Effect of dihydroergotamine on +Gz acceleration tolerance.

Dihydroergotamine is a potent vasoconstrictor of the venous capacitance vessels and has been shown to decrease blood pooling in patients with orthostatic hypotension. Acceleration acting on the long axis of the body (+Gz) pools blood into the lower body of the subject. Nine healthy men received an injection of 1 mg dihydroergotamine and 1 ml of saline intramuscularly in a randomised, double blind fashion, and had their Gz acceleration tolerances measured. Dihydroergotamine significantly increased Gz tolerance by 0.24 G and narrowed the difference between the maximum heart rate during the acceleration epoch and resting baseline by 10%. The drug had no effect on blood pressure and heart rate when the subjects changed from the supine to standing position. The increase in Gz tolerance was not sufficient for operational use.

Hemodynamic effects of anti-G suit inflation in a 1-G environment.

This study evaluated effects of various anti-G inflation pressures on cardiac volumes and the relationship of these volume changes to mean arterial pressure changes. Ventricular volumes were calculated using two-dimensional echocardiography. An anti-G suit was inflated to 2, 4, and 6 psi in the standing and supine positions for 10 male subjects. In the supine position, mean arterial pressure increased from base line for all three inflation pressures (P = 0.05). The end-diastolic volume increased after 2-psi inflation (P = 0.03). Cardiac output or stroke volume did not change. After standing, mean arterial pressure (P = 0.002), end-diastolic volume (P = 0.002), and stroke volume (P = 0.05) fell after suit deflation. Peripheral vascular resistance fell in the 2- and 4-psi inflation profiles. In the standing protocol, mean arterial pressure, end-diastolic volume, stroke volume, and cardiac output rose with all three inflation pressures (P less than 0.05). After reclining, heart rate increased (P = 0.02) and mean arterial pressure fell (P less than 0.05) in the 4- and 6-psi inflation profiles after suit deflation. Increases in mean arterial pressure are caused by increases in cardiac preload and cardiac output after inflation of the anti-G suit while subjects were standing. Increased cardiac preload was not consistently seen after inflation while subjects were supine. Changes in end-diastolic volume and mean arterial pressure were dependent on the pressure used to inflate the anti-G suit.

Long-duration +Gz acceleration on cardiac volumes determined by two-dimensional echocardiography.

To enhance protection of humans exposed to long-duration low-gravity environments such as the Space Shuttle and National Aerospace Plane during re-entry or in the short-duration high(-)+Gz environment of fighter aircraft, the effects of +Gz acceleration on cardiovascular hemodynamics must be understood. This study reports the use of two-dimensional echocardiography in normal men during +Gz acceleration. The heart's position in relation to the chest did not change during acceleration up to +7 Gz. The success in maintaining high-quality images during exposures to G-forces of this magnitude may be attributed to the relatively low rate of G onset. End-diastolic volumes (EDV) and stroke volumes (SV) decreased during a +Gz acceleration ramp that increased until the subject experienced peripheral light loss (PLL) (P < .05). An inflated G-suit partially counteracted this effect. By 30 seconds of a +3 Gz acceleration plateau, the protective effects of the inflated G-suit to maintain EDV is lost and the EDV of the inflated G-suit was lower than the EDV of the uninflated G-suit (P < .05).

Reduction of macular oedema by acetazolamide in patients with chronic iridocyclitis: a randomised prospective crossover study.

Thirty patients with cystoid macular oedema secondary to chronic iridocyclitis were enrolled in a two period, prospective, randomised, double masked, crossover study that compared sustained release acetazolamide (500 mg twice a day) with a placebo to measure the effects on the reduction of cystoid macular oedema and improvement of visual acuity. All patients were treated for 1 month with either acetazolamide or placebo, received no treatment for 1 month, and were then treated for 1 month with the other medication. Statistically significant improvement in visual acuity was seen at 14 and 28 days in the treated patients. No improvement was seen when patients received placebo. Improved visual acuity was not associated with race or sex. However, younger patients (under age 55 years) were more likely to benefit from treatment. Results of vitreous fluorophotometry, obtained at baseline and 4 weeks, demonstrated an improvement in posterior vitreous penetration ratios and mid vitreous penetration ratios after treatment with acetazolamide but not with placebo.

Slug populations in mixed deciduous woodland.

Estimates of the population density and biomass of eight species of slug dwelling in a mixed deciduous woodland are reported for a 2-year period. Data concerning the life cycles of the species are also presented. It is concluded that slug populations in woodlands vary little in terms of biomass and density from year to year. Slug species diversity appears to be higher in woodland than in open habitats.

The effects of inflation of antishock trousers on hemodynamics in normovolemic subjects.

Antishock trousers may maintain mean arterial pressure in trauma patients by increasing central blood volume and cardiac output. Hemodynamics, end-diastolic volume, stroke volume, cardiac output, and blood pressure were recorded in eight supine, healthy men in antishock trousers using two-dimensional echocardiography. Two inflation protocols were used. The antishock trousers were inflated to 50 and 100 mm Hg in a random fashion and inflation was maintained for 30 minutes before deflation. End-diastolic volume and blood pressure rose significantly (p less than 0.05) after antishock trouser inflation of 50 and 100 mm Hg. With the 50 mm Hg inflation, the stroke volume and end-diastolic volume fell below baseline over time. This did not occur with the 100 mm Hg inflation. After suit deflation, the stroke volume, end-diastolic volume, and cardiac output increased with 50 mm Hg inflation. The study shows that the antishock trousers alter several hemodynamic parameters. With lower inflation pressures, antishock trousers cause an increase in arterial pressure by increasing peripheral resistance. At higher inflation pressures, the antishock trousers increase cardiac output and as the cardiovascular system adjusts, maintain the pressure by increasing peripheral resistance.

The effects of various antishock trouser inflation sequences on hemodynamics in normovolemic subjects.

In an attempt to maximize the hemodynamic effects of antishock trousers, a pair of such trousers was modified to a five-bladder trouser (one abdominal, two thigh, and two calf bladders) and inflated using three different inflation sequences. These three sequences were simultaneous inflation of all five bladders; concurrent inflation of the calf and thigh bladders and then inflation of the abdominal bladder (standard inflation); and sequential inflation of the calf, thigh, and abdominal bladders. Simultaneous inflation resulted in the greatest increase in blood pressure and the smallest increase in end-diastolic volume, stroke volume, and cardiac output. The standard inflation sequence resulted in slightly higher increases in end-diastolic volume, stroke volume, and cardiac output than the sequential inflation sequence, and a significantly larger increase in cardiac output than the simultaneous inflation sequence. Our study indicates that of the three sequences used, the standard inflation sequence produces the greatest blood return to the heart.