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Biomedical subjects

R J Perry

Publications and source records attributed to R J Perry.

5 recordsLinked to original sources
PubMed1992

Nebulizer function during mechanical ventilation.

In the setting of mechanical ventilation, recent studies have cast doubt on the ability of nebulizer systems to deliver adequate amounts of medication. We therefore studied ventilator-related and nebulizer-related factors that could potentially affect the amount of aerosol inhaled by an intubated subject. Utilizing two separate protocols, we used a bench model of a ventilator circuit, radiolabeled (technetium pertechnetate, 99mTc) saline droplets and a filter technique to measure the percentage of radioaerosol delivered. First, we compared four commercially available jet nebulizers and found that there were significant differences in rate of aerosol production between systems, ranging from 3 to 37%. Delivered aerosol was measured at different ventilator settings, and it was found that the duty cycle can potentially influence output by sevenfold. Some nebulizers were also sensitive to changes in the initial volume of solution placed in the nebulizer. The inclusion of a humidification device significantly reduced output by a mean of 41 +/- 3.5%, but it did not affect particle distribution. Endotracheal tube diameter was not an important variable. Then, with the effects of the above variables established, a separate series of experiments was performed to test whether the use of different radiolabeling compounds can confound the measurement of inhaled drugs. Two nebulizers (AeroTech II and Twin Jet) and pentamidine as the test drug were studied with fixed ventilator settings, treatment time, endotracheal tube size, and volume fill. No humidification was used. The nebulizer solution was labeled with 99mTc, which was bound to either human serum albumin (HSA) or sulfur colloid (SC).(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1991

Calcium regulation in neurons: transport processes.

The ionic stoichiometry of the major Ca2+ transport mechanisms in neurons is still a matter for debate. The past year has seen some particularly interesting developments in this field, not least the finding that the neuronal Na(+)-Ca2+ exchange may be able to transport K+.

Animals↗
PubMed1991

Response properties of cones from the retina of the tiger salamander.

1. Spectral sensitivity measurements using the suction electrode technique reveal three types of cone in the retina of the tiger salamander, showing maximum sensitivity at wavelengths 610 nm (red-sensitive cone), 444 nm (blue-sensitive cone) and below 400 nm (UV-sensitive cone). 2. The absolute sensitivities of red- and blue-sensitive cones to flashes of optimal wavelength are 0.022 and 0.33 pA photon-1 micron 2 respectively. 3. The time-to-peak of the dim flash response and the recovery of membrane current after a flash of any intensity are fastest in red-sensitive and slowest in blue-sensitive cones. 4. In blue- and UV-sensitive cones the flash response peaks progressively earlier as the flash strength is increased, as in rods. In red-sensitive cones, however, bright flash responses take longer to peak than dim flash responses. 5. In all three cone types, voltage clamping at -40 mV reduces the time-to-peak of the response to a bright flash, showing that the rising phase of the bright flash response is normally limited by the time constant of the cell. Under voltage clamp, all cones show a decrease in time-to-peak with increasing flash intensity. 6. Voltage clamping red-sensitive cones reveals two components of the rising phase of the response to a bright flash. Most of the current is rapidly suppressed by a bright flash, and represents the closure of light-sensitive channels. The residual current decays with a mean time constant of 20 ms, and is probably attributable to the decline of electrogenic Na(+)-Ca2+, K+ exchange. The amplitude of this exchange current suggests that the proportion of the dark current carried by calcium ions is greater in red-sensitive cones than in rods of the same species. 7. In UV-sensitive cones, a prominent oscillation of light-sensitive current is observed during the recovery from flashes of intermediate intensity. A similar, but slower and less prominent oscillation is usually seen in blue-sensitive cones. 8. When a red-sensitive cone is voltage clamped an oscillation similar to those in the other two cone types is revealed. An underswing of up to 2 pA is also observed after recovery from intermediate or bright flashes in the majority of red-sensitive cones, and voltage clamping increases the amplitude of this underswing.(ABSTRACT TRUNCATED AT 400 WORDS)

Ambystoma↗
PubMed1989

Extrusion of calcium from rod outer segments is driven by both sodium and potassium gradients.

Calcium is transported across the surface membrane of both nerve and muscle by a Na+-dependent mechanism, usually termed the Na:Ca exchange. It is well established from experiments on rod outer segments that one net positive charge enters the cell for every Ca2+ ion extruded by the exchange, which is generally interpreted to imply an exchange stoichiometry of 3 Na+:1 Ca2+. We have measured the currents associated with the operation of the exchange in both forward and reversed modes in isolated rod outer segments and we find that the reversed mode, in which Ca2+ enters the cell in exchange for Na+, depends strongly on the presence of external K+. The ability of changes in external K+ concentration ([K+]o) to perturb the equilibrium level of [Ca2+]i indicates that K+ is co-transported with calcium. From an examination of the relative changes of [Ca2+]o, [Na+]o, [K+]o and membrane potential required to maintain the exchange at equilibrium, we conclude that the exchange stoichiometry is 4 Na+:1 Ca2+, 1 K+ and we propose that the exchange should be renamed the Na:Ca, K exchange. Harnessing the outward K+ gradient should allow the exchange to maintain a Ca2+ efflux down to levels of internal [Ca2+] that are considerably lower than would be possible with a 3 Na+:1 Ca2+ exchange.

Algorithms↗