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M J Spellman

Publications and source records attributed to M J Spellman.

11 recordsLinked to original sources
PubMed2000

MR virtual colonography using hyperpolarized (3)He as an endoluminal contrast agent: demonstration of feasibility.

Hyperpolarized gas MR virtual colonography was performed in plastic phantoms and in the dog colon. (3)He was laser polarized in a prototype commercial system. 2D and 3D gradient echo sequences were used to image the noble gas-filled structures. The hyperpolarized (3)He within the plastic tube and colon lumen produced high signal, providing excellent contrast from the surrounding structures. The virtual colonoscopic analysis of the canine dataset allowed visualization of the colonic features and the colonic wall from inside the colon. (3)He colonoscopy is a novel technique to visualize the colon with MRI with the application of an inert gaseous endoluminal contrast agent.

Animals↗
PubMed1992

Augmented hypoxic ventilatory response in men at altitude.

To test the hypothesis that the hypoxic ventilatory response (HVR) of an individual is a constant unaffected by acclimatization, isocapnic 5-min step HVR, as delta VI/delta SaO2 (l.min-1.%-1, where VI is inspired ventilation and SaO2 is arterial O2 saturation), was tested in six normal males at sea level (SL), after 1-5 days at 3,810-m altitude (AL1-3), and three times over 1 wk after altitude exposure (PAL1-3). Equal medullary central ventilatory drive was sought at both altitudes by testing HVR after greater than 15 min of hyperoxia to eliminate possible ambient hypoxic ventilatory depression (HVD), choosing for isocapnia a P'CO2 (end tidal) elevated sufficiently to drive hyperoxic VI to 140 ml.kg-1.min-1. Mean P'CO2 was 45.4 +/- 1.7 Torr at SL and 33.3 +/- 1.8 Torr on AL3, compared with the respective resting control end-tidal PCO2 of 42.3 +/- 2.0 and 30.8 +/- 2.6 Torr. SL HVR of 0.91 +/- 0.38 was unchanged on AL1 (30 +/- 18 h) at 1.04 +/- 0.37 but rose (P less than 0.05) to 1.27 +/- 0.57 on AL2 (3.2 +/- 0.8 days) and 1.46 +/- 0.59 on AL3 (4.8 +/- 0.4 days) and remained high on PAL1 at 1.44 +/- 0.54 and PAL2 at 1.37 +/- 0.78 but not on PAL3 (days 4-7). HVR was independent of test SaO2 (range 60-90%). Hyperoxic HCVR (CO2 response) was increased on AL3 and PAL1. Arterial pH at congruent to 65% SaO2 was 7.378 +/- 0.019 at SL, 7.44 +/- 0.018 on AL2, and 7.412 +/- 0.023 on AL3.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗
PubMed1992

Topography of cat medullary ventral surface hypoxic acidification.

The topographic relationship between previously identified medullary ventral surface respiratory chemosensitive regions and brain surface extracellular fluid (ECF) acid production during acute hypoxia was explored in anesthetized, paralyzed, and artificially ventilated cats. Glass pH electrodes (0.8-mm diam, sheathed in stainless steel tubing) were mounted in mechanical contact with surfaces of medullary surface or adjacent pyramids, pons, spinal cord, or parietal cortex. Isocapnic hypoxia of 5 min [at arterial O2 saturation (SaO2) = 48 +/- 10%] reduced pH over rostral (Mitchell) and caudal (Loeschcke) areas by 0.12 +/- 0.09 and 0.07 +/- 0.04, respectively (n = 10, P < 0.05). Change in pH (delta pH) was proportional to desaturation with slopes 100 delta pH/delta SaO2 of 0.45 (rostral) and 0.20 (caudal) (R = 0.91 and 0.88, respectively). pH drop usually began within 3 min of hypoxia, became stable between 5 and 15 min, began to rise within 2 min of reoxygenation, and returned to control within 10 min. During equally hypoxic tests, intermediate area (Schläfke), pons, and spinal cord surfaces showed no significant acid shift. Parietal cortex ECF pH dropped more slowly but steadily by 0.079 +/- 0.034 during 20 min at SaO2 = 50% after a small but significant initial alkaline shift, and acidification of cortical surface continued for > 5 min after reoxygenation. We conclude that medullary ventral chemosensitive regions produce more lactic acid during hypoxia than neighboring brain surfaces.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Anomalous hypoxic acidification of medullary ventral surface.

In castrated male goats, two flexible catheters, one open ended for reference and the other ending in a 1-mm-diam glass bulb pH electrode, were advanced ventrally through a left posterior fossa craniotomy into the subarachnoid space between the 9th and 10th cranial nerve roots, passing medially into cerebrospinal fluid (CSF) over the medullary ventral surface (MVS). They were anchored to dura and fascia, tunneled under the scalp, and terminated in connectors on the left horn. After several days for recovery, while the animals were awake, the effects of CO2 and hypoxia on pH of the film of CSF between the pia and arachnoid (pHMVS) were recorded along with end-tidal PCO2 and PO2 (mass spectrometer), ventilation (pneumotachometer) through a permanent tracheostomy, and, when possible, ear arterial O2 saturation (SaO2). High PCO2 acidified MVS as expected: delta pH MVS/delta log PCO2. = -0.64 +/- 0.14, producing a ventilatory response slope delta VI/delta pHMVS = 372 l/min. Hypoxia resulted in acid shifts even when PCO2 was allowed to fall. The development of hypoxic acidosis was related to the location of pH electrodes determined at necropsy. In isocapnic hypoxia, pH over putative chemoreceptor surfaces fell in proportion to desaturation: delta pHMVS = 0.0033(SaO2)-0.34, r = 0.80, Sy.x = 0.025. With uncontrolled arterial PCO2, similar acidosis occurred when SaO2 fell below 85-90%: delta pHMVS = 0.0039(SaO2)-0.34, r = 0.88, Sy.x = 0.032. With constant hypoxia, pH fell (tau = 3.7 +/- 2.2 min) to a plateau after 10-20 min and showed rapid recovery (tau = 2.0 +/- 1.3 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1990

Pharmacokinetics and pharmacodynamics of atracurium in the elderly.

To evaluate the effect of aging on the distribution, clearance, and neuromuscular junction sensitivity to atracurium, the authors determined the pharmacokinetics and pharmacodynamics of atracurium in five healthy elderly subjects (74-76 yr) during halothane-nitrous oxide anesthesia and compared these values to those obtained previously in five healthy young adults (22-44 yr). A brief (6.0-13.0 min) infusion of atracurium was administered until twitch tension was suppressed by approximately 70%, and atracurium plasma concentration and twitch tension data were used to determine pharmacokinetic and pharmacodynamic parameters for each patient. Total clearance (Cltotal) was similar in elderly and young adults. However, clearance via the liver and/or kidney (Clorgan) was lower in elderly patients, whereas clearance due to Hofmann elimination and ester hydrolysis (Clnonorgan) was higher. Volume of distribution at steady state (Vss) was larger in elderly patients. The increase in Vss without an age-related increase in Cltotal resulted in a longer elimination half-life [21.8 (+)/- 3.3 vs. 15.7 (+)/- 2.5 min (mean (+)/- SD)] in elderly patients. The steady state plasma concentration of atracurium required to suppress twitch tension by 50% was similar in elderly and young adults. The authors conclude that the pharmacokinetics, but not the pharmacodynamics, of atracurium differ significantly between elderly and young adults. As a result, repeated doses will be required with similar frequency in young and elderly adults, but recovery from comparable levels of neuromuscular blockade may be slightly prolonged in elderly patients.

Adult↗
PubMed1990

Pharmacokinetics and pharmacodynamics of atracurium in infants and children.

To determine whether maturational changes in body composition and organ function affect distribution and elimination of and sensitivity to atracurium, the authors determined the pharmacokinetics and pharmacodynamics of atracurium in six infants and five children and compared these results with those obtained in five adults. Atracurium, 15.8 +/- 1.7 micrograms.kg-1.min-1, was infused iv for 6-11 min to subjects anesthetized with nitrous oxide (60%) and halothane (0.9 MAC, age-adjusted) and twitch tension of the adductor pollicis muscle was measured. Plasma samples were obtained for 120 min; concentrations of atracurium were determined using a liquid chromatographic assay. A two-compartment pharmacokinetic model, adapted to account for elimination of atracurium from both central and peripheral compartments, was fit to the plasma concentration data; an effect-compartment model was fit to the twitch tension data. Volume of distribution at steady state (210 +/- 118, 129 +/- 44, and 100 +/- 22 ml/kg for infants, children, and adults, respectively) and total clearance (7.9 +/- 2.0, 6.8 +/- 1.6, and 5.3 +/- 0.9 ml.kg-1.min-1 for the three groups) decreased with increasing age. Neither elimination half-life (20.0 +/- 5.1, 17.2 +/- 5.1, and 15.7 +/- 2.5 min for the three groups) nor the steady state plasma concentration that resulted in 50% neuromuscular blockade (363 +/- 118, 444 +/- 121, and 436 +/- 122 ng/ml for the three groups) varied with age. The authors conclude that these results are consistent with and explain the previously reported findings that recovery from the neuromuscular effects of atracurium is minimally affected by age.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Pulse oximeter failure thresholds in hypotension and vasoconstriction.

The degree of systolic hypotension causing failure and recovery were tested simultaneously with three oximeters (CSI 504US, Nellcor N-200, and Ohmeda 3740) in nine normal male volunteers. Perfusion of the right hand was slowly reduced and restored by 1) elevation of the hand plus systemic hypotension with nitroprusside if needed (EL); 2) clamp compression of the brachial artery (CL); 3) brachial cuff inflation (CU); and 4) intraarterial norepinephrine (NE). With EL, pulse pressure was normal whereas right radial arterial systolic pressure (SP) was 25.3 +/- 12.4 mmHg at failure and 34.1 +/- 13.3 at recovery (mean of three oximeters, n = 189). With CL, pulse pressure fell more than did mean pressure, and failure occurred at 37.3 +/- 9.8 and recovery at 46.8 +/- 17.6 mmHg, n = 84. With CL, threshold of function, defined as the average of failure SP and recovery SP, was 47.1 +/- 13.5, n = 41 for Nellcor, higher than for either CSI (38.7 +/- 14.5, n = 17) or Ohmeda (36.0 +/- 3.4, n = 26) (P less than 0.05). With EL, no difference among instruments was found (mean 29.7 +/- 12.8, n = 189). Threshold was 58.2 +/- 8.4, n = 17 with CU if cuff inflation was slow (filling veins), but recovery was similar to EL after rapid cuff occlusion. With NE, SP threshold was increased to 58.3 +/- 21.0 with CL but only to 41.0 +/- 13.8 with EL.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Fentanyl-induced ventilatory depression: effects of age.

To determine whether infants are more sensitive than older patients to the ventilatory-depressant effects of fentanyl, patients were anesthetized with fentanyl and nitrous oxide (N2O) and ventilatory depression was assessed following elimination of N2O and in the immediate postoperative period. Three groups of patients were studied: infants (1-12 mo old, n = 14), children (1-5 yr old, n = 14), and adults (23-38 yr old, n = 13). Skin-surface PCO2 was measured to determine the peak PCO2 occurring at the end of anesthesia when end-tidal N2O concentration was less than 6%. Naloxone was administered if PCO2 exceeded 70 mmHg. During recovery from anesthesia, ventilatory pattern was recorded using impedance pneumography to determine the longest breath-to-breath interval and the number of episodes of central apnea (defined as breath-to-breath intervals greater than or equal to 10 s in infants and children and greater than or equal to 20 s in adults). Elevation of PCO2 correlated with increasing plasma fentanyl concentrations but did not differ between groups. Four patients (two infants, one child, and one adult) required naloxone. The only subject who had a low plasma fentanyl concentration but required naloxone was a 6-wk-old infant; this was the only subject younger than 3 mo. For each range of fentanyl concentrations, the incidence of apnea increased with age, as did the number of episodes of apnea per subject. Fentanyl-induced ventilatory depression, as assessed by elevation of resting PCO2 during emergence from anesthesia and disruption of ventilatory pattern during recovery from anesthesia, is not greater in infants older than 3 mo than in children and adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Pharmacokinetics of fentanyl in neonatal humans and lambs: effects of age.

To determine whether the clearance of fentanyl in neonates varies with age, the authors determined the pharmacokinetics of fentanyl in 14 humans ages 1-71 days and 15 lambs ages 3-37 days. In humans, fentanyl, 54.1 +/- 2.3 (mean +/- SD) micrograms/kg, was administered as a 2-min iv infusion; in lambs, fentanyl, 50 micrograms/kg, was administered as an iv bolus. Ventilation was controlled to maintain end-tidal or arterial PCO2 normal, and potent inhaled anesthetics were not administered; in humans, additional anesthesia was provided with iv morphine. Arterial or venous samples were obtained for 12 h, and plasma concentrations of fentanyl were determined by radioimmunoassay. Plasma concentration versus time data were fitted to two- and three-compartment pharmacokinetic models, and clearance, volume of distribution at steady-state (Vdss), and elimination half-life were determined. Clearance increased with age in both humans and lambs. Two humans who had intraabdominal surgery had no clearance of fentanyl: plasma concentrations of fentanyl remained constant for approximately 10 h after an initial distribution phase. In lambs, but not in humans, Vdss increased with age; elimination half-life did not change with age in either lambs or humans. The authors conclude that at least two factors--postnatal age and the type of surgery--affect fentanyl clearance during the neonatal period. The effect of other factors, such as inhaled anesthetics, remains to be determined.

Aging↗
PubMedDate not supplied

CT findings following the cabrol composite graft procedure.

PURPOSE: Insertion of a composite graft and reimplantation of the coronary arteries through an intermediate Dacron tube (Cabrol composite graft procedure) has been used to treat ascending aortic aneurysms and dissections. The CT findings after the Cabrol composite graft procedure have not been previously described. METHOD: Retrospective review of 12 postoperative CT and CT angiography (CTA) studies both in the immediate postoperative period as well as during long-term follow-up was conducted. RESULTS: The Cabrol composite graft procedure produces typical CT findings consisting of a coronary conduit separate from the aortic graft. The presence of perigraft flow can be normal or abnormal depending on the time point of its occurrence and the extent of its hemodynamic consequences. CONCLUSION: Knowledge of the typical CT and CTA findings following a Cabrol composite graft procedure is essential for the correct interpretation of these studies.

Adult↗