Upper respiratory dead space in the chicken: its fraction of the tidal volume

Ventilatory sensitivity to changes in inspired and arterial carbon dioxide partial pressures in the chicken

To determine if intrapulmonary chemoreceptors could be the sole peripheral chemoreceptors responsible for ventilatory responses to inhaled CO2, we studied the relationships of minute ventilation, tidal volume, and respiratory frequency to inspired and arterial partial pressure of CO2 (P(I)CO2 and PaCO2) in decerebrate upright chickens when the birds inspired gases containing four low partial pressures of CO2 (0.02, 5.0, 8.2, and 11.4 torr). Because of variability in the measured variables from time to time in the same birds, as well as between birds, and because of the limited precision in measuring PaCO2, a 4 x 4 Latin square design and four statistical methods of data analyses (modified reduced major axis estimator, maximum likelihood estimator, average slope method, and summary slope method) were used. Tidal volume, minute ventilation, and PaCO2 increased, but respiratory frequency remained unchanged, as gases containing increased partial pressures of CO2 were inhaled. The results indicate that intrapulmonary chemoreceptors are not the sole receptors stimulated by inhaling gas containing even low partial pressures of CO2 and that stimulation of arterial and central chemoreceptors also occurs. Stimulation of these latter chemoreceptors may account for the increase in ventilation. Further, the results demonstrate the importance of maintaining a low level of environmental CO2 in poultry houses to minimize its influence on ventilation.

Influence of feed deprivation on ventilation and gas exchange in broilers: relationship to pulmonary hypertension syndrome

Fast-growing broiler chickens not uncommonly exhibit elevated pulmonary vascular resistance that leads to pulmonary hypertension and right ventricular failure. We tested the hypothesis that a distended gastrointestinal tract in these full-fed birds results in an abnormally low tidal volume and minute ventilation that could lead to pulmonary hypoxia, pulmonary arterial vasoconstriction, right ventricular failure, and ascites. Tidal volume, respiratory frequency, heart rate, percentage saturation of hemoglobin with oxygen (HbO2), O2 consumption, and carbon dioxide elimination were measured on fast-growing broiler chickens when full-fed and after 3, 6, and 9 h of feed deprivation. Tidal volume of full-fed birds was not abnormally low despite HbO2 values varying from above 80% to nearly 60%. Importantly, HbO2 was found to be markedly increased in the hypoxemic birds at and beyond a 3-h period without feed, despite a reduction in minute ventilation. This response was not caused by a decrease in O2 consumption. Thus, limitation of gas intake at the mouth was not the cause of the hypoxemia. The data suggest that feed deprivation results in an increase in parabronchial ventilation, possibly from improvement in aerodynamic valving, which would reduce pulmonary hypoxic vasoconstriction and right ventricular failure.

Breathing pattern in anesthetized chickens: CO2 inhalation and vagotomy

The breathing patterns of 20 anesthetized chickens were studied during progressive suppression of intrapulmonary chemoreceptors (IPC) by various concentrations of CO2 and following bilateral vagotomy. The vagotomy breathing pattern, characterized by a marked accentuation of expiratory times with prolonged expiratory pauses, was markedly different from that induced by CO2 inhalation. Removal of neural input to the central respiratory centers from IPC does not appear to be solely responsible for the altered breathing pattern following vagotomy in birds.

Gas exchange during exercise in hypoxic ducks

We quantitatively assessed pulmonary gas exchange in Pekin ducks (Anas platyrhynchos) during running exercise (1.44 km X h-1 at 3 degrees incline) while the ducks spontaneously breathed either air (FIO2 = 0.21) or a hypoxic gas mixture (FIO2 = 0.12). During exercise, oxygen consumption increased 3 times above the resting value in normoxia and 3.6 times above rest in hypoxia. The convection requirement rose 34% and 20% in running normoxic and hypoxic ducks, respectively. The O2 extraction coefficient was the same in resting normoxic and hypoxic ducks (0.19 vs 0.18) and decreased by the same amount under exercise conditions (0.14 vs 0.15). Arterial PO2 was maintained during exercise in normoxia but increased slightly during exercise in hypoxia. Cardiac output increased by 73% and 111% during exercise in normoxic and hypoxic ducks, respectively. Calculations indicate that both the O2-diffusing capacity and the total conductance for O2 of the gas exchange system increased markedly during exercise in normoxia and hypoxia. We conclude that at this level of exercise, there was no apparent limitation to gas exchange in either the normoxic or hypoxic Pekin duck.

Interaction of temperature with extra- and intrapulmonary chemoreceptor control of ventilatory movements in the awake chicken

Several studies in artificially ventilated, anesthetized birds with opened thoracoabdominal cavities have shown that intrapulmonary chemoreceptors (IPC) sensitive to CO2 contribute to the control of ventilatory movements. Increasing colonic temperature (Tc) has been shown to increase depth and decrease frequency of ventilatory movements if PaCO2 is held constant at less than 35 torr in awake and anesthetized, artificially ventilated cockerels. The relative importances, though, of IPC and of extrapulmonary CO2-sensitive chemoreceptors (EPC) in controlling ventilation in the awake or hyperthermic bird is unknown. We dissociated the PCO2 affecting IPC and EPC in awake cockerels by ligating the left pulmonary artery, denervating the IPC in the right lung and artificially ventilating each lung separately. We found, that at constant PaCO2, ventilatory movements increased in depth and decreased in frequency with: (1) increasing PICO2 to the innervated, non-perfused lung (PipcCO2); and (2) increasing Tc. Similar responses were observed with increasing PaCO2 or Tc during constant PipcCO2. Multiple regression analyses show that IPC and EPC have about equal controlling influences on ventilatory movements in the awake and hyperthermic cockerel.

Effects of PCO2 on respiratory pattern during thermal and exercise hyperventilation in domestic fowl

The relationship between respiratory pattern and arterial PCO2 was investigated during hyperventilation induced by graded exercise and hyperthermia. Treadmill exercise was performed both in isothermic and hyperthermic conditions. Isothermic exercise was induced by spraying the birds with water before exercise at environmental temperatures of 18 +/- 2 degrees C. Hyperthermic exercise was performed in unsprayed birds at temperatures of 18 +/- 2 degrees C and 30 +/- 2 degrees C. During isothermic exercise there was no significant change in arterial PCO2 at moderate work loads and only a small drop in PCO2 at the heaviest work loads; ventilation was increased by coupled increases in tidal volume and respiratory frequency. During exercise in unsprayed birds rectal temperature rose progressively and arterial PCO2 fell progressively with work load. At each work load ventilation was higher and breathing was more rapid and shallow than during isothermic exercise. These effects were more pronounced during exercise at 30 +/- 2 degrees C than at 18 +/- 2 degrees C. When normal PCO2 was maintained during hyperthermic exercise, as a result of the administration of CO2-enriched air, polypnea was suppressed and the tidal volume-respiratory frequency relationship became identical to that observed during graded isothermic exercise. Maintenance of normal PCO2 in resting birds subjected to a gradual increase in environmental temperature also resulted in changes in respiratory pattern identical to those obtained during eucapnic exercise. It is concluded that, provided arterial PCO2 is held constant, the pattern of breathing is the same for hyperventilation induced by exercise or by body temperature increases.

Fractionation of hagfish slime gland secretions: partial characterization of the mucous vesicle fraction

This paper deals with the collection, fractionation and partial characterization of the slime gland secretion of the Pacific hagfish (Eptatretus stouti) with emphasis on the mucous fraction. Secretions were collected by electrical stimulation of the glands of anesthetized hagfish and, using three different methods, separated into three fractions: 1) the thread cells, 2) the mucous vesicles of the mucous cells, and 3) the soluble fraction. The methods take advantage of the stabilization of the thread cells and mucous vesicles by ammonium sulfate and sodium citrate.

Effects of temperature on the ventilatory response to inspired CO2 in unanaesthetized domestic fowl

The influence of raised environmental temperature on the respiratory response to CO2 in awake, spontaneously breathing domestic fowl was investigated. In terms of their effects on ventilation VE temperature and CO2 were additive and non-interactive, VE being approximately 1900 ml . min-1 greater at 33 +/- 1 degree C compared to 18 +/- 1 degree C, regardless of inspired CO2 partial pressure PICO2. Temperature had no effect on the slope of the relationship between VE and both arterial and clavicular air sac PCO2. Blood and clavicular sac PCO2 were regulated within 2-3 Torr of normal at PICO2 levels below approximately 20 Torr as a result of hyperventilation but PCO2 regulation began to fail at higher PICO2. Hypercapnia induced increases in respiratory frequency f at normal temperatures but decreases in f at 33 +/- 1 degree C. There was little change in f at 25 +/- 1 degree C. The ventilatory increase in response to CO2 at 18 +/- 1 degree C and 25 +/- 1 degree C could be described by a linear relationship between VE and tidal volume VT. However, respiration departed from this pattern at temperatures above the panting threshold (32-34 degrees C). These findings are discussed in the context of central and peripheral mechanisms which may be involved in the control of rate and depth of breathing.

The effect of CO2 and temperature on respiratory movements in the chicken

We studied the effect of increasing colonic temperature (Tc) on respiratory amplitude and frequency at different levels of PICO2 in anesthetized, unidirectionally ventilated cockerels. We also evaluated the relationship between PICO2 and PaCO2. Increased PaCO2 augmented respiratory amplitude and decreased frequency at every Tc. Respiratory amplitude increased as Tc rose from 41 to 45 degrees C at each level of PaCO2. During the same rise in Tc, respiratory frequency decreased at the low PaCO2 seen in awake, panting cockerels but increased at eucapnic PaCO2. Tc had no effect on frequency at high PaCO2. Values for respiratory frequency of unidirectionally ventilated cockerels at given Tc and PaCO2 predict those of awake cockerels. We conclude that amplitude of breathing increases in acute hyperthermia unless accompanied by hypocapnia and that without hypocapnia maximal panting frequencies cannot be reached.

Respiratory gas exchange and control in the chicken

Gas exchange in parabronchial lungs can be described by: 1) representing the entire lung as one parabronchus, 2) solving iteratively a series of equations relating CO2 and O2 levels to the partial pressures of the gases, blood pH, and flows of gas and blood at thin sections of the parabronchus to give changes of gas pressures, and 3) integrating the changes over the parabronchus. At rest, diffusion resistance to exchange between gas and blood is a relatively small effect while ventilation/perfusion inequalities between parabronchi are responsible for most of the disequilibrium between gas and blood. Ventilation is altered to control body temperature and intrapulmonary and arterial PCO2. Chickens pant at a relatively lower respiratory frequency than mammals of comparable body weight. The respiratory time constant of hyperthermic chickens predicts maximal parabronchial ventilation at usual panting frequencies. Above this frequency, CO2 would increase from the minimum in hyperthermia, decreasing frequency of respiration. Inhaling CO2-enriched air in hyperthermia slows frequency but increases ventilation, protecting against lethally hot climates. Intrapulmonary chemoreceptors reduce ventilation if intrapulmonary PCO2 falls. Left ventricular CO2-sensitive mechanoreceptors also inhibit ventilation if PaCO2 falls or blood pressure increases. Both sensory systems may buffer respiratory gas and acid-base changes at the tissue. No known system can explain ventilation during exercise.

Ventilatory response to the PCO2 profile in chicken lungs

We investigated the influence of intrapulmonary chemoreceptors (IPC) on ventilatory movements in anesthetized chickens when PCO2 profiles along the parabronchi were changed. In all experiments the right lung was denervated, both lungs unidirectionally ventilated, and PaCO2 kept constant. In series 1 (7 birds), gas flow and the PCO2 profile in the left lung were reversed. PaCO2, PECO2 and ventilatory movements did not change. In Series 2 (4 birds), PCO2 in caudal regions of the innervated lung was elevated by increasing gas flow and P1CO2 from 0 to 21 Torr. Ventilatory movements did not change. In Series 3 (4 birds), either lung was over-ventilated with 7 or 49 Torr P1CO2, alternating the gases between lungs every 100 sec. Ventilatory movements changes with P1CO2 but much less than predicted from P1CO2 effects in the non-perfused, innervated lung. From the longitudinal distribution of IPC and PCO2 profiles in the lung we predicted moderate to large changes in ventilatory movements in all series. The discrepancy between predicted and observed results in Series 1 and 2 indicates that IPC in caudal regions of the lung have little effect on ventilation under the conditions examined. In Series 3, observed ventilatory movements were less sensitive to P1CO2 than predicted, indicating that IPC sense a different PCO2 than the PCO2 profile in the parabronchial lumen and that IPC have a significant sensitivity to pulmonary blood PCO2.

A comparison between carbon dioxide inhalation and increased dead space ventilation in chickens

We compared the ventilatory response to elevated PICO2 with the response to elevation of dead space volume (delta VD) in anesthetized, hyperoxic chickens. In the first experimental series (I), PICO2 was varied between 0 and 26 Torr. In a second series (II), delta VD was raised between 0 and 17 ml by placing lengths of tubing between the bird and the source of inspired gas. In series I, ventilation increased and PaCO2 remained constant at levels of PICO2 below 20 Torr. In contrast, PaCO2 increased with low levels of delta VD in Series II. When changes in PaCO2 and ventilation were expressed as a function of the change in CO2 load reaching the lungs (delta L), the change in ventilation was greater, and that in PaCO2 less in Series I than in Series II at all levels of delta L below 25 ml (STPD) . min-1. The differences in ventilatory response to PICO2 and delta VD may qualitatively be explained by the distinct time patterns of CO2 concentration in the lungs which result in different discharge frequencies of CO2-sensitive intrapulmonary chemoreceptors and, possibly, by effects on ventilation resulting from differences in the timing of receptor discharge. Thus, these data provide additional evidence that avian intrapulmonary chemoreceptors may play a significant role in the chemical control of ventilation and regulation of PaCO2.

Cardiopulmonary responses to inhaled sulfur dioxide in the chicken

Selected cardiopulmonary variables were measured in anesthetized, male, White Leghorn type chickens before, during, and after 60 min exposure to various inhaled SO2 concentrations ranging from 0 to 5000 ppm. In one series of experiments, birds breathed through their nostrils and mouth; in a second series they breathed through a tracheal cannula. Exposure to 5000 ppm SO2 rapidly caused death in all birds with cannulated tracheae and in 4 of 5 birds with an intact respiratory system; one bird in each series of experiments died when exposed to 1000 ppm. Inhaling 100 ppm SO2 did not alter heart rate, blood pressure, tidal volume, respiratory frequency, or arterial blood gases and pH. Airway resistance was decreased by inhaling 500 ppm SO2 and was initially decreased but later greatly increased by inhaling 1000 ppm. Respiratory frequency and minute volume were decreased and PaCO2 was increased by inhaling 1000 ppm. The cardiopulmonary responses to inhaling 5000 ppm were generally augmentations of those responses which occurred when 1000 ppm was inhaled. The SO2 could not be detected in caudal thoracic or abdominal air sac gas at any concentration inhaled but vascular congestion and areas of brown discoloration appeared in the lungs of all birds that inhaled 5000 ppm and some that inhaled 1000 ppm. Mucous secretion in the trachea increased in some birds that inhaled 500 ppm SO2 and in most that inhaled higher concentrations. Chickens appear to have more tolerance for inhaled SO2 than most mammals but the pollutant gas at high concentrations detrimetally affects the cardiopulmonary system.

O2-chemoreflex drive of ventilation in awake birds at rest

Three varieties of birds (a non-flyer, the chicken; a diver, the duck; a flyer, the pigeon) were studied in resting conditions at neutral ambient temperature, while awake, either intact or sham operated, or after bilateral chronic carotid body denervation. Tidal volume (VT), ventilatory period (T) and minute volume (V = VT/T) measured plethysmographically, were recorded breath-by-breath in steady state at two levels of oxygenation, and in the course of transient pure O2 inhalation (60-sec O2-test). O2 partial pressures in the inspired and expired gases (PIO2 and PETO2), and in the arterial blood (PaO2) were also measured. In intact and sham operated birds, the abrupt switch from a normoxic gas mixture (FIO2 = 0.21) to pure O2 resulted shortly in rapid increases of PIO2, PETO2 and paO2, and in a fall of V which was completed within 20--30 sec and accounted for about 30% of the control minute volume. In the animals previously made hypoxic (FIO2 = 0.12) and hyperventilating, the O2-test provoked a 50--60% fall of V. In chickens, a decreased VT and an increased T contributed to the transient ventilatory changes; in ducks, mainly VT changed, and in the pigeon only T changed. In the birds with denervated carotid bodies, there were no ventilatory responses to hypoxia and to the O2-test. A few of these birds developed a tachypneic response to hypoxia with no apparent change in the effective pulmonary ventilation, which was partly overcome during the O2-test. It is concluded that in the three varieties of birds, the O2-chemoreflex drive from the carotid bodies controlled about 30% of the resting minute volume near sea level, and 50--60% in hypoxic conditions duplicating an altitude exposure to 4000 m.