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Biomedical subjects

G B Martin

Publications and source records attributed to G B Martin.

At least 181 records · Page 10Linked to original sources
PubMed1986

Hyperkalemia during cardiac arrest and resuscitation in the canine model.

Although recent clinical reports have noted hypokalemia after resuscitation from cardiac arrest, extensive animal work indicates that potassium is released from cells during ischemia. This study was undertaken to define the changes that occur in serum potassium ion during cardiac arrest and resuscitation in a canine model. Fourteen dogs were subjected to 5 min of cardiac arrest followed by 30 min of closed-chest CPR (CCPR). Resuscitation was performed according to a standardized protocol. Serum potassium increased significantly (p less than .001) from baseline, remained elevated 5 min after return of spontaneous circulation (ROSC), but declined to baseline levels at 15 min post-ROSC. Increases in interstitial potassium would be expected to be even greater due to the poor exchange between interstitial and intravascular compartments during CCPR. Interstitial hyperkalemia may play a role in the genesis of wide-complex electromechanical dissociation and may explain the reported success of calcium chloride in treating this problem.

Animals↗
PubMed1986

The roles of inhibin and gonadotrophin-releasing hormone in the control of gonadotrophin secretion in the ewe.

The respective roles and relative importance of ovarian inhibition and hypothalamic stimulation in the differential control of the secretion of FSH and LH were studied in the ewe. In the first experiment two groups of ten intact ewes were injected i.v. twice daily with 9 ml charcoal-extracted bovine follicular fluid (bFF), a preparation rich in inhibin (3.65 ku./ml), throughout the luteal phase of the oestrous cycle. Compared with the control ewes, this treatment significantly reduced pituitary and plasma FSH concentrations and increased the frequency and amplitude of the LH pulses, but did not affect pituitary LH concentrations. In a second experiment, five control and five bFF-treated ewes from experiment 1 were ovariectomized and the injection regime was altered to 2.5 ml s.c. every 8 h. This treatment was maintained for 21 days. In control ewes, plasma FSH concentrations rose significantly within 12 h and continued to rise for 3-4 days. Treatment with bFF abolished this increase and maintained plasma FSH concentrations below those observed in intact ewes. The rise in mean plasma LH concentrations evoked by ovariectomy was also partially inhibited in the bFF-treated ewes. The response to the gonadotrophin-releasing hormone (GnRH) agonist buserelin (5 micrograms i.v.) was measured 6, 12 and 18 days after ovariectomy. In control ewes the agonist consistently evoked large surges of both hormones but in bFF-treated ewes the FSH response was completely blocked and the initial phase of the LH response (the first 'pool') was greatly reduced. In experiment 3, six ewes were ovariectomized and passively immunized against GnRH 3 days after oestrus. The increase in plasma LH which normally follows ovariectomy was completely abolished and mean concentrations remained very low and did not change over the following 14 days. In contrast, mean FSH concentrations rose significantly within 12 h of ovariectomy and continued to rise until the third day, after which they fell gradually. Treating three of the ewes with bFF (2.5 ml s.c. every 8 h) 8 days after ovariectomy and immunization further reduced the FSH concentrations. When the ewes were injected repeatedly (200 ng i.v., hourly for 5 h) with [D-penicillamine-(But)6]-GnRH(1-9)nonapeptide-ethylamide, a synthetic GnRH analogue which does not bind to the antiserum, there was a rapid rise in the secretion of LH in both control and bFF-treated animals but, as with the responses to buserelin, the initial response was significantly lower in bFF-treated than in control ewes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Artificial induction of lactation in cattle: initiation of lactation and estrogen and progesterone concentrations in milk.

Thirty heifers were given 11 subcutaneous injections of 5 mg estradiol benzoate and 200 mg progesterone every 3 d to develop their mammary glands. Three days later groups of animals were treated with 1) 20 mg dexamethasone twice, 2) 500 micrograms cloprostenol thrice, 3) dexamethasone and cloprostenol, 4) oxytocin 4 IU six times, or 5) no further injections. Two further groups of six heifers each (6 and 7) were treated in a manner similar to groups 1 and 3 except the dose of estrogen to develop their mammary glands was doubled to 10 mg/3 d. Six lactating first calf heifers were controls (8). The proportion of animals lactating, combined milk yield for each group (kg), and mean days lactated were 1) 5/6, 3831, 142; 2) 1/6, 912, 195; 3) 6/6, 4898, 194; 4) 3/6, 1066, 128; 5) 1/6, 293, 154; 6) 6/6, 6109, 130; 7) 6/6, 6265, 130; and 8) 6/6, 19, 190, 251. The lactogenic response to dexamethasone and oxytocin is similar to that in sheep, but the response to cloprostenol indicates a species difference. Intensive blood sampling before and after injection of hormones, intended to trigger lactogenesis, showed that plasma prolactin rose to peaks above 210 ng/ml in cows of groups 2, 3, and 4 and were unchanged from the base below 40 ng/ml in groups 1 and 5. Monitoring of steroids after induction treatment showed estradiol-17 beta ranged between 35 and 400 pg/ml and 20 to 80 pg/ml in mammary secretion and plasma and progesterone concentrations were less than at diestrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Lactic acidosis as a predictor of downtime during cardiopulmonary arrest in dogs.

Studies have shown that over 50% of cardiovascular deaths occur before hospitalization. A major factor associated with survival in cases of out-of-hospital cardiac arrest is the time from cardiovascular collapse to the initiation of cardiopulmonary resuscitation (CPR) or "downtime." The purpose of this study was to determine whether blood lactate levels could be used to predict downtime in the canine cardiac arrest model. Femoral arterial and Swan-Ganz catheters were placed in 22 mongrel dogs, and ventricular fibrillation was electrically induced. The dogs remained in ventricular fibrillation without ventilation for 5, 10, 15, 30, or 60 minutes. After the predetermined fibrillation time, a left anterolateral thoracotomy was performed, and open-chest cardiac massage was begun. Arterial and mixed venous lactate levels were determined for every 5 minutes during 30 minutes of cardiopulmonary resuscitation. The correlation coefficient between the mixed venous and arterial lactate levels was 0.96 or greater during all stages of resuscitation. Peak serum lactate level increased linearly in relation to downtime. The increase in lactate level was not evident until after CPR was begun, and it remained at peak levels or decreased insignificantly, despite optimal open-chest CPR. Linear regression analysis revealed that 84% of the variability in serum lactate levels could be explained by downtime differences. In this model, blood lactate level is a reliable and objective measure of downtime and may be a useful indicator of the adequacy of CPR if levels decrease or remain stable. The clinical implications of this study lie with the use of blood lactate levels in the emergency department to guide the aggressiveness of resuscitative efforts.

Acidosis↗
PubMed1985

Central venous and mixed venous oxygen saturation: comparison during canine open-chest cardiopulmonary resuscitation.

Mixed venous oxygen saturation (MVO2) is a valuable parameter in monitoring critically ill patients because it serves as an index of the adequacy of the oxygen delivery system. Mixed venous oxygen saturation as reflected by the easily obtainable central venous oxygen saturation (CVO2) may prove useful during cardiopulmonary resuscitation (CPR) as an indicator of both the adequacy of varying CPR regimens and the efficacy of pharmacological interventions. This study investigates the relationship between CVO2 and MVO2 and its clinical usefulness during CPR. Swan-Ganz and central venous catheters were placed in 20 mongrel dogs. Ventricular fibrillation was then induced and, after predetermined downtimes ranging from 5 to 60 minutes, thoracotomy was performed, and open-chest bimanual cardiac massage was started. Central venous and mixed venous blood-gas samples were drawn every five minutes during a 30-minute period of CPR. The correlation between CVO2 and MVO2 was 0.8719 (P less than 0.001) before arrest but deteriorated at all times during CPR with values ranging from 0.1589 (P = 0.542) to 0.5781 (P = 0.024). Although statistically significant at times, the correlation between CVO2 and MVO2 during CPR is not consistently high enough to enable the routine substitution of CVO2 for MVO2 in assessing the oxygen delivery system.

Animals↗
PubMed1985

Insulin and glucose levels during CPR in the canine model.

Cardiopulmonary arrest and resuscitation produces tremendous physiological stress with resultant biochemical derangements. We undertook this study to determine insulin and glucose levels during cardiopulmonary arrest in the canine model. Baseline insulin and glucose levels were obtained from an ascending aortic arch catheter in six mongrel dogs. Ventricular fibrillation was induced by an electrical stimulus and ventilation was terminated. After five minutes of fibrillation, cardiopulmonary resuscitation (CPR) was initiated using external, mechanical CPR and a continuous epinephrine infusion at 5 micrograms/kg/min. Serum insulin and glucose levels were repeated 15 minutes after beginning CPR. Mean blood glucose 15 minutes after initiation of resuscitation (379 +/- 114 mg/dL) was significantly increased from prearrest levels (124 +/- 29 mg/dL, P less than .01). Mean serum insulin 15 minutes after initiation of resuscitation (11.3 +/- 3.3 microU/mL) was significantly decreased compared to prearrest levels (16.2 +/- 6.0 microU/mL, P less than .05). During ischemia, the myocardium becomes dependent primarily on glucose as a source of energy. Inappropriately low insulin levels during CPR may adversely affect an already compromised myocardial glucose metabolism. Further investigation is needed to determine the utility of insulin infusion during CPR.

Animals↗
PubMed1985

Immediate emergency department external cardiac pacing for prehospital bradyasystolic arrest.

Approximately 25% of patients in prehospital cardiac arrest present in bradyasystolic rhythms, and their long-term prognosis is very poor. Our study was undertaken to determine the utility of immediate emergency department (ED) external cardiac pacing in this situation. Twenty patients presenting with bradyasystolic prehospital cardiac arrest were entered in the study. All received the usual advanced cardiac life support therapy, but also were externally paced immediately using an automated external defibrillator and pacemaker (AEDP). Only two of 20 patients showed evidence of electrical capture, and none developed pulses with pacing. Four of the 20 patients developed a sinus rhythm and blood pressure during resuscitation. Three survived to leave the ED, but none survived to leave the hospital. An increase in the rate of bradycardia and pulseless idioventricular rhythms that was independent of electrical capture or pharmacologic therapy was noted occasionally. Although survival was not enhanced using the AEDP, the device was reliable, easy to use, and free of complications. External cardiac pacing warrants further investigation in the prehospital setting.

Adult↗
PubMed1985

Comparison of central venous and arterial pH and PCO2 during open-chest CPR in the canine model.

Arterial blood gases are difficult to obtain during cardiopulmonary resuscitation (CPR) in human beings, and the possibility of venous sampling is raised frequently. The reliability of central venous gases as a substitute for arterial blood gases in assessing acid base status, however, has not been investigated adequately under conditions of CPR. Therefore, femoral arterial and central venous catheters were placed in 24 mongrel dogs, and ventricular fibrillation was electrically induced. After varying predetermined downtimes from five to 60 minutes, open-chest CPR was begun, and arterial and central venous blood gases were simultaneously drawn every five minutes during a 30-minute period. Arterial pH (pHa) was consistently higher than central venous pH (pHcv) by an average of .048 units. A significant correlation existed between the pHa and pHcv at all times during CPR, with an overall r = .9771 (P less than .0001). The difference between central venous PCO2 (PcvCO2) and arterial PCO2 (PaCO2) was 5.17 mm Hg prior to cardiac arrest, but it increased 300% to a mean of 15.51 mm Hg during CPR. Correction of pHcv using conventional methods to account for this respiratory component decreased the correlation between pHa and pHcv to r = .6905. The ability of pHcv to substitute for pHa was assessed, and showed a sensitivity of 100% when pHa of 7.2 was used as a criterion for treatment. In this model, pHcv is a sensitive indicator of pHa and it may be used to guide bicarbonate therapy. The increased PcvCO2 during CPR probably results from the marked tissue lactic acid production and subsequent shift of the bicarbonate buffer into free carbon dioxide.

Analysis of Variance↗
PubMed1985

Ionized calcium during CPR in the canine model.

The purpose of our study was to determine ionized calcium levels during cardiopulmonary resuscitation (CPR). Following placement of ascending aortic catheters in 15 adult mongrel dogs, ventricular fibrillation was induced electrically. After five minutes without therapy, mechanical external CPR was instituted. Animals received either standard CPR (S-CPR, n = 8) or simultaneous compression and ventilation CPR (SCV-CPR, n = 7) for 30 minutes. Ionized calcium levels were obtained prior to fibrillation and every five minutes during CPR. Mean ionized calcium levels during CPR (1.27 +/- 0.06 mmol/L) did not differ significantly from prearrest levels (1.27 +/- 0.07 mmol/L) at any point during CPR. This was true when the dogs were analyzed together (P = 0.1293) and when the animals receiving S-CPR (P = 0.4465) and SCV-CPR (P = 0.5470) were analyzed by groups. Defibrillation was attempted in all animals and resulted in electromechanical dissociation in three. None of these dogs was hypocalcemic either prior to arrest or during CPR, and none developed an effective rhythm with the administration of calcium. Furthermore, three of the four animals receiving calcium developed markedly elevated ionized calcium levels. Hypocalcemia apparently does not occur during CPR. The beneficial effect of calcium in reported cases cannot be explained routinely by correction of hypocalcemia. Further studies are needed to define the role of calcium administration, if any, in CPR.

Animals↗
PubMed1985

Changes in pulsatile LH secretion after ovariectomy in Ile-de-France ewes in two seasons.

Two experiments were conducted in Ile-de-France ewes to study changes in pulsatile LH secretion in ewes ovariectomized during anoestrus or during the midluteal phase of the oestrous cycle. In Exp. 1, blood samples were taken every 20 min for 12 h the day before ovariectomy (Day 0). After ovariectomy, samples were taken every 10 min for 6 h (10 ewes per group), on Days 1, 3, 7 and 15. In Exp. 2 samples were taken every 10 min for 6 h (10 ewes per group) on Days 7, 15, 30, 60, 90, 120, 150 and 180 after ovariectomy. Further samples were taken (5 ewes per group) at 9 and 12 months after ovariectomy. There were significant interactions between season and day of sampling for the interval between LH pulses in both experiments. LH pulse frequency increased within 1 day of ovariectomy and the increase was more rapid during the breeding season. There were clear seasonal differences in pulse frequency in Exp. 2. Compared with ewes ovariectomized in anoestrus, pulse frequency was significantly higher for ewes ovariectomized in the breeding season, from Day 7 until Day 120. Once pulse frequency had increased in ewes about the time of the normal breeding season, pulse frequency remained high and subsequent seasonal changes were greatly reduced. Pulse amplitude increased immediately after ovariectomy to reach a maximum on Day 7 and there were no differences between season of ovariectomy in the initial changes in amplitude. In Exp. 2, changes in amplitude followed changes in pulse interval and there was a significant interaction between season and day of sampling. There were no significant effects of season on nadir LH concentrations which increased throughout the duration of the experiments. These results show that, in ovariectomized ewes, LH pulse frequency observed on a given day depends on time after ovariectomy, season at the time of sampling and on previous exposure of ewes to stimulatory effects of season. The direct effects of season on LH pulse frequency and seasonal changes in sensitivity to steroid feedback may contribute to control of the breeding season and their relative contributions to the beginning and end of the breeding season may differ.

Animals↗
PubMed1985

Gonadotrophin release in ovariectomized ewes fed different amounts of coumestrol.

Three experiments were conducted to study changes in pulsatile secretion of LH and FSH during the breeding season or anoestrus in ovariectomized Ile-de-France ewes fed different amounts of the phyto-oestrogen coumestrol. In Exp. 1, conducted during the breeding season, ewes (3-4 per group) were fed lucerne supplying 4, 18 or 30 mg coumestrol per ewe per day for 15 days. Experiments 2 and 3 were conducted during seasonal anoestrus. In Exp. 2, ewes (4 per group) were fed lucerne supplying coumestrol concentrations ranging from 4 to 38 mg/ewe/day for 15 days. In Exp. 3, ewes (10 per group) were fed lucerne supplying 14 or 125 mg coumestrol/ewe/day for 15 days. During the breeding season, an increased concentration of coumestrol in the diet significantly decreased the amplitude of LH pulses. There were no effects on LH pulse frequency or on FSH concentrations. During seasonal anoestrus, there were no significant effects on LH pulse frequency, or amplitude and no significant effect on FSH concentration. These results show that high concentrations of coumestrol in lucerne diets would not explain seasonal variation in LH pulse frequency in ovariectomized ewes. However, lucerne diets with increased coumestrol concentrations can influence LH release during the breeding season.

Anestrus↗
PubMed1985

Corpora lutea with a short life-span induced by rams in seasonally anovulatory ewes are prevented by progesterone delaying the preovulatory surge of LH.

Seasonally anovulatory Merino ewes isolated from rams were allocated to three treatments before the re-introduction of rams. Ten ewes received a single injection of progesterone (20 mg), 18 ewes received the injection of progesterone but had the ram-induced preovulatory surge of LH replaced by a series of injections of GnRH 24 h after the introduction of the rams, and 20 control ewes had no hormone treatment. Of the 48 ewes, 44 ovulated within 5 days of the introduction of rams and the treatments had no significant effect on the incidence of ovulation. The frequency of corpora lutea with a short life span (the interval between successive preovulatory surges of LH being 5.1 +/- 0.9 days) was 72% for control ewes and 58% for ewes treated with progesterone and GnRH, but such CL were prevented completely after the injection of progesterone alone (P less than 0.001). The injection of progesterone also delayed the preovulatory surge of LH (P less than 0.001). These results suggest that progesterone assures normality of corpora lutea by lengthening the period of gonadotrophin priming of follicles before ovulation.

Animals↗
PubMed1985

Diurnal variation in the response of anoestrous ewes to the ram effect.

The re-introduction of rams after a period of separation was used to stimulate LH secretion and induce ovulation in seasonally anovulatory ewes maintained under natural photoperiod. In 2 experiments, the rams were introduced in the morning or the evening to test for diurnal variations in responsiveness to the treatment. In the first experiment, with Romanov ewes, the ram-induced increase in tonic LH secretion was significantly earlier in the ewes treated (N = 6) at 07:30 h (mean +/- s.e.m. delay to first pulse: 20 +/- 6 min) than in those (N = 5) treated at 19:30 h (66 +/- 15 min; P = 0.006). The pulse interval after the ram effect was significantly shorter in ewes that subsequently ovulated (120 +/- 10 min) than in ewes that did not ovulate (288 +/- 108 min; P = 0.043). There was a significant decline in pulse amplitude from 6.7 +/- 1.2 to 3.4 +/- 0.6 ng/ml (both groups combined) after the introduction of rams (P = 0.040). Of the 11 ewes, 7 subsequently ovulated and a preovulatory LH surge was observed in 6 of these 30-36 h after ram introduction. In the second experiment, with seasonally anoestrous Préalpes-du-Sud ewes, the effect of the timing of the introduction of rams on the periovulatory events was tested. The delay to the onsets of oestrus and the LH surge was not affected, but the ovulation rate was higher after ram introduction in the morning (1.42) than in the evening (1.14). In the 12-h period before the introduction of the rams in the first experiment, there was a difference between the groups in the secretion of LH, but the existence of diurnal rhythms in the concentrations of LH or FSH were not confirmed in a later study in which 7 ewes were sampled every 20 min for 36 h. In contrast, there was a distinct diurnal variation in the secretion of prolactin, with the highest values being recorded at night and the lowest around midday (P = 0.025). The rise and fall in prolactin values did not appear to coincide with dawn or dusk.(ABSTRACT TRUNCATED AT 400 WORDS)

Anestrus↗
PubMed1984

Onset of the preovulatory LH surge and of oestrus in intact ewes: Night is a preferred period.

Oestrous cycles were induced in seasonally anoestrous ewes by introducing rams into the flock and giving to the ewes one intramuscular injection of 20 mg progesterone. At the second ovulation the onset of oestrus and the preovulatory surge of luteinizing hormone (LH) were recorded. It was found that the LH surge began in significantly more ewes during the night (79%) than during the day (21%). The onset of oestrus tended to follow a similar pattern. This temporal pattern was not related to the time of ram introduction, but may be the result of daily rhythms in ovarian activity. Furthermore, a preferred period for the LH surge indicates a preferred period for ovulation and this may be important in deciding when to begin artificial insemination.

Journal Article↗
PubMed1984

Use of calcium blockers in electromechanical dissociation.

Calcium antagonists have been shown to protect the myocardium against the deleterious effects of ischemia and reperfusion in both focal and global models. The mechanism of this protection is probably related to their ability to decrease the rapid and massive cytosolic and mitochondrial calcium overloading that occurs with reperfusion of severely ischemic myocardium. This calcium overloading uncouples oxidative phosphorylation, preventing repletion of ischemia-depleted ATP stores. The mode of action of calcium antagonists in protecting heart muscle is complex, and may ultimately depend on their ability to preserve sufficient energy to maintain intracellular ionic homeostasis. The cellular events that occur with prolonged cardiac ischemia have been well documented in animal studies, and are reflected in the clinical picture of electromechanical dissociation (EMD). ATP production is decreased during ischemia and quickly results in depleted energy stores. The electrical and mechanical activities of the heart are energy-consuming processes that gradually come to a halt in the presence of prolonged ischemia. In excised totally ischemic hearts, electrical activity persists for a time after contractions have ceased, resulting in the clinical picture of EMD. Eventually electrical activity stops as well, causing asystole. Calcium antagonists administered during resuscitation from EMD, as well as other terminal arrhythmias, may protect the myocardium from reperfusion injury and preserve the ATP stores necessary for normal cardiac function.

Arrhythmias, Cardiac↗
PubMed1984

Verapamil in the treatment of asystolic and pulseless idioventricular rhythm cardiopulmonary arrests: a preliminary report.

A randomized, double-blinded study was conducted to evaluate the effectiveness of the calcium antagonist verapamil in patients in cardiopulmonary arrest with asystole or pulseless idioventricular rhythm (PIVR). Twenty-one such patients presenting to the emergency department received either verapamil (10 mg) or normal saline placebo in an intravenous bolus as initial therapy. They were then treated according to standard American Heart Association guidelines with the exception that calcium was not used. If these rhythms persisted after ten minutes, a second bolus of verapamil or saline was given. Resuscitation was successful in two of ten patients (20%) receiving verapamil and in one of 11 patients (9%) receiving placebo. This similar outcome (P = .462) in this small series suggests that verapamil may not add to successful resuscitation in these patients. Additional studies are needed to define the role of calcium and its antagonists in the treatment of asystole and PIVR.

Aged↗