A. J. Woakes

Mechanics of breathing during strenuous exercise in Thoroughbred horses

The changes induced by exercise on the mechanics of breathing, as well as the simultaneous changes occurring in arterial blood gas tensions and in respiratory gas exchange were investigated in 6 healthy thoroughbred horses, performing a treadmill exercise of increasing intensity. Respiratory airflow and tidal volume (VT) were measured with ultrasonic flowmeters. Pleural pressure changes were measured by an oesophageal balloon catheter. Gas concentration of the expired air was analysed with a mass spectrometer; the oxygen consumption (VO2) and the carbon dioxide output (VCO2) were computed breath-by-breath. Arterial blood gas values were obtained by sampling from the carotid artery. Between rest and fast gallop VT, respiratory frequency, expired minute ventilation (VE), VO2, VCO2, total pulmonary resistance (RL), mechanical work of breathing (Wrm) and PaCO2 increased significantly while PaO2 decreased significantly. The Wrm.VO2(-1) ratio in galloping horses increased exponentially with VE. This, together with the relationship between the changes in PaO2 and in PaCO2 and the increase in the ventilatory mechanics parameters, suggests that the mechanics of breathing may be one of the factors constraining further increase in ventilation in exercising healthy horses.

Estimation of daily energy expenditure from heart rate and doubly labeled water in exercising geese

We investigated whether daily O₂ consumption (V̇o2) could be predicted from heart rate (fH) in five exercising barnacle geese (Branta leucopsis) and compared the accuracy of this method with that of the doubly labeled water (DLW) method. The regressions of V̇o2 on fH, based on incremental speed tests, differed among individual birds. The O₂ pulse (i. e., V̇o2/fH) progressively increased with exercise level from 0.22 mL O₂ heartbeat⁻¹ during resting to an estimated 0.47 mL O₂ heartbeat⁻¹ during flight. Daily V̇o2, was generally underestimated (-3.9%) by (individual) resting O₂, pulses but overestimated (+8.4%) by linear regressions of V̇o2 on fH. However, it was wellpredicted (+0.8%) by the O₂ pulses appropriate for each exercise level When using relationships derived from the group of birds, the estimations were generally improved (-3.3% for resting O₂, pulse, -0.03% for appropriate O₂ pulse) but poorer (+13.6%) for the group linear regression. Some of these predictions were better than the estimation of daily CO₂ production (V̇o2) by the two-compartment model of the DLW method (average algebraic error of +0.9%). We conclude that fH can be used to estimate daily energy expenditure in birds accuratelyprovided that (1) its application is limited to the range of exercise levels in which fH has been calibrated against V̇o2 and (2a) V̇o2-fH relationships are determined for each individual bird or (2b) the fH measurements of several free-ranging birds are averaged. Heart rate can also be used to indicate within-day variation in energy expenditure.

Implantable data logging system for heart rate and body temperature: its application to the estimation of field metabolic rates in Antarctic predators

The metabolic rate of free-ranging animals is difficult to measure, but of great importance in understanding the interactions of a species with its environment. Heart rate can, if correctly validated and calibrated, give an estimate of metabolic rate, with both a fine time resolution and over long periods. The telemetry of heart rate is well documented, but is not appropriate over long ranges (possibly several thousands of kilometres) or for diving species. An implantable data logger has therefore been developed for the long term recording of heart rate and body temperature. The logger is built using hybrid and ASIC construction techniques, weighs 20 g and measures 55×24×6 mm. The device is programmable, and its solid-state memory holds over 70 days of data if, for example, heart rate is counted and stored every minute. Current consumption is 155 μA while logging, 50 μA during a programmable initial delay period, and less than 1 μA when the logger closes down after filling its memory. These loggers have been deployed for two field seasons in gentoo penguins, black-browed albatross and fur seals.

Heart Rate and Oxygen Consumption of Exercising Gentoo Penguins

Heart rate (fH) and oxygen consumption (V̇o2) were recorded from gentoo penguins walking on a variable-speed treadmill. After an initial increase, fH and V̇o2 increased linearly with walking speed. A curvilinear regression equation best described the relationship between fH and V̇o2. Over a 3-d period, fH and V̇o2 were recorded continuously from six gentoo penguins that had been injected with doubly labeled water (DLW). When fH was used to predict V̇o2 over the 3 d, the estimate uwas not significantly different from the measured V̇o2 with an error (−1.0%) that was less than that produced by the DLW method (+ 1.6%). The estimate produced by the fH technique was also accurate when applied both to shorter periods (30 min) and to periods of activity and inactivity. Seven gentoo penguins were also swum in a water channel, and fH and V̇o2 were again recorded. The relationship between fH and V̇o2 determined from the birds in the water channel was not significantly different from that obtained from the walking birds. It is seems reasonable that, since the fH − V̇o2 relationship of most behaviors of the penguin have been determined while the animal is walking and swimming, fH can be used to predict the metabolic rate of free-ranging animals.

Validation of heart rate and doubly labelled water as measures of metabolic rate during swimming in California sea lions

1. The measurement of energy expenditures in free-ranging animals is essential if we are to understand fully the interaction between a species and its environment. This study examined the validity of heart rate (fH) and doubly labelled water (DLW) as measures of field metabolic rate (FMR) in California Sea Lions (Zalophus californianus). 2. Oxygen consumption and CO2 production were measured over 24 h by direct respirometry in six juvenile sea lions. The respirometer consisted of a hood over a flume in which the sea lions were exercised to various levels for 15 min periods throughout each experiment. The exercise regime produced a mean metabolic rate which was 2.3 times the predicted basal metabolic rate (BMR) with mean maxima of 6.27 times the predicted BMR. 3. Simultaneously with direct respirometry, mean CO2 production was estimated using DLW and O2 consumption was estimated using fH, which had previously been calibrated against O2 consumption. 4. The mean\pmSD O2 consumptions from direct respirometry, fH and DLW were 11.80\pm2.40, 11.95\pm2.17 and 15.01\pm3.77 ml min-1 kg-1 respectively. Paired Students t-tests showed no significant difference between O2 consumption by direct respirometry and the estimates from DLW and fH. DLW measurements ranged from -10% to +86% of the direct respirometry measurements (mean +36.4%) and fH measurements ranged from -28% to +23% of the direct respirometry measurements (mean +2.7%). 5. The range of estimated metabolic rates from fH was largely owing to individual differences in the slopes of the linear relationship between fH and O2 consumption. The range of metabolic rates from DLW could be partly attributed to the short duration of the experiments (24-25 h) but this was shown not to be the cause of the tendency to overestimate metabolic rate from DLW. It was concluded that both DLW and fH are valid methods for measuring FMR in California Sea Lions although it is possible that FMR could be overestimated when using DLW.

Energetics of diving in macaroni penguins.

SUMMARY Heart rate (fH), abdominal temperature (Tab) and diving depth were measured in thirteen free-ranging breeding female macaroni penguins. Measurement of these variables allowed estimation of the mass-specific rate of oxygen consumption (V̇O2) while diving and investigation of the physiological adjustments that might facilitate the diving behaviour observed in this species. In common with other diving birds, macaroni penguins showed significant changes in fH associated with diving, and these variables accounted for 36% of the variation in dive duration. When V̇O2 was calculated for dives of different durations, 95.3% of dives measured were within the calculated aerobic dive limit (cADL) for this species. Mean fH for all complete dive cycles was 147±6 beats min-1. When this fH is used to estimate V̇O2 of 26.2±1.4 ml min-1 kg-1 then only 92.8% of dives measured were within the cADL. Significant changes in abdominal temperature were not detected within individual dives, though the time constant of the measuring device used may not have been low enough to record these changes if they were present. Abdominal temperature did decline consistently during bouts of repeated diving of all durations and the mean decrease in Tab during a diving bout was 2.32±0.2°C. There was a linear relationship between bout duration and the magnitude of this temperature drop. There was no commensurate increase in dive duration during dive bouts as Tab declined, suggesting that macaroni penguins are diving within their physiological limits and that factors other than Tab are important in determining the duration of dives and dive bouts. Lowered Tab will in turn facilitate lower metabolic rates during diving bouts, but it was not possible in the present study to determine the importance of this energy saving and whether it is occurs actively or passively.

Impact of Externally Attached Loggers on the Diving Behaviour of the King Penguin

The impact of relatively small externally attached time series recorders on some foraging parameters of seabirds was investigated during the austral summer of 1995 by monitoring the diving behaviour of 10 free‐ranging king penguins (Aptenodytes patagonicus) over one foraging trip. Time‐depth recorders were implanted in the abdominal cavities of the birds, and half of the animals also had dummy loggers attached on their backs. Although most of the diving behaviour was not significantly affected by the external loggers ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Heart rate and behavior of fur seals: implications for measurement of field energetics

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