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Biomedical subjects

B K Ross

Publications and source records attributed to B K Ross.

14 recordsLinked to original sources
PubMed1991

Fetal heart rate variability and cerebral oxygen consumption in fetal sheep during asphyxia.

This study was designed to examine the relationship between fetal heart rate variability and fetal cerebral oxygen uptake. Fetal sheep were chronically prepared with catheters and electrodes to determine cerebral blood flow (microsphere method), cerebral arteriovenous oxygen difference, and the electrocardiogram. An adjustable occluder was placed on the maternal common internal iliac artery to induce fetal asphyxia by reducing uterine blood flow. Fetal heart rate variability tended to decrease in the first 11 min of asphyxia, when cerebral oxygen consumption was approximately 53% of control. Despite stable cerebral oxygen consumption and worsening metabolic acidosis, however, fetal heart rate variability progressively returned towards normal by 36 min. There was no relationship between the depression of FHR variability and the degree of reduction of cerebral oxygen consumption. Nor was there any relationship between an alteration in regional cerebral blood flow or myocardial blood flow and the return of FHR variability with increasing duration of asphyxia. We conclude that there is an association between loss of fetal heart rate variability and reduced cerebral oxygen consumption, but the reduced variability does not persist with time at this degree of reduced cerebral metabolism in fetal sheep. This appears to be at variance with human clinical experience. Among the explanations for this may be insufficiently severe asphyxia, a species difference, removal of an inhibitor to FHR variability, or progressive use of other substrates for metabolism.

Animals↗
PubMed1983

Regional blood flow during cardiopulmonary resuscitation in dogs using simultaneous and nonsimultaneous compression and ventilation.

We studied regional blood flow (QR) using radiolabeled microspheres and measured hemodynamic variables in 20 anesthetized dogs in normal sinus rhythm and during ventricular fibrillation treated with cardiopulmonary resuscitation (CPR). Nonsimultaneous compression and ventilation CPR (NSCV-CPR) was performed in seven dogs with a pneumatic piston that gave 50 chest compressions/min with an open airway with 10 ventilations at an airway pressure of 33 mm Hg interposed between each fifth and sixth compression. Simultaneous compression and ventilation (SCV-CPR) was performed in seven dogs with the piston and in six other dogs with a circumferential pneumatic vest. Both devices gave 30 compressions/min simultaneously with 30 ventilations that elevated airway pressure to 80 mm Hg., The abdomen was bound during SCV-CPR. Regional blood flow (mean +/- SD) to the cerebral hemispheres, cardiac ventricles, and kidneys, expressed as ml/min/100 g tissue, was 3.1 +/- 4.0, 3.4 +/- 3.3 and 1.5 +/- 1.5, respectively, during NSCV-CPR; 11.5 +/- 5.9, 4.9 +/- 4.7 and 2.7 +/- 2.7 during SCV-CPR (vest); and 16.2 +/- 7.2, 11.0 +/- 4.0 and 20.1 +/- 20.2 during SCV-CPR (piston) (all p less than 0.05 compared with NSCV-CPR). These results indicate that QR to all organs studied is reduced below normal sinus rhythm levels during CPR for ventricular fibrillation, QR to the brain is proportionately greater than QR to the heart and kidneys, and QR to the brain is greater with both forms of SCV-CPR than with NSCV-CPR.

Animals↗
PubMed1981

Increased hemoglobin-oxygen affinity does not decrease skeletal muscle oxygen consumption.

The importance of hemoglobin-oxygen affinity (HOA) in affecting skeletal muscle oxygen consumption (VO2) was reevaluated using an isolated canine gracilis muscle. HOA of the blood [normal O2 half-saturation pressure of hemoglobin (P50) = 30 Torr] was increased by refrigerated storage (P50 = 22 Torr), incubation in sodium metabisulfite (P50 = 24 Torr), or in sodium cyanate (P50 = 14 Torr). Stored blood caused a significant fall in VO2 to 80% of control, with no change in venous O2 partial pressure (PvO2), substantiating previous studies. However, in contrast, blood incubated in sodium metabisulfite or sodium cyanate resulted in no impairment of VO2, with a fall in PvO2 in the latter case indicating that a critical PvO2 did not cause the reduction in VO2 with stored blood. To substantiate further the lack of existence of a critical PO2, fresh and increased HOA blood was perfused at constant flow rates and varying arterial oxygen saturations. Stored blood showed a marked reduction in VO2 as compared with normal blood over a wide range of saturations. However, carbamylated blood VO2 was identical to fresh blood VO2 values. The data suggest that the position of the oxygen dissociation curve may not be as important as originally thought in determining skeletal muscle oxygen delivery. The drop in VO2 caused by perfusion with stored blood is due to some other factor unrelated to HOA.

2,3-Diphosphoglycerate↗
PubMed1980

New developments in cardiopulmonary resuscitation.

The traditional concept of cardiopulmonary resuscitation (CPR) is that the heart is squeezed between the sternum and the spine during external cardiac massage to create a pressure gradient that forces blood from the heart to the periphery. Although the heart may actually be squeezed in some persons by this maneuver, a newer view of CPR holds that closed-chest compression produces a generalized rise in intrathoracic pressure that is applied to the pulmonary vascular bed as well as the heart. Thus, the heart does not serve primarily as a pump during external cardiac massage but instead acts as a conduit for blood from the lungs. Furthermore, flow into extrathoracic vessels depends on their tendency to remain open or to collapse: forward flow occurs across the head during CPR because a pressure gradient is developed between the carotid artery and the more compressible jugular vein. These ideas have potential clinical implications and greatly increase our understanding of the physiology of CPR.

Coronary Circulation↗
PubMed1979

Gas exchange abnormalities produced by venous gas emboli.

Bubbles of either He, N2 or SF6 were infused intravenously into anesthetized dogs at a rate of 0.2 ml/kg/min. Alterations in pulmonary gas exchange were quantitated by the invert gas elimination method during control, steady state infusion and resolution phases. The hypoxemia produced was predominantly due to regions of low VA/Q rather than pure shunt, and the increase in physiological dead space was due to the addition of high VA/Q regions rather than 'pure' dead space. The VA/Q distribution returned to normal within 30 minutes of stopping the He or N2 bubbles, but remained abnormal for longer periods with SF6 bubbles. The net elimination of insoluble gases (such as He or N2) was only slightly impaired by bubble emboli, provided the cardiac output remained constant. Early pulmonary edema from bubble embolization was documented by increased wet weight/dry weight ratio, but the increased lung water was not apparent on histological examination. This form of pulmonary embolus is unique in that there is a constant fraction of the vasculature blocked although any given region with embolus is undergoing continuous resportion of the bubble. This produced a partial obstruction of the affected gas exchange units which manifests as regions of high VA/Q rather than pure dead space.

Animals↗
PubMed1979

Comparison of cardiovascular reflexes of the newborn and adult opossum.

Neural control of the cardiovascular system was compared in the newborn and adult opossum by measuring changes in blood pressure and heart rate following carotid arterial occlusion and vagal stimulation. The percent change in blood pressure of the newborn was not significantly different from that of the adult following these procedures. This would indicate that even though the newborn opossum is incompletely developed for some time after birth, its neural development was adequate for control of the cardiovascular system.

Age Factors↗
PubMed1976

Scanning electron microscopy of normoxic and hyperoxic hyperbaric exposed lungs.

Lungs from adult guinea pigs exposed to 1 ATA He-O2 with 200 mm Hg PO2 and 20 ATA He-O2 with 200, 400, and 600 mm Hg PO2 were studied with scanning electron microscopy. The appearance of normal alveoli is described. Even before pulmonary O2 toxicity became symptomatic, subtle changes occurred in the alveoli, such as an increase in macrophages and a marked increase in length of alveolar type-II cell microvilli. These changes occurred in animals exposed to 400 mm Hg PO2, heretofore considered below toxic levels. With increased toxic involvement, the number of alveolar type-II cells increased. A thick layer of material appeared in some of the alveoli, obscuring the Kohns pores and type-I and -II cell surfaces. The alveolar-capillary network with underlying erythrocytes was no longer observable. Lungs with the greatest toxic involvement possessed large numbers of macrophages encompassed by a fibrin-like matrix. The alveolar walls were broken down in many instances, and the alveoli were no longer discrete units but took on the appearance of an amorphous mass of lung tissue.

Animals↗
PubMedDate not supplied

Lack of ozone effects on oxygen hemoglobin affinity.

Ozone exposure has been shown to cause erythrocyte damage and thus may be affecting oxygen delivery by the red cell. Oxyhemoglobin affinity, heme-oxygen binding site interaction (Hill coefficient), and red cell 2,3-diphosphoglycerate concentrations were measured in a total of twenty-two New Zealand white rabbits exposed to ozone. Ozone exposures of 1 and 3 ppm for 4 hr in rabbits had no significant (P greater than .05) effect, immediate or delayed, on the parameters measured.

Animals↗
PubMedDate not supplied

Local anesthetic distribution in a spinal model: a possible mechanism of neurologic injury after continuous spinal anesthesia.

BACKGROUND AND OBJECTIVES: Cauda equina syndrome has been reported recently in patients receiving continuous spinal anesthesia using newly developed microcatheters (28 gauge). Failure of microcatheters to allow adequate mixing of local anesthetic was studied as a possible mechanism of the neurologic injury reported with these catheters. METHODS: A spinal canal model was developed and the distribution of hyperbaric lidocaine was measured after injection through catheters typically used for continuous spinal anesthesia (i.e., 20, 28, and 32 gauge). RESULTS: Lidocaine distribution was less uniform and lidocaine concentration and osmolarity in the dependent portions of the model were significantly higher after injection through microcatheters compared to the 20-gauge catheter. CONCLUSIONS: Dependent drug concentrations were greater than those reported in the literature, capable of producing permanent neurologic injury. Directing the catheter tip in the nondependent direction and injecting lidocaine rapidly or through catheters with multiple end holes improved mixing and decreased dependent drug concentration.

Anesthesia, Spinal↗
PubMedDate not supplied

Sprotte needle for obstetric anesthesia: decreased incidence of post dural puncture headache.

BACKGROUND AND OBJECTIVES: Reports have emphasized the importance of spinal needle tip configuration in the development of post dural puncture headache (PDPH). METHODS: Charts from 366 consecutive obstetric patients receiving spinal anesthesia for labor, cesarean delivery, postpartum surgical procedures, or postpartum tubal ligations were reviewed retrospectively for evidence of PDPH in the five days after dural puncture. Spinal anesthesia was administered to these patients using 25-gauge Quincke (n = 74), 26-gauge Quincke (n = 160), or 24-gauge Sprotte (n = 132) spinal needles. RESULTS: The groups were well matched demographically. The incidence of PDPH in the three groups was 9%, 8%, and 1.5%, respectively. Half of the patients developing PDPH in each group were treated with an epidural blood patch. CONCLUSIONS: Our data indicate that the Sprotte spinal needle, with its non-cutting tip, results in a significantly lower (p less than 0.05) incidence of PDPH than Quincke cutting-tip needles of smaller gauge.

Anesthesia, Obstetrical↗
PubMedDate not supplied

A comparison of postcesarean epidural morphine analgesia by single injection and by continuous infusion.

To assess the relative efficacy and incidence of side effects of a single injection versus a continuous infusion of epidural morphine sulfate (MS) in the postcesarean population, the authors report a prospective, randomized, double-blind study. Thirty-one patients received either a 5-mg MS bolus and subsequent saline infusion (n = 13) or a 2.6-mg MS bolus and subsequent MS infusion at 0.1 mg/hour (n = 18), such that after 24 hours both groups had received a total MS dose of 5 mg. No statistically significant differences were found between the two groups in overall satisfaction with analgesia, verbal pain scores, level of activity, need for supplemental opioids, or incidence of sedation during the 24-hour study period. The authors conclude that in this population, continuous epidural morphine infusion offers no obvious advantage over single morphine bolus therapy. However, the theoretical merits of continuous opioid infusion therapy are discussed.

Analgesia, Epidural↗