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Biomedical subjects

S R Powers

Publications and source records attributed to S R Powers.

At least 37 records · Page 2Linked to original sources
PubMed1979

Ventilation-perfusion imbalance after head trauma.

To investigate the role of ventilation-perfusion (VA/Q) imbalance in the hypoxemia observed after head injury, 5 male subjects (17 to 26 years of age) with isolated head trauma and subsequent hypoxemia were studied. Disturbances of ventilation and perfusion were assessed using the steady-state elimination of six inert gases of different solubilities. Paired studies were conducted during mechanical ventilation with a volume-cycled ventilator and during spontaneous ventilation. Distributions recovered from studies of spontaneous ventilation show a mode of ventilation and perfusion near a VA/Q of 1.0. In addition, 41% of the cardiac output was distributed to a second population of lung units with low VA/Q (less than 0.1) and shunt. During mechanical ventilation, perfusion to these regions of low VA/Q decreased to 21% of the cardiac output, whereas shunt fraction was unchanged. This was associated with a marked broadening of the VA/Q mode near 1.0, relative to the studies during spontaneous ventilation. Mean functional residual capacity during mechanical ventilation was not different from that during spontaneous ventilation. These results suggest that head injury can lead to hypoxemia through a failure of VA/Q regulatory mechanisms.

Adolescent↗
PubMed1979

Evaluation of glucocorticoids during resuscitation of injured patients.

This study evaluates the effects of 30 mg/kg methylprednisolone (MP) administered to eight trauma patient over a 30-minute period during initial resuscitation. Vascular pressures, cardiac index (CI), left ventricular stroke work index (LVSWI), systemic (SVR) and pulmonary (PVR) vascular resistance, oxygen delivery (OD), oxygen consumption (VO2), physiological shunt (shunt), limb blood flow (LBF), limb-oxygen delivery (LOD), and limb oxygen consumption (VLO2) were calculated at control and 1, 2, 4 and 6 hours following MP administration. At 1 hour there was an increase in CI from 2.9 +/- 0.3 to 3.5 +/- 0.3 liters/min/m2 (P less than 0.01), in OD from 961 +/- 172 to 11067 +/- 148 ml/min (P less than 0.05), in VO2 from 178 +/- 16 to 220 +/- 16 ml/min (P less than 0.01), in shunt from 25 +/- 3% to 33 +/- 3% (P less than 0.05), and a decrease in SVR from 1187 +/- 98 to 1945 +/- 87, and in PVR form 222 +/- 22 to 178 +/- 18 dyne sec/cm5 (P less than 0.05). These values returned to control by 4 hours. In spite of a pulmonary wedge pressure (PWP) that did not increase form a control of 5 +/- 2 mm Hg, and a mean arterial blood pressure (MABP) that did not decrease from a control of 86 +/- 5 mm Hg, LVSWI increased significantly at 1 hour (P less than 0.01). LBF, LOD, and VLO2 decreased at 1 hour (P less than 0.05). Since increased cardiac output was associated with increased stroke volume and left ventricular stroke work index, but without an increase in preload (PWP) or a decrease in afterload (MABP), methylprednisolone(MP), in pharmacologic dosage appears to have a positive inotropic effect on the myocardium of trauma patients during resuscitation.

Adult↗
PubMed1979

Oxygen consumption in canine skeletal muscle following massive saline infusion.

To study the effect of interstitial edema on tissue oxygen transport, we infused buffered isotonic saline solution at a rate of 200 ml/kg/hr into mongrel dogs for two hours, measuring oxygen delivery and consumption in a skinned, innervated hindlimb. Hematocrit dropped gradually to 10.8 +/- 3.9%. Muscle water content increased 13% (P less than 0.05). However, oxygen consumption did not change significantly from control of 0.228 +/- 0.029 ml/min/100 gm. Femoral venous oxygen tension fell from control of 62.6 +/- 2.6 mm Hg to 31.4 +/- 2.3 mm Hg. Mean arterial flow increased to nearly twice the control level of 12.5 +/- 1.1 ml/min/100 gm and fell gradually, with the sustained 50% drop in vascular resistance largely explained by expected decreases in blood viscosity. We conclude that interstitial edema did not cause a significant defect in canine skeletal muscle oxygen utilization.

Animals↗
PubMed1979

Cardiovascular hemodynamics after opsonic alpha-2-surface binding glycoprotein therapy in injured patients.

Depression of reticuloendothelial (RE) phagocytic function has been clearly documented following trauma and operation. This phagocytic failure is mediated in part by depletion of an opsonic glycoprotein. Depletion of this opsonic protein may result in prolonged blood retention of potentially harmful particulates that may interfere with the microcirculation and may possibly result in altered organ function. Isolation and identification of this opsonic protein has led to the finding of the identity between opsonic glycoprotein and cold insoluble globulin (CIg) or so-called plasma fibronectin. Since CIg is concentrated in cryoprecipitate, this blood component was used as a readily available source of opsonic protein for replacement studies. Nine patients were studied following a 1-hour infusion of cryoprecipitate obtained from 10 units of plasma and suspended in a volume of 250 ml. Both the pulmonary shunt fraction and the fraction of dead space ventilation decreased significantly (P = 0.02) after cryoprecipitate administration. Limb blood flow (P = 0.001), limb oxygen consumption (P = 0.001), and reactive hyperemia of the limb (P = 0.05) increased significantly following cryoprecipitate infusion. Cardiac output, total oxygen consumption did not change consistently. The data demonstrate that the infusion of cryoprecipitate resulted in improved pulmonary and microcirculatory function--possibly due to opsonic glycoprotein replacement.

Cardiac Output↗
PubMed1978

Opsonic alpha2 surface binding glycoprotein therapy during sepsis.

A pronounced depletion of an opsonic protein for hepatic reticuloendothelial (RE) phagocytosis has been demonstrated in critically ill trauma patients. This opsonic alpha(2) surface binding (SB) glycoprotein has immunologic identity and a similar amino acid composition to cold insoluble globulin (CIg). Since CIg can be concentrated in cryoprecipitate, it was utilized as a readily available source of opsonic alpha(2)SB glycoprotein for replacement therapy after injury with documented hypoopsonemia. Six septic patients (2 multiple trauma, 2 thermal burn, and 2 intra-abdominal abscess) were studied to test whether cryoprecipitate infusion would restore this humoral component. Pre- and posttherapy opsonin levels were determined by bioassay and electroimmunoassay. In all patients, severe opsonin depletion was reversed following cryoprecipitate infusion. All patients had a rapid improvement in febrile state, normalization of leukocyte levels, and improvement in pulmonary function as evidenced by decreasing requirements for end expiratory pressure at lowered levels of inspired oxygen. One patient was studied more extensively and demonstrated an increase in cardiac output, limb blood flow, total body and limb oxygen delivery, total body and limb oxygen consumption and a progressive decrease in pulmonary shunt fraction. Thus, opsonic alpha(2)SB glycoprotein deficiency can be reversed by cryoprecipitate infusion in critically ill septic injured patients. Replacement of this humoral factor may be an important therapeutic modality in prevention of multiple organ failure, but it should be administered only after documentation of hypoopsonemia in traumatized patients.

Adult↗
PubMed1978

Delayed impairment of arterial blood oxygenation in patients with severe head injury: preliminary report.

A drop in the arterial PO2 occurring 24 hours after head injury was identified in eight patients. Traditional modes of therapy include administration of supplemental oxygen and provision of an unobstructed airway. The latter proved to be inadequate to continually maintain the PaO2 at a level consistent with the O2 content of the inspired air. Initially, determination of the PaO2, after institution of supplemental oxygen, may demonstrate adequate oxygenation, but blood gas monitoring should be continued since a delayed fall in arterial oxygen tension may occur 24 hours after head injury. This period of potentially deficient blood oxygenation, if severe enough, may further aggravate preexisting brain damage and profoundly affect the ultimate outcome of the patient. The delayed fall in PaO2 is the result of intrapulmonary shunting principally due to a ventilation/perfusion mismatch. The precise mechanism of the ventilation/perfusion inequality in the brain-injured patient awaits further elucidation, but may differ from the alteration in pulmonary function seen in the Respiratory Distress Syndrome.

Brain Edema↗
PubMed1977

Cardiac output and pulmonary wedge pressure. Use for evaluation of fluid replacement in trauma patients.

Cardiac output and pulmonary wedge pressure (PWP) were used to evaluate the end point of fluid resuscitation in 20 patients suffering from multiple trauma and shock. Eleven patients received crystalloid resuscitation and nine patients received colloid resuscitation. Fifteen of 20 patients had an adequate cardiac output at the termination of resuscitation, but but only six of these patients had a PWP above 10 mm Hg. There was no significant correlation between left ventricular stroke work index and PWP in these patients, either at the completion of resuscitation or during the following three days. Five patients did not achieve adequate cardiac output and four of these patients died, suggesting that cardiac output was the most important criterion for adequate resuscitation. If the goal of fluid resuscitation is to achieve an adequate cardiac output, then PWP was not a reliable guide. Furthermore, using both cardiac output and PWP as a guide to fluid resuscitation of our patients, we found that the type of fluid (crystalloid or colloid) for resuscitation did not influence the course of respiratory distress in these patients up to three days following resuscitation.

Adult↗
PubMed1977

Spontaneous hemorrhage due to pseudocysts of the pancreas.

Spontaneous hemorrhage caused by erosion of major arteries by a pseudocyst of the pancreas is a rare condition. We have encountered three cases, one involving the abdominal aorta and two the superior pancreaticoduodenal artery. It is important to keep in mind that pseudocyst of the pancreas may cause massive gastrointestinal or intraabdominal bleeding. Operative treatment offers a better chance of survival than more conservative management.

Angiography↗