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Biomedical subjects

M C Rogers

Publications and source records attributed to M C Rogers.

At least 55 records · Page 3Linked to original sources
PubMed1986

Organ blood flow during high-frequency ventilation at low and high airway pressure in dogs.

Using the radiolabeled microsphere technique, the authors studied hemodynamic variables and regional blood flow to multiple peripheral organs during conventional positive-pressure ventilation (CV) and high-frequency ventilation (HFV) at low and high mean airway pressure (Paw). Twenty supine anesthetized, paralyzed dogs were ventilated using CV (14-16 breaths/min) and HFV (rate = 10 Hz) in random order. In the first group (low Paw, n = 10), Paw was maintained at 3 cmH2O during CV and HFV. In the second group (high Paw, n = 10), Paw was increased to 13 cmH2O during CV and HFV. Pulmonary capillary wedge pressure and right atrial pressure remained constant during low and high Paw trials. No differences in heart rate, systemic arterial pressure, intracranial pressure, or cardiac output were noted during CV and HFV within the low and high Paw groups. In addition, blood flow to multiple peripheral organs during CV and HFV remained constant within each Paw group, except for a small decrease in cerebellar blood flow during HFV at high Paw trials showed a significant decrease in hepatic arterial and outer kidney cortical flow at high Paw. Total cerebral blood flow was decreased at high Paw, as were regional flows to diencephalon, midbrain, pons, medulla, and cerebellum. However, these differences were not attributable to differences in cerebral perfusion pressure or intracranial pressure, and cerebral oxygen delivery was not different between high Paw and low Paw groups. It is concluded that under conditions of similar Paw in anesthetized dogs, HFV does not significantly alter hemodynamic patterns or regional circulation relative to CV.

Airway Resistance↗
PubMed1986

A comparison of nitroglycerin and nitroprusside for inducing hypotension in children: a double-blind study.

Intravenous nitroglycerin (NTG) and sodium nitroprusside (SNP) were compared as hypotensive agents in anesthetized children and adolescents. The drugs were studied in a prospective, randomized, double-blind fashion in 14 patients anesthetized with nitrous oxide: oxygen, morphine, and thiopental. NTG in doses as high as 40 micrograms X kg-1 X min-1 was ineffective at decreasing mean arterial pressure (MAP) below 55 mmHg or causing a decrease in MAP greater than one-third of baseline values. SNP was uniformly successful at inducing hypotension in all patients, including those patients in whom NTG failed. The dose of SNP required to induce hypotension was 6-8 micrograms X kg-1 X min-1. Both NTG and SNP decreased systemic vascular resistance, although SNP did so to a much greater degree than NTG (64% vs. 29%; P less than 0.01). Only SNP increased cardiac index significantly (2.27 +/- 0.35 to 4.44 +/- 1.36; P less than 0.003). Both drugs reflexly increased heart rate, necessitating the use of intravenous propranolol (range from 1 to 3 mg) in all patients. Both drugs produced small decreases in arterial oxygen tension and increases in the average alveolar-arterial oxygen tension gradient (SNP, 44 +/- 13 vs. NTG, 41 +/- 6). SNP use was associated with a slight metabolic acidosis (pH = 7.38 +/- 0.01; base excess [BE] = -6 +/- 1). Neither drug produced any other untoward reaction. SNP appears to be the agent of choice for the reliable and sustained induction of deliberate hypotension in children and adolescents.

Adolescent↗
PubMed1986

Effect of epinephrine on cerebral and myocardial perfusion in an infant animal preparation of cardiopulmonary resuscitation.

We assessed the efficacy of conventional cardiopulmonary resuscitation (CPR) in 2-week-old piglets. We determined intrathoracic vascular pressures, cerebral (CBF) and myocardial blood flows (MBF), and cerebral oxygen uptake during conventional CPR in this infant animal preparation and contrasted these results with those of previous work on adult animals. We further examined the effects of the infusion of epinephrine on these pressures and flows and on cerebral oxygen uptake, which has not been previously evaluated in adult preparations. Conventional CPR was performed on pentobarbital-anesthetized piglets with a 20% sternal displacement with the use of a pneumatic piston compressor. Chest recoil was incomplete, leading to an 18% to 27% reduction in anteroposterior diameter during the relaxation phase. Aortic and right atrial pressures in excess of 80 mm Hg were generated. These pressures are greater than those generally obtained in adult animals with similar percent pulsatile displacements. CBF and MBF were also initially greater than those reported in adult animals undergoing conventional CPR. However, when CPR was prolonged beyond 20 min, aortic pressure fell and CBF and MBF declined to the near-zero levels seen in adult preparations. At 5 min of CPR, CBF and MBF were 24 +/- 7 and 27 +/- 7 ml . min-1 x 100 g-1 (50% and 17% of the values during cardiac arrest), respectively. With the continuous infusion of epinephrine (4 micrograms/kg/min) in another group of animals, MBF was significantly greater at 20 min of CPR and CBF and cerebral O2 uptake were greater at 35 min of CPR as a result of higher perfusion pressures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Current concepts in brain resuscitation.

In spite of the tremendous amount of effort and money put forth to reduce morbidity and mortality associated with global cerebral ischemia, the outlook for patients suffering an ischemic insult remains dismal. The lack of a sufficient substrate supply during the period of ischemia as well as the production of toxic metabolites in response to ischemia have been incriminated as key factors causing brain damage. As discussed in this article, modes of therapy have included efforts to minimize the duration of ischemia (eg, effective cardiopulmonary resuscitation, hemodilution, heparinization, calcium antagonists) and decrease the production of toxic metabolites (eg, barbiturates, calcium antagonists). Although the barbiturates have also been proposed to decrease the metabolic needs during ischemia, they have no therapeutic value for global cerebral ischemia. The initial evaluation of the calcium antagonists has been more promising.

Animals↗
PubMed1985

Beneficial effect of epinephrine infusion on cerebral and myocardial blood flows during CPR.

It is hypothesized that epinephrine improves the ability to resuscitate the heart through a mechanism thought to be related to the increase in aortic pressure. Our results with epinephrine infusion during CPR are consistent with this hypothesis. Epinephrine selectively increased vascular resistance in noncerebral, noncoronary vascular beds, as indicated by a decrease in microsphere-determined blood flow in these areas. This increased vascular resistance raised aortic pressure during the chest compression phase and the relaxation phase of CPR. Because intracranial and right atrial pressures were only slightly higher with epinephrine, cerebral and myocardial perfusion pressures and blood flows were significantly improved. This beneficial effect (compared to no administration of a vasopressor) was more pronounced as CPR progressed beyond ten minutes. Enhanced cerebral and myocardial perfusion occurred with epinephrine when either the conventional or simultaneous compression and ventilation (SCV) mode of CPR was employed in dogs. Similar selective perfusion was sustained for 50 minutes of SCV-CPR with epinephrine, even when the onset of CPR was delayed five minutes. Regional brain blood flow differed in the delayed-CPR group in that cerebellum, brain stem, and thalamic regions initially had higher blood flows. In an infant animal model of CPR using conventional CPR in piglets, epinephrine also was found to increase cerebral and myocardial blood flows. These results show that administration of epinephrine benefits different age groups of different species with different modes of CPR; that benefits occur even with delayed onset of CPR which is associated with additional anoxia and acidosis; and that epinephrine administration is particularly effective in sustaining cerebral and coronary perfusion during prolonged CPR.

Aging↗
PubMed1985

Effect of intra-alveolar meconium on pulmonary surface tension properties.

To evaluate the effect of meconium on pulmonary surface tension properties, the mechanics of 30 excised, separated canine pulmonary lobes were studied. Meconia were blended in normal saline to produce solutions of 10% and 20%. Solutions were filtered to remove large particles and instilled endobronchially into the canine lobes. The static pressure-volume deflation curve of each lobe was determined before and 4 h after instillation of either normal saline or meconium solution. In the saline control group (eight lobes), the curve was essentially unchanged before and after instillation. In the 10% meconium group (14 lobes), the curve was significantly depressed after instillation, especially at a transpulmonary airway pressure of 10 cm H2O (p less than .05) and 5 cm H2O (p less than .005). In the 20% meconium group (eight lobes), the depression of the pressure-volume curve was essentially the same as that of the 10% solution group. It is concluded that meconium depresses the surface-active properties of the alveolar linings.

Animals↗
PubMed1985

Arterial blood gas derived variables as estimates of intrapulmonary shunt in critically ill children.

Oxygen transport data, prospectively collected from 52 critically ill children, were analyzed to determine whether any derived variable accurately estimated intrapulmonary shunt (Qsp/Qt). Arterial hemoglobin saturation was more closely correlated with Qsp/Qt than was PaO2, alveolar-arterial oxygen gradient, arterial mixed venous oxygen difference (C[a-v]O2), arterial/alveolar oxygen ratio, and the ratio of PaO2 to inspired oxygen (FIO2) (r = 0.8, p less than .0001). When C(a-v)O2 was normal, hemoglobin saturation became a very accurate (r = 0.96) assessment of Qsp/Qt. We conclude that various arterial blood gas derived variables do not accurately reflect Qsp/Qt in critically ill children. In these patients, a pulmonary artery catheter is needed to accurately assess intrapulmonary shunt.

Child↗
PubMed1985

Cerebrovascular hypoxic and autoregulatory responses during reduced brain metabolism.

The effect of reducing cerebral oxygen consumption (CMRO2) on the cerebral blood flow (CBF) responses to isocapnic hypoxic hypoxia and hypotension was examined in sheep. Newborn and adult animals were studied because of their different base-line CMRO2. Microsphere-measured CBF responses during pentobarbital coma (i.e., electroencephalographic silence) were compared with responses in conscious or lightly sedated animals. Induction of barbiturate coma reduced both CMRO2 and CBF by 50% from the awake value and by 25% from the value obtained in animals sedated with pentobarbital. The CBF response to 30 and 50% reductions in arterial O2 content (CaO2) was attenuated during coma, but only in proportion to the decrease in CMRO2. Whether CMRO2 was normal or reduced, the normoxic cerebral O2 delivery (CaO2 X CBF) was maintained during hypoxia in both newborns and adults. The relative autoregulatory index (fractional change in CBF divided by fractional change in perfusion pressure) was determined during graded hemorrhage. The index was not significantly different from zero (which represents perfect autoregulation) in awake, lightly sedated, or comatose animals. The data demonstrate that both base-line CBF and responses to hypoxia are closely tied to CMRO2 and that 50% reduction of CMRO2 does not impair cerebrovascular autoregulation.

Animals↗
PubMed1985

Effect of abdominal distension on central and regional hemodynamics in neonatal lambs.

Elevations of intraabdominal pressure (IAP) can occur during surgical repair of gastroschisis and omphalocele and lead to ischemia of abdominal organs. We examined the effect of elevated IAP on central hemodynamics and regional abdominal organ blood flow, measured by radiolabeled microspheres, in 11 pentobarbital-anesthetized neonatal lambs. Stepwise increases in IAP were obtained by inflating a large bag placed intraperitoneally with air to pressures of 15, 20, and 25 mm Hg. Measurements were made at 30 min of elevated IAP and 30 min after deflating the bag. Mean aortic pressure was not significantly altered at an IAP of 15 mm Hg (78 +/- 4 mm HG) (+/- SE) or 20 mm HG (76 +/- 4 mm Hg) compared to baseline (81 +/- 4 mm Hg), but was decreased at the highest IAP (68 +/- 5 mm Hg). Stepwise decreases in blood flow to all abdominal organs, except adrenal gland, occurred with elevated IAP, and blood flows to these organs (except spleen) returned to or above baseline on bag deflation. At IAP of 15, 20, and 25 mm Hg, cardiac output was reduced by 14, 21, and 35%, respectively. Similar percent reductions of renal blood flow occurred. However, regional gastrointestinal blood flow decreased by a greater extent (35, 50, and 54% at each respective IAP). Hepatic arterial blood flow more than doubled at each IAP, but this was not sufficient to maintain total liver blood flow, or presumably total oxygen delivery to liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗
PubMed1985

Cerebral blood flow measurement techniques in infants and children.

The tremendous growth of interest in neurologic intensive care and in the pathophysiology of the cerebral circulation in the past few years has resulted in increasing numbers of studies that document alterations in cerebral flow during the course of various diseases or as a response to treatment of them. Before pediatricians come to conclusions based on these studies, it is important to have an understanding of the techniques involved. The techniques are complex and difficult but are based on understandable principles. They also have limitations and are subject to misinterpretations. Pediatricians should become knowledgeable about some of these techniques and their limitations because it is likely that they will be applied with increasing frequency in the next several years. We are on the threshold of exciting discoveries in abnormalities of cerebral blood flow and cerebral metabolism not only in critically ill children but also in children with congenital and learning disorders.

Adolescent↗
PubMed1985

Hemodynamic responses in brain dead organ donor patients.

Because we have noticed dramatic hemodynamic responses in brain dead patients undergoing surgery for organ donation, we analyzed the anesthetic records of cadaver organ donors. Ten records contain complete data for heart rate, blood pressure, central venous pressure, and time of incision. Systolic pressure increased by a mean of 31 torr (P less than 0.01), diastolic pressure by 16 torr (P less than 0.02), and heart rate by 23 beats/min (P less than 0.01) in response to surgical stimulation. These results demonstrate the occurrence of significant hemodynamic responses to surgical stimuli in patients who fulfill the criteria of brain death, responses that do not, however, invalidate the current criteria for the diagnosis of brain death.

Adult↗
PubMed1985

Cerebral vascular diseases.

Strokes remain an important cause of mortality and morbidity despite recent advances in neurologic intensive care. Although support of ventilation and circulation improves the outcome for stroke patients, the efficacy of cerebral resuscitative measures such as hyperventilation, osmotherapy, fluid restriction, steroids, intracranial pressure control, and barbiturates remains unproven. Current specific therapies (anticoagulation, surgery) are useful in carefully selected patients. New therapies now being researched include fluorocarbons, narcotic antagonists, and calcium blockers.

Cerebral Hemorrhage↗
PubMed1985

Effect of mefenidil on cerebral and peripheral hemodynamics in dogs.

Mefenidil (5-methyl-2-phenyl-4-imidazole-acetonitrile) has been reported to be a selective cerebral vasodilator. We examined the specificity of this vasodilator by using the radiolabeled microsphere technique to compare changes in cerebral blood flow (CBF) with those in other organs. Measurements were made in pentobarbital-anesthetized dogs at 10 min of continuous i.v. infusion of mefenidil at rates of 0.025, 0.25 and 2.5 mg/min/kg. Systemic vascular resistance decreased at 0.25 mg/min/kg without a change in CBF. At the highest infusion rate, CBF increased by 54 +/- 15% (+/- S.E.; n = 9) accompanied by a 9-mm Hg rise in intracranial pressure and a 14-mm Hg fall in mean aortic pressure. However, cardiac output increased by 68 +/- 8%, which was distributed primarily to right ventricle (541 +/- 95%), left ventricle (488 +/- 109%), small intestine (136 +/- 31%) and large intestine (57 +/- 15%). Within the brain, thalamic and brainstem regions had larger increases in blood flow than cerebellum and cerebrum. Caudate nucleus had a greater percentage of response than white matter. Using the cerebral venous outflow technique in another series of seven dogs, mefenidil (40-mg/kg i.v. bolus) produced a 20 +/- 8% increase in CBF with no change in O2 uptake. These data show that mefenidil is capable of increasing CBF in healthy brain without stimulating O2 uptake. However, the clinical usefulness of mefenidil as a cerebral vasodilator may be limited by the accompanying arterial hypotension due to systemic vasodilation, which was most prominent in heart and gut.

Animals↗