The Mouse-To-Elephant Metabolic Curve: Historical Overview.

Although it is intuitive that large mammals need more food than smaller ones, it is not so obvious that, relative to their body mass, larger mammals consume less than smaller ones. In fact, on a per kg basis, the resting metabolic rate of a mouse is some 50 times higher than that of an elephant. The fact that metabolism could not be proportional to the mass of the animal was suggested by Sarrus and Rameaux in 1838.

Breath-by-breath analysis of respiratory sinus arrhythmia in dogs.

Dogs differ greatly in size, heart (HR) and breathing rates (BR). In addition, they have a clear Respiratory Sinus Arrhythmia (RSA) at rest. Therefore, better than any other mammalian species, dogs offer an opportunity to test whether resting RSA varies with body weight, HR or BR.

Social interaction and the thermogenic response of chicken hatchlings.

The aggregation of two or more individuals of the same species (huddling) is common in mammals and birds, especially in the cold. The physical contact reduces the weight-specific body surface exposed to the environment, thus lowering heat loss and the thermogenic needs. This study investigated the possibility that the mere presence of a conspecific, in absence of physical contact, may by itself influence metabolic rate during cold.

Respiratory sinus arrhythmia during a mental attention task: the role of breathing-specific heart rate.

It is known that a mental attention task (MAT) can modify the magnitude of the increase in instantaneous heart rate (HR) with inspiration, or Respiratory Sinus Arrhythmia (RSA). Here, we asked whether the RSA changes were mediated by the changes in HR, breathing frequency (f) or HR/f ('breathing specific heart rate'). This latter reflects the degree of coupling between pulmonary blood and air flows, the optimization of which may be the function of RSA.

Hypoxic hypometabolism in chicken embryos: conformism and downregulation.

Postnatally, during hypoxia the decrease in oxygen consumption ( [Formula: see text] ) can exceed what expected from the limitation in O availability, meaning that [Formula: see text] -downregulation exceeds O-conformism. We questioned whether a similar phenomenon could occur prenatally, in chicken embryos at mid- (E11, out of 20.5 days) or near end- (E18) incubation.

Behavioral thermoregulation in avian embryos: Spectrum analysis of calls in warm and cold conditions.

During the last days of incubation vocalization is a form of communication between the avian embryo and the incubating parent. Commonly, embryonic calls increase when ambient temperature (Ta) deviates from the optimal range, but no information is available on whether the characteristics of the calls differ between warming and cooling. Rate of calls, power spectra (distribution of the call's energy among its frequency components) and spectrograms (time-frequency plots) were obtained in chicken embryos during the external pipping phase, in normothermia (38 °C), during progressive cooling to Ta = 27 °C (C) or progressive warming to Ta = 43 °C (W) over a short (30 min) or a long (150 min) period.

Prenatal catch-up growth: A study in avian embryos.

Whether the growth of embryos after a period of stunt becomes accelerated (Catch-Up Growth, CUGr), as it occurs postnatally, has rarely been examined experimentally in any class of animals. Here, hypoxia or cold of different degrees and durations caused growth retardation in chicken embryos during the first or second week of incubation. On average, on the day of removal of the growth-inhibition, the weight of the experimental groups was 73% (wet) and 61% (dry) of control embryos, while near end-incubation (embryonic day E18) their weight averaged significantly more, respectively, 80% and 84% of controls (P < 0.

How to breathe? Respiratory mechanics and breathing pattern.

On theoretical grounds any given level of pulmonary or alveolar ventilation can be obtained at various absolute lung volumes and through many combinations of tidal volume, breathing frequency and inspiratory and expiratory timing. However, inspection of specific cases of newborn and adult mammals at rest indicates that the breathing pattern reflects a principle of economy oriented toward minimal respiratory work. The mechanisms that permit optimization of respiratory cost are poorly understood; yet, it is their efficiency and coordination that permits pulmonary ventilation at rest to require only a minimal fraction of resting metabolism.

The magnitude of respiratory sinus arrhythmia of a large mammal (the horse) is like that of humans.

Heart rate (FH) accelerates in inspiration and decelerates in expiration, a phenomenon known as Respiratory Sinus Arrhythmia (RSA). Although the presence of RSA has been documented in many species, how its magnitude compares among species is unknown. We asked whether the magnitude of RSA in a large mammal, the horse, differed from that of previously measured humans.

Respiratory sinus arrhythmia in the immediate post-exercise period: correlation with breathing-specific heart rate.

Background: Although the absolute values of pulmonary ventilation and cardiac output are similar, the designs of the respiratory and cardiovascular systems imply major differences in flow patterns, airflow being intermittent by comparison to the quasi-continuous pulmonary blood flow.

Purpose: We hypothesized that respiratory sinus arrhythmia (RSA, difference in heart rate (f) between inspiration and expiration, as percent of mean f) ameliorates the inevitable differences between air- and blood-flow patterns. Specifically, we hypothesized RSA to correlate more closely to the ratio between f and breathing frequency (f) (f/f "breathing-specific heart rate", a proxy for cardio-respiratory coupling) than to either f or f alone.

Thermal tachypnea in avian embryos.

Many adult mammals and birds respond to high surrounding temperatures with thermal tachypnea - an increase in breathing frequency accompanied by shallow tidal volume, with minimal increase in oxygen consumption ( ). This pattern favors heat dissipation by evaporative water loss (EWL) through the respiratory tract. We asked to what extent this response was apparent at the earliest stages of development, when pulmonary ventilation initiates.

Hematocrit of mammals (Artiodactyla, Carnivora, Primates) at 1500m and 2100m altitudes.

The rise in hematocrit (Hct) is one of the hallmarks of human acclimatization to high altitude and, in chronic conditions, reflects the hypoxia-induced polycythemia. However, it is not a uniform response among domestic species and it is not found in Andean camelids, species long adapted to high altitudes. Hence, we asked to what extent the polycythemia of humans is common among mammals.

Aerobic scope in chicken embryos.

We investigated the aerobic scope of chicken embryos, that is, the margin of increase of oxygen consumption ( [Formula: see text] ) above its normal value. [Formula: see text] was measured by an open-flow methodology at embryonic ages E3, E7, E11, E15, E19 and at E20 at the internal (IP) and external pipping (EP) phases, at the normal incubation temperature (Ta=38°C), in hypothermia (Ta=30°C) and in hyperthermia (Ta=41 and 44°C). In the cold, Q averaged ~2 at all ages, except in IP and EP when lower values (~1.

The cessation of breathing in the chicken embryo during cold-hypometabolism.

The avian embryo toward end-incubation combines gas exchange through the chorioallantoic membrane (CAM) and pulmonary ventilation (V˙E). The main experiments examined breathing activity during cold-hypometabolism. Chicken embryos close to hatching were prepared for simultaneous measurements of oxygen consumption ( [Formula: see text] ) and carbon dioxide production ( [Formula: see text] ; open-flow methodology) and breathing frequency (f; barometric technique).

Hematocrit and Hemoglobin Levels of Nonhuman Apes at Moderate Altitudes: A Comparison with Humans.

Mortola, Jacopo P. and DeeAnn Wilfong. Hematocrit and hemoglobin levels of nonhuman apes at moderate altitudes: a comparison with humans.

Gender and the circadian pattern of body temperature in normoxia and hypoxia.

Circadian patterns are at the core of many physiological processes, and their disruption can have short- and long-term consequences. This essay focuses on one of the best known patterns, the daily oscillation of body temperature (Tb), and the possibility of its difference between genders. From human and animal studies globally considered, the tentative conclusion is reached that differences in Tb circadian pattern between genders are very small and probably limited to the timing of the rhythm, not to its amplitude.

The contribution of heart rate to the oxygen consumption of the chicken embryo during cold- or hypoxia-hypometabolism.

In embryos, cooling and hypoxia cause a decrease in oxygen consumption ( [Formula: see text] ); we asked what was the relative contribution of heart rate (HR) and of the 'not-HR' factor (the product of stroke volume and arterial-venous O difference) to the drop in [Formula: see text] . Data of HR (with subcutaneous electrodes) and [Formula: see text] (by an open-flow methodology) were collected simultaneously on chicken embryos close to end-incubation. Over the last four days of incubation (E16-E20) differences in HR contributed about 30% of the differences in resting [Formula: see text] among embryos.

The hypometabolic response to repeated or prolonged hypoxic episodes in the chicken embryo.

Hypoxia (hx) in embryos causes a drop in oxygen consumption ( [Formula: see text] ) that rapidly recovers upon return to normoxia. We asked whether or not this pattern varies with the embryo's hypoxic history. The [Formula: see text] of chicken embryos in the middle (E12) or at end-incubation (E19) was measured by an open-flow methodology during 15-min epochs of moderate (15% O2) or severe hx (10% O2).

Thinking about breathing: Effects on respiratory sinus arrhythmia.

Respiratory sinus arrhythmia (RSA), the increase and decrease in instantaneous heart rate (HR) with inspiration and expiration, is commonly evaluated as function of breathing frequency f. However, to the extent that RSA plays a role in the efficiency of gas exchange, it may be expected to correlate better with HR/f ('breathing specific heart rate') than with f, because the former is a better reflection of the cardio-respiratory coupling. We measured RSA breath-by-breath in 209 young men and women during spontaneous breathing and during volitional breathing under auditory cues at vastly different f.

The cooling time of fertile chicken eggs at different stages of incubation.

We asked whether or not the thermal characteristics of fertile avian eggs changed throughout incubation. The cooling and warming times, expressed by the time constant τ of the egg temperature response to a rapid change in ambient temperature, were measured in fertile chicken eggs at early (E7), intermediate (E11) and late (E20) stages of embryonic development. Same measurements were conducted on eggs emptied of their content and refilled with water by various amounts.

Thermographic analysis of the radiant heat of chicken and duck eggs in relation to the embryo's oxygen consumption.

In eggs, the metabolic activities of the developing embryo produce heat (H) that is dissipated in various forms, including radiation. Given that much of the total heat radiated by an egg (Htot) is heat acquired passively, we asked whether it was possible to detect the fraction produced metabolically (Hmetab) and the extent of its correlation with the embryo's metabolic rate. In chicken and duck eggs at various incubation ages, under standardized experimental conditions of heat conduction and convection, Hmetab was measured by thermography as the difference in Htot between fertile and sterile eggs.

Respiratory sinus arrhythmia in young men and women at different chest wall configurations.

Respiratory sinus arrhythmia (RSA) is an acceleration of heart rate during inspiration and deceleration with expiration. We asked whether or not in humans some of the volume-related information necessary for RSA originated from the chest wall. Men and women, 19-20 years old, were breathing supine.

Chicken hatchlings prefer ambient temperatures lower than their thermoneutral zone.

We investigated whether or not the preferred ambient temperature (Tapref) of the 1-day old chicken hatchling, a precocial neonate with excellent locomotory capacity, clearly identifiable thermogenesis and independence from maternal care, coincides with the lower critical temperature (LCT) of thermoneutrality and minimal oxygen consumption (V̇(O(2))). Tapref of single chicks measured in a thermocline (N=16) averaged 33.5±0.

Thermogenesis, vocalization, and temperature preference of 1-day-old chicken hatchlings after cold-exposure in late embryogenesis.

In a thermal gradient the preferred ambient temperature (T(a) pref) of chicken hatchlings is a few degrees lower than thermoneutrality. To investigate whether a correlation may exist between T(a) pref and the autonomic thermogenic capacity or not we studied a group of hatchlings (N = 15) exposed to cold at end-incubation, a procedure known to increase their postnatal thermogenesis. Chicken embryos were exposed to cold (34.

Breathing pattern and ventilatory chemosensitivity of the 1-day old Muscovy duck (Cairina moschata) in relation to its metabolic demands.

Adult birds have a ventilatory equivalent (pulmonary ventilation-oxygen consumption ratio, V˙ E/ [Formula: see text] ) lower than mammals because of the superior gas exchange efficiency of their respiratory apparatus. In particular, adult Muscovy ducks (Cairina moschata) have been reported to have an extraordinary low ventilatory equivalent (~14mL STPD·mL BTPS(-1)). We asked if similar high efficiency was already apparent in duck hatchlings.