Cardiovascular response to submaximal exercise in sustained microgravity.

Cardiac output (Q), heart rate (HR), blood pressure, and oxygen consumption (VO2) were measured repeatedly both at rest and at two levels of exercise in six subjects during microgravity exposure. Exercise was at 30 and 60% of the workload producing the individual's maximal VO2 in 1 G. Three of the subjects were on a 9-day flight, Spacelab Life Sciences-1, and three were on a 15-day flight, Spacelab Life Sciences-2. We found no temporal differences during the flights. Thus we have combined all microgravity measurements to compare in-flight values with erect or supine control values. At rest, Q in flight was 126% of Q erect (P < 0.01) but was not different from Q supine, and HR in flight was 81% of HR erect (P < 0.01) and 91% of HR supine (P < 0.05). Thus resting stroke volume (SV) in flight was 155% of SV erect (P < 0.01) and 109% SV supine (P < 0.05). Resting mean arterial blood pressure and diastolic pressure were lower in flight than erect (P < 0.05). Exercise values were considered as functions of VO2. The increase in Q with VO2 in flight was less than that at 1 G (slope 3.5 vs. 6.1 x min-1.l-1.min-1). SV in flight fell with increasing VO2, whereas SV erect rose and SV supine remained constant. The blood pressure response to exercise was not different in flight from erect or supine. We conclude that true microgravity causes a cardiovascular response different from that seen during any of its putative simulations.

Methicillin-resistant Staphylococcus aureus eradication in a burn center.

Methicillin-Resistant Staphylococcus aureus and its detection, virulence, and significance relative to morbidity, epidemics, and cost have been widely discussed in the literature. Although some experts recommend against attempting to eradicate the organism, our health center decided that under the circumstances this course should be pursued. This article describes the outbreak of Staphylococcus aureus, the rationale for pursuing its eradication, the measures successful in doing so, and the relative costs involved.

Ionic basis of short-circuit current in toad skin at high hydrostatic pressure.

The toad skin and urinary bladder are widely used for the study of water and Na+ transport under high pressure. These tissues can be mounted in Ussing type chambers and ion transport can be measured by evaluating electrical properties of the preparation, e.g., short-circuit current (Isc). The tacit assumption in these experiments is that the preparation behaves in the same manner at high pressure as at 1 ATA; namely, that net Na+ flux is equivalent to Isc. The purpose of the experiments described here was to test that assumption. Toad skins were mounted in an Ussing chamber and Isc was measured as an index of active net Na+ transport under hydrostatic pressures up to 100 ATA. The chamber was modified so that isotopic Na+ flux from the mucosal to serosal compartments could be measured in conjunction with Isc, without decompression. A linear regression of JNa+ms on Isc was computed and found to be described by the equation, JNa+ms = 3.83 + 0.83 Isc; n = 18; r = 0.92. The slope of the line was not significantly different from unity. No correlation was made for JNa+sm because of the difficulty in measuring JNa+sm and JNa+ms in the same skin simultaneously. Independent measurement of JNa+sm demonstrated that this flux accounted for less than 2% of JNa+net. In a second set of experiments, the influence of amiloride on Isc with and without pressure was tested. 10(-4) M amiloride abolished Isc under both circumstances. It is concluded that Isc can be wholly accounted for by net Na+ flux under pressures up to 100 ATA.

Pressure increases oxygen affinity of whole blood and erythrocyte suspensions.

Effect of hydrostatic pressure (HP) on whole blood (WB) or erythrocyte suspension hemoglobin (Hb) O2 affinity has been studied using newly developed techniques. O2 partial pressure at which hemoglobin is half-saturated with O2 (P50) measurements were made at 5 HP (1, 26, 51, 76, and 126 ATA) on thin films of human WB or erythrocytes at 37 degrees C. CO2 partial pressure of WB was either 28 or 57 Torr (film pH 7.51 or 7.31). HP increased affinity of erythrocytes and WB. For erythrocytes in tris(hydroxymethyl)aminomethane buffer, the ratio (r) of P50 (1 ATA)/P50 (51 ATA) was 1.089 (P less than 0.01) at pH 7.0. WB P50 decreased with HP at a rate of -3.3 X 10(-2) Torr X atm-1; change in P50 at higher HP vs. 1 ATA was highly significant (P less than 0.01). No effect of HP was seen on the CO2 Bohr coefficient. Inert gas choice, N2 vs. helium (He), had no effect. Measurement of decrease of P50 with HP at 76 ATA in hemolyzed WB gave an r of 1.15, as great or greater than that found in WB, indicates that Donnan equilibrium alteration is not involved. No effect of HP was found in WB on the ratio of P50 of erythrocytes with normal (5 mmol/l erythrocytes) 2,3-diphosphoglycerate (DPG) to P50 of erythrocytes with less than 5% of normal DPG; i.e., no effect of pressure was seen on the independent influence of DPG on P50. WB measurements of Hb O2 uptake under simulated physiological conditions are characterized by a net decrease in partial molal volume on oxygenation of 30-35 ml/mol Hb4.

Potentiation of morphine analgesia after pretreatment with probenecid or sulfinpyrazone.

Pretreatment with uricosuric agents probenecid or sulfinpyrazone potentiate the analgesic effects of morphine sulfate as ascertained using the phenylquinone (PQ)-induced writhing test. Doses of either uricosuric agent at 50 mg/kg had no effect on the number of PQ-induced writhes in test animals while potentiating the analgesic effects of morphine. High doses of probenecid or sulfinpyrazone alone did produce decreases in PQ-induced writing. Probenecid (50 mg/kg) did not alter hot water tail flick latency nor did it influence morphine analgesia. Attempts to uncover the underlying mechanisms in the uricosuric agent plus morphine attenuation of PQ-induced writhing were directed towards a possible displacement of morphine from plasma binding sites. However, administration of N-methyl-H3-morphine and estimation of plasma and brain morphine concentrations indicate no differences in the uricosuric drug pretreated groups compared to controls. The conflicting results in the PQ writhing test vs. hot water tail flick might indicate a false positive response in the former test. On the other hand this might be indicative of differing analgesic mechanisms for different types of pain. If the latter is true, this drug interaction may prove clinically useful.

Hyperbaric chamber for evaluating hydrostatic pressure effects on tissues and cells.

A chamber system is described for the study of pure hydrostatic pressure effects on tissues and cells. The small chamber has an internal volume of 7.6 liters and is rated for working pressures up to 400 ATA. Sliding doors at each end permit easy access and quick sealing. A cam-driven pump provides constant flow of physiological solution to the tissue bath containing the preparation. Connections to the pump allow a variety of test solutions to be used in the course of an experiment. The tissue bath is designed to prevent chamber gas from diffusing in to the perfusate, thus allowing for pure hydrostatic compression of the bath contents. The bath is coupled to a motorized stage to facilitate placement of recording devices once the bath is placed inside the chamber. Temperature is controlled within 0.05 degrees C of set point by thermoelectric modules coupled to a feedback amplifier. This system has been used for electrical and mechanical studies of cardiac muscle, but its versatility makes it suitable for a wide range of other biomedical applications.

Method for separation of cells and suspending medium at high pressure.

We describe a pressure chamber designed for measuring fluxes and equilibrium distributions of substances between cells in suspension and the extracellular medium at pressures up to 400 ATA. The pressure chamber contains a filtration apparatus capable of taking four separate samples of cell-free medium from a cell suspension at timed intervals, without necessity of decompression. In addition, a high pressure injection system makes possible the addition to a cell suspension of precise quantities of agents such as ionophores or metabolic inhibitors, for observations of their effects on cell functions at pressure. The chamber of filtration apparatus functioned successfully in preliminary experiments designed to measure the equilibrium distribution of 36Cl- in human erythrocytes at high pressure.

Closed-system habitat for high pressure exposures of animal colonies.

A deep-diving system has been designed for use with colonies of small rodents at pressures up to 170 ATA. The system consists of a triple-envelope arrangement in which a modular habitat serves as the animal living quarters. The habitat contains provisions for temperature control, gas analysis, and measurement of physical performance and social interaction; it also contains food and water supplies. The surrounding envelope (an acrylic box) is used to control the composition of the gaseous environment presented to the animal colonies. The outermost envelope (a high pressure chamber) maintains the desired pressure conditions. Colonies of five deer mice have been successfully studied at pressures up to 100 ATA. Their performance has been evaluated during 1- to 4-day exposures to various gaseous environments.

Apparatus for intracellular electrophysiological measurements at 200 ATA.

An apparatus has been constructed and tested at pressures to 200 ATA which meets the basic requirements for intracellular microelectrode work. Standard microelectrodes, unaffected by pressure in this range, were used with lobster axon and frog sartorius fibers and action potentials have been recorded at pressure up to 151 ATA. The chamber itself has a simple roll-in door and a modular design that recommends it as a highly convenient multipurpose vessel for work at moderately high pressures.