Is the ventilatory decline seen in newborns during hypoxaemia centrally mediated?
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Animals↗
Biomedical subjects
M A Hanson
Publications and source records attributed to M A Hanson.
Risk factors for psychiatric inpatient assaults on staff.
The risk of psychiatric patient assaults on staff members is increasing yearly, with resultant increases in employee victim suffering, medical expense, and lost productivity. Traditionally considered a clinician responsibility, the management of patient violence also has important administrative implications. This article presents a review of the risk factors associated with violence that includes the characteristics of patients who assault but adds the characteristics of employee victims of such assaults as well as contextual variables. Additional data from a two-year study of a peer-help crisis intervention program for employee victims of patient assaults are included. The mental health administrative implications of this approach are outlined.
Adult↗
Effect of mild hypocapnia on fetal breathing and behavior in unanesthetized normoxic fetal lambs.
We hypothesized that the level of arterial PCO2 (PaCO2) affects the incidence of fetal breathing movements and electrocorticographic (ECoG) states in chronically instrumented fetal sheep. Six fetuses of 128-132 days gestational age were instrumented for recording fetal behavior and for later connection to an extracorporeal membrane oxygenation (ECMO) system to change fetal blood gases. Before ECMO fetal arterial pH and blood gases were pH 7.40 +/- 0.01, PaCO2 42.9 +/- 1.5 Torr, and arterial PO2 (PaCO2) 19.2 +/- 1.7 Torr; during ECMO in normocapnia they were pH 7.37 +/- 0.01, PaCO2 46.1 +/- 0.7 Torr, and PaCO2 27.6 +/- 3.0 Torr; and during ECMO in mild hypocapnia they were pH 7.47 +/- 0.01, PaCO2 35.3 +/- 1.7 Torr, and PaCO2 26.6 +/- 1.7 Torr. The overall incidence of breathing movements, the incidence of breathing movements during low-voltage (LV) ECoG activity, and the mean duration of periods of breathing decreased significantly during hypocapnia. Fetal ECoG activity showed normal cycling during the periods of mild hypocapnia, and the mean duration of LV ECoG periods did not change. During mild hypocapnia, eye movements remained associated with LV ECoG activity and nuchal electromyographic activity remained associated with high-voltage ECoG activity. These results suggest that the presence of breathing movements in fetal life is not only dependent on the behavioral state but also on the level of fetal PaCO2.
Animals↗
Effect of maternal hypoxemia on behavior in unanesthetized normoxic or mildly hyperoxic fetal lambs.
To determine whether hypoxemia inhibits fetal activity by substances from the mother or placenta, six fetal lambs were chronically instrumented at 128-132 days gestation for extra-corporeal membrane oxygenation (ECMO). Severe maternal hypoxemia (arterial PO2 decreased to 6.00 +/- 0.60 kPa) was produced while fetal arterial PO2 was maintained normoxic or mildly hyperoxic using ECMO. The incidences of fetal breathing movements were 34.8 +/- 3.1% (SE) during baseline before ECMO, 36.8 +/- 3.4% during baseline with ECMO, and 21.4 +/- 3.5% (P < 0.05 compared with baseline with ECMO) during maternal hypoxemia. The durations of periods of breathing were 9.8 +/- 1.2 min before ECMO, 9.3 +/- 1.1 min with ECMO, and 10.5 +/- 1.7 min (P = NS) during maternal hypoxemia. In 7 of 14 maternal hypoxemia experiments, breathing activity stopped too late (7-23 min) to be attributed to maternal hypoxemia. Fetal electrocorticographic activity (P = NS), nuchal electromyographic activity (P = NS), and eye movements were normal before ECMO, with ECMO, and during maternal hypoxemia. Fetal blood pressure and heart rate did not change. We conclude that the inhibition of fetal activity during maternal hypoxemia does not seem to be mediated by release of factors from the maternal side of the placenta or the ewe.
Animals↗
The respiratory response of healthy term infants to breath-by-breath alternations in inspired oxygen at two postnatal ages.
We have studied the reflex respiratory responses to breath-by-breath alternations in fractional inspired oxygen in a group of healthy term infants at two ages, 43 +/- 7 h (study 1) and 47 +/- 3 d (study 2). Respiration was measured noninvasively using inductance plethysmography. Responses to alternations of fractional inspired oxygen between 0.16 and 0.21 (test runs) were compared with responses to alternating the inspired gas between two lines each containing a fractional inspired oxygen concentration of 0.21 (control runs). The respiratory response was measured as the mean percentage breath-by-breath alternation for inspiratory tidal volume (VTI), expiratory tidal volume (VTE), inspiratory time (TI), expiratory time (TE), frequency (f), mean inspiratory flow (VTI/TI), mean expiratory flow (VTE/TE), timing (TI.f), and ventilation. A significant chemoreflex response was present in the infants at the time of study 1, as shown by test runs that were significantly different from control for TI, TE, f, mean inspiratory flow, mean expiratory flow, timing, and ventilation (p < 0.05), and at study 2 for VTI, VTE, TE, f, mean inspiratory flow, mean expiratory flow, timing, and ventilation (p < 0.05). When control and test runs were compared separately with respect to age, there were no significant differences for any respiratory variable between study 1 and study 2. Thus, we did not observe significant maturation of respiratory chemoreflex responses to hypoxia after an age at which we could detect an established response, and this suggests that the "resetting" of chemoreceptor responses to hypoxia is essentially complete within approximately 24-48 h of birth in humans.
Age Factors↗
Absence of ventilatory responses to alternating breaths of mild hypoxia and air in infants who have had bronchopulmonary dysplasia: implications for the risk of sudden infant death.
Infants who have had bronchopulmonary dysplasia (BPD) are at an increased risk of sudden infant death syndrome. Because failure of the cardiorespiratory response to hypoxia is suggested to play a key role in sudden infant death syndrome, we tested the hypothesis that infants who have had BPD have a reduced respiratory chemoreflex response to hypoxia. We examined the reflex respiratory responses to breath-by-breath alternations in fractional inspired oxygen concentration in eight infants who had had BPD (mean gestation = 27 wk, mean postnatal age = 93 d) who were no longer on supplemental oxygen and compared the responses with those of 12 preterm infants who had not required supplemental oxygen or been mechanically ventilated since birth (mean gestation = 30 wk, mean postnatal age = 38 d). For test runs we alternated fractional inspired oxygen concentration through two gas delivery lines between 0.21 and 0.16 on a breath-by-breath basis, and for control runs we alternated the inspirate between the two gas lines with a fractional inspired oxygen concentration of 0.21 in each. Respiration was measured using inductance plethysmography infants with BPD showed no significant differences between test and control responses for any respiratory variable. In contrast, all respiratory variables in the preterm infants showed test responses significantly greater than control. We speculate that the "blunted" chemoreflex respiratory response seen in infants with BPD may predispose them to subsequent respiratory failure, but we do not known which component of the chemoreflex is impaired.
Bronchopulmonary Dysplasia↗
Afferent and efferent components of the cardiovascular reflex responses to acute hypoxia in term fetal sheep.
1. We studied the effects of acute isocapnic hypoxia on arterial and central venous pressures, carotid and femoral blood flows and heart rate in intact and carotid denervated fetal sheep between 118 and 125 days gestation, after pre-treatment with either saline, atropine or phentolamine. Electrocortical activity (ECoG) and the incidence of fetal breathing movements (FBM) were also compared between intact and carotid denervated fetuses. 2. There were no significant differences between intact and denervated fetuses in any variable measured during normoxia. Soon after the onset of hypoxia a marked bradycardia occurred in intact, but not in denervated fetuses. Femoral blood flow and femoral vascular resistance (perfusion pressure/femoral blood flow) increased in intact, but not in denervated fetuses. Carotid blood flow increased in both groups of fetuses during hypoxia, but carotid vascular resistance did not change. During hypoxia, the incidence of FBM and low-voltage ECoG was similarly reduced in both groups of fetuses. 3. Atropine produced a rise in fetal heart rate during the control period in intact but not in denervated fetuses. At the onset of hypoxia atropine prevented the initial bradycardia seen in intact fetuses. In denervated fetuses a further increase in heart rate occurred throughout the hypoxia. 4. All denervated fetuses treated with phentolamine died during the hypoxic challenge, but nine out of fourteen intact fetuses treated with phentolamine survived. 5. In intact fetuses which survived hypoxia after treatment with phentolamine, the increase in arterial blood pressure was smaller and the increase in femoral resistance did not occur. In these fetuses a rise in heart rate occurred in hypoxia. Carotid vascular resistance decreased during hypoxia after administration of phentolamine. 6. Our results indicate that the initial cardiovascular responses of the late gestation sheep fetus to hypoxia are reflex, and that the carotid chemoreceptors provide the afferent limb of this reflex. The bradycardia is mediated through a muscarinic pathway, as it is blocked by atropine. The femoral vasoconstriction is mediated through an alpha-adrenergic mechanism, mediated both neurally by a carotid chemoreflex and via catecholamines released directly from the adrenal medulla. Both these components are blocked by phentolamine. 7. The differences in survival between intact and denervated fetuses during hypoxia after phentolamine suggest that the carotid chemoreflex response to hypoxia involves mechanisms in addition to vagal efferents to the heart and alpha-adrenergic actions at peripheral blood vessels.(ABSTRACT TRUNCATED AT 400 WORDS)
Acute Disease↗
Mimicking low amniotic pressure by chronic pharyngeal drainage does not impair lung development in fetal sheep.
OBJECTIVE: The etiology of oligohydramnios-related pulmonary hypoplasia is not understood but is known to involve chronic lung liquid loss. We tested the hypothesis that low amniotic pressure in oligohydramnios disturbs the normal tracheal-amniotic pressure gradient to increase lung liquid loss and impair lung development. STUDY DESIGN: Chronic pharyngeal catheterization with drainage to the exterior was used in 15 fetal sheep to mimic reduced amniotic pressure at the upper airway in the presence of normal amniotic fluid volume. RESULTS: Pharyngeal pressures relative to amniotic pressures were negative in all drained fetuses (mean +/- SE -3.0 +/- 0.6 mm Hg), in contrast to positive pressures in controls (0.7 +/- 0.1 mm Hg). There was no significant difference in lung weight or deoxyribonucleic acid relative to body weight, or in lung morphometry, between 10 fetuses drained for 10 to 21 days and their control cotwins. CONCLUSION: Mimicking low amniotic pressure in the upper airway by chronic fetal pharyngeal drainage does not impair lung development in fetal sheep.
Amniotic Fluid↗
Outpatient care of COPD patients.
Chronic obstructive pulmonary disease (COPD) is a disorder of airflow limitation that is often progressive. Interventions aimed at slowing this progression include smoking cessation, avoidance of exacerbating factors, and prevention or early treatment of infection. Reversible symptoms can be controlled pharmacologically, with supplemental oxygen prescribed when needed. Finally, quality of life can be improved through education and pulmonary rehabilitation.
Environment↗
Fetal breathing is not initiated after cord occlusion in the unanaesthetized fetal lamb in utero.
We investigated the role of cord occlusion in the initiation of breathing at birth using an extracorporeal membrane oxygenator system to control fetal blood gases independently of the placenta in 12 chronically instrumented fetal lambs. In group IA (n = 9; exp = 12) PaCO2 was kept constant (5.62 +/- 0.21 to 5.70 +/- 0.23 kPa) during cord occlusion. Group IB (n = 7; exp = 8) were cord occlusion experiments from group IA in which no fetal breathing movements had occurred; CO2 flow to the membrane was increased and fetal PaCO2 rose significantly (5.45 +/- 0.24 to 8.27 +/- 0.56 kPa). In group II (n = 7; exp = 12) PaCO2 was allowed to increase from 5.98 +/- 0.24 kPa to 8.09 +/- 0.48 kPa after cord occlusion. Within 5 min of cord occlusion, FBM did not occur in 11 out of 12 experiments in group IA or in 11 out of 12 experiments in group II. In contrast in group IB breathing did occur in 5 out of 8 experiments. When they occurred, fetal breathing movements were always associated with low voltage electrocortical activity. Our results do not support the hypothesis that the initiation of breathing within 5 minutes of birth is dependent on an inhibitory factor of placental origin. Furthermore these data suggest an association between the presence of breathing and a substantial rise in PaCO2.
Animals↗
Fetal behavioral state and the cardiovascular system.
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Animals↗
Amnioinfusion increases amniotic pressure in pregnant sheep but does not alter fetal acid-base status.
To investigate the recent suggestion that fetal hypoxemia and acidemia in polyhydramnios are secondary to raised amniotic pressure, 5 to 15 L of normal saline solution was infused intraamniotically at 100 ml/min in seven ewes. Amniotic pressure increased linearly by 1.0 +/- 0.013 (mean +/- SEM) mm Hg per liter infused. Infusion of 15 L produced a mean rise in amniotic pressure of 15.2 +/- 1.2 mm Hg (p less than 0.001) but no significant change in fetal pH, PCO2, PO2, fetal heart rate, or mean arterial pressure. A similar rise in amniotic pressure and lack of change in blood gas values occurred in two control ewes infused intraperitoneally. Rupture of the membranes occurred in two of three amnioinfusions of 15 L. We conclude that acute amnioinfusion raises amniotic pressure in sheep but does not alter fetal blood gas status.
Amnion↗
Behavioral changes in fetal sheep caused by vibroacoustic stimulation: the effects of cochlear ablation.
We measured the effects of 2 minutes of vibroacoustic stimulation on the activity of unanesthetized fetal sheep in utero. We were unable to detect any changes in activity after stimulation with a model 5C electrolarynx. With more powerful stimulation using a mechanical oscillator, fetal electrocortical activity desynchronized. Fetal breathing and eye movements changed with electrocortical activity and there was an increase in nuchal muscle activity. Stimulation caused a small decrease in fetal heart rate. Responses to stimulation were not seen in four of the five fetuses with bilateral cochlear ablation. These results indicate that in fetal sheep the auditory apparatus is necessary for the detection of vibroacoustic stimuli. The difference in responsiveness of the sheep and human fetus appears to be because of a difference in central processing after detection of the stimulus.
Acoustic Stimulation↗
Fetal breathing during chronic lung liquid loss leading to pulmonary hypoplasia.
The mechanism of oligohydramnios-related pulmonary hypoplasia (PH) is not understood, but is known to involve chronic loss of lung liquid. In order to investigate the recent suggestion that fetal breathing movements are absent or diminished in oligohydramnios-related PH, we made continuous recordings of fetal breathing movements (FBM) during chronic lung drainage in tracheostomized fetal sheep. FBM remained present throughout the drainage period. There was no significant difference in the number or duration of FBM epochs in tracheostomized fetuses compared to controls, although there was a slight reduction in incidence between 126 and 133 days (P = 0.02). PH in the fetuses undergoing chronic lung liquid drainage was confirmed by significant reductions in lung weight, volume, DNA, and total airspace, and in altered maturation. This study is consistent with other data suggesting that inhibition of FBM is not the primary mechanism of oligohydramnios-related pulmonary hypoplasia.
Animals↗
Drug fever. Remember to consider it in diagnosis.
Drug fever should be considered in the differential diagnosis of any patient with unexplained fever. Clues in the history, physical examination, and laboratory assessment can point to the diagnosis before extensive, costly, and potentially harmful investigations and therapies are begun.
Drug Hypersensitivity↗
Development of respiratory chemoreflexes in response to alternations of fractional inspired oxygen in the newborn infant.
1. We studied the reflex respiratory response to breath-by-breath alternations of fractional inspired oxygen (FI,O2) in full-term human infants delivered either vaginally or by caesarian section at 3-10 h (n = 6), 12-24 h (n = 12), 24-48 h (n = 18), 3-4 days (n = 21) and 5-8 days (n = 7) postnatally. 2. Respiration was measured by inductance plethysmography (Respitrace) and respiratory variables for each breath were calculated on-line by a microcomputer. Test runs (with alternations of FI,O2 between 0.21 and 0.16) and control runs (with an FI,O2 of 0.21) of 50-100 breaths were carried out during quiet sleep. For each respiratory variable the magnitude of the reflex breath-by-breath alternation was compared between control and test runs. 3. There was little respiratory response during control runs at any postnatal age. However, there was a significantly greater response to test runs in all infants studied and at all ages. 4. There were no significant differences in the degree of alternation during test runs between infants of similar postnatal ages delivered by caesarean section and those born vaginally. 5. In all infants the magnitude of the respiratory response increased with postnatal age, presumably reflecting postnatal increases in the hypoxic sensitivity of the peripheral arterial chemoreceptors. 6. The results indicate that in human infants the alternate breath method can be used to detect developmental changes in peripheral chemoreflexes between birth and postnatal day 8.
Cesarean Section↗
In vitro validation of Doppler indices using blood and water.
Using an in vitro flow model, volume flow and pressure were measured to compare calculated resistance with simultaneously measured continuous-wave Doppler indices during imposed changes in downstream resistance to pulsatile flow. With stepwise reductions in flow, the peak (S) and trough (D) points of the maximum shifted-frequency envelope fell in parallel in a linear fashion until D reached zero. Pressure remained constant, and the pressure waveform remained unchanged. As calculated resistance increased, resistance index (RI) and pulsatility index (PI) both increased in a linear fashion until the point at which D became zero. However, S/D ratio was not linear, and the slope increased as resistance increased. The results obtained from microspheres suspended in water and with heparinized sheep's blood were similar. The results indicate that, with reductions in flow at constant pressure in vitro, S/D ratio does not relate to calculated resistance in the same linear manner as PI and RI.
Animals↗
The role of peripheral chemoreceptors in the rapid response of the pulmonary vasculature of the late gestation sheep fetus to changes in PaO2.
The effect of removing the input from the peripheral arterial chemoreceptors on pulmonary vascular responses to changes in PaO2 was examined in late gestation fetal sheep. Blood flow in the left pulmonary artery and driving pressure across the pulmonary vascular bed were monitored in chronically prepared fetal sheep at 126-129 days gestation. Five fetuses had carotid sinus and vagus nerves sectioned bilaterally and four were left intact. In normoxia (PaO2 ca. 23 mmHg) pulmonary vascular resistance was slightly greater and pulmonary blood flow reduced in the denervated group relative to the intact group but these differences were not significant. When made hypoxic (PaO2 ca. 14 mmHg), pulmonary blood flow fell and pulmonary vascular resistance increased in all fetuses. However, in the intact fetuses these changes were significantly more rapid. In all fetuses the vasoconstriction was prolonged after their return to normoxia. When made hyperoxic (PaO2 ca. 27 mmHg), pulmonary blood flow increased by a similar amount in all fetuses. We conclude that in the term fetus the peripheral chemoreceptors play no appreciable role in the maintenance of the high pulmonary vascular resistance in normoxia, or the fall in resistance produced by a rise in PaO2. The chemoreceptors do however initiate the rapid phase of pulmonary vasoconstriction in hypoxia.
Animals↗