Spermophilus lateralis, the golden-mantled ground squirrel, while euthermic exhibits a strong hypoxic ventilatory response, but a relatively blunted hypercapnic ventilatory response similar to other semi-fossorial mammals. Under resting conditions, carotid body chemoreceptors provide a tonic excitatory input to the frequency component of ventilation. Carotid body denervation (CBX) results in a 40% decrease in minute ventilation (V). The overall ventilatory response to hypoxia is unaffected by CBX, although the ventilatory threshold is significantly shifted to lower levels of inspired O₂. CBX also has little effect on the overall response to hypercapnia. Thus, in S. lateralis, it appears that changes in the partial pressure of O₂ (P0₂) In the blood act centrally, rather than peripherally, to play a predominate role in ventilatory control. Chronic exposure to hypoxia and hypercapnia (CHH, 17% O₂ and 4% CO₂) does not result in overall ventilatory acclimation, with minute ventilation being similar to control squirrels acutely exposed to hypoxic and hypercapnic conditions. In spite of this, CHH exposure does result in adjustments to respiration; frequency is decreased and tidal volume is elevated compared to control squirrels acutely exposed to CHH conditions. Overall V sensitivities to both hypoxia and hypercapnia are not significantly altered by CHH exposure. It appears that acclimation to chronic hypoxic and hypercapnic conditions in S. lateralis may increase alveolar minute ventilation relative to total minute ventilation and thus minimize the changes in arterial PO₂ and Pco₂ during hypoxic and hypercapnic exposure. During entrance into hibernation, as metabolic rate and body temperature decline, concomitant decreases in ventilation occur. Two patterns of respiration occur during deep hibernation; a burst breathing pattern characterized by long non-ventilatory periods (Tnvp) separated by bursts of several breaths and a single breath pattern characterized by single breaths separated by a relatively short Tnvp. In S. lateralis during hibernation at body temperatures between 6° and 10°C, a burst breathing pattern prevails. At slightly lower body temperatures, less than 4°C, a single breath breathing pattern prevails. Both burst breathing and single breath breathing squirrels have similar overall levels of resting minute ventilation. Burst breathing squirrels exhibit a significant respiratory response to hypoxia (3% O₂) and when the decreases in metabolic rate during hibernation are taken into account (air convection requirement) their hypoxic sensitivity is similar to that in awake S. lateralis. In contrast, single breath breathing squirrels do not respond to hypoxia at any level tested (down to 3% O₂). Both burst breathing and single breath breathing squirrels show large ventilatory repsonses to hypercapnia. In the burst breathing state hypercapnic sensitivity is significantly higher compared to the single breath breathing state, due to an augmented frequency response during burst breathing. In both groups of hibernating squirrels ventilation is increased during hypercapnia solely by decreases in the nonventilatory period. When ventilation is standardized for the decreases in metabolic rate during hibernation both burst breathing and single breath breathing S. laterlis exhibit a much higher hypercapnic sensitivity than that seen in awake S. lateralis. Carotid body denervation has little effect on ventilatory pattern generation or ventilatory sensitivities to hypoxia and hypercapnia in hibernating squirrels. It appears that during hibernation in S. lateralis, ventilation is controlled primarily by changes in the partial pressure of CO₂ (Pc0₂) in tne blood acting centrally to stimulate ventilation. The burst breathing pattern is produced centrally, as are the respiratory responses to hypoxia and hypercapnia. Thus, central mechanisms involved with ventilatory control are extremely important in both the euthermic state and the hibernating state, but the chemical stimuli regulating ventilation appear to be fundamentally different in euthermic and hibernating S. lateralis. / Science, Faculty of / Zoology, Department of / Graduate

Digitized by Kansas Correctional Industries

Récemment, il a été proposé que le fait de respirer profondément à une fréquence d'environ 0,1 Hz, soit 6 respirations par minute (RPM), augmente la variabilité de la pression artérielle systolique, augmentant ainsi l'activité des barorécepteurs et la variabilité du rythme cardiaque (VRC). Le biofeedback cardiaque est une méthode qui permet d'identifier la fréquence respiratoire qui entraînera la VRC maximale pour un individu. D'autre part, de récentes études cliniques ont démontré que la respiration à 6 RPM et le biofeedback cardiaque sont efficaces pour réduire la douleur. La douleur aigüe cause plusieurs réponses physiologiques comme une augmentation du rythme respiratoire, du rythme cardiaque (RC) et de la pression artérielle (PA) via une augmentation de l'activité du système nerveux sympathique. Une augmentation de l'activité du système nerveux parasympathique (vagal) permet de rétablir l'homéostasie. Plus particulièrement, l'augmentation de la PA est rapidement tamponnée par les baroréflexes, mais en plus, l'activation des baroréflexes permet de réduire la douleur. Plusieurs différentes manières d'activer les baroréflexes ont été explorées dans le but de diminuer la douleur. Bien que la respiration lente et profonde ait été proposée comme une méthode efficace de stimuler les baroréflexes et pour réduire la douleur, aucune étude expérimentale n'a été réalisée afin de déterminer l'effet de la respiration sur la sensibilité à la douleur. L'objectif principal de cette étude est donc d'évaluer l'effet de la respiration à 6 RPM et du biofeedback cardiaque sur la douleur thermique ainsi que les effets cardiaques dans un contexte expérimental. MÉTHODOLOGIE : Nous avons mesuré le seuil de douleur et le seuil de tolérance de 20 volontaires sains durant 5 conditions différentes : niveau de base (respiration naturelle), 6 RPM, 16 RPM, distraction (jeu vidéo Tetris®) et biofeedback cardiaque. Nous avons mesuré le rythme respiratoire, la profondeur des respirations ainsi que la VRC à partir de l'électrocardiogramme (ECG). Nous avons analysé les effets de la respiration sur la douleur et sur des mesures temporelles et fréquentielles de la VRC. RÉSULTATS : Comparé au niveau de base, le seuil de douleur thermique était significativement plus élevé durant la respiration à 6 RPM (p=0.002), le biofeedback cardiaque (p<0.001) et la distraction (p=0.006), alors que le seuil de tolérance était significativement plus élevé durant la respiration à 6 RPM (p=0.003) et le biofeedback cardiaque (p<0.001). Comparé au niveau de base, seulement les conditions 6 RPM et biofeedback cardiaque ont eu un effet sur l'activité cardiaque. Ces conditions ont augmenté les mesures de l'activité vagale cardiaque (racine carrée de la moyenne des différences des intervalles RR successifs au carré ou RMSSD, p<0.005, amplitude de l'arythmie sinusale respiratoire p<0.001), ainsi que la puissance de la composante basse fréquence (p<0.001) de l'analyse fréquentielle. CONCLUSION : La respiration à 6 RPM et le biofeedback cardiaque ont un effet analgésique et augmentent l'activité vagale cardiaque. La respiration lente et profonde semble être responsable en grande partie de l'effet analgésique du biofeedback cardiaque. La distraction a aussi produit de l'analgésie, mais cet effet n'était pas accompagné de changement concomitant de l'activité vagale cardiaque. Ceci suggère que les mécanismes neurobiologiques qui permettent d'expliquer les effets analgésiques de la respiration lente et profonde et de la distraction sont probablement différents. Les implications cliniques ainsi que les mécanismes cardiorespiratoires et autonomiques responsables de la diminution de la sensibilité à la douleur avec la respiration lente et profonde sont discutés.

No description available.

No description available.

No description available.

An integrated description of the respiratory system of the abalone Haliotis iris is presented. These animals are believed to be inherently primitive and still bear the ancestral gastropod gill arrangement, thus allowing physiological examination of a 'living fossil'. Ventilation, gaseous diffusion, blood transport and the anatomical arrangement of the vascular system are examined under a range of conditions. Resting H. iris consume an average of 0.47 µmol 0₂.g live weight⁻¹ .h⁻¹, 87% of which is taken up across the gills, the remainder diffuses directly into the foot and epipodium. A 300g abalone ventilates its gills at a rate of 28mL.min⁻¹, a rate which, due to low resistance to diffusion (diffusion limitation index = 0.47) and a well matched ventilation/perfusion conductance ratio, is adequate to support the quiescent animal. Increased oxygen demand is accommodated by an increase in cardiac stroke volume, elevating output from 9.1 to 24.4 µL.g⁻¹.min⁻¹. At rest the right gill is the predominant gas exchanger, receiving 95.7% of the branchial blood flow, when cardiac output is elevated the left gill becomes equally perfused, effectively doubling the diffusing surface. Ventilation does not increase, and an increased reliance on assistance from external water currents is seen. Previously undescribed components of the vascular system, notably an extensive sinus of mixed venous and arterial blood surrounding the gut and a large vessel that offers a bypass to the right kidney, provide a low resistance circuit between the heart and gills, bypassing the major organs and muscles. The low resistance circuit allows haemolymph to pass from the aorta to the base of the gills with minimal loss of pressure and no phase shift in the pulse, allowing blood to cross the gills with maximal inertia and instantaneous pressure gradient. Haliotis iris therefore appears to have exploited its limited physiological resources to the maximum in the routine operation of its gas exchange system. It is concluded that further improvement could not occur without substantial remodeling of the body plan, which may account for the abandonment of the system by higher gastropods.

No description available.

No description available.

No description available.