Effect of upper airway carbon dioxide on ventilation and blood gases in the awake pony

Carbon dioxide concentrations were increased during expiration in the upper one-half of the trachea, pharynx, and nasal sinuses to determine if elevation of upper airway CO2 would alter breathing or arterial blood gases in the awake pony. Carbon dioxide (100%) was injected into the midcervical trachea via a chronically implanted transcutaneous cannula during the first part of the animal's expiration. This maneuver elevated upper airway expiratory CO2 concentrations but prevented any exogenous CO2 from entering the lung and being absorbed into the arterial blood. Twelve experiments were performed on six ponies in which upper airway CO2 was elevated 2, 4, and 6% above the normal expired CO2 concentrations. Tidal volume increased in a dose dependent manner during upper airway CO2 exposure, but total ventilation was unchanged from base-line measurements made while the animal breathed room air. Arterial Po2 also increased during upper airway CO2 administration, reaching a mean value 6 Torr (1 Torr = 133.322 Pa) greater than the base-line values at the +6% CO2 exposure. We conclude that upper airway CO2 exposure alters breathing pattern slightly (increases tidal volume) and increases arterial PO2 in the awake pony.

Cerebrovascular response to acute decreases in arterial PO2

The purpose of these studies was to examine the time course of the cerebrovascular response to acute hypoxia in unanesthetized ponies. An electromagnetic flow transducer chronically placed on the internal carotid artery of the pony allowed continuous recording of internal carotid artery blood flow (ICBF) which has been shown to be representative of cerebral blood flow (CBF). The ponies were subjected to three levels of acute isocapnic hypoxia (PaO2 = 62, 44, and 39 mm Hg for hypoxia level I, II, and III, respectively), and the temporal and steady-state cerebrovascular response was examined. ICBF increased significantly at all three hypoxia levels (8, 25, and 40% at hypoxia I, II, and III, respectively). This increase was rapid in the two most severe levels of hypoxia, beginning within 45 s, and was complete within 90 s. The increase lagged behind the reduction in PaO2 by 24-28 s. During the very mild level of hypoxia (I), no such rapid increase in flow was observed; rather, the increase occurred only after 5 min of hypoxia. Microsphere (15 microns diameter) measurements from six ponies during the most severe level of hypoxia (III) demonstrated that CBF increased 38%. Noncerebral tissues known to be vascularly connected to the circle of Willis, and thus capable of receiving blood flow via the internal carotid artery, either did not change or increased so slightly during hypoxia that their effect on ICBF was minimal.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional cerebral blood flow during hypercapnia in the anesthetized rabbit

These experiments were designed to test the hypothesis that increases in blood flow to the lower brainstem would be greater than forebrain regions during arterial hypercapnia. Total and regional cerebral blood flow (CBF) was measured via the tracer microsphere technique in seven anesthetized New Zealand white rabbits during normocapnia (arterial PCO2 congruent to 40 torr) and hypercapnia (arterial PCO2 congruent to 80 torr). During normocapnia average CBF was 0.77 ml/min/g, and regional measurements of blood flow indicated significantly greater flow to the cerebrum (0.86 ml/min/g) than either the medulla (0.52 ml/min/g) or the pons (0.49 ml/min/g). When arterial PCO2 was increased average CBF increased 113%, and a significant linear regression was calculated for arterial PCO2 vs CBF [CBF (ml/min/g) = 0.028 PCO2 (torr) - 0.502]. The distribution of blood flow within the brain was similar to normocapnia except that blood flow to the cerebellum was now greater than any other brain region (1.97 ml/min/g for the cerebellum compared to 1.66 ml/min/g for the cerebrum). Absolute increases in blood flow to the lower brainstem were equal to or less than other areas of the brain. We conclude that ponto-medullary blood flow does not increase disproportionate to other areas of the brain during hypercapnia, but some redistribution of CBF does occur in that cerebellar blood flow increased significantly more than the cerebrum, medulla, or pons.

Distribution of internal carotid artery blood flow in the pony

This study determined whether blood flow through the internal carotid artery (ICA) could be used to sample total cerebral blood flow in the pony. To answer this question we considered both the anatomic arrangement of the ICA in cadavers and the relative distribution of ICA blood flow to cerebral and extracerebral tissue using radioactive microspheres. Acrylic corrosion casts of the ICA indicated that this vessel traveled directly to the base of the brain, contributing to the formation of the circle of Willis, and did not send any significant branches to other tissues. Two vessels (internal ethmoidal artery and internal ophthalamic artery) did arise anteriorly from the circle of Willis and were, therefore, indirectly supplied by the ICA. Injection of radioactive microspheres of 15 microns diameter indicated that blood flow to extracerebral structures supplied by the internal ethmoidal and internal ophthalamic arteries was less than 5% of total ICA blood flow. Increases in ICA blood flow as measured with an electromagnetic flowmeter during isocapnic hypoxia (arterial PO2 near 40 Torr) in the awake pony (n = 6) were compared with increases in total brain flow as measured with radioactive microspheres (n = 6). ICA blood flow increased 40% compared with a 38% increase in total brain blood flow as measured with microspheres. We conclude that the ICA supplies predominantly brain tissue (approximately 95%) and that changes in ICA blood flow are representative of changes in total brain blood flow in the awake pony.

Circulatory mechanoreceptors in the pond turtle Pseudemys scripta

This study was undertaken to characterize cardiovascular receptors in the turtle, Pseudemys scripta, with particular attention being given to neural activity changes associated with alterations in blood pressure. Vagal afferent nerve traffic, synchronous with heart contractions, was recorded in anesthetized artificially ventilated turtles. Action potentials, from receptors that fired regularly during each heart cycle, occurred during ventricular systole. Mechanical probing and vascular occlusion indicated that these receptors were located in the proximal common pulmonary artery including the bulbus cordis region. Bolus injections of saline into the ventricle or the common pulmonary artery caused immediate but transient increases in cardiac synchronous traffic. Prolonged elevation of arterial and ventricular blood pressure, by either saline injection or arterial occlusion, caused increases in receptor discharge of the same duration as the pressure increases. Although these receptors could participate in the regulation of the systemic and the pulmonary circulation, the physiological role for them is presently unknown.

Cerebral blood flow during normocapnic hyperoxia in the unanesthetized pony

The effect of hyperoxia on cerebral blood flow (CBF) was examined in 12 unanesthetized ponies. CBF was determined using radioactive microspheres, 15 micrometer in diam, durijng inspriation of the following gases: 1) room air (control); 2) 40% I2 in N2; and 3) approximately 100% O2 with 2.2-4.5% CO2 added to maintain isocapnia. CBF did not change from control values during either level of hyperoxia. However, cerebrospinal fluid (CSF) carbon dioxide tension (PCO2) increased during 40% O2 (delta 1.0 Torr) and approximately 100% O2 (delta 2.9 Torr). This rise in CSF PCO2, not due to a change in CBF, may have resulted from a decrease in the CO2 carrying capacity of cerebral venous blood during hyperoxia (Haldane effect). Although respiration did not change during 40% O2, expired minute volume increased 25% during approximately 100% O2 due to an increase in tidal volume. This rise in respiration was not associated with changes in any of the conventional stimuli to breathing (arterial pH, O2 tension, or PCO2 or CSF pH). One possible explanation was that cerebral extracellular fluid pH, in the vicinity of the central chemoreceptors, or cerebral intracellular fluid pH changed in a direction unlike CSF pH. An alternate explanation was that the CO2 in the inspired gas activated CO2-sensitive receptors in the lungs.

Nursing and the process of scientific inquiry

Nurse education has to confront the problem of developing in students an understanding of the different perspectives put forward in nursing. However, all the perspectives adhere to the scientific method and it is therefore necessary to examine the process of scientific inquiry. As nursing occupies a position at the interface between physical and social sciences, it is also necessary to offer students an examination of the different paradigms which exist within the social sciences.

Isocapnic hyperpnea in awake ponies during inspiration of 4% CO2

Unanesthetized ponies were given 4% CO2 (inspired CO2 pressure = 28 Torr) to breathe at two levels of arterial O2 pressure (PaO2): 1) near 75 Torr and 2) near 200 Torr. During 4% CO2 breathing, at either level of PaO2, the mean arterial CO2 pressure (PaCO2) was unchanged from control measurements (control measurements were made at the same PaO2, but with no CO2 in inspired air), suggesting that awake ponies can "clear" 4% CO2. The ability of individual ponies to clear 4% CO2 was quite variable: some ponies did not clear 4% CO2 and others cleared 4% CO2 on one day but not on the following day. Based on the average of 20 experiments, however, PaCO2 was unchanged from 40 Torr during inspiration of 4% CO2. Direct measurement of chemical stimuli to breathing in arterial blood and cisternal cerebrospinal fluid indicate that ventilation increased during CO2 breathing even though PaCO2, pHa, PaO2, and CSF pH were not changed in a direction that might explain the accompanying change in ventilation. The authors suggest that stimuli to receptors other than peripheral or medullary chemoreceptors may be responsible for the reported "isocapnic hyperpnea."

Hemodynamic effects of long term feeding of sympathomimetic amines to swine

The hemodynamic effects of long term feeding of sympathomimetic amines (SPMA) to swine were studied. Three groups of female swine (N = 20 for each group) were fed either aminorex fumarate, d-amphetamine sulfate, or dextrose (control) for as long as 8 months in dosages up to 15 mg/kg/day. After 4 months of this feeding regiment, the weight gain of the pigs fed either aminorex or amphetamine was significantly less than the control animals. Hemodynamic measurements on awake swine indicated no elevation of pulmonary arterial blood pressure in the pigs fed SPMA. Measurement of systemic hemodynamics revealed that cardiac index was lower in the treated pigs than in control animals, but that heart rate and systemic arterial blood pressure were not altered by the drugs. In addition to baseline measurements of hemodynamic variables, the animals were exposed to acute hypoxia (12 percent O2 in N2) for 5 minutes. Although pulmonary arterial blood pressure increased similarly in the 3 groups of pigs, total pulmonary resistance increased to a greater extent in the pigs fed SPMA, indicating perhaps an enhancement of the hypoxic pulmonary pressor response after chronic ingestion of either amphetamine or aminorex. In a limited number of pigs, SPMA were fed for a period of 8 months, of which the last 3 months were during pregnancy. Hemodynamic measurements on sedated (metomidate, IV) swine revealed no difference in pulmonary arterial blood pressures between treated and control animals. We conclude that chronic ingestion of large doses of aminorex or amphetamine in swine does not lead to pulmonary arterial hypertension, but that slight reductions in cardiac output and subtle alterations in the pulmonary pressor response to acute hypoxia may occur.

Hemodynamic effects of acute hypoxia and minute amounts of endotoxin in awake swine

Hemodynamic measurements and arterial blood gases were determined from awake swine (n = 8) during acute hypoxia (12% O2, balance N2 for 5 minutes) and following injection of Escherichia coli endotoxin (4 microgram/kg of body weight) into the pulmonary artery. Comparison of baseline data with these treatments indicated: (1) swine exhibited a marked pulmonary pressor response to acute hypoxia (deltaBPpul = 9 to 12 mm of Hg): (2) injection of minute amounts of endotoxin led to a marked increase of pulmonary arterial blood pressure 10 to 20 minutes following the injection (deltaBPpul = 15 mm of Hg); and (3) the pulmonary pressor response to a 2nd exposure of acute hypoxia was unaffected by the intervening endotoxin injection.

Ventilatory control in peripheral chemoreceptor-denervated ponies during chronic hypoxemia

The present study was designed to provide further insight into the role of the carotid and aortic chemoreceptors in ventilatory (VE) acclimatization during sojourn at altitude. Measurements were made: 1) on 10 ponies near sea level (SL, 740 Torr) under normal conditions, 2) on 6 of these at SL following chemoreceptor denervation (CD), and 3) subsequently on all 10 during 4 days of hypobaric hypoxia (PaO2 = 40-47 Torr). CD resulteo in hypoventilation at SL (deltaPaCO2 = d8 Torr, P less than 0.05), and it prevented hyperventilation normally observed with injection of NaCN and acute exposure to hypoxia (less than 1 h). In contrast, hyperventilation was evident in normal ponies during acute hypoxia (deltaPaCO2 = -6.7 Torr). Ventilation increased in both groups between the 2nd and 8th h of hypoxia (deltaPaCO2 from 1 h = -4 Torr, P less than 0.05). This change, a common characteristic of acclimatization, persisted throughout 4 days of hypoxia in the normal ponies. However, in the CD ponies this change was evident consistently only through the 12th h and after the 44 h hyperventilation was no longer evident. We conclude that the peripheral chemoreceptors are essential in ponies for normal VE acclimatization to this degree of hypoxemia. Two additional findings in CD ponies suggest the presence of a CNS inhibitory influence on the VE control center during chronic hypoxemia. First, acute hyperoxygenation on the 4th day of hypoxemia induced hyperventilation (deltaPaCO2 = -5 Torr, P less than 0.05). Second, again on the 4th day and during hyperoxygenation, VE responsiveness to CO2 and doxapram HCl was greater than at sea level.

Cardiopulmonary effects of the combination of neuroleptic azaperone and hypnotic metomidate in swine

Cardiopulmonary measurements were made at given intervals up to 120 minutes on 6 awake, unanesthetized pigs given azaperone and metomidate. Decreases from control values occurred in arterial blood pressure (deltaBPart = 30 mm of Hg), heart rate (deltaHR = 30 to 35 beats/minute), and cardiac index (deltaCI = 1.5 L/minute/m2). Blood gas and pH measurements indicated no severe impairment of pulmonary function or arterial acidosis. Although the drugs led to decreases in the various functions, cardiopulmonary function remained stable and uncompromised.

Cardiopulmonary effects of mechanical distension of the rumen in nonanesthetized sheep

The cardiopulmonary effects of mechanical distension of the rumen were studied in nonanesthetized sheep. Results in group I ewes indicated that simply increasing intraruminal pressure by compressed air insufflation did not seriously affect cardiopulmonary hemodynamics. Changes were more serious in group II ewes when water injection was followed by ruminal insufflation with compressed air. Heart rate, total peripheral resistance, and total pulmonary resistance increased, with a concommitant increase in arterial and pulmonary blood pressure and decrease in stroke volume. Infusion of water alone increased heart rate and cardiac output. The blood gas data indicated a definite arterial hypoxemia and hypercapnia, suggesting impaired ventilation during ruminal distension. The increase in total pulmonary resistance was thought to be due to alveolar hypoxia caused by a significant decrease in ventilation.

Effect of exercise on cardiac output and distribution of uterine blood flow in pregnant ewes

This study was designed to determine what effect physical training has on heart rate and stroke volume responses to exercise stress and to determine if exercise altered the distribution of uterine blood flow. Measurements were made in ten pregnant ewes at rest and immediately following exercise on a treadmill. Five ewes underwent physical training for 3 wk prior to measurement. An increase in heart rate with no change in stroke volume was observed following exercise in both trained and untrained ewes. Total uterine blood flow was not changed following exercise, but distribution was altered in favor of the placenta. Blood flow was evenly distributed within the placenta before and after exercise. The redistribution of flow to the placenta that occurs after exercise. tphe redistribution of flow to the placenta that occurs after exercise might represent a compensatory mechanism for the fetus.

Salivary gland tumors: review of 643 cases

643 cases of salivary gland tumors constitute two series of histological sections that were studied from hospitals and dental schools in Southeast Scotland and Southern Ontario. The Scottish series represented epithelial tumors of the parotid and intra-oral salivary glands, but the Canadian series also included tumors of the submandibular and sublingual glands. Classification was based on that recommended by the World Health Organisation (Thackray 1972). While direct statiscal comparisons between the two series are not appropriate, the differences between them suggest that malignant tumors are more common in Canada. The Scottish series contains the largest proportion of benign salivary tumors so far reported. In the Scottish series, 88.7% of parotid tumors were benign compared with 51.9% of Canadian series. In the Canadian series from the submandibular glands, 21.2% only were benign. Of the intra-oral salivary tumors, 62.2% from the Scottish series were benign compared with only 34.7% from the Canadian series.

Hypoventilation in ponies after carotid body denervation

Seven ponies were subjected to carotid body denervation (CD) and two ponies were sham operated (S). Measurement of arterial blood gases and arterial blood and cerebrospinal fluid (CSF) acid-base balance were made prior to and 1,2,4,9, and 17 wks after surgery in unanesthetized animals. Resting ventilation and ventilatory responsiveness to hypoxia and NaCN infusion were assessed prior to and 2,9, and 17 wks after surgery. Alveolar hypoventilation in the CD ponies was marked 1-2 wk after surgery when VE and VA were reduced 40% and 10%, respectively, from control and PaCO2 was 12-15 mmHg above control. However, the effect was not nearly as great 4, 9, and 17 wk after surgery when the PaCO2 stabilized at approximately 6 mmHg above control PaCO2. Arterial blood pH was normal in the hypercapnic CD ponies, but CSF pH remained acid relative to normal throughout the 17-wk period. Changes in ventilatory responsiveness to hypoxia and NaCN tended to parallel changes in resting ventilation. These findings suggest: 1) the carotid bodies are essential in ponies to maintain normal ventilation: 2) in CD ponies peripheral chemosensitivity is partially regained at some unestablished locus; and 3) pH compensating mechanisms in chronically hypercapnic ponies function relatively better in blood than in CSF.

Cardiopulmonary measurements in nonanesthetized, resting normal ponies

Cardiopulmonary measurements were determined in 19 nonanesthetized, normal ponies. Mean values for arterial pressure, pulmonary arterial pressure, cardiac output, heart rate, packed cell volume, and hemoglobin are reported, as well as acid-base determinations of arterial blood and cerebrospinal fluid. Respiratory function test data include total ventilation, respiratory rate, alveolar ventilation, oxygen uptake, and carbon dioxide output. The data compare favorably with the available data from previous reports on ponies. Because of large day-to-day variations in total ventilation, alveolar ventilation should be measured if ponies are used in the study of pulmonary function.

Cerebrospinal fluid alkalosis during high-altitude sojourn in unanesthetized ponies

Unanesthetized adult female ponies were studied near sea level (250 m) and during sojourns to 3400 m (N=6) and 4300 m (N=7) altitude. The pH, PCO2, and PO2 of arterial blood and pH and PCO2 of cerebrospinal fluid (CSF) were measured under conditions of acute (1 hr) and chronic (1-45 days) hypoxia. Cerebrospinal fluid was sampled from the cisterna magna of the awake pony and arterial blood withdrawn from an indwelling arterial catheter. In both groups of animals, PaCO2 decreased slightly after 1 hr of hypoxia (delta PaCO2= - 0.6 mm Hg at 3400 m; - 3.9 mm Hg at 4300 m), decreased further after 1-5 days at high altitude (delta PaCO2= - 7.2 mm Hg at 3400 m; - 12.3 mm Hg at 4300 m) and then increased significantly after 6 days of chronic hypoxia (delta PaCO2= + 4.1 mm Hg at 3400 m; + 4.7 mm Hg at 4300 m). Although PaO2 decreased markedly during acute hypoxia, subsequent changes in PaCO2 at high altitude did not alter PaO2 from that observed during acute hypoxia (PaO2=52 mm Hg at 3400 m; 41 mm Hg at 4300 m). The pH of CSF increased during acute hypoxia (delta pH= + 0.013 unit at 3400 m; + 0.033 unit at 4300 m) and became more alkaline after 1-2 days at high altitude (delta pH= + 0.031 unit at 3400 m; + 0.064 unit at 4300 m). At 4300 m, CSF pH remained alkaline to control values throughout sojourn. Under these conditions of chronic hypocapnic hypoxia, CSF pH was imperfectly regulated and regulated in a magnitude equal to (3400 m) or less than (4300 m) arterial blood. Furthermore, the similarity of relative changes in CSF [HCO3-] and arterial [HCO3-] during chronic hypoxia may indicate a passive regulation of CSF [HCO3-] rather than local 'CSF-specific' mechanisms as previously proposed.

Hypoxic pulmonary hypertension in the pony

Hemodynamic measurements were made in 6 ponies at low altitude (Madison, WI, altitude, 250 m) and after 1, 2, 4, and 6 weeks at high altitude (Climax, CO, altitude, 3,400 m). The salient findings were that ponies maintain an increased heart rate and cardiac output and develop significant pulmonary hypertension at high altitude. The average control resting mean pulmonary artery pressure (BPpul) was 25.1 mm of Hg at 250 m; this value increased to 56.3 mm of Hg after 6 weeks at 3,400 m. An additional finding was that the pulmonary vascular response to acute hypoxia seemed to increase with time at high altitude.