To breathe or not to breathe; the newt's problem

In a number of experiments designed to investigate the interaction between sexual behaviour and breathing, male newts were presented with females whose behaviour was controlled by the experimenter. In some experiments the male received sufficient positive feedback from the female to enable him to complete his sexual sequence; in others he did not. The results are interpreted in terms of McFarland's (1969) hypothesis that the transitions from one activity of another may occur either by competition or by disinhibition. It is suggested that in the absence of sufficient positive stimulation to enable the male to complete his sexual sequence, breathing occurs by competition with sexual behaviour. When the male has sufficient stimulation the temporal patterning of his behaviour becomes more under his control and breathing occurs by disinhibition.     

Hypoxia,angiogenesis and cancer therapy: To breathe or not to breathe?

As an expanding tumor conquers space within the host, it calls out for an increased oxygen supply. This demand is rarely matched by tumor blood vessels because neo-angiogenesis generates a structurally aberrant and functionally impaired vasculature. As a result of this unbalance, tumor progression is invariably associated with cancer cell hypoxia. Insufficient oxygenation appears to have opposing effects on cancer biology: on one hand, it limits tumor cell division; on the other, it selects for more malignant cells and it induces a series of cellular adaptations that sustain and foster tumor invasion. When designing a therapeutic strategy, how should we resolve this dichotomy? Should we cut oxygen supply, thereby halting neoplastic expansion, or should we let the tumor breathe, in order to prevent its malignant conversion? Recent studies using angiogenesis inhibitors or oxygen transporters finally provide some clue.     

To breathe or not to breathe: optimal strategies for finding prey in a dark, three-dimensional environment

The use of sophisticated telemetry logging devices has revealed that short-finned pilot whales employ energetic sprints to chase down their deep-dwelling prey. These sprints are costly in terms of energy, and therefore oxygen, which is a valuable resource for an animal that has to hold its breath while hunting. This finding highlights the challenges faced by ecologists when trying to develop foraging models for marine predators because many of the key parameters, such as movements in three dimensions, marine prey fields and metabolic adaptations of diving animals, remain largely unknown.     

Fetal neurogenesis: breathe HIF you can

Microvascular circulation creates a supporting niche for neurogenesis through the secretion of angiocrine factors. The emerging concept that energy balance and metabolic status play a role in the modulation of stem cells suggests that oxygen delivery by nearby capillary vascular beds could also regulate neurogenesis. Blood vessel formation and neuron production proceed in a coordinated fashion in the developing cerebral cortex, providing a unique opportunity to test the possibility that oxygen supply regulates cell fate decisions in neurogenic niches. The interesting study by the Carmeliet laboratory yields evidence that this is indeed the case and identifies HIF‐1α as the central element.     

Do lizards breathe through their mouths while running?

We measured the partitioning of airflow between nasal and oral circuits in five species of lizards before, during and after exercise. Expired gases were measured separately from the mouth and nose circuits in order to estimate the relative contribution of each circuit to ventilatory airflow. Nasal breathing dominates before exercise; however, during exercise the breathing pattern switched to oronasal expiration. Airflow averaged 30% oral expiration across all species during and after exercise. These results have important implications for the design of appropriate masks for respirometry in lizards. In order to ensure that all gases are captured, it is critically important that both the nose and mouth circuits are sampled.     

Mitigating the squash effect: sloths breathe easily upside down

Sloths are mammals renowned for spending a large proportion of time hanging inverted. In this position, the weight of the abdominal contents is expected to act on the lungs and increase the energetic costs of inspiration. Here, we show that three-fingered sloths Bradypus variegatus possess unique fibrinous adhesions that anchor the abdominal organs, particularly the liver and glandular stomach, to the lower ribs. The key locations of these adhesions, close to the diaphragm, prevent the weight of the abdominal contents from acting on the lungs when the sloth is inverted. Using ventilation rate and body orientation data collected from captive and wild sloths, we use an energetics-based model to estimate that these small adhesions could reduce the energy expenditure of a sloth at any time it is fully inverted by almost 13%. Given body angle preferences for individual sloths in our study over time, this equates to mean energy saving of 0.8–1.5% across individuals (with individual values ranging between 0.01 and 8.6%) per day. Given the sloth''s reduced metabolic rate compared with other mammals and extremely low energy diet, these seemingly innocuous adhesions are likely to be important in the animal''s energy budget and survival.     

Hypoxic and hypercapnic drives to breathe generate equivalent levels of air hunger in humans.

Anecdotal observations suggest that hypoxia does not elicit dyspnea. An opposing view is that any stimulus to medullary respiratory centers generates dyspnea via "corollary discharge" to higher centers; absence of dyspnea during low inspired Po(2) may result from increased ventilation and hypocapnia. We hypothesized that, with fixed ventilation, hypoxia and hypercapnia generate equal dyspnea when matched by ventilatory drive. Steady-state levels of hypoxic normocapnia (end-tidal Po(2) = 60-40 Torr) and hypercapnic hyperoxia (end-tidal Pco(2) = 40-50 Torr) were induced in naive subjects when they were free breathing and during fixed mechanical ventilation. In a separate experiment, normocapnic hypoxia and normoxic hypercapnia, "matched" by ventilation in free-breathing trials, were presented to experienced subjects breathing with constrained rate and tidal volume. "Air hunger" was rated every 30 s on a visual analog scale. Air hunger-Pet(O(2)) curves rose sharply at Pet(O(2)) <50 Torr. Air hunger was not different between matched stimuli (P > 0.05). Hypercapnia had unpleasant nonrespiratory effects but was otherwise perceptually indistinguishable from hypoxia. We conclude that hypoxia and hypercapnia have equal potency for air hunger when matched by ventilatory drive. Air hunger may, therefore, arise via brain stem respiratory drive.     

The breathing pattern after breath-holding: the influence of chest position and the drive to breathe.

The pattern of breathing following the breaking-point of sixty breath-holds has been studied in five healthy adults and compared with the pattern during recovery from CO2-rebreathing. The volume and direction of the first respiratory movement, and the VT, V relation for the first four complete breaths was measured. Only when breath-holds were terminated with an inspiration was the accumulated drive to breathe reflected in an increased volume of the first respiratory movement: terminating expirations simply returned the chest to the resting respiratory level. The volume of the first inspiration was not influenced by the intervention of a terminating expiration, suggesting that expiratory movements do not dissipate the non-chemical component of the drive to breathe. In three of the five subjects the tidal volumes for given levels of ventilation were greater following breath-holding than following rebreathing. This altered pattern of breathing has been interpreted in terms of an insiratory-augmenting reflex.