Mogens L. Glass

Control of breathing in an amphibian Bufo paracnemis: effects of temperature and hypoxia

Lung ventilation was measured in the toad, Bufo paracnemis, weight 500-800 g, at 15, 25 and 32 degree C during normoxia and hypoxia (5, 10, and 15% inspired O2). Arterial blood gases were measured during normoxic breathing. Typically breath-holds alternated with ventilatory periods, which were initiated by a stepwise pulmonary deflation. Then a series of breaths consisting of both expiratory and inspiratory volumes followed. At the end of the period the lungs were inflated in several steps. Increased temperature markedly augmented ventilation mostly through a five-fold increase in the number of ventilatory periods per unit time. Ventilation was also enhanced by hypoxia and this response was greatest at the highest temperature. Arterial PO2 rose from 35 to 96 Torr when temperature increased from 15 to 32 degrees C. Bufo resembles reptiles regarding these responses.

The application of pneumotachography on small unrestrained animals

Abstract 1. 1. Pneumotachography, as a method of measuring ventilation is common in human physiology. 2. 2. In contrast, comparative physiology has not taken advantage of the method due to difficulties in applying the conventional version of the method on small animals. 3. 3. These difficulties have been solved by combining a close-fitting face mask with a built-on, lightweight flow transducer head. This modification of the method is inexpensive and permits measurement on unrestrained animals.

Effects of temperature on respiration and acid-base balance in a monitor lizard

SummaryVentilation, gas exchange, blood gas tensions and arterial pH were measured simultaneously in monitor lizards,Varanus exanthematicus. In contrast to previously studied poikilotherms, the arterial pH is independent of body temperature within the normally encountered temperature range (Fig. 1). This exception to the relative alkalinity concept (Rahn, 1966) is correlated with the finding thatV. exanthematicus maintains a constant ratio of ventilation to oxygen uptake (and CO2 production) at different temperatures (Fig. 3). The increase in arterial

Aerobic metabolism of the lizardVaranus exanthematicus: Effects of activity, temperature, and size

P_{{\text{CO}}_{\text{2}} }

Acid‐Base Regulation in the South American Lungfish Lepidosiren paradoxa: Effects of Prolonged Hypercarbia on Blood Gases and Pulmonary Ventilation

(Fig. 1) is related to an increase in physiological dead space; i.e., alveolar ventilation increases less with temperature than total ventilation (Fig. 4). This may result from the increased frequency of breathing which results in a reduced breath holding time (Fig. 2). Varanid lizards have a higher oxygen requirement than other reptiles. This is reflected in the control of ventilation, the specialized lung morphology, the high arterial saturation due to low intracardiac shunting, pH regulation and other mammal-like features ofVaranus.

Responses of aerial ventilation to hypoxia and hypercapnia inChanna argus, an air-breathing fish

Ventilation and oxygen uptake were measured in the elephant trunk snake, Acrochordus javanicus, during normal, undisturbed breathing. Ventilation is periodic, with ventilatory periods (VP) lasting 2.5-3.5 min, interrupted by nonventilatory periods (NVP) averaging 10 times longer at 25 C. Average tidal volumes ranged from 27.8 to 47.7 ml·kg⁻¹, while breathing frequency during VP ranged from 78 h⁻¹ to 155 h⁻¹. Total ventilation (V̇I) ranged from 250 to 543 ml·kg⁻¹·h⁻¹ BTPS (body temperature and pressure, saturated with water vapor). Oxygen uptake (V̇o2) averaged 16.6 mlO₂· kg⁻¹·h⁻¹ STPD (standard temperature and pressure, dry) at 20 C and 29.3 mlO₂· kg⁻¹·h⁻¹ at 30 C. Corresponding ventilations were 225 ml·kg⁻¹·h⁻¹ and 504 ml·2kg⁻¹· h⁻¹ BTPS. Ventilatory requirements, V̇I/V̇o2, were 13.8 and 17.2 for 20 and 30 C. Both ventilation and oxygen uptake are low in Acrochordus, compared with other reptiles. Also, the V̇I/V̇o2 ratio is much lower for Acrochordus than for most reptiles. A well-developed, richly vascularized lung and the long NVP contribute to unusually high extractions of O₂ from the ventilated air. The mode of breathing of Acrochordus allows it to stay submerged more than 90% of total lapsed time. During hypoxic breathing, ventilation is stimulated when inspired O₂ concentration is less than 10%. Large alveolar-to-blood Po2 gradients indicate that blood and lung O₂ stores are nearly exhausted when the hypoxic stimulus breaks the breath holds. The increased ventilation resulted from a shortening of NVP while tidal volumes and the frequency of breathing during VP remained unchanged. Breathing 100% O₂ significantly reduced ventilation. Hypercapnic breathing showed no ventilatory change when breathing 2% and 4% CO₂. Breathing 6% and 8/% caused an actual depression of ventilation. The results indicate an effective elimination of CO₂ by cutaneous exchange, which may account for the lack of a ventilatory response to CO₂ breathing. Ventilation in Acrochordus appears controlled for maximum utilization of oxygen stores and rapid recovery during breathing.

Effects of dry season dormancy on oxygen uptake, heart rate, and blood pressures in the toad, Bufo paracnemis

SummaryOxygen consumption