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Biomedical subjects

R A Darnall

Publications and source records attributed to R A Darnall.

29 records · Page 2Linked to original sources
PubMed1985

Noninvasive blood pressure measurement in the neonate.

Measurements of blood pressure are important in the care of the critically ill neonate. Although direct measurement of mean arterial pressure remains the standard, noninvasive methods provide clinically useful estimations of pressure. Clinicians are often faced with situations where measurements of pressure obtained by direct and indirect methods do not agree. Although the explanation for this is not entirely clear, at least two factors are important: first, direct techniques measure pressure while indirect (noninvasive) methods measure flow; second, neither direct or indirect measurements are straightforward and both are subject to error. Of the noninvasive methods, the oscillometric and Doppler devices appear to be most clinically useful in the newborn intensive care unit.

Auscultation↗
PubMed1982

The effect of sleep state on active thermoregulation in the premature infant.

Alterations in thermoregulatory mechanisms related to sleep state may play an important role in the problems of homeostasis experienced by the premature infant. In the adult, homeothermic regulation of body temperature may be suspended during REM. We measured oxygen consumption (VO2) in six premature infants 33-35 wk gestation both at thermoneutrality and during a mild thermal stress to determine whether thermoregulatory responses were intact during REM sleep. All infants were studied under radiant warmers. Skin temperature was allowed to fall 7-8 times during a 6-8 h study period while VO2, VCO2, heart rate and TcPO2 were continuously recorded. Sleep state was scored using EEG, EOG, EMG and behavioral criteria. A total of 1,162 one-min epochs were scored. In all states including REM, VO2 was significantly higher during the cool periods. The mean increases: 21.5%, 23.3%, 11.1% and 5.3% for Awake, Indeterminate, REM and NREM respectively. When REM and NREM were compared at thermoneutrality, there was no difference in the VO2 (8.80 +/- 0.11 and 8.93 +/- 0.15 cc/kg/min, mean +/- S.E., for REM and NREM, respectively). We conclude that in contrast to the adult, active thermoregulation occurs in the premature infant during REM sleep.

Body Temperature Regulation↗
PubMed1979

Refractory hypoxemia associated with neonatal pulmonary disease: the use and limitations of tolazoline.

Thirty-nine critically ill infants with pulmonary disease received tolazoline because of severe hypoxemia refractory to administration of 100% O2 and mechanical ventilation. Twenty-seven (69%) of the infants responded with an increase in PaO2 greater than or equal to 20 torr in the first umbilical arterial gas after completion of the initial ten-minute infusion (1 to 2 mg/kg) of the drug. A response was not correlated with survival. The overall survival was 46%, essentially unchanged from our previous report (44%). Infants with hyaline membrane disease had the poorest survival rate (33%). Complications associated with the use of tolazoline occurred in 82% of the infants. A hypotensive reaction, defined as a 25% decrease in mean arterial pressure from the pre-tolazoline level, occurred in 67% of the infants, and more commonly in the infants with RDS (87%). In 11 infants who did not respond to the initial dose of tolazoline, the dose was increased up to 10 mg/kg/hour; only one infant responded, and eight (73%) had a hypotensive reaction.

Carbon Dioxide↗
PubMed1979

Resting oxygen consumption of premature infants covered with a plastic thermal blanket.

Premature infants in single-wall incubators covered with "thermal blankets" made of plastic packing material have large reductions in insensible water loss (IWL) compared with naked infants. We postulated that such reductions inevaporative heat loss would not result in decreases in caloric expenditure if body temperature were maintained by a servocontrolled heat source. Using an open-circuit technique, we measured oxygen consumption (VO2), carbon dioxide production (VCO2), heart rate (HR), respiratory rate (RR), and abdominal skin (Tabd), cheek, thigh, rectal, incubator air, wall, and room air temperatures in ten infants less than 37 weeks gestational age and from 2 to 24 days of age both naked and covered with a plastic thermal blanket. Tabd temperature was maintained between 36.2 and 36.8 C and rectal temperature between 36.8 and 37.2 C in each environment by manual or automatic servocontrol. A "resting state" was defined by using a combination of subjective and objective criteria. The mean values of VO2 during the "resting state" were 7.31 and 7.59 cc/kg of body weight per minute for naked and covered infants, respectively. There were no significant differences between mean values of VCO2, respiratory quotient, HR, RR, abdominal, cheek, thigh, or rectal temperatures in the two environments. Operant temperatures averaged 0.5 C lower when the infants were covered. These data support the hypothesis that decreases in insensible water loss do not necessarily imply reductions in caloric requirements in infants where Tabd is maintained by servocontrol.

Body Temperature Regulation↗
PubMed1978

Minimal oxygen consumption in infants cared for under overhead radiant warmers compared with conventional incubators.

Infants under radiant warmers have large increases in insensible water loss compared with infants in single wall incubators. To answer the question of whether or not a minimal rate of oxygen consumption could be achieved under overhead radiant warmers, we measured oxygen consumption, carbon dioxide production, and abdominal skin, cheek, rectal, thigh, and environmental temperature in ten healthy newborn infants in incubators and radiant warmers, using each infant as his/her own control. The minimal VO2 ranged from 4.41 to 8.87 and from 4.35 to 9.06 cc/kg/minute in the incubator and radiant warmer, respectively. The differences were clearly not significant (paired Student t-test, P greater than 0.60). There were no significant differences between the respiratory quotients, VCO2, or abdominal skin, check, rectal or environmental temperatures. These data support the hypothesis that a thermoneutral environment can be provided with a radiant warmer and imply that large increases in insensible water loss can occur without affecting minimal oxygen consumption.

Birth Weight↗
PubMedDate not supplied

Aminophylline reduces hypoxic ventilatory depression without increasing catecholamines.

Aminophylline reduces hypoxic ventilatory depression in newborn piglets and can enhance the release of catecholamines (CATs), which in turn may stimulate ventilation. To determine if the effect of aminophylline on ventilation was due to the release of CATs, we measured plasma CATs and ventilation in two groups of spontaneously breathing newborn piglets less than 4 days old, treated with either aminophylline (n = 7) or normal saline solution (n = 6) during both normoxia and hypoxia. The piglets were anesthetized with ketamine and xylazine and intubated, and the femoral artery was catheterized. Epinephrine and norepinephrine were measured before and 30 minutes after treatment with aminophylline (15 mg/kg) or normal saline. The animals were exposed to 10% oxygen and the CATs again measured after 5 minutes of hypoxia. Respiratory rate, expiratory flow integrated to minute ventilation (VE), heart rate, and blood pressure were continuously recorded. CATs were assayed by high-pressure liquid chromatography with electrochemical detection. Treatment with aminophylline during normoxia was associated with an increase in tidal volume. During hypoxia, treatment with aminophylline prevented a fall in VE and respiratory rate seen in the normal saline group. Epinephrine and norepinephrine increased during hypoxia, but there was no difference between the groups at 5 minutes. In our model the increase in CATs observed during hypoxia was not enhanced by aminophylline. This is consistent with the hypothesis that some mechanism other than catecholamine release is responsible for the effect of aminophylline in reducing neonatal hypoxic respiratory depression.

Aminophylline↗
PubMedDate not supplied

Effects of adenosine and xanthine derivatives on breathing during acute hypoxia in the anesthetized newborn piglet.

Neonates of animals and humans exhibit a paradoxical ventilatory response to hypoxia characterized by an initial increase in minute ventilation followed by a late, sustained decrease. Exogenous adenosine analogues cause respiratory depression, and the xanthine derivative aminophylline, a competitive inhibitor of adenosine receptors, decreases the amount of hypoxic ventilatory depression in the newborn piglet. Other xanthine derivative such as enprofylline are weak adenosine antagonists. The purpose of this report is to test the hypothesis that enprofylline would not reverse ventilatory depression caused by hypoxia, supporting the suggestion that adenosine contributes to hypoxic ventilatory depression. To confirm the weak adenosine antagonism of enprofylline, L-N6-(phenylisopropyl)adenosine (PIA) was administered to six newborn piglets until respiratory depression was achieved. Either aminophylline or enprofylline was then administered. Aminophylline, but not enprofylline, reversed the respiratory depression caused by PIA. In seven additional piglets, respiratory depression was first produced by 10% oxygen breathing and the ability of saline, aminophylline, and enprofylline to reverse the decrease in ventilation was evaluated. The administration of either saline or enprofylline produced little change in minute ventilation (9.8% +/- 3.7% and -11.7% +/- 7.7%, respectively), whereas aminophylline consistently produced an increase (43.5% +/- 7.3% [P less than 0.001]). Both aminophylline and enprofylline increased heart rate (P less than 0.01), whereas saline produced no significant change. Blood pressure was increased by enprofylline but not by aminophylline or saline. These findings suggest that, in the anesthetized newborn piglet, adenosine contributes to ventilatory depression caused by hypoxia.

Adenosine↗
PubMedDate not supplied

Phrenic response to hypercapnia in the unanesthetized, decerbrate, newborn rat.

We developed a decerebrate, vagotomized, newborn rat preparation to investigate brainstem respiratory control mechanisms without the influence of anesthesia, supra-pontine structures, or vagally mediated feedback mechanisms. We measured the changes in phrenic nerve electrical activity in response to breathing 3% and 5% CO2 in unanesthetized, vagotomized, decerebrate newborn rats from 0 to 10 days of age and compared them with the changes in anesthetized, vagotomized, newborn rats and adult, vagotomized, decerebrate or anesthetized, animals. Phrenic nerve activity was irregular in the young newborn rats and became more regular between 7 and 10 days of age. T1 and T1/Ttot increased with age but increasing age had no influence on the response to CO2. The response to CO2 was dominated by increases in phrenic amplitude, minute activity, and inspiratory slope with no change in timing variables. These responses are similar to those that have been reported previously in vagally intact animals, suggesting that vagal feedback contributes little to the response to hypercapnia in the newborn rat. In summary, decerebrate newborn rats consistently respond to hypercapnia by increasing inspiratory drive similar to conscious animals.

Animals↗