Cardiac and peripheral vascular responses to head-up tilt during whole body thermal stress.

During acute orthostatic stress, neurally mediated control of cardiac output (CO) and total peripheral vascular resistance (TPR) play an important role in the maintenance of systemic blood pressure. To examine the influence of thermal stress on the CO and TPR responses to orthostatic stress, 10 healthy male volunteers were exposed to normothermic control conditions followed by whole-body thermal stress produced by a cold or hot water-perfused suit during 5 min-70 degrees head-up tilt (HUT). HUT increased mean arterial pressure (MAP) by 3% of the pre-tilt value during normothermic control and cooling, whereas it decreased MAP by 4% of the pre-tilt value during heating. HUT decreased CO by 16-17% of the pre-tilt value under each thermal condition. The increase of TPR during HUT was exaggerated during cooling and inhibited during heating compared to normothermic control. Tilt-induced decrease of skin blood flow was greater during heating than cooling. These results suggest that the smaller increase of TPR rather than the CO change is responsible for the decreased MAP during acute orthostatic stress in hyperthermic humans. The contribution of skin vascular constriction to TPR changes during HUT is increased during heating and decreased during cooling.

Kinetic factors determining wheelchair propulsion in marathon racers with paraplegia.

OBJECTIVE: To assess the different factors that determine the propulsion of wheelchair in long distance racers with spinal cord injuries. DESIGN AND METHODS: Nine highly handicapped men who competed at the Oita International Wheelchair Marathon in 1995, participated in this study. Subjects performed steady and exhaustive wheelchair propulsion at their optimal speed on wheelchair rollers in a laboratory setting during a 5-min period. Movements of the trunk and arms were filmed by a video camera then analyzed kinetically using a two-dimensional analysis system. In order to determine the actual pushing time and angle of wheelchair, we measured the duration between hand contact and hand release from handrim. SETTING: Department of Rehabilitation Medicine University of Occupational and Environmental Health, Japan. RESULTS: The push time, cycle time, total push time, and angular velocity did not relate with the race time or wheelchair velocity. However, the total push angle correlated significantly (P<0.01) with the race time and wheelchair velocity. Improvement of the pushing angular velocity and pushing duration did not contribute to the race time. CONCLUSION: The skilful wheelchair propulsion in long distance racing depends on the total push angle. Improvement of the total push angle should be achieved by both prolongation of the total push time and increased pushing angular velocity.

Changes in insulation of wetsuits during repetitive exposure to pressure.

This investigation was intended to a) establish a relationship between pressure and thickness (and hence insulation) of wetsuits during acute changes in pressure from 0.5 to 5 atmospheres absolute (ATA); b) determine the effect of repetitive compression-decompression (C-D) procedures on the insulation properties of wetsuits; and c) assess the possible recovery of insulation after cessation of repetitive C-D. Various wetsuits with different thicknesses and types of linings were selected. In all wetsuits, insulation and thickness were both reduced as similar, curvilinear functions of acutely increasing pressure in the range of 0.5-5.0 ATA. Effects of repetitive C-D (3 ATA) were studied in 5-mm-thick suit samples with various linings. The insulation of suits (0.100-0.120 degrees C.W-1.m-2) rapidly decreased after the first 5000 C-D. In suits without linings (skin suits), the insulation was reduced to 0.080 degrees C.W-1.m-2 at 5000 C-D and revealed no further reduction during the continuation of C-D cycles up to 30,000. Suits lined with single- or double-sided jersey showed a continuous decrease in the insulation and thickness as the number of cycles increased up to 12,000 and remained at a lowered value (0.060 degrees C.W-1.m-2) until the termination of C-D (30,000 times). A nearly complete recovery of thickness was seen 10 days after cessation of C-D treatment in the skin suit when C-D cycles were less than 3500; however, no recovery was observed in suits with linings (either single- or double-sided) in 25 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of a conventional bicycle ergometer for underwater use.

With a few simple modifications, a conventional row-bicycle ergometer could be made suitable for underwater use. By attaching three sizes of fins to the pedal cranks of the ergometer, work load in water could be achieved to an oxygen consumption (VO2) level range of 400 to 2000 ml/min. The preferable range of pedaling speeds was 30-40 rpm to maintain a constant speed for a prolonged time. When using three different fins VO2 was found to be: VO2 = 254.3 + 4.50n - 0.12n2 + 0.0030n3 for no fins, VO2 = 250.1 + 8.30n - 0.32n2 + 0.0062n3 for small fins, VO2 = 254.0 + 6.10n - 0.24n2 + 0.0068n3 for medium fins, and VO2 = 256.4 + 13.77n - 0.72n2 + 0.0131n3 for large fins, when n is the number of pedaling rate. Major advantages of this modified ergometer for underwater exercise are 1) the modification is simple and the size of the device is small enough to place in a tank of a climatic chamber, 2) the ergometer can be biologically calibrated and used for a wide range of exercise oxygen uptakes, and 3) a subject can exercise in a comfortable upright position.