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Biomedical subjects

R M Peters

Publications and source records attributed to R M Peters.

At least 91 records · Page 5Linked to original sources
PubMed1979

Mechanical work on the lungs and work of breathing with positive end-expiratory pressure and continuous positive airway pressure.

The mechanical work on the lung required during spontaneous breathing with positive end-expiratory pressure (PEEP) was compared with different methods of continuous positive airway pressure (CPAP) in nine young healthy athletes (surfers) at levels of 5, 10, 15, and 20 cm H2O. At the level of 20 cm H2O, PEEP increased the mean total work per minute by 116 percent and the total work per liter by 121 percent. The percent increase rose linearly with the level of PEEP. In contrast, with methods of CPAP that maintained the airway pressure (Paw) constant, the total work per minute decreased by 45 per cent at a PEEP of 10 cm H2O and remained at this level with PEEP of 15 and 20 cm H2O. Use of PEEP did not increase the functional residual capacity (FRC) in these spontaneously breathing subjects. In contrast, CPAP resulted in a rise in FRC proportional to the level of CPAP. This suggests that CPAP must be applied in a manner that maintains Paw constant to provide optimal assistance to ventilation.

Adult↗
PubMed1979

Predicting the need for prolonged ventilatory support in adult cardiac patients.

Forty-nine cardiac surgical patients had ventilatory function tests and measurements of maximum inspiratory (MIP) and maximum expiratory (MEP) pressures preoperatively. The differences between the values of various function tests were compared for patients requiring less than 24 hours of ventilator support and those requiring more than 24 hours. There was a significant difference in the mean values for the two groups in vital capacity (VC) first-second forced expired volume (FEV) midexpiratory flow between 50 and 75 (MMEF 50--75) and 75--85 percent of expired volume (MMEF 75--85), and MEP. The standard deviations of each of the variables were so large that the clinical usefulness was limited. However, when discriminant analysis was used for more than one variable, the combination of MMEF 75--85 and MEP predicted success or failure to wean in 24 hours correctly in 90 percent of instances. On the basis of these simple tests, patients predicted to succeed should be weaned from ventilator support on recovery from anesthesia. Those predicted to fail should be placed on intermittent mandatory ventilation (IMV) and should be weaned following a planned, logical process.

Adult↗
PubMed1979

Crystalloid vs. colloid resuscitation: is one better? A randomized clinical study.

The effects of hemodynamic resuscitation with protein-containing or balanced salt solution were studied prospectively in 29 patients undergoing abdominal aortic surgery. Blood loss was replaced with packed red cells and extracellular volume with either Ringer's Lactate (RL) or 5% albumin in Ringer's lactate (ALB). Fluids were given to maintain the pulmonary capillary wedge pressure (PCWP) equal to or within 5 torr above preoperative (PO) levels, the cardiac output (CO) equal to or greater than preoperative values, and the urine output at least 50 ml/hr. Serum colloid osmotic pressure (COP), CO, PCWP, the gradient between COP and PCWP (COP-PCWP), and intrapulmonary shunt (Qs/Qt) were measured PO, intraoperatively (IO), and daily for 3 days. The measured variables were similar PO in both groups. Operation time, estimated blood loss, and transfusions were similar. Total fluids received for resuscitation (day of operation) was 11.3 +/- 0.8 liters (RL) and 6.2 +/- 0.4 liters (ALB). Fluid balance at the end of resuscitation was 8.4 +/- 0.8 liters (RL) and 3.4 +/- 0.5 liters (ALB). Maximum decrease in COP was 40% (P less than 0.001) in the RL group and was insignificant in the ALB group. The COP-PCWP decreased from 11 +/- 1 to 2 +/- 1 in RL (P less than 0.001) and insignificantly in ALB. Qs/Qt increased slightly in both groups following operation but was not different between groups. Fluid balance, total fluid infused, sodium balance, total sodium infused, COP, or COP-PCWP did not significantly correlate with Qs/Qt. Two patients in the ALB group experienced pulmonary edema associated with normal COPs and elevated PCWPs. There were no cases of pulmonary edema associated with low COPs and normal PCWPs in the crystalloid group. These data seriously question the necessity to maintain COP by using protein-containing solutions during acute hemodynamic resuscitation. When titrated to physiological end points, even large volumes of balanced salt solutions are tolerated well.

Albumins↗
PubMed1978

Chest dimensions in young adults with spontaneous pneumothorax.

Chest dimensions measured from standard chest roentgenograms of 46 young adult patients with pneumothorax were compared with measurements from an age- and sex-matched control group. The ratio of men to women was 3:1. On the average, the male patients had longer chests and greater height-to-width ratios than the controls. The only significant difference between female groups was a diminished anteroposterior diameter in the patients with pneumothorax. The study suggests that the physical shape of the chest, probably because of stress distribution in the lungs, can play a major role in the development of spontaneous pneumothorax.

Adolescent↗
PubMed1978

Fluid overload and post-traumatic respiratory distress syndrome.

A series of dogs was given massive fluid infusions at two dose levels, 60 cc/kg and 100 cc/kg. The dogs were prepared in three ways: shock induced by bleeding; intravenous injection of oleic acid; and combined oleic acid injection and shock. The studies showed that type of injury was a more important determinant of lung dysfunction than the fluid dose. Shock animals were not hurt by fluid infusion; in oleic acid-injected dogs, the fluid infusion magnified the effect of oleic acid. When shock, oleic acid, and high fluid dose were combined, all animals died. The animals that died had high pulmonary artery diastolic pressures.

Animals↗
PubMed1978

Hemodynamic and respiratory response to varying gradients between end-expiratory pressure and end-inspiratory pressure in patients breathing on continuous positive airway pressure.

Nine patients on intermittent mandatory ventilation (IMV) and continuous positive airway pressure (CPAP) were allowed to breathe spontaneously at varying end expiratory pressure-end inspiratory pressure (EEP-EIP) gradients up to 10 cm H2O. There was no change in the mean cardiac output and oxygen delivery despite a lowered mean airway pressure (MAWP) when the gradient was increased. Three patients were uncomfortable at the higher gradients and another manifested evidence of fatigue of the muscles of respiration by raising her arterial PCO2 (PaCO2) and intrapulmonary shunt (Qs/Qt). In view of the difficulty experienced by some patients and lack of improvement in cardiac outputs (CO) during spontaneous inspiration when the EEP-EIP gradient is raised from zero to 5 and 10 cm H2O, it is recommended that the variation in airway pressure during spontaneous breaths while a patient is on CPAP be minimized.

Hemodynamics↗
PubMed1978

Lymph and pulmonary response to isobaric reduction in plasma oncotic pressure in baboons.

Plasma colloid osmotic pressure was reduced by 76% (from 19.6 +/- 0.6 to 4.7 +/- 1.5 mm Hg) in five baboons while pulmonary capillary hydrostatic pressure was maintained at a normal level. This resulted in fluid retention, weight gain, peripheral edema and ascites, but no pulmonary edema. Thoracic duct lymph flow increased 6-fold and pulmonary lymph flow 7-fold. Thoracic duct lymph had a lower colloid osmotic pressure (2.0 +/- 0.7 mm Hg) than plasma (4.7 +/- 1.5 mm Hg), whereas the colloid osmotic pressure of pulmonary lymph (4.7 +/- 0.7 mm Hg) was the same as that of plasma. The lymph-plasma ratio for albumin fell in thoracic duct lymph but remained unchanged in pulmonary lymph. The difference between plasma colloid osmotic pressure and pulmonary artery wedge pressure decreased from 15.3 +/- 1.9 to -0.7 +/- 2.9 mm Hg. Despite this increase in filtration force, the lungs were protected from edema formation by a decrease of 11 mm Hg in pulmonary interstitial colloid osmotic pressure and a 7-fold increase in lymph flow.

Animals↗
PubMed1978

A simplified method to determine functional residual capacity during mechanical ventilation.

We describe a nonrecirculating helium-rebreathing method providing rapid and simple measurement of the functional residual capacity (FRC) in spontaneously breathing subjects and patients receiving mechanical ventilation. Results of triplicate determinations in 24 normal subjects revealed a repeatability of +/- 5.2 percent of the measured FRC, results similar to those predicted for these subjects. Results in six additional subjects were not significantly different from those obtained with a standard method using helium equilibration in the pulmonary function laboratory. Triplicate determinations in eight patients after cardiac surgery demonstrated similar repeatability. In 22 other patients studied after open-heart surgery, the FRC fell more in those who could not be weaned than in those who could be weaned from the respirator. Since an increase in FRC is the goal of therapy with positive end-expiratory pressure, this method should be useful in determining the efficacy of a particular level of positive end-expiratory pressure.

Adolescent↗
PubMed1978

Central venous pressure or pulmonary capillary wedge pressure as the determinant of fluid replacement in aortic surgery.

Both central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) have been used as guides to fluid replacement in patients undergoing abdominal aortic surgery. To test the hypothesis that changes in PCWP (deltaPCWP) may be reliably estimated from changes in CVP (deltaCVP), 55 patients had simultaneous measurements (302 paired observations) of CVP and PCWP, as well as of cardiac output, before and during operation. The correlation between deltaCVP and deltaPCWP was high (r = 0.716, P less than 0.001). The estimated slope for the linear regression was 0.88. The standard error of the estimate was +/- 3.75 torr, making the prediction of deltaPCWP from deltaCVP accurate only to within 7.5 torr. There were five patients who each had a low and failing CVP accompanied by a stable cardiac output and a rising PCWP; for them, a decision to administer fluid based on the CVP might have resulted in pulmonary edema. Although deltaCVP accurately predicted direction and magnitude of deltaPCWP in the majority of patients (90%), there was a small group in whom there was no substitute for direct measurement of PCWP.

Adult↗