measurements of net formation of fetal central CSF and also for producing changes in the ionic composition of the fetal CSF.

Animals↗
PubMed1980

Effect of oxygen and of carbon dioxide tension on the incidence of apnea in fetal lambs.

Fetal breathing movements (FBM) in unanesthetized lambs in utero were correlated with measurements of arterial blood gases. One hundred and eighty-seven observations, consisting of the incidence of FBM during the hour preceding and the hour after the blood gas determinations, were made on 125 separate days in 30 fetuses of 117 to 146 days' gestational age. Fifty-eight percent of the observations with fetal apnea (FBM 0 to 9% in 2 hours) showed hypoxia (PaO2 less than or equal to 16 torr), whereas only 4% of the observations with FBM greater than 10% were associated with hypoxia. Sevety-eight percent of the hypoxic and normocarbic (PaCO2 42 to 53 torr) observations demonstrated apnea. However, only 44% of hypoxic plus hypercarbic (PaCO2 57 to 63 torr) fetuses were apneic, and with an elevated PaCO2, apnea tended to develop at a lower level of PaO2. We conclude that FBM may persist in the presence of hypercarbia with hypoxia.

Animals↗
PubMed1980

Uterine oxygen uptake in the pregnant Pygmy goat.

The diffusion equilibrium method was used to measure uterine blood flow (Qut) and oxygen consumption (VutO2) of 7 Pygmy goats in the last third of pregnancy. VutO2 was 9.3 +/- 1.3 (mean +/- SEM) ml.min-1.kg-1 weight of the uterus and its contents: the placenta, fetus and fetal membranes. This O2 requirement was provided by a high blood flow (349 +/- 48 ml.min-1.kg-1) and a narrow arteriovenous difference (2.4 +/- 0.1 vol%) across the uterus. Maternal arterial O2 content (CaO2) was varied by incurring chronic anemia in 3 animals. CaO2 over the range 6.5 - 12.8 vol% did not affect uterine blood flow or the arteriovenous oxygen content difference across the uterus. Weight specific (ml.min-1.kg-1) VutO2 did not differ in animals whose total uterine weights varied over a wide range and uterine vein oxygen tension and content did not fall prior to delivery. We conclude that the absolute uterine blood flow varies over a wide range to meet the requirements of the uterine contents.

Animals↗
PubMed1979

Decreased renal blood flow in the baboon during mild dynamic leg exercise.

Twelve chair-restrained baboons (Papio cynocephalus) were conditioned with operant techniques and a food reward to perform 4 min of dynamic leg exercise. During the last minute of exercise, blood flow through the left renal artery, measured by an electromagnetic flow transducer, was decreased 19 +/- 2% SEM with respect to the minute of rest preceding the exercise. This response occurred within 1.5 min, was maintained throughout the exercise, and recovered to control within 2 min. Mean arterial blood pressure rose 17 +/- 2%; renal vascular resistance, 46 +/- 6%; heart rate, 42 +/- 4%; and whole-body oxygen consumption, 233 +/- 19%. Behavioral situations simulating the arousal and feeding components of the exercise task, but not requiring muscular exertion, did not alter renal blood flow. In four animals, blood flow to the contralateral but surgically denervated kidney was measured; it increased transiently at the onset of exercise, but returned to control by the last minute of work. Thus, the baboon, like man, shows a decrease in renal blood flow during exercise. This response has a rapid onset and recovery and is primarily neurally mediated.

Animals↗
PubMed1979

Effect of implant duration on in vivo sensitivity of electromagnetic flow transducers.

Twenty-three electromagnetic flow transducers with lumen diameters of 3.5-6.0 mm were implanted in rhesus monkeys and baboonss for 12 h to 120 days. Each flow transducer was calibrated 1) in vitro on dialysis tubing with saline before implantation, 2) in vivo the last day of the implant period, and 3) again in vitro after the flow transducer was recovered. Three other flow transducers were implanted on femoral arteries of baboon just central to an arteriovenous Silastic shunt, and were calibrated in vivo daily for 23-47 days. In vitro sensitivity was not affected by implant durations of up to 120 days. In vivo sensitivity fluctuated unpredictably for the first 3-4 wk of implant, after which it followed a systematic course that depended on the lumen size. In vivo sensitivity at any time during implant (after the initial period) could be accurately predicted by knowing either the in vitro sensitivity or the terminal in vivo sensitivity.

Animals↗
PubMed1979

Renal and hindlimb vascular control during acute emotion in the baboon.

Blood pressure, heart rate, oxygen consumption, and blood flow to the renal and hind-limb vasculatures were measured in healthy, unanesthetized baboons (Papio cynocephalus) in a controlled environment. Appropriate behavioral techniques were applied to allow the reproducible elicitation of a conditional emotional response (CER). Section of renal nerves and autonomic pharmacologic interventions were used to determine the mechanisms for the cardiovascular responses accompanying the CER. The resistance changes in the renal and hind-limb vascular beds were generated by rapid, neurally mediated vasoconstriction of the renal vasculature and by a slower acting, circulating vasoactive agent, most probably epinephrine, which causes a delayed second constriction in the renal bed and a net dilation in the hind limbs.

Animals↗