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Biomedical subjects

G M Davis

Publications and source records attributed to G M Davis.

At least 73 records · Page 4Linked to original sources
PubMed1996

Does laparoscopy adversely affect gas exchange and pulmonary mechanics in the newborn? An experimental study.

Notwithstanding the clinical acceptability of pediatric laparoscopy, the physiological consequences of carbon dioxide (CO(2)) peritoneal insufflation on lung mechanics and gas exchange are not established. This study seeks to establish the affects of increased intraabdominal pressure (P ABD) from CO(2) insufflation on lung mechanics, the compliance of the respiratory system (CRS stat), and gas exchange. Ten anesthetized tracheostomized, and paralyzed rabbits (2.5-3.1 kg) were examined. Mechanical ventilation was established to produce normal ventilation (PaCO(2) 35-45 Torr). Continuous pulse, blood pressure (BP), and serial arterial blood gas measurements were obtained by femoral arteriotomy. The animals were examined at baseline conditions (P ABD = 0 mm Hg), at 2 levels of external compression (P ABD = 6 and 12 mm Hg, respectively), and at two levels of intraperitoneal CO(2) insufflation (P ABD=6 and 12 mm Hg, respectively). Increased P ABD, whether applied externally or by intraperitoneal insufflation, did not alter the CRS stat (ANOVA p = 0.557), nor systematically change the pH, PaCO(2) or PaO(2) (ANOVA p = 0.541, p = 0.545, p = 0.446, respectively). Neither BP nor pulse rate showed any change. Under conditions encountered during laparoscopy, P ABD of 0-12 mm Hg did not have a deleterious effect on ventilation and gas exchange in the ventilated and paralyzed small animal.

Animals↗
PubMed1995

Maternal asthma and idiopathic preterm labor.

Previous studies suggest that women with asthma are at increased risk of preterm birth. Moreover, drugs (especially beta-agonists) used to treat asthma are also used to treat preterm labor. The authors carried out a case-control study of 555 women from three hospital centers with idiopathic preterm labor (< 37 weeks), including two overlapping (i.e., non-mutually exclusive) subsamples: cases with early idiopathic preterm labor (< 34 weeks) and cases with idiopathic recurrent preterm labor (< 37 weeks plus a previous history of preterm delivery or second-trimester miscarriage). Controls were matched to cases according to race and smoking history prior to and during pregnancy. All subjects responded in person to questions about atopic, respiratory, obstetric, and sociodemographic histories. Subjects in the early and recurrent preterm labor subsamples were also asked to undergo spirometric testing with methacholine challenge 6-12 weeks after delivery. Cases were significantly more likely to report histories of asthma symptoms and physician-diagnosed asthma (matched odds ratios of 2-3) than controls, particularly those cases with recurrent preterm labor. No significant associations were observed, however, with methacholine responsiveness. These results could not be explained by residual confounding by smoking or other variables, nor by selective recall of asthma symptoms and histories by cases. Women with asthma are at increased risk of idiopathic preterm labor. The fact that no such association was seen with methacholine responsiveness suggests that nonatopic, noncholinergic mechanisms may link bronchial and uterine smooth muscle lability.

Adult↗
PubMed1995

Late pulmonary function following repair of tracheoesophageal fistula or esophageal atresia.

Although tracheoesophageal fistula and esophageal atresia (TEF-EA) are surgically correctable, late respiratory complications have been reported. We administered a respiratory and gastrointestinal symptom questionnaire and performed standard pulmonary function tests (PF T's) and methacholine challenge testing on an unselected group of 25 subjects with TEF-EA who underwent surgery at our institution between 1963 and 1985. Results were compared to predicted normals, as well as 10 sibling controls. While the mean values of lung function test results for the TEF-EA group were within the normal range, they were significantly different from their siblings. Thirteen of the 25 TEF-EA group (52%), but none (0%) of the controls, had abnormal pulmonary function. This was classified as restrictive in 9 (36%), obstructive in 3 (12%), and mixed in 1. In addition, airway hyperreactivity [defined as a positive methacholine challenge (PC20 < or = 8 mg/mL)], was found in 6 of 18 TEF-EA subjects and 4 of the 9 controls who were evaluated. Comparison of TEF-EA subjects with normal and abnormal PFTs showed no difference in the incidence of tracheomalacia, esophageal strictures or dilatation, recurrent pneumonias, or gastroesophageal reflux. The respiratory symptom score in the subjects and controls was similar, and did not correlate with abnormal pulmonary function. The cause of the pulmonary function abnormalities remains unexplained.

Adolescent↗
PubMed1995

Diaphragmatic pacing in children with congenital central alveolar hypoventilation syndrome.

BACKGROUND: The purposes of this study were to study congenital central alveolar hypoventilation syndrome (CCAHS), to report the experience at our institution with this disorder, and to describe the surgical technique of diaphragmatic pacing. Three patients are in our diaphragmatic pacing program. They all have CCAHS, documented by means of lack of respiratory drive to hypercapnia and normal peripheral nerve and muscle studies. Two patients have associated Hirschsprung's disease. METHODS: The ages of patients at insertion of bilateral phrenic nerve pacemakers were 1, 2, and 5 years. A bilateral axillary thoracotomy in the third interspace was used in two patients, and anterior thoracotomy was used in one for insertion of electrodes on the phrenic nerves. Counterincisions in both flanks were used in all patients for insertion of the receivers in subcutaneous pockets. RESULTS: In all patients pacing was commenced within 1 week of the surgical procedure, because no primary pacemaker failures occurred. One patient has experienced no failure of the equipment and no infectious complications at 4 years. A second patient has had the pacemakers for 6 months without complications. The third patient underwent placement of bilateral pacemakers in 1984. In this patient a 10-year experience has resulted in subcutaneous implant failure on two separate occasions; also the presence of a staphylococcal empyema necessitated the temporary removal of one phrenic nerve electrode for 6 months, with successful reinsertion. All patients now receive mechanical assisted ventilation when sleeping and phrenic nerve pacing when awake. CONCLUSIONS: Pediatric surgeons should be aware of CCAHS because it may be treated with surgically implanted electrodes that allow for pacing of the diaphragm. The technique has an acceptable complication rate, and it can greatly decrease the impact of the disease on the lifestyle and activity of the patient. CCAHS also may be associated with Hirschsprung's disease.

Artificial Organs↗
PubMed1995

Reduction mammaplasty: long-term efficacy, morbidity, and patient satisfaction.

This retrospective study was designed to determine if reduction mammaplasty relieved preoperative symptoms in patients with macromastia. Seven-hundred and eighty women who had reduction mammaplasties between 1981 and 1992 were surveyed. Responses to questions concerning the preoperative and postoperative symptoms, breast size, complications, and satisfaction were elicited. Completed surveys were returned by 406 patients (52 percent) who had bilateral operations. The mean age at surgery was 38 years, with an average follow-up of 4.7 years. Preoperative complaints of shoulder grooving (94 percent), shoulder pains (93 percent), and back pains (81 percent) were significantly reduced following surgery (McNemar test, p < 0.0001). Cup size decreased an average of two sizes in 72 percent. There were 215 women (53 percent) with postoperative complications, and although most were minor, 20 (5 percent) required surgical correction. Self-esteem improved in 358 (88 percent), and most would have surgery again (93 percent) and would encourage others to have the same (94 percent). Reduction mammaplasty decreases breast size and significantly relieves preoperative symptoms associated with mammary hypertrophy. Relief of symptoms was the most common reason women gave for having the operation, and 87 percent were satisfied with the results despite frequent minor postoperative complications.

Adult↗
PubMed1994

Changes in lung mechanics following sighs in premature newborns without lung disease.

Sighs, the interspersed breaths of larger tidal volume (VT) than those preceding or following them, occur more frequently in the newborn than in adults. It has been postulated that the sigh augments functional residual volume (FRC), increases lung compliance (CL), and recruits atelectatic alveoli. Since the premature infant has relatively low FRC, we hypothesized that sighs might be more frequent in these babies and that CL could be shown to change before and/or after a sigh. We studied 14 premature infants (gestational age, 30 +/- 2.2 weeks; mean +/- SD) without lung disease during quiet sleep. Minute ventilation (VE) was measured by pneumotachography and pleural pressure changes via a water-filled catheter in the esophagus. In the 78 sighs examined, the incidence was 0.71 sighs/min, similar to previous reports for full-term newborns. There was no change in respiratory frequency, VT, VE, nor mean inspiratory flow (VT/TI, where TI is the inspiratory time) before or after the event. The volume of the sigh increased from 7.8 +/- 0.2 mL/kg to 21.5 +/- 0.5 mL/kg, in concert with an increase in breath duration (TTOT) from 0.98 +/- 0.02 s to 2.56 +/- 0.12 s, resulting in an unchanged VE, VT/TI, and respiratory duty cycle (TI/TTOT). This suggests that the increased VT was matched by a prolongation in both TI and TTOT. Following the sigh, CL increased from 1.43 +/- 0.13 mL/cmH2O/kg to 1.66 +/- 0.27 mL/cmH2O/kg (paired t-test, P < 0.001) whilst the lung resistance RL fell from 62 +/- 8 cmH2O/L/s/kg to 55 +/- 3.8 cmH2O/L/s/kg (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Functional Residual Capacity↗
PubMed1994

Pulmonary impedance as an index of severity and mechanisms of neonatal lung disease.

The measurement of resistive and elastic components of the respiratory system in neonates has been used to define disease severity and the response to therapy. The lung resistance (RL) and dynamic lung compliance (CLdyn) partition the impediment to gas flow into two components, each of which may be altered independently. The concept of lung impedance (ZLdyn) is the combined effect of the elastic and resistive loads presented to the respiratory muscles, which determines the gas flow that will result from the pressures generated by the respiratory muscles. In a first order system where RL and CLdyn are single values (independent of volume or respiratory rate), ZLdyn is the vector sum of the reactive [1/2 pi fb x CLdyn)] and resistive (RL) components at the infant's breathing rate (fb), if the transpulmonary pressure (Ptp) generated by the respiratory muscles during spontaneous respiration can be modeled mathematically by a sinusoidal function. Furthermore, the phase angle (theta) between the impedance and the resistive component will represent the relative magnitude of the resistive and reactive components. The validity of this model can be establishing by comparing the calculated theta to the observed temporal difference (measured theta) between the Ptp and flow derived from the polygraph tracing. This hypothesis was tested in 10 spontaneously breathing neonates with lung disease of differing etiology and severity. No significant difference was found between the measured and calculated theta values (mean difference, 1.2 +/- 3.9 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchopulmonary Dysplasia↗
PubMed1994

Role of adenosine in the hypoxic ventilatory response of the newborn piglet.

The role of intracerebral adenosine levels in the control of ventilatory response to hypoxia was explored in 15 spontaneously breathing intubated piglets, 1-5 days old, sedated with chloral hydrate. Respiration was recorded via by a pneumotachograph. In all animals exposed to hypoxia (12% O2) for 10 minutes. There was an initial increase in ventilation followed by a late decrease (the biphasic ventilatory response). Both intravenous caffeine citrate (20 mg/kg) and an FiCO2 of 0.05 separately abolished or attenuated the late ventilatory depression associated with hypoxia. In the same piglets, the administration of 10 micrograms dipyridamole, a competitive inhibitor of adenosine receptors, directly into the cerebral ventricles abolished the hyperventilatory response to hypoxia. Conversely, the use of 20 micrograms intraventricular 8-phenyltheophylline abolished the late ventilatory depression associated with hypoxia. Neither drug had a direct effect on ventilation at the time of injection. These results suggest that adenosine is a part of the diphasic ventilatory response to hypoxia.

Adenosine↗
PubMed1994

Specificity in social support: perceptions of helpful and unhelpful provider behaviors among irritable bowel syndrome, headache, and cancer patients.

Perceived social support was assessed among 53 patients suffering from non-life-threatening chronic illnesses (i.e., irritable bowel syndrome or recurrent headache). Subjects recalled predominantly helpful support interactions and reported the three major types of social support as equally helpful. In addition, irritable bowel syndrome patients, who experience embarrassing physical symptoms, reported fewer instances of tangible assistance than chronic headache patients. Comparisons to cancer patients studied by Dakof and Taylor (1990) revealed differences in perceived social support as a function of diagnosis. These results offer insight into the needs of patients with noncatastrophic illnesses and suggest that the challenges and tasks confronting these individuals are unique from those encountered by patients with catastrophic diseases.

Adaptation, Psychological↗
PubMed1994

Snail hosts of Paragonimus in Asia and the Americas.

We have undertaken a comprehensive review of snail hosts of Paragonimus world-wide exclusive of Africa based on modern malacological data, where available, and with consideration of the phylogeny of the snail groups involved. This is the first comprehensive review since those made by Chen (1979) and Chen et al. (1983), and there have been considerable taxonomic changes over the past decade. A number of names and concepts found in the medical malacological and parasitological literature up to the present time require revision or correction. There are vast radiations of snails of the superfamilies Cerithiacea and Rissoacea involved in the transmission of Paragonimus in China. We list 54 species world-wide of which 35(65%) occur in China. Revisions and corrections pertaining to China include: (i) The family Hydrobiidae does not occur in China or S.E. Asia, and the Pomatiopsidae should be used. (ii) The genus Bythinella is entirely European (Hydrobiidae: Amnicolinae). The so-called Bythinella of China belongs to the genus Erhaia (Pomatiopsidae). (iii) The generic name Pseudobythinella described from China is preoccupied, a junior synonym of Pseudobythinella Melville 1956, a fossil from England. All Chinese Pseudobythinella are now classified as Erhaia. (iv) Akiyoshia has been used as a generic name for some snails in Hunan transmitting Paragonimus. Akiyoshia is from Japan and biological/ecological data indicate that the Chinese taxon is not Akiyoshia. (v) The genus Tricula in recent Chinese literature is comprised of four genera determined by detailed comparative anatomical data: Tricula, Neotricula, Gammatricula, and Jinhongia. Shells cannot be used to discriminate among them. (vi) Tricula cristella has been consistently misidentified in collections in China and literature. However, genuine T. cristella does transmit Paragonimus skrjabini. (vii) Tricula minutoides in the Chinese literature has been misidentified, and specimens are T. cristella. (viii) The genus Melania and the family Melaniidae are used in the Chinese literature. The so-called melaniidae snails belong to the families Thiaridae, Pleuroceridae, and Melanopsidae. Asian Semisulcospira is pleurocerid while Melanoides and Tarebia are thiarid (ix) Semisulcospira libertina is correctly identified for populations ranging throughout Japan to Taiwan. This species is most probably not distributed throughout all south China, and intense systematic research on Semisulcospira is needed. A modern classification is given for snails transmitting Paragonimus.

Americas↗
PubMed1994

[Snail hosts of Paragonimus in Asia and America].

This is a comprehensive review of snail hosts of Paragonimus distributed worldwide exclusive of Africa. Fifty-eight species of snails are listed, of which 67% occur in China. Most of the Chinese snails are classified as Pomatiopsinae Erhaiini or Triculinae of the family Pomatiopsidae. Problems associated with a number of names and concepts have been clarified.

Americas↗
PubMed1994

[Study on allele frequency in Oncomelania from the mainland of China].

Nine populations of Oncomelania, field-collected from Anhui, Shanghai, Jiangsu, Zhejiang, Jiangxi, Hunan, Hubei, Sichuan and Yunnan were studied by horizontal starch gel electrophoretic method with 24 enzyme systems (AAT, AcPH, AK, AO, APH, CK, EST, GDH, GPI, G6PD, HBD, ISDH, LAP, LDH, ME, MDH, MPI, NADD, OCT, PGM, 6PGD, SDH, SOD, XDH) analyzed. 40 loci and 117 alleles were detected in the Oncomelania. Both of GPI and PGM-I, with 7 alleles, were the most variable loci. 22 loci had more than 3 alleles each. Of 40 loci examined in the 24 isozyme systems, 14 were found to be polymorphic, the proportion of multilocus enzymes being 58.3%. Our results showed that the genetic polymorphism existing in the populations of Oncomelania in the mainland of China. PGM and MDH, were found in both the populations of Oncomelania and strains of Schistosoma japonicum in the mainland of China. The results provided a new idea for studying snails and Schistosoma. Also, we found that there might be some correlation between the polymorphic locus and the feature of the shell of Oncomelania snail.

Alleles↗
PubMed1993

A simplified method for determining the frequency response of pneumotachographs used in infants.

In all rapidly changing systems, an appropriate response time of all sensing devices is essential for the accurate conversion of a physiological parameters to a proportional electrical signal. The frequency response of equipment is the ability to accurately reflect both the magnitude and temporal relationship of dynamic events over a defined frequency range. The phase lag expresses the temporal delay between the physical event being measured and the output signal. The attenuation expresses diminution of the amplitude ratio of the output signal in relation to the input signal over a range of frequencies. We have developed a method that specifically addresses the measurement of frequency response and attenuation of pneumotachographs and low pressure transducers. The system consists of a 81 liter rectangular box separated in the middle by a 30.5 cm acoustic loudspeaker, the cone sealed by latex, and driven by a signal generator coupled to a low frequency amplifier. This system can produce an undistorted sinusoidal signal between 0 and 20 Hz, and the peak flow through the pneumotachograph is only minimally affected by changes in frequency. Rapid analysis is possible using an oscilloscope to produce Lissajou loops. There is no measurable attenuation between the electrical signal and the pressure generated over frequencies from 1 to 20 Hz. The system is accurate at low frequencies and can generate appropriate signals over the frequency range of interest for respiratory applications, and it can be inexpensively constructed.

Humans↗
PubMed1993

The measurement of thoraco-abdominal asynchrony in infants with severe laryngotracheobronchitis.

Retractions of the lower ribcage (chest wall distortion [CWD]) during inspiration are frequently observed with moderate to severe respiratory disease in the infant. Laryngotracheobronchitis (LTB) results in a reversible partial airway obstruction with severe CWD. We wished to measure the motion of the chest wall during distortion to determine the changes in minute ventilation (VE) and to evaluate this clinical sign as a means of assessing disease severity. The respiratory inductance plethysmograph was used to determine the distortion of the lower chest wall, and distortion was correlated with VE, measured at the mouth, in six infants with severe LTB and ventilatory failure. As the conditions of these infants improved, the CWD decreased with decreasing transcutaneous carbon dioxide tension (tcPCO2), VE increased from 0.27 +/- 0.12 L.min-1 x kg-1 at a tcPCO2 of 64 mm Hg to 0.64 +/- 0.06 L.min-1 x kg-1 when the tcPCO2 had fallen to 28 mm Hg. Over the same change in tcPCO2, the tidal volume (VT) increased from 4.8 +/- 0.5 ml.kg-1 to 15.7 +/- 1.4 ml.kg-1. In the most severe disease state, the excursion of the chest wall (as an inductance) was -14 +/- 3 mV in severe obstruction, but increased to 75 mV +/- 4 mV with resolution of the illness. The timing and vector of movement of the abdomen and chest wall were expressed as a Lissajous figure, which is measured as a phase angle. The severity of the disease process, as determined by tcPCO2 was directly related to the phase relationship, and thus reflected both VE and VT. The severity of the CWD may be assessed rapidly by the use of Lissajous figures.

Abdomen↗
PubMed1993

Exercise capacity of individuals with paraplegia.

Spinal cord injury below the first thoracic vertebra defines the condition of paraplegia, with common medical sequelae including impaired motor function, bone and muscle atrophy, poor myocardial function, and a general decline of physical fitness. Recently, there has been renewed interest in the role of exercise for improving the physical fitness, health, and rehabilitation potential of individuals rendered wheelchair dependent following spinal cord injury. This brief review examines the pathophysiology of paraplegia, outlines useful strategies for cardiorespiratory fitness assessment, discusses the current levels of cardiorespiratory fitness in individuals with paraplegia, and highlights a few unique responses to acute exercise in this population.

Cardiovascular System↗
PubMed1992

Clinical information systems: 25-year history and the future.

Clinical information Systems have not advanced rapidly enough to meet the growing needs for clinical data. This is due primarily to the industry's past focus on financial information processing. Pressure is increasing for clinical data to support health-care professionals in the delivery of patient care, and in the establishment and monitoring of quality of care indicators. This article summarizes the history of clinical systems, and presents key issues regarding future clinical information systems.

Clinical Medicine↗