Biomedical subjects

C Weissman

Publications and source records attributed to C Weissman.

At least 91 records · Page 5Linked to original sources

PubMed1989

Variation in the resting metabolic rate of mechanically ventilated critically ill patients.

There has been increasing interest in the nutritional support of the critically ill patient. The day-to-day variation in resting energy expenditure (REE) was studied over a 3-5-day period in 17 postoperative mechanically ventilated critically ill patients to gain insight as to how often caloric intake should be reassessed, whether changes observed over 3-5 days are of sufficient magnitude to make frequent adjustments in caloric intake, and what factors are associated with large alterations in metabolic rate. REE was measured daily for 3-5 days, and the percent variation in REE [(highest REE--lowest daily REE)/(lowest daily REE) x 100] calculated. The variation ranged from 4 to 56%, and on further analysis two distinct groups were identified, one with a mean variation of 12 +/- 4% (SD) (range 4-18%) and the other with a mean variation of 46 +/- 8% (range 37-56%). The former group was clinically stable, whereas the latter was not. Clinically stable patients need less frequent measurements than those who are more ill, but when designing a nutritional regimen for them, at least 20-25% should be added to the REE, 15% to account for day-to-day variation and 5-10% for activity.

Adolescent↗

PubMed1988

Azathioprine's inhibitory effect on prostaglandin E2 production is not via cyclooxygenase inhibition.

Azathioprine, a widely used antimetabolite, is also known for its anti-inflammatory action in rheumatic disorders and in uveitis, an inflammation of the eye, both of which are associated with increased production of prostaglandin E2. Recently we demonstrated that prostaglandin E2 production by rabbit retina/choroid was inhibited by azathioprine and suggested that this inhibitory effect may underlie the drug's antiinflammatory action. In the present study we showed that azathioprine's inhibition of prostaglandin E2 synthesis by the rat retina/choroid was reversed by addition of arachidonic acid, indicating that inhibition occurred through lack of availability of arachidonic acid, similar to the mechanism underlying the inhibitory effect of the steroidal anti-inflammatory drugs on prostaglandin E2. This study rules out the possibility that azathioprine's suppressive activity is via inhibition of the cyclooxygenase pathway.

Animals↗

PubMed1988

Changes in respiratory control induced by amino acid infusions.

We compared the metabolic and respiratory responses to a 4-h infusion of an amino acid solution consisting primarily of branched-chain amino acids (BCAA) to those after a standard amino acid solution in healthy subjects. Both the BCAA solution and the standard amino acid solution increased minute ventilation (mean increase 22%, p less than .001, and 18%, p less than .01, respectively), mean inspiratory flow (19%, p less than .01, and 19%, p less than .05) and oxygen consumption (9%, p less than .02, and 5%, NS). PaCO2 decreased (mean decrease 6%, p less than .01); there was a major increase in the ventilatory response to CO2 inhalation during administration of the BCAA solution but not the standard amino acid solution. Increased plasma norepinephrine concentration (mean increase 75%, p less than .001) during the infusion of the standard amino acid solution but not the BCAA solution suggested increased sympathetic activity. The results demonstrate augmented respiratory effects of amino acid infusions by BCAA enrichment, and a dissociation between the respiratory stimulation, metabolic rate, and sympathetic activity.

Adult↗

PubMed1988

Intravenous infusion of a medium-chain triglyceride-enriched lipid emulsion.

There has been much interest in the parenteral use of medium-chain triglycerides (MCT) as a noncarbohydrate energy source. This study examines the effects of infusion iv into postabsorptive normal subjects with three doses (0.5, 1.0, 1.5 g/kg.15 h) of an emulsion containing 56% MCT and 44% long-chain triglyceride (LCT) and comparing its metabolic effect with infusions of normal saline (NS) and an emulsion containing LCT alone. There were significant increases in serum beta-hydroxybutyrate and acetoacetate 5 and 15 h after the start of the MCT-LCT infusions. Increases were seen only after 15 h of NS, while none was observed during LCT alone. Triglycerides were increased in a dose-related fashion with MCT-LCT and were increased even further with LCT alone. Glycerol increased in a dose-related fashion both during the MCT-LCT and LCT infusion beginning immediately (0.5 h) after the start of the infusion. With NS infusion, glycerol increased significantly only after 15 h of infusion. The MCT-LCT mixture and the highest LCT dose resulted in a significant (12%) increase in oxygen consumption after 5 h of infusion. There was no difference in oral glucose tolerance between the various infusions. Infusion of MCT results in significant ketogenesis and more study is needed to determine its clinical utility.

Acetoacetates↗

PubMed1988

Attenuation of the hemodynamic responses to chest physical therapy.

Chest physiotherapy (CPT) is a commonly used technique in mechanically ventilated critically ill patients. This study examines the hemodynamic and metabolic changes associated with CPT and measures the attenuation by two doses of intravenous fentanyl (1.5 micrograms/kg and 3.0 micrograms/kg) on these changes. Heart rate, systolic and mean blood pressures, cardiac output, oxygen consumption (VO2), and carbon dioxide production (VCO2) all increased during CPT. Decreases in arterial pH and VE and increases in PaCO2 were also observed. The higher, but not lower dose, of fentanyl significantly attenuated increases in blood pressure and heart rate during CPT and no substantial hemodynamic changes occurred once CPT had stopped. The increases in VO2 and VCO2 were not attenuated. Short acting narcotics attenuate the hemodynamic responses to stressful stimuli such as CPT.

Analgesia↗

PubMed1988

Prostaglandin E2 and protein levels in rabbit aqueous humor following ND:YAG laser iridotomy.

Prostaglandin E2 (PGE2) and protein levels were measured in the aqueous humor of rabbits' eyes subjected to iridotomy with the neodymium:YAG laser. Following irradiation, PGE2 levels were elevated to the highest elevation of 20.0 +/- 7.7 ng/ml (mean +/- SD) at 30 minutes as compared to control levels of 0.625 +/- 0.075 ng/ml. PGE2 concentrations progressively decreased, however, after 8 hours they remained high and did not resume control levels. Protein levels in the aqueous humor of ND:YAG irradiated eyes reached peak levels at 30 minutes to 7.8 +/- 2.2 mg/ml compared to control level of 1.3 +/- 0.4 mg/ml. A progressive decrease in protein levels was observed after peak time, but they were still above control levels, at 8 hours. Our study demonstrated that ND:YAG irradiation of the iris involves an immediate increase in PGE2 aqueous levels associated with a blood aqueous barrier disruption and augmented aqueous protein levels.

Animals↗

PubMed1987

Do oxygen consumption and carbon dioxide production affect cardiac output after cardiopulmonary bypass?

This study examines the oxygen consumption (VO2) and carbon dioxide production (VCO2) occurring before, during, and after cardiopulmonary bypass (CPB) and whether they correlate with changes in cardiac output. Twenty-three patients undergoing open heart surgery were studied. Group 1 (N = 11) received fentanyl citrate, 50 micrograms/kg, intravenously during the induction of anesthesia. Group 2 (N = 12) received 100 micrograms/kg of fentanyl citrate intravenously. We measured VO2, VCO2, as well as hemodynamic and biochemical factors. Initial statistical analyses failed to show any differences in the VO2, VCO2, hemodynamic, or biochemical factors between groups 1 and 2. Therefore, the data from both groups were combined. In comparing the average (for all data) of the post-CPB with the pre-CPB periods in both groups for the metabolic factors, there were 9.0%, 11.5%, and 2.4% increases in the VO2, VCO2, and respiratory quotient, respectively. There was an 80% increase in total serum lactate levels seen in the post-CPB periods when compared with the pre-CPB periods. Serum triglyceride and free fatty acid levels measured in the post-CPB period decreased 39% and 25%, respectively, when compared with the pre-CPB periods. Although there were no changes in the cardiac outputs following CPB, the post-CPB periods showed a 37% increase in central venous pressure when compared with the pre-CPB periods. These data suggest that although there are significant metabolic and biochemical sequelae to CPB, the modest increases in post-CPB VO2, and VCO2 did not affect cardiac output following cardiovascular surgery. Increasing doses of narcotic do not have an effect on those relationships.

Blood Gas Analysis↗

PubMed1987

Metabolic and ventilatory responses during very low level exercise.

1. Nine male and six female healthy subjects were studied during supine bicycle exercise at workloads of 12 and 37 W; pedalling rates varied between 30 and 50 cycles/min at each workload. Measurements were made of oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), tidal volume (VT), respiratory frequency (fR), inspiratory and expiratory time (TI, TE) and mean inspiratory flow (VT/TI) using a non-invasive canopy-computer-spirometer system. 2. At rest, males had greater values of VE, VT, TI, inspiratory duty cycle (TI/TTOT), VCO2 and VO2, and a lower fR, than females. 3. At the lower workload, VO2, VCO2, VE, VT and VT/TI increased linearly with increasing pedalling rate, whereas at the higher workload there was a decrease in VO2 and little or no change in ventilatory parameters from 30 to 50 cycles/min except for an increase in fR in females. 4. While performing supine exercise, there was an effect of pedalling rate on ventilatory and metabolic parameters at the low workload (12 W) which diminished at the higher workload (37 W). An increase in pedalling rate appears to enhance efficiency at these low workloads. 5. Differences between the sexes during exercise generally include: (a) a higher breathing frequency, (b) a greater mechanical efficiency, and (c) lower ventilatory equivalents of O2 and CO2 (VE/VO2 and VE/VCO2) during the higher workload in females than males.

Adult↗

PubMed1987

Energy expenditure in patients with chronic obstructive pulmonary disease.

Energy expenditure was studied in ten patients with chronic obstructive pulmonary disease (COPD) and weight loss, and in five malnourished patients without clinical evidence of COPD (control group) prior to and after a two-week refeeding regimen. Patients received 5 percent dextrose solution (plus electrolytes) for 36 hours to establish standard baseline conditions and were then randomly assigned to either a carbohydrate-based (CB; 53 percent of calories) or fat-based (FB; 55 percent of calories) diet for the first week. The alternate diet was given the following week. Total calorie intake was set at 70 percent above the energy expenditure measured prior to institution of nutritional support. During energy repletion, energy expenditure was greater than predicted (116 percent) in patients with COPD and less than predicted (90 percent) in the control patients. Thermic effect of nutrients during administration of either regimen was significantly greater (p less than .05) in patients with COPD than in those without COPD during both diets. The difference between the two groups was enhanced during the CB regimen. These observations suggest that malnourished patients with COPD have an elevated resting energy expenditure, and an enhanced thermic response to nutrients as compared to malnourished patients without COPD. Increased diet-induced thermogenesis may contribute to weight loss in patients with COPD, in addition to factors previously described such as decreased caloric intake and increased resting energy expenditure.

Aged↗

PubMed1987

Metabolic and respiratory changes during weaning from mechanical ventilation.

Weaning from mechanical ventilation is a procedure performed daily in intensive care units. This study sought to determine whether among postoperative patients there were any differences in the changes in oxygen consumption (VO2) and carbon dioxide production (VCO2) between those patients in whom mechanical ventilation was successfully discontinued and those in whom it was continued or reinstituted. A stepwise reduction in mandatory breaths (from 10 to 12 to 4 to 6), followed by a period of continuous positive airway pressure (CPAP), was the weaning method. In the group of patients (N = 18) who were successfully weaned, VO2 and VCO2 increased 10 +/- 8 (SD) percent and 10 +/- 9 percent, respectively, while VE decreased 9 +/- 8 percent and PaCO2 was unchanged when values at an IMV of 10 to 12 were compared with those on CPAP. In the group (N = 17) who were not successfully weaned, VO2 and VCO2 increased 8 +/- 10 percent and 6 +/- 9 percent, respectively, while PaCO2 rose (37.9 +/- 4 to 42.5 +/- 2.9) significantly (p less than 0.02). There was a significantly greater decrease (15 +/- 3 percent) in VE than in the other group. Changes in VO2 or VCO2 did not aid in predicting which patients would be successfully weaned.

Adult↗

PubMed1987

Nutritional care of the critically ill patient with respiratory failure.

Nutritional support is an integral part of the therapy for lung dysfunction because malnutrition can predispose an already critically ill patient to pneumonia and respiratory failure. Physicians must, however, be sensitive to the changes in cardiac and respiratory function that certain nutrients can cause.

Critical Care↗

PubMed1987

Energy measurements and requirements of critically ill patients.

The energy expenditure of the critically ill patient is influenced by many factors, thus making it difficult to predict. Measurement of energy expenditure in mechanically ventilated patients receiving elevated oxygen concentrations requires a good understanding of the measurement technique and its limitations, whether it be the gas exchange or Fick method. More investigation is needed to better understand the determinants of energy expenditure, as well as the total energy requirements of the critically ill patient.

Critical Care↗

PubMed1987

Antipyrine metabolism not influenced by level of carbohydrate intake.

The effects on antipyrine metabolism of two levels of carbohydrate, fed intravenously as the sole source of nutrition, were compared. After a 36-hour baseline period during which they received 5% dextrose, 440 kcal per day, intravenously, 8 healthy men were administered 2 sequential intravenous nutritional regimens for 3 days each. One regimen consisted of dextrose 8.1 kcal per kg per day and the other 30.7 kcal per kg per day. The order of the 2 regimens was randomized. Antipyrine metabolism was studied on the last day of each nutritional regimen. Antipyrine kinetics were not influenced by level of carbohydrate intake. Our study indicates that in humans carbohydrate does not by itself have an effect on oxidative drug-metabolizing capacity.

Adult↗

PubMed1986

The effects of posture on the metabolic and ventilatory response to low level steady state exercise.

Low level exercise is frequently used to assess cardiac and pulmonary function. This study examines the differences in both metabolic and respiratory patterns between the sitting and supine position. Six normal male subjects were studied in both positions during four levels of exercise (12.5, 25, 37.5 and 50 W). Oxygen consumption (VO2), carbon dioxide production (VCO2) and minute ventilation (VE) were greater when sitting as were the ventilatory equivalents to O2 (VE/VO2) and CO2 (VE/VCO2). Respiration was compared at equivalent workloads; the greater minute ventilation observed during sitting was due to greater tidal volumes (VT) and mean inspiratory flows (VT/TI). Expiratory time (TE) was longer and inspiratory duration shorter under most conditions when sitting. When breathing patterns were compared at similar degrees of minute ventilation, VT, TE and VT/TI were greater when sitting, while respiratory frequency (fR) was slower.

Carbon Dioxide↗

PubMed1986

Response to tubular airway resistance in normal subjects and postoperative patients.

Critically ill patients must often breathe spontaneously through an endotracheal tube that acts as a fixed inspiratory and expiratory tubular airway resistor. Although this practice is common, its effect on the pattern of breathing is not known. The mean breathing patterns of seven normal, healthy male subjects and eight male patients who had undergone upper abdominal surgery 2-4 days previously were studied breathing through a mouthpiece fitted in random order with a 5, 6, 7, 8, or 15 mm diameter (17 mm long) resistor. These diameters were selected because they simulate the pressure-flow relationships of adult endotracheal tubes. With the 15 mm aperture, the patients had a greater breathing frequency (f) than did the normal subjects (21 +/- 5 [SD] vs. 14 +/- 4 breaths/min, P less than 0.01) as well as a smaller mean tidal volume (VT). In both groups, minute ventilation (VE) and f progressively decreased as resistance was increased by decreasing the aperture size from 15 to 16 mm. In the normal subjects but not the patients, VT also progressively decreased. When the diameter was decreased from 6 mm to 5 mm, there were increases in VT and decreases in f that were more marked in the normal subjects. In both groups, the changes in VE were accompanied by decreases in mean and peak inspiratory and expiratory flow rates. Throughout the study, oxygen consumption (VO2) and carbon dioxide production (VCO2) did not change. This, coupled with the decreases in VE resulted in decreases in the ventilatory equivalents to CO2 and O2 (VE/VCO2, VE/VO2).(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗

PubMed1986

Resting metabolic rate of the critically ill patient: measured versus predicted.

Critically ill patients requiring mechanical ventilation are particularly susceptible to malnutrition. A knowledge of the energy requirements of these patients is essential in designing nutritional regimens. This study examines 45 resting energy-expenditure measurements performed in a group (n = 40) of postoperative, critically ill patients who were hemodynamically stable, noncomatose, and receiving mechanical ventilation. It examines in particular to what degree the resting energy expenditure of such patients can be predicted using the Harris-Benedict and Aub-Dubois formulae. Resting energy expenditure was measured using indirect calorimetry. There was only a moderate correlation between measured resting energy expenditure and that predicted using the Harris-Benedict (r = 0.57) and Aub-Dubois (r = 0.59) formulae. There was little correlation between the ratio of the measured to the predicted (Harris-Benedict) resting energy expenditure and age, or the ratio of actual to ideal body weight and body weight. The measured resting energy expenditure differed widely (70-140%) from predicted, reflecting the many complex factors that influence these patients' metabolic rate. The role of standard predictive formulae in such patients is as an arbitrary reference point to be used to define hypermetabolism (measured greater than predicted) and hypometabolism (predicted greater than measured).

Adolescent↗

PubMed1986

The metabolic and ventilatory response to the infusion of stress hormones.

Sepsis and trauma result in increases in epinephrine, glucagon, and cortisol secretion as well as alterations in respiratory pattern that is characterized by increased minute ventilation, decreased tidal volume, and increased frequency. Six male subjects were infused for 5.5 hours with cortisol, epinephrine, and glucagon in amounts designed to simulate plasma levels seen in patients following trauma. During the initial 20 minutes of the hormone infusion, minute ventilation (VE), oxygen consumption (VO2), and carbon dioxide production (VCO2) increased above preinfusion values. VCO2 increased more than VO2 resulting in an increase in respiratory quotient (RQ) from 0.93 to 1.14. The increase in VE was due to increased tidal volume and not frequency (f). After 4.5 hours, the VE, VO2, and VCO2 were still above preinfusion levels but the RQ had decreased to 0.98 because of a decrease in VCO2. Frequency had increased from 19 +/- 4.8 breaths/min preinfusion to 22 +/- 4.7 after 4.5 hours. After 4.5 hours, VT was still above preinfusion levels while pH and PaCO2 had decreased below them. The latter was associated with an increase in serum lactate. At no time was a decrease in tidal volume observed. Therefore, the infusion of these hormones does not simulate all the alterations observed during trauma and sepsis.

Adult↗

PubMed1986

Cardiovascular changes during transport of critically ill and postoperative patients.

We examined cardiovascular changes in 37 patients transported to an ICU after major general or vascular surgery (n = 14), open heart surgery (n = 13), or carotid endarterectomy (n = 10). Cardiovascular variables were also measured in a control group of 11 patients transported from an ICU for diagnostic or therapeutic procedures. All patients were followed for 30 min before transport until approximately 30 min after they arrived at their destinations. During this period, systolic BP and heart rate significantly increased only in patients recovering from major general/vascular surgery or carotid endarterectomy. These changes were apparently related to acute emergence from inhalational anesthesia (isoflurane plus nitrous oxide), since the other surgical patients were anesthetized with narcotic anesthesia, and the control group did not receive any anesthesia.

Blood Pressure↗