Richard E. Justice

Presence of negative inotropic agents in canine plasma during positive end-expiratory pressure.

Application of positive end-expiratory pressure (PEEP) will reduce cardiac output (CO). Humoral mediation of this event by circulating negative inotropic agents was examined using a rat papillary muscle bioassay. Twenty-seven dogs were anesthetized with an iv pentobarbital infusion. Plasma was obtained before and after 30 minutes of PEEP. The plasma was oxygenated in a small (4.5-ml) papillary muscle chamber using a diffusion membrane. An average POi of 416 mm Hg was achieved. PEEP plasma reduced developed tension (Tpd) from 2.18 ± 1.0 to 1.90 ± 1.05 g (P < 0.0001). A fall in Tpd was observed whether or not CO was maintained constant with fluid infusion. Resting tension was unchanged. The percent reduction in Tpd correlated with the fall in CO (r · = 0.63, P < 0.01) when fluid was not infused to maintain CO. Reapplication of control plasma restored Tpd. Barbiturate levels in anesthetized dogs rose from 17.3 to 19.4 μg/ml during PEEP (P < 0.1). Addition of pentobarbital to normal plasma led to a slight decrease in Tpd only when the concentration exceeded 99 μg/ml. In three experiments on ex vivo perfused hearts, application of PEEP led to lowering of peak systolic pressure (PSP) within 5 minutes. Removal of PEEP restored PSP in a similar time. The results support the hypothesis that the decline in CO with PEEP is mediated in part by a circulating negative inotropic agent. Ore Res 45: 460-467, 1979

Postoperative nitrous oxide analgesia and the functional residual capacity

Surgery of the upper abdomen is associated with the greatest demand for postoperative analgesia and also is marked by depressed pulmonary function, arterial hypoxemia, and pulmonary complications. Nitrous oxide (N2O) in concentrations of 15–25% is a potent analgesic and is relatively free of untoward side effects if administered for a maximum of 48 h. In the present study, the effect of N2O analgesia on postoperative lung function, in particular, the functional residual capacity (FRC), is examined. Eighteen cholecystectomy patients received either a narcotic (N = 11) or N2O (N = 7) for postoperative analgesia. N2O-treated patients had satisfactory analgesia and maintained FRC at normal levels. Narcotic treated patients had a fall of 22% in FRC. N2O had no effect on the formed elements in peripheral blood.

Left Ventricular Filling Pressure as a Determinant of Subendocardial Blood Flow

Abstract The effect of ventricular diastolic pressure on subendocardial flow was studied during isovolumic contraction in an isolated heart. In 9 experiments flow averaged 95 ± 8 ml/min ˙ 100 gm of tissue (mean ± standard deviation). With balloon inflation to 50 ml, diastolic pressure increased from 1 ± 2 mm Hg to 14 ± 4 mm Hg ( p p p p p p r = −0.84; p r = 0.87; p r = 0.97; p

A cooling system for prostaglandin infusions

A simple system has been developed-for the prolonged infusion of an iced solution of prostacyclin (PGI2). In a 24 h period at pH 10, there is a theoretical loss in activity of 6%, while a 5 h infusion leads to a 2% reduction in activity. The stability of the cooling system was demonstrated in six dog experiments where mean arterial pressure (MAP) was reduced to 58±3.8 Torr (x±SEM) over a 5 h period of infusing 500 ng/kg/min. In a saline medium, at 3°C, a 5 h PGI2 infusion led to a stable reduction in MAP, whereas, at a temperature of 24°C, a 70 loss of infusate activity was noted.

A new papillary muscle chamber to test small plasma volumes

Abstract A system to measure contratility of a rat papillary muscle is described. It is unique in that the unit requires less than 5 ml plasma as the bathing medium. A membrane oxygenator built into the muscle chamber permits the development of stable oxygen tensions of over 500 mm Hg and the elimination of plasma foaming.

Helium meter correction equations for oxygen and nitrous oxide.

Helium detectors utilizing thermal conductivity are sensitive to the presence of nitrous oxide (N2O) and oxygen (O2). Measurement of the level of these gases within the spirometer may be used to obtain the true helium concentration for use in the calculation of functional residual capacity (FRC). Linear relationships were obtained relating the change (delta) in reading of the helium meter by nitrous oxide and oxygen. The regression equations are: delta O2 = 0.027 (%O2) - 0.513; delta N2O = -0.276 (%N2O). Failure to correct the helium reading for N2O will overestimate lung volume; elevations of O2 above 21% will underestimate the lung volume.