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B Meehan

Publications and source records attributed to B Meehan.

23 records · Page 2Linked to original sources
PubMed1996

Respiratory responses to rapid-onset, repetitive vs. continuous hypoxia in piglets.

Repeated, frequent hypoxic exposures may precede Sudden Infant Death. This study assessed whether such hypoxic modality, vs. continuous hypoxia, compromised compensatory cardiorespiratory responses. Following aseptic, chronic instrumentation, 10 to 20 day-old, unsedated piglets underwent measurements of arterial O2 saturation, pH and gas tensions, respiration, heart rate, physical activity, O2 consumption and rectal temperature on several experimental days. The piglets were exposed to 21 min of either 10% or 6% O2 in N2, each comprising either seven, 3-min exposures alternating with 3-min intervals in 21% O2 balance N2, or 7 consecutive hypoxic exposures. Responses to 6% hypoxia were greater than those to 10% hypoxia. In 10% hypoxia, responses to repetitive vs. continuous exposure differed only in PaCO2. In 6% hypoxia, repetitive vs. continuous exposure resulted in lower respiratory frequency (p < 0.05) and in lower ventilation equivalent (p = 0.07) despite higher activity levels. Thus, the mode of hypoxic exposure determines the extent of the respiratory response: Severe, repetitive hypoxia mitigates protective respiratory responses when compared to equivalent, but sustained hypoxia.

Animals↗
PubMed1996

Age-dependent vulnerability to carotid chemodenervation in piglets.

We sought to determine the age of greatest vulnerability in piglets to the loss of carotid chemoreceptor function. We studied four groups of carotid body-denervated (CBD) piglets whose carotid bodies were surgically removed at 4-5, 9-10, 12-15, and 21-22 days and who are herein referred to, respectively, as the CBD5, CBD10, CBD15, and CBD20 groups. Four intact groups, at corresponding ages, underwent a sham surgical procedure. After a postsurgery recovery of at least 7 days, we studied all animals to detect the presence of apnea and the consequences of it, if any. Two days before the experiments, we implanted in all animals a fiber-optic arterial catheter for continuous monitoring of arterial O2 saturation, and electroencephalographic electrodes for the recording of sleep states. During quiet sleep in the CBD15 group, we found numerous prolonged central apneic events accompanied by a profound desaturation, tachycardia, a rise in blood pressure, and, eventually, a flattening of the electroencephalogram. No prolonged apneic events occurred, however, in the other CBD groups nor in the intact animals. During active sleep, no prolonged apneic events occurred at all. We thus conclude that, in piglets, the absence of normally functioning carotid chemoreceptors at approximately 2 wk of age can lead to life-threatening apneic events with severe hypoxemia, events that are state specific.

Aging↗
PubMed1995

Effect of theophylline on metabolic and ventilatory response to hypoxemia during quiet sleep in piglets.

Theophylline, a drug frequently used in newborns, stimulates respiration and increases the metabolic rate in a sustained fashion; hypoxemia, on the other hand, decreases metabolic rate and increases ventilation slightly and, at times, only transiently. This study looked at the effect of theophylline on the metabolic and ventilatory response to hypoxemia in piglets. We studied two groups of piglets during normoxia and hypoxemia: first during a baseline period; and second, after the infusion of either theophylline or a placebo. All studies were done in quiet sleep, 2 d after instrumentation was performed to place vascular catheters and electroencephalographic electrodes. O2 consumption (VO2) and CO2 production (VCO2) were measured in a metabolic chamber, and alveolar ventilation (VA) was then derived from VCO2 and PaCO2. We found that theophylline did not abolish the small decrease in oxygen consumption brought about by hypoxemia. Nor did theophylline augment the ventilatory response to hypoxemia. In fact, the percent change in alveolar ventilation decreased slightly: going from 17 +/- 8% during the baseline period to 9 +/- 6% (p < 0.005) after theophylline administration. We found a significant increase in respiratory exchange ratio (R) in response to hypoxemia (from 0.87 +/- 0.05 to 0.97 +/- 0.04, p < 0.001). However, after the administration of theophylline, additional exposure to hypoxemia did not result in a change in R. In summary, our results show that, in sleeping newborn piglets, theophylline does not abolish the decrease in oxygen consumption observed in response to hypoxemia; nor does it enhance the ventilatory response to a moderate degree of hypoxemia.

Animals↗
PubMed1992

Metabolic and cardiorespiratory effects of doxapram and theophylline in sleeping newborn piglets.

To evaluate the contribution of a change in metabolic rate to ventilatory changes after the administration of respiratory stimulants, we studied the effect of two respiratory stimulants, doxapram and theophylline, on ventilation and metabolic rate during sleep in piglets. Metabolic rate (O2 consumption and CO2 production) was measured in a metabolic chamber, and alveolar ventilation (VA) was derived from arterial PCO2 and CO2 production. We studied the animals during a baseline period and for 2 h after the administration of theophylline or doxapram. With doxapram, there was no change in VA, metabolic rate, or arterial PCO2. In contrast, with theophylline, VA increased [20 +/- 14% (SD), P less than 0.003] as a result of both an increased metabolic rate and hyperventilation. Doxapram, however, increased mean blood pressure (from 67 +/- 11 to 75 +/- 13 mmHg, P less than 0.005), whereas theophylline did not result in blood pressure changes. In summary, during quiet sleep, doxapram, unlike theophylline, does not stimulate either respiration or metabolic rate. We speculate that the previous reports of increased ventilation after the administration of doxapram are due to the general stimulation of activity in the awake state, an effect not seen during sleep.

Animals↗