Episodes Of Hypercapnia Research Articles

Hypothermia reduces cerebral metabolic rate and cerebral blood flow in newborn pigs.

We examined effects of hypothermia on cerebral metabolic rate and cerebral blood flow in anesthetized, newborn pigs (1-4 days old). Cerebral blood flow (CBF) was determined with 15-micronS radioactive microspheres. Regional CBF ranged from 44 to 66 ml . min-1.100 g-1, and cerebral metabolic rate was 1.94 +/- 0.23 ml O2.100 g-1 . min-1 during normothermia (39 degrees C). Reduction of rectal temperature to 34-35 degrees C decreased CBF and cerebral metabolic rate 40-50%. In another group of piglets, we examined responsiveness of the cerebral circulation to arterial hypercapnia during hypothermia. Although absolute values for normocapnic and hypercapnic CBF were reduced by hypothermia and absolute values for normocapnic and hypercapnic cerebrovascular resistance were increased, the percentage changes from control in these variables during hypercapnia were similar during normothermia and hypothermia. In another group of animals that were maintained normothermic and exposed to two episodes of hypercapnia, there was no attenuation of cerebrovascular dilatation during the second episode. We conclude that hypothermia reduces CBF secondarily to a decrease in cerebral metabolic rate and that percent dilator responsiveness to arterial hypercapnia is unaltered when body temperature is reduced.

Regulation of blood flow to respiratory muscles during hypoxia and hypercapnia.

AbstractThe effect of systemic hypoxia or hypercapnia on regional blood flow was measured in respiratory muscles, limb muscles, and kidneys of rabbits by using radioactive microspheres. Blood flow to both the diaphragm and the intercostal muscles was increased in a direct relationship with the severity of the hypoxia or hypercapnia in spontaneously breathing animals. Blood flow to the kidneys decreased while blood flow to limb muscle remained unchanged. During mechanical ventilation, following paralysis with Flaxedil, blood flow to the respiratory muscles was about 10% of that seen during quiet breathing and was unchanged by hypoxia or hypercapnia. Renal flow decreased as in the nonparalyzed animals while flow to limb muscle remained unchanged during the hypoxic and hypercapnic episodes. It is concluded that the major factor involved in regulating blood flow to the respiratory muscles is their level of activity.

A neurophysiological analysis of the effects of hypercapnia on the embryonic spinal cord.

Progressive hypercapnia in the normal chick embryo late in incubation (14-19 days) is temporally associated with a gradual decline in motor activity and the corresponding frequency of polyneuronal (burst) activity in the spinal cord. We have studied the possible correlation between the increasing hypercapnia and the declining frequency of burst activity seen during these later stages of incubation by systematic manipulation of CO2 levels. Burst frequency was seen to decrease as a result of a 5-min exposure to different carbon dioxide environments at all ages studied. The magnitude of this inhibition and the ability to recover from consecutive bouts of hypercapnia (pulses) is pulse and age dependent. These short-term (less than 5.0 min) changes differ qualitatively from the long-term (greater than 2.5 h) effects of subsequent hypercapnic episodes. This evidence suggests a role for metabolic factors in the normal developmental changes in motility and electrophysiological activity in the chicken embryo spinal cord.

The ventilatory response to hypercapnia and to hypoxemia in chronic obstructive lung disease.

SUMMARY _ The ventilatory response to breathing 3 per cent and 5 per cent carbon dioxide in either a hypoxic gas mixture (oxygen = 10 per cent) or a hyperoxic gas mixture (oxygen> 2 per cent) was measured in normal individuals (group I) and in 3 groups of patients with chronic obstructive lung disease: those who demonstrated hypoxia but no previous episodes of carbon dioxide retention (group II), those who demonstrated hypoxia and had had one or more episodes of carbon dioxide retention but were normocapneic when studied (group III), and those who demonstrated chronic hypoxia and carbon dioxide retention (group IV). The ventilatory response to hypercapnea was significantly lower in groups III and IV than in groups I and II. The ventilatory response to the combined stimuli of hypoxia and hypercapnea was significantly lower than normal for all patient groups. The response of the patients who had had previous hypercapnic episodes or were chronically hypercapnic was significantly different from those who had never been hypercapnic, while there was a significant correlation between the ventilatory responses and indices of airflow obstruction, the best correlation being with arterial oxygen tension. These findings indicate that chronic hy­ poxemia in patients with chronic obstructive lung disease may modify the function of the periph­ eral chemoreceptor. An increase in severity of this disturbance may in turn affect the response to hypercapnia and ultimately lead to the development of chronic carbon dioxide retention.