Air Breathing and Gill Ventilation Frequencies in Juvenile Tarpon, Megalops atlanticus: Responses to Changes in Dissolved Oxygen, Temperature, Hydrogen Sulfide, and PH

This study quantified the air-breathing frequency (ABf in breaths h^–1) and gill ventilation frequency (Vf in ventilations min^–1) of tarpon Megalops atlanticusas a function of PO₂, temperature, pH, and sulphide concentration. Ten tarpon held at normoxia at 22–33°C without access to atmospheric oxygen survived for eight days, and seven survived for 14 days (at which point the experiment was terminated) suggesting that the species is a facultative, rather than an obligate, air breather. At temperatures of 29°C and below ABf was highest and Vf was lowest at low oxygen partial pressures. Tarpon appear to switch from aquatic respiration to air breathing at PO₂levels of roughly 40 torr. The gills were the primary organ for oxygen uptake in normoxia, and the air-breathing organ the primary mechanism for oxygen uptake in hypoxia. At 33°C, both ABf and Vf were elevated but highly variable, regardless of PO₂. There were no mortalities in tarpon exposed to total H₂S concentrations of 0–232µM (0–150.9µM H₂S); however, high sulfide concentrations resulted in very high ABf and Vf near zero. Vf was reduced when pH was acidic. We conclude that air breathing provides an effective means of coping with the environmental conditions that characterize the eutrophic ponds and sloughs that juvenile tarpon typically inhabit.     

Changes in cardiac output during swimming and aquatic hypoxia in the air-breathing Pacific tarpon

Pacific tarpon (Megalops cyprinoides) use a modified gas bladder as an air-breathing organ (ABO). We examined changes in cardiac output (V(b)) associated with increases in air-breathing that accompany exercise and aquatic hypoxia. Juvenile (0.49 kg) and adult (1.21 kg) tarpon were allowed to recover in a swim flume at 27 degrees C after being instrumented with a Doppler flow probe around the ventral aorta to monitor V(b) and with a fibre-optic oxygen sensor in the ABO to monitor air-breathing frequency. Under normoxic conditions and in both juveniles and adults, routine air-breathing frequency was 0.03 breaths min(-1) and V(b) was about 15 mL min(-1) kg(-1). Normoxic exercise (swimming at about 1.1 body lengths s(-1)) increased air-breathing frequency by 8-fold in both groups (reaching 0.23 breaths min(-1)) and increased V(b) by 3-fold for juveniles and 2-fold for adults. Hypoxic exposure (2 kPa O2) at rest increased air-breathing frequency 19-fold (to around 0.53 breaths min(-1)) in both groups, and while V(b) again increased 3-fold in resting juvenile fish, V(b) was unchanged in resting adult fish. Exercise in hypoxia increased air-breathing frequency 35-fold (to 0.95 breaths min(-1)) in comparison with resting normoxic fish. While juvenile fish increased V(b) nearly 2-fold with exercise in hypoxia, adult fish maintained the same V(b) irrespective of exercise state and became agitated in comparison. These results imply that air-breathing during exercise and hypoxia can benefit oxygen delivery, but to differing degrees in juvenile and adult tarpon. We discuss this difference in the context of myocardial oxygen supply.     

Reflex bradycardia does not influence oxygen consumption during hypoxia in the European eel (Anguilla anguilla)

Most teleost fish reduce heart rate when exposed to acute hypoxia. This hypoxic bradycardia has been characterised for many fish species, but it remains uncertain whether this reflex contributes to the maintenance of oxygen uptake in hypoxia. Here we describe the effects of inhibiting the bradycardia on oxygen consumption (MO₂), standard metabolic rate (SMR) and the critical oxygen partial pressure for regulation of SMR in hypoxia (Pcrit) in European eels Anguilla anguilla (mean ± SEM mass 528 ± 36 g; n = 14). Eels were instrumented with a Transonic flow probe around the ventral aorta to measure cardiac output (Q) and heart rate (f _H). MO₂ was then measured by intermittent closed respirometry during sequential exposure to various levels of increasing hypoxia, to determine Pcrit. Each fish was studied before and after abolition of reflex bradycardia by intraperitoneal injection of the muscarinic antagonist atropine (5 mg kg⁻¹). In the untreated eels, f _H fell from 39.0 ± 4.3 min⁻¹ in normoxia to 14.8 ± 5.2 min⁻¹ at the deepest level of hypoxia (2 kPa), and this was associated with a decline in Q, from 7.5 ± 0.8 mL min⁻¹ kg⁻¹ to 3.3 ± 0.7 mL min⁻¹ kg⁻¹ in normoxia versus deepest hypoxia, respectively. Atropine had no effect on SMR, which was 16.0 ± 1.8 μmol O₂ kg⁻¹ min⁻¹ in control versus 16.8 ± 0.8 μmol O₂ kg⁻¹ min⁻¹ following treatment with atropine. Atropine also had no significant effect on normoxic f _H or Q in the eel, but completely abolished the bradycardia and associated decline in Q during progressive hypoxia. This pharmacological inhibition of the cardiac responses to hypoxia was, however, without affect on Pcrit, which was 11.7 ± 1.3 versus 12.5 ± 1.5 kPa in control versus atropinised eels, respectively. These results indicate, therefore, that reflex bradycardia does not contribute to maintenance of MO₂ and regulation of SMR by the European eel in hypoxia.     

Performance of the isolated rainbow trout heart perfused under self-controlled coronary pressure conditions: effects of high and low oxygen tension, arachidonic acid and indomethacin

The effects of arachidonic acid (AA) and indomethacin (IM) on performance, oxygen consumption and lactate release of the trout heart were studied in vitro TPa s m⁻³ using a perfusion system, which allowed the evaluation of the integrated function of ventricle and coronary system by continuously setting the input coronary flow and pressure proportional to the pressure and flow output of the heart. The heart was working against a fixed resistance. A reduction of input oxygen partial pressure (P_O2) from 175 torr (high P_O2) to 76 torr (low P_O2) increased the coronary flow (from 0.51 ml min⁻¹ kg⁻¹ to 1.21 ml min⁻¹ kg⁻¹, respectively) due to a strong reduction in coronary resistance (from 0.60 TPa s m⁻³ to 0.19 TPa s m⁻³, respectively). Oxygen consumption by the heart was significantly reduced from 20.7 ml min⁻¹ g⁻¹ at high P_O2 to 4.6 ml min⁻¹ g⁻¹ at low P_O2, while lactate production was increased from 24 μmol h⁻¹ g⁻¹ to 42 μmol h⁻¹ g⁻¹, indicating a higher contribution of anaerobic respiration to mechanical work. Mechanical efficiency was significantly higher at low than at high P_O2. Exogenous AA caused a depression of inotropism and a reduction in the aerobic metabolic rate (by 25–35%), which was not accompanied by increased lactate production. IM enhanced the depression of both inotropism and aerobic metabolism. The effect of AA and IM on the heart were amplified at low P_O2. Accepted: 20 October 1997     

Partitioning of respiration between the gills and air-breathing organ in response to aquatic hypoxia and exercise in the pacific tarpon, Megalops cyprinoides

The evolution of air-breathing organs (ABOs) is associated not only with hypoxic environments but also with activity. This investigation examines the effects of hypoxia and exercise on the partitioning of aquatic and aerial oxygen uptake in the Pacific tarpon. The two-species cosmopolitan genus Megalops is unique among teleosts in using swim bladder ABOs in the pelagic marine environment. Small fish (58-620 g) were swum at two sustainable speeds in a circulating flume respirometer in which dissolved oxygen was controlled. For fish swimming at 0.11 m s(-1) in normoxia (Po2 = 21 kPa), there was practically no air breathing, and gill oxygen uptake was 1.53 mL kg(-0.67) min(-1). Air breathing occurred at 0.5 breaths min(-1) in hypoxia (8 kPa) at this speed, when the gills and ABOs accounted for 0.71 and 0.57 mL kg(-0.67) min(-1), respectively. At 0.22 m s(-1) in normoxia, breathing occurred at 0.1 breaths min(-1), and gill and ABO oxygen uptake were 2.08 and 0.08 mL kg(-0.67) min(-1), respectively. In hypoxia and 0.22 m s(-1), breathing increased to 0.6 breaths min(-1), and gill and ABO oxygen uptake were 1.39 and 1.28 mL kg(-0.67) min(-1), respectively. Aquatic hypoxia was therefore the primary stimulus for air breathing under the limited conditions of this study, but exercise augmented oxygen uptake by the ABOs, particularly in hypoxic water.     

The emersion response of the Australian Yabby Cherax destructor to environmental hypoxia and the respiratory and metabolic responses to consequent air-breathing

The Australian Yabby Cherax destructor voluntarily emerges from water to breathe air with increased frequency as water PO₂ decreases. When the water PO₂ declined below 2.7 kPa the crayfish spent >50% of time breathing air. The respiratory gas transport, acid-base, ionic and energetic status were quantified in simulations of this emersion behaviour to determine the benefits that the crayfish may gain from switching to air-breathing. C. destructor initially showed an elevated O₂ uptake rate on emerging from hypoxic water, but after 1 h the O₂ uptake rate was not different from that of crayfish in normoxic water. During 3 h of air breathing, subsequent to 2.7 kPa aquatic hypoxia, the haemolymph PO₂ increased while oxygen content was essentially unchanged, although cardiac output increased 5-fold. The haemolymph PCO₂ increased from 0.44 to 1.21 kPa after 3 h while the CO₂ content increased from 3.47 to 8.66 mmol · l⁻¹ and the pH decreased from 7.73 to 7.57 after 1 h in air. In air C. destructor eventually achieved an O₂ uptake rate similar to that achieved in water. A general hyperglycaemia occurred without anaerobiosis. In air-breathing C. destructor, small changes in lactate appear to offset the decrease in haemocyanin-O₂ affinity caused by acid Bohr shift. During air-breathing, decreased haemocyanin-O₂ affinity assisted in maintaining O₂ diffusion into the tissues, but the ATP content of the tail muscle decreased so that after 3 h in air the energy charge was only 0.59. The data are consistent with a specific depression of the Emden-Meyerhof pathway, preventing either lactate formation or oxidative phosphorylation in the tail muscle, despite a concomitant glycogenolysis. Accepted: 26 February 1998     

The Antarctic notothenioid fish <Emphasis Type="Italic">Pagothenia borchgrevinki</Emphasis> is thermally flexible: acclimation changes oxygen consumption

Antarctic marine organisms are considered to have extremely limited ability to respond to environmental temperature change. However, here we show that the Antarctic notothenioid fish Pagothenia borchgrevinki is an exception to this theory. P. borchgrevinki was able to acclimate its resting metabolic rate and resting ventilation frequency after a 5°C rise in temperature. Acute exposure to 4°C resulted in an elevation in metabolic rate (57.8 ± 4.79 mg O₂ kg⁻¹ h⁻¹) and resting ventilation rate (40.38 ± 1.61 breaths min⁻¹) compared with fish at −1°C (metabolic rate 34.45 ± 3.12 mg O₂ kg⁻¹ h⁻¹; ventilation rate 29.88 ± 3.72 breaths min⁻¹). However, after a 1-month acclimation period, there was no significant difference in the metabolic rate (cold fish 29.52 ± 3.01; warm fish 31.13 ± 2.30 mg O₂ kg⁻¹ h⁻¹), or the resting ventilation rate (cold fish 28.75 ± 0.98; warm fish 34.25 ± 2.28 breaths min⁻¹) of cold and warm acclimated fish. Acclimation changes to the rate of oxygen consumption following exhaustive exercise were complex. The pattern of oxygen consumption during recovery from exhaustive exercise was not significantly different in either cold or warm acclimated fish.     

The development of an isokinetic squat device: reliability and relationship to functional performance

The aims of the present study were: (1) to assess aerobic metabolism in paraplegic (P) athletes (spinal lesion level, T4–L3) by means of peak oxygen uptake (V˙O_2peak) and ventilatory threshold (VT), and (2) to determine the nature of exercise limitation in these athletes by means of cardioventilatory responses at peak exercise. Eight P athletes underwent conventional spirographic measurements and then performed an incremental wheelchair exercise on an adapted treadmill. Ventilatory data were collected every minute using an automated metabolic system: ventilation (l · min⁻¹), oxygen uptake (V˙O₂, l · min⁻¹, ml · min⁻¹ · kg⁻¹), carbon dioxide production (V˙CO₂, ml · min⁻¹), respiratory exchange ratio, breathing frequency and tidal volume. Heart rate (HR, beats · min⁻¹) was collected with the aid of a standard electrocardiogram. V˙O_2peak was determined using conventional criteria. VT was determined by the breakpoint in the V˙CO₂−V˙O₂ relationship, and is expressed as the absolute VT (V˙O₂, ml · min⁻¹ · kg⁻¹) and relative VT (percentage of V˙O_2peak). Spirometric values and cardioventilatory responses at rest and at peak exercise allowed the measurement of ventilatory reserve (VR), heart rate reserve (HRr), heart rate response (HRR), and O₂ pulse (O₂ P). Results showed a V˙O_2peak value of 40.6 (2.5) ml · min⁻¹ · kg⁻¹, an absolute VT detected at 23.1 (1.5) ml · min⁻¹ · kg⁻¹ V˙O₂ and a relative VT at 56.4 (2.2)% V˙O_2peak. HRr [15.8 (3.2) beats · min⁻¹], HRR [48.6 (4.3) beat · l⁻¹], and O₂ P [0.23 (0.02) ml · kg⁻¹ · beat⁻¹] were normal, whereas VR at peak exercise [42.7 (2.4)%] was increased. As wheelchair exercise excluded the use of an able-bodied (AB) control group, we compared our V˙O_2peak and VT results with those for other P subjects and AB controls reported in the literature, and we compared our cardioventilatory responses with those for respiratory and cardiac patients. The low V˙O_2peak values obtained compared with subject values obtained during an arm-crank exercise may be due to a reduced active muscle mass. Absolute VT was somewhat comparable to that of AB subjects, mainly due to the similar muscle mass involved in wheelchair and arm-crank exercise by P and AB subjects, respectively. The increased VR, as reported in patients with chronic heart failure, suggested that P athletes exhibited cardiac limitation at peak exercise, and this contributed to the lower V˙O_2peak measured in these subjects. Accepted: 22 April 1997     

Oxygen transport in the green sea turtle

Summary Green sea turtles (Chelonia mydas) are well known as endurance swimmers and divers. Physiological correlates of these traits were studied in 9 adult sea turtles (mean body mass=87 kg) at a body temperature of 25°C. The respiratory properties of the blood were similar to those of other turtles except for a higher oxygen affinity (P ₅₀=18.2 Torr, pH 7.6), which may be an allometric function. Resting, systemic blood flow, calculated from the Fick principle was 21.5 ml·kg⁻¹. min⁻¹, similar to values reported for other turtles. Pulmonary blood flow, measured by mass spectrometry of acetylene uptake in the lungs was 24.0 ml·kg⁻¹·min⁻¹, not significantly different from the calculated systemic flow. Other evidence of a small (net) intracardiac shunt is the high arterial saturation (ca. 90%) of arterial blood. This distinctive feature of O₂ transport inC. mydas provides an content difference of 4.1 ml· dl⁻¹. This results in a relatively low blood convection requirement at rest =24.4 mlbtps·mlstpd ⁻¹), similar to that for many mammals. This would favor a high maximum O₂ uptake, as measured by others in this species. The relatively high O₂ affinity of blood in this species could be adaptive to “loading” O₂ during intermittent breathing while swimming and to utilizing the lung O₂ store during the progressive hypoxia of diving.     

Reduced performance of male and female athletes at 580 m altitude

This study examined the effect of mild hypobaria (MH) on the peak oxygen consumption (O_2peak) and performance of ten trained male athletes [ (SEM); O_2peak = 72.4 (2.2) ml · kg⁻¹ · min⁻¹] and ten trained female athletes [O_2peak = 60.8 (2.1) ml · kg⁻¹ · min⁻¹]. Subjects performed 5-min maximal work tests on a cycle ergometer within a hypobaric chamber at both normobaria (N, 99.33 kPa) and at MH (92.66 kPa), using a counter-balanced design. MH was equivalent to 580 m altitude. O_2peak at MH decreased significantly compared with N in both men [− 5.9 (0.9)%] and women [− 3.7 (1.0)%]. Performance (total kJ) at MH was also reduced significantly in men [− 3.6 (0.8)%] and women [− 3.8 (1.2)%]. Arterial oxyhaemoglobin saturation (S_aO₂) at O_2peak was significantly lower at MH compared with N in both men [90.1 (0.6)% versus 92.0 (0.6)%] and women [89.7 (3.1)% versus 92.1 (3.0)%]. While S_aO₂ at O_2peak was not different between men and women, it was concluded that relative, rather than absolute, O_2peak may be a more appropriate predictor of exercise-induced hypoxaemia. For men and women, it was calculated that 67–76% of the decrease in O_2peak could be accounted for by a decrease in O₂ delivery, which indicates that reduced O₂ tension at mild altitude (580 m) leads to impairment of exercise performance in a maximal work bout lasting ≈ 5 min. Accepted: 30 July 1996     

Aerobic swimming performance of juvenile Schizothorax chongi (Pisces, Cyprinidae) in the Yalong River, southwestern China

Schizothorax chongi (locally known as Xilian Yu), a fish species commonly found in Yalong River, has been declining quickly in recent years. One of the important factors, among many, is the interruption of the free flowing river by dams. To obtain data that can be applied to the design of a fishway for S. chongi and other species in the community, a laboratory study of juvenile S. chongi’s swimming energetics and kinematics was conducted in a flume-type respirometer equipped with a high speed video camera system to record swimming behavior. The aerobic metabolic rate, tail beat frequency (TBF) and tail beat amplitude (TBA) were measured during steady swimming at varying flow rates for fish of similar mass. A power function accurately describes the relationship between oxygen consumption rate (MO₂) and swimming speed (U). The estimated standard metabolic rate (SMR) calculated from the power function was 445.34 mg O₂ kg⁻¹ h⁻¹, similar to the experimental result of 431.5 mg O₂ kg⁻¹ h⁻¹. The relationship between cost of transport (COT) and U was, characteristically, inverse bell-shaped, with COT_min = 44.6 J kg⁻¹ m⁻¹ at U _opt = 5.5 body lengths per second (bl s⁻¹). There was a significant positive linear correlation between TBF and U. The slope of the correlation (0.33) was lower than for many other species, implying that S. chongi swim efficiently. The TBA, ranging from 0.15 to 0.2 bl, was found to be independent of U. Kinematic analyses indicates that S. chongi primarily depends on the caudal fin to generate forward thrust and employs three velocity-dependent swimming gaits. This investigation provides data on the swimming ability of S. chongi that will add to the basic science required for fishway design.     

Thermal sensitivity of scope for activity in Pagothenia borchgrevinki, a cryopelagic Antarctic nototheniid fish

The thermal sensitivity of scope for activity was studied in the Antarctic nototheniid fish Pagothenia borchgrevinki. The scope for activity of P. borchgrevinki at 0°C was 189 mg O₂ kg⁻¹ h⁻¹ (factorial scope 6.8) which is similar to that of temperate and tropical species at their environmental temperatures, providing no evidence for metabolic cold adaptation of maximum activity. The scope for activity increased to a maximum value of 266 mg O₂ kg⁻¹ h⁻¹ (factorial scope 8.3) at 3°C and then decreased from 3 to 6°C. The thermal sensitivity of critical swimming speed was also investigated and followed a similar pattern to aerobic scope for activity, suggesting oxygen limitation of aerobic performance. Oxygen consumption rates and ventilation frequencies were monitored for 24 h after the swimming challenge and the recovery of both parameters to resting levels was rapid and independent of temperature.     

The influence of either no fluid or carbohydrate-electrolyte fluid ingestion and the environment (thermoneutral versus hot and humid) on running economy after prolonged, high-intensity exercise

This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (V˙O_2max). Tests were undertaken in either a thermoneutral (22–23°C; 56–62% relative humidity, RH) or a hot and humid natural environment (Singapore: 25–35°C; 66–77% RH). The subjects were 15 young adult male Singaporeans [V˙O_2max = 55.5 (4.4 SD) ml kg⁻¹ min⁻¹]. The RE was measured at 3 m s⁻¹ [65 (6)% V˙O_2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined from prior tests, to maintain body mass (group mean = 17.4 ml min⁻¹). The V˙O₂ during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase in V˙O₂ from RE1 to RE2 ranged from 3.4 to 4.7 ml kg⁻¹ min⁻¹ across treatments. In conclusion, the deterioration in RE at 3 m s⁻¹ (65% V˙O_2max) after 60 min of running at 80% V˙O_2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or electrolytes, in both a thermoneutral and in a hot, humid environment. Accepted: 30 October 1997     

Role of the left aortic arch and blood flows in embryonic American alligator (<Emphasis Type="Italic">Alligator mississippiensis</Emphasis>)

All embryonic and fetal amniotes possess a ductus(i) arteriosus(i) that allows blood to bypass the pulmonary circulation and the non-functional lungs. The central hemodynamic of embryonic reptiles are unique, given the additional systemic aorta that allows pulmonary circulatory bypass, the left aorta (LAo). The LAo exits in the right ventricle or ‘pulmonary side’ of reptilian hearts in both embryos and adults, but its functional significance in ovo is unknown. This study investigated the role of the LAo in embryonic American alligators by surgically occluding the LAo and measuring oxygen consumption and, in addition, measured hemodynamic responses to hypoxia in embryonic alligators. We measured systemic cardiac output and primary chorioallantoic membrane (CAM) artery blood flow for normoxic and hypoxic-incubated (10% O₂) American alligator embryos (Alligator mississippiensis). Chronic blood flow (1–124 h) in the primary CAM artery for hypoxic-incubated embryos (92 ± 26 ml min⁻¹ kg⁻¹) was elevated when compared with normoxic-incubated embryos (29 ± 14 ml min⁻¹ kg⁻¹, N = 6; P = 0.039). For hypoxic-incubated embryos, acute LAo blood flow (49.6 ± 24.4 ml min⁻¹ kg⁻¹) was equivalent to the combined flow of the three systemic great vessels that arise from the left ventricle, the right aorta, common carotid and subclavian arteries (43.6 ± 21.5 ml min⁻¹ kg⁻¹, N = 5). Similarly, for normoxic-incubated embryos, LAo blood flow (27.3 ± 6.6 ml min⁻¹ kg⁻¹) did not statistically differ from the other three vessels (18.4 ± 4.9 ml min⁻¹ kg⁻¹, N = 5). This study contains the first direct test of LAo function and the first measurements of blood flow in an embryonic reptile. These data support the hypotheses that embryonic alligators utilize the LAo to divert a significant amount of right ventricular blood into the systemic circulation, and that CAM blood flow increases following chronic hypoxic conditions. However, surgical occlusion of the LAo did not affect egg [(V)\dot]_\textO2, \dot{V}_{{\text{O}}_{2}}, supporting the hypothesis that the LAo of reptiles is not critical to maintain in ovo oxygen consumption.     

Energetic cost of hovering flight in a nectar-feeding bat measured with fast-response respirometry

Hover-feeding glossophagine bats provide, in addition to the hummingbirds, a second vertebrate model for the analysis of hovering flight based on metabolic measurement and aerodynamic theory. In this study, the power input of hovering Glossophaga soricina bats (11.9 g) was measured by standard respirometry and fast-response (<0.2 s) oxygen analysis. Bats needed 5–7 s after a rest-to-flight transition to return to a respiratory steady state. Therefore, only hovering events preceeded by a 7-s flight interval were evaluated. V˙_O2 during hovering fluctuated with a frequency of 3–5 Hz, which corresponded in frequency to the licking movement of the tongue. During hovering, bats often may have hypoventilated as indicated by reduced V˙_O2 and a respiratory exchange ratio (RER) well below the steady-state value of 1. Steady-state oxygen consumption (and derived power input) during hovering was estimated to be 27 (25–29) ml O₂ g⁻¹ h⁻¹ (158 W kg⁻¹ or 1.88 W) in the 11.9-g bats as indicated by three independent findings: (1) V˙_O2 was 26 ml O₂ g⁻¹ h⁻¹ after 6.5 s of hovering, (2) the mean RER during single hovering events was at its steady-state level of 1 only at oxygen uptake rates of 25–29 ml g⁻¹ h⁻¹, and (3) when the oxygen potentially released from estimated oxygen stores was added to the measured oxygen uptake, the upper limit for oxygen consumption during hovering was found to be 29 ml O₂ g⁻¹ h⁻¹. Hovering power input was about 1.2 times the value of minimum flight power input (Winter and von Helversen 1998) and thus well below the 1.7–2.6 difference in power output postulated by aerodynamic theory (Norberg et al. 1993). Mass specific power input was 40% less than in hummingbirds. Thus, within the possible modes of hovering flight, Glossophaga bats seem to operate at the high-efficiency end of the spectrum. Accepted: 28 April 1998     

Relationship between maximal oxygen uptake on different ergometers, lean arm volume and strength in paraplegic subjects

The present experiment was designed to study the importance of strength and muscle mass as factors limiting maximal oxygen uptake (V˙O_{2 max} ) in wheelchair subjects. Thirteen paraplegic subjects [mean age 29.8 (8.7) years] were studied during continuous incremental exercises until exhaustion on an arm-cranking ergometer (AC), a wheelchair ergometer (WE) and motor-driven treadmill (TM). Lean arm volume (LAV) was estimated using an anthropometric method based upon the measurement of various circumferences of the arm and forearm. Maximal strength (MVF) was measured while pushing on the rim of the wheelchair for three positions of the hand on the rim (−30°, 0° and +30°). The results indicate that paraplegic subjects reached a similar V˙O_{2 max} [1.23 (0.34) l · min⁻¹, 1.25 (0.38) l · min⁻¹, 1.22 (0.18) l · min⁻¹ for AC, TM and WE, respectively] and V˙O_{2 max} /body mass [19.7 (5.2) ml · min⁻¹ · kg⁻¹, 19.5 (6.14) ml · min⁻¹ · kg⁻¹, 19.18 (4.27) ml · min⁻¹ · kg⁻¹ for AC, TM and WE, respectively on the three ergometers. Maximal heart rate f _{c max} during the last minute of AC (173 (17) beats · min⁻¹], TM [168 (14) beats · min⁻¹], and WE [165 (16) beats · min⁻¹], were correlated, but f _{c max} was significantly higher for AC than for TM (P<0.03). There were significant correlations between MVF and LAV (P<0.001) and between the MVF data obtained at different angles of the hand on the rim [311.9 (90.1) N, 313.2 (81.2) N, 257.1 (71) N, at −30°, 0° and +30°, respectively]. There was no correlation between V˙O_{2 max} and LAV or MVF. The relatively low values of f _{c max} suggest that V˙O_{2 max} was, at least in part, limited by local aerobic factors instead of central cardiovascular factors. On the other hand, the lack of a significant correlation between V˙O_{2 max} and MVF or muscle mass was not in favour of muscle strength being the main factor limiting V˙O_{2 max} in our subjects. Accepted: 31 January 1997     

Effect of intense interval workouts on running economy using three recovery durations

The purposes of this study were to determine whether running economy (RE) is adversely affected following intense interval bouts of 10 × 400-m running, and whether there is an interaction effect between RE and recovery duration during the workouts. Twelve highly trained male endurance athletes [maximal oxygen consumption; V˙O_{2 max} =72.5 (4.3) ml·kg⁻¹·min⁻¹; mean (SD)] performed three interval running workouts of 10 × 400 m with a minimum of 4 days between runs. Recovery duration between the repetitions was randomly assigned at 60, 120 or 180 s. The velocity for each 400-m run was determined from a treadmill V˙O_{2 max} test. The average running velocity was 357.9 (9.0) m · min⁻¹. Following the workout, the rating of perceived exertion (RPE) increased significantly (P < 0.01) as recovery duration between the 400-m repetitions decreased (14.4, 16.1, and 17.7 at 180s, 120s, and 60 s recovery, respectively). Prior to and following each workout, RE was measured at speeds of 200 and 268 m · min⁻¹. Changes in RE from pre- to post-workout, as well as heart rate (HR) and respiratory exchange ratio (R) were similar for the three recovery conditions. When averaged across conditions, oxygen consumption (V˙O₂) increased significantly (P < 0.01) from pre- to post-test (from 38.5 to 40.5 ml · kg⁻¹ · min⁻¹ at 200 m · min⁻¹, and from 53.1 to 54.5 ml · kg⁻¹ · min⁻¹ at 268 m · min⁻¹, respectively). HR increased (from 124 to 138, and from 151 to 157 beats · min⁻¹ respectively) and R decreased (from 0.90 to 0.78, and from 0.93 to 0.89, respectively) at 200 and 268 m · min⁻¹, respectively (P < 0.01). This study showed that RE can be perturbed after a high-intensity interval workout and that the changes in V˙O₂, HR and R were independent of the recovery duration between the repetitions. Accepted: 23 June 1997     

Size and distribution of oxygen stores in harp and hooded seals from birth to maturity

Pinnipeds rely primarily on oxygen stores in blood and muscles to support aerobic diving; therefore rapid development of body oxygen stores (TBO₂) is crucial for pups to transition from nursing to independent foraging. Here, we investigate TBO₂ development in 45 harp (Pagophilus groenlandicus) and 46 hooded (Cystophora cristata) seals ranging in age from neonates to adult females. We found that hooded seal adults have the largest TBO₂ stores yet reported (89.5 ml kg⁻¹), while harp seal adults have values more similar to other phocids (71.6 ml kg⁻¹). In adults, large TBO₂ stores resulted from large blood volume (harp169, hood 194 ml kg⁻¹) and high muscle Mb content (harp 86.0, hood 94.8 mg g⁻¹). In contrast, pups of both species had significantly lower mass-specific TBO₂ stores than adults, and stores declined rather than increased during the nursing period. This decline was due to a reduction in mass-specific blood volume and the absence of an increase in the low Mb levels (harp 21.0, hood 31.5 mg g⁻¹). Comparisons with other phocid species suggests that the pattern of blood and muscle development in the pre- and post-natal periods varies with terrestrial period, and that muscle maturation rates may influence the length of the postweaning fast. However, final maturation of TBO₂ stores does not take place until after foraging begins.     

Bimodal oxygen uptake in a freshwater air-breathing fish,Notopterus chitala

Measurements of bimodal oxygen uptake have been made in a freshwater air-breathing fish,Notopterus chitala at 29.0±1(S.D.)°C. xhe mean oxygen uptake from continuously flowing water without any access to air, was found to be 3.58±0.37 (S.E.) ml O₂ · h^?1 and 56.84+4.29 (S.E.) ml O₂ · kg^?1 · h^?1 for a fish weighing 66.92 + 11.27 (S.E.) g body weight. In still water with access to air, the mean oxygen uptake through the gills were recorded to be 2.49 ± 0.31 (S.E.) ml O₂ · h^?1 and 38.78 ± 1.92 (S.E.) ml O₂ · kg^?1 · h^?1 and through the accessory respiratory organs (swim-bladder) 6.04±0.87 (S.E.) ml O₂ · h^?1 and 92.32±2.91 (S.E.) ml O₂ · kg^?1 · h^?1 for a fish averaging 66.92±11.27 (S.E.) g. Out of the total oxygen uptake (131.10 ml O₂ · kg^?1 · h^?1), about 70% was obtained through the aerial route and the remainder 30% through the gills.     

Energy metabolism of underwater swimming in river-otters (Lutra lutra L.)

We used a still-water swim channel in conjunction with open-flow oxygen and carbon dioxide respirometry to examine the energy requirements of river-otters (Lutra lutra L.) swimming voluntarily underwater in Neumünster Zoo (Germany). While at rest on land (5 °C), river-otters had a respiratory quotient of 0.77 and a resting metabolic rate of 4.1 W kg⁻¹. This increased to an estimated 6.4 W kg⁻¹ during rest in water (11–15 °C) and to 12.3 W kg⁻¹ when the animals were feeding in the channel. River-otters swimming under water preferred a mean speed of 0.89 m s⁻¹, and their energy requirements attained 11.6 W kg⁻¹. Cost of transport, however, was minimal at 1.3 m s⁻¹ and amounted to 0.95 J N⁻¹ m⁻¹. Accepted: 3 November 1997