It has generally been thought that homeostatic mechanisms of renal origin are responsible for minimizing the alkalemia produced by chronic hypocapnia. Recent observations from this laboratory have demonstrated, however, that the decrement in [HCO(-) (3)], which "protects" extracellular pH in normal dogs, is simply the by-product of a nonspecific effect of Paco(2) on renal hydrogen ion secretion...

In the present study we investigated whether hypocapnia that accompanies hypoxic hyperventilation might affect the biphasic, stimulatory/depressant, ventilatory response to hypoxia. The experiments were carried out in anesthetized, vagotomized, spontaneously breathing, and poikilocapnic rats. The animals were subjected to acute steady-state hypoxia consisting of 12% O(2) in N(2) in inspiratory ...

Hypoxia is known to impair cerebral autoregulation (CA). Previous studies indicate that CA is profoundly affected by cerebrovascular tone, which is largely determined by the partial pressure of arterial O(2) and CO(2). However, hypoxic-induced hyperventilation via respiratory chemoreflex activation causes hypocapnia, which may influence CA independent of partial pressure of arterial O(2). To id...

Measurements of lung mechanical behaviour as a function of respiratory frequency may be associated with significantly increased ventilation at high breathing rates. It follows that these measurements may be influenced by hypocapnia which has been shown to increase airflow resistance and to decrease dynamic compliance. To examine this possibility we continuously monitored the end-tidal CO2 tensi...

Hypopneas or pauses in respiratory effort frequently precede episodes of obstructive sleep apnea resulting in mixed apneas. We studied five subjects after chronic tracheostomy for obstructive sleep apnea. During stable non-REM (NREM) sleep, subjects breathed entirely through the tracheostomy. Tracheostomy occlusion caused experimental obstructive apnea which lasted 13.9 +/- 4.7 sec and ended wi...

In order to examine anaesthetic effects on the distribution of cerebral blood flow (CBF) during normoand hypocapnia, male adult SpragueDaw/ey rats were a/located randomly to four groups in a 2x2 factorial design, using PaC(,2 value and anaesthetic agent as between-group factors. Animals were anaesthetized with either 1.38% isoflurane (inspired) or 1.05% halothane (inspired) and the lungs ventil...

The aim of this study was to develop a nonlinear mixed-effects model for the increase in cerebral oximetry (rSO(2)) during the rapid introduction of desflurane, and to determine the effect of hypocapnia and N(2)O on the model. Twelve American Society of Anesthesiologist physical status class 1 and 2 subjects were allocated randomly into an Air and N(2)O group. After inducing anesthesia, desflur...

We noninvasively evaluated the effects of nicardipine on cerebral vascular responses to hypocapnia and blood flow velocity in the middle cerebral artery of 10 patients aged 17-60 (mean +/- SD 46.1 +/- 11.8) years. During fentanyl/diazepam/nitrous oxide anesthesia, mean blood flow velocity in the middle cerebral artery was measured and cerebral vascular reactivity to hypocapnia induced by hyperv...

BACKGROUND AND PURPOSE Cerebrovascular responses to hypoxia and hypocapnia in Peruvian altitude dwellers are impaired. This could contribute to the high incidence of altitude-related illness in Andeans. Ethiopian high altitude dwellers may show a different pattern of adaptation to high altitude. We aimed to examine cerebral reactivity to hypoxia and hypocapnia in healthy Ethiopian high altitude...