Biomedical subjects

R J Full

Publications and source records attributed to R J Full.

24 records · Page 2Linked to original sources

PubMed1988

Elimination kinetics of acetylene and Freon 22 in resting and active lungless salamanders.

To quantify diffusion limitation in cutaneous gas exchange, the elimination of two inert gases of different diffusivity, Freon 22 (CHC1F2) and acetylene (C2H2), was measured simultaneously in exclusively skin-breathing lungless salamanders, Desmognathus quadramaculatus. In resting salamanders, elimination of both gases could be described as the sum of three exponential terms. For both the medium and the slow exponential component, the ratio of the respective rate constants (k) for acetylene and Freon averaged 1.77. This value is between the values expected for perfusion limitation (1.00) and diffusion limitation (1.94), indicating combined diffusion and perfusion limitation. In salamanders stimulated to run on a treadmill, the elimination rates and the rate constants increased more for Freon than for acetylene. During spontaneous activity, the increase in elimination of Freon was larger than that of acetylene. These findings suggest an increase in the diffusing capacity of the skin during exercise. Thus the diffusing capacity of salamander skin for gases appears to be variable and to be adjusted to meet the increased O2 requirement during exercise.

Acetylene↗

PubMed1986

Locomotion without lungs: energetics and performance of a lungless salamander.

Lungless salamanders (4.1 g) were exercised on a treadmill enclosed in a Plexiglas respirometer at a range of speeds (0.05-0.24 km/h). O2 consumption (VO2) was determined continuously by open-flow respirometry. At the onset of exercise VO2 increased to a "steady state" in approximately 2-5 min. VO2 (ml O2 X g-1 X h-1) increased linearly with speed (S), VO2 = 2.3 (S) + 0.1 (r2 = 0.74). The minimum cost of transport (2.3 ml O2 X g-1 X km-1) was three-fourths of that predicted for a vertebrate of the same mass. Maximum O2 consumption (VO2max) was attained at 0.16 km/h (maximum aerobic speed), where this VO2 was six to nine times above standard rates. The net rate of whole-body lactate production (WBL) was insignificant at slow speeds (less than 46% VO2max) but did increase at submaximal work loads (85% VO2max). The highest WBL (0.07 mg X g-1 X min-1) was measured at a speed (0.20 km/h) that exceeded the maximum aerobic speed. Salamanders sustained exercise at slow speeds for over 2 h. The greatest decline in endurance (i.e., from 120 to 10 min) occurred at speeds below the maximum aerobic speed, where being lungless may have little consequence. At fast rates of locomotion a limited VO2max was associated with a low maximum aerobic speed and a modest capacity for sustained activity.

Animals↗

PubMed1983

Aerobic response to exercise of the fastest land crab.

To view the aerobic response to exercise, the ghost crab Ocypode guadichaudii was run in a treadmill respirometer at three velocities (0.13, 0.19, and 0.28 km/h) while oxygen consumption (VO2) was monitored. A steady-state VO2 that increased linearly with velocity was attained. VO2 transient periods at the beginning and end of exercise were extremely rapid with half times from 50 to 150 s. The magnitude of oxygen deficit and debt were small and both showed increases with an increase in velocity. Oxygen debt was measured at each velocity after 4-, 10-, and 20-min exercise bouts. No change in the magnitude of oxygen debt was observed with respect to exercise duration. Maximal VO2 was 11.9 times the average resting VO2. Oxygen uptake kinetics have shown only very sluggish and reduced rates in five other more sedentary crab species previously tested. The aerobic response pattern observed in the present study is more comparable to that of exercising mammals and highly aerobic ectothermic vertebrates. This suggests that the ghost crab meets the energy demand of sustained exercise by aerobic ATP production in contrast to many other crab species.

Aerobiosis↗

PubMedDate not supplied

Intermittent locomotion increases endurance in a gecko.

Nocturnal geckos can actively forage at low temperatures. A low minimum cost of locomotion allows greater sustainable speeds by partially offsetting the decrease in maximal oxygen consumption (VO2max) associated with low nocturnal temperatures. The nocturnality hypothesis (Autumn et al. 1997) proposes that the reduced cost of continuous locomotion is a shared, derived characteristic that increases the capacity to sustain locomotion at low temperatures. Yet many lizards move intermittently at speeds exceeding those that elicit VO2max. We exercised the frog-eyed gecko, Teratoscincus przewalskii, continuously and intermittently on a treadmill. At an exercise speed of 0.90 km h-1 (270% maximum aerobic speed), lizards alternating a 15-s exercise period with a 30-s pause period exhibited a 1.7-fold increase in distance capacity (total distance traveled before fatigue) compared with lizards exercised continuously at the same average speed (0.30 km h-1). The average aerobic cost of intermittent exercise was not significantly different from VO2max. Locomoting intermittently could augment the increase in endurance resulting from the low minimum cost of continuous locomotion in nocturnal geckos. Intermittent behavior could increase the endurance of lizard movement in general.

Animals↗

PubMedDate not supplied

Low cost of locomotion in the banded Gecko: a test of the nocturnality hypothesis.

This study tested the hypothesis that there has been an evolutionary increase in locomotor performance capacity at low temperature in nocturnal lizards. Nocturnal lizards are often active at low and suboptimal body temperatures. An evolutionary decrease in the minimum cost of locomotion could increase endurance capacity at low temperature, partially offsetting the thermal handicap of nocturnality. In support of the nocturnality hypothesis, we discovered that minimum cost of locomotion of a nocturnal gecko, Coleonyx variegatus (4.2 g), was only 58% of the minimum cost of locomotion of Phrynosoma douglassii, a diurnal lizard (4.5 g). As a result, maximum aerobic speed was 2.3 times as great in the nocturnal lizard compared to the diurnal lizard. By using the method of phylogenetically independent contrasts at the species level, we showed that the relationship between mass and minimum cost of locomotion in diurnal lizards was similar to that of the ahistorical standard allometry and that low minimum cost of locomotion in geckos represents a significant evolutionary change from the ancestral diurnal pattern. The decrease in the minimum cost of locomotion concordant with the evolution of nocturnality suggests that geckos evolved a greater capacity for sustained locomotion at low temperature.

Animals↗

PubMedDate not supplied

Performance limits of low-temperature, continuous locomotion are exceeded when locomotion is intermittent in the ghost crab.

Since a decline in temperature decreases aerobic capacity and slows the kinetics of exercise-to-rest transitions in ectotherms, we manipulated body temperature to better understand the performance limits of intermittent locomotion. Distance capacity (i.e., the total distance traveled before fatigue) of the ghost crab, Ocypode quadrata, was determined during acute exposure to 15 degrees C inside a treadmill-respirometer. Instead of exacerbating the near-paralyzing effects of low body temperature resulting from the frequent transitions, intermittent locomotion allowed animals to exceed the performance limits measured during steady-state locomotion. At low temperature, distance capacity for continuous locomotion at 0.04 m s(-1) (83% maximum aerobic speed) was 60 m. When 30 s of exercise at 0.08 m s(-1) (166% maximum aerobic speed) was alternated with 30 s of rest, distance capacity increased to 271 m, 4.5-fold greater than continuous locomotion at the same average speed (83% maximum aerobic speed). A 30-s pause following a 30-s exercise period was sufficient for maintaining low lactate concentrations in muscle and for partial resynthesis of arginine phosphate. A greater dependency on nonoxidative metabolism due to slowed oxygen uptake kinetics at low temperature resulted in a decreased duration of the critical exercise period, which increased performance relative to that measured at higher temperatures (30 s at 15 degrees C vs. 120 s at 24 degrees C). Despite the ghost crab's limited aerobic capacity at 15 degrees C, distance capacity during intermittent locomotion at low temperature can be comparable to that of a crab moving continuously at a body temperature 10 degrees C warmer. While endurance capacity is generally correlated with maximum aerobic speed, we have demonstrated that both locomotor behavior and body temperature must be considered when characterizing performance limits.

Acclimatization↗